Conversion of natural forests to farmlands and its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016): in the case of southwestern Ethiopia

Tamiru Kefalew; Mulugeta Betemariyam; Motuma Tolera

doi:10.12688/f1000research.28336.1

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Research Article

Conversion of natural forests to farmlands and its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016): in the case of southwestern Ethiopia

[version 1; peer review: 1 approved with reservations, 1 not approved]

Tamiru Kefalew¹, Mulugeta Betemariyam ¹, Motuma Tolera²

PUBLISHED 22 Mar 2021

Author details Author details

¹ Forestry, Madda Walabu University, Bale Robe, Oromia, 247, Ethiopia
² Hawassa University, Wondo Genet College of Forestry and Natural Resources, Shashemene, 128, Ethiopia

Tamiru Kefalew
Roles: Conceptualization, Data Curation, Methodology, Writing – Original Draft Preparation

Mulugeta Betemariyam
Roles: Formal Analysis, Investigation, Methodology, Software, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

Motuma Tolera
Roles: Formal Analysis, Funding Acquisition, Supervision

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Abstract

Background: Gura-Ferda forest is one of the Afromontane rainforests in the southwestern region of Ethiopia. However, since 1984, large parts of this forest have become increasingly disturbed and fragmented due to forest conversion into forest farm interface and farmlands. The study was conducted to assess changes of woody species diversity and carbon stock in association with the conversion of natural forest to forest farm interface and farmlands.
Methods: Data were collected from natural forest, forest farm interface and farmland which are historically forest lands before 1984. A total of 90 nested plots (20m×20m for natural forest and forest farm interface; 50m*100m for farmland)) were established for inventory of woody species. Three 1m×1m subplots were established to collect litter and soil samples. A total of 180 soil samples were collected. The total carbon stocks were estimated by summing carbon stock in the biomass and soil (0-60 cm depth).
Results: Results showed that Shannon-Wiener diversity (H’) in forest farm interface (H’ = 1.57) is relatively lower than that of natural forest (H’ = 3.33) but higher than farmland (H’ = 1.42). The total carbon stocks of natural forest were approximately 1.21 and 2.54 times higher than that of forest farm interface and farmland.
Conclusion: Our study revealed that the changes of Natural Forest to Forest Farm Interface and Farmland have effects on the diversity of woody species and carbon stocks.

Keywords

Forest Farm Interface, Biomass Carbon, Soil Organic Carbon, Litter

Corresponding author: Mulugeta Betemariyam

Competing interests: No competing interests were disclosed.

Grant information: This study was funded by Centre for International Forestry Research (CIFOR) and Ministry of Higher Education and Technology Transfer in Ethiopia
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2021 Kefalew T et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

How to cite: Kefalew T, Betemariyam M and Tolera M. Conversion of natural forests to farmlands and its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016): in the case of southwestern Ethiopia [version 1; peer review: 1 approved with reservations, 1 not approved]. F1000Research 2021, 10:227 (https://doi.org/10.12688/f1000research.28336.1) First published: 22 Mar 2021, 10:227 (https://doi.org/10.12688/f1000research.28336.1) Latest published: 29 Nov 2021, 10:227 (https://doi.org/10.12688/f1000research.28336.2)

Introduction

Forests and forest management have changed greatly over the past two decades. In 1990, the world had 4.13 billion hectares (ha) of forests (31.6% of total land area of Earth). However, according to the Food and Agriculture Organization of the United Nations, by 2015 this area has decreased to 3.99 billion ha (30.6% of total land area of Earth) (FAO, 2015). This caused a net loss of 129 million ha of forests (natural and planted) from 1990 to 2015. However, the net annual rate of loss has reduced from 0.18% in the 1990 to 0.08% in 2015. The net annual natural forest loss between 1990 to 2000 was 8.5 million ha per year; however, from 2010 to 2015, natural forest decreased by a net of 6.6 million ha per year (8.8 million ha of loss and 2.2 million ha of gain). This resulted in a reduction of 697 million mega tons per year or about 2.5 gigaton (GT) of carbon dioxide (CO2) for the past 25 years (FAO, 2015). The world forest assessment in 2015 also indicated that world’s forests store an estimated 296 GT of carbon in both aboveground and belowground biomass (FAO, 2015).

Ethiopia has a wide range of ecological conditions ranging from the arid lowland in the East to high altitudes in the central high lands (Hurni, 1998). This wide range of ecological conditions coupled with the corresponding heterogeneous flora and fauna has made the country one of the internationally recognized major centers for biodiversity (Scholte, 2012). However, through time to time, there has been a dramatic decline in forested area in the country. Accordingly, from 1990 to 2000 and from 2000 to 2010, forest losses were estimated at 8.3 million ha and 5.2 million ha respectively (Eshetu, 2014). These days major parts of the remaining natural forests which harbor high biodiversity are located on steep slopes at high altitude and in the remote southern and southwestern parts of the country. These few remaining high forests are also threatened by anthropogenic activities and converted to agricultural and other land use systems (Abere, 2011). Similarly, other remaining natural forests have also been threatened by pressure from investors and changed to industrial plantation like coffee and tea (Abere, 2011; Moges et al., 2010). This reduction and conversion of natural forest to other land use systems in many parts of Ethiopia has led to the decline in number and distribution of many plant species, shortage of raw materials for wood processing industries and disturbance of ecosystem services (Lemenih & Kassa, 2014). Subsequently, it has resulted the expansion of forest farm interface in and around the forest ecosystem.

“For this study forest farm interface is defined as a complex geographic and temporal mosaic landscape of integrated management and production practices that combine agriculture, forest and livestock land uses and formed from shifting of forest land uses by smallholder farmers and /or investors. The interface is not a discrete line separating farms and forests.” (CIFOR, 2017)

For the past five decades, the government of Ethiopia has attempted to reforest degraded forests. Hundreds of aid projects have been implemented in different parts of the country to reverse deforestation and forest degradation in the country. However, the success stories were below expectations and the problems are still immense. This resulted from the lack of effective management practices and quantification of the available forest resources. This insufficiency of scientific quantitative data brought lack of responsiveness for sound management of natural resources in the country.

Gura-Ferda forest is one of the Afromontane rainforests in the southwestern region of Ethiopia and grows at altitudes from 700 to 2,300 meter above sea level. This forest area is one of the areas in Ethiopia where traditional beliefs and ecological knowledge have assisted the conservation of forests up to now. During the past decades, especially since 1984, large parts of this forest have progressively been disturbed and fragmented due to forest conversion to settlements, agriculture, and industrial plantation (Schmitt et al., 2010). Nowadays, pressure produced by immigration and investors is increasing forest disturbance. However, there is no quantitative information on the change of species diversity and carbon stocks resulting from the conversion of natural forests to forest farm interface and farmlands. The overall objective of this study was, therefore, to analyze the woody species diversity and carbon stock change in association with the change of natural forests to forest farm interface and farmlands. The study hypothesized that, the conversion of natural forests to forest farm interface and farmlands affect the woody species diversity, biomass and soil organic carbon (SOC) stocks.

Methods

Description of the study area

The study was conducted at Gura-Ferda district of southwestern Ethiopia which is located at 603 km southwest of the capital city Addis Ababa (Figure 1). Geographically, it is positioned between 6°29’12” N and 7°13’22” N latitude and 34°52’23” E and 35°23’59” E longitude. The area coverage of this district is estimated to be 2565.42 km². The annual average rainfall over the period of 1983–2012 was 1639.8 mm, with a maximum of 1946.3 mm and a minimum of 1289.8mm. The area receives a maximum rainfall in October and minimum rainfall in February. The average annual temperature is 23.4°C with a range from 16.1°C-30.6°C. The dominant soil type of the study area is nitisols with soil textural class loam to clay (Dewitte et al., 2013).

Figure 1. The nested map of Ethiopia showing the map of study region and zonal map of the study district.

As the past data of the Gura-Ferda district specified, since 1984, there was a degradation of natural forest in the area (Table 1). The notable drivers of this forest area decrement were resettlement, crop investment and fuel wood. According to the office of Gura-Ferda district, in 1984, the populations of the district were 149. However, in 2016 they were increased to 45,028 (GFDAO, 2016). Moreover, during 2003/4 legal resettlement, massive deforestation of natural forest were accompanied for house construction of immigrates (Abere, 2011; Gessese, 2018). Next to resettlement, the taken up of forest by investors is other key drivers for the degradation and deforestation of natural forests in the area. According to (GFDAO, 2016), there were more than 30 investors who were involved in different agricultural investment especially coffee and rubber tree plantation. These investors had been used shrub land, natural forest, and grass lands for investment.

Table 1. Converted area from natural forest to forest farm interface and farmland within the span of 33 years (1984 and 2016).

Land Use Class	1984	Area (%)	2016	Area (%)
Natural Forest	90872	100	67049	73.78
Forest Farm Interface	-	-	21155	23.28
Farmland/Settlement	-	-	2668	2.94
Total	90872	100	90872	100

Source (Authors Data)

Methodology

Data source

For the purpose of this research both primary and secondary data were employed. Primary data were obtained through field survey of the study area. Secondary data used were satellite images and publications such as articles, data from district land administration offices and censuses results. Multi-sensor and multi-temporal Landsat images were downloaded from United States Geological Survey (USGS) (https://earthexplorer.usgs.gov) (Table 2). Accordingly, satellite images of 1984 and 2016 were used for this study. Images of the year 1984 were taken because it was the time when the government organized a resettlement program at the study area. Similarly, images from the year 2016 was selected because it was the time when recent agricultural systems were expanded and government was focused on commercial investments in the area. Since it is a time of free atmospheric cloud, satellite images in the months of December to January were used.

Table 2. Time series satellite images of the study area.

Acquisition date	Path/Row	Cloud cover (%)	Sensor type	Spatial resolution (m)	LU/LCC related events
28/12/1984	170/055	0.0	TM	30x30	Government Organized Resettlement Program
26/12/2016	171/055	0.0	OLI/TIRS	30x30**	Recent Agricultural Expansion and focusing of government on commercial investments

** Panchromatic sharpened to 15m to favor visual interpretation

Stratification of study area

Before the resettlement program of 1984, all areas used for the sampling unit in this study time were covered by forest. However, nowadays, it is observed that the area has three discrete categories. These are: natural forest, forest farm interface and farmland (Figure 2; Figure 3).

Figure 2. map of Natural Forest of Gura-Ferda district in 1984 (Source: Authors).

Figure 3. map of Natural Forest, Forest Farm Interface and Farmlands of Gura-Ferda district in 2016 (Source: Authors).

Natural forest (NF): a landform consisting of trees, shrubs and other vegetation that originally emerged on its own without the influence or direct intervention of man and found adjacent to FFI.
Forest-farm interface (FFI): a neither agriculture nor forest mosaic landscape of integrated management and production practices which is typically used by smallholder farmers/investors and found between natural forest and farmlands (find full definition in the introduction).
Farmland (FL): an area which has been converted to intensive mono cropping with few/no scattered trees due to high disturbance and adjacent to FFI.

Sampling techniques

Field level data was collected from NF, FFI and FL which are adjacent to each other and historically forest land before 1984. With the help of a compass and Geographic Positioning System (GPS), three transects with a total of 30 plots (10 plots on each transect) were established for each land use system. Transect lines and samples plots were laid by a gap of 200m from each other (Figure 4). The sample plot size was determined based on expected density of woody species in each land use system (Tadesse et al., 2014; Tolera et al., 2008). Accordingly, for both NF and FFI a nested plot design of 400m² with 25m² and 1m²size was used to collect vegetation data (tree, sapling and seedling respectively). In each of the quadrat (1m*1m), a number of all seedlings that have eight ≤ 50 cm and diameter at breast height (DBH) ≤ 2.5cm were recorded. Individuals attaining height > 50cm and DBH ≤ 2.5 cm were considered as sapling and counted. In the 400m² sample plots, the diameter and height of all woody species ≥ 5cm DBH were measured. As per density and distribution of woody species is lower, plot size of 50 m x 100 m was used for FL (UNFCCC, 2015).

Figure 4. Sampling design of woody species in in the studied land use systems of Gura-Ferda district.

DBH of sampled dead wood was measured following the techniques used by Pearson et al. (2005) and UNFCCC (2015). A complete list of woody species was made for each plot throughout the whole area and documented by local name. Species identification for common species was done in the field via different plant identification keys. However, for the less common species plant sample specimens were pressed and identified at the National Herbarium of Ethiopia, Addis Ababa University. Litter samples were collected from 1 m x 1 m subplot within the main plot. The collected fresh litter was weighed right on the site. Then the evenly mixed samples were taken to the laboratory and oven dried at 65ºC for 24 hours to determine dry to fresh weight ratio. Soil samples were collected from the sub-plots used for litter sampling. Two sets of soil samples were taken, one set for the determination of organic carbon fraction (%C), and one set for the determination of soil bulk density. A total of 90 soil samples (layers of 0–30 and 30–60 cm) were collected for %C analysis using soil auger. In addition, similar size of undisturbed soil samples were collected separately for determination of soil bulk density.

Data analysis

Diversity analysis. Shannon-Wiener index (H`) was used to determine diversity of woody species of the study area. H` was determined through the analysis of two components of species diversity. These are the species richness (the number of species in the sample plots) and evenness of species (abundance distribution among species).

H^{'} = \sum_{i = 1}^{S} P i l n P i (1)

Where pi, is the proportion of individuals found in the i^th species

Beta diversity (β) which measures the change in the diversity of species among a set of land uses is determined using the formula provided by Whittaker (1972).

β = \frac{b + c}{2 a + b + c} (2)

Where a, is the number of shared species in two land uses, and b and c are the numbers of species unique to each land use.

Biomass carbon stock estimation

Allometric equation developed by Chave et al. (2014) was used for estimating the aboveground biomass of woody species in NF (Table 3). Biomass of standing dead wood which has branches was also estimated using this allometric equation. This equation was selected since it was established for estimating the biomass of woody species in tropical natural forests. Moreover, this equation used diameter at breast height and wood density which was the most important biomass predictor variables. The biomass of woody species in FFI and FL was estimated using allometric equation developed by Kuyah et al. (2012a); Kuyah et al. (2012b) since it was developed for land use systems having more or less similar climatic properties as those in the current study area. Woody density was taken from the document of Ethiopia’s fForest reference level submission to the United Nation Framework Convention on Climate Change (UNFCCC) (EFRLS, 2016).

Table 3. Allometric equations used to estimate the biomass carbon stocks of natural forest, forest farm interface and farmlands in Gura-Ferda district, southwestern Ethiopia.

Land Use		Equation	R²	D (cm)	% C	Source
Natural Forest	Woody species	AGB = ρ × d² × H × 0.0559 BGB = 0.20 × AGB	- -	≥5 ≥5	50 50	(Chave et al., 2014) (IPCC, 2006)
Forest Farm Interface	Woody species	AGB = 0.225 × d^2.341 × ρ^0.73 BGB = 0.28 × AGB	0.98 -	≥5 ≥5	48 48	(Kuyah et al., 2012a) (Kuyah et al., 2012b)
Farmlands	Woody species	AGB = 0.225 × d^2.341 × ρ^0.73 BGB = 0.28 × AGB	0.80 -	≥5 ≥5	48 48	(Kuyah et al., 2012a) (Kuyah et al., 2012b)

Aboveground biomass of standing dead wood which has no leaves was estimated following the procedure used by Pearson et al. (2005). The biomass of felled dead wood was estimated using allometric equation developed by Grais & Casarim (2013). The total biomass of the dead wood was estimated by summing up of the standing, logged and felled dead wood. Finally, estimated biomass of woody tree species in NF, FFI and FL were converted to carbon (C) stock using carbon fraction value of 0.5, 0.48, and 0.48 respectively (IPCC, 2006; Kuyah et al., 2012a). The loss on ignition method was used to estimate percentage of organic matter in the litter. The amount of C in the litter was estimated through multiplying of litter organic matter by 0.50 (Pearson et al., 2007).

Soil organic carbon stock estimation. Soil analyses were undertaken at Wondo Genet College of Forestry and Natural Resources soil laboratory. The soil samples for bulk density were oven-dried at 105 °C for 48 hours. Bulk density was estimated by the core method (Blake & Hartge, 1986). The soil samples for %C were air –dried and analyzed using Walkley-Black method (Schnitzer, 1982). A SOC stock (Mg C ha^-1) was calculated by multiplying of %C, bulk density (g/cm³) and soil depth (cm)).

Total carbon stocks. Total C stock (Mg C ha^-1) was calculated by summing up of biomass C stocks (above-and-below) and SOC stocks.

Statistical analysis

C stock of the three land uses were compared using one-way ANOVA and two-way ANOVA. All data were checked for normality prior to doing the analysis of variance using Kolmogorov-Smirnov test. The data were analyzed using Statistical Package for Social Science (SPSS version 20). All tests were conducted at 95% confidence level.

Results

Woody Species Diversity

A total of 59, 24 and 19 woody species belonging to 34 families were recorded and identified in the sample plots of Gura-Ferda NF, FFI, and FL respectively (Table 4). Among these woody species, Moraceae, Rubiaceae and Sapotaceae were the richest family all represented by six species (8.82%) of total floristic composition. The remaining families represented less than 3% of species each.

Table 4. Species richness, evenness and diversity indices of Natural Forest, Forest Farm Interface and Farm Land in Gura-Ferda District, southwestern Ethiopia.

Land use	Species richness	Shannon ('H)	Evenness (J)
Natural forest	59	3.33	0.82
Forest-Farm interface	24	1.57	0.49
Farm land	19	1.42	0.48

The overall mean H’, species richness and evenness of NF were 3.33, 59 and 0.82 respectively. FFI enriched with 24 woody species has an overall mean H’ of 1.57. The results of H’ and evenness indices indicated a difference in species diversity and evenness among the land uses. NF is relatively the most diversified one followed by FFI. Relatively, highest evenness was exhibited by NF followed by FFI (Table 4).

Sorensen’s similarity coefficient indicated the highest floristic similarity was found between NF and FFI (0.51) followed by FFI and FL (0.37). The magnitude of beta diversity indicates the change in woody species composition between adjacent land uses along the land use changes. The highest change in woody species diversity was observed between the changes from NF to FL (0.67) followed by FFI to FL (0.63) (Table 5). Cordia africana, Croton macrostachyus and Lepidotrichlea volkensi were some of common woody species in all land uses.

Table 5. Pair wise comparison of Sorensen’s similarity coefficient and beta diversity index in species composition among Natural Forest, Forest Farm Interface and Farm Land in Gura-Ferda District, southwestern Ethiopia.

Land Uses	Natural Forest	Forest Farm Interface	Farmland
Natural Forest	1	0.51 (0.49)	0.33 (0.67)
Forest Farm Interface	0.51 (0.49)	1	0.37 (0.63)
Farmland	0.33 (0.67)	0.37 (0.63)	1

Carbon stocks

The basal area of woody species in NF (54.31±2.95 m²ha^-1) was 2.3 and 4.1 times higher than FFI (26.66±2.28 m²ha^-1) and FL (6.12±0.37 m²ha^-1) respectively. The density of woody species ≥ 5cm DBH in the study area was 746±15.25 individuals per hectare for NF, 876±120 individuals per hectare for FFI and 158±6.9 individuals per hectare for FL.

The mean aboveground biomass (tree/shrub, dead wood and litter) C stocks of FFI (99.63± 9.72 Mg C ha^-1) are significantly lower than the adjacent NF (134.40± 10.09 Mg C ha^-1), but higher than that of FL (16.80± 1.18 Mg C ha^-1). The mean aboveground biomass C stocks of NF were approximately 2.24 and 8.47 times higher than FFI and FL. The mean overall dead wood C stock of the study area was 2.3 ± 1.51 Mg C ha^-1 for NF and 9 ± 2.56 Mg C ha^-1 for FFI (Table 6). The mean litter biomass for aboveground biomass was 1.29 ±0.14 Mg C ha^-1for natural forest and 0.88 ±0.06 Mg C ha^-1 for forest farm interface.

Table 6. (Mean ± SD) of above and belowground biomass carbon stocks of Natural Forest, Forest Farm Interface and Farm Land (Mg C ha^-1) in Guraferda District, southwestern Ethiopia.

Biomass component	Natural Forest	Forest Farm Interface	Farm Land
AGBC (Mg C ha^-1)	134.40± 10.09	99.63± 9.72	16.80± 1.18
BGBC (Mg C ha^-1)	26.16±2.02	17.95±1.94	3.36±0.23
TBC (Mg C ha^-1)	160.57±12.01^c	117.58±11.88^b	20.16±1.36^a

Different letters show significant (p<0.05) different between Land Uses, and similar letters not significance differences

A belowground biomass C stock in the NF was significantly higher (p< 0.001) than the belowground biomass C stocks of FFI and FL (Table 6). The mean belowground biomass C stocks in the NF, FFI and FL were 26.16±2.02 Mg C ha^-1, 17.95±1.94 Mg C ha^-1and 3.36±0.23 Mg C ha^-1 respectively. The total biomass C stocks in NF was by 7.73% and 38.84% higher than FFI and FL. Cash generating coffee ≥2.5 DBH shared 0.5% and 2.3% of the total biomass C stocks in NF and FFI respectively. The contribution of litter for total biomass C in both NF and FFI was 1%.

Within each land use, SOC stock was significantly higher (p<0.001) in the top layer (0–30cm) than in the lower layer (30–60 cm) (Table 7). The top layer stocked 57.84%, 54.76% and 56.98 of the total SOC in the NF, FFI and FL respectively. The total SOC stocks (0–60 cm depth) were significantly different among all land uses. SOC stock significantly differs along depths for all land uses. With respect to conversion of NF to FFI, 5.78% of SOC stocks (0–60 cm) were lost. Similarly, 21.82% of SOC stocks (0–60 cm) were lost in conversion of the NF to the FL.

Table 7. (Mean ± SD) of soil organic carbon (SOC) of Natural Forest, Forest Farm Interface and Farm Land (Mg C ha^-1) in Gura-Ferda District, southwestern Ethiopia.

Depth, cm	Natural Forest	Forest Farm interface	Farm Land
0 – 30 cm	128.65± 17.66	108.47± 22.87	74.45±15.90
30 – 60 cm	93.77± 11.55	89.62±23.13	56.21±8.68
Total (0 – 60 cm)	222.42±21.89^c	198.09±36.18^b	130.66±21.01^a

Different letters show significant (p<0.05) different between Land Uses, and similar letters not significance differences

The total C stock of the study area was calculated by summing up all the C value of each pool. Accordingly, the total C stock (Mg C ha^-1) is significantly different among the three-land uses. The total C stock in NF was 382.97 ± 50.8 Mg C ha^-1. While the total C stocks for FFI and FL were 315.68 ± 30.5 Mg C ha^-1 and 150.76 ± 7.6 Mg C ha^-1 respectively (Table 8). Of which, the SOC accounted for 58.07%, 62.75 and 86.63% for NF, FFI and FL, respectively. The total C stock of NF was approximately 1.21 and 2.54 times higher than that of FFI and FL.

Table 8. Total carbon stocks of Natural Forest, Forest Farm Interface and Farmland (Mg C ha^-1) in Gura-Ferda District, southwestern Ethiopia.

Land use	Mean (±SE)
Land use	Total Biomass Carbon	SOC (0–60 cm)	Total Carbon Stocks
NF	160.57±12.01	222.4 ±5.6	382.97 ± 50.8^c
FFI	117.58±11.88	198.1 ± 9.3	315.68 ± 30.5^b
FL	20.16±1.36	130.6 ± 5.4	150.76 ± 7.6^a

Different letters show significant (p<0.05) different among Land Uses

Discussion

Woody species diversity

Gura-Ferda forest is among the most degraded and deforested forest in southwestern region of Ethiopia. A change in NF to FFI and FL are the major threats to forest woody species diversity. In association with the conversion of natural forest to forest farm interface more than 17 species are lost. While, in connotation with the conversion of NF to FL, more than 33 species are lost. More specifically, Sapotaceae, Moraceae, and Rubiaceae which are the dominant families in NF of this study area are the most threatened families as a result of the conversion of NF to FFI and FL. Almost all woody species recorded in the FFI and FL were not planted rather they were the remnants of trees and shrubs during conversion of NF to FFI and FL.

The observed lowered H’ in FFI and FL in Gura-Ferda district is directly attributed by conversion of NF to coffee farms and indirectly by population growth, colonization of previously uncultivated land by subsistence crops and the expansion of settlements. As shown in Table (1), FFI which emerged after the resettlement program of 1984 accounts for 23.28% of the NF within 1984–2016-year interval. As reported by Gessese (2018), and GFDAO (2016) the main problem related to land use land cover change at Gura-Ferda district was agricultural investment, fuel wood collection, wood for house construction and farm implementation, wildfire, resettlement, land certification, poor governance within the district, and subsistence agricultural land expansion.

According to a Gura-Ferda district land administration report, large areas of extra land were recorded for each farmer. The farmers had expanded their farmland into nearby forest, shrub/bush land and grass land and used those land uses for commercial crop production. Therefore, this increment of unregistered or unplanned farms and FL resulted from above mentioned drivers are the main causes for the loss of woody species diversity in the study area.

The main reason for the lower woody species diversity in FFI in relation to NF in the study area is due to the application of intensive thinning of different woody species in the system in order to reduce shading effect. (Gole, 2003) also reported that, managing forest for coffee production has resulted in significant changes in species diversity, composition and vegetation structure in coffee forests of southwestern Ethiopia. The number of woody species recorded in Gura-Ferda NF is comparable to the Komba-Daga moist evergreen forest in southwestern Ethiopia (62 woody species) (Geneme et al., 2015). For instance, the number of woody species recorded in the Gura-Ferda NF of the current study area is substantially higher than those reported for Agama tropical Afromontane forest of Ethiopia (39 woody species) (Addi et al., 2016). However, the number of woody species in the current studied NF is lower than the woody species recorded for Wondo Genet Afromontane forest in the central highlands of Ethiopia (72 woody species) (Kebede et al., 2013).

Our results also indicated that, the woody species richness in FFI of the current study is comparatively lower than woody of species in agroforestry system of south-central and southern highlands of Ethiopia (Asfaw, 2003; Seta & Demissew, 2017). Since maximizing coffee production is the main goal, most of the native trees have been cleared by cultivators and few shade plant species are retained in highly populated coffee shrubs.

Carbon stocks

The study showed how C stocks in biomass and soils were varied across different land use systems. NF had higher biomass C stocks compared to FFI and that of the FL. Rajput et al. (2017) and Solomon et al. (2018) reported higher biomass C in forest land use system as compared to other land cover types in northwestern Himalaya and northern Ethiopia, respectively. From the studied land use systems of this area, most of the C was stocked in NF. FFI and FL biomass C stocks were 7.73% and 38.84% lower than the C stocks in the NF. The accumulation of high C stock in NF was attributed by the presence of diversified woody species in the NF in comparison with FFI and FL. Additionally, the NF has found to accumulate larger aboveground biomass in the litter compared with that of FFI. This result is in line with the result of Solomon et al. (2018) which stated that tree density, diversity and diameter have an effect on biomass C.

Case studies have showed as different land use systems stocked different amounts of C in their biomass component. Accordingly, the biomass C stocks recorded in the NF of the current study area is substantially lower than the biomass C stocks of Adaba-Dodola community forest, southeastern Ethiopia (Bazezew et al., 2015). The biomass C stocks of NF of the current study area was approximately three times lower than the biomass C stocks reported for woody plants of Mount Zequalla Monastery in Ethiopia (Girma et al., 2014). Similarly, the biomass C stocks of FFI in this study was higher than that of the coffee based agroforestry system in Gera, Jimma Zone, South-West Ethiopia (Mohammed & Bekele, 2014). The difference in biomass C stocks might be due to various factors such as difference in diversity of trees (woody and non woody) of larger sizes, the used allometric equation, soil condition and climate factors. For instance, in the coffee based agroforestry system studied by Mohammed & Bekele (2014), trees aboveground biomass was determined using Brown et al. (1989) allometric equations. But, for this study, the generic equation developed by Chave et al. (2014) and Kuyah et al. (2012a) were used for woody tree species. The biomass C stocks of the FFI of the current study area was relatively equivalent with the total biomass C stocks of fruit coffee system of indigenous agroforestry systems of the south-eastern Rift Valley escarpment, Ethiopia (Negash & Starr, 2015).

The average mean above ground biomass C stock of the FFI was higher than the mean biomass C stocks of organic polyculture coffee, non-organic polyculture coffee and organic Inga species in Chiapas, Mexico (Soto-Pinto & Aguirre-Dávila, 2014). The variability among these systems in this respect might be because of differences in species composition, site characteristics, management practices, land holding sizes, ancillary factors (e.g. soil condition, climate, system age, land-use history), and adopted allometric model for biomass estimation (Montagnini & Nair, 2004).

Concentrations of SOC decreased with an increment of depth in all NF, FFI and FL. The highest SOC stock in the NF might be attributed to the lower organic carbon turnover rate as a result of minimum soil disturbance in the system, and more litter fall inputs from different wood tree species. While in the FFI, common intensive management practices like cleaning, weeding, burning and relocation of biomass might influence accumulation of litter carbon. It was in agreement with results by Aticho (2013) who claimed the diminishing trend of SOC content with depth in his study in Kafa, Southwest Ethiopia. Yimer et al. (2015) also observed a declining trend in SOC concentration with depth in the Central Rift Valley area of Ethiopia.

The total SOC stocks at soil depth for the three land use systems in this study were within the range of SOC stocks reported for other similar systems in Ethiopia (Gebeyehu et al., 2017). The upper layer (0–30 cm depth) SOC stock of FFI in this study area was higher than the mean SOC (65.2 Mg C ha^-1) of Nitisol soil under agroforestry systems in Ethiopia (Gebeyehu et al., 2017). The result of SOC in 0–30 systems cm depth in FFI was also higher than the 0–30 cm depth SOC recorded in Gununo watershed agroforestry practices (Bajigo et al., 2015), and 0–30 cm depth SOC (60.8 Mg C ha^-1) of Indonesia homegarden agroforestry system (Roshetko et al., 2002).

The results indicate that 5.78 % and 21.82% of SOC stocks (0–60 cm) were lost in conversion of the NF to the FFI and FL respectively within 33 years. Another meta-analysis of Wei et al. (2014) found that SOC decreased by 44.5% following conversion from a NF to a crop field. Yimer et al. (2007) also found that SOC decreased by 30.9% after 15 years of deforestation in the Bale Mountains of Ethiopia.

Conclusion

FFI in the southwestern part of Ethiopia plays an important role in maintaining more woody species and sinks of C. The higher contribution of NF to climate change mitigation is mainly due to the higher diversity and density of larger woody species in the system as compared to the adjacent FFI and FL. Trees in particular play substantial roles for enhancing biomass C stocks in forests and any other land use systems. However, the increment of FL found adjacent to the NF and FFI showed a lower role of biodiversity conservation and C stock. This shows that sustainability of the system is questionable. If the NF is not sustainably managed and certification of land is not carried out in the area, there will be expansion of FFI and FL which will cause further deforestation and forest degradation. Therefore, it needs to recognize FFI as part of climate change mitigation strategies, as it can also provide much benefit to the community and a potential to reduce pressure on adjacent NF.

Data availability

Underlying data

Zenodo: Conversion of Natural Forests to Farmlands and Its Associated Woody Species Diversity and Carbon Stocks in a Span of 33 Years (1984 To 2016): In the Case of Southwestern Ethiopia, http://doi.org/10.5281/zenodo.4601418 (Betemariyam et al., 2021).

This project contains the following underlying data:

Average DBH and Height per Plot.xlsx
Processed data of SOC.xlsx
Processed data of TBC.xlsx
Processed Data of Woody Species Diversity.xlsx

Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

Acknowledgements

We acknowledge the logistic and technical support we got from Wondo Genet College of Forestry and Natural Resources Soil Laboratory, Hawassa University. We sincerely thank the farmers of the study area for their kindness and enthusiasm to talk to us and for allowing us to take measurements on their farms. Our gratitude goes to experts at National Herbarium of Ethiopia, Addis Ababa University, for their generous support on species identification that makes our research very fruitful.

Faculty Opinions recommended

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Version 2

VERSION 2 PUBLISHED 22 Mar 2021

Author details Author details

¹ Forestry, Madda Walabu University, Bale Robe, Oromia, 247, Ethiopia
² Hawassa University, Wondo Genet College of Forestry and Natural Resources, Shashemene, 128, Ethiopia

Tamiru Kefalew
Roles: Conceptualization, Data Curation, Methodology, Writing – Original Draft Preparation

Mulugeta Betemariyam
Roles: Formal Analysis, Investigation, Methodology, Software, Visualization, Writing – Original Draft Preparation, Writing – Review & Editing

Motuma Tolera
Roles: Formal Analysis, Funding Acquisition, Supervision

Competing interests

No competing interests were disclosed.

Grant information

This study was funded by Centre for International Forestry Research (CIFOR) and Ministry of Higher Education and Technology Transfer in Ethiopia
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Article Versions (2)

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Revised

Published: 29 Nov 2021, 10:227

https://doi.org/10.12688/f1000research.28336.2

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Published: 22 Mar 2021, 10:227

https://doi.org/10.12688/f1000research.28336.1

© 2021 Kefalew T et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Kefalew T, Betemariyam M and Tolera M. Conversion of natural forests to farmlands and its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016): in the case of southwestern Ethiopia [version 1; peer review: 1 approved with reservations, 1 not approved]. F1000Research 2021, 10:227 (https://doi.org/10.12688/f1000research.28336.1)

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Reviewer Report 20 Oct 2021

Sigit D. Sasmito, NUS Environmental Research Institute, Singapore, Singapore

Approved with Reservations

https://doi.org/10.5256/f1000research.31345.r92406

This manuscript presents a set of assessments of tree species diversity and carbon stocks following land-use change. Such of this study is of interest broad audience in the context of land-based climate change mitigation strategies.

I have ... Continue reading

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section.
I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.
Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.
Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?
For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.
For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.
To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression?. Global Change Biology, 9(11), 1507-1514¹.
In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Good luck!

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

References

1. Gifford R, Roderick M: Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression?. Global Change Biology. 2003; 9 (11): 1507-1514 Publisher Full Text

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Wetlands ecology and greenhouse gas monitoring

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above.

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Author Response 29 Nov 2021

Mulugeta Betemariyam, Forestry, Madda Walabu University, Bale Robe, 247, Ethiopia

29 Nov 2021

Author Response
Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern ... Continue reading
Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I have a few suggestions below which may be used to improve the current manuscript.

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section

Thank you for your comments; the carbon stock values have been added to the revised manuscript abstract.

I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.

Thank you for your constructive comment. We kindly revised accordingly.

Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.

Thanks for the information; the suggested paragraph for removal from the introduction section has been removed.

Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?

Thank you for your input; in the amended manuscript, the technique for obtaining the data in table one, as well as the unit of the area shown in the table, are clearly defined.

For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.

Thank you for your comment; the sample size has been put to the table's heading as recommended.

For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.

Thank you for your comment; the sample values of organic matter lost as a result of the conversion of natural forest to forest farm interface and farmland are mentioned in the amended manuscript's discussion section.

To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression? Global Change Biology, 9(11), 1507-15141.

Thank you for sharing us with the sources from which we can obtain additional information. In this study, we employed the fixed depth method to determine the soil organic carbon. As stated in the results section, there was no significant variation in bulk density among the land uses. The estimation of soil organic carbon by employing fixed depth is recommended by authors who were cited in our paper method section if the bulk density is not indicated as a significant difference.

In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Thank you for your suggestion. We include a statement in the conclusion section outlining how our research could contribute to current literature on the issue and carbon monitoring in the context of Ethiopia's climate change mitigation strategy.
Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I have a few suggestions below which may be used to improve the current manuscript.

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section

Thank you for your comments; the carbon stock values have been added to the revised manuscript abstract.

I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.

Thank you for your constructive comment. We kindly revised accordingly.

Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.

Thanks for the information; the suggested paragraph for removal from the introduction section has been removed.

Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?

Thank you for your input; in the amended manuscript, the technique for obtaining the data in table one, as well as the unit of the area shown in the table, are clearly defined.

For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.

Thank you for your comment; the sample size has been put to the table's heading as recommended.

For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.

Thank you for your comment; the sample values of organic matter lost as a result of the conversion of natural forest to forest farm interface and farmland are mentioned in the amended manuscript's discussion section.

To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression? Global Change Biology, 9(11), 1507-15141.

Thank you for sharing us with the sources from which we can obtain additional information. In this study, we employed the fixed depth method to determine the soil organic carbon. As stated in the results section, there was no significant variation in bulk density among the land uses. The estimation of soil organic carbon by employing fixed depth is recommended by authors who were cited in our paper method section if the bulk density is not indicated as a significant difference.

In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Thank you for your suggestion. We include a statement in the conclusion section outlining how our research could contribute to current literature on the issue and carbon monitoring in the context of Ethiopia's climate change mitigation strategy.
Competing Interests: No competing interests Close
Report a concern
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COMMENTS ON THIS REPORT

Author Response 29 Nov 2021

Mulugeta Betemariyam, Forestry, Madda Walabu University, Bale Robe, 247, Ethiopia

29 Nov 2021

Author Response
Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern ... Continue reading
Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I have a few suggestions below which may be used to improve the current manuscript.

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section

Thank you for your comments; the carbon stock values have been added to the revised manuscript abstract.

I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.

Thank you for your constructive comment. We kindly revised accordingly.

Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.

Thanks for the information; the suggested paragraph for removal from the introduction section has been removed.

Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?

Thank you for your input; in the amended manuscript, the technique for obtaining the data in table one, as well as the unit of the area shown in the table, are clearly defined.

For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.

Thank you for your comment; the sample size has been put to the table's heading as recommended.

For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.

Thank you for your comment; the sample values of organic matter lost as a result of the conversion of natural forest to forest farm interface and farmland are mentioned in the amended manuscript's discussion section.

To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression? Global Change Biology, 9(11), 1507-15141.

Thank you for sharing us with the sources from which we can obtain additional information. In this study, we employed the fixed depth method to determine the soil organic carbon. As stated in the results section, there was no significant variation in bulk density among the land uses. The estimation of soil organic carbon by employing fixed depth is recommended by authors who were cited in our paper method section if the bulk density is not indicated as a significant difference.

In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Thank you for your suggestion. We include a statement in the conclusion section outlining how our research could contribute to current literature on the issue and carbon monitoring in the context of Ethiopia's climate change mitigation strategy.
Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I have a few suggestions below which may be used to improve the current manuscript.

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section

Thank you for your comments; the carbon stock values have been added to the revised manuscript abstract.

I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.

Thank you for your constructive comment. We kindly revised accordingly.

Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.

Thanks for the information; the suggested paragraph for removal from the introduction section has been removed.

Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?

Thank you for your input; in the amended manuscript, the technique for obtaining the data in table one, as well as the unit of the area shown in the table, are clearly defined.

For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.

Thank you for your comment; the sample size has been put to the table's heading as recommended.

For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.

Thank you for your comment; the sample values of organic matter lost as a result of the conversion of natural forest to forest farm interface and farmland are mentioned in the amended manuscript's discussion section.

To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression? Global Change Biology, 9(11), 1507-15141.

Thank you for sharing us with the sources from which we can obtain additional information. In this study, we employed the fixed depth method to determine the soil organic carbon. As stated in the results section, there was no significant variation in bulk density among the land uses. The estimation of soil organic carbon by employing fixed depth is recommended by authors who were cited in our paper method section if the bulk density is not indicated as a significant difference.

In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Thank you for your suggestion. We include a statement in the conclusion section outlining how our research could contribute to current literature on the issue and carbon monitoring in the context of Ethiopia's climate change mitigation strategy.
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Reviewer Report 04 Jun 2021

Arshad Ali, Department of Forest Resources Management, College of Forestry, Nanjing Forestry University, Nanjing, China

Not Approved

https://doi.org/10.5256/f1000research.31345.r83476

I read your paper carefully, and found it an interesting idea to compare three land use types such as NF, FFI and FL. I found a very interesting hypothesis at the end of introduction, but unfortunately your experimental design and statistical analyses do not allow to test this hypothesis in a clear way.

For example, you selected plots with different sizes and hence it is hard to compare with ANOVA only or any other simple statistics. I suggest testing the direct and indirect effects of plot size, and land use types (i.e., three categories) on species diversity, structure and biomass using structural equation models or multiple linear mixed effect models. Otherwise, it is hard to understand results and hence hard to get right conclusions.

Why did you used different biomass equations for NF, FFI and FL? Is this not affecting the biomass estimation amongst three types?

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

No
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

No
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: My broad-scale research interests are in the area of forest or plant ecology, particularly related to multiple abiotic and biotic controls on ecosystem functions and processes.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to state that I do not consider it to be of an acceptable scientific standard, for reasons outlined above.

CITE

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Author Response 29 Nov 2021

Mulugeta Betemariyam, Forestry, Madda Walabu University, Bale Robe, 247, Ethiopia

29 Nov 2021

Author Response
Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern ... Continue reading
Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I read your paper carefully, and found it an interesting idea to compare three land use types such as NF, FFI and FL. I found a very interesting hypothesis at the end of introduction, but unfortunately your experimental design and statistical analyses do not allow to test this hypothesis in a clear way. For example, you selected plots with different sizes and hence it is hard to compare with ANOVA only or any other simple statistics. I suggest testing the direct and indirect effects of plot size, and land use types (i.e., three categories) on species diversity, structure and biomass using structural equation models or multiple linear mixed effect models. Otherwise, it is hard to understand results and hence hard to get right conclusions.

In the statistical analysis section, we apologize for not explicitly expressing which types of statistical tests we utilized for the investigated parameters. We explicitly detailed how we test parameters in the revised manuscript. On comparison, the authors agreed that differences in sample sizes (plot size) affect carbon stocks, species richness, and structure. However, even if the sample size (plot size) for Farmland and other land uses for which comparison was made (NF, FFI) were different, the authors reached the comparison result after the individual plot size for each land use was converted to Ha (hectare) base, which the ANOVA can do for statistical differences. So, after similarizing the unit (ha) for each land use, we compared carbon stocks, diversity indices, and structural parameters among the three land uses following the ANOVA procedures.

Why did you used different biomass equations for NF, FFI and FL? Is this not affecting the biomass estimation amongst three types?

Many researchers have suggested that site conditions, management strategies, socioeconomic considerations, and farmer preferences could influence the distribution, diversity, and type of woody species (Tolera et al. 2008; Faye et al. 2011; IPCC, 2006; Chave et al. 2014; Kuyah et al., 2012). In our study area, 75 percent of the 70 different species identified do not have a specific allomnetric equation developed for them. As a result, we used an allometric equation developed for an agricultural landscape in Kenya (Kuyah et al., 2012), which has essentially similar bio-physical features to the research area for estimating the biomass of FFI and FL, and an allometric equation developed for natural forests in the tropical region by Chave et al. (2014) to estimate the biomass carbon stocks of natural forest.
Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I read your paper carefully, and found it an interesting idea to compare three land use types such as NF, FFI and FL. I found a very interesting hypothesis at the end of introduction, but unfortunately your experimental design and statistical analyses do not allow to test this hypothesis in a clear way. For example, you selected plots with different sizes and hence it is hard to compare with ANOVA only or any other simple statistics. I suggest testing the direct and indirect effects of plot size, and land use types (i.e., three categories) on species diversity, structure and biomass using structural equation models or multiple linear mixed effect models. Otherwise, it is hard to understand results and hence hard to get right conclusions.

In the statistical analysis section, we apologize for not explicitly expressing which types of statistical tests we utilized for the investigated parameters. We explicitly detailed how we test parameters in the revised manuscript. On comparison, the authors agreed that differences in sample sizes (plot size) affect carbon stocks, species richness, and structure. However, even if the sample size (plot size) for Farmland and other land uses for which comparison was made (NF, FFI) were different, the authors reached the comparison result after the individual plot size for each land use was converted to Ha (hectare) base, which the ANOVA can do for statistical differences. So, after similarizing the unit (ha) for each land use, we compared carbon stocks, diversity indices, and structural parameters among the three land uses following the ANOVA procedures.

Why did you used different biomass equations for NF, FFI and FL? Is this not affecting the biomass estimation amongst three types?

Many researchers have suggested that site conditions, management strategies, socioeconomic considerations, and farmer preferences could influence the distribution, diversity, and type of woody species (Tolera et al. 2008; Faye et al. 2011; IPCC, 2006; Chave et al. 2014; Kuyah et al., 2012). In our study area, 75 percent of the 70 different species identified do not have a specific allomnetric equation developed for them. As a result, we used an allometric equation developed for an agricultural landscape in Kenya (Kuyah et al., 2012), which has essentially similar bio-physical features to the research area for estimating the biomass of FFI and FL, and an allometric equation developed for natural forests in the tropical region by Chave et al. (2014) to estimate the biomass carbon stocks of natural forest.
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Author Response 29 Nov 2021

Mulugeta Betemariyam, Forestry, Madda Walabu University, Bale Robe, 247, Ethiopia

29 Nov 2021

Author Response
Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern ... Continue reading
Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I read your paper carefully, and found it an interesting idea to compare three land use types such as NF, FFI and FL. I found a very interesting hypothesis at the end of introduction, but unfortunately your experimental design and statistical analyses do not allow to test this hypothesis in a clear way. For example, you selected plots with different sizes and hence it is hard to compare with ANOVA only or any other simple statistics. I suggest testing the direct and indirect effects of plot size, and land use types (i.e., three categories) on species diversity, structure and biomass using structural equation models or multiple linear mixed effect models. Otherwise, it is hard to understand results and hence hard to get right conclusions.

In the statistical analysis section, we apologize for not explicitly expressing which types of statistical tests we utilized for the investigated parameters. We explicitly detailed how we test parameters in the revised manuscript. On comparison, the authors agreed that differences in sample sizes (plot size) affect carbon stocks, species richness, and structure. However, even if the sample size (plot size) for Farmland and other land uses for which comparison was made (NF, FFI) were different, the authors reached the comparison result after the individual plot size for each land use was converted to Ha (hectare) base, which the ANOVA can do for statistical differences. So, after similarizing the unit (ha) for each land use, we compared carbon stocks, diversity indices, and structural parameters among the three land uses following the ANOVA procedures.

Why did you used different biomass equations for NF, FFI and FL? Is this not affecting the biomass estimation amongst three types?

Many researchers have suggested that site conditions, management strategies, socioeconomic considerations, and farmer preferences could influence the distribution, diversity, and type of woody species (Tolera et al. 2008; Faye et al. 2011; IPCC, 2006; Chave et al. 2014; Kuyah et al., 2012). In our study area, 75 percent of the 70 different species identified do not have a specific allomnetric equation developed for them. As a result, we used an allometric equation developed for an agricultural landscape in Kenya (Kuyah et al., 2012), which has essentially similar bio-physical features to the research area for estimating the biomass of FFI and FL, and an allometric equation developed for natural forests in the tropical region by Chave et al. (2014) to estimate the biomass carbon stocks of natural forest.
Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I read your paper carefully, and found it an interesting idea to compare three land use types such as NF, FFI and FL. I found a very interesting hypothesis at the end of introduction, but unfortunately your experimental design and statistical analyses do not allow to test this hypothesis in a clear way. For example, you selected plots with different sizes and hence it is hard to compare with ANOVA only or any other simple statistics. I suggest testing the direct and indirect effects of plot size, and land use types (i.e., three categories) on species diversity, structure and biomass using structural equation models or multiple linear mixed effect models. Otherwise, it is hard to understand results and hence hard to get right conclusions.

In the statistical analysis section, we apologize for not explicitly expressing which types of statistical tests we utilized for the investigated parameters. We explicitly detailed how we test parameters in the revised manuscript. On comparison, the authors agreed that differences in sample sizes (plot size) affect carbon stocks, species richness, and structure. However, even if the sample size (plot size) for Farmland and other land uses for which comparison was made (NF, FFI) were different, the authors reached the comparison result after the individual plot size for each land use was converted to Ha (hectare) base, which the ANOVA can do for statistical differences. So, after similarizing the unit (ha) for each land use, we compared carbon stocks, diversity indices, and structural parameters among the three land uses following the ANOVA procedures.

Why did you used different biomass equations for NF, FFI and FL? Is this not affecting the biomass estimation amongst three types?

Many researchers have suggested that site conditions, management strategies, socioeconomic considerations, and farmer preferences could influence the distribution, diversity, and type of woody species (Tolera et al. 2008; Faye et al. 2011; IPCC, 2006; Chave et al. 2014; Kuyah et al., 2012). In our study area, 75 percent of the 70 different species identified do not have a specific allomnetric equation developed for them. As a result, we used an allometric equation developed for an agricultural landscape in Kenya (Kuyah et al., 2012), which has essentially similar bio-physical features to the research area for estimating the biomass of FFI and FL, and an allometric equation developed for natural forests in the tropical region by Chave et al. (2014) to estimate the biomass carbon stocks of natural forest.
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Arshad Ali, Nanjing Forestry University, Nanjing, China
Sigit D. Sasmito, NUS Environmental Research Institute, Singapore, Singapore
Girma Shumi, Leuphana University, Lüneburg, Germany

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15 Feb 2022 | for Version 2

Girma Shumi, Social-ecological Systems Institute (SESI), Faculty of Sustainability, Leuphana University, Lüneburg, Germany

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Not Approved

I read the manuscript carefully, and appreciate authors attempt to integrate ecological and GIS skills for analyzing the change in woody plant diversity and carbon sequestration potential in Gura-Ferda moist evergreen Afromontane forest. Nevertheless, the manuscript has many limitations to be considered for indexing, see my comments under each specific section below.

Title
“Conversion of natural forests to farmlands and its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016): in the case of southwestern Ethiopia”- it is not fit with or well represent the contents of the manuscript. The inconsistency can be illustrated, for example, from:

The title reads “Conversion of natural forests to farmlands”, but in the text starting from introduction up to the conclusion, the authors deal with Forest land use, forest farm interface land use and farmland use, although forest farm interface land use is not yet known in Ethiopia and elsewhere in the world.
Again, the title reads “its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016)”, but the authors analyse the current woody species diversity and carbon stocks across land use gradients, i.e. not change of species and carbon stock in a span of 33 years (from 1984 to 2016). The authors did not conduct any analysis that shows woody plant species and carbon stocks change across the land use gradients (the change could be positive (e.g. species gain or native species conservation) or negative (e.g. loss of species)) within specified period of time.

Thus, I recommend the authors to change the title.

Abstract
I also have concerns in abstract. Specifically:

First, Gura-Ferda forest belongs to moist evergreen Afromontane forest, see Friis et al. (2010): Atlas of the potential vegetation of Ethiopia. Royal Danish Academy of Science and Letters, Copenhagen.

Thus, I recommend authors to use " moist evergreen Afromontane forest" here in Abstract and throughout the text.

Second, what is forest farm interface land use? Is it degraded forest or agroforestry system or what? Somewhere in the text (I think in the discussion section), is treated as coffee management system, authors can use it for stratifying the study site (as they did it in methods section), but as to me it is confusing to use it as a land use. I suggest you find other universally known or acceptable term, at least from Ethiopian perspective. For study area stratification, it is okay to use "forest farm interface"
Third, the authors did not conduct analysis that show or revealed changes in species diversity and carbon stocks across the land-use gradients; See your methods and results and other related studies. Off course, you did land cover change analysis but not woody plant species and carbon stocks change (see my comment above also).

Thus, these need attention and clarification to improve the abstract and its conclusion.

Introduction
The introduction is hard to follow and to identify research gap/s.

a) The authors start with the problem of forest management and conversion. The introduction can benefit more on understanding the impact of land use change (i.e. deforestation, forest degradation and agricultural intensification) on biodiversity, if authors acquainted with and incorporated recent findings from IPBES: The global assessment report on and ecosystem biodiversity services summary for policymakers; WWF: Living planet report 2020: Bending the curve of biodiversity loss globally; Shumi et al. (2019): Conservation value of moist evergreen Afromontane forest sites with different management and history in southwestern Ethiopia¹, and other related works that focus on the problems of sustainable land use nowadays.

b) In the introduction, the authors stated that “Ethiopia’s ecosystem is diverse, ranging from the dry lowlands in the east to the high altitudes of the central highlands (Hurni, 1998). The country’s unique ecological conditions, as well as its rich flora and fauna, have made it one of the most important biodiversity hotspots on the world”, I suggest getting out of such notions, especially in higher education system of Ethiopia, as we are in era of Anthropocene and those kind of approaches are misleading biodiversity conservation and land management practices. E.g. see Jackson and Sax (2010): Balancing biodiversity in a changing environment: extinction debt, immigration credit and species turnover².

c) After introducing southwestern biodiverse forest, the authors stated “Similarly, other remaining natural forests have also been threatened by pressure from investors and changed to industrial plantation like coffee and tea”, this breaks the flow of idea. As far as the study is conducted in southwestern Ethiopia, I would suggest if the narratives of introduction could start with global aspects of biodiversity loss, then, in Ethiopia, and finally specific in southwestern Ethiopia.

d) Then, they wrote “This reduction and conversion of natural forest to other land use systems in many parts of Ethiopia has led to the decline in number and distribution of many plant species, shortage of raw materials for wood processing industries and disturbance of ecosystem services⁶. As a consequence, forest farm interface has expanded within and around the natural forest. Subsequently, it has resulted the expansion of forest farm interface in and around the forest ecosystem.”, here, one can ask or raise concerns such as:

A contradicting arguments, loss of species at local or landscape level in southwestern Ethiopia (or ???) and lack of raw materials for industries – large plantation or advocating for land use intensification.
I do not think that the cited reference (6) is the correct one here.
What is the impact of deforestation, forest degradation and agricultural or land use intensification on to local people, e.g. Meinit people, who used to live in forest (I think in that forest)? But see Ango et al. (2014): Balancing Ecosystem Services and Disservices: Smallholder Farmers’ Use and Management of Forest and Trees in an Agricultural Landscape in Southwestern Ethiopia³; and Shumi et al. (2019a): Woody plant use and management in relation to property rights: a social-ecological case study from southwestern Ethiopia⁴, for how the local community depend on woody plant species than favoring raw materials for wood processing industries or commodification of landscape, business as usual approaches. In fact, granting such provisioning and cultural ecosystem service to local people at local level also underpins important regulating and supporting ecosystem services. See Raudsepp-Hearne et al. (2010): Ecosystem service bundles for analyzing tradeoffs in diverse landscapes⁵.
What is forest farm interface? Is it degraded forest or degraded farmland (arable land, grazing land and homegarden)? Or is it secondary forest? I do not agree with the definition provided by authors in subsequent paragraph. (See my comment above).
Check for redundancy of the last two sentences.

e) The authors stated: “Hundreds of aid projects have been implemented in different parts of the country to reverse deforestation and forest degradation in the country. However, the success stories were below expectations and the problems are still immense. This resulted from the lack of effective management practices and quantification of the available forest resources. This insufficiency of scientific quantitative data brought lack of responsiveness for sound management of natural resources in the country.”. According to these statements, the problem of biodiversity loss is not land use change (i.e. deforestation, forest degradation and agricultural intensification), rather it is lack of monitoring of restoration, and existing forest management in the country. I suggest to clearly focus on what to be studied in the region.

f) What is the need of bringing “Gura-Ferda forest is one of the Afromontane rainforests in the southwestern region of Ethiopia and grows at altitudes from 700 to 2,300 meter above sea level.” into introduction? Better to take it to methods section.

g) The reason why the authors analyze the woody species diversity and carbon stock change in Gura-ferda forest (i.e. the research gap/s) is not indicated or stated clearly. Specifically, why carbon stock? The hypothesis is also weak or, obvious, i.e. change in woody plant species diversity and carbon stock from forest to degraded forest and then, to farmland is obvious, so what makes their hypothesis unique?

Materials and methods

1) If I am not mistaken Gura-Ferda district is situated in Bench-Majii zone, in SNNP region, I do not know why the authors afraid to mention this give clear information of about their study area.

2) I suggest taking “Table 1” under methodology.

3) Under methodology, instead of “Data source”, I suggest land use mapping and stratification of study area”. Then, remove “Table 2”; “Figure 2”; and “Figure 3”, as these are not the focus of the study. Here, maybe see the methods in my paper, Shumi et al. (2019): Conservation value of moist evergreen Afromontane forest sites with different management and history in southwestern Ethiopia¹.

4) I suggest deleting “Figure 4”, as sampling method is described well in text.

5) Take subtitle “Biomass carbon stock estimation” and “Soil organic carbon (SOC) stock estimation” under methodology before data analysis.

Results

a) Where is the results of spices change analysis? Change analysis is the aim of the study.

b) How the authors compare species diversity in forest with forest farm interface and farmland? Here, different ecosystems, land use types are suitable for different groups or guilds of species, mainly forest specialist species, generalist species and pioneer species. See my paper, Shumi et al. (2019): Conservation value of moist evergreen Afromontane forest sites with different management and history in southwestern Ethiopia¹.

c) Why the Simpson (D) index? As it is not specified under methods section. What is the difference between the Simpson (D) and Shannon diversity index (H’)?

d) Here, many abbreviations “NF”, “FFI”, “FL”, “D”, “H’” may confuse the readers.

e) Where is the results of carbon stock change analysis? Carbon stocks change analysis is the aim of the study.

f) I suggest taking “Where, AGBC is aboveground biomass C stocks, BGBC is belowground biomass C stocks, TBC is total biomass C stocks, SOC is soil organic C stocks and TCS is total C stocks. Different letters show significant (p<0.05) different between Land Uses, and similar letters not significance differences” to “Table 5” caption.

g) Again, “Different letters on similar soil parameters of different land uses indicate a significant difference across Land Uses (p<0.05), but similar letters do not show a significant difference across Land Uses.” to “Table 6”.

h) Take “The total C stock of the study area was calculated by summing up all the C value of each pool.” to the methods section.

Discussions

1) The discussion opened by statement: “The degree of human interference and disturbance caused by overexploitation of forest resources, overgrazing, the establishment of new settlements, and the conversion of forest to coffee plantation for long periods could be attributed to the variation in species composition among the NF, FFI, and FL of Gura-Ferda district. Almost all of the woody species found in the FFI and FL were not planted, but rather were left over from the conversion of the NF to the FFI and FL.”. What about species adaptation to different environment or land uses? See my comment above.

2) It is not clear why the authors compare this forest, “moist evergreen Afromontane forest” with Jibat humid Afromontane forest, “Dry Afromontane forest”. The same with Gendo moist afromontane forest, Gole Forest, and Wondo Genet Afromontane forest. Here, not only the biophysical conditions of the forests, but also the methods used by matters. Maybe check this?

3) The authors said “As shown in Table (1), FFI which emerged after the resettlement program of 1984 accounts for 23.28% of the NF within 1984–2016-year interval. As reported by 11, and 10, the main problem related to land use land cover change at Gura-Ferda district was agricultural investment, fuel wood collection, wood for house construction and farm implementation, wildfire, resettlement, land certification, poor governance within the district, and subsistence agricultural land expansion.”, here, they want to discuss species diversity change – forest degradation or land cover change? How does land certification and poor governance within the district affect land cover change?

4) While their analysis did not quantify species loss, why the authors reported species loss in “Therefore, this increment of unregistered or unplanned farms and FL resulted from above mentioned drivers are the main causes for the loss of woody species diversity in the study area.”, is not clear.

5) Why are farmers blamed here? Alternatively, are they investors? Very contradicting statement “According to Gura-Ferda district land administration report, large areas of extra land were recorded for each farmer. The farmers had expanded their farmland into nearby forest, shrub/bush land and grass land and used those land uses for commercial crop production.”

6) Is there coffee management systems in the area? If so, I suggest to discuss or brining in this issue in the introduction also.

7) The discussion on carbon stocks also needs attention, including justification – clearly stating problem statement in the introduction for conducting carbon stock study in the area.

Conclusion
Authors suggest the needs for land use certification for the system to be sustainable, i.e. “If the NF is not sustainably managed and certification of land is not carried out in the area, there will be expansion of FFI and FL which will cause further deforestation and forest degradation.”. But, in Ethiopia, particularly in southwestern Ethiopia, land use certification did not guarantee land tenure security and biodiversity conservation. See my paper Shumi et al. (2019a): Woody plant use and management in relation to property rights: a social-ecological case study from southwestern Ethiopia⁴.

The authors call for landscape commodification than biodiversity conservation. As I read it from the manuscript, although not yet clearly stated, carbon stock assessment for landscape commodification seems to be the main essence of this study. In emerging social-ecological system research, however, researchers in this field argued that landscape commodification or marketing has an impact on both the ecosystem services (biodiversity protection) and human, particularly local people well-being, for example, see Go´mez-Baggethun and Naredo (2015): In search of lost time: the rise and fall of limits to growth in international sustainability policy⁶; Osborne et al (2021): The political ecology playbook for ecosystem restoration: Principles for effective, equitable, and transformative landscapes⁷; and Pham et al (2021): REDD+ finance in Brazil, Indonesia and Vietnam: Stakeholder perspectives between 2009-2019⁸. From Ethiopian context, how could the authors concede this argument? I would like to know the stand of the authors in this regard.

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Partly
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

No
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

No

References

1. Shumi G, Rodrigues P, Schultner J, Dorresteijn I, et al.: Conservation value of moist evergreen Afromontane forest sites with different management and history in southwestern Ethiopia. Biological Conservation. 2019; 232: 117-126 Publisher Full Text
2. Jackson ST, Sax DF: Balancing biodiversity in a changing environment: extinction debt, immigration credit and species turnover.Trends Ecol Evol. 2010; 25 (3): 153-60 PubMed Abstract | Publisher Full Text
3. Ango T, Börjeson L, Senbeta F, Hylander K: Balancing Ecosystem Services and Disservices: Smallholder Farmers’ Use and Management of Forest and Trees in an Agricultural Landscape in Southwestern Ethiopia. Ecology and Society. 2014; 19 (1). Publisher Full Text
4. Shumi G, Dorresteijn I, Schultner J, Hylander K, et al.: Woody plant use and management in relation to property rights: a social-ecological case study from southwestern Ethiopia. Ecosystems and People. 2019; 15 (1): 303-316 Publisher Full Text
5. Raudsepp-Hearne C, Peterson GD, Bennett EM: Ecosystem service bundles for analyzing tradeoffs in diverse landscapes.Proc Natl Acad Sci U S A. 2010; 107 (11): 5242-7 PubMed Abstract | Publisher Full Text
6. Gómez-Baggethun E, Naredo J: In search of lost time: the rise and fall of limits to growth in international sustainability policy. Sustainability Science. 2015; 10 (3): 385-395 Publisher Full Text
7. Osborne T, Brock S, Chazdon R, Chomba S, et al.: The political ecology playbook for ecosystem restoration: Principles for effective, equitable, and transformative landscapes. Global Environmental Change. 2021; 70. Publisher Full Text
8. Pham T, Moeliono M, Yuwono J, Dwisatrio B, et al.: REDD+ finance in Brazil, Indonesia and Vietnam: Stakeholder perspectives between 2009-2019. Global Environmental Change. 2021; 70. Publisher Full Text

Competing Interests

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Reviewer Expertise

My research areas are social-ecological system resilience, particularly woody plant biodiversity conservation and ecosystem services, local people well-being, human-nature connectedness and landscape sustainability.

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17 Dec 2021 | for Version 2

Sigit D. Sasmito, NUS Environmental Research Institute, Singapore, Singapore

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Approved

The authors have addressed my previous concerns adequately. The revised version of the manuscript is much improved. I have only two minor comments: 1) authors may need to use less abbreviation throughout the manuscript text to improve the paper readability, 2) please add fieldwork sampling year in the sampling technique for any future relevant study.
Great work!

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No competing interests were disclosed.

Reviewer Expertise

Wetlands ecology and greenhouse gas monitoring

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Reviewer Report

21 Views

20 Oct 2021 | for Version 1

Sigit D. Sasmito, NUS Environmental Research Institute, Singapore, Singapore

21 Views Cite this report Responses(1)

Approved With Reservations

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section.
I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.
Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.
Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?
For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.
For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.
To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression?. Global Change Biology, 9(11), 1507-1514¹.
In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Good luck!

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

References

1. Gifford R, Roderick M: Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression?. Global Change Biology. 2003; 9 (11): 1507-1514 Publisher Full Text

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Wetlands ecology and greenhouse gas monitoring

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Author Response

29 Nov 2021

Mulugeta Betemariyam, Forestry, Madda Walabu University, Bale Robe, 247, Ethiopia

Dear Sigit D. Sasmito
We are grateful for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I have a few suggestions below which may be used to improve the current manuscript.

I’d suggest providing carbon stocks value across land-use change in the abstract’s result section

Thank you for your comments; the carbon stock values have been added to the revised manuscript abstract.

I’d drop the current first paragraph in the intro. It is too broad and you have to be direct to the Ethiopia case.

Thank you for your constructive comment. We kindly revised accordingly.

Some references may be needed for the following statement “For the past five decades, the government of Ethiopia has attempted to reforest degraded forests.” and other few next sentences in this paragraph.

Thanks for the information; the suggested paragraph for removal from the introduction section has been removed.

Table 1: I didn’t see how the authors get the data presented in Table 1. What is the unit of the area data in 1984 and 2016?

Thank you for your input; in the amended manuscript, the technique for obtaining the data in table one, as well as the unit of the area shown in the table, are clearly defined.

For Tables 6,7 and 8: I’d suggest authors provide n sample size in addition to the current mean and SD. The soil C stocks are pretty high indeed. To support your soil carbon stocks numbers, I’d suggest providing the bulk density and %C (carbon content) in an additional table.

Thank you for your comment; the sample size has been put to the table's heading as recommended.

For the discussion section under carbon stocks: could you further explore whether soil erosion occurs following forest degradation? This erosion may lead to organic matter loss from the upper soil layer.

Thank you for your comment; the sample values of organic matter lost as a result of the conversion of natural forest to forest farm interface and farmland are mentioned in the amended manuscript's discussion section.

To test if the forest conversion or land-use change generates soil carbon loss, you may use both the fixed depth and mass balance approach. See the following paper for further information about two approaches: Gifford, R. M., & Roderick, M. L. (2003). Soil carbon stocks and bulk density: spatial or cumulative mass coordinates as a basis of expression? Global Change Biology, 9(11), 1507-15141.

Thank you for sharing us with the sources from which we can obtain additional information. In this study, we employed the fixed depth method to determine the soil organic carbon. As stated in the results section, there was no significant variation in bulk density among the land uses. The estimation of soil organic carbon by employing fixed depth is recommended by authors who were cited in our paper method section if the bulk density is not indicated as a significant difference.

In the conclusion section, I’d suggest adding a few sentences describing how your study could support current literature on this topic and carbon monitoring in the context of climate change mitigation strategy in Ethiopia.

Thank you for your suggestion. We include a statement in the conclusion section outlining how our research could contribute to current literature on the issue and carbon monitoring in the context of Ethiopia's climate change mitigation strategy.

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Reviewer Report

44 Views

04 Jun 2021 | for Version 1

Arshad Ali, Department of Forest Resources Management, College of Forestry, Nanjing Forestry University, Nanjing, China

44 Views Cite this report Responses(1)

Not Approved

Is the work clearly and accurately presented and does it cite the current literature?

Partly
Is the study design appropriate and is the work technically sound?

No
Are sufficient details of methods and analysis provided to allow replication by others?

No
If applicable, is the statistical analysis and its interpretation appropriate?

No
Are all the source data underlying the results available to ensure full reproducibility?

Partly
Are the conclusions drawn adequately supported by the results?

Partly

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

My broad-scale research interests are in the area of forest or plant ecology, particularly related to multiple abiotic and biotic controls on ecosystem functions and processes.

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Author Response

29 Nov 2021

Mulugeta Betemariyam, Forestry, Madda Walabu University, Bale Robe, 247, Ethiopia

Dear Arshad Ali
We are grateful to the reviewer for insightful and constructive comments on our manuscript, "Conversion of natural forests to farmlands and associated woody species diversity and carbon stocks in southwestern Ethiopia during 33 years (1984 to 2016)." We have attempted to address all comments in this revised manuscript and believe that the manuscript, especially the language, has substantially improved. Track changes for changes made to the original version were added to the page where specific changes were required. Our responses to the specific comments are presented below.

I read your paper carefully, and found it an interesting idea to compare three land use types such as NF, FFI and FL. I found a very interesting hypothesis at the end of introduction, but unfortunately your experimental design and statistical analyses do not allow to test this hypothesis in a clear way. For example, you selected plots with different sizes and hence it is hard to compare with ANOVA only or any other simple statistics. I suggest testing the direct and indirect effects of plot size, and land use types (i.e., three categories) on species diversity, structure and biomass using structural equation models or multiple linear mixed effect models. Otherwise, it is hard to understand results and hence hard to get right conclusions.

In the statistical analysis section, we apologize for not explicitly expressing which types of statistical tests we utilized for the investigated parameters. We explicitly detailed how we test parameters in the revised manuscript. On comparison, the authors agreed that differences in sample sizes (plot size) affect carbon stocks, species richness, and structure. However, even if the sample size (plot size) for Farmland and other land uses for which comparison was made (NF, FFI) were different, the authors reached the comparison result after the individual plot size for each land use was converted to Ha (hectare) base, which the ANOVA can do for statistical differences. So, after similarizing the unit (ha) for each land use, we compared carbon stocks, diversity indices, and structural parameters among the three land uses following the ANOVA procedures.

Why did you used different biomass equations for NF, FFI and FL? Is this not affecting the biomass estimation amongst three types?

Many researchers have suggested that site conditions, management strategies, socioeconomic considerations, and farmer preferences could influence the distribution, diversity, and type of woody species (Tolera et al. 2008; Faye et al. 2011; IPCC, 2006; Chave et al. 2014; Kuyah et al., 2012). In our study area, 75 percent of the 70 different species identified do not have a specific allomnetric equation developed for them. As a result, we used an allometric equation developed for an agricultural landscape in Kenya (Kuyah et al., 2012), which has essentially similar bio-physical features to the research area for estimating the biomass of FFI and FL, and an allometric equation developed for natural forests in the tropical region by Chave et al. (2014) to estimate the biomass carbon stocks of natural forest.

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Competing Interests

No competing interests

Alongside their report, reviewers assign a status to the article:

Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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Conversion of natural forests to farmlands and its associated woody species diversity and carbon stocks in a span of 33 years (1984 to 2016): in the case of southwestern Ethiopia

Abstract

Keywords

Introduction

Methods

Description of the study area

Figure 1. The nested map of Ethiopia showing the map of study region and zonal map of the study district.

Table 1. Converted area from natural forest to forest farm interface and farmland within the span of 33 years (1984 and 2016).

Methodology

Data source

Table 2. Time series satellite images of the study area.

Stratification of study area

Figure 2. map of Natural Forest of Gura-Ferda district in 1984 (Source: Authors).

Figure 3. map of Natural Forest, Forest Farm Interface and Farmlands of Gura-Ferda district in 2016 (Source: Authors).

Sampling techniques

Figure 4. Sampling design of woody species in in the studied land use systems of Gura-Ferda district.

Data analysis

Biomass carbon stock estimation

Table 3. Allometric equations used to estimate the biomass carbon stocks of natural forest, forest farm interface and farmlands in Gura-Ferda district, southwestern Ethiopia.

Statistical analysis

Results

Woody Species Diversity

Table 4. Species richness, evenness and diversity indices of Natural Forest, Forest Farm Interface and Farm Land in Gura-Ferda District, southwestern Ethiopia.

Table 5. Pair wise comparison of Sorensen’s similarity coefficient and beta diversity index in species composition among Natural Forest, Forest Farm Interface and Farm Land in Gura-Ferda District, southwestern Ethiopia.

Carbon stocks

Table 6. (Mean ± SD) of above and belowground biomass carbon stocks of Natural Forest, Forest Farm Interface and Farm Land (Mg C ha-1) in Guraferda District, southwestern Ethiopia.

Table 7. (Mean ± SD) of soil organic carbon (SOC) of Natural Forest, Forest Farm Interface and Farm Land (Mg C ha-1) in Gura-Ferda District, southwestern Ethiopia.

Table 8. Total carbon stocks of Natural Forest, Forest Farm Interface and Farmland (Mg C ha-1) in Gura-Ferda District, southwestern Ethiopia.

Discussion

Woody species diversity

Carbon stocks

Conclusion

Data availability

Underlying data

Acknowledgements

References

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Table 6. (Mean ± SD) of above and belowground biomass carbon stocks of Natural Forest, Forest Farm Interface and Farm Land (Mg C ha^-1) in Guraferda District, southwestern Ethiopia.

Table 7. (Mean ± SD) of soil organic carbon (SOC) of Natural Forest, Forest Farm Interface and Farm Land (Mg C ha^-1) in Gura-Ferda District, southwestern Ethiopia.

Table 8. Total carbon stocks of Natural Forest, Forest Farm Interface and Farmland (Mg C ha^-1) in Gura-Ferda District, southwestern Ethiopia.