1. Submitted to “Journal of Chinese Soil and Water Conservation” (13-6- 2019)
2. Notification of article status from editor (18-6-2021)
3. Manuscript review: Accepted with mayor revision (26-6-2019) 4. Revision has been sent (30-6-2019)
5. The 2nd stage Revision Notice (18 -8-2019) 6. Manuscript improvement stage 2 (16-9-2019) 7. Manuscript improvement stage 3 (5-10-2019) 8. Proof (30-10-2019)
9. Accepted for publication (6-11-2019)
Submitted (13-6-2019)
SUBMISSION OF NEW MANUSCRIPT FOR EVALUATION
Naharuddin Sumani <[email protected]> 13 Jun 2019 04.40
I am enclosing herewith a abstract manuscript entitled “EROSİON HAZARD ASSESSMENT İN FOREST AND LAND REHABİLİTATİON FOR TAMBUN WATERSHED MANAGEMENT, TOLİTOLİ, CENTRAL SULAWESİ, INDONESİA” Submitted to Journal of Chinese Soil and Water Conservation for possible evaluation.
With the submission of this manuscript I would like to undertake that the above mentioned manuscript has not been published elsewhere, accepted for publication elsewhere or under editorial review for publication elsewhere; and that my Institute’s UNIVERSITAS TADULAKO representative is fully aware of this submission.
Best Regards,
Naharuddin
EROSION HAZARD ASSESSMENT IN FOREST AND LAND REHABILITATION FOR TAMBUN WATERSHED
MANAGEMENT, TOLITOLI, INDONESIA
Naharuddin1*, Abdul Wahid1, Rukmi1 and Sustri1
1Tadulako University, Faculty of Forestry, Forestry Department, Palu City, Central Sulawesi, Indonesia
* Coresponding author: [email protected]
ABSTRACT
In conducting Forest and Land Rehabilitation (FLR), the watershed is the major unit of watershed management. The watershed approach is also the basis of FLR evaluation including evaluations of the hydrology aspect, land erosion, and other environmental aspects. The FLR in Tambun watershed has been done since 10 years ago in 2002 to 2012. Currently, sustainable FLR planning is under the progress. This research was conducted to identify the level of erosion hazard as the impact of FLR done in Tambun Watershed, Tolitoli, Central Sulawesi. The analysis of erosion hazard level was conducted using USLE equation. The results of this research showed that the FLR done in community forest and nursery in which sengon and nantu trees were planted has been able to decrease the rate of soil erosion from 952.5 ton/ha/year (before FLR) to 920.59 ton/ha/year. After the FLR, the average erosion level was considered in the moderate category between 15-60 ton/year which included 124 ha (0.91%) in community nursery and 10 ha (0.07%) in community forest.
Keywords: erosion, watershed, rehabilitation, forest, land
INTRUDUCTION
A total of 96.3 millions ha of forest area in Indonesia has been degraded due to illegal logging, fires, land conversion, and unplanned land expansion for agricultural purposes.
54.6 millions ha out of the total forest area mentioned above has been predicted to face degradation including the area of productive forest, conservation forest and protected forest, while 41.7 millions ha of the degraded land were land outside forest area. Forests reduced sediment yield consequensi of erosion by tolerating negative consequences of other factors in the watershed area (Reis et al., 2016). Land use and land cover change are important research objects as they relate with the interaction between human activities and the natural environment (Alkharabsheh et al., 2013).
Watershed is the area where watershed management is done to maintain the water quality (Komaruddin, 2008). The land use around watershed affects the water quality and causes increases in erosion sediment rate. Increases in the rate of soil erosion and increases in the total area of critical land are obvious impacts of land shifts in land use (Pawitan, 2004). The shift in the land use and land cover change, rain falls, the kind of soil, including improper exploration of land affect the erosion rate (Chaudhry, 1988; Fu et al., 2000; García-Ruiz, 2010). Planting system, land and water conservation, land management system and water management system need to be designed to control land erosion and degradation (El-Swaify, 1997; Abu-Hamdeh et al., 2018)
Erosion is the movement or transport of soil particles or sediments due to the pressure caused by the movement of wind or water on the surface of the ground or the bottom of the water (Poerbandono et al., 2006; Pimentel, 2006; Gitas et al., 2009). Soil erosion decreases the soil fertility and brings negative impacts on watershed in the form of environmental problems. It also threatens the sustainability of agriculture and water quality (Bakker et al., 2005; Panomtaranichagul and Nareuban, 2005; Pandey et al., 2007). Along watershed environment, erosion rates are affected by the speed of water flow and the characteristics of the sediments (Herawati, 2010). To assess estimate the amount of soil loss from erosion, Universal Soil Loss Equation method can be used (Gitas et al., 2009; Pham et al., 2018). This method can be applied in any watersheds prior to preparing conservation master plans and enabling efficient use of resources (Bewket and Teferi, 2009).
Forest and land degradation causes decreases in land productivity as it increases the area of critical land and brings other ecological impacts. Therefore forest and land rehabilitation (FLR) programs are needed. Some important points should be considered in planning FLR programs and benchmarks in overcoming surface runoff and erosion as well as improving the quality and function of watersheds should be determined to evaluate the success of the program. Agricultural land management practices play an important role in controlling soil erosions such as land loss that decreases exponentially due to increases in vegetation cover (Khan et al., 2003; Gyssels et al., 2005). It is also
necessary to have proper understanding regarding basic processes and factors that influence land degradation, especially soil erosion and other phenomena in implementing the concept, design, and implementation of productive, stable and sustainable agricultural systems (El-Swaify, 1997).
The map of soil erosion hazard is important in erosion-prone areas because it explains and displays the distribution of hazards and areas that are likely to be affected within watershed management (Rahman et al., 2009).
Tambun watershed is administratively located in Tolitoli District, Central Sulawesi with an area of 13,563.42 ha. The position and height of the place make the Tambun watershed function as a buffer zone for the capital of Tolitoli Regency. The function of this area as buffer zone in relation to the amount of critical land, frequent flooding and landslides makes RFL an urgent agenda. The effectiveness of FLR can be seen in the effects of FLR programs implemented in Tambun watershed in 2011 namely community forest development, which program covered an area of 10 ha and the program done in in 2012 in the form of reconstruction of 124 ha of community nursery.
In the implementation of watershed management and to find out the impact of FLR watershed management in Tambun watershed, an analysis of erosion hazard level after FLR program needs to be conducted. It is also important to analyze its effect on the management of watersheds. Therefore, development simulations can be arranged towards for better sustainability of Tambun watershed in the future.
This study was conducted to identify the post-FLR erosion level in Tambun watershed, Tolitoli using the USLE equation. The results of this research were expected to provide valuable insights in the planning of Tambun watershed management for healthier watershed, especially in overcoming the level of erosion hazard.
MATERIALS AND METHODS
Research Setting: This research was conducted from March to October 2018 in Tambun Watershed, Tolitoli, Central Sulawesi, Indonesia. As large as 10 ha of land in
the location was developed in 2011 as community forest, and in 2012, 124 ha of land was developed as community nursery.
Tambun watershed is geographically located at the coordinate of 120° 49' 52.98"
E 0° 58' 27.29" N (Figure 1).
Figure 1: Location of the Research
Research Method: The research was conducted in the form of surveys by obtaining soil samples from the research location to be further analyzed in the laboratory of the
Faculty of Agriculture, Tadulako University. The soil sampling technique was carried out using purposive sampling based on the land use and on FLR land, slope and soil conditions.
The data were then analyzed using the Universal Soil Loss Equation (USLE) equation.
Furthermore, the erosion hazard level (TBE) was determined by comparing the actual (A) erosion to the tolerable erosion (T). The data included time series data regarding the last 10 years rainfall, soil physical properties, slope length, soil and plant management.
Data Collection
The data collected in this research included primary and secondary data in the forms of desciptions of soil properties, length and incline of the slope, plant management system from the field and the data regarding rainfall amount obtained from the nearest climatology station. Furthermore, samples of whole soil and non-whole soil were retrieved based on ring sample in order to measure the permeability, texture, bulk density and organic contents in the soil (Figure 2).
Figure 2. Soil Sample Data Collection
Creating Land Unit Map: A land unit map was prepared by overlaying maps in the form of: geomorphological maps, rainfall maps, geological maps, attack maps, land maps, land use maps, slope class maps, basic maps of visual maps at 1:25.000 scale to calculate the erosion hazard. Information on this land unit were obtained from the results of interpretation of aerial photographs, ground checks, retrieval and sample soil information and some other information from related institutions.
Data Analysis: As instructed by Wischmeier and Smith, (1978), erosion rate is calculated using the USLE method (Ma et al, 2003; Cardei et al., 2009; Patil, 2018; Lin et al., 2019) as follows:
A = R * K * L * S * C * P
Remarks A: maximum amount of land loss (ton / ha / year); R: rainfall factor; K: soil erodibility factor; LS: factor length and slope; C: vegetation cover and plant management factors; P: soil conservation action factor.
The erosion hazard rate (TBE) is determined by comparing potential erosion (A) with tolerable erosion (T), using this following formula:
TBE = A / T with erosion hazard criteria according to Table 1:
Table 1: Criteria of Erosion Hazard Level Classification of Erosion
Hazard
Land Loss Criteria
I <15 Very Low
II 15-60 Low
III 60-180 Moderate
IV 180-480 Hight
V >480 Very High
RESULTS AND DISCUSSIONS
Land Use: Based on the results of image analysis and current ground check, land use in the Tambun watershed after FLR consisted of primary dryland forests, secondary dryland forests, plantations, settlements, dry land agriculture, dry land agriculture mixed with shrubs, rice fields, community nurseries, and community forest (Table 2).
Table 2: The Use of Land in Tambun Watershed after FLR
Land Use Total Area
(ha) (%)
Primary dryland forest Secondary dryland forest Plantation area
Settlement
Dryland agriculture Mixed dryland agriculture Rice fields
Community nursery Community forest
2,781.26 1,984.95 194.86 145.45 1,863.46 5,672.74 786.70 124 10
20.51 14.63 1.44 1.07 13.74 41.82 5.80 0.91 0.07
Total 13,563.42 100
Land use indicates the accomplishment of regional development in terms of land productivity and the influence of human activities. Alkharabsheh et al. (2013) stated that the risk of soil erosion is strongly influenced by the use and form of land management besides it is also affected by watershed configuration (topography, shape), soil characteristics, climate conditions. Land use strongly influences the erosion rate in a watershed as it either reduces or increases the effect of rainfall that occurs.
Prediction of Erosion: The prediction of soil erosion was administered on each land use using the USLE method involving all factors; rainfall (R), soil erodibility (K), slope length and slope (LS), vegetation cover and crop management (C), and soil conservation action factor (P). The actual erosion scores after forest and land rehabilitation in the Tambun watershed are presented in Table 3.
Table 3: Actual Erosion in Tambun Watershed before FLR
Land Use R K LS C P A
(ton/ha/tahun)
Primary dryland forest 1358.73 0.59 9.5 0.001 1 7.61
Secondary dry forest 1358.73 0.56 9.5 0.005 1 36.14
Plantation area 1358.73 0.55 3.1 0.32 1 741.31
Settlement 1358.73 0.29 1.20 0.1 1 47.28
Dryland agriculture 1358.73 0.56 6.8 0.01 1 51.74
Mixed dryland agriculture 1358.73 0.52 6.8 0.01 1 48.04
Rice fields 1358.73 0.15 0.2 0.5 1 20.38
Total 952.5
As seen in Table 3, the actual erosion that occurred before FLR was 952.5 tons / ha / year (range 7.61 - 741.31 tons / ha / year), the largest actual erosion was 741.31 tons / ha / year occurred in the form of plantation land use at the slope rate of 25% -40%
(steep) red yellow podsolic type. Meanwhile the smallest actual erosion of 7.61 tons / ha / year occured in primary dryland forest land use at an average slope rate of 25% -40%
(steep) to> 45% (very steep) red yellow podsolic type .
The strong erosion potential in the use of land for plantation was due to the fact that the land was mostly planted with Syzygium aromaticum and Theobroma cacao, making this land less capable in reducing rainwater collisions on the soil and shallow root systems, and causing soil drainage system less effective. To control the rate of soil erosion in this area, it is necessary to perform mulching techniques and conservation farming systems.
This idea is supported by Keesstra et al. (2019), who also believe that mulch can be used as a land management practice to control the rate of soil erosion.
In primary dryland forests, the average erosion rate was relatively smaller at 7.61 tons / ha / year. Based on the results of the ground check, the presence of trees with various strata formed canopy strata (Figure 3). Complete canopy structure plays a role in helping to reduce the kinetic rate of rainwater falling into the canopy. Therefore, when rainwater reaches the lowest canopy strata, the size of the raindrops becomes much smaller and the kinetic energy of the rain becomes weaker. Although this land is on a steep slope to very steep yet it does not have a significant effect. Litter that falls on the surface of the soil also plays a role in protecting the soil surface from direct collisions of rainwater and can improve soil infiltration capacity, making erosion on this type of land relatively lower. In line with Rashid et al., (2015), plant cover is the most appropriate method to apply for soil and water conservation.
Figure 3: Primary dry land forest cover in Tambun Watershed Table 4: Actual Erosion in Tambun Watershed after FLR
Land Use R K LS C P A (ton/ha/year)
Primary dryland forest 1384.29 0.59 9.5 0.001 1 7.15
Secondary dryland forest 1384.29 0.56 9.5 0.005 1 33.94
Plantation area 1384.29 0.55 3.1 0.32 1 696.09
Settlement 1384.29 0.29 1.20 0.1 1 44.39
Dryland agriculture 1384.29 0.56 6.8 0.01 1 48.58
Mixed dryland agriculture 1384.29 0.52 6.8 0.01 1 45.11
Rice fields 1384.29 0.15 0.2 0.5 1 19.13
Community nursery 1384.29 0.55 3.1 0.01 1 23.60
Community forest 1384.29 0.55 3.1 0.01 1 23.60
Total 920.59
Table 3 presents the estimated actual erosion rate that occurred in the Tambun watershed area after FLR averaged at 124.77 tons / ha / year (range 7.15-696.09 tons / ha / year). 696.09 tons / ha / year occurred in the form of plantation land use planted with Syzygium aromaticum and Theobroma cacao at a slope rate of 25% -40% (steep) red yellow podsolic type. Meanwhile the smallest actual erosion at 7.15 tons / ha / year was found on primary dryland forest land with an average attack rate of 25% -40%
(steep) to> 45% (very steep) red yellow podsolic type.
In the area of FLR (community forest and community nursery) planted with sengon and nantu, rehabilitation activities have been able to reduce the rate of soil erosion from 952.5 tons / ha / year (before FLR) to 920.59 tons / ha / year (post FLR ) The decrease in erosion rate was the effect of FLR plants that grew well (Figure 4) and the
advancement of interconnected system that protected the soil surface from direct rainfall. Forest litter allowed lower plants to grow under trees to protect the soil surface from the kinetic energy of rainwater. The presence of understorey and litter piles on the forest floo were found quite effective in reducing the kinetic energy of rainwater, preventing rainwater from directly hitting the ground surface. This condition eliminated soil grains which would erode when surface runoff occurred during peak discharge.
This is in accordance with the statement of Bukhari et al. (2014) that cover vegetation factors act as a protective soil against erosion forces. Headings, roots, litter and remnants of plant roots can protect the soil against erosion by reducing raindrops, inhibiting runoff flow rates and improving soil structure
Figure 4: The growth of FLR plants; (a) Paraserianthes falcataria ,(b) Palaquium obovatum Engl.
Table 3 and 4 show a decrease in erosion after FLR from 952.50 to / ha / year to 920.59 to / ha / year or a difference of 31.91 tons / ha / year. The key factor in this reduced erosion were forest rehabilitation and land that has been planted with sengon and nantu plants. This view is supported by Azmoudeh et al., (2010) and Schönbrodt et al., (2010) who mentioned that vegetation cover and plant species are key factors in controlling soil erosion. Changes in land use, especially the transformation of natural ecosystem strongly affects soil physicochemistry and its biological characteristics besides it also helps reducing the soil erosion.
a b
Erosion Hazard Level : Erosion hazard level refers the level of threat of damage caused by erosion of a land. Soil erosion can turn into a disaster if the rate of erosion is faster than the rate of soil formation which will gradually deplete the soil, revealing the main material or base material. Indonesia has applied a set of standards in estimating the rate of reasonable erosion ranging from 15-33 tons / ha / year or 1.25-2.5 mm / year.
The erosion hazard level in the observation field was found lower than the standard reasonable erosion rate that applies in Indonesia. Based on the erosion hazard level classification according to USLE, the observed land which has a depth of soil solum less than 30 cm is classified within class I erosion hazard level or very high .
Based results of erosion assessment using ArcGIS, the erosion scores varied from very low to very high on all land cover, both before FLR and post FLR. Detailed information is presented in Figure 5 and Figure 6.
Figure 5: The map of erosion hazard level before FLR
Figure 5 presents the erosion hazard level before FLR which is considered very low at erosion rate of <15 tons / ha / year occurring in primary dryland forests covering an area
of 2,781.26 ha (20.5%). Low erosion (erosion rate of 15 - 60 tons / year) covering secondary dryland forest area of 1,984.95 ha (14.63%), settlements covering 145, 45 ha (1.07%), dryland agriculture covering 1,863.46 ha (13.74%), bush mixed dryland agriculture covering an area of 5,806.74 ha (42.81%), rice fields covering an area of 786.70 ha (5.80%) while very heavy erosion> 480 tons / ha / year occurred in plantation area of 194.86 ha (1.44%).
In the post-rehabilitation area of forests and land in the Tambun watershed which were utilized as community nursery and community forests, average erosion hazard level is categorized low at15-60 tons / year covering 124 ha (0.91%) and 10 ha (0.07%) of the total Tambun watershed area (Figure 6).
Figure 6: The map of erosion hazard level after FLR
Conclusions: FLR land (community forest and community nursery) planted with sengon and nantu, successfully reduced the rate of soil erosion from 952.5 tons / ha /
year (before FLR) to 920.59 tons / ha / year post FLR. Before the FLR, the erosion hazard level was categorized low <15 tons / ha / year occurred in primary dryland forests covering an area of 2,781.26 ha (20.5%), to very high erosion rate > 480 tons / ha / year occurred in plantations as wide as 194.86 ha (1.44%). The post-FLR erosion hazard rates were mostly under low erosion category of 15-60 tons / year with an area of 124 ha (0.91%) in community nurseries and 10 ha (0.07%) in community forests. This condition supports the view that well-designed forest and land rehabilitation is a good alternative in reducing the level of erosion hazard in watersheds based on the functions of ecology and hydrology.
Acknowledgement: Gratitude is expressed to the Ministry of Watershed Environment and Forestry Protection of Poso Palu for the assistance and independent research funding of 2018 fiscal year, based on the letter of cooperation request Number: S.301 / BPDASHL.PP-2/11/2018.
REFERENCES
Abu-Hamdeh, N. H., Ismail, S. M., Al-Solaimani, S. G., and Hatamleh, R. I. 2018.
Runoff and erosion as affected by tillage system and polyacrylamide in two sandy loam soils differing in silt and clay contents in semi-arid regions. Soil &
Environment, 37(1).
Alkharabsheh, M. M., Alexandridis, T. K., Bilas, G., Misopolinos, N., and Silleos, N.
2013. Impact of land cover change on soil erosion hazard in northern Jordan using remote sensing and GIS. Procedia Environmental Sciences, 19, 912-921.
Azmoudeh, A. L. I., Kavian, A., Soleymani, K., and Vahabzadeh, G. 2010. Comparing runoff and soil erosion in forest, dry farming and garden land uses soils using rainfall simulator.
Bakker, M. M., Govers, G., Kosmas, C., Vanacker, V., Van Oost, K., and Rounsevell, M. 2005. Soil erosion as a driver of land-use change. Agriculture, Ecosystems &
Environment, 105(3), 467-481.
Bewket, W., and Teferi, E. 2009. Assessment of soil erosion hazard and prioritization for treatment at the watershed level: case study in the Chemoga watershed, Blue Nile basin, Ethiopia. Land Degradation & Development, 20(6), 609-622.
Bukhari, I., Lubis, K. S., and Lubis, A. 2014. Pendugaan Erosi Aktual Berdasarkan Metode USLE Melalui Pendekatan Vegetasi, Kemiringan Lereng dan Erodibilitas di Hulu Sub DAS Padang (Estimation of Actual Erosion by USLE Method Approach Vegetation, Slope and Erodibility in the Upstream Sub Watershed Padang). Agroekoteknologi, 3(1).
Cardei, P., Herea, V., Muraru, V., and Sfaru, R. 2009. Vector representation for the soil erosion model USLE, a point of view. Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. Agriculture, 66(2), 46-53.
Chaudhry, M. A. A. 1988. A comparative study of effectiveness of cement and lime as stabilizers to reduce soil erosion. Pakistan Journal of Agricultural Sciences.
El-Swaify, S. A. 1997. Factors affecting soil erosion hazards and conservation needs for tropical steeplands. Soil technology, 11(1), 3-16.
Fu, B., Chen, L., Ma, K., Zhou, H., and Wang, J. 2000. The relationships between land use and soil conditions in the hilly area of the loess plateau in northern Shaanxi, China. Catena, 39(1), 69-78.
García-Ruiz, J. M. 2010. The effects of land uses on soil erosion in Spain: a review. Catena, 81(1), 1-11.
Gitas, I. Z., Douros, K., Minakou, C., Silleos, G. N., and Karydas, C. G. 2009. Multi- temporal soil erosion risk assessment in N. Chalkidiki using a modified USLE raster model. EARSeL eProceedings, 8(1), 40-52.
Gyssels, G., Poesen, J., Bochet, E., and Li, Y. 2005. Impact of plant roots on the resistance of soils to erosion by water: a review. Progress in physical geography, 29(2), 189-217.
Herawati, T. 2010. Analisis Spasial Tingkat Bahaya Erosi Di Wilayah Das Cisadanekabupaten Bogor (Spatial Analysis of Erosion Danger Level at Cisadane Watershed Area Bogor District). Jurnal Penelitian Hutan dan Konservasi Alam, 7(4), 413-424.
Keesstra, S. D., Rodrigo-Comino, J., Novara, A., Giménez-Morera, A., Pulido, M., Di Prima, S., and Cerdà, A. 2019. Straw mulch as a sustainable solution to decrease runoff and erosion in glyphosate-treated clementine plantations in Eastern Spain.
An assessment using rainfall simulation experiments. Catena, 174, 95-103.
Khan, F., Ahmad, W., Bhatti, A. U., Khattak, R. A., and AgriculturalUniv, N. W. F. P.
2003. Effect of soil erosion on physical properties of some soil series inNWFP, Pakistan. Pakistan Journal of Soil Science (Pakistan).
Komaruddin, N. 2008. Penilaian Tingkat Bahaya Erosi di Sub Daerah Aliran Sungai Cileungsi, Bogor (Assessment of Erosion Hazard Levels in the Sub Watershed Cileungsi, Bogor). Agrikultura, 19(3).
Lin, B. S., Chen, C. K., Thomas, K., Hsu, C. K., and Ho, H. C. 2019. Improvement of the K-Factor of USLE and Soil Erosion Estimation in Shihmen Reservoir Watershed. Sustainability, 11(2), 355.
Ma, J. W., Xue, Y., Ma, C. F., and Wang, Z. G. 2003. A data fusion approach for soil erosion monitoring in the Upper Yangtze River Basin of China based on Universal Soil Loss Equation (USLE) model. International Journal of Remote Sensing, 24(23), 4777-4789.
Pandey, A., Chowdary, V. M., and Mal, B. C. 2007. Identification of critical erosion prone areas in the small agricultural watershed using USLE, GIS and remote sensing. Water resources management, 21(4), 729-746.
Panomtaranichagul, M., and Nareuban, S. 2005. Improvement of water harvesting and anti-erosive cultural practices for sustainable rainfed multiple crop production on sloping land. In Conference on International Agricultural Research for Development. Stuttgart-Hohenheim.
Patil, R. J. 2018. USLE–GIS-Based Soil Erosion Assessment: An Overview. In Spatial Techniques for Soil Erosion Estimation(pp. 7-27). Springer, Cham.
Pawitan, H. 2004. Perubahan penggunaan lahan dan pengaruhnya terhadap hidrologi Daerah Aliran Sungai (Land Use Changes and Their Impacts on Watershed Hydrology). Laboratorium Hidrometeorologi FMIPA IPB, Bogor.
Pham, T. G., Degener, J., and Kappas, M. 2018. Integrated universal soil loss equation (USLE) and Geographical Information System (GIS) for soil erosion estimation in A Sap basin: Central Vietnam. International Soil and Water Conservation Research, 6(2), 99-110.
Pimentel, D. 2006. Soil erosion: a food and environmental threat. Environment, development and sustainability, 8(1), 119-137.
Poerbandono, A. B., Harto, A. B., and Rallyanti, P. 2006. Evaluasi perubahan perilaku erosi daerah aliran sungai Citarum Hulu dengan pemodelan spasial (Evaluate changes in erosion behavior of Upper Citarum watershed with spatial modeling. Jurnal Infrastruktur dan Lingkungan Binaan, 2(2), 21-28.
Rahman, M. R., Shi, Z. H., and Chongfa, C. 2009. Soil erosion hazard evaluation an integrated use of remote sensing, GIS and statistical approaches with biophysical parameters towards management strategies. Ecological Modelling, 220(13-14), 1724-1734.
Rashid, M., Kausar, R., Alvi, S., and Sajjad, M. R. 2015. Assessment of runoff and sediment losses under different slope gradients and crop covers in semi -arid watersheds. Soil & Environment, 34(1).
Reis, M., Dindaroglu, T., & Akay, A. E. 2016. Assessment of Sediment Yield And Water Quality For Two Neighbouring Watersheds In Kahramanmaras, Turkey. Pak. J. Agri. Sci, 53(3), 653-659.
Schönbrodt, S., Saumer, P., Behrens, T., Seeber, C., and Scholten, T. 2010. Assessing the USLE crop and management factor C for soil erosion modeling in a large mountainous watershed in Central China. Journal of Earth Science, 21(6), 835- 845.
Wischmeier, W. H., and Smith, D. D. 1978. Predicting rainfall erosion losses-a guide to conservation planning. Predicting rainfall erosion losses-a guide to conservation planning.
Notification of article status from editor
(18-6-2021)
jcswc <[email protected]> 18 Jun 2019 19.01 Dear Editor
Your paper has been received.
Topic: EROSION HAZARD ASSESSMENT IN FOREST AND LAND
REHABILITATION FOR TAMBUN WATERSHED MANAGEMENT, TOLITOLI, INDONESIA
No. : #20837 best wishes
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Manuscript review: Accepted with mayor
revision (26-6-2019)
jcswc <[email protected]> Rab, 26 Jun 2019 19.27
JOURNAL OF THE CHINESE SOIL AND WATER CONSERVATION, EDITORIAL COMMITTEE
Topic: Erosion Hazard Assessment In Forest And Land Rehabilitation For Tambun Watershed Management, Tolitoli, Indonesia
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Other modification comments:
Date: 2019 / 06 /21(year/month/day) 1. Add the unit of Land Loss in Table.1
2. Please explain how to determine the six factors of USLE.
3. Table 3 and 4 should be estimated values of soil loss, not actual values.
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Topic: erosion hazard assessment in forest and land rehabilitation for tambun watershed management, tolitoli, indonesia
No. : #20837
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For JOURNAL OF THE CHINESE SOIL AND WATER CONSERVATION Article Number：20837 Date: 2019 / 06 / 26(year/month/day) Topic：Erosion Hazard Assessment In Forest And Land Rehabilitation For Tambun Watershed Management, Tolitoli, Indonesia Erosion Hazard Assessment In Forest And Land Rehabilitation For Tambun Watershed Management, Tolitoli, Indonesia
Evaluation comments：
Review point Excellent
(1)
Good (2)
Fair (3)
Poor (4) Importance：
Is there substantial contribution (New concept, ideas, method, materials) to science or engineering
development in soil and water conservation field?
v
Quality:
Are the research method or application method effective? Is the result discussed in an appropriate and balanced way (Referring to related studies, proper citation)?
v
Presentation：
Is the choice of words clear and specific? Is the research result and conclusion presented in good structure? Is the number and quality of graph used properly?
v
Suggest to classify this article into” thesis”
▓ Suggest to classify this article into “technical report”
Suggest to accept publication
Suggest to accept publication after modification and proofreading of chief editor
▓ Suggest to re-evaluate after modification
Revision Needed (Refer to modification suggestions)
The topic in Chinese and English is not clearly reflecting to the text of article or being redundant. Topic in English should be less than 400 letters.
Article abstract is not concise and uncompleted
Article abstract in English should be adjusted to about 200 words
Should have accurate English translation if using literature in Chinese (Suggested to use the original English translation)
Reference is missing or over listing, too many or too few or inappropriate.
Authors should properly quote from other’s research (literature) and point out new and original contribution of their own
▓ Description of experiment and calculation should be complete and precise so other researcher can follow and remake the result
▓ Reinforce the interpretation and discussion of research result
▓ Conclusion should be more specific and precise
Words and symbols in the graph are too small. Please enlarge the font size
Low resolution of graph. Graph is not clear
Text, Formula, Graph…etc. should be simplified, integrated or deleted
▓Chapter arrangement and Structure are inappropriate
▓ Sentences, terms are inappropriate. Writing should be smoother and precise. Should express clearly.
Should define the mathematical formula correctly and use symbol, abbreviation and unit correctly.
Other modification details please refer to Word comment PDF comment
Do not accept Reason
Against the goal of journal
No new concept, ideas, method or material
No specific conclusion
Inappropriate method and hypothesis/ Wrong research design
The result cannot support author’s interpretation and conclusion
Duplicate Submission
Similar text or result to another’s work that has been presented before
Others (Please explain)
Other modification comments:
This study is merely a general report using USLE, the very well-known and common empirical method, to estimate the soil loss and erosion hazard before and after the FLP project was carried out in the study area and to show the positive effect of FLP on soil and water conservation. Despite that the topic of this study falls in the scope of this journal, there are several flaws in the method, calculations, results, and discussion. In addition, the lack of scientific novelty and application significance make this manuscript not qualified as considered to be a scientific paper. However, with careful justification and correction of the method, results, and discussion, as well as the addition of actual field data showing the positive effects of vegetation on soil conservation, this manuscript may be considered as a technical report after extensive revisions. Some specific questions/comments are shown as follows:
1. There are grammatical errors and typos throughout the manuscript. I suggest that the English language and style need extensive editing by native speakers.
2. Page 1: If a sentence starts with a number, it should be spelled out. For example, “54.6 millions ha” should be “Fifty four point six millions ha”. Or, I suggest the sentence rearranged so that it does not start with a number.
3. Page 1: what is “sediment yield consequensi”? Is “consequensi” a typo?
4. Page 1: how to you define “critical land”?
5. The time periods mentioned in the abstract and in the research setting are different. Is it
“2002 to 2012” (in the abstract) or “2011 and 2012” (in the research setting)? How about “March to October 2018”?
6. Page 5: What is “attack maps”?
7. Page 5: scale “1:25.000” means one to twenty five? Or “1: 25,000”?
8. Page 5 and 6: What are the values of T? The “Land loss” in Table 1? By the way, what is the unit of “Land loss”?
9. Page 7: What does “actual erosion scores” means? How are the factors in Table 3 determined? Any assumption, references, and evaluation method? By the way, the unit of “A” in Table 3 should be consistent.
10. Titles of Table 3 and 4 use “Actual erosion…”. However, in my opinion, the annual soil loss estimated by USLE is just an estimation of soil loss, not the actual soil loss value. I do not think there are any “measured” soil loss data shown in this manuscript.
11. In addition, the values resulted from USLE are highly affected by the factors.
Especially, factors like C and P can be objective and thus arbitrary. Again, the evaluations of each factor in USLE should be justified.
12. Nearly all the “A” numbers in Table 4 are wrong! By comparing the factor values in
Table 3 and 4, it is impossible that the total soil loss in Table 4 can be smaller than that in Table 3. All the calculations have to be checked and corrected. Based on the current numbers, I do not see any improvement from the FLR project.
13. Terms of Table 3 and Table 4 are mixed in the content. Please check and make the correction.
14. Since the numbers in Table 4 are wrong, the numbers in Figure 6 is not correct neither.
Figure 6 need to be revised.
15. The statements regarding Table 4, Figure 6, and the comparison between the “before”
and “after” FLR project should be revised.
16. The authors only describe the soil loss values calculated from USLE and the relative erosion hazard level before and after the FLR project has been carried out. These are just the statements which show the results but I do not see any further academic discussion. In addition to that, based on the current results, the positive effects of FLR project on soil loss reduction is not illustrated, which makes no sense to give positive evaluation of the project and no rationale for this study to be published.
Date: 2019/ 06 / 26 (year/month/day) Journal of the Soil and Water Conservation editorial department
Email：jcswc@ nchu.edu.tw Contact:
Department of Soil and Water Conservation
No. 145, Xingda Rd., South Dist., Taichung City 402, Taiwan (R.O.C) TEL: +886-4-22840381-109
FAX: 04-22876851
Revision has been sent (30-6-2019)
Naharuddin Sumani <[email protected]> 30 Jun 2019 14.05
Dear Editor In chief
Journal of Chinese Soil and Water Conservation
Thank you for the process of article review number: 20837, attached article number: 20837 the author reiterates the results of the article improvement, hopefully it can be processed for publication in future editions.
Best regards, Dr. Naharuddin
EROSION HAZARD ASSESSMENT IN FOREST AND LAND REHABILITATION FOR TAMBUN WATERSHED MANAGEMENT,
TOLITOLI, INDONESIA
Naharuddin1*, Abdul Wahid1, Rukmi1 and Sustri1
1Tadulako University, Faculty of Forestry, Forestry Department, Palu City, Central Sulawesi, Indonesia
* Coresponding author: [email protected]
ABSTRACT
In conducting Forest and Land Rehabilitation (FLR), the watershed is the major unit of watershed management. The watershed approach is also the basis of FLR evaluation including evaluations of the hydrology aspect, land erosion, and other environmental aspects. The FLR in Tambun watershed has been done since 10 years ago in 2011 to 2012. Currently, sustainable FLR planning is under the progress. This research was conducted to identify the level of erosion hazard as the impact of FLR done in Tambun Watershed, Tolitoli, Central Sulawesi. The analysis of erosion hazard level was conducted using USLE equation. The results of this research showed that the FLR done in community forest and nursery in which Paraserianthes falcataria and Palaquium obovatum trees were planted not has been able decrease the rate of soil erosion from 955.63 ton/ha/year (before FLR) to 1,097.52 ton/ha/year (after the FLR), Selection of the right type of plant is needed especially needle-leaved in forest and land rehabilitation activities to minimize soil erosion.
Keywords: erosion, watershed, rehabilitation, forest, land
INTRUDUCTION
Fifty four point six millions ha of forest area in Indonesia has been degraded due to illegal logging, fires, land conversion, and unplanned land expansion for agricultural purposes. 54.6 millions ha out of the total forest area mentioned above has been predicted to face degradation including the area of productive forest, conservation forest and protected forest, while 41.7 millions ha of the degraded land were land outside forest area. Forest cover play important role in reducing sediment yield (Reis et al., 2016). Land use and land cover change are important research objects as they relate with the interaction between human activities and the natural environment (Alkharabsheh et al., 2013).
Watershed is the area where watershed management is done to maintain the water quality (Komaruddin, 2008). The land use around watershed affects the water quality and causes increases in erosion sediment rate. Increases in the rate of soil erosion and increases in the total area of critical land are obvious impacts of land shifts in land use (Pawitan, 2004). The shift in the land use and land cover change, rain falls, the kind of soil, including improper exploration of
land affect the erosion rate (Chaudhry, 1988; Fu et al., 2000; García-Ruiz, 2010). Planting system, land and water conservation, land management system and water management system need to be designed to control land erosion and degradation (El-Swaify, 1997; Abu-Hamdeh et al., 2018)
Erosion is the movement or transport of soil particles or sediments due to the pressure caused by the movement of wind or water on the surface of the ground or the bottom of the water (Poerbandono et al., 2006; Pimentel, 2006; Gitas et al., 2009). Soil erosion decreases the soil fertility and brings negative impacts on watershed in the form of environmental problems. It also threatens the sustainability of agriculture and water quality (Bakker et al., 2005;
Panomtaranichagul and Nareuban, 2005; Pandey et al., 2007). Along watershed environment, erosion rates are affected by the speed of water flow and the characteristics of the sediments (Herawati, 2010). To assess estimate the amount of soil loss from erosion, Universal Soil Loss Equation method can be used (Gitas et al., 2009; Pham et al., 2018). This method can be applied in any watersheds prior to preparing conservation master plans and enabling efficient use of resources (Bewket and Teferi, 2009).
Forest and land degradation causes decreases in land productivity as it increases the area of critical land and brings other ecological impacts. Therefore forest and land rehabilitation (FLR) programs are needed. Some important points should be considered in planning FLR programs and benchmarks in overcoming surface runoff and erosion as well as improving the quality and function of watersheds should be determined to evaluate the success of the program. Agricultural land management practices play an important role in controlling soil erosions such as land loss that decreases exponentially due to increases in vegetation cover (Khan et al., 2003; Gyssels et al., 2005). It is also necessary to have proper understanding regarding basic processes and factors that influence land degradation, especially soil erosion and other phenomena in implementing the concept, design, and implementation of productive, stable and sustainable agricultural systems (El-Swaify, 1997).
The map of soil erosion hazard is important in erosion-prone areas because it explains and displays the distribution of hazards and areas that are likely to be affected within watershed management (Rahman et al., 2009).
Tambun watershed is administratively located in Tolitoli District, Central Sulawesi with an area of 13,563.42 ha. The position and height of the place make the Tambun watershed function as a
buffer zone for the capital of Tolitoli Regency. The function of this area as buffer zone in relation to the amount of critical land, frequent flooding and landslides makes RFL an urgent agenda. The effectiveness of FLR can be seen in the effects of FLR programs implemented in Tambun watershed in 2011 namely community forest development, which program covered an area of 10 ha and the program done in in 2012 in the form of reconstruction of 124 ha of community nursery.
In the implementation of watershed management and to find out the impact of FLR watershed management in Tambun watershed, an analysis of erosion hazard level after FLR program needs to be conducted. It is also important to analyze its effect on the management of watersheds.
Therefore, development simulations can be arranged towards for better sustainability of Tambun watershed in the future.
This study was conducted to identify the post-FLR erosion level in Tambun watershed, Tolitoli using the USLE equation. The results of this research were expected to provide valuable insights in the planning of Tambun watershed management for healthier watershed, especially in overcoming the level of erosion hazard.
MATERIALS AND METHODS
Research Setting: This research was conducted from March to October 2018 in Tambun Watershed, Tolitoli, Central Sulawesi, Indonesia. As large as 10 ha of land in the location was developed in 2011 as community forest, and in 2012, 124 ha of land was developed as community nursery.
Tambun watershed is geographically located at the coordinate of 120° 49' 52.98" E 0° 58' 27.29" N (Figure 1).
Figure 1: Location of the Research
Research Method: The research was conducted in the form of surveys by obtaining soil samples from the research location to be further analyzed in the laboratory of the Faculty of Agriculture, Tadulako University. The soil sampling technique was carried out using purposive sampling based on the land use and on FLR land, slope and soil conditions.
The data were then analyzed using the Universal Soil Loss Equation (USLE) equation.
Furthermore, the erosion hazard level (TBE) was determined by comparing the actual (A) erosion to the tolerable erosion (T). The data included time series data regarding the last 10 years rainfall, soil physical properties, slope length, soil and plant management.
Data Collection
The data collected in this research included primary and secondary data in the forms of desciptions of soil properties, length and incline of the slope, plant management system from the field and the data regarding rainfall amount obtained from the nearest climatology station.
Furthermore, samples of whole soil and non-whole soil were retrieved based on ring sample in order to measure the permeability, texture, bulk density and organic contents in the soil (Figure 2).
Figure 2. Soil Sample Data Collection
Creating Land Unit Map: A land unit map was prepared by overlaying maps in the form of:
geomorphological maps, rainfall maps, geological maps, slope maps, land maps, land use maps, slope class maps, basic maps of visual maps at 1 : 25,000 scale to calculate the erosion hazard.
Information on this land unit were obtained from the results of interpretation of aerial photographs, ground checks, retrieval and sample soil information and some other information from related institutions.
Data Analysis: As instructed by Wischmeier and Smith, (1978), erosion rate is calculated using the USLE method (Ma et al, 2003; Cardei et al., 2009; Patil, 2018; Lin et al., 2019) as follows:
A = R * K * L * S * C * P
Remarks A: maximum amount of land loss (ton / ha / year); R: rainfall factor; K: soil erodibility factor; LS: factor length and slope; C: vegetation cover and plant management factors; P: soil conservation action factor.
The erosion hazard rate (TBE) is determined by comparing potential erosion (A) with tolerable erosion (T), using this following formula:
TBE = A / T with erosion hazard criteria according to Table 1:
Table 1: Criteria of Erosion Hazard Level Classification of Erosion
Hazard
Soil Loss Criteria
I <15 Very Low
II 15-60 Low
III 60-180 Moderate
IV 180-480 Hight
V >480 Very High
RESULTS AND DISCUSSIONS
Land Use: Based on the results of image analysis and current ground check, land use in the Tambun watershed after FLR consisted of primary dryland forests, secondary dryland forests, plantations, settlements, dry land agriculture, dry land agriculture mixed with shrubs, rice fields, community nurseries, and community forest (Table 2).
Table 2: The Use of Land in Tambun Watershed after FLR
Land Use Total Area
(ha) (%)
Primary dryland forest Secondary dryland forest Plantation area
Settlement
Dryland agriculture Mixed dryland agriculture Rice fields
Community nursery Community forest
2,781.26 1,984.95 194.86 145.45 1,863.46 5,672.74 786.70 124 10
20.51 14.63 1.44 1.07 13.74 41.82 5.80 0.91 0.07
Total 13,563.42 100
Land use indicates the accomplishment of regional development in terms of land productivity and the influence of human activities. Alkharabsheh et al. (2013) stated that the risk of soil erosion is strongly influenced by the use and form of land management besides it is also affected by watershed configuration (topography, shape), soil characteristics, climate conditions. Land use strongly influences the erosion rate in a watershed as it either reduces or increases the effect of rainfall that occurs.
Prediction of Erosion: The prediction of soil erosion was administered on each land use using the USLE method involving all factors; rainfall (R), soil erodibility (K), slope length and slope (LS), vegetation cover and crop management (C), and soil conservation action factor (P). The
actual erosion scores after forest and land rehabilitation in the Tambun watershed are presented in Table 3.
Table 3: Estimated values of soil loss in Tambun Watershed before FLR
Land Use R K LS C P A
(ton/ha/tahun)
Primary dryland forest 1358.73 0.59 9.5 0.001 1 7.62
Secondary dry forest 1358.73 0.56 9.5 0.005 1 36.14
Plantation area 1358.73 0.55 3.1 0.4 0.5 463.33
Settlement 1358.73 0.29 1.2 0.2 0.1 9.46
Dryland agriculture 1358.73 0.56 6.8 0.1 0.4 206.96
Mixed dryland agriculture 1358.73 0.52 6.8 0.1 0.4 192.18
Rice fields 1358.73 0.28 1.4 0.15 0.5 39.95
Total 955.63
As seen in Table 3, the estimated values of soil loss that occurred before FLR was 955.63 tons / ha / year (range 7.62 - 463.33 tons / ha / year), the largest erosion was 463.33 tons / ha / year occurred in the form of plantation land use at the slope rate of 25% -40% (steep) red yellow podsolic type. Meanwhile the smallest erosion of 7.62 tons / ha / year occured in primary dryland forest land use at an average slope rate of 25% -40% (steep) to> 45% (very steep) red yellow podsolic type .
The strong erosion potential in the use of land for plantation was due to the fact that the land was mostly planted with Syzygium aromaticum and Theobroma cacao, making this land less capable in reducing rainwater collisions on the soil and shallow root systems, and causing soil drainage system less effective. To control the rate of soil erosion in this area, it is necessary to perform mulching techniques and conservation farming systems. This idea is supported by Keesstra et al.
(2019), who also believe that mulch can be used as a land management practice to control the rate of soil erosion.
In primary dryland forests, the average erosion rate was relatively smaller at 7.62 tons / ha / year.
Based on the results of the ground check, the presence of trees with various strata formed canopy strata (Figure 3). Complete canopy structure plays a role in helping to reduce the kinetic rate of rainwater falling into the canopy. Therefore, when rainwater reaches the lowest canopy strata, the size of the raindrops becomes much smaller and the kinetic energy of the rain becomes weaker. Although this land is on a steep slope to very steep yet it does not have a significant effect. Litter that falls on the surface of the soil also plays a role in protecting the soil surface
from direct collisions of rainwater and can improve soil infiltration capacity, making erosion on this type of land relatively lower. In line with Rashid et al., (2015), plant cover is the most appropriate method to apply for soil and water conservation.
Figure 3: Primary dry land forest cover in Tambun Watershed Table 4: Estimated values of soil loss in Tambun Watershed after FLR
Land Use R K LS C P A (ton/ha/year)
Primary dryland forest 1384.29 0.59 9.5 0.001 1 7.76
Secondary dryland forest 1384.29 0.56 9.5 0.005 1 36.82
Plantation area 1384.29 0.55 3.1 0.4 0.5 472.04
Settlement 1384.29 0.29 1.2 0.2 0.1 9.63
Dryland agriculture 1384.29 0.56 6.8 0.1 0.4 210.86
Mixed dryland agriculture 1384.29 0.52 6.8 0.1 0.4 195.79
Rice fields 1384.29 0.28 1.4 0.15 0.5 40.70
Community nursery 1384.29 0.55 3.1 0.05 0.9 106.21
Community forest 1384.29 0.55 3.1 0.01 0.75 17.70
Total 1,097.52
Table 3 presents the estimated values of soil loss rate that occurred in the Tambun watershed area after FLR averaged at 121.95 tons / ha / year (range 7.76-472.04 tons / ha / year). 472.04 tons / ha / year occurred in the form of plantation land use planted with Syzygium aromaticum and Theobroma cacao at a slope rate of 25% -40% (steep) red yellow podsolic type. Meanwhile the smallest erosion at 7.76 tons / ha / year was found on primary dryland forest land with an average attack rate of 25% -40% (steep) to> 45% (very steep) red yellow podsolic type.
In the area of FLR (community forest and community nursery) planted with Paraserianthes falcataria and Palaquium obovatum, rehabilitation activities have been not able to reduce the rate of soil erosion from 955.63 tons / ha / year (before FLR) to 1,097.52 tons / ha / year (post FLR ) The enhancement in erosion rate was the effect of FLR plants that not grow well (Figure 4) and tend to open the canopy of plants, so erosion can occur easily. Forest litter allowed lower plants to grow under trees to protect the soil surface from the kinetic energy of rainwater. The presence of understorey and litter piles on the forest floo were found quite effective in reducing the kinetic energy of rainwater, preventing rainwater from directly hitting the ground surface.
This condition eliminated soil grains which would erode when surface runoff occurred during peak discharge. This is in accordance with the statement of Bukhari et al. (2014) that cover vegetation factors act as a protective soil against erosion forces. Headings, roots, litter and remnants of plant roots can protect the soil against erosion by reducing raindrops, inhibiting runoff flow rates and improving soil structure
Figure 4: The growth of FLR plants; (a) Paraserianthes falcataria ,(b) Palaquium obovatum Engl.
Table 3 and 4 show a enhancement in erosion after FLR from 955.63 to / ha / year to 1,097.52 to / ha / year or a difference of 141.89 tons / ha / year. The key factor in this enhancement erosion were forest rehabilitation and land that has been planted with sengon and nantu plants hasn't grown well and the plant canopy is not linked to one another. This view is supported by Azmoudeh et al., (2010) and Schönbrodt et al., (2010) who mentioned that vegetation cover and plant species are key factors in controlling soil erosion. Changes in land use, especially the transformation of natural ecosystem strongly affects soil physicochemistry and its biological characteristics besides it also helps reducing the soil erosion.
a b
Erosion Hazard Level : Erosion hazard level refers the level of threat of damage caused by erosion of a land. Soil erosion can turn into a disaster if the rate of erosion is faster than the rate of soil formation which will gradually deplete the soil, revealing the main material or base material. Indonesia has applied a set of standards in estimating the rate of reasonable erosion ranging from 15-33 tons / ha / year or 1.25-2.5 mm / year. The erosion hazard level in the observation field was found lower than the standard reasonable erosion rate that applies in Indonesia. Based on the erosion hazard level classification according to USLE, the observed land which has a depth of soil solum less than 30 cm is classified within class I erosion hazard level or very high .
Based results of erosion assessment using ArcGIS, the erosion scores varied from very low to very high on all land cover, both before FLR and post FLR. Detailed information is presented in Figure 5 and Figure 6.
Figure 5: The map of erosion hazard level before FLR
Figure 5 presents the erosion hazard level before FLR which is considered very low at erosion rate of <15 tons / ha / year occurring in primary dryland forests covering an area of 2,781.26 ha (20.5%). Low erosion (erosion rate of 15 - 60 tons / year) covering secondary dryland forest area
of 1,984.95 ha (14.63%), settlements covering 145, 45 ha (1.07%), dryland agriculture covering 1,863.46 ha (13.74%), bush mixed dryland agriculture covering an area of 5,806.74 ha (42.81%), rice fields covering an area of 786.70 ha (5.80%) while very heavy erosion> 480 tons / ha / year occurred in plantation area of 194.86 ha (1.44%).
In the post-rehabilitation area of forests and land in the Tambun watershed which were utilized as community nursery and community forests, average erosion hazard level is categorized low at15-60 tons / year covering 124 ha (0.91%) and 10 ha (0.07%) of the total Tambun watershed area (Figure 6).
Figure 6: The map of erosion hazard level after FLR
Conclusions: FLR land (community forest and community nursery) planted with sengon and nantu, not successfully reduced the rate of soil erosion from 955.63 tons / ha / year (before FLR) to 1,097.52 tons / ha / year post FLR. Before and after the FLR, the erosion hazard level was categorized low <15 tons / ha / year occurred in primary dryland forests covering an area of 2,781.26 ha (20.5%), to very high erosion rate > 400 tons / ha / year occurred in plantations as wide as 194.86 ha (1.44%). The changes in function of the forest area patterns of forest and land rehabilitation that are not well designed, especially the selection of improperly plant species cannot reduce soil erosion.
