International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
3.4 Identifying Forest Areas Critical to Erosion Control
Dominant soil in the tropical rain forests in Indonesia is the red-
yellow podzolic (Acrisols), which is highly vulnerable to
erosion. Exposed tropical soils degrade quickly due to leaching
of nutrients, burning of humus, laterisation of minerals and
accelerated erosion of top soil. Forest areas, which are
important in maintaining terrain stability (Le. to control
excessive erosion, which can lead to landslides and serious
siltation), in an area where the consequences are severe, should
be considered as HCVF. In this study, an estimation of potential
erosion risk in the study area was carried out to identify the
areas with high erosion risk. To spatially estimate the potential
erosion risk, distribution of rainfall intensity, slope length and
slope steepness factor derived from Digital Elevation Model
(DEM), soil map and land cover map were used to establish a
map of potential erosion risk. A universal model developed by
USDA-ARS, Universal Soil Loss Equation (USLE)
(Weischmeier and Smith 1978) is used to estimate the erosion
risk of the study area. Figure 4 illustrates the general process in
estimating relative soil loss in GIS environment.
4. RESULTS
4.1 Identification of High Conservation Value Forest
(HCVF)
4.1.1 Forest Areas Function as Unique Source of Drinking
Water (HCVF 4.1)
Considering major and minor river systems in the study area,
stream network map and division of river systems in Berau
area, the delineated catchment partitions then were grouped
based on river system where the flow of the catchments
accumulate. The major river systems are Segah and Kelay
River, while the minor river systems are Sidu’ung and Siagung
River. The grouped catchments partitions with the river systems
were identified. The catchment partitions within these particular
villages are also considered as important for unique source
drinking water. The areas functions as unique source of
drinking water are presented in Figure 5.
4.1.2 Forest Areas as part of Critical Major Catchments
(HCVF 4.2)
According to the result of the prioritisation of major catchments
throughout the East Kalimantan Province, which is done by
Ministry of Forestry, the priority scale to major catchments in
the study area are all in level III. Based on the definition given
by the Ministry of Forestry, priority scale I and II are given to
critical catchment that need immediate action with regard to
land rehabilitation and soil conservation, while priority III does
not need such immediate rehabilitation, therefore the study area
does not contain HCVF 4.2 elements.
4.1.3 Forest Areas Critical to Erosion Control (HCVF 4.3)
Factors contributing to annual soil loss estimation were
determined using a Spatial Modeler, resulting in raster maps of
rainfall erosivity (R factor), soil erodibility (K factor), slope
length and steepness (LS factor) and vegetation cover and
management (C factor). Since the identification of HCVF 4.3
requires the erosion risk in the forested area, then the resulted
erosion risk map was masked with land cover type map and
resulting in the map of estimated soil erosion risk in the forest
area. Annual soil loss of 11 ton.ha’'.yr' was adopted as the
166
threshold to differentiate high erosion risk with low erosion
risk, therefore a reclassified map of forest area with high soil
erosion risk is also produced and presented as orange and red
pixels in Figure 6. By having the map of forest area with high
soil erosion risk, the HCVF 4.3 is identified.
4.2 The identified HCVF related to
conservation
soil and water
Considering the ultimate objective of this research, which is
“identifying high conservation value forest related to soil and
water conservation”, a final map as compilation of the
identified HCVF in the study area is presented in Figure 7. As
can be seen in this final map, the concentration of forest areas
function as unique source of drinking water for local
communities (HCVF 4.1) are in the northern and northeastern
part, exactly in the center and the eastern part of the FMU.
Forest areas critical to erosion control (HCVF 4.3) are highly
concentrated in the steep-hilly forest in the southern part of the
FMU and sparsely concentrated in the eastern part of the FMU
as well. Considering the current logging operations of the FMU,
which is located within the boundary of identified HCVF 4.1 in
the northeastern part of the FMU, special attention should be
paid to minimize the logging impact to the supply of drinking
water for communities in the transmigration settlement (Trans
SP6).
S. CONCLUSIONS
Remote sensing and Geographic Information System had
proved to be useful to support the identification of High
Conservation Value Forests (HCVF) in the study area.
The Digital Elevation Model derived from a contour line map is
an essential input for analyses of physical hydrological features.
The analyses are including catchment delineation, automatic
derivation of stream network, flow routing and calculation of
flow accumulation.
Visual interpretation and manual digitising process allow
delineation of several catchments simultaneously, while
automatic catchment delineation provided by most GIS
software concentrates to one catchment. Therefore, manual
delineation is preferable to use.
The national guideline for identification of HCVF in Indonesia,
which provided by Proforest, is found very useful in building
up the framework of preliminary HCVF identification.
6. REFERENCE
Fauzi, A. (2001). Remote sensing for detection tropical logged
forest (A case study of Labanan Concession, East Kalimantan,
Indonesia). ITC Enschede. Unpublished M.Sc Thesis. 91.
Smartwood (2001). Smartwood Certification Assessment
Report for: PT Inhutani I Labanan. Jakarta.
Wastono, D. H. (2003) Interview Towards Common
Perception of HCVF Guideline. Y. B. Sulistioadi. Labanan,
East Kalimantan.
Weischmeier, W. H. and D. D. Smith (1978). Predicting
Rainfall Erosion Losses: A guide to conservation planning.
Washington DC, US Department of Agriculture.
Internation
TIC
pan
490000
Forest
as Ur
FD
|
Legend
240000
M
FI
210000
1
200000
A
Figure 5. ]
water (HC?
—
Estim
ton ha
100000
Ir
Figure 6. S
soil erosior
Table 1. In
No
[HCV4 | F
4.1 | F
S(
| ——
42|F
Ci
43lF
C(
