P-143
Impact of forest management system on runoff and soil erosion in a tropical Indonesia rainforest
1Laboratory of Erosion Control, Division of Forest and Biomaterials Science,
Graduate School of Agriculture, Kyoto University, Japan
2
Educational Unit for Adaptation and Resilience for a Sustainable Society, Centerfor the Promotion of Interdisciplinary Education and Research, Kyoto University,
Japan

1. Introduction
Indonesia is one of the countries which have alarge of forest area. It covered 60% of total area or 10%of total world tropical rainforest. Land conversion andillegal logging are threatening the biodiversity andhydrological cycle in particular runoff and soil erosion
at forested area. Indonesian forest is managed bysilviculture systems. The selective logging andintensive line planting, or Tebang Pilih Tanam
Indonesia Intensif (TPTII), is the latest forest
management system, started in 2002.
Timber extraction using heavy machines destroys
the soil structure that plays an important role in waterand nutrient cycling, accelerating the soil erosion rate.
Heavy machines in timber collection areas and on
skidder roads increase soil compaction by up to 40%[1], and 10-30% of the soil surface may be laid bare in
the form of logging roads, skidder tracks and log
landings [3]. In a previous study, the infiltration
capacity of a tropical rainforest 1 year after TPTII
treatment decreased to 81.8% of a virgin forest [2].
Many studies have considered runoff and soil
erosion of plots with different land cover, but
information on the direct impact of selective logging
and intensive line planting in tropical rainforests
remains limited. Therefore, in this study, we quantified
and compared the direct runoff and soil erosion among
virgin forest and two line plantations.
2. Methods
2.1 Study site
This study was conducted in tropical rainforest at
the Sari Bumi Kusuma company concession area, aprivate forest in Central Kalimantan, Indonesia. Thislocation is part of the high-biodiversity area known as
the “Heart of Borneo”. The study site was located in
the headwater region of the Katingan watershed, one oflargest watersheds in Central Kalimantan.
According to the forest climate classification
system of Schmidt and Ferguson, the area is a type A(very wet) tropical rainforest (monthly average rainfall> 100 mm). The mean annual precipitation for theperiod 2001–2009 was 3,601 mm, with the highest
average monthly precipitation (367 mm) occurring inNovember and the lowest average monthly
precipitation (183 mm) occurring in August. The mean
temperature is 30ºC–33ºC at noon and 22ºC–28ºC atnight.

- 612 -〇Hatma Suryatmojo1
Fujimoto Masamitsu2
Ken’ichiro Kosugi1
Takahisa Mizuyama1

2.2 Forest management system
The intensive line planting is implemented after
selective logging of about 25% of the forest; the rest(75%) is maintained in its natural condition forbiodiversity purposes. The scheme of the TPTII system
is shown in Fig. 1.

Fig. 1: Scheme of plantation in the TPTII

Typically, about 200 seeds per hectare are planted,
and the expected standing stok at the end of the rotation(30 years) is around 400 m3 per hectare, assuming 160
trees per hectare with an average diameter of 50
centimetres (or 2.5 m3 per tree).
TPTII implementation decreased the number oftrees per hectare. In the virgin forest, the percentage ofcanopy trees cover was 80.1%. After selective logging
and intensive line planting, it decreased to 49.3%. The
implementation of TPTII decreased the canopy trees
cover by 38.5%.
2.3 Research catchment
This research was conducted at three small
catchments with different forest canopy cover densities:
a virgin forest, a1-year-old line plantation, and a10-year-old line plantation. Hereafter, these catchments
are referred to as the “virgin forest catchment”, the“2008 catchment” and the “1999 catchment”,respectively. The catchment areas of the three were110.33, 191.54 and 149.49 hectares, respectively.
2.4 Field observation and analysis
A weir was installed at each catchment outlet.
Rainfall data were collected from a weather station and2 manual rain-gauges. At 3 m wide of weir, we devided
into 3 sections then measured the suspended sedimenton several water level variation by a suspended
sampler.
During the research period (June 2009–June2010), we selected several paired of rainfall andhydrograph data at each catchment. We found 38 paired
data in the virgin forest catchment, 67 paired data in the1999 catchment and 42 paired data in the 2008
catchment.
We separated the discharge hydrograph data into
direct runoff and baseflow using a straight-line method.
Furthermore, we calculated the direct runoff anderosion for each hydrograph.
3. Result and discussion
3.1 Runoff characteristics

Fig. 4: Relationship between direct runoff and soil erosion

Fig. 4 shows the relationship between direct
runoff and soil erosion in the three catchments. There
was a strong relationship between the two, and soil
erosion was significantly higher in the 2008 catchment(28.91 kg ha-1) than in the 1999 (14.93 kg ha-1) andvirgin forest (8.9 kg ha-1) catchments. The highest soilerosion value in the 2008 catchment was 338.18 kg ha-1
for 141.25 mm of rainfall.

Fig. 2: Relationship between rainfall amounts per eventand direct runoff

Fig. 2 shows the total direct runoff was lowest in
the virgin forest catchment, and highest in the 1999
catchment, which was only slightly higher than that inthe 2008 catchment. Accordingly, the average direct
runoff (and percentage of rainfall as runoff) in thevirgin forest, 1999 catchment and 2008 catchment was
3.62 mm (15.4%), 7.44 mm (25.3%), 8.03 mm (31.3%)
respectively. Hence, the direct runoff rate in the 1999
catchment and 2008 catchment was 2.05 and 2.22 times
that of the virgin forest catchment, respectively.
3.2 Discharge of suspended sediment and soilerosion

Fig. 3: Discharge of suspended sedimentFig. 3 shows the relationship between water
discharge and suspended discharge. The suspended
discharge was significantly higher in the 2008
catchment than in the virgin forest and 1999
catchments. Timber extraction has proved to increase
the suspended sediment.

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3.3 Effects of forest management system on runoff
and soil erosion
Selective logging and intensive line plantingsignificantly increase direct runoff and soil erosion.
The average direct runoff was 15.4% of rainfall in thevirgin forest catchment, but 25.3% and 31.3% in the1999 and 2008 catchments, respectively. The direct
runoff rates in the 1999 and 2008 catchment were 2.05
and 2.22 times that of the virgin forest, respectively.
4. Conclusion and recommendations
TPTII significantly increase direct runoff and soilerosion. Forest land cover was a main factor
determining the differences in runoff and soil erosion
among the three catchments. Proper protection of theforest floor with plant cover under canopy trees would
help control runoff and soil erosion.
We recommended controlling human erosional
activities and combining ecologically based vegetation
structure design and erosion control techniques for theeffective control of runoff and soil erosion.
References[1] Nussbaum, R., Anderson, J., and Spencer, T., Planting
Dipterocarps For Rehabilitation of Log Landings andSkid Trails in Sabah, Malaysia. in: S.Appanah dan
K.C. Khoo (eds.),
Proceedings of The Fifth
Round-Table Conference on Dipterocarps. Chiang
Mai, pp. 299-315, 1996.
[2] Suryatmojo, H., The Effect of Line Planting Toward
Infiltration. Proceeding of International Seminar“Research on Plantation Forest Management :Challenges and Opportunities”, Bogor. 2009.
[3] Van Der Plas, M.C. and Bruijnzeel, L.A., Impact ofMechanized Selective Logging of Rainforest onTopsoil Infiltrability in the Upper Segama Area, Sabah,Malaysia. Hydrology of Warm Humid Regions. IAHSPubl. no. 216, pp. 203-211. 1993.