RESEARCH METHOD Prosiding INAFOR III 2015 FullIssue low rest

Bogor, 21-22 October 2015 650 One of the benefits of forests environmental services is to prevent soil erosion. In the context of sustainable economic development, prevention of soil erosion could be interpreted as an effort to maintain the stock of soil capital. Based on the description in advance, this paper studies the changes of economic value of soil capital due to the conversion of forests into plantations and agriculture land and their impact on the green GDRP of agricultural sector of Riau Province in 2000 until 2009.

2. RESEARCH METHOD

Forest conversion to other land uses, such as for oil palm plantations and agricultural land could increase the rate of soil erosion, reduced availability of water in the dry season drought and floods in the rainy season. Impact of soil erosion can override the location of the affected land erosion on-site and off-site Sihite, 2001, p.31. Forest benefits for the prevention of soil erosion, flooding and drought can not be assessed directly. It is need a special approach proxy to be get a value. The value of forest benefits for prevention of soil erosion at the location where erosion occurs on-site are generally valued using the replacement cost approach. Then, the assessment of forest benefits for soil erosion prevention which are considered in the off-site area generally uses the avoided cost approach. Moreover, the economic value of forest benefits for soil erosion prevention, flood and drought in the outside location off-site can be assessed using the contingent valuation method. The methods of assessing the benefits of forests contingency as prevention of erosion and flooding from the point of view of the people who live around the watershed area DAS. The approach used in the method of contingency is the willingness to pay WTP if the community forest conservation efforts will be made to prevent erosion, flooding and drought Barbier, E., Acreman, M., Knowler, D. 1997, p.42. The economic value of forests as the prevention of erosion and flooding is the sum of the cost of replacement, the cost of which can be avoided and willingness to pay. Replacement cost value in this study used to assess losses due to soil erosion in forest plantations and oil palm plantations. WTP methods used to assess the benefits of natural forests as preventing erosion, flooding and drought. Meanwhile, the avoided cost approach is not used in this study given in the study site there are reservoirs. Assessment for on-site impact of soil erosion due to the loss of forests area The value of forest benefits for the prevention of erosion and flooding is calculated with reference to the formula proposed by Hufschmidt et al. in 1983 which is cited by Sihite 2001. The equation is as follows:         m i n j LAj HPi JUHij NMH 1 1 1        m i n j PUHij ERij JUHij 1 1 2 NMH = the lost of forests environmental service value due to the soil erosion Rp JUHij = number of i nutrient which was released due to the soil erosion in j watershed area kg ha HPi = prices of i fertilizer Rpkg LAj = area of j watershed ha ERij = number of eroded soil per hectare in land unit j t ha PUHij = proportion of i nutrients in 1 ton of eroded soil kg i = type of nutrient fertilizer Urea, TSP, KCl j = land use in the watershed Bogor, 21-22 October 2015 651

3. RESULT AND DISCUSSION