SOIL AND WATER LOSSES FROM THE TERRACED REFORESTATION AT ANGKHANG HIGHLAND, CHIANG MAI

Abstract

Soil and water losses from terraced reforestation at Angkhang Highland, Fang District, Chiang Mai was carried out during August 1983 to October 1984. Five 4x15 m plots were set up on the terraced reforestation of five exotic tree species namely: Aleurites montana Wilt., Zelkova formosana Hay., Liquidambar formosana Hance.,: Acacia confusa Merr., and Fraxinus griffithii C.B. Clarke. These species were introduced from Taiwan through the Forest Development Administration of VACRS and the Highland Agriculture Project of KU, then, to be planted in 1982 with spacing of 2.0x2.5 m. Two additional plots were established in 1984 aiming to compare soil and water losses from unterraced planting of Paulownia taiwaniana Hu et Chang, sp. nov. to those mentioned species. It was also aimed to determine soil erodibility (K-Factor) and crop management and conservation practice factor (CP-Factor) used for predicting soil erosion in Universal Soil Loss Equation (USLE) at Angkhang Highland Reforestation Project. Results obtained from the 1983-investigation plots indicated that average soil and water losses from those five plots were 0.2 ton/ha and 17 mm, respectively with highly statistical significance. In 1984, the average soil and water losses were reduced to 0.1 ton/ha and 14 mm, respectively but with non-significant difference. There was however highly statistical significance between the former five plots and the latter two plots. It was also found that the average soil loss from non-terraced Paulownia and bare plot with up and down fallow was estimated at 16 and 600 times (per mm of runoff) greater than those measured from the terraced reforestation plots. In a similar manner, the amount of water loss was found to be 6 and 15 times, respectively. Soil erodibility (K) estimated based on soil loss from up and down bared plot and 1984 rainfall factor (R) was averaged at 0.04. The combination of crop management factor and conservation factor (terracing) (called CP-Factor) for 2 years investigation was estimated at 0.00035 which more or less equals to C-factor of the natural hill-evergreen forest occupying on montainous watershed of northern Thailand.