PERFORMANCE OF SIX NATIVE TREE SPECIES, PLANTED TO RESTORE DEGRADED FORESTLAND IN NORTHERN THAILAND AND THEIR RESPONSE TO FERTILISER

The performance of six native forest tree species, planted to restore forest in a degraded watershed in Doi Suthep-Pui National Park, Thailand and their responses to four fertiliser treatments are reported. The species were chosen for their potential to i) shade out competing weeds rapidly and ii) enhance tree species richness by attracting seed-dispersing wildlife. All species planted, except Gmelina arborea, performed well. Relative performance indices, which combined survival and relative growth rate, were 87.5 for Erythrina subumbrans, 45.3 for Melia toosendan, 36.9 for Prunus cerasoides, 32.5 for Sapindus rarak, 22.2 for Hovenia dulcis and 3.5 for Gmelina arborea. Application of fertiliser at the time of planting and twice during the first rainy season after planting resulted in much higher performance than application of fertiliser only at the time of planting, for all species except Prunus cerasoides. Although the highest dosage of fertiliser (200 g at the time of planting and twice during the rainy season) resulted in the highest growth rates, it also lowered survival of planted saplings. For planting mixtures of native tree species, the recommended fertiliser treatment is therefore 50-100 g fertiliser, applied at the time of planting and at least twice during the first rainy season after planting. Further research is needed to determine whether more frequent fertiliser application would further improve performance.