Growth Performance of Four Dipterocarp Species Planted in a Leucaena leucocephala Plantation and in an Open Site on Degraded Land under a Tropical Monsoon Climate

To develop silvicultural methods for dipterocarp species in degraded lands in a tropical monsoon climate, we examined uneven-aged forest management, in which dipterocarp trees were planted under nurse trees, by monitoring their growth for 20 years. In 1989, seedlings of four dipterocarp species (Dipterocarpus alatus, D. turbinatus, Hopea odorata and Shorea henryana) were planted beneath a 3-year-old Leucaena leucocephala plantation and in an open site in Sakaerat, north-east Thailand. The survival rate and tree size of the dipterocarp seedlings were monitored at both sites until 1995. Surand svival rates of the dipterocarp trees were significantly better under the Leucaena plantation. However, no apparent difference was observed in basal area between both sites, since saw vigorous growth of the surviving seedlings compensated for the loss of dead seedlings at the open site. Our results showed that D. alatus and H. odorata could be planted in an open site due to the vigorous growth of the seedlings, but that it was preferable to plant D. turbinatus beneath nurse trees. The Leucaena plantation was partially thinned to 50, 75 and 100% (clear-cut) in 1993, and the survival rate and growth of the dipterocarps was monitored until 2009. Thinning had no apparent effect on the survival rates of the dipterocarp seedlings. Although relative growth rates (RGR) of the dipterocarps reduced after thinning, thinning rates did not affect the growth of the dipterocarps. After thinning, dipterocarp trees overtook Leucaena in height at all thinning rates, possibly from 1999. An uneven-aged system combining Leucaena and dipterocarp trees is likely to be applicable to several dipterocarp species.