LITTERFALL, NUTRIENT FLUX AND NUTRIENT USE EFFICIENCY IN SAKAERAT SEASONAL RAIN FOREST, NORTHEAST THAILAND 1. LITTERFALL VARIATIONS AND SEASONALITY

摘要

Litterfall in a seasonal rain forest at Sakaerat Biosphere Reserves, northeast Thailand was investigated over 1 - year period both by examining the litterfall fraction types and leaffall of the 5 most dominant tree species of the stand. Overall leaffall and total litterfall show the continuous falling pattern in contrast to branchfall and trash which exhibit greater monthly fall rates in the wet season than in the dry season. Total annual litterfall of 8.17 t ha~(-1) yr~(-1) is found to be largest in the stand dominated by Hopea ferrea as compared to the values found in the same site investigated by some previous researchers considering to be the uppermost value record for this forest and other similar types in the same forest and elsewhere. Leaffall of H. ferrea (3.32 t ha~(-1) yr~(-1)) constitutes the greatest contribution to total litterfall and leaffall of this forest and exhibits no seasonal variation. Leaffall of Memecylon ovatum, Hydnocarpus ilicifolius. Walsura trichostemon and Linociera microstigma is of minority and only that of M. ovatum shows some seasonal variations, being larger in the wet season than in the dry season, the 3 species show positive and significant relationship to monthly mean air temperature of the wet season. However, only M. ovatum and H. ilicifolius show similar relationship to the same temperature parameter of the whole year but not related to monthly precipitation in any season of the year. Leaffall of L. microstigma is found to exhibit no seasonality and no relationship with any prevailing climatic factors of the site.