Leaf life span and leaf characteristics of some dominant tree species in the dry Dipterocarp forest at Sakaerat

Study on leaf life span and leaf characteristics of some dominant tree species in the dry dipterocarp forest at Sakaerat was carried out for 7 dominant tree species, namely, Shorea obtusa wall., Shorea siamensis Miq., Shorea floribunda Kurz, Dipterocarpus intricatus Dyer, Sindora siamensis Teijsm. ex Miq., Pterocarpus macrocarpus Kurz and Xylia xylocarpa Taub. The investigation was carried out during February 1996 - March 1997, flushing period of leaves, falling of leaves, leaves life span, chlorophyll content in various leaf life span and branch elongation were recorded, moreover the relationship between branch elongation and number of leaves was also analyzed. Flushing period of S. obtusa Wall., S. siamensis Miq., S. floribunda Kurz, S. siamensis Teijsm. ex Miq., P. macrocarpus Kurz and X. xylocarpa Taub. were in March, whereas D. intricatus Dyer was in April. The falling period of leaves of S.obtusa Wall., S. siamensis Miq., S. floribunda Kurz, D. intricatus Dyer, S. siamensis Teijsm. ex Miq., P. macrocarpus Kurz and X. xylocarpa Taub. were in january - March, December - March, July - March, January - March, January - March, September - February and January - March, respectively. Everage leaf life span of S. obtusa Wall. was 8.5 months, S. siamensis Miq. was 5.7 months, S. siamensis Teijsm. ex Miq. was 9.6 months and P. macrocarpus Kurz was 8.9 months and X. xylocarpa Taub. was 6.9 months. Low chlorophyll content in leaves was found in young leaves and old leaves before falling. The maximum chlorophyll content in leaves of S. obtusa Wall., S. siamensis Miq. S. floribunda Kurz., D. intricatus Dyer, S. siamensis Teijsm. ex Miq. and X. xylocarpa Taub. were 0.6515, 0.4949, 0.7963, 0.7718, 1.1421, 0.7621 and 0.4833 mmol/square m respectively. All species except S. siamensis Teijsm. ex Miq. had maximum branch elongation rate in the first month after leaf flushing, whereas the rest had constant branch elongation rate. The relationship between branch elongation and number of leaves in all species showed a simple linear regression.