REGENERATION, LEAF PHENOLOGY AND NUTRITIONAL ADAPTATION OF SAL (Shorea robusta Roxb. ex Gaertn.) IN THE DECIDUOUS FORESTS OF BANGLADESH

Abstract

The present study investigated the effects of forest management on the regeneration of the dominant tree species Sal (Shorea robusta Roxb. ex Gaertn.) of the Madhupur Sal forest by conducting a survey using the quadrat method in four different seasons namely Spring, Summer, Autumn and Winter as well as by examining the seed germination and growth of seedlings and saplings between the Core zone and Buffer zone. This study also investigated the deciduousness of Sal plants by counting leaf every month in two different Sal forest stands namely Madhupur Sal forest in Tangail and Charkai Sal forest in Dinajpur for 31 months and examined the effects of soil moisture on the leaf exchange period of Sal plants under different moisture treatment conditions in the garden for 16 months. Results showed that a maximum number of juvenile Sal plants of 0–10 cm girth class was found in the Core zone (11,833 plants per ha) and Buffer zone (15,500 plants per ha) in Autumn and a minimum number in the Core zone (533 plants per ha) and Buffer zone (766 plants per ha) in winter. The maximum IVI value of Core zone (154.18) and Buffer zone (154.33) was found in the Autumn season while those were minimum in winter with the values 84.40 and 71.90, respectively. Sal seed germination rate was higher in the Buffer zone (77.33%) than in the Core zone (51%). Seedling survival rate was also higher in Buffer zone than in the Core zone. Phenological data revealed a maximum of 22.5% of completely leafless twigs in the Madhupur Sal forest while that was 12.5% in the Charkai Sal forest during the leaf exchange period. Sal plants started to shed their leaves in dry conditions when the soil moisture content started to decrease indicating the effect of soil moisture on the deciduousness of Sal plants. Data also indicated that Sal was semi-deciduous in nature in both these two forests. The present study also investigated the nutritional adaptation of Sal plants by comparing nutrient (N, P and K) resorption in old leaves of the Sal plants grown in Madhupur Sal forest and Charkai Sal forest. Results showed that old leaves withdrew nutrients (N, P and K) significantly before leaf fall occured. The resorption of N, P and K was 25%, 23.92% and 11.96%, respectively, in the Madhupur Sal forest; whereas in the Charkai Sal forest, it was 38.07%, 45.66% and 49.82%, respectively indicating that efficient resorption of nutrients might help Sal plants with the soil environment.