Tree regeneration in a subtropical humid forest: effect of cultural disturbance on seed production, dispersal and germination.
Abstract
The subtropical humid forest of Meghalaya (India) has been exposed to various kinds of disturbance of varying magnitude during recent years; felling of trees for timber and fuelwood by the local people has become common. In order to analyse the effect of disturbance on natural regeneration of a few dominant and commercially important tree species (Schima khasiana, and the oaks Lithocarpus dealbatus (syn. Quercus dealbata) and Quercus griffithii) a study on seed production, dispersal and germination was carried out in 3 stands with differing degrees of disturbance (undisturbed, and mildly and highly disturbed, respective disturbance indexes of 0, 10 and 60%), during the years 1988-91. Seed production in Q. dealbata and S. khasiana varied significantly between the 3 stands and increased with increasing disturbance. It increased with increase in d.b.h. (diameter at breast height) of the trees in all three species. Heavy seeding occurred in different years in different species. Quercus spp. produced heavier seeds in the disturbed stands than in the undisturbed stand. The number of seeds dispersed from the trees decreased with distance from the parent tree. The dispersal distance for Quercus spp. was greater in the disturbed stands than in the undisturbed stand. However, the dispersal distance in the forest was very low irrespective of degree of disturbance. Seed predation decreased and germination increased with distance from the parent tree in all stands, suggesting that distance-related seed predation was not influenced by disturbance. In an in situ experiment with 4 microsite treatments (seeds sown on the moss layer, on or below the litter layer, and on the cleared forest floor) the greatest germination of seeds was observed on the moss layer, irrespective of species and forest stand. The presence of litter inhibited germination of seeds to a large extent in all species. Germination of Quercus spp. was better in the undisturbed stand than in the disturbed stands, while that of Schima khasiana was better in the disturbed stands. An analysis of the fate of seed populations of the oak species revealed that loss of seeds caused through consumption by rodents and insects and transportation by various agents accounted for more than 98% of the seeds, while fewer than 1% of them germinated.