TREE SEED-GERMINATION AND SEEDLING ESTABLISHMENT IN TREEFALL GAPS ANDUNDERSTOREY IN A SUBTROPICAL FOREST OF NORTHEAST INDIA

Seed germination, and survival and growth of seedlings of four dominan t tree species, Quercus dealbata, Quercus griffithii, Quercus glauca a nd Schima khasiana were studied in the treefall gaps and forest unders torey of an undisturbed mature-phase humid subtropical broadleaved for est in northeast India. Three important microenvironmental factors nam ely photosynthetically active radiation (PAR), soil moisture and litte r depth, were also measured in the forest understorey and gaps and cor related with seedling mortality. Seed germination of S. khasiana was s ignificantly higher in the treefall gaps than in the understorey; amon g the tree species studied, it had the highest germination. Quercus se edlings were abundant in the understorey and small gaps, while S. khas iana seedlings were more numerous in the large gaps. The survivorship curves for the seedling populations revealed that the three Quercus sp ecies survived better in the understorey, while S. khasiana did so in the gaps. PAR and soil moisture were positively correlated with tree s eedling mortality, which occurred mainly during the winter months. The Quercus seedlings grew better in the forest understorey and small gap s and S. khasiana seedlings in the large gaps. The differential perfor mance of the tree seedlings to the conditions prevailing in the unders torey and gaps of two sizes indicates that different species were adap ted to different light environments depending upon their optimum requi rements. This could be an effective mechanism for promoting species co existence in the forest community.