MICROENVIRONMENTAL VARIABILITY AND SPECIES-DIVERSITY IN TREEFALL GAPS IN A SUBTROPICAL BROADLEAVED FOREST

Microenvironmental variability and species diversity in gaps and forest understorey were studied to assess the role of treefall gaps in maintaining composition and patchy distribution in a broad-leaved sub-tropical climax forest, Mawphlang, Meghalaya. India. Photon flux density was higher in gaps than in the surrounding understorey. Relative humidity was low and the litter layer was relatively thin in gaps throughout the year. Soil moisture and photon flux density in the gaps significantly varied between seasons and gaps of different sizes. Relative humidity significantly varied between seasons but difference among gaps was insignificant. Among-gap and among-season variations in soil and air temperature were insignificant. The number of tree species in the gaps was positively correlated with gap area, and tree species abundance showed higher equitability in larger than in smaller gaps. In gaps, alpha-diversity was highest for herbs and lowest for shrubs. Beta-diversity was highest for shrubs and lowest for tree seedlings. Alpha-diversity of tree seedlings was higher in the gaps than in the forest understorey. Conversely, beta-diversity was higher in the understorey than in the gaps. Low species similarity for tree seedlings among the gaps could be an effect of patchy distribution of parent tree species in the forest. Thus a significant change in light and moisture regimes along the gap size gradient played an important role in influencing the composition and abundance of shade tolerant and intolerant tree species in gaps on one hand, and affected the overall species diversity of the forest, on the other.