Plant diversity and community patterns along the disturbance gradient in plantation forests of sal (Shorea robusta Gaertn.)

Depending upon its magnitude and recurrence, a disturbance could structure forest communities in a variety of ways. A 30 km long disturbance gradient was identified across the managed (plantation) forests of sal (Shorea robusta Garten,) in Gorakhpur Forest Division and the impact of different degrees of disturbance on the community attributes and diversity pattern of sal stands, arranged along this gradient, was observed. The sum of frequency for species components of different stands increased along the gradient with marked fluctuations. The sum of density, however, increased only up to a few peripheral stands and stabilized further, The trend of the two indices and fluctuations in these values indicated highly patchy and heterogeneous communities along the disturbance gradient. Several potential undertrees like Mallotus and Clerodendron dominated the shrub layer with greater abundance under high disturbance while other non-leguminous species of shrubby habit dominated the stands facing intermediate disturbance. The relative density of leguminous shrubs decreased along the gradient. The efficiently sprouting trees like Holarrhena and Terminalia had maximum importance value index (IVI) at moderate disturbance while Scleichera oleosa did so towards the core. A maximum Shannon's Index of Diversity H of 3.53 was observed for the last but three stands towards the core. The trends of dominance and beta-diversity were reverse to that of alpha-diversity along the gradient. From these observations, it may be inferred that the disturbance should be contained at the level suited for maximum diversity beside sparing a few disturbance-friendly' species in highly disturbed stands from complete destruction in order to provide bare minimum herbage cover, required for ecosystem attributes of managed forests of the region.