Soil seed bank dynamics of selected wet and dry forests in Southern Sri Lanka

Abstract

Studies on natural regeneration dynamics o f soil seed banks are important in determining the regeneration potential o f natural forests. This study was carried out to study the regeneration potential and floristic composition o f two natural forests in wet and dry zones o f Sri Lanka. Two natural forests in Wilpita (low country wet zone) and Hambantota (low country dry zone) were selected for the study. Sampling was carried out in the top 10cm o f the soil using a quadrant (30cm*30cmxl0cm) along the transects and the number o f seedlings emerged enumerated. The seedlings were transferred into poly bags once a week and allowed to grow for a few months to determine the floristic composition. The means o f viable seeds in the Wilpita and Hambanthota forests were 162 m2 and 146 m2, respectively. The number seedlings per square meter among the samples collected along the transect was not significantly different (P>0.05). The floristic composition and biological diversity o f soil seed banks varied among the forest types. The population density was higher in the wet zone forest compared to the dry zone forest. Alstonia macrophylla (hawari nuga), Macaranga peltata (kenda), Trema orientalis (gedumba) and Melastoma malabathricum (bovitiya) were prominent tree species in the Wilpita forest. Moreover, affinity analysis showed that A. macrophylla was the most prominent tree species in this forest type. This study showed that the regeneration potential o f the wet zone forest is much higher than that o f the dry zone forest. The study also identified the major early successful species occurring in the soil seed banks and this information will be useful in developing an effective strategic management regime to restore degraded forest lands in these areas.