Diversity, composition and richness of soil seed banks in different forest communities at Dotalugala Man and Biosphere Reserve, Sri Lanka

Abstract

The soil seed bank provides an indication of the regenerative potential of forest ecosystems following disturbances. The present study was conducted to examine the spatial and temporal distribution of soil seed bank in three different forest communities identified in an upper montane forest ecosystem (Dotalugala Forest Reserve) in the Knuckles Range, Sri Lanka. The three forest communities were upper-montane forest (UMF), midelevational wet face forest (MWF) and midelevational dry face forest (MDF), hereafter referred to as UMF, MWF and MDF, respectively. Ten surface soil samples were collected from five, 10 m × 15 m permanent plots (2 composite samples from each plot) established in each of the three forest communities. The soil samples were spread on seed beds in a glasshouse and emerging seedlings were counted and identified into different morphospecies. Two soil samplings were conducted during dry and wet seasons. Seed beds were maintained for nearly 3-4 months until no seedlings emerged. The results revealed higher number of germinable seeds in the wet season (1,157, 1,381 and 1,231 seeds) than in the dry season (507, 641 and 597 seeds) in UMF, MWF and MDF forest communities, respectively. The richness had similar trend between seasons (31, 35 and 34 morphotypes in the wet season and 24, 27 and 27 in the dry season in UMF, MWF and MDF, respectively). However, the density and richness showed no significant differences between forest communities during both seasons. Species composition differed between seasons and forest communities. Woody species dominated the soil seed bank during the dry season, while non-woody species dominated in the soil seed bank during the wet season. These temporal fluctuations in seed banks may possibly be due to site-specific (predation, senescence and germination of seeds) and plant-specific (phenology, dormancy of seeds) factors prevailing in these forest communities. Seeds of invasive species were represented comparatively less in all three communities, indicating no significant threat from invasive species to these forest communities. A number of pioneer species including Maesa indica, Acronychia pedunculata and Macaranga spp. were recorded in all three sites signifying their resilience and regenerative potential following a disturbance.