SEEDLING SURVIVAL AND GROWTH OF Mesua AND Dipterocarpus SPECIES IN A SRI LANKAN RAIN FOREST

Abstract

Seedlings of Dipterocarpus (D. hispidus and D. ievlanicusi and Mesua 1M. [errea and M.nagassarium, were investigated for their survival and growth 111 differentmicroenvironments in a lowland rain forest in south-west of Sri Lanka. These species occurtogether as canopy dominants of late-successional rain forest. Partitioning of theregeneration niche can be one explanation for the co-existence of ecologically similarcanopy tree species within a forest. This study tested that differences in disturbances acrossthe topography of lowland rain forest cause different survival and growth rates 111 closelyrelated tree species among and within canopy openings of different size.

Seedlings were planted in plots located in five zones representing a range of forestgroundstorey micro-environments found adjacent to and across canopy openings of threesites- valley, midslope and ridgetop. Plots were located from north to south across each gap(i) undcrstorey 10m to the south of the gap, (ii) southern gap edge, (iii ) centre, (iv) northernedge and (v) understorey 10m to the north of the gap. Experiments were designed tomonitor survival and growth of planted seedlings for two years. At the end of two yearssurvival was calculated, height increment recorded and destructive samples were taken tomeasure dry mass gain of root, stem and leaves.

Seedlings of Mesua [errea, M. nagassarium and D. zevlanicus showed high survival on allsites and in all gap/ canopy conditions. D. hispidus showed the lowest survival in all sites.Growth measures attained maxima in the centre gap/ canopy condition in the three sites forall species. Results also demonstrated clear differences among species. Dipterocarpusexhihited greater growth responsiveness than Mesne species. These differences appeared tohe related to availability of soil moisture and groundstorey radiation regimes. This studydemonstrated that closely related species have specific growth characteristics that alloweach to establish and grow hetter than its relatives in particular forest microenvironments.