SEEDLING SURVIVAL AND GROWTH OF Mesua AND Dipterocarpus
SPECIES IN A SRI LANKAN RAIN FOREST
B.M.P. Singhakumara1 and P.M.S. Ashton2
1 Department of Forestry and Environmental Science, University
of Sri Jayewardenepura.
2 School of Forestry and Environmental Studies, Yale University New Haven,
Seedlings of Dipterocarpus (D. hispidus and D. zeylanicus) and Mesua (M.
ferrea and M. nagassarium) were investigated for their survival and growth
in different microenvironments in a lowland rain forest in south-west
of Sri Lanka. These species occur together as canopy dominants of late-successional
rain forest. Partitioning of the regeneration niche can be one explanation
for the co-existence of ecologically similar canopy tree species within
a forest. This study tested that differences in disturbances across the
topography of lowland rain forest cause different survival and growth
rates in closely related tree species among and within canopy openings
of different size.
Seedlings were planted in plots located in five zones representing a range
of forest groundstorey micro-environments found adjacent to and across
canopy openings of three sites- valley, midslope and ridgetop. Plots were
located from north to south across each gap (i) understorey 10 m to the
south of the gap, (ii) southern gap edge, (iii) centre, (iv) northern
edge and (v) understorey 10 m to the north of the gap. Experiments were
designed to monitor survival and growth of planted seedlings for two years.
At the end of two years survival was calculated, height increment recorded
and destructive samples were taken to measure dry mass gain of root, stem
Seedlings of Mesua ferrea, M. nagassarium and D. zeylanicus showed high
survival on all sites 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 for all species. Results
also demonstrated clear differences among species. Dipterocarpus exhibited
greater growth responsiveness than Mesua species. These differences appeared
to be related to availability of soil moisture and groundstorey radiation
regimes. This study demonstrated that closely related species have specific
growth characteristics that allow each to establish and grow better than
its relatives in particular forest microenvironments.
Department of Forestry and Environmental Science,
of Sri Jayewardenepura,Sri Lanka. 1995-2000. All rights reserved.