NATURAL REGENERATION OF GAPS IN A SELECTIVELY LOGGED AREA AT MORAPITIYA PROPOSED RESERVE.

Abstract

Species composition and girth class distribution of pioneer (early successional) and climax (primary forest) tree species were investigated in gaps of different sizes created by selective logging in 1984-85 at Pitakele, Morapitiya proposed forest reserve, a lowland evergreen rain forest, in Ratnapura/ Kalutara districts.

Eleven gaps of different sizes were selected for the study in 1992. In each gap, 9 plots of 2 by 2 metres, were demarcated along N-S and E-W directions. All species found in plots were recorded and identified. The height and girth of saplings and seedlings were also measured.

There were 120 species, belonging to 84 genera and 44 families, found in all gaps. The ten dominant families were: Euphorbiaceae, Clusiaceae, Dipterocarpaceae, Melastomataceae, Myrtaceae, Sapotaceae, Lauraceae, Anacardiaceae, Annonaceae and Rubiaceae.

There was a gradual increase in the number of pioneer species and their stem density from small to large gaps. However, this pattern was not shown by climax species. The number of climax species was higher at the periphery of large gaps than in the gap centre. The number of pioneer stems was higher at the centre of gaps. Light intensity (photosynthetically active radiation- PAR) varies within (centre and periphery) and between (small, medium and large) gaps.

The gradual increase of number of pioneer species, which were not present before logging, is due to the increased light intensity and higher Red/ Far Red ratio. These conditions are essential for the germination of seeds of pioneer species in the soil seed bank. Seedlings and saplings of climax species found in undisturbed forest were found in all gaps (63- 620 m2 in size) selected for the present study.

Further studies should investigate regeneration methods that allow fruit dispersal from a residual parent tree source, and that creates a below canopy radiation regime that initiates and then releases regeneration of tree species that ordinarily dominate the mature phase of a stand development. This needs partial opening of the canopy and sub-canopy which is banned at present under the moratorium on felling of natural forests.