GROWTH AND SURVIVAL OF PIONEER AND LATE SUCCESSIONAL SPECIES IN SIMULATED LIGHT ENVIRONMENTS IN A SRI LANKAN LOWLAND RAIN FOREST

Abstract

Growth and survival of two pioneer and four late successional species in different light levels inshade houses were investigated over a period of one year from January 2000 to January 200 1 atthe Sinharaja field research station.

Schumacheria castaneifo/ia (Dilleniaceae) and Vltex altissima (Verbenaceae) represented thepioneer species. Psychotria nigra, Gaertnera vaginans (Rubiaceae), Syzygium operculatum andS. rubicundum and (Myrtaceae) were selected as late successional species. The four latesuccessional species were further subdivided into two canopy species (S. operculatum and S.rubicundum) and two understorey species (Psychotria nigra and Gaertnera vaginans) based onheight at maturity oftheir parent trees. Seedlings were grown under four light environments (fullsun, 1200; partial sun, 800; partial shade, 350; shade, 50j.Lmolm-2s-1) that represented a range ofPPFD (photosynthetic photon flux density) found within the forest. Five seedlings of eachspecies were grown in each light environment, which was replicated three times. At the end ofone year the height increments and percentage survival of seedlings were measured.

The study revealed that two Syzygium species, Gaertnera vaginans and S. castaneifolia showingthe lowest height increments 'when grown in shade. But no significant difference was observedbetween shade and full sun for these species. Although the lowest height increments for Valtissima and P. nigra were observed in full sun and in partial shade respectively, there is nosignificant difference among shade, partial sun and full sun for V altissima. Psychotria nigra didnot show any significant difference among four light treatments. The greatest relative heightgrowth was observed in partial shade for G. vag/nans and S. castaneifoliz; V altissima, and inpartial sun for two Syzygium species. Plasticity (ratio between highest and lowest values amonglight treatments) measurement of height increment was highest in G. vaginans (3.47), the lowestin P. nigra (l.52) compared to s. operculatum (1.79), S rubicundum (2.18), V altissima (2.19),S. castaneifolia (3.08). Percentage seedling survival of S. castaneifolia, and V a/tissima was100% under all light levels .All species survived equally well in partial sun light level. In shade,seedling survival of G. vaginans, and S operculatum was 93% and in Psychotria nigra, it was80%. G. vaginans and P. nigra showed 93% seedling survival in partial shade .In full sun G.vaginans and S. rubicundum exhibited 93.3% survival while P nigra showed 67 % survival.These results suggest that pioneer species grow and survive well in all light levels than latesuccessional species in early stage of their life cycle.