EFFECT OF CANOPY GAPS A'ND TOPOGRAPHIC REGIMES IN SEEDLINGS PERFORMANCE IN SINHARAJA RAIN FOREST, SOUTHWEST SFU LANKA

Abstract

Growth and survival of tree canopy dominant seedlings in the Sinharaja lowland rain forest insouthwest Sri Lanka were monitored. Twelve canopy gaps and closed canopy sites wereselected, as four of each on different topographic positions- valley, midslope and ridgetop.Measurements of height, number of leaves and mortality were recorded over a two-year period.Hemispherical canopy photographs were taken to calculate Indirect Site Factor (ISF), Direct SiteFactor (DSF), and canopy openness. Greatest canopy openness, highest DSF values wererecorded for ridgetop sites and smallest values were recorded for valley sites. Over the two-yearperiod sixty-six (11.45%) seedlings died in the ridge top, which indicated the highest mortalityrate. Survival of seedlings in the canopy gap ani .orest understorey declined on progressingfrom valley to ridgetop sites. Seedlings of Mesua ferrea had a higher survival than other speciesin the canopy opening and understorey conditions. Height growth and leaf number were greatestin the gap sites. A significant relationship was found between DSF and maximum height growth(33.05,P>O.OO) for Syzygium rubicundum. Shorea trapezlfolta, Shorea distich a and Syzygiumrubicundum showed greatest height increment .n the valley, midslope and ridgetop sitesrespectively. No relationship was found between DSF and leaf numbers in all seedlings exceptSyzygium rubicundum, where has increased with increasing DSF.