EFFECT OF SHADING ON SURViVAL AND GROWTH OF Mesua (CLUSIACEAE) AND Shorea (DIPTEOCARPACEAE) SEEDLINGS ACROSSTOPOGRAPHIC GRADIENT IN SINHARAJA RAIN FOREST, SOUTHWEST SRI lANKA

Abstract

The effect of shading on survival and growth of two species of Mesua (Clusiaceae) andfour species of Shorea (Dipteocarpaceaeh planted seedlings were investigated at differenttopographic positions in Sinharaja rain forest All occur together as canopy dominant treesIII Sinharaja rain forest Twelve-understory sites were selected, four each on differenttopographic posilions valley, midslope and ridgetop. Measurements of height, number ofleaves, root collar diameter and the mortality were recorded over a five-year period.Hemispherical canopy photographs were taken to calculate Indirect Site Factor (ISF),Direct Site Factor (DSF), and the Leaf Area Index (LAI). Analysis of photographsdemonstrated that LAI decreased from valley to ridge top while DSF and ISF increasedfrom the valley to ridge top. After five years thirty-four (34 %) seedlings died in the ridgelop and the lowest mortality was recorded in the midslope. Seedlings of Mesua ferrea L.had the highest survival than other species in all understory conditions and the lowestsurvival rate recorded for Shorea trapezifolia (Thw.) Ashton. Results showed cleardifferences in survival and growth among species. These differences appeared related (0availability of soil moisture and understory radiation regimes.