SEEDLING GROWTH OF SHOREA (DIPTEROCARPACEAE) ACROSS AN ELEVATIONAL RANGE IN SOUTHWEST SRI-LANKA

Performance of seedlings of seven rain forest, canopy dominant Shorea species was studied in a transplant experiment ir! forest sites at thr ee different elevations (low, mid and high) within the humid zone of s outhwest Sri Lanka. Five species generally inhabit low-to mid-elevatio ns, one at mid-and lower montane elevations, and one exclusively at lo wer montane elevations. Temperature, rainfall and cloudiness varied wi th elevation. For each site seedlings were grown in pots under partial shade conditions using similar soils and evermoist conditions. All gr owth measures showed differences among elevation sites, among species and in the interaction between species and elevation sites. Performanc es of species collectively showed (i) decline in height and leaf numbe r with increase in elevation, (ii) higher dry mass at low-and mid-elev ation sites compared to that at high-elevation and (iii) a higher mass of single leaves at the mid-elevation site than at the high-elevation site. Rank order of species changed across elevations for both height and dry mass. Dry mass declined with elevation in four of the seven s pecies studied. S. gardneri, the only exclusively lower montane specie s, increased dry mass with elevation. Height declined with elevation f or six of the species with only S. gardneri showing no change. Changes with elevation in the rank order of species for total leaf number and mass of single leaves were small. However, total leaf number and mass es of single leaves differed among species and among elevations. S. me gistophylla and S. disticha had a few leaves with high individual mass es, while S. gardneri, S. affinis and S. trapezifolia had many leaves with less mass per individual leaf. One group of species showed relati vely little change in leaf number per seedling and large changes in ma ss of single leaves. The other group varied more in leaf number but ma ss of individual leaves remained constant. Growth allocation to leaf p roduction versus individual leaf size appears related to the successio nal division of Shorea section Doona. Also all species grew better at the low-elevation site irrespective of their natural ranges except S. gardneri, whose natural range is restricted to high elevations, and ex hibits markedly lower growth responsiveness than the other wider rangi ng species.