Altitudinal Variation of the Floristic Communities in Monaragala, an Isolated Hill in Eastern Sri Lanka

Résumé fourni par la source

Compared to wet zonehills of Sri Lanka, the floristic communities of hills in drier regions ofits first peniplane has been poorly studied. This study investigatedthe floristic communitiesalong the altitudinal gradient in Monaragala, an isolated hill in the intermediate zone of theisland, by sampling trees and lianas >10 cm g bh, in 99 randomly located 10 m x10 m plots infour transects laid on different aspects of the hill.In the 9,900 m2 sampled in the study, 1,322 individuals were enumerated. They represented44 families, 103 genera and 149 species, among which 45 were endemic to Sri Lanka. Frommultivariate analysis of the plot data, one grassland / savanna and five forest communitiesseparated in relation to their variations in elevation and topography, disturbance level andphysiognomy of the vegetation. These communities were: two disturbed tall forests, onerestricted to low-elevation 210-780 m (LDT) and the other widespread at 540 – 620 m / 920 –950 m (WDT); three undisturbed tall forests, one at mid-elevation 600-880 m (MUT) and theother two on ridge slopes of Sirigala (RUT) and Maragala (IUT) at 880 -1100 m, and the lasta high-elevation disturbed grassland/savanna at 720 – 870 m (HDG).The five leading families in each of the six communities collectively represented 31 of the 44families identified in the study, reflecting familial diversity among the communities. Thedominant families were Sterculiaceae and Rutaceae in the lower elevation, while Lauraceae,Dipterocarpaceae, Myrtaceae, Bombacaceae and Apocynaceae were in mid - and upperelevations. Euphorbiaceae was common to all altitudinal ranges.Most species were restricted to a particular elevation range. At the lower range, Diospyrosebenum, Pterospermum suberifolium, Miliusa indica, Acronychia pedunculata, Alphonseasclerocarpa, Chlorocarpa pentaschista and Drypetes sepiaria. The mid- and higher rangeharboured endemic species and those common to wet zone rainforests, eg. Actinodaphneelegans, A. ambigua, Cullenia ceylanica, Cryptocarya wightiana, Hunteria zeylanica,Calophyllum tomentosum, Dipterocarpus zeylanicus.This study emphasizes that isolated hill forests located outside the wet zone, like Moneragala,harbour diverse and unique floral assemblages which need urgent conservation in a rapidlydeveloping era.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.