An assessment of vegetation and canopy structure of moderately exploited natural forest area in Yagirala forest reserve

W. M. P. S. B. Wahala, W. A. J. M. De Costa, D. M. S. H. K. Ranasinqhe


Study assessed the vegetation composition and structure and the forest canopy structure in terms ofLeaf Area Index (LAI), Mean Leaf Angle (MLA) and canopy openness in different elevationalclasses of moderately exploited natural forest area which covers about 82% of total natural forestcover in Yagirala forest reserve, a tropical lowland rain forest selectively logged by State TimberCooperation in late 70's.

Canopy architecture termed as angle distribution of foliage elements (Chen et al. 1992), can bequantified by the leaf area index (LAI) and mean leaf angle (MLA). In this study Hemisphericalphotographic method was used to characterize canopy architecture at three elevational classes (i.e.valley, mid-slope and ridge top). At each elevational class, hemispherical photos ofthe forest canopywere taken at each sampling point at a height of l m above the ground along transects up to 200m at50m intervals. Hemispherical photographs were analyzed using Hemiview 2.1 canopy analysis software

A vegetation survey was carried out to determine floristic composition of dam inant species and fam i!ies,which contribute more to the forest canopy. The enumeration was carried out using 0.05 ha circularplots at three elevational classes, totally covering 0.6ha of the area. Individuals taller 1m were enumeratedand species, diameter at breast height (dbh) and total height measurements were recorded and relativebasal area, relative frequency, relative density and Importance Value Index (IVI), diameter classdistribution were estimated.

Leaf area index (LAI) and mean leaf angle (MLA) did not show significant variation between threeelevational classes. LAlmean value of low elevation areas show high value of2.256 and mean valueof high elevation areas show low value of 2.087. Average MLA value for the moderately exploitedarea is 29.14. Canopy openness given in terms of visual sky fraction is also not significantly diferentbetween three elevational classes. The results give an estimation of homogeneity of canopy opennesswithin the moderately exproited natural forest.


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Proceedings of International Forestry and Environment Symposium, Sri Lanka. Published by Department of Forestry and Environmental Science, University of Sri Jayewardenepura