Influence of Physical and Environmental Factors on Yield Prediction Variability in Sri Lankan Pinus Plantations

Abstract

This study investigates the influence of slope and agro-ecological regions on the growth and timber volume of Pinus plantations in the wet and intermediate zones of Sri Lanka. Annually, the Forest Department of Sri Lanka releases approximately 1,000 hectares of Pinus plantations for thinning and clear felling to the State Timber Corporation, which estimates timber yield using enumeration data. Notable discrepancies between estimated and actual timber volumes prompted a detailed analysis of the physical and environmental factors affecting plantation growth. The study covered 48 coupes from 11 plantations across three districts Nuwara Eliya, Matara, and Ratnapura selected based on regional representation. Data collected included actual timber volumes extracted in 2020 and 2021, slope measurements, standing tree counts, and agro-ecological region classifications. Statistical analysis focused on identifying correlations between slope, agro-ecological regions, and recorded timber volume. Results indicated a predominantly negative correlation between slope and timber volume, with volumes decreasing progressively from up-country to low-country regions. Steeper slopes were consistently associated with reduced timber yields, while agro-ecological zone significantly influenced overall plantation productivity across all sampled sites. These findings highlight the importance of incorporating topographical and ecological factors into timber yield forecasting models. Improved integration of such variables would reduce estimation discrepancies, support more accurate harvest planning, and contribute to the long-term sustainable management of forest plantation resources across Sri Lanka.