Assessing tree mortality intensity at two different periods of resin tapping in Uganda

Abstract

Resin tapping is an emerging alternative economic activity in Ugandan Pinus plantations despite the fact that they are mainly managed for timber production. During resin extraction at Kikonda forest reserve the outer layers of pine trees are incised over many years, leaving typical ‘fish bone’-like patterns on the stem face. This mechanical damage inflicted by resin tapping incisions is likely to affect tree health. This makes tapped pine trees more susceptible to extreme weather events like strong winds leading to stem breakage, rotting, drying due to droughts and more susceptible to pests. In this study, diameter at breast height (DBH) of resin tapped trees was measured and observed for major causes of mortality at two different stages of resin tapping. More specifically, tree mortality intensity of pine trees tapped at four years was compared with those tapped for two years and the effect of resin tapping periods on DBH of tapped trees at two and four years period were assessed. 20 alternating square sample plots of 100m2 (at a spacing of 3mx3m) along the-transects from two compartment were established. A total of 1200 trees sampled from 40 plots were marked, DBH measured and observed for any causes of mortality. The results indicate that four-year tapped trees in F01 compartment had smaller stem diameter compared to stem tree diameter in F08 compartment tapped for two years. The influence of years of resin tapping on mortality of trees tapped for two and four years indicates that mortality occurred most in the four years tapped trees with 18% trees drying and 17% trees breaking. This indicates that mortality increases with years of resin tapping. Therefore, trees whose diameter is less than 20 cm must be tapped for maximum of 2 years since there is less damage.