Allelopathical Effects of Gmelina arborea on Diameter and Height of Pinus kesiya

This study aims at investigating the effects of allelopathy of G. arborea on the growth of P. kesiya. Forty sample plots were established on five transects using systematic sampling in which Diameter at Breast Height (DBH), Height (H) of 400 trees and Distance (d) from G. arborea firebreak were measured. The statistical analysis was done based on regression analysis, while analysis of variance (ANOVA) was used to establish the statistical difference of plots at different distances from the G. arborea firebreak. The results from this study showed that height and DBH of P. kesiya depend on the planting distance from G. arborea fire breaks. Two independent models of the form ln(Y) = a+xln (d) were formulated based on height and DBH as response variables, and distance from the fire breaks as explanatory variable. The models had a good fit and explained over 80% of the variation of the dependent variable. More importantly, our findings also revealed that P. kesiya trees which were closer to G. arborea fire break had smaller diameters and heights as compared to those which were further away. There was a significant difference (p-value<0.05) on both height and diameter amongst the 8 plots which were established at different distances from the G. arborea trees. Further follow ups using a post‑hoc analysis by employing a Least Square (LSD) indicated that there was a significant variation between groups which were before and after 25 m from the firebreaks. Thus, the mean height and diameter of the trees which were before 25 m were smaller compare to the mean height and diameter after 25 m, indicating that when P. kesiya is planted at least 25 m away from G. arborea, the impact of allelopathy is reduced. For this reason, we recommend planting P. kesiya at least 25 m from G. arborea for the allelopathical effect to be negligible.