The effect of tree spacing on early growth and performance of Eucalyptus grandis/ Eucalyptus camandulensis(GC 550) grown in Uganda

Abstract

There is high demand of wood by people in Uganda and yet there is limited information about most of the tree species especially hybrid eucalyptus clones like GC550, GUs that grow quickly so as to meet the demands of wood requirements. This study was aimed at providing information on the effect of tree spacing on the early growth and performance of GC550 in Uganda. The study was conducted in Bujawe Cental Forest Reserve, Hoima District Uganda in a plantation established by Core Woods Limited(CWL). A total of 228 trees were assesssed in 10 sample plots in the forest blocks of two year old GC550 that were established at different tree spacing regimes (3m x 3m and 4m x 4m). Stem diameter(DBH at 1.3cm), Tree height, number of branches at a stem height of 2-3m were assessed in forest blocks of the different tree spacing regimes. To determine the effect of tree spacing on the early growth and performance of GC550, the mean stem diameter, mean tree height, mean number of branches at stem height of 2-3m were compared using a T-test in SPSS. The trees established at a tree spacing of 4m x4m attained a significantly larger mean diameter (10.672cm) compared to trees established at a tree spacing of 3m x 3m (9.005cm) at 2 years. This was attributed to the limited competition for growing space (nutrients and moisture) within the trees since they are few and so utilise the available space to increase in stem diameter. In addition, trees established at a tree spacing of 3m x 3m (2.8-12.4cm) exhibited a higher variation in stem diameter compared to the trees established at a tree spacing of 4m x 4m (7.1-13.7cm). This was attributed to lack of uniformity in accessibility of light during stem diameter growth since trees are less spaced indicating high competition for sunlight (Hébert et al., 2016). An assessment of the effect of tree spacing on tree height growth at 2 years of age revealed that trees established at a tree spacing of 3m x 3m attained a significantly higher mean tree height (11.096m) compared to the trees established at a tree spacing of 4m x 4m (7.612m). This was attributed to enhanced competition for sunlight for trees estabished at higher densities. The trees established at a treespacing of 4m x 4m attained a significantly more mean number of branches at 2-3m (8.216 branches) compared to trees established at a tree spacing of 3m x 3m (2.847 branches ) at the age of 2 years. This was attributed to less competition for light that penetrates within the tree plantation at the widest spacing and lengthens the survival of lower branches. In addition, trees established at a tree spacing 4m x 4m exhibited a higher variation in the number of branches at a stem height of2-3m(4-14 branches) compared to the trees established at a tree spacing of 3m x 3m (0-6 branches) at the age of 2 years. This was attributed to less competition for light by the trees that are widely spaced and so they access uniform light very easily and develop branches quickly and maintain them for stability. The study recommends that further research should be conducted to determine the effect of tree spacing on the early growth and performance of GC550 beyond the 2 year age that was considered for this study. Further more, the effect of tree spacing on other attributes of tree growth such as stem taper and wood quality should be assessed.