Landscape Heterogeneity Drives the Growth of Invasive Acacia Melanoxylon in Humid Forests in Kenya (Nabkoi and Timboroa Forests)

Invasion of forest by Acacia species is widespread in many terrestrial environments. However, their response to variation in forest environmental conditions has received less attention. This study determined the influence of landscape heterogeneity on growth of Australian Blackwood (<i>Acacia melanoxylon</i>) in tow tropical highland humid forests (Nabkoi Forest and Timboroa Forest) in Kenya. Sampling was done by laying three-500 m long transect, followed by overlaying three plots 0.1 ha. plot (10 m × 10 m) longitudinally at 235 m intervals. Tree density, diameter at breast height (DBH) > 1.3 m, tree height and tree density were measured in each plot. The study established that one of the sites was capable of supporting a larger number of trees (in terms of density) whose growth (in terms of DBH and height) is constrained while the other site supports low density of fast-growing acacia. The tree density, DBH, and height of acacia responded to variation in forest landscape heterogeneity. DBH of the invasive species was significantly (<I>P</I> < 0.05) affected by altitude (-ve), slope (+ve), and aspect (+ve). The current study demonstrates that altitude, slope, and aspect significantly influenced the growth of <i>A. melanoxylon</i> in the studied forest. To gain insight on how these environmental gradients affect growth of the invasive species without compounding factors, future studies should be conducted under controlled conditions.