Environmental and anthropogenic variables influencing the distribution of the non-native tree species in Tropical Montane Forests of West Usambara, Tanzania

Abstract

A study to determine environmental and anthropogenic factors driving distribution of non-native tree species, Acacia melanoxylon and Eucalyptus grandis was conducted from January to March 2023 in Magamba Nature Forest Reserve (MNFR), West Usambara, Tanzania. Ninety-six (20 m x 20 m) plots were purposively set in which altitude, slope, soil, human disturbance indices and vegetation data were collected. Redundancy Analysis was employed to identify factors influencing the distribution of the non-native tree species in MNFR. The explanatory variables altitude, slope, human disturbance, soil organic carbon, pH, total nitrogen and bulk density were significant (p < 0.05) in influencing the distribution pattern of A. melanoxylon and E. grandis. Soil sand, silt, clay content, water content, available phosphorus and cation exchange capacity were not important (p > 0.05). The association between human disturbance and distribution of E. grandis recorded in this study implies that the MNFR faces serious human disturbances that need an urgent management response. We recommend more efforts to be directed towards the control of the human disturbances to circumvent encroachment of the tropical montane forests by non-native tree species. The findings of this study may be valuable for devising forest restoration programmes to sustain the ecosystem functioning in the West Usambara montane forests and similar ecosystems.