The Status and Extent of Eucalyptus grandis Invasion in Kindoroko Forest Reserve, Mwanga District, Tanzania

Early detection and the ability to remove new populations of species showing signs of becoming invasive have been acknowledged as the most cost-effective and effective ways of managing invasive alien species globally. This study assessed the status and extent of Eucalyptus grandis invasion in the Kindoroko Forest Reserve (KFR), located in Mwanga District, Kilimanjaro Region, Tanzania. Specifically, the study aimed to assess (i) the population status and abundance of E. grandis in relation to other woody species in KFR, (ii) the spatial distribution of E. grandis in KFR, and (iii) factors influencing the abundance of E. grandis in KFR. Vegetation data were collected from 60 concentric sample plots of a 15m radius established along 17 cardinal transect lines across the forest area of 885 ha. The study revealed that E. grandis is most abundant near the forest boundary within 50m in comparison with other native species, contributing 44% of the total species counts and accounting for 23% of the overall species counts across the entire forest area. Its abundance and spread are strongly linked to the presence of favourable environmental factors and human disturbances. Canopy cover exhibited a strong negative effect (p<0.001), indicating that invasion decreases with high canopy cover, while slope showed a significant positive relationship (p = 0.044), suggesting that steeper terrains facilitate E. grandis growth. Medium disturbances negatively affected abundance (0.001), meaning decreases in the rate of invasion, whereas high disturbances had a significant positive effect (0.031), meaning invasion increases with increasing disturbances. It is concluded that E. grandis is showing all signs of becoming a problematic species in KFR. Thus, forest management efforts should focus on removing the identified population and reducing disturbances currently occurring in the forest reserve to contribute to mitigating the spread of E. grandis in the KFR