Distribution of expansive shrubs under climate change scenarios and their socio-economic impacts in a dry Afromontane Forest

Abstract

Native plants that expanded into new geographical areas after human-induced disturbances and climate change are referred to as expansive species. This study aimed to model the current and future distribution of Cadia purpurea and Tarchonanthus camphoratus, two expansive shrubs in the Desa'a dry Afromontane Forest in northern Ethiopia, and analyze their socio-economic impacts. Using ArcGIS and MaxEnt, the distributions were modeled under two shared socio-economic pathways (SSP2.6 and SSP8.5) of climate change scenarios for three time periods: 1970–2000 (current), 2050s, and 2070s (future). About 124 records of species occurrence, elevation, aspect, slope, and 19 bioclimatic variables were used to determine the current and future distribution. The socio-economic impacts of the two expansive shrubs were assessed through household surveys, focus group discussions, and interviews with key informants. We used a t-test for continuous variables and a chi-square for categorical variables to test the significance of differences in means between invaded and uninvaded areas by the expansive shrubs using R software. The result showed that the mean area under the curves (AUC) for the replicate runs were 0.901 and 0.903 for Cadia purpurea and Tarchonanthus camphoratus, respectively, indicating that the model's predicted result was very accurate and reliable. Precipitation was determined to be the most significant bioclimatic variable, accounting for 82.6% and 79.5% of the variability in the distribution of Tarchonanthus camphoratus and Cadia purpurea, respectively, in the study area. The socio-economic result indicated that human activities such as illegal cutting, settlement expansion, road construction, agricultural expansion, and free grazing were found to facilitate the spread of these species. The expansive species provide a number of services, such as firewood, charcoal production, construction material, shading, erosion control, bee forage, medicine, and fencing. However, they also have adverse impacts, such as biodiversity loss, reduced crop yields, reduced water sources, suppressed grass growth, and reduced tourism income. Local communities recommended physical, chemical, and biological mechanisms to manage and control the expansion of these species in the Desa'a forest, as their negative impacts outweigh their positive impacts.