Modelling the distribution of Ekebergia capensis sparrm. (Meliaceae) under the current and future climate change scenarios in Ethiopia.

Abstract

Background: Ekebergia capensis is a valuable tropical tree occurring on highlands of Ethiopia and used for traditional medicines, fodder for livestock and fruits are eaten by birds and other wild animals. However, it faces climate change threats and increased anthropogenic pressure, mainly, selective cutting for timber, firewood and expansions of agriculture across its range. Understanding the impacts of climate change on its suitable ranges is crucial to identify high-priority areas for its effective conservation and management plans. The study aimed to predict suitable habitats of Ekebergia capensis and examine factors influencing its distribution under current climate and future climate scenarios.

Methods: We used an ensemble modeling approach with 10 replications of five algorithms: BRT (boosted regression trees), RF (random forest), GLM (generalized linear model), GAM (generalized additive model), and Maxent (maximum entropy). Model performance was evaluated using the area under the receiver operating characteristic curve (AUC), the true skill statistic (TSS), and visual assessment of ROC curves.

Results: The AUC and TSS of the ensemble model are 0.88 and 0.68, respectively, showing a very good performance. The currently predicted suitable habitat for Ekebergia capensis covers an area of approximately 215,869.87 km², representing 19.05% of the country. Under climate projections for the 2050s based on emission scenarios, the range of this species will decline by 31.71% under the medium (SSP2-4.5) and by 33.56% under the worst-case (SSP5-8.5) scenario. In the 2070s, the suitable habitats of this species will decrease by 45.44% and 47.14% under SSP2-4.5 and SSP5-8.5, respectively. Ekebergia capensis will lose a large portion of its suitable habitats between 2050s and 2070s, i.e., 16.92% under SSP2-4.5 and 15.24% under SSP5-8.5. This study suggests that southern, central, southwestern, and eastern highlands of Ethiopia provide suitable areas for the species. In contrast, suitable habitats in the northern part of the country will be either lost or fragmented in the future.

Conclusions: Our findings show that climate change significantly affects the suitable habitats of Ekebergia capensis. Only selected parts of its current habitat will remain suitable, while others will be lost or become isolated in the future. This species has recalcitrant seeds and cannot be stored ex-situ. Therefore, conservation efforts should prioritize in situ strategies such as habitat restoration, reintroduction, and assisted migration across its range. In addition, combining in situ efforts with carefully selected ex situ methods could offer a more comprehensive approach to conserving this species.