Predicting the potential impact of environmental factors on the distribution of Triplochiton scleroxylon (Malvaceae): An economically important tree species in Nigeria

Abstract

Triplochiton scleroxylon is a lowland rainforest tree species distributed in Central and West Africa, with economic and medicinal importance. Given that its population is threatened by overexploitation for timber, poor seed production, and habitat destruction, it becomes important to project its distribution along environmental gradients to bolster our understanding of its conservation. This study thus examines the combined effect of overexploitation and climate change on its distribution in Nigeria. We used MaxEnt algorithm and spatial analysis module of ArcGIS to model the current and future habitat suitability of T. scleroxylon in Nigeria. We utilized 95 unique occurrence points and eight environmental variables (Bio7, Bio8, Bio9, Bio13, Bio14 & Bio18, elevation, and slope) to understand the response of the species to changing climates during the time periods 1970–2000, and to project species responses to temperature and precipitation in the years 2050 and 2070, using two Global Climate Models. Results indicated that the prediction of the suitable habitat for T. scleroxylon under the model was very reliable (AUC ≥ 0.9; TSS ≥ 0.6). Annual temperature range (Bio7) was the most influential bioclimatic variable for predicting habitat suitability and distribution for the species in Nigeria. Highly suitable habitat has an optimum temperature of 28.5 ◦C, precipitation ≤600 mm, an elevation of ≤400 m, and a slope of 90◦; it is currently estimated at 23.3% of the total land cover, and predicted to reduce to <15% by the year 2050. The methods of SDM have a great potential in understanding species richness, and also provide data for the support of conservation strategies at local scales. Hence, this study advocates for the conservation of the remaining habitats of T. scleroxylon through the implementation of strategic plans, especially in South-western Nigeria where there is a high potential for its regeneration owing to favourable environmental conditions.