Southeast- and Northeast-facing slopes have the least tree cover in the Northern and Southern Tropics, respectively

Increasing tree cover (TC) through afforestation/reforestation (A/R) in the tropics - one of the most deforested regions - has become a widely adopted strategy to sequester atmospheric CO2, and mitigate the effects of climate change. However, the factors that influence the plantation site’s suitability for tree growth, essential for effective A/R programs, remains insufficiently understood. Our analysis of TC in 127 protected areas from the tropics revealed a previously unrecognized influence of topography on establishment of TC at the landscape scale. Slopes facing southeast in the Northern Hemisphere and northeast in the Southern Hemisphere have the least potential to have TC. In contrast, northwest- and southwest-facing slopes generally have higher potential for TC in the Northern and Southern hemispheres, respectively. We suggest that tropical A/R programs, especially in hilly areas with 10 to 80% TC, should consider the influence of slope direction on TC establishment and adopt appropriate strategies.