Southeast and Northeast facing slopes have the Least Tree Cover in Northern and Southern Tropics, respectively

Reforestation in the tropics, one of the most deforested regions, can help mitigate climate change and conserve biodiversity. Its effective implementation requires assessing suitability of a given site for tree growth. By analyzing tree cover (TC) in 127 protected areas across the tropics, we show that southeast and northeast-facing slopes are least favorable for tree growth in the Northern and Southern tropics, respectively. In contrast, northwest (north-, northwest, and west-facing) and southwest (south-, southwest, and west-facing) slopes are more suitable for tree growth in the Northern and Southern hemispheres, respectively. This pattern likely results from the combined effects of Pole-Equator and West-East asymmetries in TC. Tropical reforestation programs, especially in hilly areas with intermediate TC, could benefit from considering the influence of slope direction on tree growth and adopting appropriate plantation strategies.