Topographical patterns of tropical forest loss in the early 21st century

Abstract:

Tropical forests play a critical role in balancing the carbon cycle between the biosphere and atmosphere, as they act both as a sink and an emission source. Massive deforestation across the tropic, which is assumed to be constraint in lowlands, has released a great amount of carbon previously stored above and below the ground. However, recent studies show substantial new forest loss in highland regions of Southeast Asia, challenging previous understanding that may underestimate the carbon emissions from tropical forest loss. Here we analyzed multiple high-resolution remote sensing datasets, all in 30-meter resolution, of forest cover change, carbon density map, and topography to investigate the topographical patterns of tropical forest loss and associated carbon emission from 2001 to 2017. Tropical forest loss shows an accelerating and unprecedented gross loss rate of 1.26×10⁷ ha yr^-1, with a significant increase (p < 0.05) in the mean elevation and slope of lands occurring forest loss. Loss of forests across the tropics contributes to releasing much more carbon emission (gross rate of 2.19 Pg C yr^-1) than estimated in prior studies. Tropical mountains contribute to 13.6% of gross forest loss and 15.5% of gross carbon loss from tropical deforestation. This implies that tropical forest loss has a clear mountain loss component during the early 21st century, and ignorance of mountain forest loss by previous studies results in an underestimation of carbon emission from forest loss. Our results highlight the need for an accurate representation of topographical patterns of tropical forest loss in environmental assessments.