Edge fires drive the shape and stability of tropical forests

TL;DR

This study investigates how edge fires influence the shape and stability of tropical forests, revealing a scaling relation and modeling fire propagation to predict forest patch dynamics and regional stability.

Contribution

Introduces a fire propagation model explaining forest shape scaling and stability, linking edge effects to large-scale forest dynamics in tropical regions.

Findings

Forest shapes follow a perimeter-area scaling relation.

Deviations from the scaling predict patch stability.

Model predicts conditions for continuous or discontinuous forest collapse.

Abstract

In tropical regions, fires propagate readily in grasslands but typically consume only edges of forest patches. Thus forest patches grow due to tree propagation and shrink by fires in surrounding grasslands. The interplay between these competing edge effects is unknown, but critical in determining the shape and stability of individual forest patches, as well the landscape-level spatial distribution and stability of forests. We analyze high-resolution remote-sensing data from protected areas of the Brazilian Cerrado and find that forest shapes obey a robust perimeter-area scaling relation across climatic zones. We explain this scaling by introducing a heterogeneous fire propagation model of tropical forest-grassland ecotones. Deviations from this perimeter-area relation determine the stability of individual forest patches. At a larger scale, our model predicts that the relative rates of tree growth due to propagative expansion and long-distance seed dispersal determine whether collapse of regional-scale tree cover is continuous or discontinuous as fire frequency changes.