Start, speed, and direction of secondary forest succession.

Succession is a foundational concept in ecology, describing changes in populations, communities, and ecosystems over time following a disturbance. Predicting successional pathways is challenging because of high spatiotemporal variability. Here, we present a unifying mechanistic framework that integrates three core components of succession (start, speed, and direction) that define successional pathways. We monitored the first 5 years of forest succession in recently abandoned agricultural fields in six tropical landscapes across three countries that differ in land-use intensity and between dry and wet forests. We found that (i) secondary succession typically started with woody legacies and progressed slowly but directionally toward structurally complex, biodiverse forests, and (ii) the start and speed were greater in areas with short-duration, low-intensity (nonmechanized) land use associated with more biological legacies. This framework advances mechanistic understanding of succession by disentangling the start, speed, and direction, and provides a tool for designing effective forest restoration strategies.