Recovery of forest structural complexity during secondary succession in a human‐modified neotropical landscape

Abstract Forest structural complexity is an essential determinant of forest ecosystem functions and biodiversity. The natural dynamics of structural complexity of tropical forests remain largely unexplored, especially for naturally regenerating forests during secondary succession. Better understanding the trajectories of forest structural complexity recovery is crucial to inform the development of forest landscape restoration strategies and to predict the reassembly of ecological networks during secondary succession. Here, we investigate the recovery of forest structural complexity during secondary succession following land use abandonment in a human‐modified landscape in Ecuador. We employ a terrestrial laser scanning‐based index of forest structural complexity to quantify the three‐dimensional vegetation structure of agricultural lands (cacao plantations and pastures, n = 10), naturally regenerating sites ( n = 30) and primary old‐growth forests ( n = 16) along a chrono‐sequence of secondary succession. We find that sites recovering after land use abandonment attain levels of forest structural complexity comparable to old‐growth forest within 40 years. Changes in forest structural complexity along the successional gradient follow a saturating pattern, with rapid increases in the first years and only minor potential for further increases after 40 years. Increasing tree species diversity during secondary succession is identified as a major driver of the recovery of forest structural complexity. Using a structural equation modelling approach, we find that the effects of tree species diversity on forest structural complexity are mediated by its effects on vertical stratification, as the effective number of canopy layers increases with increasing recovery age. Synthesis . Our results suggest that land use abandonment and subsequent natural regeneration facilitate the restoration of forest structural complexity in human‐modified neotropical landscapes. Increasing tree species diversity during secondary succession is an important driver of forest structural complexity recovery. To better understand the role of tree species diversity in shaping the three‐dimensional structure of recovering forests, future studies should address the role of intra‐ and interspecific differences in crown morphology and functional traits as potential drivers of forest structural complexity.