Landscape-scale changes in forest canopy structure across a partially logged tropical peat swamp

Forest canopy structure is strongly influenced by environmental factors and disturbance, and in turn influences key ecosystem processes including productivity, evapotranspiration and habitat availability. In tropical forests increasingly modified by human activities, the interplaying effects of environmental factors and disturbance legacies on forest canopy structure across landscapes are practically unexplored. We used high-fidelity airborne laser scanning (ALS) data to measure the canopy of old-growth and selectively logged peat swamp forest across a peat dome in Central Kalimantan, Indonesia, and quantified how canopy structure metrics varied with peat depth and under logging. Several million canopy gaps in different height cross-sections of the canopy were measured in 100 plots of 1 km² spanning the peat dome, allowing us to describe canopy structure with seven metrics. Old-growth forest became shorter and had simpler vertical canopy profiles on deeper peat, consistently with previous work linking deep peat to stunted tree growth. Gap Size Frequency Distributions (GSFDs) indicated fewer and smaller canopy gaps on the deeper peat (i.e. the scaling exponent of pareto functions increased from 1.76 to 3.76 with peat depth). Areas subjected to concessionary logging until 2000, and informal logging since then, had the same canopy top height as old-growth forest, indicating the persistence of some large trees, but mean canopy height was significantly reduced; the total area of canopy gaps increased and the GSFD scaling exponent was reduced. Logging effects were most evident on the deepest peat, where nutrient depletion and waterlogged conditions restrain tree growth and recovery. A tight relationship exists between canopy structure and the peat deph gradient within the old-growth tropical peat swamp. This relationship breaks down after selective logging, with canopy structural recovery being modulated by environmental conditions.We are grateful to the Indonesia–Australia Forests and Carbon Partnership and (the no longer operating) Kalimantan Forests and Climate Partnership for sharing the ALS and peat depth data. This research was carried out in collaboration with the Governments of Australia and Indonesia, but the analysis and findings of this paper represent the views of the authors and do not necessarily represent the views of those Governments. We thank G. Vaglio Laurin for useful comments. We are grateful to A. Tanentzap for help with the RStan code and R. Kent and M. Dalponte for technical advice. B. M. M. Wedeux is funded by an AFR PhD Fellowship (1098188) from the Fonds National de la Recherche, Luxembourg.This is the final version of the article. It first appeared from the European Geosciences Union via http://dx.doi.org/10.5194/bgd-12-10985-201