Articles | Volume 12, issue 22
Biogeosciences, 12, 6707–6719, 2015
Biogeosciences, 12, 6707–6719, 2015

Research article 25 Nov 2015

Research article | 25 Nov 2015

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

B. M. M. Wedeux and D. A. Coomes B. M. M. Wedeux and D. A. Coomes
  • Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK

Abstract. 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 interplay between environmental factors and disturbance legacies on forest canopy structure across landscapes is practically unexplored. We used 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, consistent 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 illegal 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. With logging, 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 peat depth gradient within the old-growth tropical peat swamp forest. This relationship breaks down after selective logging, with canopy structural recovery, as observed by ALS, modulated by environmental conditions. These findings improve our understanding of tropical peat swamp ecology and provide important insights for managers aiming to restore degraded forests.

Short summary
Canopy height and gaps of tropical peat swamp forests, measured by airborne laser scanning, were influenced by an interplay of environmental factors and selective logging. Structural recovery after logging depended strongly on peat depth and the landscape-scale relationship between forest height and canopy gap structure was lost in selectively logged forests. Results suggest slowest recovery on deep waterlogged and infertile peat, which is of relevance to management and conservation activities.
Final-revised paper