Journal Article

Net primary production of a temperate deciduous forest exhibits a threshold response to increasing disturbance severity

Fahey, Robert T., Stuart-Haëntjens, Ellen J., Gough, Christopher M., Curtis, Peter S., Vogel, Christoph S.

2015

Overview

The global carbon (C) balance is vulnerable to disturbances that alter terrestrial C storage. Disturbances to forests occur along a continuum of severity, from low-intensity disturbance causing the mortality or defoliation of only a subset of trees to severe stand-replacing disturbance that kills all trees; yet considerable uncertainty remains in how forest production changes across gradients of disturbance intensity. We used a gradient of tree mortality in an upper Great Lakes forest ecosystem to: (1) quantify how aboveground wood net primary production (ANPP w ) responds to a range of disturbance severities; and (2) identify mechanisms supporting ANPP w resistance or resilience following moderate disturbance. We found that ANPP w declined nonlinearly with rising disturbance severity, remaining stable until >60% of the total tree basal area senesced. As upper canopy openness increased from disturbance, greater light availability to the subcanopy enhanced the leaf-level photosynthesis and growth of this formerly light-limited canopy stratum, compensating for upper canopy production losses and a reduction in total leaf area index (LAI). As a result, whole-ecosystem production efficiency (ANPP w /LAI) increased with rising disturbance severity, except in plots beyond the disturbance threshold. These findings provide a mechanistic explanation for a nonlinear relationship between ANPP w and disturbance severity, in which the physiological and growth enhancement of undisturbed vegetation is proportional to the level of disturbance until a threshold is exceeded. Our results have important ecological and management implications, demonstrating that in some ecosystems moderate levels of disturbance minimally alter forest production.

• Publisher: Ecological Society of America
• Subject: Aquatic ecosystems / Canopies / canopy / carbon / carbon cycling / carbon sequestration / Conservation of Natural Resources / Deciduous forests / Defoliation / Disturbance / Ecological disturbance / Ecosystems / Environmental Monitoring / Forest canopy / Forest ecology / Forest ecosystems / Forests / Great Lakes / Great Lakes Region / Human Activities / Humans / LAI / leaf area index / leaf area index (LAI) / Leaves / light / Michigan / Mixed forests / Models, Biological / Mortality / Net primary production / Nitrogen / northern Michigan, USA, forest / Photosynthesis / Plants - classification / Primary production / primary productivity / Production efficiency / resilience / resistance / stand basal area / Temperate forests / timber production / tree mortality / Trees / Trees - physiology / Uncertainty / Vegetation / wood