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

Published on 2016-08-10T10:27:28Z (GMT) by
<p>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<sub>w</sub>) responds to a range of disturbance severities; and (2) identify mechanisms supporting ANPP<sub>w</sub> resistance or resilience following moderate disturbance. We found that ANPP<sub>w</sub> 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<sub>w</sub>/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<sub>w</sub> 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.</p>

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Stuart-Haëntjens, Ellen J.; S. Curtis, Peter; Fahey, Robert T.; Vogel, Christoph S.; Gough, Christopher M. (2016): Net primary production of a temperate deciduous forest exhibits a threshold response to increasing disturbance severity. Wiley.