Dynamic mechanisms support forest carbon cycling stability following disturbance

Abstract:

Future climate change mitigation requires terrestrial carbon (C) cycling stability in an era of rising disturbance. Recent observations suggest that forest ecosystems can exhibit surprising C cycling stability following disturbance, but the mechanistic basis for sustained functioning remains poorly understood. Marshalling a collection of disturbance manipulations and long-term (>20-yr) observations from the University of Michigan Biological Station, we synthesize the temporally dynamic mechanisms that support C cycling stability in the early, middle, and late stages of disturbance and recovery. In the early (1 to 10-year) stage that follows disturbance, stem girdling manipulations along with opportunistic observations following insect and pathogen invasions show that C cycling processes are more stable when forests are structurally complex and biomass-rich because sustained resource acquisition and biological legacies, respectively, sustain C fixation. Initially, structural changes lag behind C cycling shifts because physiological changes from boring insects and pathogens unfold in advance of significant changes in canopy structure and chemistry, presenting challenges for detecting, inferring and scaling early-stage C cycling responses to some disturbances. In the middle (10 to 100-year) range of the disturbance and recovery cycle, C cycling stability depends on the interacting reclamation of growth-limiting resources and redevelopment of structural complexity, the depletion of which may persist for decades to centuries when disturbance is severe. In the long-term (century+) period that follows disturbance, mounting evidence from regrown or moderately disturbed late successional forests suggests that patchy mortality from low to moderate disturbance reinvigorates forest growth when an intact subcanopy is present, by increasing structural complexity and reshuffling critical resources to suppressed individuals. Broadly, these findings indicate that the mechanisms supporting C cycling stability vary depending on the interacting effects of recovery stage and forest age. Moreover, our findings point to opportunities and challenges in the detection, prediction, management of forest disturbance for the purpose of C cycling maintenance and climate change mitigation.