Forest Structural Complexity and Biomass Predict First-Year Carbon Cycling Responses to Disturbance
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Forest Structural Complexity and Biomass Predict First-Year Carbon Cycling Responses to Disturbance Christopher M. Gough,1* Jeff W. Atkins,1 Ben Bond-Lamberty,2 Elizabeth A. Agee,3 Kalyn R. Dorheim,2 Robert T. Fahey,4 Maxim S. Grigri,1 Lisa T. Haber,1 Kayla C. Mathes,1 Stephanie C. Pennington,2 Alexey N. Shiklomanov,5 and Jason M. Tallant6 1
Department of Biology, Virginia Commonwealth University, 1000 West Cary St., Box 842012, Richmond, Virginia 23284, USA; 2Joint Global Change Research Institute, Pacific Northwest National Laboratory, 5825 University Research Ct, College Park, Maryland 20740, USA; 3Environmental Sciences Division, Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA; 4Department of Natural Resources and the Environment, Center for Environmental Sciences and Engineering, University of Connecticut, 1376 Storrs Road, Storrs, Connecticut 06269, USA; 5NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA; 6Biological Station, University of Michigan, Pellston, Michigan 49769, USA
ABSTRACT The pre-disturbance vegetation characteristics that predict carbon (C) cycling responses to disturbance are not well known. To address this gap, we initiated the Forest Resilience Threshold Experiment, a manipulative study in which more than 3600 trees were stem girdled to achieve replicated factorial combinations of four levels (control, 45, 65, and 85% gross defoliation) of disturbance severity and two disturbance types (targeting upper or lower canopy strata). Applying a standardized stability framework in which initial C cycling resistance to disturbance was calculated as the first-year natural log response ratio of disturbance and control
Received 4 May 2020; accepted 1 August 2020 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00544-1) contains supplementary material, which is available to authorized users. Author contributions CMG and BBL conceived and designed the study; CMG, JWA, BBL, KRD, RTF, MSG, LTH, KCM, SCP, ANS, and JMT performed research and analyzed data; CMG led and all others contributed to the writing of the paper. *Corresponding author; e-mail: [email protected]
treatments, we investigated to what extent predisturbance levels of species diversity, aboveground woody biomass, leaf area index, and canopy rugosity—a measure of structural complexity—predict the initial responses of subcanopy light-saturated leaf CO2 assimilation (Asat), aboveground wood NPP (ANPPw), and soil respiration (Rs) to phloem-disrupting disturbance. In the year following stem girdling, we found that aboveground C cycling processes, Asat and ANPPw, were highly resistant to increases in disturbance severity, while Rs resistance declined as severity increased. Disturbance type had no effect on first-year resistance. Pre-disturbance aboveground woody biomass, and canopy rugosity were positive predictors of ANPPw resistance and, conversely, negatively related to Rs resistance. Subcanopy Asat resistance was not relat
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