PNNL

Abstract

1. Across the globe, the future of the land carbon (C) sink comprised by forests is under threat from a diverse and expanding array of disturbances ranging in severity and spatial extent. 2. In contrast to severe, stand-replacing events, moderate severity disturbances do not always result in near-term dramatic declines in forest production because of the potential for compensatory mechanisms to offset tree mortality with sustained or even enhanced surviving tree growth. 3. In particular, community-wide functional trait shifts prompted by disturbance may play a key mechanistic role in stabilizing ecosystem net primary production. However, we lack thorough characterization of the identity, timing, and magnitude of such shifts across temperate forest landscapes experiencing a realistic range of moderate severity disturbance. 4. In this study, we leverage a four-year data set from an experimental forest disturbance in northern lower Michigan to assess the extent of pre- to post-disturbance subcanopy community trait shifts as well as their utility in predicting ecosystem production stability. The Forest Resilience Threshold Experiment, or FoRTE, was initiated in 2018 and implemented disturbance via stem girdling at 0, 45, 65, and 85 % LAI loss within four replicates nested in distinct forest ecosystem types. 5. We found that some subcanopy community mean traits associated with production shifted rapidly in response to disturbance and in advance of closed canopy deterioration. In contrast with post-disturbance “snapshots” of community traits, our lengthened timescale of analysis captures a more complete pre- to post-disturbance window of change and highlights a probable mechanistic switch from nutrient-driven to light-driven trait shifts as disturbance unfolded. 6. Our findings suggest that remotely sensed traits such as the red edge normalized difference vegetation index (reNDVI) could be particularly early and strong predictors of production response to disturbance, even across compositionally diverse forest types. We conclude that dynamic functional trait shifts following disturbance can be used to predict production response across a wide range of disturbance severities.