PNNL

Abstract

Soil respiration (Rs) represents a large flux of carbon (C) from forests to the atmosphere, but the long-term influence of phloem-disrupting disturbance on Rs is poorly understood. Using a decade of observations from the Forest Accelerated Succession Experiment (FASET), we examined relationships among Rs, soil temperature, soil moisture, and leaf area index (LAI) following the stem-girdling induced mortality of 40% of all canopy trees within a 39-ha area. Mean annual Rs declined by about 20% relative to the control two years after disturbance and recovered to near pre-disturbance values within five years; this reduction correlated with LAI losses and lower Rs temperature sensitivity (i.e., Q10), with the latter mitigating soil warming caused by partial canopy defoliation. These observations are consistent with progressive limitations in belowground labile C causing reductions in Rs. We conclude that the effects of stem-girdling on Rs: were not immediate, occurring two years after the treatment; were primarily influenced by biotic changes; and persisted for nearly a decade, underscoring the value of long-term experiments.