Leaf physiology response across a disturbance gradient in a temperate deciduous forest: Implications for earth systems modeling

Project Overview
Project Abstract: 
Light response curves were constructed in situ for 117 sapling trees (between 1 and 7 m in height) of four common tree species in a disturbed northern Michigan deciduous forest. Saplings were examined in a manipulated area (University of Michigan Biological Station’s “Forest Accelerated Succession Experiment) in which >6700 Populus (aspen) and Betula (birch) trees were stem-girdled within a 39-ha area to identify mechanisms responsible for sustaining C uptake through partial canopy defoliation. In this study, physiological parameters of apparent quantum yield and Amax – measures of photosynthetic efficiency – were examined across a disturbance gradient that could help explain maintenance of carbon uptake rates of the manipulated area. Amax was significantly different across species, and Amax increased significantly over a disturbance gradient (modeled by fraction basal area senesced) considering all species in aggregate (p < .1). Examining this trend at the species level revealed significance in red oak and American beech, and was nearly significant for white pine (p < .15). Red oak had a slightly but significantly lower apparent quantum yield than the other species, but this parameter did not vary over a disturbance gradient for any species. The strong physiological response of white pine and particularly red oak suggests a strong capacity to take advantage of canopy gaps created by successional patterns or climate-related disturbance events, and may improve chances of sapling success and allow for greater representation in future forest composition in the area. The trends suggested by the data may be of use to earth systems modelers interested refining the physiological parameters of their models in response to disturbance.
Investigator Info
Funding agency: 
National Science Foundation