Sustained Carbon Uptake and Storage Following Moderate Disturbance in a Great Lakes Forest
Carbon uptake rates in many forests are sustained, or decline only briefly, following disturbances that partially defoliate the canopy. The mechanisms supporting such functional resistance to moderate forest disturbance are largely unknown. Researchers used a large-scale experiment to identify mechanisms sustaining carbon uptake through partial canopy defoliation. The Forest Accelerated Succession Experiment in northern Michigan employs a suite of carbon-cycling measurements within paired treatment and control meteorological flux tower footprints. They found that enhancement of canopy light-use efficiency and maintenance of light absorption maintained net ecosystem production and aboveground wood net primary production (NPP) when leaf-area index (LAI) of the treatment forest temporarily declined by nearly half its maximum value. In the year following peak defoliation, redistribution of nitrogen in the treatment forest from senescent early successional aspen and birch to nongirdled later successional species facilitated the recovery of total LAI to predisturbance levels. Sustained canopy physiological competency following disturbance coincided with a downward shift in maximum canopy height, indicating that compensatory photosynthetic carbon uptake by undisturbed, later successional subdominant and subcanopy vegetation supported carbon-uptake resistance to disturbance. These findings have implications for ecosystem management and modeling, demonstrating that forests may tolerate considerable leaf-area losses without diminishing rates of carbon uptake. They conclude that the resistance of carbon uptake to moderate disturbance depends not only on replacement of lost leaf area, but also on rapid compensatory photosynthetic carbon uptake during defoliation by emerging later successional species.
Gough, C. M., B. S. Hardiman, L. E. Nave, G. Bohrer, K. D. Maurer, C. S. Vogel, K.J. Nadelhoffer, and P. S. Curtis. 2013. “Sustained Carbon Uptake and Storage Following Moderate Disturbance in a Great Lakes Forest,” Ecological Applications 23(5), 1202–15. DOI: 10.1890/12-1554.1.