title: Sustained carbon uptake and storage following moderate disturbance in a Great Lakes forest.
abstract: Carbon (C) 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. We used a large-scale experiment, in which > 6700 Populus (aspen) and Betula (birch) trees were stem-girdled within a 39-ha area, to identify mechanisms sustaining C uptake through partial canopy defoliation. The Forest Accelerated Succession Experiment in northern Michigan, USA, employs a suite of C-cycling measurements within paired treatment and control meteorological flux tower footprints. We found that enhancement of canopy light-use efficiency and maintenance of light absorption maintained net ecosystem production (NEP) 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 (N) in the treatment forest from senescent early successional aspen and birch to non-girdled later successional species facilitated the recovery of total LAI to pre-disturbance levels. Sustained canopy physiological competency following disturbance coincided with a downward shift in maximum canopy height, indicating that compensatory photosynthetic C uptake by undisturbed, later successional subdominant and subcanopy vegetation supported C-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 C uptake. We conclude that the resistance of C uptake to moderate disturbance depends not only on replacement of lost leaf area, but also on rapid compensatory photosynthetic C uptake during defoliation by emerging later successional species.
authors: Virginia Commonwealth University, Department of Biology, Box 842012, 1000 West Cary Street, Richmond, Virginia 23284-2012, USA. cmgough@vcu.edu
authors: Christopher M
authors: CM
authors: Gough
authors: Brady S
authors: BS
authors: Hardiman
authors: Lucas E
authors: LE
authors: Nave
authors: Gil
authors: G
authors: Bohrer
authors: Kyle D
authors: KD
authors: Maurer
authors: Christoph S
authors: CS
authors: Vogel
authors: Knute J
authors: KJ
authors: Nadelhoffer
authors: Peter S
authors: PS
authors: Curtis
mesh_terms: D029662:Betula; D002244:Carbon / Q000737:chemistry* / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D017753:Ecosystem; D004784:Environmental Monitoring; D006114:Great Lakes Region; D006802:Human Activities; D006801:Humans; D008824:Michigan; D009584:Nitrogen; D018515:Plant Leaves; D018526:Plant Transpiration; D032107:Populus; D013997:Time Factors; D014197:Trees
chemical_list: D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen