Impacts of disturbance and land-use change on forest carbon dynamics

Background/Question/Methods

Two major unknowns in our understanding of terrestrial carbon (C) dynamics are how disturbances and land use change impact net CO₂ exchange with the atmosphere over time.  We measured net CO₂ exchange using eddy covariance and used forest biometric measurements to quantify C dynamics in a forested landscape in the New Jersey Pine Barrens that has experienced invasive insect defoliation, prescribed fires and wildfires.  We collected similar data at a suburban site at the Baltimore LTER, and compared seasonal, annual and multi-year C dynamics among sites. 

Results/Conclusions

Insect defoliation in the summer resulted in a maximum loss of 293 g C m^-2 yr^-1 in an Oak dominated stand in the Pine Barrens in 2007, but < 130 g C m^-2 yr^-1 in conifer dominated stands where only deciduous species were defoliated.  Prescribed fire treatments conducted in the spring in the Pine Barrens resulted in C losses of 7 to 474 g C m^-2, with an average of 244 ± 34 g C m^-2 (mean ± 1 SE, n = 17 stands), resulting in only moderate sources of CO₂ to the atmosphere on an annual basis.  The greatest loss from a forested ecosystem occurred in a ca. 8000 ha wildfire in the Pine Barrens in the spring of 2007, estimated at ca. 1580 ± 350 g C m^-2.  Annual net CO₂ exchange at the Baltimore LTER flux site indicated that this site lost from 500 to 1100 g C m^-2 yr^-1, with the largest losses occurring during the winter months, corresponding with leaf-off conditions, use of fuel oil for heating, and other sources of CO₂ emissions.  When integrated over multiple years, forested ecosystems recovered from all disturbances and approached C neutrality relatively rapidly, while the suburban system remained a large source of CO₂ to the atmosphere through time.  Our research helps define the range of C losses that can be expected from disturbed forest  ecosystems and land use change.  It also suggests that mitigation activities directed towards developed ecosystems, such as enhancing canopy cover and/or reducing surface albedo, could reduce the large, long-term impacts of land use change.