I am interested in the organismal biology and environmental ecology of trees and how they influence the functioning of forest ecosystems. Global change is creating novel environmental conditions, and how trees respond to changing environments will shape future forests. I am working with Jeremy Lichstein and Grant Domke (US Forest Service) to evaluate the effects of increasing atmospheric carbon dioxide concentrations on recent decadal trends in USA forest production and tree growth.
Climate change determines the sign of productivity trends in US forests
J. A. HOGAN, G. M. DOMKE, K. ZHU, D. J. JOHNSON, J. LICHSTEIN
Department of Biology, University of Florida, 220 Bartram Hall, PO Box 118525 Gainesville, FL 32611-8525, USA
U.S. forests offset about 10% of annual U.S. carbon emissions, potentially slowing climate change. Forest recovery from past land use is known to influence the U.S. carbon sink, however, previous studies on forest responses to CO2 fertilization show mixed evidence. Therefore, the contributions of forest recovery and growth enhancement (ge, defined as the change in biomass stock/production at a given stand age) to the US forest carbon sink remain uncertain. Using non-linear models applied to national forest inventory data (2000-2022), we quantified ge by ecoprovince in non-plantation forests. We explored a variety of model forms and data subsets (e.g., excluding selectively-harvested plots). In most analyses, ge ranged from -1.7 to +2.1%/year, being positive in the East but negative in the Interior West and Pacific. Stand age-dependent biomass change was always positive, ranging from 0.11 Mg/ha/yr in Nevada-Utah Coniferous Forest to 1.35 Mg/ha/yr in Cascade Mixed Forest. These results suggest that disturbances in the western U.S. are causing biomass reductions at a given stand age, rather than reductions in reported stand age. While aging stands contribute significantly to forest carbon balance across the entire USA, growth enhancement is greatest where non-stand-age-resetting disturbances (e.g., pests/pathogens, minor wind/fire, warming, drying) are absent.