Research

jwl_siberia_camp4 bristlecone_grove_small dougfir_wide_small

Overview

We are broadly interested in the factors that control forest diversity and function (e.g., carbon storage) and the response of these ecosystem properties to disturbance, climate change, rising atmospheric CO2 levels, and other aspects of global change.

Projects

Joyce Kilmer Memorial Forest. North Carolina, USA.

Joyce Kilmer Memorial Forest.
North Carolina, USA.

  • Forest response to increasing atmospheric CO2. See project summary.
  • Improving existing global vegetation models. See project summary.
  • Developing a next-generation global vegetation model. See project summary.
  • Forest disturbance. See project summary.
  • Response of tropical forest carbon balance to climate warming. See project website.
  • Plant and microbial functional diversity (see Abstract). This is a collaborative, NSF-funded project involving plant ecologists, plant systematists, and microbial ecologists. We aim to understand linkages between plant and microbial functional diversity and phylogeny across eastern North America and eastern Asia.
  • Plant functional trait variation within and among species. We are especially interested in understanding the mechanisms underlying trait correlations (e.g., the global “leaf economics spectrum”), and improving the representation of functional trait diversity in global vegetation/carbon-cycle models.

Forest response to increasing atmospheric CO2Mauna_Loa_CO2

Theory and experiments suggest that elevated CO2 should stimulate photosynthesis (“CO2 fertilization”), thereby offsetting some anthropogenic CO2 emissions. However, the strength of the CO2 fertilization effect in real forests, and the sustainability of this effect in the future as nitrogen and other factors become limiting, is highly contentious. The policy implications are significant, as the emissions reductions required to stabilize atmospheric CO2 at a given target (e.g., 500 ppm) depends critically on the strength and sustainability of terrestrial carbon sinks. We are using long-term datasets from the U.S. Forest Service’s FIA program to quantify how forest biomass and productivity have changed over recent decades, and to attribute these changes to forest succession (e.g., aging of secondary forests recovering from logging and/or previous non-forest land-use) vs. CO2 fertilization and other non-age-related aspects of global change.

Back to Top

Improving existing global vegetation modelsLM3V_FIA_biomass_50yrs_small

Ecosystem response to global change spans a range of time scales, from fast-time-scale physiological processes such as the response of individual leaves to diurnal and seasonal temperature fluctuations, to slow-time-scale processes such as species turnover within broad functional types (e.g., tropical, temperate, or boreal trees). Variation in forest biomass and growth across spatial climate gradients contains valuable information that can be used to test and improve the representation of slow-time-scale processes in global vegetation models. We used U.S. Forest Inventory and Analysis (FIA) data to optimize vegetation parameters in the NOAA-GFDL LM3V dynamic global vegetation model (which has now been replaced by the newer LM3 model). The figure on the right shows observed (FIA data) and predicted (LM3V model, prior to optimization) aboveground biomass (kg C m-2) in 50-year-old forests in the eastern USA. To learn more about this project, including some new ideas on how to improve ecosystem models with multiple data streams, check out our paper published Ecological Applications, or download the poster we presented at the 2011 North American Carbon Program meeting.

Back to Top

Developing a next-generation global vegetation modelLM3-PPA_small

We are part of a team (led by collaborators at Princeton University and NOAA-GFDL) that is developing more realistic treatments of biodiversity and individual-tree level processes (e.g., height-structured competition for light) in dynamic global vegetation models (DGVMs). This research aims to (1) understand and quantify feedbacks between vegetation and climate; (2) enable improved management of forests and the forest carbon cycle in the context of global change; and (3) improve the land component of global climate models to support climate policy. A paper led by Ensheng Weng describes the new LM3-PPA model we have developed.

Forest disturbance

Post-fire regeneration in central Alaska.

Post-fire regeneration in central Alaska.

We are using a variety of empirical and theoretical approaches to better understand the role of natural and anthropogenic disturbances in determining forest community and ecosystem dynamics. Empirical work focuses on using forest inventory and other data sources to develop more realistic representations of tree mortality and disturbance in carbon-cycle models. Theoretical work focuses on the role of disturbance in allowing multiple tree species to coexist (Lichstein and Pacala 2011). We are developing new approaches to scaling up individual-level competitive interactions to heterogeneous landscapes in which disturbance rates depend on forest structure and species composition (e.g., due to interspecific differences in flammability).

Back to Top