Global Change

Principal Investigator: Steven Perakis, USGS Forest and Rangeland Ecosystem Science Center

Co-Investigators: Ed Schreiner, USGS-FRESC; Robert McKane, USEPA; Robert Edmonds, University of Washington; David Peterson, USFS; Steven Acker, NPS

Introduction

This study examines how precipitation interacts with nitrogen (N) cycling to control carbon (C) storage in conifer forests of the Pacific Northwest.  Carbon stores (Mg/ha) of forests in the Pacific Northwest exceed those of any other biome, anywhere on Earth, and are highly sensitive to current and future anticipated changes in precipitation.  Global circulation models predict that precipitation will increase 20-75% in the Pacific Northwest over the next century, but effects of this changing precipitation on C storage and dynamics in the region remain highly uncertain.  This work will link field studies, experiments, and simulation modeling to understand how future changes in precipitation regimes will influence linked N cycling and C storage in Pacific Northwest conifer forests. 

Field work and experiments for this study occur at five sites arrayed across a natural rainfall gradient on the Olympic Peninsula, Washington.  Mean annual precipitation (MAP) across the gradient ranges from 1 - 5 m, but other factors are held constant, providing a unique opportunity to examine how climate alone influences forest C and N pools and fluxes.  All sites are old-growth Douglas-fir forests at isoclines of 10 ºC mean annual temperature, on marine sedimentary parent materials.  Four sites are located in Olympic National Park, with a fifth adjacent site in Olympic National Forest. 

Since changes in forest fire regimes are one important expected consequence of climate change in the west, we are focusing effort on fire-carbon interactions starting in 2007.  This work will take advantage of a prescribed fire that is planned at the driest site along our precipitation gradient.  Burn areas overlap with half of our long-term field plots, providing both a well-replicated experimental design and also building on 3 years of pre-fire baseline data for evaluating fire effects.  This fire research component will use ongoing methods and measurements, combined with new process level studies of charcoal effects on soil biogeochemistry, to examine how this critical climate-related disturbance affects coupled C and N dynamics and storage.   

Field measurements for all work focus on key hydrologic and biogeochemical fluxes in these forests.  Total ecosystem stocks of C and N are being measured in plants, soils, and detritus.  C and N in litterfall and soil water leaching are measured monthly, and measurements of in situ incubated and cross-site transplanted litter (by litterbags), soils (by resin cores), and microbial biomass (by fumigation) are made quarterly.  Collectively, these measurements will provide information needed to determine how ecosystem C and N dynamics are likely to change under trajectories of altered precipitation scenarios in the future, be they wetter or drier, or in response to altered fire regimes.  These data are being used to modify and parameterize the Multiple Element Limitation ecosystem simulation model to predict how regional changes in precipitation will drive short- vs. long-term changes in carbon storage and greenhouse gas emissions.  Simulations will assist NPS, BLM, and USFS resource managers in developing management plans for wildlife, resource use and preserving ecosystem function in light of predicted changes in climate.

Contact Information

Steven Perakis
USGS Forest and Rangeland Ecosystem Science Center, FRESC
3200 SW Jefferson Way
Corvallis, OR  97331
Phone: 541-758-8786
Fax: 541-758-8806
E-mail: sperakis@usgs.gov