I am interested in forest biogeochemistry and ecosystem studies, watershed science, riparian forests, global change, nutrient cycling, forest soil fertility and stable isotopes.
Professional Experience
2001-present: Supervisory Research Ecologist, USGS Forest and Rangeland Ecosystem Science Center, Corvallis, OR
2001: Post Doctoral Position, Stanford University, Stanford, CA
Education and Certifications
Ph.D., Cornell University, Ithaca, NY (2000)
M.S., University of Washington, Seattle, WA (1994)
B.S., University of Pennsylvania, Philadelphia, PA (1990)
Science and Products
Terrestrial Ecosystems Laboratory (FRESC)
Novel multi‐scale synthesis of nitrogen fixation rates and drivers across the terrestrial biosphere
Terrestrial Ecosystems Laboratory (FRESC)
Riparian Forests
Nitrogen Deficiency and Excess in Forests: Patterns, Mechanisms and Management
Fire Effects and Forest Recovery
Ecosystem Baselines and Restoration
Climate and Ecosystem Biogeochemistry
Forecasting forest response to N deposition: integrating data from individual plant responses to soil chemistry with a continental-scale gradient analysis
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.
Invasive Grasses Cheatgrass and Medusahead Yield Responses to Sucrose in Experimental Plots in the Northern Great Basin, USA Dataset, 2005-2006
Data supporting the study of tree species' access to rock-derived nutrients, Tillamook State Forest, 2015
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.
Exploring the role of cryptic nitrogen fixers in terrestrial ecosystems: A frontier in nitrogen cycling research
N and P constrain C in ecosystems under climate change: Role of nutrient redistribution, accumulation, and stoichiometry
Hypotheses and lessons from a native moth outbreak in a low-diversity, tropical rainforest
Climatic aridity shapes post-fire interactions between Ceanothus spp. and Douglas-fir (Pseudotsuga menziesii) across the Klamath Mountains
Early growth and ecophysiological responses of Koa (Acacia koa A. Gray) seedlings to reduced water and phosphorus
N supply mediates the radiative balance of N2O emissions and CO2 sequestration driven by N-fixing vs. non-fixing trees
A roadmap for sampling and scaling biological nitrogen fixation in terrestrial ecosystems
Climate-mediated changes to linked terrestrial and marine ecosystems across the northeast Pacific coastal temperate rainforest margin
Decadal-scale decoupling of soil phosphorus and molybdenum cycles by temperate nitrogen-fixing trees
Trait integration and functional differentiation among co-existing plant species
A spatially explicit, empirical estimate of tree-based biological nitrogen fixation in forests of the United States
Frequent burning causes large losses of carbon from deep soil layers in a temperate savanna
Non-USGS Publications**
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
To request an interview, contact fresc_outreach@usgs.gov or call (541) 750-1030.
Science and Products
- Science
Terrestrial Ecosystems Laboratory (FRESC)
Research in our laboratory centers on the ecology and biogeochemistry of forest ecosystems, as well as grassland and riparian systems. We examine how factors such as natural and human disturbances, climate and climate change, succession, and soil fertility shape ecosystem biogeochemistry - and the reciprocal effect of biogeochemical cycles on these and other factors.Novel multi‐scale synthesis of nitrogen fixation rates and drivers across the terrestrial biosphere
Biological nitrogen fixation (BNF) is a critical biogeochemical process that converts inert atmospheric N2 gas into biologically usable forms of the essential nutrient nitrogen. A variety of free-living and symbiotic organisms carry out BNF, and in most regions worldwide, BNF is the largest source of nitrogen that fuels terrestrial ecosystems. As a result, BNF has far reaching effects on ecosystemTerrestrial Ecosystems Laboratory (FRESC)
Research in our laboratory centers on the ecology and biogeochemistry of forest ecosystems, as well as grassland and riparian systems. We examine how factors such as natural and human disturbances, climate and climate change, succession, and soil fertility shape ecosystem biogeochemistry - and the reciprocal effect of biogeochemical cycles on these and other factors.Riparian Forests
Riparian vegetation is an often ignored yet critical source of nutrition for riparian food webs. Many food webs are supported at their base by the breakdown and incorporation of leaf litter into fungi, insects, etc. In headwater streams, riparian leaf litter inputs provide essential subsidies that fuel in-stream productivity, in addition to subsidizing food chains of terrestrial riparian habitats...Nitrogen Deficiency and Excess in Forests: Patterns, Mechanisms and Management
This research theme facilitates the sound management and restoration of Pacific Northwest Douglas-fir forests, as well as to refine broader-scale predictions of how temperate forests will function in an increasingly nitrogen-rich world.Fire Effects and Forest Recovery
This research theme examines the impacts of prescribed fire on plant productivity, soil physical, chemical, and biological characteristics, and nutrient leaching. Results from this research will enable improved decision-making of how to manage fire-prone forests to maintain long-term forest fertility and productivity, especially across wide climate gradients characteristic of the Pacific Northwest...Ecosystem Baselines and Restoration
This research theme coalesces studies of old-growth temperate forests in several major thematic areas including landscape and ecosystem controls on watershed nutrient export, wildfire disturbance legacies on biogeochemical cycling, and the imprint of tree species on soil nutrients in old-growth forests.Climate and Ecosystem Biogeochemistry
This research theme advance fundamental understanding of climate-biogeochemistry interactions, with wide applicability to virtually all terrestrial ecosystems.Forecasting forest response to N deposition: integrating data from individual plant responses to soil chemistry with a continental-scale gradient analysis
Nitrogen deposition is altering forest dynamics, terrestrial carbon storage, and biodiversity. However, our ability to forecast how different tree species will respond to N deposition, especially key response thresholds, is limited by a lack of synthesis across spatial scales and research approaches. To develop our best understanding of N deposition impact on tree growth and survival, we will inte - Data
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.
Invasive Grasses Cheatgrass and Medusahead Yield Responses to Sucrose in Experimental Plots in the Northern Great Basin, USA Dataset, 2005-2006
Comma-separated values (.csv) files containing data related to plant biomass and seed production responses of invasive Bromus tectorum (cheatgrass) and Taeniatherum caput-medusae (medusahead) to varying sucrose treatments.Data supporting the study of tree species' access to rock-derived nutrients, Tillamook State Forest, 2015
This dataset describes foliar and soil chemistry and isotopes for six tree species in Tillamook State Forest, 2015. - Multimedia
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.
- Publications
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request, including the full citation, or call (541) 750-1030.
Filter Total Items: 71Exploring the role of cryptic nitrogen fixers in terrestrial ecosystems: A frontier in nitrogen cycling research
Biological nitrogen fixation represents the largest natural flux of new nitrogen (N) into terrestrial ecosystems, providing a critical N source to support net primary productivity of both natural and agricultural systems. When they are common, symbiotic associations between plants and bacteria can add more than 100 kg N ha−1 y−1 to ecosystems. Yet, these associations are uncommon in many terrestriN and P constrain C in ecosystems under climate change: Role of nutrient redistribution, accumulation, and stoichiometry
We use the Multiple Element Limitation (MEL) model to examine responses of twelve ecosystems to elevated carbon dioxide (CO2), warming, and 20% decreases or increases in precipitation. Ecosystems respond synergistically to elevated CO2, warming, and decreased precipitation combined because higher water-use efficiency with elevated CO2 and higher fertility with warming compensate for responses to dHypotheses and lessons from a native moth outbreak in a low-diversity, tropical rainforest
Outbreaks of defoliating insects in low-diversity tropical forests occur infrequently but provide valuable insights about outbreak ecology in temperate environments and in general. We investigated an extensive outbreak of the endemic koa moth (Scotorythra paludicola), which defoliated endemic koa trees (Acacia koa) over a third of their range on Hawai‘i Island during 2013 and 2014. At Hakalau ForeClimatic aridity shapes post-fire interactions between Ceanothus spp. and Douglas-fir (Pseudotsuga menziesii) across the Klamath Mountains
Climate change is leading to increased drought intensity and fire frequency, creating early-successional landscapes with novel disturbance–recovery dynamics. In the Klamath Mountains of northwestern California and southwestern Oregon, early-successional interactions between nitrogen (N)-fixing shrubs (Ceanothus spp.) and long-lived conifers (Douglas-fir) are especially important determinants of foEarly growth and ecophysiological responses of Koa (Acacia koa A. Gray) seedlings to reduced water and phosphorus
Sites in need of restoration typically have one or more environmental factors that limit seedling establishment. Identifying ecophysiological responses to environmental stressors can provide important insights into mitigating measures that would allow seedlings to overcome such constraints to survival. Koa (Acacia koa A. Gray) is a nitrogen-fixing tree species endemic to Hawaiʻi that is highly valN supply mediates the radiative balance of N2O emissions and CO2 sequestration driven by N-fixing vs. non-fixing trees
Forests are a significant CO2 sink. However, CO2 sequestration in forests is radiatively offset by emissions of nitrous oxide (N2O), a potent greenhouse gas, from forest soils. Reforestation, an important strategy for mitigating climate change, has focused on maximizing CO2 sequestration in plant biomass without integrating N2O emissions from soils. Although nitrogen (N)-fixing trees are often recA roadmap for sampling and scaling biological nitrogen fixation in terrestrial ecosystems
Accurately quantifying rates and patterns of biological nitrogen fixation (BNF) in terrestrial ecosystems is essential to characterize ecological and biogeochemical interactions, identify mechanistic controls, improve BNF representation in conceptual and numerical modelling, and forecast nitrogen limitation constraints on future carbon (C) cycling.While many resources address the technical advantaClimate-mediated changes to linked terrestrial and marine ecosystems across the northeast Pacific coastal temperate rainforest margin
Coastal margins are important areas of materials flux that link terrestrial and marine ecosystems. Consequently, climate-mediated changes to coastal terrestrial ecosystems and hydrologic regimes have high potential to influence nearshore ocean chemistry and food web dynamics. Research from tightly coupled, high-flux coastal ecosystems can advance understanding of terrestrial–marine links and climaDecadal-scale decoupling of soil phosphorus and molybdenum cycles by temperate nitrogen-fixing trees
Symbiotic nitrogen- (N) fixing trees can influence multiple biogeochemical cycles by fixing atmospheric N, which drives net primary productivity and soil carbon (C) and N accumulation, as well as by mobilizing soil phosphorus (P) and other nutrients to support growth and metabolism. The soil micronutrient molybdenum (Mo) is essential to N-fixation, yet surprisingly little is known of whether N-fixTrait integration and functional differentiation among co-existing plant species
PremiseDetermining which traits characterize strategies of coexisting species is important to developing trait‐based models of plant communities. First, global dimensions may not exist locally. Second, the degree to which traits and trait spectra constitute independent dimensions of functional variation at various scales continues to be refined. Finally, traits may be associated with existing cateA spatially explicit, empirical estimate of tree-based biological nitrogen fixation in forests of the United States
Quantifying human impacts on the nitrogen (N) cycle and investigating natural ecosystem N cycling depend on the magnitude of inputs from natural biological nitrogen fixation (BNF). Here, we present two bottom‐up approaches to quantify tree‐based symbiotic BNF based on forest inventory data across the coterminous United States and SE Alaska. For all major N‐fixing tree genera, we quantify BNF inputFrequent burning causes large losses of carbon from deep soil layers in a temperate savanna
Fire activity is changing dramatically across the globe, with uncertain effects on ecosystem processes, especially below‐ground. Fire‐driven losses of soil carbon (C) are often assumed to occur primarily in the upper soil layers because the repeated combustion of above‐ground biomass limits organic matter inputs into surface soil. However, C losses from deeper soil may occur if frequent burning reNon-USGS Publications**
Perakis, S.S., Hedin, L.O., 2002, Response to commentary on "Nitrogen loss from unpolluted South American forests mainly via dissolved organic compounds": Nature, v. 418, p. 665-665.Perakis, S.S., Welch, E.B., Jacoby, J.M., 1996, Sediment-to-water blue-green algal recruitment in response to alum and environmental factors: Hydrobiologia, v. 318, no. 3, p. 165-177.**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
- News
To request an interview, contact fresc_outreach@usgs.gov or call (541) 750-1030.