Education
Postdoc, 2001, Stanford University
Ph.D. 2000, Cornell University
M.S. 1994, University of Washington
B.S. 1990, University of Pennsylvania
Specialty
Forest biogeochemistry and ecosystem studies, watershed science, riparian forests, global change, nutrient cycling, forest soil fertility, stable isotopes
A complete list of publications is available on Steve's google scholar page.
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...
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 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...
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.
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...
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.
This research theme advance fundamental understanding of climate-biogeochemistry interactions, with wide applicability to virtually all terrestrial ecosystems.
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...
There is a black box hidden beneath the forests of the Pacific Northwest, guarding the secrets to why the trees grow so large! The black box is soil, which harbors immense biological diversity and controls the release of water and nutrients that support the life above ground. Join us as Sue Powell interviews USGS ecologist Steve Perakis and discusses his research about the
Symbiotic nitrogen-fixing trees enhance forest fertility by increasing nitrogen and organic matter in soil.
Plant traits, such as leaf size and rooting depth, can affect plant performance and hence, how plants might respond to environmental change. Plant traits can be integrated, or correlated, with a particular functional plant response, such as how plants use water efficiently. Alternatively, plants can differentiate along multiple trait dimensions.
Symbiotic nitrogen-fixing trees influence soil fertility and provide a large background source of nitrogen in watersheds.
Fire activity is changing worldwide, with unclear effects on ecosystem carbon storage. Fire effects on carbon storage are better known for vegetation than for soil, and fire effects on deep soil carbon are especially uncertain.
Pacific salmon transport large amounts of marine nutrients to freshwater and forest ecosystems when they migrate from the ocean, spawn, and die.
There is scientific controversy about whether nitrogen deposition increases forest carbon sequestration. All tree species do not exhibit the same response to nitrogen and responses may be complicated by interactions with biotic and other abiotic factors such as sulfur deposition.