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Fire Effects and Forest Recovery

Prescribed Fire in Olympic National Park

Olympic National Park conducted its first-ever prescribed fire for late summer 2007. This prescribed fire is intended to mimic low-intensity, infrequent wildfires that have been suppressed for much of the century in dry Douglas-fir forests of the Park. The ecological impact of such fire restoration remains largely unstudied in Olympic forests, and prescribed fire can have especially intense effects on soils, since it is intended specifically to consume ground fuels. Overall, fires in this area of the Park are likely to be more common in the future as both restoration activities continue and as wildfire frequency increases because of climate change.

This work examines the impacts of prescribed fire on plant productivity, soil physical, chemical, and biological characteristics, and nutrient leaching. Measurements build directly on baseline data that we have been collecting from the burn plot area for the past 4 years as part of a climate change study. We are: quantifying fuels consumption of interest to wildlife biologists and fire managers, documenting nutrient leaching that may impact water quality, evaluating interactions between prescribed fire and climate change, quantifying fire impacts on carbon and nitrogen budgets, and providing benchmarks against which to interpret future ecosystem recovery.

Collaborators

Ed Schreiner, Sarah Beldin, Chris Catricala (USGS)

Funding

USGS

Post-Fire Nitrogen Fixation by Shrubs

Nitrogen (N) fixing shrubs are frequent components of early successional, post-fire forest communities. Functionally, these shrubs can contribute to ecosystem recovery after fire by replenishing soil nitrogen and carbon that is lost to combustion. High rates of N-fixation by shrubs can restore lost nitrogen in as little as 10 years, in comparison to roughly 1000 years from precipitation alone. The absence of N-fixing shrubs after fire (whether by management, or by chance) can therefore result in a loss of long-term soil fertility and forest productivity.

To date, no studies have evaluated shrub N-fixation in the Klamath-Siskiyou Douglas-fir forest zone of southwestern Oregon and northwestern California. Fire is frequent and sometimes intense in this region, and Douglas-fir forests growing here are strongly N-limited. Post-fire forests can also have significant cover of N-fixing shrubs, yet field rates of N-fixation by shrubs are unknown, which makes it difficult to evaluate their role in aiding forest recovery after fire.

We are characterizing the rates and significance of N-fixation by shrubs, primarily Ceanothus integerrimus (deerbrush), in forests burned by intense wildfire ~ 20 years ago. N-fixation rates are being measured using stable isotope 15N tracers across a precipitation-productivity gradient and in response to P fertilization. N fertilization plots (150 kg N/ha) are being used to assess whether plant growth is N limited, and how added N shapes plant dynamics. Site treatments have been in place since 2007, with measurements beginning in 2009. Results of this work 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 this region.

Collaborators

Stephanie Yelenik, David Hibbs, Jeff Shatford (OSU)

Funding

USGS, Oregon BLM, and Oregon Department of Forestry

Long-Term Legacies of Wildfire

Episodic stand-replacing wildfire is a significant disturbance in mesic and moist Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests of the Pacific Northwest. We studied 24 forest stands with known fire histories in the western Cascade Range in Oregon to evaluate long-term impacts of stand-replacing wildfire on carbon (C) and nitrogen (N) pools and dynamics within the forest floor (Oe and Oa horizons) and the mineral soil (0–10 cm). Twelve of our stands burned approximately 150 years ago (“young”), and the other 12 burned approximately 550 years ago (“old”).

Forest floor mean C and N pools were significantly greater in old stands than young stands (N pools: 1823 ± 132 kg·ha–1 vs. 1450 ± 98 kg·ha–1; C pools: 62,980 ± 5403 kg·ha–1 vs. 49,032 ± 2965 kg·ha–1, mean ± SE) as a result of significant differences in forest floor mass. Forest floor C and N concentrations and C/N ratios did not differ by time since fire, yet potential N mineralization rates were significantly higher in forest floor of old sites. Old and young mineral soils did not differ significantly in pools, concentrations, C/N ratios, or cycling rates. Our results suggest that C and N are sequestered in forest floor of Pacific Northwest Douglas-fir forests over long (~400 year) intervals, but that shorter fire return intervals may prevent that accumulation.

Collaborators

Tom Giesen, Kermit Cromack (OSU)

Funding

OSU Richardson Fellowship, USGS

Research Team

Terrestrial Ecosystems Laboratory - Team Page

Primary Investigator

Perakis, Steven S. - View Profile

Related Publications

Yelenik, S.G., Perakis, S.S., Hibbs, D.E., 2013, Regional constraints to biological nitrogen fixation in post-fire forest communities: Ecology, v. 94, no. 3, p. 739-750, https://doi.org/10.1890/12-0278.1[Details]

Giesen, T.W., Perakis, S.S., Cromack, K., 2008, Four centuries of soil carbon and nitrogen change after stand-replacing fire in a forest landscape in the western Cascade Range of Oregon: Canadian Journal of Forest Research, v. 38, p. 2455-2464, https://doi.org/10.1139/X08-092[Details]

Giesen, T.W., 2006, Four Centuries of Soil Carbon and Nitrogen Change after Severe Fire in a Western Cascades Forest Landscape: Corvallis, OR, Oregon State University--M.S. Thesis, p. 108. [Details]



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