Research Database
Displaying 81 - 100 of 105
Does Wood Bioenergy Increase Carbon Stocks in Forests?
Year: 2012
Wood bioenergy is touted as carbon neutral because biological regrowth recaptures the carbon released in energy production. However, some argue that using wood as an energy feedstock will result in decreased forest stocks and thereby a net reduction of carbon sequestered by forests. Such arguments fail to recognize that increased demand for wood bioenergy could increase stocks of wood, a renewable resource. We address the carbon neutrality question using a dynamic optimization forest management model to examine the effect of increasing or decreasing wood bioenergy demand on an existing forest…
Publication Type: Journal Article
Arbuscular Mycorrhizal Fungi Increase Organic Carbon Decomposition Under Elevated CO2
Year: 2012
The extent to which terrestrial ecosystems can sequester carbon to mitigate climate change is a matter of debate. The stimulation of arbuscular mycorrhizal fungi (AMF) by elevated atmospheric carbon dioxide (CO 2 ) has been assumed to be a major mechanism facilitating soil carbon sequestration by increasing carbon inputs to soil and by protecting organic carbon from decomposition via aggregation. We present evidence from four independent microcosm and field experiments demonstrating that CO 2 enhancement of AMF results in considerable soil carbon losses. Our findings challenge the assumption…
Publication Type: Journal Article
Climatic, Landform, Microtopographic, and Overstory Canopy Controls of Tree Invasion in a Subalpine Meadow Landscape, Oregon Cascades, USA
Year: 2012
Tree invasions have been documented throughout Northern Hemisphere high elevation meadows, as well as globally in many grass and forb-dominated ecosystems. Tree invasions are often associated with large-scale changes in climate or disturbance regimes, but are fundamentally driven by regeneration processes influenced by interactions between climatic, topographic, and biotic factors at multiple spatial scales. The purpose of this research was to quantify spatiotemporal patterns of meadow invasion; and how climate, larger landforms, topography, and overstory trees have interactively influenced…
Publication Type: Journal Article
Long and Short-Term Effects of Fire on Soil Charcoal of a Conifer Forest in Southwest Oregon
Year: 2012
In 2002, the Biscuit Wildfire burned a portion of the previously established, replicated conifer unthinned and thinned experimental units of the Siskiyou Long-Term Ecosystem Productivity (LTEP) experiment, southwest Oregon. Charcoal C in pre and post-fire O horizon and mineral soil was quantified by physical separation and a peroxide-acid digestion method. The abrupt, short-term fire event caused O horizon charcoal C to increase by a factor of ten to >200 kg C ha−1. The thinned wildfire treatment produced less charcoal C than unthinned wildfire and thinned prescribed fire treatments. The…
Publication Type: Journal Article
Fuel treatment impacts on estimated wildfire carbon loss from forests in Montana, Oregon, California, and Arizona
Year: 2012
Using forests to sequester carbon in response to anthropogenically induced climate change is being considered across the globe. A recent U.S. executive order mandated that all federal agencies account for sequestration and emissions of greenhouse gases, highlighting the importance of understanding how forest carbon stocks are influenced by wildfire. This paper reports the effects of the most common forest fuel reduction treatments on carbon pools composed of live and dead biomass as well as potential wildfire emissions from six different sites in four western U.S. states. Additionally, we…
Publication Type: Journal Article
Feedback from Plant Species Change Amplifies CO 2 Enhancement of Grassland Productivity
Year: 2012
Dynamic global vegetation models simulate feedbacks of vegetation change on ecosystem processes, but direct, experimental evidence for feedbacks that result from atmospheric CO 2 enrichment is rare. We hypothesized that feedbacks from species change would amplify the initial CO 2 stimulation of aboveground net primary productivity (ANPP) of tallgrass prairie communities. Communities of perennial forb and C 4 grass species were grown for 5 years along a field CO 2 gradient (250-500 microL/L) in central Texas USA on each of three soil types, including upland and lowland clay soils and a sandy…
Publication Type: Journal Article
Changes to Dryland Rainfall Result in Rapid Moss Mortality and Altered Soil Fertility
Year: 2012
Arid and semi-arid ecosystems cover ~40% of Earth's terrestrial surface, but we know little about how climate change will affect these widespread landscapes. Like many drylands, the Colorado Plateau in southwestern United States is predicted to experience elevated temperatures and alterations to the timing and amount of annual precipitation. We used a factorial warming and supplemental rainfall experiment on the Colorado Plateau to show that altered precipitation resulted in pronounced mortality of the widespread moss Syntrichia caninervis. Increased frequency of 1.2mm summer rainfall events…
Publication Type: Journal Article
Carbon Outcomes from Fuels Treatment and Bioenergy Production in a Sierra Nevada Forest
Year: 2012
In temperate conifer forests of the Western USA, there is active debate whether fuels reduction treatments and bioenergy production result in decreased carbon emissions and increased carbon sequestration compared to a no-action alternative. To address this debate over net carbon stocks, we performed a carbon life-cycle analysis on data from a fuels reduction treatment in a temperate, dry conifer forest in the northern Sierra Nevada of California, USA. The analysis tracks the net ecosystem carbon balance over 50 years for two scenarios (1) fuels reduction treatment combined with bioenergy…
Publication Type: Journal Article
Evidence of Enhanced Freezing Damage in Treeline Plants During Six Years of CO 2 Enrichment and Soil Warming
Year: 2012
Climate change and elevated atmospheric CO 2 levels could increase the vulnerability of plants to freezing. We analyzed tissue damage resulting from naturally occurring freezing events in plants from a longterm in situ CO 2 enrichment (+ 200 ppm, 2001-2009) and soil warming (+ 4°C since 2007) experiment at treeline in the Swiss Alps (Stillberg, Davos). Summer freezing events caused damage in several abundant subalpine and alpine plant species in four out of six years between 2005 and 2010. Most freezing damage occurred when temperatures dropped below -1.5°C two to three weeks after snow melt…
Publication Type: Journal Article
Soil-mediated effects of subambient to increased carbon dioxide on grassland productivity
Year: 2012
Grasslands are structured by climate and soils, and are increasingly affected by anthropogenic changes, including rising atmospheric CO 2 concentrations. CO 2 enrichment can alter grassland ecosystem function both directly and through indirect, soil-specific effects on moisture, nitrogen availability and plant species composition, potentially leading to threshold change in ecosystem properties. Here we show that the increase in aboveground net primary productivity (ANPP) with CO 2 enrichment depends strongly on soil type. We found that the ANPP-CO 2 response of grassland was 2.5× greater on…
Publication Type: Journal Article
Harmful filamentous cyanobacteria favoured by reduced water turnover with lake warming
Year: 2012
Anthropogenic-induced changes in nutrient ratios have increased the susceptibility of large temperate lakes to several effects of rising air temperatures and the resulting heating of water bodies. First, warming leads to stronger thermal stratification, thus impeding natural complete water turnover (holomixis), which compensates for oxygen deficits in the deep zones. Second, increased water temperatures and nutrient concentrations can directly favour the growth of harmful algae. Thus, lake-restoration programmes have focused on reducing nutrients to limit toxic algal blooms. Here we present…
Publication Type: Journal Article
Forest Protection and Forest Harvest as Strategies for Ecological Sustainability and Climate Change Mitigation
Year: 2012
An important consideration in forest management to mitigate climate change is the balance between forest carbon (C) storage and ecological sustainability. We explore the effects of management strategies on tradeoffs between forest C stocks and ecological sustainability under five scenarios, three of which included management and two scenarios which provide baselines emulating the natural forest. Managed forest scenarios were: (a) Protection (PROT), i.e., management by suppression of natural disturbance and harvest exclusion; (b) Harvest at a higher rate removing all sustainably available wood…
Publication Type: Journal Article
Estimating Consumption and Remaining Carbon in Burned Slash Piles
Year: 2012
Fuel reduction treatments to reduce fire risk have become commonplace in the fire adapted forests of western North America. These treatments generate significant woody debris, or slash, and burning this material in piles is a common and inexpensive approach to reducing fuel loads. Although slash pile burning is a common practice, there is little information on consumption or even a common methodology for estimating consumption. As considerations of carbon storage and emissions from forests increase, better means of quantifying burn piles are necessary. This study uses two methods, sector…
Publication Type: Journal Article
The push and pull of climate change causes heterogeneous shifts in avian elevational ranges
Year: 2012
Projected effects of climate change on animal distributions primarily focus on consequences of temperature and largely ignore impacts of altered precipitation. While much evidence supports temperature-driven range shifts, there is substantial heterogeneity in species' responses that remains poorly understood. We resampled breeding ranges of birds across three elevational transects in the Sierra Nevada Mountains, USA, that were extensively surveyed in the early 20th century. Presence absence comparisons were made at 77 sites and occupancy models were used to separate significant range shifts…
Publication Type: Journal Article
Timing of carbon emissions from global forest clearance
Year: 2012
Land-use change, primarily from conventional agricultural expansion and deforestation, contributes to approximately 17% of global greenhouse-gas emissions. The fate of cleared wood and subsequent carbon storage as wood products, however, has not been consistently estimated, and is largely ignored or oversimplified by most models estimating greenhouse-gas emissions from global land-use conversion. Here, we estimate the fate of cleared wood and timing of atmospheric carbon emissions for 169 countries. We show that 30 years after forest clearance the percentage of carbon stored in wood products…
Publication Type: Journal Article
Afternoon Rain More Likely Over Drier Soils
Year: 2012
Land surface properties, such as vegetation cover and soil moisture, influence the partitioning of radiative energy between latent and sensible heat fluxes in daytime hours. During dry periods, soil-water deficit can limit evapotranspiration, leading to warmer and drier conditions in the lower atmosphere. Soil moisture can influence the development of convective storms through such modifications of low-level atmospheric temperature and humidity, which in turn feeds back on soil moisture. Yet there is considerable uncertainty in how soil moisture affects convective storms across the world,…
Publication Type: Journal Article
Northwest Forest Plan -- The First 15 Years: Status and Trends of Northern Spotted Owl Populations and Habitats
Year: 2011
This is the second in a series of periodic monitoring reports on northern spotted owl (Strix occidentalis caurina) population and habitat trends on federally administered lands since implementation of the Northwest Forest Plan in 1994.Here we summarize results from a population analysis that included data from long-term demographic studies during 1985–2008. This data was analyzed separately by study area, and also in a meta-analysis across all study areas to assess temporal and spatial patterns in fecundity, apparent survival, recruitment, and annual rates of population change. Estimated…
Publication Type: Report
Synthesis of Knowledge of Extreme Fire Behavior: Volume I for Fire Managers
Year: 2011
The National Wildfire Coordinating Group definition of extreme fire behavior (EFB) indicates a level of fire behavior characteristics that ordinarily precludes methods of direct control action. One or more of the following is usually involved: high rate of spread, prolific crowning/spotting, presence of fire whirls, and strong convection column. Predictability is difficult because such fires often exercise some degree of influence on their environment and behave erratically, sometimes dangerously. Alternate terms include “blow up” and “fire storm.” Fire managers examining fires over the last…
Publication Type: Report
Short- and Long-term Effects of Fire on Carbon in US Dry Temperate Forest Systems
Year: 2011
Forests sequester carbon from the atmosphere, and in so doing can mitigate the effects of climate change. Fire is a natural disturbance process in many forest systems that releases carbon back to the atmosphere. In dry temperate forests, fires historically burned with greater frequency and lower severity than they do today. Frequent fires consumed fuels on the forest floor and maintained open stand structures. Fire suppression has resulted in increased understory fuel loads and tree density; a change in structure that has caused a shift from low- to high-severity fires. More severe fires,…
Publication Type: Journal Article
Both topography and climate affected forest and woodland burn severity in two regions of the western US, 1984 to 2006
Year: 2011
Fire is a keystone process in many ecosystems of western North America. Severe fires kill and consume large amounts of above- and belowground biomass and affect soils, resulting in long-lasting consequences for vegetation, aquatic ecosystem productivity and diversity, and other ecosystem properties. We analyzed the occurrence of, and trends in, satellite-derived burn severity across six ecoregions in the Southwest and Northwest regions of the United States from 1984 to 2006 using data from the Monitoring Trends in Burn Severity project. Using 1,024 fires from the Northwest (4,311,871 ha) and…
Publication Type: Journal Article