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Filters: Tags: R1-Vulnerability Forest Species and Communities to Climate Change (X)

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Detailed observations of stream, soil, and groundwater chemistry were used to determine the role of fire, permafrost and snowmelt processes on the fluxes of carbon, nitrogen and major solutes from interior Alaskan catchments. We examined an experimentally burned watershed and two reference watersheds that differ in permafrost coverage (high, 53%; medium-burn, 18%; and low, 4%) during the FROSTFIRE prescribed burn in July 1999. The fire elevated stream nitrate concentrations for a short period during the first post-fire storm, but nitrate declined thereafter, suggesting that less severe fires that leave an intact riparian zone may have only a short-term effect on stream chemistry. Nevertheless, we found fundamental...
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The Spatial Alaskan Forest Ecosystem Dynamics (SAFED) model was validated across four of the most common vegetation types found in interior Alaska. The vegetation types were an aldef (Alnus spp.) - balsam poplar (Populus balsamifera L.) site (FP2), an old-growth balsam poplar and white spruce (Picea glauca (Moench) Voss) site (FP3), a mixed deciduous (primarily birch (Betula papyrifera Marsh.) and aspen (Populus tremuloides Michx.)) and white spruce site (UP2), and a mature white spruce site (UP3). The FP site types are common on the floodplain along the Tanana River and the UP site types are common in the uplands in interior Alaska. SAFED is based on nitrogen productivity for vegetation growth, litter fall quantity...
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The likely direction of change in soil organic carbon (SOC) in the boreal forest biome, which harbors roughly 22% of the global soil carbon pool, is of marked concern because climate warming is projected to be greatest in high latitudes and temperature is the cardinal determinant of soil C mineralization. Moreover, the majority of boreal forest SOC is harbored in surficial organic horizons which are the most susceptible to consumption in wildfire. This research focuses on mechanisms of soil C accumulation in recently burned (2004) and unburned (61850-1950) black spruce (Picea mariana [Mill.] BSP) forests along gradients in stand productivity and soil temperature. The primary research questions in these three chapters...
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A 1000-yr record of forest fire activity has been developed using three annually dated ice cores from Eclipse Icefield, Yukon, Canada. Forest fire signals were identified as NH4+ residuals above a robust spline and corroborated by an empirical orthhogonal function (EOF) analysis that identified a chemical association in the NH4+ , C2 O42- and K+ records similar to that observed in forest fire plumes. These statistical techniques yielded similar records of forest fire activity, although the EOF analysis provides more conservative identification of forest fire signals. Comparison of forest fire signals in the Eclipse ice cores with the record of annual area burned in Alaska and the Yukon demonstrates that 80% of high...
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Disturbances are mechanisms that mediate ecosystem changes in response to climate-driven vegetation changes. While many studies have looked at the effect of fire on ecosystem components, few have considered the response of fire to climate and vegetation change. The effects that past climate and vegetation shifts have on fire regimes and the potential consequences to ecosystem change are examined here. Charcoal and pollen analyses were used to determine geographic and temporal patterns of past fire regimes in the North American western boreal forest. Seventeen high-resolution records from north-central Canada (NWT and Manitoba), interior Alaska, and northwestern Ontario were analyzed for large charcoal particles...
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Carbon dioxide accumulating in our atmosphere is one of the most important environmental threats of our time. Humans and changing climate, separately or in concert, have affected global vegetation, biogeochemical cycles, biophysical processes, and primary production. Recent studies have found temporary carbon stores in North American vegetation due to land-cover land-use change, but have yet to characterize regional mechanisms across the continent. This research implemented multi-resolution remote sensing data, coupled with ecosystem simulations, to determine the importance of fine-scale disturbance in our understanding of dynamics that drove and/or perturbed carbon sequestration in North America from 1982 through...
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Northern and high-latitude alpine treelines are generally thought to be limited by available warmth. Most studies of tree-growth?climate interaction at treeline as well as climate reconstructions using dendrochronology report positive growth response of treeline trees to warmer temperatures. However, population-wide responses of treeline trees to climate remain largely unexamined. We systematically sampled 1558 white spruce at 13 treeline sites in the Brooks Range and Alaska Range. Our findings of both positive and negative growth responses to climate warming at treeline challenge the widespread assumption that arctic treeline trees grow better with warming climate. High mean temperatures in July decreased the growth...
In the boreal biome, fire is the major disturbance agent affecting ecosystem change, and fire dynamics will likely change in response to climatic warming. We modified a spatially explicit model of Alaskan subarctic treeline dynamics (ALFRESCO) to simulate boreal vegetation dynamics in interior Alaska. The model is used to investigate the role of black spruce ecosystems in the fire regime of interior Alaska boreal forest. Model simulations revealed that vegetation shifts caused substantial changes to the fire regime. The number of fires and the total area burned increased as black spruce forest became an increasingly dominant component of the landscape. The most significant impact of adding black spruce to the model...
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In Alaska, there exists a substantial knowledge gap of key climate drivers and filling these gaps is vital since life and the economy are inexorably linked with climate in the state. This thesis identifies and investigates three topics that advance the understanding of Alaska climate variability: the role of large-scale climate in Interior river ice breakup, the link between climate and arctic tundra vegetation, and climate divisions based on objective methods. River ice breakup in the Yukon-Kuskoswim watershed is occurring earlier by 1.3 days decade-1 1948-2008 and displays large year-to-year variability. April-May Interior Alaska air temperatures are the best predictor of river ice breakup and were linked to El...
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Boreal forests contain significant quantities of soil carbon that may be oxidized to CO2 given future increases in climate warming and wildfire behavior. At the ecosystem scale, decomposition and heterotrophic respiration are strongly controlled by temperature and moisture, but we questioned whether changes in microbial biomass, activity, or community structure induced by fire might also affect these processes. We particularly wanted to understand whether postfire reductions in microbial biomass could affect rates of decomposition. Additionally, we compared the short-term effects of wildfire to the long-term effects of climate warming and permafrost decline. We compared soil microbial communities between control...
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Global vegetation models predict that boreal forests are particularly sensitive to a biome shift during the 21st century. This shift would manifest itself first at the biome?s margins, with evergreen forest expanding into current tundra while being replaced by grasslands or temperate forest at the biome?s southern edge. We evaluated changes in forest productivity since 1982 across boreal Alaska by linking satellite estimates of primary productivity and a large tree-ring data set. Trends in both records show consistent growth increases at the boreal?tundra ecotones that contrast with drought-induced productivity declines throughout interior Alaska. These patterns support the hypothesized effects of an initiating...


map background search result map search result map Mountain Pine Beetle in British Columbia Assessment of boreal forest historical C dynamics in the Yukon River Basin: relative roles of warming and fire regime change Assessing river ice breakup date, coastal tundra vegetation and climate divisions in the context of Alaska climate variability Fire history of boreal forests: Implications for past climate change Forest Structure and Downed Woody Debris in Boreal, Temperate, and Tropical Forest Fragments The role of mosses in ecosystem succession and function in Alaska's boreal forest Spruce beetle outbreaks on the Kenai Peninsula, Alaska, and Kluane National Park and Reserve, Yukon Territory: Relationship to summer temperatures and regional differences in disturbance regimes Interactive effects of wildfire and permafrost on microbial communities and soil processes in an Alaskan black spruce forest Identifying and understanding North American carbon cycle perturbations from natural and anthropogenic disturbances Rapid Cycling of Organic Nitrogen in Taiga Forest Ecosystems Human Impacts on the Fire Regime of Interior Alaska: Interactions among Fuels, Ignition Sources, and Fire Suppression A 1000-yr record of forest fire activity from Eclipse Icefield, Yukon, Canada Export of carbon, nitrogen and major solutes from a boreal forest watershed: The influence of fire and permafrost Mechanisms of soil carbon stabilization in black spruce forests of interior Alaska: Soil temperature, soil water, and wildfire Reduced growth of Alaskan white spruce in the twentieth century from temperature-induced drought stress Modeling the Impact of Black Spruce on the Fire Regime of Alaskan Boreal Forest Human Impact on Fire Regime in Interior Alaska Boreal forest ecosystem dynamics. II. Application of the model to four vegetation types in interior Alaska The role of mosses in ecosystem succession and function in Alaska's boreal forest Rapid Cycling of Organic Nitrogen in Taiga Forest Ecosystems Modeling the Impact of Black Spruce on the Fire Regime of Alaskan Boreal Forest Interactive effects of wildfire and permafrost on microbial communities and soil processes in an Alaskan black spruce forest Export of carbon, nitrogen and major solutes from a boreal forest watershed: The influence of fire and permafrost A 1000-yr record of forest fire activity from Eclipse Icefield, Yukon, Canada Reduced growth of Alaskan white spruce in the twentieth century from temperature-induced drought stress Fire history of boreal forests: Implications for past climate change Assessing river ice breakup date, coastal tundra vegetation and climate divisions in the context of Alaska climate variability Forest Structure and Downed Woody Debris in Boreal, Temperate, and Tropical Forest Fragments Spruce beetle outbreaks on the Kenai Peninsula, Alaska, and Kluane National Park and Reserve, Yukon Territory: Relationship to summer temperatures and regional differences in disturbance regimes Human Impacts on the Fire Regime of Interior Alaska: Interactions among Fuels, Ignition Sources, and Fire Suppression Boreal forest ecosystem dynamics. II. Application of the model to four vegetation types in interior Alaska Assessment of boreal forest historical C dynamics in the Yukon River Basin: relative roles of warming and fire regime change Mechanisms of soil carbon stabilization in black spruce forests of interior Alaska: Soil temperature, soil water, and wildfire Human Impact on Fire Regime in Interior Alaska Mountain Pine Beetle in British Columbia Identifying and understanding North American carbon cycle perturbations from natural and anthropogenic disturbances