Skip to main content
USGS - science for a changing world
Advanced Search

Filters: Tags: Monitoring 1-Changes in Plant and Animal Distribution: Ecosystems (X)

345 results (130ms)   

View Results as: JSON ATOM CSV
thumbnail
The latitudinal gradient of the start of the growing season (SOS) and the end of the growing season (EOS) were quantified in Alaska (61°N to 71°N) using satellite-based and ground-based datasets. The Alaskan evergreen needleleaf forests are sparse and the understory vegetation has a substantial impact on the satellite signal. We evaluated SOS and EOS of understory and tundra vegetation using time-lapse camera images. From the comparison of three SOS algorithms for determining SOS from two satellite datasets (SPOT-VEGETATION and Terra-MODIS), we found that the satellite-based SOS timing was consistent with the leaf emergence of the forest understory and tundra vegetation. The ensemble average of SOS over all satellite...
thumbnail
The extensive boreal biome is little studies relative to its global importance. Its high soil moisture and low temperatures result in large below-ground reservoirs of carbon (C) and nitrogen (N). Presently, such high-latitude ecosystems are undergoing the largest temperature increases in global warming. Change in soil temperature or moisture in the large pools of soil organic matter could fundamentally change ecosystem C and N budgets. Since 1990, we have conducted treeline studies in a small (800 ha) watershed in Noatak National Preserve, northwestern Alaska. Our objectives were to (1) gain an understanding of treeline dynamics, structure, and function; and (2) examine the effects of global climate change, particularly...
thumbnail
The northern treeline is generally limited by available warmth. However, in recent years, more and more studies have identified drought stress as an additional limiting factor for tree growth in northern boreal forests and at treelines. Three growth responses to warming have been identified: increase in growth, decrease in growth, and nonsignificant correlation of tree growth with climate. Here we investigate the effect of drought stress on radial growth of white spruce at northern treelines along a longitudinal gradient spanning the entire Brooks Range in Alaska. We systematically sampled 687 white spruce at seven treeline sites. Where possible, we sampled three site types at a given site: high-density forest,...
thumbnail
Neotyphodium are fungal endosymbionts of grasses that reproduce asexually by infecting the host's seed. This relationship has traditionally been considered mutualistic, with the fungus improving host fitness by alleviating important stresses. To determine the importance of biotic and abiotic stresses in mediating the endophyte-grass interaction, I investigated the relationship between grazing pressure by collared pikas and Neotyphodium sp. infection frequency in the grass Festuca altaica in an alpine meadow. I conducted a factorial design experiment combining endophyte infection, grazing history, fungicide and fertilizer. Leaf demography and herbivory damage were monitored every two weeks. In areas with chronic...
thumbnail
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...
This study describes the community, population, and growth dynamics of Alnus tenuifolia (thinleaf alder) and implications for nutrient cycling on the Tanana River floodplains. Through symbiotic N-fixation inputs, alder contributed to soil N accumulation with time. N-fixation itself was likely limited by soil P. Soil N was positively related to alder stem density in early successional stands. Community structure varied along a temporal gradient of changing environmental characteristics, but variations in successional patterns were found. Landscape scale alder recruitment varied temporally and was apparently linked to interactions between geofluvial processes, seed production and dispersal, and herbivory. A widespread...


map background search result map search result map Method for Attenuation of White Phosphorus Contamination in Wetlands Fungal endophyte infection in an alpine meadow: Testing the mutualism theory Indirect and Long-Term Effects of Fire on the Boreal Forest Carbon Budget RELATIONSHIPS AMONG FIRES, FUNGI, AND SOIL DYNAMICS IN ALASKAN BOREAL FORESTS Competitive interactions across a soil fertility gradient in a multispecies forest Alder (Alnus crispa) effects on soils in ecosystems of the Agashashok River valley, northwest Alaska Comment on 'Wetland drying and succession across the Kenai Peninsula Lowlands, south-central Alaska' Exploring ecological changes in Cook Inlet beluga whale habitat though traditional and local ecological knowledge of contributing factors for population decline Spruce beetles and forest ecosystems of south-central Alaska Longitudinal variation of radial growth at Alaska's northern treeline; recent changes and possible scenarios for the 21st century Soil nitrogen transformations and retention during a deciduous to coniferous successional transition Denali National Park and Preserve Landcover Mapping Project Volume 2: Landcover classes and plant associations Treeline biogeochemistry and dynamics, Noatak National Preserve, northwestern Alaska Boreal forest ecosystem dynamics. II. Application of the model to four vegetation types in interior Alaska Latitudinal gradient of spruce forest understory and tundra phenology in Alaska as observed from satellite and ground-based data Method for Attenuation of White Phosphorus Contamination in Wetlands Soil nitrogen transformations and retention during a deciduous to coniferous successional transition RELATIONSHIPS AMONG FIRES, FUNGI, AND SOIL DYNAMICS IN ALASKAN BOREAL FORESTS Fungal endophyte infection in an alpine meadow: Testing the mutualism theory Denali National Park and Preserve Landcover Mapping Project Volume 2: Landcover classes and plant associations Alder (Alnus crispa) effects on soils in ecosystems of the Agashashok River valley, northwest Alaska Treeline biogeochemistry and dynamics, Noatak National Preserve, northwestern Alaska Comment on 'Wetland drying and succession across the Kenai Peninsula Lowlands, south-central Alaska' Exploring ecological changes in Cook Inlet beluga whale habitat though traditional and local ecological knowledge of contributing factors for population decline Spruce beetles and forest ecosystems of south-central Alaska Longitudinal variation of radial growth at Alaska's northern treeline; recent changes and possible scenarios for the 21st century Indirect and Long-Term Effects of Fire on the Boreal Forest Carbon Budget Boreal forest ecosystem dynamics. II. Application of the model to four vegetation types in interior Alaska Competitive interactions across a soil fertility gradient in a multispecies forest Latitudinal gradient of spruce forest understory and tundra phenology in Alaska as observed from satellite and ground-based data