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

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Climate changes impose requirements for many species to shift their ranges to remain within environmentally tolerable areas, but near-continuous regions of intense human land use stretching across continental extents diminish dispersal prospects for many species. We reviewed the impact of habitat loss and fragmentation on species? abilities to track changing climates and existing plans to facilitate species dispersal in response to climate change through regions of intensive land uses, drawing on examples from North America and elsewhere. We identified an emerging analytical framework that accounts for variation in species' dispersal capacities relative to both the pace of climate change and habitat availability....
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At northern high latitudes, biosphere responses to and interactions with climate warming are expected to be significant during the 21st century. Most predictions of climate?biosphere interactions rely on experiments and observations in contemporary landscapes, e.g., modern distributions of vegetation types and their structural features are used to delimit potential biosphere?atmosphere feedbacks. Paleorecords look beyond the present to examine vegetation configurations under climatic regimes that approximate future scenarios. To enhance the knowledge of arctic and subarctic ecosystems under varying climatic conditions, we analyzed pollen and macrofossil data from Beringia (northeast Siberia, Alaska, and northwest...
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We examined the effects of fire disturbance on permafrost degradation and thaw settlement across a series of wildfires (from ~1930 to 2010) in the forested areas of collapse-scar bog complexes in the Tanana Flats lowland of interior Alaska. Field measurements were combined with numerical modeling of soil thermal dynamics to assess the roles of fire severity and climate history in postfire permafrost dynamics. Field-based calculations of potential thaw settlement following the loss of remaining ice-rich permafrost averaged 0.6 m. This subsidence would cause the surface elevations of forests to drop on average 0.1 m below the surface water level of adjacent collapse-scar features. Up to 0.5 m of thaw settlement was...
Trends in the growing season Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI) time-series were analyzed for the time period from 2000 to 2010 to understand landscape-level patterns of vegetation change in ecosystems of interior Alaska. The analysis compared data-sets for Alaska vegetation cover types, wetland cover classes, wildfire boundaries since the 1940s, permafrost type, and elevation to identify the most likely combination of factors driving regional changes in habitat quality and ecosystem productivity. Approximately 48% of all ecosystem areas in interior Alaska were detected with significant (p < 0.05) positive or negative MODIS growing season EVI trends from 2000 to...
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...
Climate warming in high latitudes is expected to alter the carbon cycle of the boreal forest. Warming will likely increase the rate of organic matter decomposition and microbial respiration. Faster organic matter decomposition should increase plant available nutrients and stimulate plant growth. I examined these predicted relationships between C cycle components in three similar black spruce forests ( Picea mariana [Mill] B.S.P) near Fairbanks, Alaska, that differed in soil environment and in-situ decomposition. As predicted, greater in-situ decomposition rates corresponded to greater microbial respiration and black spruce aboveground growth. However root and soil respiration were both greater at the site where...
Maximum thaw depths were measured annually in an unburned stand, a heavily burned stand, and a fireline in and adjacent to the 1971 Wickersham fire. Maximum thaw in the unburned black spruce stand ranged from 36 to 52 cm. In the burned stand, thaw increased each year to a maximum depth of 302 cm in 1995. In 1996, the entire layer of seasonal frost remained, creating a new active layer depth at 78 cm. An unfrozen soil zone (talik) remained between the two frozen layers until 2006 when the entire profile remained frozen. Permafrost returned to the burned site by the formation of a layer of seasonal frost that remained frozen through subsequent years. The fireline displayed a similar pattern with a maximum thaw of...
Global levels of reactive nitrogen are predicted to rise in the coming decades as a result of increased deposition from the burning of fossil fuels and the large-scale conversion of nitrogen into a useable form for agriculture. Many plant communities respond strongly to increases in soil nitrogen, particularly in northern ecosystems where nitrogen levels are naturally very low. An experiment in northern Canada that was initiated in 1990 has been investigating the effects of long-term nutrient enrichment (fertilizer added annually) on a boreal forest understory community. We used this experiment to investigate why some species increase in abundance under nutrient enrichment whereas others decline. We focused on four...
CO2 [carbon dioxide] and CH4 [methane] fluxes were monitored over 4 years in a range of taiga forests along the Tanana River in interior Alaska. Floodplain alder and white spruce sites and upland birch/aspen and white spruce sites were examined. Each site had control, fertilized, and sawdust amended plots; flux measurements began during the second treatment year. CO2 emissions decreased with successional age across the sites (alder, birch/aspen, and white spruce, in order of succession) regardless of landscape position. Although CO2 fluxes showed an exponential relationship with soil temperature, the response of CO2 production to moisture fit an asymptotic model. Of the manipulations, only N fertilization had an...
Understanding the temperature sensitivity of soil respiration is critical for predicting the response of ecosystems to climate change, yet the microbial communities responsible are rarely considered explicitly in studies or models. In this study, we assessed total microbial community composition, quantified bacterial respiration temperature response, and investigated the temperature dependence of bacterial carbon substrate utilization in tropical, temperate, and taiga soils (from Puerto Rico, California, and Alaska). Microbial community composition was characterized using phospholipid fatty acid analysis. Bacterial community respiration on a standardized set of substrates was ascertained using the BiOLOG™ substrate...
map background search result map search result map Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests Ecosystem Dynamics of the Boreal Forest: the Kluane Project Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests Ecosystem Dynamics of the Boreal Forest: the Kluane Project