Treesearch

The high water retention of hummock-forming Sphagnum species minimizes soil moisture fluctuations and might protect forest floor organic matter from burning during wildfire. We hypothesized that Sphagnum cover reduces overall forest floor organic matter consumption during wildfire compared with other ground-layer vegetation. We characterized variability in soil organic layer depth and organic matter stocks in two pairs of burned and unburned black spruce (Picea mariana (Mill.) BSP) stands in interior Alaska. In the unburned stands, microsites dominated by Sphagnum had more than twice as...

This work evaluates whether continuity between Advanced Very High Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS) normalized difference vegetation index (NDVI) is achievable for monitoring phenological changes in Alaska. This work also evaluates whether NDVI can detect changes in start of the growing season (SOS) in this region. Six quadratic regression models with NDVI as a function of accumulated growing degree days (AGDD) were developed from 2001 through 2004 AVHRR and MODIS NDVI data sets for urban, mixed, and forested land covers. Model parameter...

Thawing permafrost and the resulting microbial decomposition of previously frozen organic carbon (C) is one of the most significant potential feedbacks from terrestrial ecosystems to the atmosphere in a changing climate. In this article we present an overview of the global permafrost C pool and of the processes that might transfer this C into the atmosphere, as well as the associated ecosystem changes that occur with thawing. We show that accounting for C stored deep in the permafrost more than doubles previous high-latitude inventory estimates, with this new estimate equivalent to twice...

In an earlier publication (Houlahan et al. 2007) we reviewed trends in population covariances within communities across a range of long-term empirical data sets. We used these results to argue that compensatory dynamics are rare in natural communities. Ranta et al. (2008) explored interspecific interactions in a simulated environment and showed that 'negative community covariance can be absent even in strongly competitive communities and can be found present in communities without competitive interactions'. On this basis they conclude that 'the negative community covariance method . .. is...

The spread of invasive tree species has caused increasing harm to the environment. This study was motivated by the considerations that earlier studies generally ignored the role of economic factors related to the occurrence and abundance of invasive species, and empirical analyses of invasive trees on forestland have been inadequate. We assessed the impact of ecological and economic factors on the occurrence and number of invasive tree species on Alabama forest land since 1990. Count data models were used to analyze the 2004 Alabama Forest Inventory Analysis (PIA) data. The proportion of...

Large domestic and native ungulates have the potential to disperse large quantities of seeds throughout the landscape. Many studies have found that ungulates are capable of dispersing seeds but few quantify the relative importance of ungulate dispersal across the landscape. We investigated the potential for cattle, elk, and deer to disperse native and exotic plants in two different western North American ecosystems in northeast Oregon. We collected fecal samples of cattle, elk and deer that had been deposited during the current growing season. In the greenhouse we monitored the density and...

Land use provides many economic and social benefits but often comes at a substantial cost to the environment. Although most economic costs are figured into land use decisions, most environmental externalities are not. These environmental externalities cause a divergence between private and social costs for some land uses, leading to an inefficient land allocation. For example, developers may not bear all the environmental and infrastructure costs generated by their projects. Such market failures provide a justification for private conservation efforts and public land use planning and...

As climate change intensifies, there is increasing interest in developing models that reduce uncertainties in projections of global climate and refine these projections to finer spatial scales. Forecasts of climate impacts on ecosystems are far more challenging and their uncertainties even larger because of a limited understanding of physical controls on biological systems. Management and conservation plans that explicitly account for changing climate are rare and even those generally rely on retrospective analyses rather than future scenarios of climatic conditions and associated responses...

A common-garden study of Festuca roemeri (Pavlick) E. B. Alexeev (Poaceae) revealed substantial genetic variation within and among 47 populations from throughout its range in the Pacific Northwest, USA, for growth, fitness, phenological, and morphological traits. Using climatic and physiographic variables, genetic patterns over the landscape were examined through principal component and regression analysis. Elevation and latitude of the seed source, and to a lesser extent temperature and precipitation, explained a significant proportion of the genetic variation, suggesting that observed...

Soboliphyme baturini, a stomach-dwelling nematode of American martens (Martes americana). reaches high levels of infection; however, its effects on the nutritional condition of the host are unknown. To understand the effects of this parasite on American martens, we collected S. baturini and measured abdominal fat deposits from 155 marten carcasses on Prince of Wales Island, southeastern Alaska, in the winter 2006-2007. We analyzed how the dried mass of abdominal fat varied as a function of S. baturini intensity. Parasite intensity and nutritional condition were not correlated; these...