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Sage-grouse (Centrocercus urophasianus and C. minimus) historically inhabited much of the sagebrush-dominated habitat of North America. Today, sage-grouse populations are declining throughout most of their range. Population dynamics of sage-grouse are marked by strong cyclic behavior. Adult survival is high, but is offset by low juvenile survival, resulting in low productivity. Habitat for sage-grouse varies strongly by life-history stage. Critical habitat components include adequate canopy cover of tall grasses (? 18 cm) and medium height shrubs (40?80 cm) for nesting, abundant forbs and insects for brood rearing, and availability of herbaceous riparian species for late-growing season foraging. Fire ecology of...
Book Review: R. W. Adler, Restoring Colorado Ecosystems: A Troubled Sense of Immensity. Robert Adler has written a thoughtful and important meditation on the restoration of the Colorado River ecosystem. From his perch at the University of Utah Law School, Adler?s treatment of the Gordian knot of law facing restoration efforts in the Colorado Basin transforms this book from merely good to truly great. For example, John Wesley Powell, an important figure in this history, may have been unusually prescient in suggesting simple reforms such as reorganizing the Homestead Act to reflect drainage boundaries rather than survey lines. However, the failure to convince legislators of this wisdom is but one instance of a legal...
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Elk (Cervus elaphus) populations in Rocky Mountain National Park are higher than at any time in the past century, and heavy browsing by elk may interfere with aspen (Populus tremuloides Michx.) regneration. We used aerial photographs to identify all aspen stands within Rocky Mountain National Park, and all aspen stands within the elk winter range range (defined as 2400 to 2800 m elevation) in three portions of the adjacent Roosevelt National Forest. From this population of aspen stands, we randomly selected 57 stands for evaluation of aspen regeneration. Stands that contained stems younger than 30 years and taller than 2.5 m tall were classified as regenerating successfully. Only 20% of the aspen stands in Estes...
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The influence of landscape spatial structure on ecological processes has recently received much attention. Comparisons are made here between the spatial structure of grasslands, and active and extirpated Gunnison's prairie dog (Cynomys gunnisoni Hollister) towns at the Petrified Forest National Park, Arizona, U.S.A. The spatial structure of bare ground was quatified using a box-counting technique to extract landscape fractal dimensions, D, and bare-ground patch size. These landscapes are fractal, and active prairie dog towns had higher fractal dimensions, i.e. a more homogeneous spatial structure as D approaches 2, than inactive towns, which had higher fractal dimensions than unmodified grasslands. Morisita's index...
Quantifying landscape dynamics is a central goal of landscape ecology, and numerous metrics have been developed to measure the influence of human activities on natural landscapes. Composite scores that characterize human modifications to landscapes have gained widespread use. A parsimonious alternative is to estimate the proportion of a cover type (i.e. natural) within a spatial neighborhood to characterize both compositional and structural aspects of natural landscapes. Here I extend this approach into a multi-scale, integrated metric and apply it to national datasets on land cover, housing density, road existence, and highway traffic volume to measure the dynamics of natural landscapes in the conterminous US....
Landscape connectivity is critical to species persistence in the face of habitat loss and fragmentation. Graph theory is a well-defined method for quantifying connectivity that has tremendous potential for ecology, but its application has been limited to a small number of conservation scenarios, each with a fixed proportion of habitat. Because it is important to distinguish changes in habitat configuration from changes in habitat area in assessing the potential impacts of fragmentation, we investigated two metrics that measure these different influences on connectivity. The first metric, graph diameter, has been advocated as a useful measure of habitat configuration. We propose a second area-based metric that combines...
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Previous studies have shown that landscape structure influences animal movement and population structure. In this study, we show an indirect interaction between beetles and prairie dogs due to prairie dog ecosystem engineering. Gunnison's prairie dog (Cynomys gunnisoni Hollister) towns have more bare ground and are structurally less complex than adjacent unmodified grasslands. This results in bare ground facilitating beetle movement. Differences in landscape structure between prairie dog towns and unmodified grasslands had a significant effect on the movement of the darkling beetle, Eleodes hispilabris Say. Beetle movement tended to be more linear (pathway fractal dimension approached 1) on prairie dog habitats...
Laboratory incubations of15N-amended soils from a sagebrush steppe in south-central Wyoming indicate that nutrient turnover and availability have complex patterns across the landscape and between microsites. Total and available N and P and microbial C and N were highest in topographic depressions characterized by tall shrub communities. Net and gross N mineralization rates and respiration were also highest in these areas, but microbial efficiencies expressing growth relative to respiration cost were highest in soils of exposed ridgetop sites (prostrate shrub communities). Similar patterns occurred between shrub and intershrub soils, with greater nutrient availability under shrubs, but lower microbial efficiencies...
Studies to identify gaps in the protection of habitat for species of concern have been inconclusive and ham- pered by single-scale or poor multi-scale sampling methods, large minimum mapping units (MMU?s of 2 ha to 100 ha), limited and subjectively selected field observations, and poor mathematical and ecological models. We overcome these obstacles with improved multi-scale sampling techniques, smaller MMU?s (< 0.02 ha), an unbiased sampling design based on double sampling, improved mathematical models including species-area curves corrected for habitat heterogeneity, and geographic information system-based ecological models. We apply this landscape analysis approach to address resource issues in Rocky Mountain...
Water is a key driver of ecosystem processes in aridland ecosystems. Thus, changes in climate could have significant impacts on ecosystem structure and function. In the southwestern US, interactions among regional climate drivers (e.g., El Ni�o Southern Oscillation) and topographically controlled convective storms create a spatially and temporally variable precipitation regime that governs the rate and magnitude of ecosystem processes. We quantified the spatial and temporal distribution of reduced grassland greenness in response to seasonal and annual variation in precipitation at two scales at the Sevilleta Long Term Ecological Research site in central New Mexico, using Normalized Difference Vegetation Index (NDVI)...
Synopsis: This book provides important foundational concepts in landscape ecology, with a particular focus on the effects of land use and landscape fragmentation. Building on Forman’s patterns of landscape change, the book cites the McIntyre and Hobbs model of landscape change, which suggests that landscape modification often increases through time. Four broad classes of landscape condition can therefore be identified along a continuum of increasing human landscape modification: intact, variegated, fragmented, and relictual (figure 3). Similarly to Forman’s model, these classes represented correspond to different spatial patterns in the landscape. Therefore, as the extent of human land use increases, the amount...
In semiarid landscapes, the linkage between runoff and vegetation is a particularly close one. In this paper we report on the results of a long-term and multiple-scale study of interactions between runoff, erosion, and vegetation in a piñon–juniper woodland in New Mexico. We use our results to address three knowledge gaps: (1) the temporal scaling relationships between precipitation and runoff; (2) the effects of spatial scale on runoff and erosion, as influenced by vegetation; and (3) the influence of disturbance on these relationships. On the basis of our results, we tested three assumptions that represent current thinking in these areas (as evidenced, for example, by explicit or implicit assumptions embedded...
We determined changes in willow (Salixspp.) cover in two valleys of the eastern slope of Rocky Mountain National Park,Colorado, USA, and related these changes to suspected causative factors. Changes in vegetation were inferred from digital maps generated from aerial photo-interpretation and field surveys conducted with a global positioning system. The decrease in riparian shrub cover was approximately 20% in both valleys over the period between 1937/46 and 1996, while the decline in tall willow (> 2 m tall) cover was estimated to be approximately 55%in both valleys. Suppressed willows (< 1.5 m tall) were predominantly located in areas affected by flooding and in areas where major river reductions were observed....
The lack of management experience at the landscape scale and the limited feasibility of experiments at this scale have increased the use of scenario modeling to analyze the effects of different management actions on focal species. However, current modeling approaches are poorly suited for the analysis of viability in dynamic landscapes. Demographic (e.g., metapopulation) models of species living in these landscapes do not incorporate the variability in spatial patterns of early successional habitats, and landscape models have not been linked to population viability models. We link a landscape model to a metapopulation model and demonstrate the use of this model by analyzing the effect of forest management options...
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Conclusions: The nature of the surrounding matrix contributes significantly to the degree of patch isolation; matrix modification may improve habitat connectivity and genetic distribution in fragmented landscapes. Thresholds/Learnings: Synopsis: This study challenges traditional assumptions about the uniform nature of the matrix, and the reliance on distance alone as an indicator of patch isolation, by testing whether the type of inter-patch matrix contributes significantly to patch isolation in butterfly populations. The author tracked the movement of six butterfly species between patches of meadow habitat through two natural matrix types (conifer forest and willow thicket). All taxa of butterflies studied responded...
Synopsis: This study aimed to independently examine the effects of varying amounts and configurations of habitat at a landscape scale, with particular attention to critical persistence thresholds. A discrete reaction-diffusion model was used to estimate long-term equilibrium population persistence of a hypothetical species in a patchy landscape. When examined over a broad range of habitat amount and arrangements, population size was largely determined by the proportion of habitat (amount) in a landscape. However, when habitat coverage dropped below 30-50%, population response deviated, coinciding with a persistence threshold. Species persistence declined rapidly at this threshold range (50% for low degrees of aggregation,...
The cascade of uncertainty that underscores climate impact assessments of regional hydrology undermines their value for long-term water resources planning and management. This study presents a statistical framework that quantifies and propagates the uncertainties of hydrologic model response through projections of future streamflow under climate change. Different sources of hydrologic model uncertainty are accounted for using Bayesian modeling. The distribution of model residuals is formally characterized to quantify predictive skill, and Markov chain Monte Carlo sampling is used to infer the posterior distributions of both hydrologic and error model parameters. Parameter and residual error uncertainties are integrated...
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Synopsis: A simulation model, modified from percolation theory, was empirically tested to determine if population distribution patterns correlated with different landscape patterns, for different species across a landscape. Using two grasshopper species in a short-grass prairie of north-central Colorado, the experiment found that the threshold for population aggregation (random to clumped distribution) was differentially affected by dispersal ranges and habitat specialization for habitat generalists and habitat specialists, respectively. Habitat generalists aggregated differentially depending on dispersal abilities. Generalist species with good dispersal abilities aggregated when <35% of the landscape consisted...
Accurate, time dependent control options are required to halt biological invasions prior to equilibrium establishment, beyond which control efforts are often impractical. Although invasions have been successfully modeled using diffusion theory, diffusion models are typically confined to providing simple range expansion estimates. In this work, we use a Susceptible/Infected cellular automaton (CA) to simulate diffusion. The CA model is coupled with a network model to track the speed and direction of simulated invasions across heterogeneous landscapes, allowing for identification of locations for targeted control in both time and space. We evaluated the role of the location of initial establishment insofar as it affected...
Landscape-level variables operating at multiple spatial scales likely influence wetland amphibian assemblages but have not been investigated in detail. We examined the significance of habitat loss and fragmentation, as well as selected within-wetland conditions, affecting amphibian assemblages in twentyone glacial marshes. Wetlands were located within ttrban and agricultural regions of central and southwestern Minnesota, USA and were distributed across two ccoregions: tallgrass prairie and northern hardwood forest. We surveyed amphibian assemblages and used a geographic information system to quantify land-use variables at lhree scales: 500, 1000, and 2500 m. Ten species of amphibians were detected, the most abundant...
map background search result map search result map The Gunnison's prairie dog structures a high desert grassland landscape as a keystone engineer Aspen regeneration in the Colorado Front Range: differences at local and landscape scales Prairie dog engineering indirectly affects beetle movement behavior The matrix matters: effective isolation in fragmented landscapes. Critical thresholds in species responses to landscape structure. The matrix matters: effective isolation in fragmented landscapes. The Gunnison's prairie dog structures a high desert grassland landscape as a keystone engineer Prairie dog engineering indirectly affects beetle movement behavior Aspen regeneration in the Colorado Front Range: differences at local and landscape scales Critical thresholds in species responses to landscape structure.