Treesearch

The variability of topography, geology, climate; vegetation, and land use in the Pacific Northwest creates considerable spatial and temporal variability of fluvial processes and reach-scale channel type. Here we identify process domains of typical Pacific Northwest watersheds and examine local physiographic and geologic controls on channel processes and response potential in the Puget Sound region. We also review the influence of different channel types on opportunities and limitations for channel restoration. Finally, we develop regime diagrams that identify typical combinations of...

The western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles) is a threatened species of the tallgrass prairie. Invasion by leafy spurge (Euphorbiaes esula L.) is a serious threat to western prairie fringed orchid habitat. The obiectives of this study were to develop a herbicide treatment to control leafy spurge while sustaining western prairie fringed orchid populations and to evaluate the soil seedbank composition of leafy spurge-infested sites to guide long-term management strategies. Quinclorac (3,7-dichloro-8-quinolinecarboxylic acid), imazapic ((±)-2-[4,5-dihydro-4-met...

Southern maidenhair fern (Adiantum capillus-veneris L.; Pteridaceae) is a cosmopolitan species that is widely distributed in southern North America. Stream orchid (Epipactis gigantea Dougl. ex Hook.; Orchidaceae) occurs in western North America from British Columbia, Canada; south to California, Arizona and New Mexico; and east to Texas. The species co-occur in disjunct populations in mineral warm springs habitats in South Dakota and British Columbia. Both species prefer warm, moist habitats and expand via rhizomatous growth and by wind- or waterdispersed propagules. In the Black Hills,...

This indicator monitors the number of native species that are associated with forest habitats. Because one of the more general sign of ecosystem stress is a reduction in the variety of organisms inhabiting a given locale, species counts are often used in assessing ecosystem wellbeing. Data on the distribution of 689 tree and 1,486 terrestrial animal species associated with forest habitats (including 227 mammals, 417 birds, 176 amphibians, 191 reptiles, and 475 butterflies) were analyzed. Species richness (number of species) is highest in the Southeast and in the arid ecoregions of the...

As the number of species classified as rare increases, the likelihood of species extinction also increases. This indicator focuses on species that have the greatest chance of being lost from the biotic community and therefore presages potential declines in species richness. The trend in species extinction since the turn of the 20th century varies by taxonomic group. Very few species of crustaceans, amphibians, or mammals, and no reptiles, are known to have become extinct in the last 100 years. Birds are prominent on the list of extinct species, but their numbers have remained fairly...

This indicator measures the portion of a species' historical distribution that is currently occupied as a surrogate measure of genetic diversity. Based on data for 1,642 terrestrial animals associated with forests, most species (88 percent) were found to fully occupy their historic range - at least as measured by coarse state-level occurrence patterns. Of the 193 species that have been extirpated from at least one state, 72 percent still occupy less than/equal to 90 percent of their former range. The number of species that now occupy greater than/equal to 80 percent of their former range...

Contemporary efforts to conserve populations and species often employ population viability analysis (PVA), a specific application of population modeling that estimates the effects of environmental and demographic processes on population growth rates. These models can also be used to estimate probabilities that a population will fall below a certain level. This information is helpful in understanding the threat of a species' extinction from environmental and demographic factors.

As you have seen in exercise 12, plants, such as the western prairie fringed orchid, typically have distinct life stages and complex life cycles that require the matrix analyses associated with a stage-based population model. Some statistics that can be generated from such matrix analyses can be very informative in determining which variables in the model have the greatest effect on population growth rate and persistence. One such statistic is that of elasticity. Elasticity analysis is a type of sensitivity analysis that measures the effect of a variable on model outcomes (Burgman et al....

To this point, our analysis of population processes and viability in the western prairie fringed orchid has used only deterministic models. In this exercise, we conduct a similar analysis, using a stochastic model instead. This distinction is of great importance to population biology in general and to conservation biology in particular. In deterministic models, transition probabilities are held constant throughout the projected time period, and populations are allowed to increase without bound (Beissinger and Westphal 1998). Deterministic models are mathematically convenient, but biological...

The western prairie fringed orchid is dependent on wetland habitat (U.S. Fish and Wildlife Service 1996). Prairie wetlands in which the orchid has historically thrived are usually ephemeral, filling with water in wet years and drying up during droughts. Wetland abundance and persistence is a function not only of variations in annual precipitation, but also of changes in groundwater levels beneath the prairie surface. The U.S. Fish and Wildlife Service makes this relationship explicit in its definition of wetlands by stating that "wetlands are lands transitional between terrestrial and...