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Browsing by Author "Stohlgren, Thomas J., advisor"

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    Differentiating existing habitat of the invasive tamarisk (Tamarix spp.) from potential habitat of the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) through maximum entropy modeling
    (Colorado State University. Libraries, 2010) York, Patricia M., author; Stohlgren, Thomas J., advisor; Graham, James J., committee member; Flather, Curtis H., committee member; Sloane, Sarah, committee member
    Biological control of the exotic plants known collectively as tamarisk (Tamarix spp, saltcedar, tamarisk) in southwestern states is controversial regarding the protection of the federally endangered Southwestern Willow Flycatcher (Empidonax traillii extimus). The songbird sometimes nests in tamarisk where floodplain-level invasion replaces native habitat. Biological control with the saltcedar leaf beetle (Diorhabda elongate) began along the Virgin River, Utah, in 2006, enhancing the need for comprehensive understanding of the tamarisk-Flycatcher relationship. I used maximum entropy (Maxent) modeling to separately quantify the current extent of dense tamarisk habitat (>50% cover) and the potential extent of habitat available for E. traillii extimus within the studied watersheds. I used transformations of 2008 Landsat Thematic Mapper images and a digital elevation model as environmental input variables. Maxent models performed well for the Flycatcher and tamarisk with Area Under the ROC Curve (AUC) values of 0.960 and 0.982, respectively. Classification of thresholds and comparison of the two Maxent outputs indicated little spatial overlap between predicted suitable habitat for E. traillii extimus and predicted dense Tamarisk stands. Dense tamarisk habitat comprised 1,000 km2 within the study area, of which 8.5% was also modeled as potential habitat for E. traillii extimus. Potential habitat modeled for the Flycatcher constituted 230 km2, of which 38.1% also contained dense tamarisk habitat. Results showed that both native vegetation and dense tamarisk habitats exist in the study area and that most tamarisk infestations do not contain characteristics that satisfy the habitat requirements of E. traillii extimus. Based on this study, effective biological control of Tamarix spp. may initially reduce the suitable habitat available to E. traillii extimus within the study area, but has the potential to increase suitable habitat if native vegetation replaces tamarisk in biocontrol areas.
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    Early detection and rapid assessment of invasive organisms under global climate change
    (Colorado State University. Libraries, 2009) Holcombe, Tracy R., author; Laituri, Melinda J., advisor; Stohlgren, Thomas J., advisor
    Invasive species alter native species assemblages, effect ecosystem processes, and threaten biodiversity worldwide. Early detection and rapid assessment will help stem the problem, focusing managers attention on newly established invasive species before they spread. This is a big task requiring a coordinated effort and a centralized data sharing effort. One tool that can be used in this effort is Geographic Information Systems (GIS). GIS can be used to create potential distribution maps for all manner of taxa, including plants, animals, and diseases, and may perform well in early detection and rapid assessment of invasive species. As an example application, I created maps of potential spread of the cane toad (Bufo marinus) in the southeastern United States at an 8-digit Hydrologic Unit Code (HUC) level using regression and environmental envelope techniques. Equipped with this potential map, resource managers can target field surveys to areas most vulnerable to invasion. However, there is a general need in invasive species research to quantify the potential habitat of many invasive plant species. I was interested in modeling the shifts in suitable habitat over time, environmental space, and climate change. I used 4-km2 climate scenarios projected to the years 2020 and 2035 for the continental United States, to examine potential invasive species habitat distributions. I used maximum entropy modeling (Maxent) to create three models for 12 invasive plant species: (1) current potential habitat suitability; (2) potential habitat suitability in 2020; and (3) potential habitat suitability in 2035. These models showed areas where habitat suitability remains stable, increases, or decreases with climate change. Area under the receiver operating characteristic curve (AUC) values for the models ranged from 0.92 for Pennisetum ciliare to 0.70 for Lonicera japonica, with 10 of the 12 being above 0.83 suggesting strong and predictable species-environment matching. Change in area between the current potential habitat and the year 2035 ranged from a potential habitat loss of about 217,000 km2 for Cirsium arvense, to a potential habitat gain of about 133,000 km2 for Microstegium vimineum. These results have important implications for developing a triage approach to invasive species management under varying rates of climate change.
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    Linking culture, ecology and policy: the invasion of Russian-olive (Elaeagnus angustifolia l.) on the Crow Indian Reservation, south-central Montana, USA
    (Colorado State University. Libraries, 2013) Pretty Paint-Small, Valerie, author; Beck, K. George, advisor; Stohlgren, Thomas J., advisor; Brown, Cynthia S., committee member; Sherman, Kathleen A., committee member
    Native plant diversity in riparian systems is currently threatened by the invasive Russian olive (Elaeagnus angustifolia L.) replacing woody riparian species, including plains cottonwood (Populus deltoides Marsh), used for centuries by the Apsáalooke or Crow Tribe of south-central Montana. The Dawes Act of 1887, also known as the Allotment Act, created a land tenure system that restricted ownership rights and forced an unfamiliar agro-economy on the Crow people. Land cessations, illegal land sales and/or leases over the last century resulted in a mosaic of private non-Indian land ownership parcels interspersed within Crow tribal and individual allotment lands. Crow Tribe and individual land allotments are held in trust by the federal government and managed by the federal trust agent, U.S Department of Interior-Bureau of Indian Affairs (BIA). Elaeagnus angustifolia was intentionally planted in the early 20th century along the floodplains of the Little Bighorn and Bighorn Rivers to support a largely non-Indian owned agro-economy. Mapped presence points of E. angustifolia trees within land use type and land ownership status were used as an indirect measure of policy induced invasion. Stem density of E. angustifolia (stem/km2) varied significantly by land use type (13 predictor variables) (p < 0.001), and densities were significantly higher in wetlands, crop/pasture, mixed rangeland, residential and transportation (p < 0.001), and grass rangeland (p < 0.01), and mean stem density was highest in wetlands than other land use types. Fee patent (private non-Indian) land had marginally higher stem numbers than tribal and Reservation trust lands combined, although not significant. The Bighorn and Little Bighorn Rivers of Montana are highly regulated with diversion dams, irrigation canals and ditches heavily dominated by E. angustifolia. The Crow people use cottonwoods for socio-cultural and ritual purposes; however they have witnessed a decline in availability to harvest specific size classes of cottonwood. Further, given predicted climate changes of warmer mean annual temperatures and increased precipitation for Montana, I used Maximum Entropy Modeling (MaxEnt) to predict suitable habitat and future spread of E. angustifolia along riparian corridors of the Little Bighorn and Bighorn Rivers. Climate variables (n = 22) used in the model contributed significantly to the model (AUC > 1.0) suggesting that near-term climate changes may influence the spread of E. angustifolia, particularly downstream from diversion dams used for irrigation purposes. Personal interviews of Crow Elders overwhelmingly agreed (~80%) that sub-adult cottonwood trees were the most difficult to find now compared to 25 years ago. Maximum distances to travel to obtain sub-adult size classes used exclusively in ceremony increased in present-day by 30 km compared to recent history. Plot data comparing near and far from ceremonial and Crow Fair campground sites indicated that cottonwood stem heights (from 7.32 m plots where n=10) were significantly shorter near ceremony sites (< 150 m near) compared to sites farther away (> 2.4 km away; p < 0.01). There were more cottonwood trees with diameter at breast height (dbh) < 5 cm in plots located far from ceremony sites than near (p < 0.05). Near-term (10 years) climate change predictions, coupled with reduced cottonwood availability to harvest indicated that mid-sized cottonwoods will continue to decline, while E. angustifolia populations will spread. Personal interviews with Elders and Crow community surveys reported 23 uses of cottonwood with the branch as the most often used plant part. Elders also mentioned Pine (Pinus sp.) and buffaloberry (Shepherdia canadensis (L.) Nutt. argentea) woody species are equally important to Crow culture. Traditional food sources such as chokecherry (Prunus virginiana L.) are also mentioned as becoming more difficult to find for traditional harvest. Elaeagnus angustifolia is not used by the Crow people who consider this species to be problematic, changing the visual landscape and making it difficult to find historical home sites and sacred places. Gender differences in knowledge of E. angustifolia were significant, as males had more knowledge than females, and the oldest age groups (> 55 years) had higher knowledge than younger age groups. Taken in total, I conclude that E. angustifolia is displacing culturally important native biota harvested by the Crow people, and has heavily invaded private or fee-patent lands. Density of this species in allotted lands, however, is not managed by the Crow, as approximately two thirds are leased to non-Indians for farming or ranching operations. Lack of access and management oversight by the Crow Tribe for all lands within the reservation boundaries resulted in drastic changes in vegetation from the once dominant plains cottonwood to an almost mono-culture of E. angustifolia. Growth of this thorny shrub severely restricts the ability to harvest important woody species used in the expression of Crow culture through ceremony. Traditional Crow knowledge related to harvesting practices of culturally important native biota may be in the initial stages of erosion. Future land policy should reflect the ability of the Crow Tribe to manage invasive species within reservation boundaries, regardless of ownership class. To preserve traditional knowledge of native biota, E. angustifolia removal projects coupled with re-vegetation of culturally important species closer to Crow communities will allow access by Elders, and hence preserve their rich cultural knowledge for generations to come.
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    Regional data refine local abundance models: modeling plant species abundance distributions on the Central Plains
    (Colorado State University. Libraries, 2010) Young, Nicholas E., author; Stohlgren, Thomas J., advisor; Kelly, Eugene Francis, committee member; Graham, James J., committee member; Evangelista, Paul Harrison, committee member
    Species distribution models are frequently used to predict species occurrences in novel conditions, yet few studies have examined the effects of extrapolating locally collected data to regional scale landscapes. Using boosted regression trees, I examined the issues of spatial scale and errors associated with extrapolating species distribution models developed using locally collected abundance data to regional extents for a native and alien plant species across a portion of the central plains in Colorado. Topographic, remotely sensed, land cover and soil taxonomic predictor variables were used to develop the models. Predicted means and ranges were compared among models and predictions were compared to observed values between local and regional extent models. All models had significant predictive ability (p < 0.001). My results suggested: (1) extrapolating local models to regional extents may restrict predictions; (2) modeling species abundance may prove more useful than models of species presence; (3) multiple sources of predictors may improve model results at different extents; and (4) regional data can help refine and improve local model predictions. Regional sampling designed in concert with large sampling frameworks such as the National Ecological Observatory Network, Inc (NEON) may improve our ability to monitor changes in local species abundance.