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Browsing by Author "Beck, K. George, advisor"

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    Dispersal of an invasive tumbleweed
    (Colorado State University. Libraries, 2007) Baker, Dirk V., author; Beck, K. George, advisor
    Dispersal is of critical importance for species conservation and reducing the spread of invasive species. I investigated the dispersal of the invasive tumbleweed, Centaurea diffusa. Tumbleweed dispersal is composed of three components; the plant stem must break free; wind must be sufficient to move plants; and seed must be retained in the plant with time and distance. Dispersal peaks were variable in space and time. Dispersal events correlated with wind gusts and variability in temperature. However, 18 and 78% of plants tumbled over 2 years at sites near Larkspur and Superior, CO, respectively. Weather did not fully explain the differences in dispersal magnitude. Raising plants from the sites in common garden revealed that Larkspur plants required 57% greater force to break than plants from the Superior site. In addition, plants under dry post-senescence soil conditions required four to six times greater force to break compared to plants under moderate to high soil moisture. Based on wind tunnel measurements, wind velocities necessary to break C diffusa stems ranged from 16 to 37 m/s. I developed a GIS-based model for the movement patterns of this plant based on topography, vegetation and wind patterns. Such modeling could provide information to help reduce the spread of this important invasive weed. However, model accuracy needs to be improved before it will be applicable to management. I conducted field and wind tunnel experiments to estimate seed dispersal with time and distance. The 95 percentile confidence limits for the half-life of seed retention in non-dispersed plants were 3 and 14 weeks suggesting that even late-dispersing plants have strong potential for longer distance dispersal of seeds. Seeds were commonly retained in plants for distances of 200 to 400 m and one still had seed in it after traveling over 1 km. Seed dispersal with distance seems linear, though exponential decay may better represent extreme dispersal events. Both models substantially overpredicted dispersal distances for field data collected during a drought year in the presence of biocontrol insects. This research has substantially increased knowledge of the dispersal of this plant and has highlighted future research needs.
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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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    ItemOpen Access
    Litter reduction by prescribed burning can extend downy brome control
    (Colorado State University. Libraries, 2014) Kessler, Kallie C., author; Beck, K. George, advisor; Nissen, Scott J., committee member; Meiman, Paul J., committee member
    Downy brome (Bromus tectorum L.) is a highly successful invasive species primarily because it fills an open niche in native plant communities. It also produces large amounts of litter over time. We hypothesized that removing accumulated litter with a prescribed burn before applying herbicides would improve herbicide efficacy, extending the duration of control. In January 2012, two downy brome infested sites were burned. In March 2012, post-emergent applications of glyphosate, imazapic, and tebuthiuron were made in a split-plot design. Aboveground biomass was collected at 6, 18 and 27 months after treatment (MAT) to evaluate treatment effects. In non-burned areas, all herbicide treatments were similar to the control 27 MAT; however, burning combined with imazapic or tebuthiuron reduced downy brome biomass 27 MAT by 81% ± 4.6 SE and 84% ± 19.3 SE, respectively. Remnant species responded positively to burning and herbicide treatments. Native cool season grass biomass increased after burning while native warm season grass biomass increased following tebuthiuron treatments. The impact of litter on imazapic and tebuthiuron availability was also evaluated. Herbicide interception increased in a linear relationship with increasing litter. For every 50 g•m-2 increase in litter there was a 7% increase in the amount of herbicide intercepted, meaning that 75% of the applied herbicide was intercepted by 360 g•m-2 of litter. A simulated rainfall event of 5 mm, 7 days after application, removed a significant amount of herbicide. This indicates that at sites with surface litter, timely precipitation could be critical for herbicide efficacy; however, when burning was used to remove litter and was followed by herbicides with residual soil activity, downy brome control was extended. Due to downy brome's relatively short seed viability in the soil, extending herbicide efficacy to several years could help to reduce the soil seed bank.