Theses, Dissertations and Student Research Papers (Rangeland Ecology and Management & Rangeland Resources)

Physiological impacts of groundwater and surface water application on desert graminoids of different geographic origin

2013-05-16T21:34:10Z

Physiological impacts of groundwater and surface water application on desert graminoids of different geographic origin Abdallah, Mohamed (Mohamed Ahmed B.) Desert plant communities are among the most sensitive to changes in soil water conditions. In areas with shallow aquifers, it is important to understand both the effects of groundwater alterations on vegetation and how changes in surface-soil water affect plant water uptake. Studies in arid environments have evaluated the effect of groundwater variation and simulated precipitation on plant production and vegetation condition but it is not clear if plants respond equally to the availability of surface water or groundwater. This study was conducted in a greenhouse to evaluate growth and physiology of three desert graminoids (Distichlis spicata, Leymus triticoides, and Juncus arcticus) as affected by surface water availability (mimicking precipitation) or subsurface water availability (mimicking groundwater). The species of study are amply distributed in wetlands and open rangelands of western USA and were collected from two sources of ecological distribution: an area near Bishop, California, and an area near Burns, Oregon. The Bishop, California area has a characteristic shallow aquifer and plants in this area are considered somewhat dependent on groundwater. The Burns, Oregon, area sustains the same species but in a variety of soil moisture conditions. We had two general hypotheses for this study: 1) that the use of surface water is favored over groundwater and 2) that there are ecotypic differences in the response of the species to water availability. The first hypothesis was partially supported by the results of the study, but variability existed among species. However, when all species had equal access to both surface soil water and groundwater plants tended to preferentially use surface water. The second hypothesis was clearly supported by our results. Although the mechanism is not clear, it is possible that an area with periodic and predictable shallow groundwater underlying a dry or saline soil layer, such as the California site, might favor plant ecotypes with high proficiency in water acquisition by deeper roots. Knowledge of water use characteristics of vegetation is essential to provide management guidelines for areas where plants depend on both surface-soil water and groundwater. This study contributed to that knowledge. Further studies on ecotypic variation and an expansion to different species that inhabit areas with shallow aquifers are recommended. Graduation date: 2013

Community analysis of the Wyoming big sagebrush alliance and functional role of Wyoming big sagebrush

2012-05-08T15:56:07Z

Community analysis of the Wyoming big sagebrush alliance and functional role of Wyoming big sagebrush Davies, Kirk W. This study consisted of two research projects in the Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh) alliance, the most extensive of the big sagebrush complex in the Intermountain West. In the first project, we intensively sampled 107 relatively undisturbed, late seral Wyoming big sagebrush sites across the High Desert, Humboldt, and western Snake River Ecological Provinces to investigate vegetation heterogeneity and the relationship of environmental factors with vegetation characteristics. Vegetation characteristics were highly variable across the region. Perennial grass and total herbaceous cover varied more than six and sevenfold, respectively between minimum and maximum values. Sagebrush cover averaged 12%, but ranged between 3 and 25%. With the exception of perennial grass cover (p<0.0001, r²=0.52), limited variability in other vegetation characteristics was explained by environmental variables. In the second project, we investigated the functional role of Wyoming big sagebrush by using undisturbed and sagebrush removed (with burning) treatments and comparing vegetation and microsite characteristics under (subcanopy) to between sagebrush canopy (interspace) zones. Wyoming big sagebrush influenced associated vegetation and microsites. On sites receiving high incidental radiation, perennial grass and total herbaceous cover and density were greater in the subcanopy than interspace zones (p<0.05). On north aspects, these differences were not as pronounced suggesting sagebrush's influence on associated vegetation is site dependent. Temperature extremes were mediated and soil water content was greater in the subcanopy than interspace zones during the growing season. Results indicated that the subcanopy zone can be a more favorable environment to herbaceous vegetation than the interspace zone. Wyoming big sagebrush is important to community resource capture and use. Plots with sagebrush had greater soil water content at the start of the growing season and produced more total biomass compared to where sagebrush had been removed in both post-fire years (p<0.05). However, higher Thurber's needlegrass photosynthetic rates and greater herbaceous cover and production where sagebrush had been removed suggested that more resources were available to herbaceous vegetation in the absence of sagebrush. Graduation date: 2006

Detecting medusahead (Taeniatherum caput-medusae (L.) Nevski) using high frequency, sequential, globally positioned digital images

2011-09-06T20:29:42Z

Detecting medusahead (Taeniatherum caput-medusae (L.) Nevski) using high frequency, sequential, globally positioned digital images Ndzeidze, Stephen Koghan Invasive plant species are expanding and transforming vegetative communities across Oregon and throughout the United States. Over the past three decades remote sensing, geographic information system (GIS), and Global Positioning System (GPS) technologies have been integrated to detect and map the distribution of noxious rangeland plants. This study developed low-cost protocols to detect and map Medusahead (Taeniatherum caput-medusae (L.) Nevski) weed infestations using GPS loggers to track aircraft/camera position, altitude, and bearing, as well as Aerial Image Positioning Tool software to geographically rectify and project each aerial image. We then mapped the extent of medusahead in target areas and evaluated patterns of infestation. Flying in a single engine fixed-wing aircraft, images were collected every five seconds, with a total of 10,362 images obtained. All of the aerial images were processed and, on average, 23.9 % of the area was classified as medusahead infested, with 76.1 % without infestation. Each image covered 215 ha (531 acres), with 60% overlap, at a cost of $ 0.54/km². Our study also employed mobile mapping technology to map medusahead on the ground by digitizing infestations using a laptop computer equipped with a GPS antenna and GIS software. Mobile mapping was also done from aircraft, but yielded coarser infestation maps, as the observation distance was greater. These maps covered the full study area. Aerial reconnaissance and mobile survey is cost effective, because thousands of digital images were collected, automatically positioned, and stored. Graduation date: 2012

Biomass production and water use of common plant species in Owens Valley, California, USA

2011-06-20T18:05:24Z

Biomass production and water use of common plant species in Owens Valley, California, USA Evans, Tracie L. This study evaluated biomass production, water-use efficiency (WUE), biomass allocation, and water use characteristics of common plant species in Owens Valley, California, USA. The species studied were the grasses Distichlis spicata, Leymus triticoides, and Sporobolus airoides, the forbs Glycyrrhiza lepidota, Juncus arcticus, and Salsola tragus (annual), the desert shrubs Artemisia tridentata, Atriplex confertifolia, and Ericameria nauseosa, and the riparian shrub Salix exigua. Plants of each species were established and grown in 2.4 m X 2.4 m plots in a common garden since 2005. Our first experiment was conducted in 2009 and 2010 and included four monthly summer water treatments: control (no additional water), low (1.3 cm), medium (2.6 cm) and high (3.9 cm). Biomass production and WUE (the amount of water that a plant uses to produce a unit of biomass) were lower in 2009 than in 2010. Water-use efficiency of grasses increased with increasing water application in 2009 but decreased with increasing water application in 2010. The difference between years was attributed to the difference in timing of natural precipitation with higher spring precipitation in 2010. Biomass production and WUE of desert shrubs were not significantly affected by water treatments. Water-use efficiency varied by species; some desert shrubs and the annual S. tragus were 13 times more efficient than the riparian S. exigua. Total standing crop and root-to-shoot ratio (RSR) varied by species, but not by watering treatments. Although in general desert shrubs had higher standing crop than herbaceous species, the grass S. airoides had the highest standing crop overall. Graminoids had much higher RSR (3 to 6) than the shrubs did (< 1). Our second experiment was conducted in 2010 using the experimental setting of the first experiment with the objective of determining soil water use and depth of soil water extraction by species. Three monthly watering treatments were applied during the summer months: low (1.3 cm), medium (2.6 cm), and high (3.9 cm). Plant water use was determined by calculating soil water depletion during irrigation cycles using time domain reflectometry (TDR) at two depths (0 - 25 cm and 0 - 50 cm) in vegetated plots. Evaporation was also obtained by water depletion on bare ground plots and subtracted from evapotranspiration to calculate water use. Water use varied by species; those with shallow, fibrous, and rhizomatous root systems such as J. arcticus and L. triticoides had higher water use than shrubs, including the riparian S. exigua. The ratio of deep water (25 - 50 cm) to shallow water (0 - 25 cm) use was 19 to 21 in desert shrubs and 1 to 2 in herbaceous species, indicating that shrubs may be more dependent on groundwater that shallow-rooted species such as grasses. In general, we observed large variability in biomass production, water-use efficiency, biomass allocation, and water-use characteristics among the typical plants of the Owens Valley, which should be considered in land and water management decisions. A potential increase in summer precipitation in the area might favor higher water utilization and higher production of shallow-rooted, high RSR plants such as grasses in detriment of desert shrubs. Graduation date: 2012