Matching Items (3)
Description
The introduction of livestock to the vast majority of public lands may be used to simulate the conditions provided by herbivorous grazers in the past, however little data has been collected on the effects of livestock grazing in Sonoran desert habitats. Vegetative species that are characteristic of the Arizona Upland subdivision of the Sonoran desert did not evolve with extensive grazing by large ungulate populations, and therefore the response to livestock grazing is of particular interest. Four historic Parker 3-step clusters in south-central Arizona were sampled in three cohorts between 1953 and 2016 to interpret changes in rangeland health using soil coverage data, species richness and frequency, and long-term photo point comparisons. Cattle grazing was active across the allotment until 1984, allowing approximately 30 years of rest before the third and final cohort was measured. Over the entirety of this study, there was a 66.67% increase in perennial basal hits, a 56.29% increase in rock, and a 44.55% increase of forage basal hits. Decreases were seen in litter (-57.69%) and bare soil hits (-8.76%). Cluster 3 consistently had a lower percent of cover across all classes of vegetation in the 2014 cohort
(-81.61%), however the average percent of cover increased by 63.16% (40 hits) across the allotment. Available species richness data from 1971 and 2014 cohorts indicates a 112% increase in unique species; however, species richness increases in the 2014 cohort are largely based on recruitment of non-palatable species (71%). Although the status of some species were undetermined, all individuals identified to species in the invader class (non-palatable) were determined to be native to the study site. Perennial grass frequency became less abundant over the duration of this study, while growth was predominantly observed in shrubs. Increases in species frequency was detected on two of the four clusters measured in the 2014 cohort; the growth was primarily observed in jojoba (Simmondsia chinensis), oak (Quercus spp.), and catclaw acacia (Senegalia greggii) in C4, and hopseed bush (Dodonaea viscosa) in C2.
(-81.61%), however the average percent of cover increased by 63.16% (40 hits) across the allotment. Available species richness data from 1971 and 2014 cohorts indicates a 112% increase in unique species; however, species richness increases in the 2014 cohort are largely based on recruitment of non-palatable species (71%). Although the status of some species were undetermined, all individuals identified to species in the invader class (non-palatable) were determined to be native to the study site. Perennial grass frequency became less abundant over the duration of this study, while growth was predominantly observed in shrubs. Increases in species frequency was detected on two of the four clusters measured in the 2014 cohort; the growth was primarily observed in jojoba (Simmondsia chinensis), oak (Quercus spp.), and catclaw acacia (Senegalia greggii) in C4, and hopseed bush (Dodonaea viscosa) in C2.
ContributorsDunn, Kellie Ann (Author) / Alford, Eddie (Thesis advisor) / Cunningham, Stanley (Committee member) / Stutz, Jean (Committee member) / Arizona State University (Publisher)
Created2018
Description
Rangelands are an extensive land cover type that cover about 40% of earth’s ice-free surface, expanding into many biomes. Moreover, managing rangelands is crucial for long-term sustainability of the vital ecosystem services they provide including carbon (C) storage via soil organic carbon (SOC) and animal agriculture. Arid rangelands are particularly susceptible to dramatic shifts in vegetation cover, physical and chemical soil properties, and erosion due to grazing pressure. Many studies have documented these effects, but studies focusing on grazing impacts on soil properties, namely SOC, are less common. Furthermore, studies testing effects of different levels of grazing intensities on SOC pools and distribution yield mixed results with little alignment. The primary objective of this thesis was to have a better understanding of the role of grazing intensity on arid rangeland soil C storage. I conducted research in long established pastures in Jornada Experimental Range (JER). I established a 1500m transect in three pastures originating at water points and analyzed vegetation cover and SOC on points along these transects to see the effect of grazing on C storage on a grazing gradient. I used the line-point intercept method to measure and categorize vegetation into grass, bare, and shrub. Since soil adjacent to each of these three cover types will likely contain differing SOC content, I then used this vegetation cover data to calculate the contribution of each cover type to SOC. I found shrub cover and total vegetation cover to decrease, while grass and bare cover increased with decreasing proximity to the water source. I found areal (g/m2) and percent (go SOC to be highest in the first 200m of the transects when accounting for the contribution of the three vegetation cover types. I concluded that SOC is being redistributed toward the water source via foraging and defecation and foraging, due to a negative trend of both total vegetation cover and percent SOC (g/g). With the decreasing trends of vegetation cover and SOC further from pasture water sources, my thesis research contributes to the understanding of storage and distribution of SOC stocks in arid rangelands.
ContributorsBoydston, Aaron (Author) / Sala, Osvaldo (Thesis advisor) / Throop, Heather (Committee member) / Hall, Sharon (Committee member) / Arizona State University (Publisher)
Created2018
Description
Urbanization and woody plant encroachment, with subsequent brush management, are two significant land cover changes that are represented in the southwestern United States. Urban areas continue to grow, and rangelands are undergoing vegetation conversions, either purposely through various rangeland management techniques, or by accident, through inadvertent effects of climate and management. This thesis investigates how areas undergoing land cover conversions in a semiarid region, through urbanization or rangeland management, influences energy, water and carbon fluxes. Specifically, the following scientific questions are addressed: (1) what is the impact of different urban land cover types in Phoenix, AZ on energy and water fluxes?, (2) how does the land cover heterogeneity influence energy, water, and carbon fluxes in a semiarid rangeland undergoing woody plant encroachment?, and (3) what is the impact of brush management on energy, water, and carbon fluxes?
The eddy covariance technique is well established to measure energy, water, and carbon fluxes and is used to quantify and compare flux measurements over different land surfaces. Results reveal that in an urban setting, paved surfaces exhibit the largest sensible and lowest latent heat fluxes in an urban environment, while a mesic landscape exhibits the largest latent heat fluxes, due to heavy irrigation. Irrigation impacts flux sensitivity to precipitation input, where latent heat fluxes increase with precipitation in xeric and parking lot landscapes, but do not impact the mesic system. In a semiarid managed rangeland, past management strategies and disturbance histories impact vegetation distribution, particularly the distribution of mesquite trees. At the site with less mesquite coverage, evapotranspiration (ET) is greater, due to greater grass cover. Both sites are generally net sinks of CO2, which is largely dependent on moisture availability, while the site with greater mesquite coverage has more respiration and generally greater gross ecosystem production (GEP). Initial impacts of brush management reveal ET and GEP decrease, due to the absence of mesquite trees. However the impact appears to be minimal by the end of the productive season. Overall, this dissertation advances the understanding of land cover change impacts on surface energy, water, and carbon fluxes in semiarid ecosystems.
The eddy covariance technique is well established to measure energy, water, and carbon fluxes and is used to quantify and compare flux measurements over different land surfaces. Results reveal that in an urban setting, paved surfaces exhibit the largest sensible and lowest latent heat fluxes in an urban environment, while a mesic landscape exhibits the largest latent heat fluxes, due to heavy irrigation. Irrigation impacts flux sensitivity to precipitation input, where latent heat fluxes increase with precipitation in xeric and parking lot landscapes, but do not impact the mesic system. In a semiarid managed rangeland, past management strategies and disturbance histories impact vegetation distribution, particularly the distribution of mesquite trees. At the site with less mesquite coverage, evapotranspiration (ET) is greater, due to greater grass cover. Both sites are generally net sinks of CO2, which is largely dependent on moisture availability, while the site with greater mesquite coverage has more respiration and generally greater gross ecosystem production (GEP). Initial impacts of brush management reveal ET and GEP decrease, due to the absence of mesquite trees. However the impact appears to be minimal by the end of the productive season. Overall, this dissertation advances the understanding of land cover change impacts on surface energy, water, and carbon fluxes in semiarid ecosystems.
ContributorsTempleton, Nicole Pierini (Author) / Vivoni, Enrique R (Thesis advisor) / Archer, Steven R (Committee member) / Mascaro, Giuseppe (Committee member) / Scott, Russell L. (Committee member) / Wang, Zhi-Hua (Committee member) / Arizona State University (Publisher)
Created2017