Matching Items (6)
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- All Subjects: desert
- All Subjects: Stream Ecology
- All Subjects: verde river
- Creators: Stromberg, Juliet C.
Description
The explicit role of soil organisms in shaping soil health, rates of pedogenesis, and resistance to erosion has only just recently begun to be explored in the last century. However, much of the research regarding soil biota and soil processes is centered on maintaining soil fertility (e.g., plant nutrient availability) and soil structure in mesic- and agro- ecosystems. Despite the empirical and theoretical strides made in soil ecology over the last few decades, questions regarding ecosystem function and soil processes remain, especially for arid areas. Arid areas have unique ecosystem biogeochemistry, decomposition processes, and soil microbial responses to moisture inputs that deviate from predictions derived using data generated in more mesic systems. For example, current paradigm predicts that soil microbes will respond positively to increasing moisture inputs in a water-limited environment, yet data collected in arid regions are not congruent with this hypothesis. The influence of abiotic factors on litter decomposition rates (e.g., photodegradation), litter quality and availability, soil moisture pulse size, and resulting feedbacks on detrital food web structure must be explicitly considered for advancing our understanding of arid land ecology. However, empirical data coupling arid belowground food webs and ecosystem processes are lacking. My dissertation explores the resource controls (soil organic matter and soil moisture) on food web network structure, size, and presence/absence of expected belowground trophic groups across a variety of sites in Arizona.
ContributorsWyant, Karl Arthur (Author) / Sabo, John L (Thesis advisor) / Elser, James J (Committee member) / Childers, Daniel L. (Committee member) / Hall, Sharon J (Committee member) / Stromberg, Juliet C. (Committee member) / Arizona State University (Publisher)
Created2014
Description
In riparian ecosystems, reptiles and amphibians are good indicators of environmental conditions. Herpetofauna have been linked to specific microhabitat characteristics, microclimates, and water resources in riparian forests. My objective was to relate herpetofauna abundance to changes in riparian habitat along the Virgin River caused by the Tamarix biological control agent, Diorhabda carinulata, and riparian restoration.
During 2013 and 2014, vegetation and herpetofauna were monitored at 21 riparian locations along the Virgin River via trapping and visual encounter surveys. Study sites were divided into four stand types based on density and percent cover of dominant trees (Tamarix, Prosopis, Populus, and Salix) and presence of restoration activities: Tam, Tam-Pros, Tam-Pop/Sal, and Restored Tam-Pop/Sal. Restoration activities consisted of mechanical removal of non-native trees, transplanting native trees, and introduction of water flow. All sites were affected by biological control. I predicted that herpetofauna abundance would vary between stand types and that herpetofauna abundance would be greatest in Restored Tam-Pop/Sal sites due to increased habitat openness and variation following restoration efforts.
Results from trapping indicated that Restored Tam-Pop/Sal sites had three times more total lizard and eight times more Sceloporus uniformis captures than other stand types. Anaxyrus woodhousii abundance was greatest in Tam-Pop/Sal and Restored Tam-Pop/Sal sites. Visual encounter surveys indicated that herpetofauna abundance was greatest in the Restored Tam-Pop/Sal site compared to the adjacent Unrestored Tam-Pop/Sal site. Habitat variables were reduced to six components using a principle component analysis and significant differences were detected among stand types. Restored Tam-Pop/Sal sites were most similar to Tam-Pop/Sal sites. S. uniformis were positively associated with large woody debris and high densities of Populus, Salix, and large diameter Prosopis.
Restored Tam-Pop/Sal sites likely supported higher abundances of herpetofauna, as these areas exhibited greater habitat heterogeneity. Restoration activities created a mosaic habitat by reducing canopy cover and increasing native tree density and surface water. Natural resource managers should consider implementing additional restoration efforts following biological control when attempting to restore riparian areas dominated by Tamarix and other non-native trees.
During 2013 and 2014, vegetation and herpetofauna were monitored at 21 riparian locations along the Virgin River via trapping and visual encounter surveys. Study sites were divided into four stand types based on density and percent cover of dominant trees (Tamarix, Prosopis, Populus, and Salix) and presence of restoration activities: Tam, Tam-Pros, Tam-Pop/Sal, and Restored Tam-Pop/Sal. Restoration activities consisted of mechanical removal of non-native trees, transplanting native trees, and introduction of water flow. All sites were affected by biological control. I predicted that herpetofauna abundance would vary between stand types and that herpetofauna abundance would be greatest in Restored Tam-Pop/Sal sites due to increased habitat openness and variation following restoration efforts.
Results from trapping indicated that Restored Tam-Pop/Sal sites had three times more total lizard and eight times more Sceloporus uniformis captures than other stand types. Anaxyrus woodhousii abundance was greatest in Tam-Pop/Sal and Restored Tam-Pop/Sal sites. Visual encounter surveys indicated that herpetofauna abundance was greatest in the Restored Tam-Pop/Sal site compared to the adjacent Unrestored Tam-Pop/Sal site. Habitat variables were reduced to six components using a principle component analysis and significant differences were detected among stand types. Restored Tam-Pop/Sal sites were most similar to Tam-Pop/Sal sites. S. uniformis were positively associated with large woody debris and high densities of Populus, Salix, and large diameter Prosopis.
Restored Tam-Pop/Sal sites likely supported higher abundances of herpetofauna, as these areas exhibited greater habitat heterogeneity. Restoration activities created a mosaic habitat by reducing canopy cover and increasing native tree density and surface water. Natural resource managers should consider implementing additional restoration efforts following biological control when attempting to restore riparian areas dominated by Tamarix and other non-native trees.
ContributorsMosher, Kent (Author) / Bateman, Heather L (Thesis advisor) / Stromberg, Juliet C. (Committee member) / Miller, William H. (Committee member) / Arizona State University (Publisher)
Created2014
Description
Climate change has the potential to affect vegetation via changes in temperature and precipitation. In the semi-arid southwestern United States, heightened temperatures will likely lead to accelerated groundwater pumping to meet human needs, and altered storm patterns may lead to changes in flood regimes. All of these hydrologic changes have the potential to alter riparian vegetation. This research, consisting of two papers, examines relationships between hydrology and riparian vegetation along the Verde River in central Arizona, from applied and theoretical perspectives. One paper investigates how dominance of tree and shrub species and cover of certain functional groups change along hydrologic gradients. The other paper uses the Verde River flora along with that river's flood and moisture gradients to answer the question of whether functional groups can be defined universally. Drying of the Verde River would lead to a shift from cottonwood-willow streamside forest to more drought adapted desert willow or saltcedar, a decline in streamside marsh species, and decreased species richness. Effects drying will have on one dominant forest tree, velvet ash, is unclear. Increase in the frequency of large floods would potentially increase forest density and decrease average tree age and diameter. Correlations between functional traits of Verde River plants and hydrologic gradients are consistent with "leaf economics," or the axis of resource capture, use, and release, as the primary strategic trade-off for plants. This corresponds to the competitor-stress tolerator gradient in Grime's life history strategy theory. Plant height was also a strong indicator of hydrologic condition, though it is not clear from the literature if plant height is independent enough of leaf characteristics on a global scale to be considered a second axis. Though the ecohydrologic relationships are approached from different perspectives, the results of the two papers are consistent if interpreted together. The species that are currently dominant in the near-channel Verde River floodplain are tall, broad-leaf trees, and the species that are predicted to become more dominant in the case of the river drying are shorter trees or shrubs with smaller leaves. These results have implications for river and water management, as well as theoretical ecology.
ContributorsHazelton, Andrea Florence (Author) / Stromberg, Juliet C. (Thesis advisor) / Schmeeckle, Mark W (Committee member) / Franklin, Janet (Committee member) / Arizona State University (Publisher)
Created2011
Description
Stream flow permanence plays a critical role in determining floristic composition, abundance, and diversity in the Sonoran Desert, but questions remain about the effects of stream flow permanence on butterfly composition, abundance, and diversity. Understanding the effects of flow permanence on butterflies and relevant subsets of butterflies (such as butterflies whose host plants are present) and comparing them to these same effects on plants and relevant subsets of plants (such as butterfly nectar plants and larval host plants) provided insight into pollinator and riparian conservation and restoration.
I surveyed four Sonoran desert stream sites, and found significant relationships between flow permanence and plant and butterfly species richness and abundance, as well as strong relationships between plant and butterfly abundance and between plant and butterfly species richness. Most notably, my results pointed to hosted butterflies as a break-out category of butterflies which may more clearly delineate ecological relationships between butterfly and plant abundance and diversity along Sonoran Desert streams; this can inform conservation decisions. Managing for hosted (resident) butterflies will necessarily entail managing for the presence of surface water, nectar forage, varying levels of canopy cover, and plant, nectar plant, and host plant diversity since the relationships between hosted butterfly species richness and/or abundance and all of these variables were significant, both statistically and ecologically.
I surveyed four Sonoran desert stream sites, and found significant relationships between flow permanence and plant and butterfly species richness and abundance, as well as strong relationships between plant and butterfly abundance and between plant and butterfly species richness. Most notably, my results pointed to hosted butterflies as a break-out category of butterflies which may more clearly delineate ecological relationships between butterfly and plant abundance and diversity along Sonoran Desert streams; this can inform conservation decisions. Managing for hosted (resident) butterflies will necessarily entail managing for the presence of surface water, nectar forage, varying levels of canopy cover, and plant, nectar plant, and host plant diversity since the relationships between hosted butterfly species richness and/or abundance and all of these variables were significant, both statistically and ecologically.
ContributorsButler, Lane (Author) / Stromberg, Juliet C. (Thesis advisor) / Makings, Elizabeth (Committee member) / Pearson, David L (Committee member) / Boggess, May (Committee member) / Buchmann, Stephen (Committee member) / Arizona State University (Publisher)
Created2015
Description
As an industrial society, humans have increasingly separated agricultural processes from natural ecosystems. Many areas of the Southwestern US, however, maintain traditional practices that link agricultural systems to the natural environment. One such practice, diverting river water into fields via earthen irrigation canals, allows ditch water to recharge groundwater and riparian vegetation to prosper along canal banks. As there is growing interest in managing landscapes for multiple ecosystem services, this study was undertaken to determine if irrigation canals function as an extension of the riparian corridor. I was specifically interested in determining if the processes within semi-arid streams that drive riparian plant community structure are manifested in earthen irrigation ditches. I examined herbaceous and woody vegetation along the middle Verde River, AZ, USA and three adjacent irrigation ditches across six months. I also collected sieved hydrochores--seeds dispersing through water--within ditches and the river twelve times. Results indicate that ditch vegetation was similar to streamside river vegetation in abundance (cover and basal area) due to surface water availability but more diverse than river streamside vegetation due to high heterogeneity. Compositionally, herbaceous vegetation along the ditch was most similar to the river banks, while low disturbance fostered woody vegetation along the ditches similar to high floodplain and river terrace vegetation. Hydrochore richness and abundance within the river was dependent on seasonality and stream discharge, but these relationships were dampened in the ditches. Species-specific strategies of hydrochory, however, did emerge in both systems. Strategies include pulse species, which disperse via hydrochory in strict accordance with their restricted dispersal windows, constant species, which are year round hydrochores, and combination species, which show characteristics of both. There was high overlap in the composition of hydrochores in the two systems, with obligate wetland species abundant in both. Upland species were more seasonally constant and abundant in the ditch water than the river. The consistency of river processes and similarity of vegetation suggest that earthen irrigation ditches do function as an extension of the riparian corridor. Thus, these man-made irrigation ditches should be considered by stakeholders for their multiple ecosystem services.
ContributorsBetsch, Jacqueline Michelle (Author) / Stromberg, Juliet C. (Thesis advisor) / Hall, Sharon J (Committee member) / Merritt, David M. (Committee member) / Arizona State University (Publisher)
Created2010
Description
River and riparian areas are important foraging habitat for insectivorous bats. Numerous studies have shown that aquatic insects provide an important trophic resource to terrestrial consumers, including bats, and are key in regulating population size and species interactions in terrestrial food webs. Yet these studies have generally ignored how structural characteristics of the riverine landscape influence trophic resource availability or how terrestrial consumers respond to ensuing spatial and temporal patterns of trophic resources. Moreover, few studies have examined linkages between a stream's hydrologic regime and the timing and magnitude of aquatic insect availability. The main objective of my dissertation is to understand the causes of bat distributions in space and time. Specifically, I examine how trophic resource availability, structural components of riverine landscapes (channel confinement and riparian vegetation structure), and hydrologic regimes (flow permanence and timing of floods) mediate spatial and temporal patterns in bat activity. First, I show that river channel confinement determines bat activity along a river's longitudinal axis (directly above the river), while trophic resources appear to have stronger effects across a river's lateral (with distance from the river) axis. Second, I show that flow intermittency affects bat foraging activity indirectly via its effects on trophic resource availability. Seasonal river drying appears to have complex effects on bat foraging activity, initially causing imperfect tracking by consumers of localized concentrations of resources but later resulting in disappearance of both insects and bats after complete river drying. Third, I show that resource tracking by bats varies among streams with contrasting patterns of trophic resource availability and this variation appears to be in response to differences in the timing of aquatic insect emergence, duration and magnitude of emergence, and adult body size of emergent aquatic insects. Finally, I show that aquatic insects directly influence bat activity along a desert stream and that riparian vegetation composition affects bat activity, but only indirectly, via effects on aquatic insect availability. Overall, my results show river channel confinement, riparian vegetation structure, flow permanence, and the timing of floods influence spatial and temporal patterns in bat distributions; but these effects are indirect by influencing the ability of bats to track trophic resources in space and time.
ContributorsHagen, Elizabeth M (Author) / Sabo, John L (Thesis advisor) / Fisher, Stuart G. (Committee member) / Grimm, Nancy (Committee member) / Schmeeckle, Mark W (Committee member) / Stromberg, Juliet C. (Committee member) / Arizona State University (Publisher)
Created2010