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Throughout the Southwest, complex geology and physiography concomitant with climatic variability contribute to diverse stream hydrogeomorphologies. Many riparian plant species store their seeds in soil seed banks, and germinate in response to moisture pulses, but the climatic controls of this response are poorly understood. To better understand the ecological implications of a changing climate on riparian plant communities, I investigated seed bank responses to seasonal temperature patterns and to stream hydrogeomorphic type. I asked the following questions: Are there distinct suites of warm and cool temperature germinating species associated with Southwestern streams; how do they differ between riparian and terrestrial zones, and between ephemeral and perennial streams? How does alpha diversity of the soil seed bank differ between streams with ephemeral, intermittent, and perennial flow, and between montane and basin streams? Do streams with greater elevational change have higher riparian zone seed bank beta-diversity? Does nestedness or turnover contribute more to within stream beta-diversity?
I collected soil samples from the riparian and terrestrial zones of 21 sites, placing them in growth chambers at one of two temperature regimes, and monitoring emergence of seedlings for 12 weeks. Results showed an approximately equal number of warm and cool specialists in both riparian and terrestrials zones; generalists also were abundant, particularly in the riparian zone. The number of temperature specialists and generalists in the riparian zones did not differ significantly between perennial headwater and ephemeral stream types. In montane streams, alpha diversity of the soil seed bank was highest for ephemeral reaches; in basin streams the intermittent and perennial reaches had higher diversity. Spatial turnover was primarily responsible for within stream beta-diversity—reaches had different species assemblages. The large portion of temperature specialists found in riparian seed banks indicates that even with available moisture riparian zone plant community composition will likely be impacted by changing temperatures. However, the presence of so many temperature generalists in the riparian zones suggests that some component of the seed bank is adapted to variable conditions and might offer resilience in a changing climate. Study results confirm the importance of conserving multiple hydrogeomorphic reach types because they support unique species assemblages.
I collected soil samples from the riparian and terrestrial zones of 21 sites, placing them in growth chambers at one of two temperature regimes, and monitoring emergence of seedlings for 12 weeks. Results showed an approximately equal number of warm and cool specialists in both riparian and terrestrials zones; generalists also were abundant, particularly in the riparian zone. The number of temperature specialists and generalists in the riparian zones did not differ significantly between perennial headwater and ephemeral stream types. In montane streams, alpha diversity of the soil seed bank was highest for ephemeral reaches; in basin streams the intermittent and perennial reaches had higher diversity. Spatial turnover was primarily responsible for within stream beta-diversity—reaches had different species assemblages. The large portion of temperature specialists found in riparian seed banks indicates that even with available moisture riparian zone plant community composition will likely be impacted by changing temperatures. However, the presence of so many temperature generalists in the riparian zones suggests that some component of the seed bank is adapted to variable conditions and might offer resilience in a changing climate. Study results confirm the importance of conserving multiple hydrogeomorphic reach types because they support unique species assemblages.
ContributorsSetaro, Danika (Author) / Stromberg, Juliet (Thesis advisor) / Franklin, Janet (Committee member) / Makings, Elizabeth (Committee member) / Arizona State University (Publisher)
Created2016
Description
Die-off of screwbean mesquite (Prosopis pubescens), a species native to the American Southwest, has been documented regionally within the last decade. Historical causes for episodic mortality of the more widely distributed velvet mesquite (Prosopis velutina) and honey mesquite (Prosopis glandulosa) include water table declines and flood scour. Causes of the recent die-offs of P. pubescens have received little study. Numerous riparian restoration projects have been implemented regionally that include screwbean mesquite. Restoration propagules from foreign sources can introduce diseases, and low genetic diversity plantings may allow for disease irruptions. I asked: 1) Are die-offs associated with a particular age class, 2) Is die-off suggestive of a pathogen or related to specific environmental stressors, 3) Are mortality influences and outcomes the same between restoration and local populations, 4) Are particular land uses and management associated with die-off, and 5) Are populations rebounding or keeping pace with mortality?
I documented the screwbean mesquite population status at rivers and wetlands in Arizona with varying levels of restoration. I used logistic regression and Pearson correlation analysis to explore mortality response to site factors and disease related variables. I compared mortality response and disease severity between local and restoration populations.
Biotic damage surfaced as the most important factor in statistical analyses, suggesting that mortality was caused by a pathogen. Mortality was greatest for young size classes (3 to 14 cm), and biotic damage was higher for individuals at infrequently flooded areas. Strong differences were not found between local and restoration populations – however restoration populations were less stressed and had lower biotic damage. Novel urban and restored sites may provide refuge as site conditions at other locations deteriorate. A culmination of past water diversion, development and land use may be surfacing, rendering riparian species vulnerable to diseases and triggering such events as region-wide die-off.
I documented the screwbean mesquite population status at rivers and wetlands in Arizona with varying levels of restoration. I used logistic regression and Pearson correlation analysis to explore mortality response to site factors and disease related variables. I compared mortality response and disease severity between local and restoration populations.
Biotic damage surfaced as the most important factor in statistical analyses, suggesting that mortality was caused by a pathogen. Mortality was greatest for young size classes (3 to 14 cm), and biotic damage was higher for individuals at infrequently flooded areas. Strong differences were not found between local and restoration populations – however restoration populations were less stressed and had lower biotic damage. Novel urban and restored sites may provide refuge as site conditions at other locations deteriorate. A culmination of past water diversion, development and land use may be surfacing, rendering riparian species vulnerable to diseases and triggering such events as region-wide die-off.
ContributorsMadera, Robert (Author) / Stromberg, Juliet (Thesis advisor) / Stutz, Jean (Committee member) / McCue, Kimberlie (Committee member) / Arizona State University (Publisher)
Created2016