Treesearch

This dissertation explores the climate, ecology and hydrology of Chihuahuan Desert ecosystems in the context of global climate change. In coming decades, the southwestern United States is projected to experience greater temperature-driven aridity, possible small decreases in annual precipitation, and a later onset of summer monsoon rainfall. These changes may have profound consequences for ecological systems in the Chihuahuan Desert, which are intensely water-limited and respond to even small pulses of moisture availability. The first chapter (Chapter 2) compares change in the properties...

Within grasslands, precipitation, fire, nitrogen (N) addition, and extreme temperatures influence community composition and ecosystem function. The differential influences of these abiotic factors on Chihuahuan Desert grassland communities was examined within the Sevilleta National Wildlife Refuge, located in central New Mexico, U.S.A. Although fire is a natural disturbance in many grasslands, fire during drought temporarily increased forb cover and decreased grass cover for several years. The seasonal timing of fire was not important, rather community recovery was more influenced by the...

A recurrent challenge in the conservation of wide-ranging, imperiled species is understanding which habitats to protect and whether we are capable of restoring degraded landscapes. For Greater Sage-grouse (Centrocercus urophasianus), a species of conservation concern in the western United States, we approached this problem by developing multi-scale empirical models of occupancy in 211 randomly located plots within a 40 million ha portion of the species' range. We then used these models to predict sage-grouse habitat quality at 826 plots associated with 101 post-wildfire seeding projects...

Invasive annual grasses alter fire regimes in shrubland ecosystems of the western USA, threatening ecosystem function and fragmenting habitats necessary for shrub-obligate species such as greater sage-grouse. Post-fire stabilization and rehabilitation treatments have been administered to stabilize soils, reduce invasive species spread and restore or establish sustainable ecosystems in which native species are well represented. Long-term effectiveness of these treatments has rarely been evaluated.

Restoration of abandoned agricultural lands to create resilient ecosystems in arid and semi-arid ecosystems typically requires seeding or transplanting native species, improving plant-soil-water relations, and controlling invasive species. We asked if improving water relations via irrigation or surface mulch would result in negative tradeoffs between native species establishment and invasive species competition. We examined the effects of sprinkler irrigation and straw mulch on native seed mixtures planted in two consecutive years in an abandoned agricultural field in a cold desert...

In 2002, the Hayman Fire burned across 55 800 ha of Colorado Front Range P. ponderosa-P. menziesii forest. Also burned in the fire were 20 upland and five riparian plots within a 400-ha study area. These plots had been surveyed for understorey plant composition and cover 5-6 yrs prior. We re-measured all plots annually from 2003 to 2007, 1-5 yrs post-fire. Changes in the occurrence of common understorey plant species and in metrics of understorey plant richness and cover were analysed with regard to fire severity and time since fire using repeated measures ANOVA. Compositional changes were...

Anthropogenic changes in land use and cover (LULC) in stream catchments can alter the composition of riparian plant communities, which can affect ecosystem functions of riparian areas and streams from local to landscape scales.We conducted a study to determine if woody plant species composition and abundance along headwater streams were correlated with categorical and continuous LULC and environmental variables along an urban-to-rural gradient. These variables were calculated at different spatial scales (subcatchment level and within 0.5 and 1 km radii of plots) and used % impervious...

Cross-linked polyvinyl alcohol (PVA)–cellulose nanofibril (CNF) hybrid organic aerogels were prepared using an environmentally friendly freeze-drying process. The resulting PVA/CNF aerogel was rendered both superhydrophobic and superoleophilic after being treated with methyltrichlorosilane via a simple thermal chemical vapor deposition process. Successful silanization on the surface of the porous aerogel was confirmed by various techniques including scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS), Fourier transform infrared spectroscopy (FTIR), and contact angle...

Wood is perhaps the quintessential material used in most human cultures. In prehistoric times, it was employed, either directly or indirectly, to provide most human needs: warmth, shelter, and nearly all manner of tools suitable for procuring food, water and security (Beeckman, 2003). In modern times it continues to play important roles in human cultures (Radkau, 2012). Despite its ubiquity as a technological material, it is often a surprise to the general public, and even to other biologists, that xylaria, or collections of wood specimans, exist.

Ruffed grouse (Bonasa umbellus) are native upland game birds and a management indicator species (MIS) for aspen (Populus tremuloides) in the Black Hills National Forest (Black Hills). Our objective was to assess resource selection of male ruffed grouse to identify the most appropriate scale to manage for aspen and ruffed grouse in the Black Hills. During spring 2007 and 2008, we conducted drumming surveys throughout the central and northern Black Hills to locate used and unused sites from which we compared habitat characteristics at increasing spatial scales. Aspen with >70% overstory...