Publications

A 60-hour release of water at 1,203 cubic meters per second (m3/s) from Glen Canyon Dam in March 2008 provided an opportunity to analyze channel-margin response at discharge levels above the normal, diurnally fluctuating releases for hydropower plant operations. We compare measurements at sandbars and associated campsites along the mainstem Colorado River, downstream from Glen Canyon Dam...

Riparian plant communities exhibit various levels of diversity and richness. These communities are affected by flooding and are vulnerable to colonization by nonnative species. Since 1996, a series of three high-flow experiments (HFE), or water releases designed to mimic natural seasonal flooding, have been conducted at Glen Canyon Dam, Ariz., primarily to determine the effectiveness of...

Species invasions are often associated with large-scale human alteration of ecosystems. One classic example is the increasing dominance of non-native taxa below and above dams on large rivers. These dams substantially alter the physical template of river ecosystems, and exotic taxa often proliferate with potentially large impacts on coexisting taxa and ecosystem processes. Here we...

Riparian areas of flood plains typically provide a mosaic of productive habitats (Stanford and others, 2005; Latterell and others, 2006) capable of supporting many wildlife species, particularly in the arid and semiarid Western United States. The establishment of nonnative invasive plants can alter riparian habitat by inhibiting native plant recruitment and by increasing the risk of...

The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races) can advance ecological research efforts by determining connectivity between the non-breeding and breeding grounds for migrant species, identifying the origin of migrants, and helping to refine boundaries between subspecies or geographic races. Multiple methods are available to identify...

Long-term monitoring in national parks is essential to meet National Park Service and other important public goals. Terrestrial mammals are often proposed for monitoring because large mammals are of interest to visitors and small mammals are important as prey. However, traditional monitoring strategies for mammals are often too expensive and complex to sustain for long periods...

The completion of Glen Canyon Dam in 1963 drastically altered the downstream flow regime and resulted in more than a 90 percent reduction of sand supply to the Colorado River in Grand Canyon National Park. Sandbars that were maintained by annual floods and a large sediment supply are now fewer in number and smaller in area and volume. Efforts to maintain sandbars in the current era of...

Biological soil crusts (biocrusts) are an integral part of the soil system in arid regions worldwide, stabilizing soil surfaces, aiding vascular plant establishment, and are significant sources of ecosystem nitrogen and carbon. Hydration and temperature primarily control ecosystem CO2 flux in these systems. Using constructed mesocosms for incubations under controlled laboratory...

Biological soil crusts (biocrusts) cover up to 60–70% of the soil surface in grasslands rehabilitated during the "Grain for Green" project implemented in the hilly Loess Plateau region in 1999. As biocrusts fix nitrogen (N), they are an important part of restoring soil fertility. We measured nitrogenase activity (NA) in biocrusts from sites rehabilitated at six different time periods to...

Peniocereus striatus (Brandegee) Buxb. (Cactaceae) is an endemic Sonoran Desert cactus that reaches its northern range limit in southwestern Arizona. One U.S. population occupies a small area of Organ Pipe Cactus National Monument near the U.S./Mexico international boundary, which has been monitored since 1939. An extensive survey conducted in 2002, covering 177 ha, resulted in the...

Climate models predict precipitation changes for much of the humid tropics, yet few studies have investigated the potential consequences of drought on soil carbon (C) cycling in this important biome. In wet tropical forests, drought could stimulate soil respiration via overall reductions in soil anoxia, but previous research suggests that litter decomposition is positively correlated...

We investigated the phylogeography of the closely related relict leopard frog Rana onca (=Lithobates onca) and lowland leopard frog Rana yavapaiensis (=Lithobates yavapaiensis) – two declining anurans from the warm‐desert regions of south‐western North America. We used sequence data from mitochondrial DNA (mtDNA) to assess 276 individuals representing 30 sites from across current...