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Flow regulation has reduced the exchange of water, energy, and materials between rivers and floodplains, caused declines in native plant populations, and advanced the spread of nonnative plants. Naturalized flow regimes are regarded as a means to restore degraded riparian areas. We examined the effects of flood regime (short [SIFI] vs. long [LIFI] inter-flood interval) on plant community and soil inorganic nitrogen (N) dynamics in riparian forests dominated by native Populus deltoides var. wislizenii Eckenwalder (Rio Grande cottonwood) and nonnative Tamarix chinensis Lour. (salt cedar) along the regulated middle Rio Grande of New Mexico. The frequency of inundation (every 2–3 years) at SIFI sites better reflected...
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Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to...
We compared beaver (Castor canadensis) foraging patterns on Fremont cottonwood (Populus deltoides subsp. wislizenii) saplings and the probability of saplings being cut on a 10 km reach of the flow-regulated Green River and a 8.6 km reach of the free-flowing Yampa River in northwestern Colorado. We measured the abundance and density of cottonwood on each reach and followed the fates of individually marked saplings in three patches of cottonwood on the Yampa River and two patches on the Green River. Two natural floods on the Yampa River and one controlled flood on the Green River between May 1998 and November 1999 allowed us to assess the effect of flooding on beaver herbivory. Independent of beaver herbivory, flow...
Floodplain plant-herbivore-hydroperiod interactions have received little attention despite their potential as determinants of floodplain structure and functioning. We used five types of exclosures to differentially exclude small-, medium-, and large-sized mammals from accessing Fremont cottonwood (Populus deltoides Marshall subsp. wizlizenii (Watson) Eckenwalder) seedlings and saplings growing naturally on four landform types at an alluvial reach on each of two rivers, the Green and Yampa, in Colorado and Utah. The two study reaches differed primarily as a result of flow regulation on the Green River, which began in 1962. Landforms were a rarely flooded portion of the alluvial plain, geomorphically active slow-...
Significant ecological, hydrologic, and geomorphic changes have occurred during the 20th century along many large floodplain rivers in the American Southwest. Native Populus forests have declined, while the exotic Eurasian shrub, Tamarix, has proliferated and now dominates most floodplain ecosystems. Photographs from late 19th and early 20th centuries illustrate wide river channels with largely bare in-channel landforms and shrubby higher channel margin floodplains. However, by the mid-20th century, floodplains supporting dense Tamarix stands had expanded, and river channels had narrowed. Along the lower Green River in eastern Utah, the causal mechanism of channel and floodplain changes remains ambiguous due to...
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To investigate the evolution of clinal variation in an invasive plant, we compared cold hardiness in the introduced saltcedar (Tamarix ramosissima, Tamarix chinensis, and hybrids) and the native plains cottonwood (Populus deltoides subsp. monilifera). In a shadehouse in Colorado (41°N), we grew plants collected along a latitudinal gradient in the central United States (29–48°N). On 17 occasions between September 2005 and June 2006, we determined killing temperatures using freeze-induced electrolyte leakage and direct observation. In midwinter, cottonwood survived cooling to −70°C, while saltcedar was killed at −33 to −47°C. Frost sensitivity, therefore, may limit northward expansion of saltcedar in North...
Nutrient availability strongly affects the species composition and productivity of most upland ecosystems, but the importance of nutrient availability is largely undefined for riparian ecosystems in semiarid regions of the western United States. The establishment and persistence of riparian cottonwood (Populus spp.) seedlings depends largely on water availability, but this does not preclude an important role for nutrient availability. To investigate how nitrogen availability may influence the composition and productivity of riparian communities, we tested the hypothesis that the growth and survival of first-year Fremont cottonwood seedlings is limited by the availability of both water and nitrogen. Plots of naturally...
Dynamics of nutrient exchange between floodplains and rivers have been altered by changes in flow management and proliferation of nonnative plants. We tested the hypothesis that the nonnative, actinorhizal tree, Russian olive (Elaeagnus angustifolia), alters dynamics of leaf litter decomposition compared to native cottonwood (Populus deltoides ssp. wislizeni) along the Rio Grande, a river with a modified flow regime, in central New Mexico (U.S.A.). Leaf litter was placed in the river channel and the surface and subsurface horizons of forest soil at seven riparian sites that differed in their hydrologic connection to the river. All sites had a cottonwood canopy with a Russian olive-dominated understory. Mass loss...
Most major rivers in the southwestern United States have been hydrologically altered to meet human needs. Altered hydrological regimes have been associated with declines in native riparian forests. Today, many riparian areas have little or no regeneration of native riparian species and are now dominated by exotic Saltcedar (Tamarix chinensis Lour.). Success of riparian restoration efforts at least partially depends on the number of seedlings surviving the first growing season. Seedling survival is influenced by many abiotic and biotic factors including competition from other plants and available soil moisture, which is partially dependent on soil texture. In this study, we evaluated the relative importance of four...
Elaeagnus angustifolia L., a nonnative N2-fixer, has established within riparian corridors of the interior western United States and is now the fourth most frequently occurring woody riparian plant in this region. We examined whether E. angustifolia alters pools and fluxes of soil inorganic N at eight sites dominated by Populus deltoides ssp. wislizeni along the Rio Grande in New Mexico over 2 years. E. angustifolia contributed a small fraction of total leaf fall (<5% across sites) but accounted for a disproportionately high amount of N (19%) that entered the system from P. deltoides and E. angustifolia leaf fall, due to the high N content (>2%) of E. angustifolia senesced leaves. Soil inorganic N concentrations...
    map background search result map search result map Processes of Tamarix invasion and floodplain development along the lower Green River, Utah. Latitudinal variation in cold hardiness in introduced Tamarix and native Populus Processes of Tamarix invasion and floodplain development along the lower Green River, Utah. Latitudinal variation in cold hardiness in introduced Tamarix and native Populus