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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-...
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Dinosaur National Monument, in northwestern Colorado, has become a test case in the establishment of a federal reserved water right to instream flows. For the first time, the Interior Department was forced to rigorously defend its claims in a watershed where the federal government did not control the upstream reaches. Inadequate quantification of minimum flow requirements, court orders, and an apparent Congressional ban on the spending of Water Resources Program funds by the Park Service to quantify its water rights have already placed the Service in a difficult position to protect instream flows for maintaining the ecological integrity of the Monument. As late as 1983, administrators of the Park Service were divided...
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Canyon riparian zone vegetation is vulnerable to effects of upstream river regulation. We studied box elder (Acer negundo) dominated canyon riparian forests intensively on the Green and Yampa rivers in Dinosaur National Monument, Colorado, and extensively in four other major rivers of the upper Colorado River Basin to determine the effects of river regulation on riparian tree establishment patterns. We: 1) aged individuals to determine if establishment was correlated with high annual peak flows, 2) mapped cohorts to determine if the areal extent of post-regulation cohorts was reduced on regulated compared to unregulated river reaches, and 3) measured the floodplain position of cohorts in regulated and unregulated...
In northwestern Colorado, flow regulation on the Green River has created a transitional plant community that features encroachment by upland vegetation into cottonwood (Populus fremontii)-dominated, riparian forest on topographically high floodplain sites and reduced cottonwood regeneration on low floodplain sites. To assess how these changes might have affected small mammal distributions, in 1994 and 1995 we live-trapped during periods surrounding spring flooding at 3 sites: above and below the confluence of the regulated Green River and at the ecologically similar, but unregulated, Yampa River (reference site). More species were captured at the most regulated site along the Green River above its confluence, with...
During the 20th Century the flow of most rivers in the United States was regulated by diversions and dams, with major impacts on riparian forests. Few unregulated rivers remain to provide baseline information for assessing these impacts. We characterized patterns in riparian plant communities along chronosequences on the unregulated Yampa River and the regulated Green River in northwestern Colorado, examining patterns in plant species diversity in relation to the ages of floodplain terraces. On both rivers, mean plant species richness in cottonwood (Populus deltoides Marshall subsp. wislizenzii (Watson) Eckenwalder) dominated riparian forests declined by more than 50% from young sites (<20 years) to old upland terraces...
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We evaluated distribution, habitat use, spawning, and species associations of the endangered humpback chub (Gila cypha) in the Yampa and Green rivers, Dinosaur National Monument, from 1986 to 1989. Adult and juvenile humpback chub were captured in high-gradient reaches of Yampa and Whirlpool canyons where they were rare (n = 133, G. robusta) were widely distributed in eddies, pools, runs, and riffles. Humpback chub (n = 39) and roundtail chub (n = 242) in reproductive condition were sympatric in eddy habitats during the 5-6 week period following highest spring runoff. River temperatures at this time averaged about 20 C. Nonnative channel catfish (Ictalurus punctatus) were abundant in eddies yielding humpback and...
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* 1 The structure and functioning of riverine ecosystems is dependent upon regional setting and the interplay of hydrologic regime and geomorphologic processes. We used a retrospective analysis to study recruitment along broad, alluvial valley segments (parks) and canyon segments of the unregulated Yampa River and the regulated Green River in the upper Colorado River basin, USA. We precisely aged 811 individuals of Populus deltoides ssp. wislizenii (native) and Tamarix ramosissima (exotic) from 182 wooded patches and determined the elevation and character of the germination surface for each. We used logistic regression to relate recruitment events (presence or absence of cohort) to five flow and two weather parameters....
    map background search result map search result map Effects of river regulation on riparian box elder (Acer Negundo) forests in Canyons of the upper Colorado River Basin, USA Dinosaur National Monument: The evolution of a federal reserved water right Humpback chub ( Gila cypha ) in the Yampa and Green rivers, Dinosaur National Monument, with observations on roundtail chub ( G. robusta ) and other sympatric fishes Multiple pathways for woody plant establishment on floodplains at local to regional scales Effects of river regulation on riparian box elder (Acer Negundo) forests in Canyons of the upper Colorado River Basin, USA Dinosaur National Monument: The evolution of a federal reserved water right Humpback chub ( Gila cypha ) in the Yampa and Green rivers, Dinosaur National Monument, with observations on roundtail chub ( G. robusta ) and other sympatric fishes Multiple pathways for woody plant establishment on floodplains at local to regional scales