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Ground-water and surface flow depletions are altering riparian ecosystems throughout the southwestern United States, and have contributed to the decline of forests of the pioneer trees Populus fremontii (Fremont cottonwood) and Salix gooddingii (Goodding willow). On some rivers, these forests have been replaced by shrublands of Tamarix ramosissima (tamarisk), a drought-tolerant species from Eurasia. The physiological response of these three riparian plant species to decreases in water availability is well studied, but little attention has been given to shifts in community and population structure in response to declines in surface flow and ground-water levels. Based on study of 17 sites spanning a hydrologic gradient,...
Riparian ecosystems in the south-western United States have undergone extensive physical and biological changes, due, in part, to alteration of natural flow regimes and suppression of fluvial processes. Many riparian ecosystem restoration projects are achieving success because they recognize the importance of restoring the hydrologic regime. In other words, these projects are restoring flows of water and sediment in sufficient quantities and with appropriate temporal and spatial patterns. Other projects have proceeded without recognition of the need to incorporate environmental stream flow requirements into management plans. To increase success rate of riparian ecosystem restoration, this paper describes some changes...
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Many of the streams and aquifers that sustain Interior riparian deciduous forests in the US Southwest are being dewatered, yet we know little about how the plant communities are being affected by these hydrologic changes. This study found that several measures of biotic integrity, including Platanus wrightii xylem water potential, P. wrightii radial growth rate, tree species diversity, and woody plant wetland indicator scores, varied significantly with ground water depth and fluctuation among nine sites in Arizona. P. wrightii trees had highest productivity, and the forests had greatest compositional diversity, where ground water averaged less than 2 m below the tree base during the growing season and less than...
After a long period in which fuel loads were sparse, fire recently has occurred with high frequency in the ungrazed riparian zone of the Upper San Pedro River in southern Arizona’s Chihuahuan Desert. We studied four accidental fires that occurred during 1994–2003 (two in different years at the same site). Woody vegetation was contrasted between three burned sites and matched spatial controls, and before and after the most recent fire. Herbaceous vegetation was sampled in multiple years producing a chronosequence of time since fire (from 4 months to 8 years). Riparian fire was associated with reductions in woody plant species diversity and canopy cover. In contrast, fire caused a short-term (2 year) pulse of...
    map background search result map search result map Biotic integrity of Platanus wrightii riparian forests in Arizona: first approximation Biotic integrity of Platanus wrightii riparian forests in Arizona: first approximation