Colorado River Ecology and Dam Management Proceedings of a Symposium May 24-25, 1990 Santa Fe, New Mexico (1991) / Chapter Skim
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Historic Changes in Vegetation Along the Colorado River in the Grand Canyon
Historic Changes in Vegetation Along the Colorado River in the Grand Canyon
Pages 178-206
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From page 178... ...
Prior to the construction of Glen Canyon Dam the components of the natural riverine ecosystem of the Colorado River in Grand Canyon were driven by high energy, pulsing events typical of southwestern rivers. Three pulsing features of the river affected by the dam included, in decreasing importance to the riparian ecosystem (1)
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From page 179... ...
Grand Canyon National Park receives more than three million visitors annually, approximately 22,000 travel down the Colorado River, considered by many to be the world's premiere whitewater river. Approximately 100, 000 additional recreationists use the river between Glen Canyon Dam and Lees Ferry, half as fishermen, the others on raft trips.
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From page 180... ...
The possible loss of integrity of the ecological fabric of the region, or even modification of critical features of the region, is of interest to us here as we evaluate vegetational changes, specifically changes in riparian vegetation along the Colorado River. Johnson and Carothers (1987)
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From page 181... ...
Since the terms subecotone and subzone are not in common usage, the riparian zone of the Colorado River in Grand Canyon has, by convention, been further divided into even smaller "zones." The terms Old High Water Zone and New High Water Zone are so widely used that they are commonly abbreviated OHWZ and NHWZ (and will be so designated throughout this paper)
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From page 182... ...
HISTORY AND BACKGROUND OF BOTANICAL EXPLORATION ALONG THE COLORADO RIVER IN GRAND CANYON The first humans cognizant of riparian vegetation along the Colorado River in Grand Canyon were prehistoric groups to which certain floristic components of the vegetation were of subsistence or ceremonial importance. Since these early canyon inhabitants left no written record we must rely on plant and animal lists from archeological excavations—for summaries see Fowler, et al.
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From page 183... ...
After being left from early plant lists for Grand Canyon, it was finally included in the latest checklist (Phillips et al., 1987) as "common on sand dunes along the Colorado River from CRM [Colorado River Mile]
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From page 184... ...
In the late 1960s and early 1970s there was increasing interest in the biological, physicochemical, and socioeconomic parameters of the Colorado River in the Grand Canyon. There was much concern about the"carrying capacity" for campers on the alluvial terraces, or "beaches," along the river and interrelationships between campers, vegetation, and other components of the riverine environment (Dolan et al., 1977; Johnson et al., 1977~.
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From page 185... ...
In addition to referencing the more important summary and synthesis papers from that bibliography, throughout this paper we also reference works from throughout the 1980s that are most important to our discussions of vegetation (see also USDI, 1988~. DISCUSSION Prior to the construction of Glen Canyon Dam the riparian and aquatic components of the natural riverine ecosystem of the Colorado River in Grand Canyon were driven by high energy, pulsing events typical of southwestern rivers.
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From page 186... ...
Riparian ecosystems of arid regions are noted for their high recreational and wildlife values (Johnson and Carothers, 1982~. The riparian zone along the Colorado River in Grand Canyon is no exception.
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From page 187... ...
Bacchans Jpp., Equisotum (Rapid Proliferation) NHWZ Zone of ~ Human Impact i FLOOD ZONE At_ RIVER POST DAM HIGH WATER RELEASES RIVER FIGURE 8-1 Profile of the vegetative zones of the Colorado River floodplain in the Grand Canyon prior to the construction of Glen Canyon Dam (after Johnson and Carothers, 1982~.
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From page 188... ...
, vegetation is not a requirement of a riparian environment and in the Grand Canyon much of the riparian zone consists of bare soil, rocks, or sand. THE COLORADO RIVER AS AN EXCEPTION TO RIPARIAN DESERTIFICATION The concept of desertification was originally applied to desert upland regions, usually in third world countries, notably Africa.
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From page 189... ...
The riparian ecosystem of the Colorado River in the Grand Canyon is the only major riverine ecosystem in the Southwest where there has been an appre
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From page 190... ...
Birds are discussed further under"Fauna." IMPACTS OF FLOODING AND FIRE ON THE RIPARIAN ZONE Flooding is a natural phenomenon in riparian habitats, thus riparian species are generally flood adapted. In the Grand Canyon, however, the modification of flow levels have resulted in an artificial, humanly created environment.
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From page 191... ...
Nonnative Species Since there have been drastic modifications to the aquatic biota of the Colorado River in Grand Canyon there has also been concern about the possible loss of riparian species due to the changed flow regimes of the river. To date we know of no riparian species that have been extirpated since 1963.
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From page 192... ...
Since both tamarisk and camelthorn have proliferated profusely along the river there has been concem about Russian Olive also becoming an invasive species. Native Species A few of the more important woody native species of the OHWZ and NHWZ are discussed briefly here.
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From page 193... ...
This species is relatively common downstream to about kilometer 93.3 (Turner and Karpiscak, 1980~. Many of the stands of this species are in poor condition, presumably from the lack of water since the construction of Glen Canyon Dam.
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From page 194... ...
REPZ TERRACED ~ - it FLOOD ZONE OT PRE-DAM FLOOD ZONE RIVER | FIGURE 8-2 Profile of the vegetative zones of the Colorado River floodplain in the Grand Canyon 25 years after the impoundment of Colorado River waters by Glen Canyon Dam (after Johnson and Carothers, 1982~.
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From page 195... ...
FAUNA AND CHECKLISTS Numerous species of plants and animals were added to lists of the Grand Canyon biota during scientific investigations along the Colorado River in the 1970s. All of these newly discovered species are not from the river corridor but the work being done along the river served as a stimulus to gather additional information for updating these checklists.
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From page 196... ...
of which 250 (83%) have been recorded from the Colorado River corridor (Brown et al., 1985~.
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From page 197... ...
Since nearly all breeding avian species along the Colorado River are insectivores these high insect populations presumably provide an abundant avian food source. However, this still does not explain the preferential selection of tamarisk over other species for nesting.
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From page 198... ...
Feral burros, on the other hand, built up to such high populations along the Colorado River during the 1970s that they unfavorably impacted both the natural riparian environment and recreational activities (Carothers et al., 1976~. Endangered Species Two endangered birds of the riparian zone are the Bald Eagle (Haliaeetus leucocephalus)
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From page 199... ...
Carothers further proposes that, based on his studies of the fishes of the Colorado River in Grand Canyon (Carothers and Minckley, 1981) , several native species were nearing extinction before the construction of Glen Canyon Dam (see also Minckley, this volume)
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From page 200... ...
Thus, riparian vegetation in the canyon is uniquely valuable since the Colorado River in Grand Canyon is the only major riverine ecosystem in the Southwest where there has been an appreciable increase rather than a decrease in riparian vegetation and associated animal populations during the 1900s. Continuing scientific investigations in the Grand Canyon need to examine the interrelationships between water releases from Glen Canyon Dam and the riparian and aquatic ecosystems of the downstream Colorado River.
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From page 201... ...
1985. Glen Canyon Dam, fluctuating water levels and riparian breeding birds: the need for management compromise on the Colorado River in Grand Canyon.
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From page 202... ...
1983. Status of the Colorado River ecosystem in Grand Canyon National Park and Glen Canyon National Recreation Area.
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From page 203... ...
. Aquatic resources management of the Colorado River ecosystem.
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From page 204... ...
. Aquatic resources management of the Colorado River ecosystem.
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From page 205... ...
1980. Recent vegetation changes along the Colorado River between Glen Canyon Dam and Lake Mead, Arizona.
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From page 206... ...
validus Cactus, Barrel - Echinocactus polycephalus and Ferocactus acanthodes Camelthorn - Alhagi camelorum Catclaw, Catclaw Acacia - Acacia greggii Cattail - Typha domingensis and T Iatifolia Clover, Sweet - Melilotus spp.
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