8221

• UCREFRP Catalog Number: 8221
• Author: Van Steeter, M. M.
• Title: Historic and Current Processes Affecting Channel Change and Endangered fish Habitats of the Colorado River Near Grand Junction, Colorado.
• USFW Year: 1996.
• USFW - Doc Type: Doctor of Philosophy.
• Copyright Material: NO

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Nonnative Vegetation and Bank Stabilization
Nonnative vegetation and bank stabilization are two additional
factors which can lead to a decrease in channel complexity, and potentially
a loss of fish habitats. The nonnative shrub tamarisk (Tamarix chinensis)
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is widespread throughout the Colorado River basin. Hereford (1984)
reported that the width of the Little Colorado River had decreased by
approximately 50 percent, since around 1930, due to low flows during 1940-
50 and the subsequent establishment of tamarisk. Similarly, Graf (1978)
used historic photographs and field surveys to measure the effects of
tamarisk on the channel width of the Green River in Canyonlands
National Park. He concluded that tamarisk had become established during
low flow periods, primarily before the closing of Flaming Gorge Dam in
1962. This resulted in a 27% decrease in channel width, the stabilization of
dynamic channel features, and the elimination of narrow chute channels
that separated islands from the floodplain.
There are two characteristics of tamarisk which give it an advantage
over most native vegetation. First, it can survive under a wide range of
conditions. It can survive up to 70 days of total submersion in water
(Warren and Turner, 1975), but it is also drought tol~rant relative to
native riparian species (Turner, 1974). Secondly, tamarisk sets seed for up
to 5.5 months (Warren and Turner, 1975), giving it a competitive
advantage over native species such as willow and cottonwood which
usually set seed for only one month (Turner, 1974). Since tamarisk sets
seed well into the summer, it can colonize bars and side channels which
are only exposed at low flow.
Bank stabilization is another factor potentially affecting channel
morphology since it inhibits a river's ability to migrate and often causes

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