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Tucson Audubon Society
Santa Cruz River Restoration Project
The
lower Santa Cruz River in the Marana area has been carrying treated effluent
from Tucson since the 1970s. The effluent currently reaches somewhat beyond
the Pima-Pinal County line before sinking into the great sandy basins
between Tucson and Phoenix. Since the flow began, Goodding's willows,
Fremont cottonwoods and other vegetation has begun to spring up on their own
along the river. To the right are photos showing what one area looks like in
both the winter and spring.
Historically,
this part of the Santa Cruz River would have only held flowing water briefly
during floods, while other stretches upstream flowed perennially or
intermittently. Those upstream areas (such as the stretch from San Xavier to
central Tucson) harbored vast resources for bird 
species that require
"riparian areas" (streamside vegetation) for their migration or
for nesting. Those resources have vanished due to cattle grazing, stream
diversions, and especially groundwater pumping.
The narrow strip of riparian vegetation now growing along the "effluent-dominated" lower Santa Cruz River is only a faint glimmer of what has been lost. But it is, nonetheless, helpful to birds that are accustomed to migrating north each spring along the north-south trending Santa Cruz River course, and to others that must look for this kind of habitat in order to nest. These include species such as Abert's towhee, Bell's vireo, Lucy's warbler, and Yellow-breasted chat. Species such as these have declined greatly due to the loss of 80-90% of southern Arizona's lowland riparian areas.
The
Tucson Audubon Society, in coordination with the City of Tucson (which owns
the land), is working to enhance the wildlife habitat along one stretch of
the lower Santa Cruz River and to restore native vegetation to adjacent
abandoned farm fields.
The habitat enhancement strategy for the river stretch focuses on widening and diversifying the vegetation growing along the channel, to make more and richer wildlife habitat. Some water-loving trees and plants have been planted close to the river, such as walnut (Juglans major), ash (Fraxinus velutina) and desert honeysuckle (Anisicanthus thurberi).
However,
the main strategy has been to use trees and shrubs that will do well on
the river berms away from direct influence of the stream (since we don't
know if effluent flow will always be there). These species will broaden
the swath of vegetation along the river corridor but will be able to
survive on rainwater alone. These include mesquite (Prosopis velutina),
blue palo verde (Parkinsonia florida), desert willow (Chilopsis
linearis), graythorn (Ziziphus obtusifolia), alkali sacaton (Sporobolus
airoides), and many others. At left is a newly planted desert willow.
The
abandoned farm fields surrounding the river have very low vegetation
diversity and density. Here we plant and sow seeds of a similar array of
native, drylands species. At right, a volunteer prepares a planting basin
in one of the old farm fields. For a year or two the plants here will be
on a drip irrigation system. But the basin holding the plants also fills
with water during heavy rains, focusing runoff from surrounding areas
around the roots of the plant. Volunteers are an important part of our
habitat restoration strategy as well as an important form of community
outreach. (Go back to restoration home
page to see more about volunteering.)
The project also does large-scale "imprinting" on old farm fields. This involves pulling a cylindar with protrusions over the fields with a tractor, leaving a pattern of shallow indentations in the ground. Then another tractor spreads seed on the imprinted land, which tends to settle into the indentations along with finer sediments and blown organic materials. The indentations also help focus rainwater on the seeds which then have a greater chance of surviving and growing.
Long-term
monitoring will determine the success of plantings at the restoration
site, and how they are affecting wildlife. Regular avian surveys are
carried out (left) to see whether habitat is really being enhanced in a
way that increases numbers and diversity of birds. We are also monitoring
survivorship of plantings, changes in vegetation coverage and diversity,
and changes in the river channel morphology.
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This page was updated on 02/22/06