A major project was conducted on the Workman watersheds to evaluate
the hydrology of higher elevation mixed conifer forests and to determine
the changes in streamflow and sedimentation from manipulating the
forest vegetation. The 3 watersheds on Workman Creek are North Fork,
Middle Fork, and South Fork. The treatments evaluated were selected
to cover the range of water yields possible through manipulation or
removal of the forest vegetation (Rich
and Gottfried 1976). These treatments were not intended to be
examples or recommendations for actual management applications, but
instead they were used to obtain basic hydrologic information on streamflow
responses to vegetation manipulations.
North Fork.Studies on the North Fork of Workman Creek were
designed to evaluate streamflow responses to clearing the forest cover
in stages, starting on the wettest and progressing to the driest sites.
The first treatment was implemented in 1953.
Workman Creek watershed
Riparian trees, mainly Arizona alder (Alnus oblongifolia) and
bigtooth maple (Acer grandidentatum), growing adjacent to streams,
springs, and seeps, were cutand their stumps were treated with herbicides
to prevent sprouting. The cut removed 0.6% of the total basal area.
The next treatment on North Fork converted the moist site forest vegetation,
mostly Douglas-fir and white fir, to grass on about 80 acres. Larger trees
were harvested, and smaller and unmerchantable material was windrowed
and burned. The cleared areas were seeded with grass species.
The final treatment on North Fork removed the adjacent dry-site forest
of ponderosa pine trees and converted the site to grass (image, above).
South Fork.Treatments on South Fork of Workman Creek were
designed to test the current forest management prescriptions of 1953.
The watershed was harvested according to a standard single-tree selection
prescription starting in June 1953.
The objective of the second treatment on South Fork was to convert mixed
conifers to a pure ponderosa pine stand by removing the other conifer
species, and to maintain the stand at a density of 40 ft2/acre. The hypothesis
tested was that this forest density should optimize both timber and water
Treatment being applied on Workman Creek
Middle Fork.Middle Fork watershed was left untreated so
it could be used as a control for quantifying changes in streatnflow after
treating North Fork and South Fork watersheds.
A number of organizations cooperated with the Rocky Mountain Station's
research effort on the Sierra Ancha Experimental Forest. The Salt River
Water Users' Association provided financial support for the treatments
on Workman Creek. The Tonto National Forest assisted with implementation
of these forest management treatments. Faculty and students from Arizona
State University and the University of Arizona conducted collaborative
experiments on Sierra Ancha. University-sponsored researhc has increased
in recent years.