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Workman Creek Watershed

Description and History

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.

Workman Creek watershed
Workman Creek watershed

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.

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).

Workman Creek watershed
Workman Creek watershed

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 production.

Treatment being applied on Workman Creek
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.

Cooperators

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.
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8 May 2002
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