Studies in mixcd conifer watersheds at Workman Creek demonstrated that
large and significant increases in streamflow could obtained by replacing
the forest with a grass cover on large or strategically located parts
of a watershed or by greatly reducing the forest overstory density (Gottfried
et al. 1999).
Workman Creek watershed in mixed conifer vegetation
The objectives of research in the White Mountains was to determined if
results from Workman Creek experiments could be confirmed, and if they
were transferable to other mixed conifer areas in Arizona. Information
from the Workman Creek studies provided the basis for designing forest
overstory treatments that were beneficial for timber production and wildlife
habitat values and that would produce significant increases in streamflow.
Two kinds of timber overstory removal were considered: thinning and patch
clear cutting. These studies were designed to test multiple-use forest
Mixed conifer watershed in White Mountains of Arizona
ResultsResults from the experiments and studies conducted
in the mixed conifer on the White Mountain watersheds have been reported
in numerous publications including USDA Forest Service releases, journal
ariticles, and special publication pulication on specific topics. A status-of-knowledge
publication presented the results of water yield improvement experiments
and other research conducted on the watersheds through the early 1970s
and Thompson 1974).
Weir stream gage
Annual water yield increases of 30 to 50 % (0.5 to 3.8 inches) were
realized due to reduction in evapotranspiration and increase in snow
accumulation in openings. These increases have remained stable for 21
years, probably because new tree roots had not fully occupied the soil
et al. 1999).
Overland flow and sediment delivery from severely disturbed and undisturbed
sites were low and inconsequential.
Incresesed streamflow after treatment caused the natural channel
adjustment process to accelerate.
No increase in average annual water yields after a prescribed fire,
which was understandable because the burn did not affect the forest
overstory conditions or consume much of the forest floor.
Concentrations of NH4-N and NO3-N, PO4, and K increased during the
first 2 post-fire snowmelt periods. The changes in nutrient concentrations,
while statistically signinficant, were small and of little consequence
in terms of site productivity and downstream water quality.
Mule deer, elk, and livestock benefitted from the harvested openings
because of increased production of herbaceous species.