Treatments and Results
Because of the importance of finding additional sources of water in an
arid environment and because manipulations of pinyon-juniper vegetation
resulted in only minor changes in streamflow, attention in the late 1960s
on Beaver Creek was turned to studying the influence of manipulating pine
vegetation on resource outputs.
Two basic kinds of timber overstory removal were considered: thinning
and clear openings (strips or patches). Different basal areas and spacing
of openings were tested to evaluate a range of treatment intensities.
Clearing all the woody vegetation was tested as the most severe level
of treatment to determine maximum possible water yields (Brown
et al 1974, Baker
1999b). A paired watershed approach
was used to determine water yield response.
Results—Results from the experiments and studies conducted in
the ponderosa pine on the Beaver Creek watershed have been reported in numerous
publications including USDA Forest Service releases, journal articles, and
special publications on specific topics. A status-of-knowledge publication
presented the results of water yield improvement experiments and other research
conducted on the pilot watersheds through the early 1970s (Brown,
et al. 1974).
- Annual water yield increases of 1 to 2 inches were realized in the
initial (up to 10 years) post-treatment periods as a result of various
intensities and patterns of forest overstory reduction on shallow,
volcanic-derived soils. These increases in water yield diminished
over time, approaching pretreatment levels after 10 or fewer years (Baker
1986).
- There are indications that water yield response on watersheds with
northern exposure will persist for a longer period or on watersheds
with deeper soil development (Gottfried
and DeBano 1990).
- No meaningful changes in total sediment production or water quality
occurred as a result of the treatments applied (Dong
1996).
- Repeated inventories of the timber resource indicate that volume
production has been maintained, although at generally lower levels than
those represented by pre-treatment conditions.
- Reductions in the density of the pine overstories have resulted in
increases in the production of herbaceous plants (Bojorquez-Tapia
et al. 1990). These increases can approach 500 lbs/acre after
complete overstory removal including forage and non-forage plants.
Average pretreatment forage production was 200 lbs/acre.
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