Forests and Water: A State of the Art Review for Colorado

• Year: 2003
• Title: Forests and Water: A State-of-the-Art Review for Colorado
• Author: Colorado State University
• Description: Colorado State University 2003
• Publications - Doc Type: Other

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On Fool Creek the annual water yield increase ranged
from 1.6 inches in the very dry year of 1963 to 6.4
inches in the exceptionally wet year of 1957 (Figure
2.4). Figure 2.5 shows that the increase in annual water
yields observed at Fool Creek generally is proportional
to the estimated runoff in the absence of any forest
harvest. Since annual runoff is directly proportional to
the annual precipitation, this means that the increase in
runoff due to forest harvest in any given year is directly
proportional to annual precipitation. In the case of Fool
Creek, approximately 40% of the observed increase in
annual water yields can be attributed to the variation
in the amount of SWE on 1 April (Troendle and King,
1985). The remaining scatter in Figure 1 can be attrib-
uted to differences in seasonal precipitation, snowpack
sublimation, and numerous other factors that affect the
amount of runoff.
The tendency to have larger water yield increases in
wetter years was also apparent in the Wagon Wheel
Gap study. Here the water yield increase in a wet year
was twice as large in an average year, and the water
yield increase dropped to zero in years with below nor-
mal precipitation (Bates and Henry, 1928). A series of
paired- watershed studies on ponderosa pine stands in
Arizona also showed that forest harvest caused much
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larger increases in water yields in wet years than dry
years (Baker, 1986).
2.2.4. Rate of hydrologic recovery.
The values in Table 2.1 and the water yield increases
discussed to this point all represent the average change
that would be expected in the first year after harvest. In
the absence of any other management activities, these
increases in runoff will decline over time with for-
est regrowth (Figure 2.6) (Troendle and King, 1985).
Colorado's relatively cold, dry climate means that forest
regrowth is slow relative to most other areas, and one
would therefore expect slower hydrologic recovery rates.
The long -term snowpack and streamflow records from
the FEF allow a more rigorous quantification of hydro-
logic recovery in the sub - alpine forest than most other
areas (e.g., Troendle and King, 1985). These basin -scale
hydrologic data are complemented by more detailed
studies on the rate at which leaf area, basal area, and
other key characteristics recover following forest harvest
(e.g., Kaufmann, 1985).
Since the Wagon Wheel Gap study was only monitored
for seven years after harvest (Bates and Henry, 1928),
the longest - running paired - catchment study is the Fool
Creek experiment. After forty years annual water yields
1956 1961 1966 1971 1976 1981
Year
Figure 2.4. Natural and increase in water yields by year for the Fool Creek catchment for the first 27 years after
harvest.
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