. Effects of defoliation by Douglas-fir tussock moth on timing and quantity of streamflow. 160 r 150 140 130 120 110 100 90 80 70 \. 0 30 4 0 50 60 70 80 90 100 Annual runoff, Mill Creek (cm) Figure 5.—Annual runoff from the South Fork of Walla Walla River compared to annual runoff from Mill Creek. The number beside each solid dot is the year of measurement for that point. From these and previously published results, it appears that at least three factors are involved in determining the amount of annual runoff increase following vegetation reduction. These are (1) percent of the total drainage
. Effects of defoliation by Douglas-fir tussock moth on timing and quantity of streamflow. 160 r 150 140 130 120 110 100 90 80 70 \. 0 30 4 0 50 60 70 80 90 100 Annual runoff, Mill Creek (cm) Figure 5.—Annual runoff from the South Fork of Walla Walla River compared to annual runoff from Mill Creek. The number beside each solid dot is the year of measurement for that point. From these and previously published results, it appears that at least three factors are involved in determining the amount of annual runoff increase following vegetation reduction. These are (1) percent of the total drainage area deforested, (2) location of the deforested area with respect to the stream channel, and (3) current annual precip- itation as a percent of the longterm mean value. Hibbert (1965) con- cluded from his world wide literature survey that at least 20 percent of a basin must be deforested before runoff significantly increases. Hibbert gave two reasons for this result: First, removing a smaller percentage of vegetation, such as thinnings, allows remaining trees to increase their water use rates, especially in areas such as eastern 10. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Helvey, J. D; Tiedemann, Arthur R; Pacific Northwest Forest and Range Experiment Station (Portland, Or. ). Portland, Or. : Pacific Northwest Forest and Range Experiment Station, Forest Service, U. S. Dept. of Agriculture
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Keywords: ., bookcentury1900, booksubjectstreammeasurements, booksubjecttrees
