| Popis: |
Timber was harvested for the first time in a mixed conifer forest of the Arǐzona White Mountains in 1978–1979. Trees were harvested by patch cuts and group selection. Logs were yarded by crawler tractors. After harvest, 19 small subdrainages were equipped with runoff and sediment collectors. The forest floors in the subdrainages were classed as undisturbed, moderately disturbed, or severely disturbed. Severe disturbance, caused by logging and monitoring activities, was associated with a pre-existing erosion pavement that had developed for unknown reasons. Although overland flow and sediment delivery differed significantly between the severely disturbed and undisturbed groups during the 5 yr postharvest period, all quantities were practically insignificant. The group severely disturbed by logging had an average of only 0.006 mm yr −1 annual soil loss. Overland flows ranged between 0.7 and 15.4 mm yr −1 and sediment between 5.67 and 268.78 kg ha −1 yr −1 . Summer yields of overland flow and sediment delivery were significantly higher than those in winter. Precipitation amounts were about equal for both seasons, but summer precipitation is of monsoon origin. Flow and sediment yields were not significantly different between moderately disturbed and undisturbed forest floor. Recovery from disturbance could not be detected. |
