Influences of brush conversion and weather patterns on runoff from a northern California watershed.

Highlight: Sixteen years of data were evaluated to determine the inBuence of annual weather patterns and a brush conversion project on subsequent runoff from an 86.2-ha watershed. Grassy vegetation released 39% more total runoff than did woody vegetation. Total runoff for each hydrologic year was directly proportional to total precipitation, regardless of vegetative cover. However, runoff as a proportion of total precipitation increased 59% following conversion of woody to grassy vegetation, and most closely correlated with March cover. Unfortunately, brush conversion also drastically increased the number of soil slips and sediment discharged from the watershed. All major landslides occurred in the vicinity of streams when the root systems of woody vegetation along these streams began to decay. Leaving this streambank vegetation intact may have prevented some of the undesirable results of brush conversion on the watershed.