Three Bar Watersheds

Treatments and Practices

The Three-Bar experimental watersheds were established to determine the effects of chaparral shrub-to-grass conversions on increasing water yields, on dissolved chemical constituents and sediment, and of fire and herbicide applications in controlling shrub re-growth.

Conversion

While these research objectives provided a framework for treatment of Watersheds B, C, and F, other research agendas evolved as the understanding of chaparral response to treatment increased. Foliar sprays, initially used to control chaparral shrubs, inadequately eliminated all of the shrubs and required repeated application (Hibbert et al. 1974). Because of this inadequacy, soil-applied herbicides in subsequent treatments of Watersheds C, B, and F were tested. Above-normal nitrate levels were discovered in stream water as a result of earlier, herbicide treatment on Watershed C. These high nitrate responses led to studies on water quality and nitrogen losses as a result of shrub treatments.

The treatment pattern changed from treating entire watershed areas (Watersheds C and F) to
selectively controlling shrub plants in a mosaic pattern to provide protection from erosion on steep slopes, better habitat diversity for wildlife, and maintenance of increased streamflow (Watershed B). The mosaic treatment pattern of chaparral control was ultimately tested on the Whitespar watersheds (DeBano et al. 1999b).