WOODY RIPARIAN VEGETATION
Grazing in the early part of the growing season does not appear to harm woody production as long as herbaceous plants are abundant and growing actively. Streams that depend on shrubs or trees for stabilization can be severely impacted by heavy, late-summer, fall, or winter grazing or by frequent sheep grazing. Woody riparian vegetation is discouraged by heavy grazing late in the growing season. At that time, most grasses, sedges, and rushes have completed their reproductive cycle and are entering, or are in, a dormant stage. The herbaceous vegetation is frequently unpalatable, dry, lacking in succulence, and often low in protein and energy content. The woody vegetation is still green and succulent, palatable, and high in protein and energy content (Buckhouse and Elmore, 1991). Livestock will actively select woody vegetation at this time of year.
Willows should be grazed in a rotation of spring and early summer use. A rest rotation or deferred rotation system that includes prolonged or intense periods of late-season use should be avoided. Two years of rest, or grazing during a non critical season, cannot make up for a grazing impact that removes three years growth on woody species (Swanson, 1987).
Some evidence shows that summer use levels of below 50% on herbaceous vegetation along streams keeps woody vegetation from being grazed significantly (Buckhouse and Elmore 1991). Watch when animals switch from herbaceous to woody vegetation.
Note: Three-pasture rest-rotation grazing usually doesnt promote improved woody riparian vegetation, even though it may be very positive for the herbaceous component. In a three-pasture system, a pasture is rested the first year, grazed early the second year, and deferred from grazing the third year. The year it receives late-season grazing often makes the lighter use of the two previous years a waste of time; the third year allows too much use on the woody vegetation. There are a number of variations to rest-rotation involving more pastures with different plans for rest, partial use, and full use (Buckhouse and Elmore, 1991)