Changes in standing crop, cover, and percent botanical composition of annual vegetation as influenced by microsite and type conversion were investigated on an 86.2 hectare watershed at the Hopland Field Station, Mendocino County, California.

Type conversion from woody vegetation to grassland tripled total standing crop of herbaceous plants on the watershed, with much of this increase occurring on sites formerly supporting a dense and semi-dense woodland overstory. However, the sites that were originally woodland never produced as much forage as those that were originally open grassland. The managerial problem of seasonally adjusting stocking rates in response to changing forage availability was heightened by type conversion, since much of the increased forage production occurred at the end of the growing season.

Short annual plants, such as nitgrass, silver hairgrass, rattlesnake weed, filaree, bur-clover, and true clovers, attained their greatest percent botanical composition on the historically open grassland sites. Type conversion produced increases in botanical composition primarily for those taller annual and perennial plant species capable of colonizing the formerly dense woodland sites mainly occurring on north-facing slopes. These plant species included wild oats, ripgut, vetches, and Italian thistle.

In the sheep-grazing system employed, adding animal units to utilize increased spring forage following brush conversion required alternative sources of feed during other periods of the year.