Population Changes of Invasive Annuals in California Annual and Perennial Grasslands

Some non-native annual forbs and grasses can be invasive in California\u27s annual grassland region. Taeniatherum caput-medusae (L.) Nevski and Centaurea solstitialis L. can spread quickly, become nearly monospecific stands, and reduce carrying capacity for livestock and wildlife. Centaurea also can be toxic to horses. Lathyrus hirsutus L. is less invasive, but the seed is toxic to various livestock. Since 1991, the author has raised beef cattle on 16 ha of predominantly annual grassland where these 3 species occur, and a family member has raised cattle on approximately 40 ha of adjacent property. Surface soils in this hilly land are loamy (1/3) or high shrink-swell clay (2/3); Centaurea does not grow on the clay. This paper reports observed population changes of these 3 invasive annual species on both farms from 1991-2004 on the following 6 sites: 1. (12 ha)Domestic oat hay dry farmed for decades until 1991; trial seed mix of perennial species broadcast, 2. (40 ha)Oat hay dry farmed for decades until about 1980 when Dactylis glomerata L. and/or Phalaris aquatica L. were planted as pasture; only 50-60% of this area were successful plantings; then sheep and cattle ised here until 1991; Centaurea populations were suppressed by sheep utilisation, 3a. (4 ha)Dry farmed prior to 1941; pastured with cattle since 1941 along with Sites 3b and 3c below, 3b. Asphalt & gravel roadbed abandoned circa 1935-40 within a corner of Site 3a; litter/forbs/grass cover 95%, 3c. Relict area strip (3 x 15m) within Site 3a and also pastured since 1941; likely never cropped due to limited se and access; predominantly native perennial species; part of an elevated island between 2 roads cut into a hill, 4. Roadside relict area strip (3 x 15m) adjacent to Site 3c but not pastured since 1941; likely never cropped. Cattle did not overgraze the 3 invasive species. All sites except Site 3b had areas of perennial grassland; Dactylis stands developed in Site 1 after 1991. Sites 1, 2, & 3a also had substantial areas of annual grassland