California Valley and Coastal Grassland

This ecological system is found from 10-1200 m (30-3600 feet) elevation, in the Great Central Valley and along the southern coastal regions of California. It receives on average 50 cm (range 25-100 cm) of precipitation per year, mainly as winter rain. It is found with fine-textured soils, moist or even waterlogged in winter, but very dry in summer. Historically, these grasslands were common among oak savanna and woodland and probably experienced similar frequent fire regimes. Characteristic plant species include Nassella pulchra, Aristida spp., Achillea millefolium var. borealis, Achyrachaena mollis, Agoseris heterophylla, Bloomeria crocea, Triteleia ixioides, Chlorogalum pomeridianum, Clarkia purpurea, Dodecatheon jeffreyi, Elymus glaucus, Leymus triticoides, Festuca californica, Melica californica, Castilleja attenuata, and Poa secunda.

Characteristic plant species include Nassella pulchra, Aristida spp., Achillea millefolium var. borealis (= Achillea borealis), Achyrachaena mollis, Agoseris heterophylla, Bloomeria crocea, Triteleia ixioides (= Brodiaea lutea), Chlorogalum pomeridianum, Clarkia purpurea, Dodecatheon jeffreyi, Elymus glaucus, Leymus triticoides, Festuca californica, Melica californica, Castilleja attenuata (= Orthocarpus attenuatus), and Poa secunda (= Poa scabrella).

This ecosystem occurs from 10 to 1200 m (30-3600 feet) in elevation; receiving on average 50 cm (range 25-100 cm) of precipitation per year, mainly as winter rain. It is found with deep fine-textured soils, moist or even waterlogged in winter, but very dry in summer (Sawyer et al. 2009).

These grasslands have evolved to survive fire and long seasonal droughts (Keeley 2006). Invasion of non-native annual grasses out-compete natives through prolific seed production and the ability to re-seed quickly after fires, which generally means they maintain themselves at the expense of the native grasses and forbs (Sawyer et al. 2009).

Conversion of this type has commonly come from agricultural and urban development, increased drought and increased fire frequency via Native American ignitions. Common stressors and threats include invasion of non-native annual species, heavy continuous grazing, and more frequent fire that favors the non-native annuals over the native bunch grasses. However, intact native grasslands also are stressed by fire suppression.

Conversion to agriculture and urban development are the greatest change agents to these grasslands rather than invasion by exotic species. Current thinking is that deep ripping and disruption of soil conditions makes way for exotics and if soil structure is in tact it is likely that native species will persist. Persistence of natives is more significant than dominance by natives. Many non-natives are here to stay and do not necessarily supplant or out compete the native species. These grasslands have experienced a long history of variable climate that supports a natural gradient from annual forblands in the southern portion of California to perennial grasslands in the northern portion. Loss of perennial grasses was thought to have been significant throughout the entire range but is now thought to have been over estimated. Many of the most spectacular wildflower fields in the South Coast Ranges and in southern California are the remaining pieces of this annual portion of the annual and perennial grasslands system (T. Keeler-Wolf pers. comm. 2013). There are, however, documented cases in particular where invasives such as Centaurea solstitialis, Brassica nigra, Taeniatherum, and others have swamped out the native species through thatch or shading (Stromberg et al. 2007, T. Keeler-Wolf pers. comm. 2013).

In the Central Valley, regional climate models project mean annual temperature increases of 1.4-2.0°C (1.8-3.6°F) by 2070. The projected impacts will be warmer winter temperatures; earlier warming in spring and increased summer temperatures. Regional models project a decrease in mean annual rainfall of 47-175 mm (1-7 inches) by 2070. While there is greater uncertainty about the precipitation projections than for temperature, some projections call for a slightly drier future climate relative to current conditions (PRBO Conservation Science 2011). In southwestern California, regional climate models project mean annual temperature increases of 1.7 to 2.2°C by 2070. In southwestern California, regional climate models project a decrease in mean annual rainfall of 51 to 184 mm by 2070. There is relatively little consensus about the projected effects of climate change on precipitation patterns in southwestern California: some projections suggest almost no change, others project decreases of up to 37% (PRBO Conservation Science 2011). Increase in drought length and magnitude will further favor the exotic annual species. Fires may increase with warmer temperatures and drier fuels, which may further favor non-native species, which survive fires through prolific seed production.

Found from in California from 10-1200 m (30-3600 feet) elevation, in the Great Central Valley and along the southern coastal region.