SPENCEVILLE VEGETATION TYPES
The Blue-Oak Woodland occurs in the foothills of California's Central Valley and central Coast Ranges. Blue-oak Woodlands are not common in comparison to other oak communities and tend to occur as a narrow ring along the valley's edge. Figure 2 depicts the general habitat distribution of Blue-Oak Woodland throughout California. The Blue-Oak Woodland is a dominant habitat type within SWA. This habitat is typically composed of scattered Blue oaks that, in better quality sites, can create a closed canopy forest (DFG 1988). The typical understory is an extension of annual grassland that does not involve an extensive matrix of understory shrubs, although they are present (DFG 1988). The Blue-oak is the dominant tree species. Valley-oak is a common associate as well as poison oak, California coffeeberry, buckbrush, redberry, and California Buckeye (DFG 1988). The ground cover consists mainly of annuals such as bromegrass, foxtail, fillaree, and others.
Past studies of this habitat type indicate that as many as 29 amphibian and reptile species, 57 bird species, and 10 mammal species find this mature habitat community suitable or optimum for breeding (DFG 1988). At SWA, acorn woodpeckers, bluebirds, and tree swallows are common to this habitat type as well as the California ground squirrel. From spring through summer this habitat type is extremely important to nesting mourning doves (DFG 1988). Another significant breeding bird species of the oak woodland communities is the red-shouldered hawk (DFG 1988), and it is a common bird of prey at the Spenceville Wildlife Area. Many of the squirrel and bird species, such as the Yellow billed magpie and Scrubjay, play an integral part to the successful regeneration of oak seedlings. Oaks in general are an important food source for many species of animals, and in the case of many woodpeckers, the acorns are instrumental in the way they get insects that are crucial to their diet. Spenceville has numerous cache trees located on the wildlife area giving evidence of the high activity of woodpeckers there.
BLUE-OAK GREY (DIGGER) PINE
This habitat type is much like the Blue-Oak Woodland of SWA but is structurally more diverse in the canopy story, such as tree height and canopy closure. It has a mix of hardwoods, conifers, and understory of shrubs that tend to be clumped and interspersed with patches of annual grassland (DFG 1988). Tree species include Blue-Oak, which is typically the most abundant, and Grey Pine. Interior Live Oak and California Buckeye are also common to this habitat type. At lower elevations, such as those areas of Blue-Oak Grey Pine that exist at Spenceville, the understory is most often annual grasses with few clumping dispersement of California redbud, ceanothus, coffeeberry, poison oak, and blue elder among others.
Like the Blue-Oak Woodland, Blue-Oak Grey Pine communities also provide breeding habitats for a diverse group of animals. Twenty-nine species of amphibians and reptiles, 79 species of birds, and 22 species of mammals find this habitat type conducive to breeding (DFG 1988). The most common species seen in this habitat type at SWA include those of the Blue-Oak Woodland as well as wild turkeys, deer, and grey squirrels. Much like the Blue-Oak Woodland, the Blue-Oak Grey Pine communities are found along the foothills surrounding the Central Valley at a slightly higher elevation (DFG 1988) and are not an abundant habitat type. Figure 3 depicts the distribution of the Blue-Oak Gray Pine habitat throughout California. Although there is not a large amount of the Blue-Oak Grey Pine forest within Spenceville, its presence contributes significantly to the diversity of the area.
Annual grasslands have been historically abundant in California's Central Valley and Coast Ranges and are still a substantial part of the state's landscape. Figure 4 depicts the distribution of annual grassland habitat throughout California. This habitat type is largely composed of annual grasses, which are also common to the understory of some oak woodland habitats and occur mostly on flat plains to gently rolling hills (DFG 1988). Annual grasslands are significantly affected by grazing and weather patterns. Introduced annual grasses are the dominant plant species and include wild oats, ripgut brome, and fescue foxtail among others. Other plant species include fiddleneck, clovers, poppies, popcorn flower, and blue dicks among others (DFG 1988). There are numerous wildlife species that utilize annual grasslands for foraging purposes, including many birds of prey like the northern harrier, American kestrel, and black-shouldered kite. Loss of this type of habitat is detrimental to the survival of birds of prey as it reduces the availability of hunting grounds that support crucial prey species. At SWA, this habitat is particularly valuable to winter migrant raptors. Sensitive species include the ferruginous hawk, merlin, black-shouldered kite, and although not technically a raptor, the loggerhead shrike as well. Sensitive passerine birds include the chipping sparrow and the grasshopper sparrow (DFG 1996). The western fence lizard, common garter snake, western rattlesnake, black tailed jackrabbit, western harvest mouse, the giant kangaroo rat, and coyote are among many of the common species that are found in this community. Burrowing owls and the western meadowlark regularly use the grassland to breed.
VALLEY FOOTHILL RIPARIAN
The Valley Foothill Riparian community occurs along the California coast and inland to about 3,000 feet. It is often associated with valley bottoms along slow moving streams with deep alluvial soils and a high water table (Rogers et al. 1996). Figure 5 depicts the distribution of Valley Foothill Riparian habitat throughout California. This habitat has three distinct structural layers: canopy cover of 20-80 percent, subcanopy layer, and an understory shrub layer. The California wild grape is an important vine species to this habitat, providing 30-50 percent of the ground cover (DFG 1988). Valley oaks are the dominant vegetation type along major streams in Spenceville's riparian habitat. Cottonwoods play an important role in these areas and interior live oaks are present too. The sub-canopy trees include willows, Oregon ash, and white alder. The understory shrub layer consists mostly of willows, wild rose, blackberry, and poison oak, including a herbaceous layer of sedges, rushes, and grasses (Rogers et al. 1996). The Foothill Valley Riparian habitat provides resources that make it the most diverse and densely populated habitat in the Western United States, and it plays a crucial role in the migration and dispersal of wildlife as they use these riparian habitats as corridors (Rogers et al. 1996). Northern orioles are numerous breeders in the riparian areas of SWA.
FRESH EMERGENT WETLANDS
This habitat type is also among the most productive habitats in California, providing food, cover, and water for numerous species of birds, amphibians, reptiles, and mammals (DFG 1988). This habitat type was common throughout California before the turn of the century, unfortunately the acreage of these wetlands have decreased dramatically in acreage due to drainage and water diversions for others uses such as agriculture. Figure 6 depicts the distribution of Fresh Emergent Wetland habitat throughout California. It is characteristic for vegetation to occur in a series of concentric rings following the Central Valley basin contours. Plants are adapted to wet conditions; SWA species include big leaf sedge, baltic rush, and redroot nutgrass with cattails and bullrushes dominating the wettest sites (Rogers 1996). Animals that often benefit from Spenceville's wetland habitats include river otter, ducks, beaver, fish, belted kingfisher, and the California black rail.
Lacustrine habitats can be thought of as open water areas supporting aquatic food chains (Rogers et al. 1996). At SWA this habitat type is supportive to reptile, amphibian, bird, and mammal species and also include crayfish and 10 species of fish (Rogers et al. 1996). Lacustrine incorporates lakes, reservoirs, intermittent lakes, and ponds including vernal pools (DFG 1988).
Vernal pools are also a wetland type habitat that is included at SWA. Vernal pools are seasonally flooded depressions in the landscape that support a distinctive array of plant and animal species that are adapted to periodic or continuous inundation during the wet season and the absence of water during the dry seasons (Jones 1990). Vernal pools support a unique variety of plant species that are often endemic to the area, meaning they are restricted to a specific area and conditions. Vernal pools are well known for the abundance of rare, threatened, or endangered species, and are characterized by concentric rings of plants that flower as the pools dry (Jones 1990). These seasonal pools also support a particular variety of invertebrates such as fairy shrimp and tadpole shrimp, insects, and several amphibians such as the spadefoot toad and the California tiger salamander (Jones 1990). Many waterbirds also frequent the diverse pools including mallards and killdeer. Vernal pools are becoming increasingly uncommon due to the rapid development of lands supporting these habitat types.