and shrub density, and plant type. An example of this can be seen by the commonality of annual grasses in open woodlands, a phenomenon that is not seen in dense woodland areas. All three oak species which characterize California oak woodlands can be defined as "long-lived, slow-growing trees." The frequent fires seen within the region have resulted in species such as coastal live oak and Englemann oak (which grow in drier, more fire prone regions) to have developed a resistance to low-intensity fires. This resiliency has resulted in coastal live oak emerging as the predominant species in cleared regions, as the trees have higher fitness to survive compared to less resistant, deciduous oaks. The same cannot be said for Oregon white oak, which populate traditionally wetter, less fire-prone regions, resulting in the trees having little built-up fire resistance. Because of the lack of fires in these northern regions, white oaks can have the threat of being outgrown by conifers growing in the understory. California oak woodland habitats contain some of the most wildlife in California. More than half of the species of terrestrial vertebrates in California are found in oak woodlands. This includes more than 120 species of mammals, 147 species of birds, and 60 species of amphibians or reptiles. The most diversity occurs when there is both multiple levels of vegetation heights and varied spacing between vegetation to create complex habitat structure both vertically and horizontally because there are more places for species that live in different layers of the vegetation. Among these species, the California quail (Callipepla californicus), Beechey ground squirrels (Spermophilus beecheyi), Botta pocket gopher (Thomomys bottae mewa), Audubon cottontail (Sylvilagus audubonii vallicola), deer (Odocoileus spp), bobcat (Lynx rufus californicus), coyote (Canis latrans) and the Pacific rattlesnake (Crotalus viridis oreganus) can commonly be found in California oak woodlands. Aspects of the California oak woodland that are important for wildlife of these habitats are habitat corridors, snags and downed wood. Natural vegetation create habitat corridors that connect the patches of habitat that host species. Habitat corridors provide protection and food for animals that migrate between patches such as deer, mountain lions, bobcats, or gray foxes. Snags are the standing wood that is left when trees die and are home to wood-eating insects that are food for animals such as birds. Snags provide temporary refuge for small birds, bats, swallows, salamanders, and lizards. Similarly, downed wood provide refuge for