Wildlands of Cal Poly Pomona

 Natural Communities

The wildlands belong to three ecological communities. Two of them, Coastal Sage Scrub and Oak Woodland, are intermixed along the west side of campus. The third, Walnut Woodland, covers the hills on the south side.

Coastal sage scrub is the most diverse community on campus. Over 150 different species of plants occur in the wildlands, and almost all of them can be found in coastal sage. The “sage” of coastal sage refers to two different kinds of plants, the “true sage” of the mint family (Cal Poly has two common species, black sage and white sage), and California sage, which is a sagebrush of the sunflower family. All of these, and a number of other species, are fragrant, especially in the late spring and early summer.

Fire is a major force that shapes coastal sage scrub. Most of the species are adapted to fire. Many of the shrubs and trees resprout from underground roots or stems after a fire. There are some wildflowers that require fire for seed germination; these are only seen in the years following a fire. About half of Cal Poly’s coastal sage burned in August of 1981, and virtually all of it burned at the end of July in 1989. Its current vigorous growth attests to its adaptation to fire.

Large tracts of southern California were once dominated by coastal sage scrub. Many of these areas now support tracts of houses, businesses, and industry. Coastal sage scrub is perhaps the most quickly vanishing community in the region.

Oak woodlands are scattered in small patches among the coastal sage scrub, primarily in north-facing canyons. Because these canyons get little direct sunlight, they tend to be cooler and wetter than surrounding areas. In areas closer to the coast, oak woodlands are more continuous.

Few plants grow in the deep shade of the evergreen oaks, but the clearings support most of the same species found in coastal sage scrub. These oaks are very fire-resistant, and none were killed in either the 1981 or the 1989 fires. The slow-growing oaks are probably the oldest trees on campus.

Southern California black walnut trees are found throughout the region in a variety of habitats, including coastal sage scrub and oak woodland. But Cal Poly has the distinction of being one of the few places in the world where they are the dominant trees in their own community, the walnut woodland.

Walnut woodlands in other parts of southern California often include other tree species, such as live oak and toyon, as well a shrubs, but the woodlands of Cal Poly and other parts of the San José Hills have few other trees or shrubs, and are dominated by grasses in the understory, in the valleys, and on south-facing slopes. These grasses are currently introduced Eurasian weedy grasses, and intentionally-planted, largely non-native range grasses. No one knows what grew between the walnuts before European settlement and grazing.

Grazing has been blamed for the low plant species diversity of the walnut woodlands, but diversity is low even in areas that have not been grazed for years or decades. It is likely that grazing has an impact on walnut woodlands, but there are no studies of what that impact might be.

A more likely explanation for the low diversity also explains the sharp contrast between the coastal sage scrub/oak woodland in the western part of campus and the walnut woodland in the south: these communities are on different soil types, and the soil that supports the walnuts is unusual for the area, being higher in calcium carbonate than many other regional soils.