California’s extreme drought has stressed many of San Luis Obispo County’s plant and wildlife ecosystems, but the situation has not yet become a crisis, experts say.
Hardest hit are the county’s threatened steelhead populations, which have been blocked from coastal spawning streams because of low water levels.
Other wildlife species are under pressure from the drought, but most are surviving because they are adapted to seasonal dry periods. In Cambria, however, native Monterey pine stands are showing elevated levels of mortality.
“When we have an extended drought like this, most animals are adaptive, mobile and can find sources of food and water,” said Jason Holley, a supervising wildlife biologist with the state Department of Fish and Wildlife. “Small mammals and salamanders are not so mobile, so if the drought persists, they could have a hard time.”
Plant communities, such as chaparral and native bunchgrass, are brown and sickly looking in many areas. Some plants have died but many are dormant and will rebound once wetter conditions return, said Robert Hill, San Luis Obispo’s natural resources manager.
The county has a Mediterranean climate with hot, rainless summers and much variability in precipitation from year to year. This means native plants are well-suited to survive even during extended dry conditions.
Even the small amount of rain the county has received since the first of the year is having a positive effect, Hill said.
But the situation could turn dire if the drought persists into next year. Plants on south-facing slopes with shallow soil generally are the most vulnerable. Such sites are hotter and drier than other areas.
“I am seeing signs of stress, but I am not seeing catastrophe,” Hill said. “We are concerned and monitoring.”
Steelhead trout top the list of species imperiled by the drought, because starting in December they swim up coastal streams to spawn and then return to the sea. Low stream flows from the drought either prevent the fish from entering the stream or cause them to be stranded in pools.
The U.S. Geological Survey estimates that most streams along the Central Coast are flowing at less than 10 percent of normal.
Creeks and tributaries are little more than dusty draws this winter, said Kaila Dettman, executive director of the Land Conservancy of San Luis Obispo County.
“In areas where we are normally seeing adult fish, we aren’t seeing them at all,” she said. “Even streams like San Luis Obispo Creek. That still has a little water in it, (but it) doesn’t have any steelhead that I can see.”
In response, state wildlife officials recently closed to fishing all streams in the county between Highway 1 and the ocean. It will probably take several years to determine the long-term effect of the drought on the steelhead population, officials say.
Trees are also feeling the effect of the dry conditions. Trees such as oaks are normally drought tolerant, but leaves on some trees are brown and falling off this winter and the acorn crop is stunted, Dettman said.
Drought stresses trees and lowers their defense to diseases and parasites such as decay fungi and boring beetles. Small trees and very old ones are particularly vulnerable.
About a quarter of the native Monterey pine forest in Cambria is dying, said Rick Hawley, executive director of Greenspace-The Cambria Land Trust. He attributes this to the drought rather than bark beetles.
The pines have been hurt because of a combination of a lack of rain and fog. In coastal areas, fog provides moisture even during rainless times because it condenses on plants and drips to the ground, a phenomenon called fog drip.
“Fog is down anecdotally, and even the dew has been marginal,” Hawley said. “I’ve lived here 40 years, and I’ve never seen so many trees die, both Monterey pines and oaks.”
One plant species of particular concern around San Luis Obispo is the Chorro Creek bog thistle, which is federally listed as endangered under the federal Endangered Species Act. As the name implies, the bog thistle is adapted to wet areas and needs a constant source of water, usually in the form of a seep to survive, even if it is a trickle.
“We have bog thistle sites at Laguna Lake and other places, and the seeps are continuing to flow,” Hill said.
Although large wildlife species are avoiding the worst effects of the drought, they are also showing signs of stress. The main indicator is that they are beginning to congregate near lakes and populated areas in search of food and water.
“There are fewer food sources for everything from butterflies to deer,” Dettman said.
When prey species such as deer begin to congregate around people, they are likely to attract large predators such as mountain lions and bears that can cause problems or pose a public safety threat.
“I have noticed the local deer populations eating plants like hedges that have never been on their preferred menus,” Hawley said.
People should resist the temptation to feed and water wildlife. It is illegal to feed wild animals and ultimately increases the danger to deer in terms of predation and disease, wildlife officials say.
“For most wildlife, it’s too early to predict the outcome of the drought,” Holley said. “The drought also increases the fire danger which can damage wildlife habitat.”