The day I visit Cosumnes River, I am shown around by Sara Sweet, a restoration ecologist with The Nature Conservancy, the organization that helped establish the preserve. Even after a dry winter, the green, moist signs of spring are everywhere. Valley oaks leaf out with bright, light green foliage. Wildflowers pop from oak-sheltered glades.
“At Cosumnes, you see not only oak restoration but the whole rich ecosystem that oaks help create,” Sweet says. For Cosumnes is an even more complex story than it first appears. This green refuge is in part manmade—an attempt to atone for all the bad things we’ve done to oaks over the past 150 years.
Almost as soon as American settlers arrived in California, they began chopping oaks down. In the 19th century, farmers cleared oak woodlands to make way for crops and grazing; by 1900, an estimated 90 percent of the oak forests that edged the Central Valley’s rivers had been destroyed. In the second half of the 20th century, suburban development from the San Fernando Valley to the Sacramento Valley reduced the oak population even more. Biologists estimate that more than a third of California’s original millions of acres of oak woodlands has been lost. And the California Oaks organization estimates that another 750,000 acres of oaks are at risk in the next 30 years.
The bulldozer isn’t the only threat. Sudden oak death, a pathogen first detected in 1995, has now spread through oak forests of Northern and central California, killing more than a million oaks of several species and infecting at least another million.