Humans worsening the spread of forest-killing disease in California
Humans worsening the spread of forest-killing disease in California
mongabay.com
August 15, 2007
The spread of Sudden Oak Death, a disease that is rapidly killing forests in the western United States, is being worsened by human activities, report studies recently published in the Journal of Ecology and Ecological Applications.
In the research, Ross Meentemeyer, a landscape ecologist at the University of North Carolina at Charlotte, and colleagues show that “years of fire suppression and other land-use practices have altered structure and composition of forests in way that may facilitate spread of the disease.” The researchers found that over the past 58 years California’s oak forests have grown larger and denser, making them more susceptible to outbreaks of sudden oak death.
“More connected forests have more disease,” said Meentemeyer. “Smaller and more isolated forests have less disease. Being smaller and more isolated doesn’t necessarily prevent disease, but it occurs at smaller levels in those areas.”
Meentemeyer and colleagues say that Bay laurel — another common California woodland tree — is the culprit.
“Bay laurel is the primary carrier for the disease, since it acquires a non-lethal but highly contagious leaf infection,” explained a statement from University of North Carolina at Charlotte. “Bay laurel seems to be increasing in abundance in the changing forests and to make matters worse denser forests create cooler and moister understory microclimates that encourage the spread of the bay laurel leaf infection, which in turn can lead to the fatal infection of the oaks.”
Meentemeyer says that humans may be further facilitating the spread of the disease by unintentionally transporting small amounts of infected soil.
“There is some compelling evidence that humans could be moving the disease in infested soil,” Meentemeyer said. “We have found evidence for human involvement at three different scales of analysis. First of all, the pathogen is much more likely to occur along hiking and biking trails, where humans travel. Second, using some of our landscape and regional data, we have shown that highly visited state and county parks have more disease than private ranches and lands that have very limited visitation. We have also found on an even broader scale across the state of California that forests surrounded by high human population densities are more likely to be infected”
“People tend to not care about plants and forests as much as we do about humans and animals, but sudden oak death could be a bird flu of the plant world waiting to happen,” added Meentemeyer. “This may be even worse than chestnut blight in its impact on our forests, since it is affecting multiple keystone species.”