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Humans fostering forest-destroying disease
Date:8/15/2007

olleagues report 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. Californias oak woodlands have grown larger and denser over the past six decades. Counter-intuitively, this has made them more susceptible to being wiped out by the rapid onset 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 doesnt necessarily prevent disease, but it occurs at smaller levels in those areas.

This finding connects with research presented in the article forthcoming in Ecological Applications. Meentemeyer and colleagues discuss findings that further suggest humans have been causing landscape changes that are encouraging the spread of the disease. The study examines detailed aerial photography records for an area of northern California and shows that oak woodlands have increased in area by 25% over a 58-year period, while grasslands and chaparral shrublands (non-host vegetation types) have both significantly decreased.

The researchers suspect that the reason larger and denser patches of forest encourage the spread of the disease involves the role played by another California woodland treeBay laurel. Bay laurel is the primary carrier for the disease, since it acquires a non-lethal but highly contagious leaf infection. 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.

The effect of larger, cooler forests explained significant variation in infection level of P. ramorum, the article argues. We conclude that enlargement of woodlands and closure of canopy gaps, likely due to years of fire suppression, f
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Contact: James Hathaway
jbhathaw@uncc.edu
794-687-6675
University of North Carolina at Charlotte
Source:Eurekalert

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