Deadly blister rust targets sugar pines
November 6, 2007
A lone sugar pine, rising behind a North Shore neighborhood near Brockway Summit, is bursting with yellow-orange blisters – a sign that the tree will likely die within the coming year.
Like the canary in a coal mine, the ailing conifer is among a vanguard of Tahoe Basin pines that have fallen to a pernicious invader.
That’s what John Pickett, founder of the Sugar Pine Foundation, told the Reno-based Patagonia Environmental Grants Council, the foundation’s funding partner, at an informal meeting Monday morning.
The affected sugar pine is one of countless five-needle white pine trees throughout the Tahoe Basin and North America that have fallen victim to the deadly white pine blister rust, a nonnative and invasive pathogen, Pickett said.
Sugar pines, western white pines and whitebark pines in the Tahoe Basin are all threatened to the point of elimination by the deadly fungus.
Once it infects a tree, the exotic fungus disrupts the tree’s photosynthetic process by forming a “perennial canker” that blocks nutrient flow between the pine needles and the roots – essentially starving the tree, Pickett said.
“[Blister rust] is here to stay like any nonnative invasive [species],” Pickett said in a phone interview Friday. “It just thrives and it’s going to continue to thrive.”
But in the face of devastation inflicted by the blister rust, some sugar pines have resisted the fungus and remain alive and healthy.
On average, three out of every 100 sugar pines prove to be completely resistant to the fungus’ deadly grip, said foundation Executive Director Maria Mircheva.
The key lies in the tree’s genetic code, she said. And the Sugar Pine Foundation has found 19 such genetically resistant sugar pines in the Tahoe Basin.
While nothing can be done for the majority of Tahoe’s vulnerable sugar pines, the Sugar Pine Foundation is partnering with the U.S. Forest Service to breed disease-resistant seedlings for reforestation.
“We are going to capitalize on that,” Pickett said. “We are going to find those resistant trees and plant them.”
According to Pickett, the Sugar Pine Foundation is “speeding up a million-year process.”
“Speed up or slow down a naturally occurring process – that’s all a forester can do,” he told the Patagonia council.
Founded in 2004, the Sugar Pine Foundation is one dominant-gene-holding tree away from its goal of finding 20 resistant mother trees. The foundation intends to plant 2,000 to 3,000 seedlings by next fall, Mircheva said. The offspring of the resistant sugar pines have a 50 percent chance of carrying the genetic code that will make them invincible to blister rust.
Mircheva said the seedlings will be available to replenish the trees destroyed in the Angora Fire.
Though the Tahoe nonprofit group has not found any seedlings for blister rust-resistant western white pines, suitable trees are known to exist, Pickett said. The future is grim, however, for whitebark pines, which are found in the highest elevations of the Sierra Nevada, he said.
“The prognosis for whitebark pine is poor,” Pickett told the Patagonia team. While scientists are “working feverishly” to find a resistant whitebark dominant gene, Pickett said their elimination, at the current rate, is probable.
Blister rust reduces the infected tree’s capacity to compete with neighboring healthy trees for food and water, said Assistant Staff Officer Dave Fournier of the Vegetation, Urban Lots, Fire and Fuels department in the U.S. Forest Service Lake Tahoe Basin Management Unit.
“If we are indeed on the cusp of another drought year, you would see the effect of [blister rust] even more dramatically,” Fournier said.
The rust also heightens the sugar pine susceptibility to bark beetles, which are attracted to weakened trees, he said. The infected tree in the Kingswood West neighborhood was finished off by bark beetles – evident in the pervasive red pitch dripping down the trunk.
By killing off trees, the rust further exacerbates the threat of catastrophic wildfire, Fournier said.
“On a tree-by-tree basis, what you would end up having is, say, more limbs dying and falling to the ground,” he said. “If a fire were to occur, that additional fuel at the base of the tree could spell doom.”
Pickett said the resistant seedlings will be planted throughout the entire Tahoe Basin. To maximize the genetic exchange, seedlings from the North Shore will be planted on the South Shore, and vice versa. The idea is to prevent the growth of a monoculture of resistant trees that would be more vulnerable to blister rust’s evolution or other pathogens, he said.
White Pine Blister Rust was introduced to North America through Vancouver, Canada, in the early 1900s. The native Asian disease has since wreaked havoc on five-needle pine populations throughout North America, from sea-level to elevations of 13,000 feet, said John Pickett, who founded the Sugar Pine Foundation.
The fungus spreads through its spores – like dust in the wind, said Executive Director Maria Mircheva of the Sugar Pine Foundation.
Besides the five-needle pines, the pathogen is dependent on a secondary host – Ribes plants, which include gooseberries and currants, Mircheva said.
The fungus matures on the plant and then spreads to a tree, she said.
For more information, visit http://www.sugarpinefoundation.org.