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Despite Wet Winter, Bark Beetles Still Attacking Trees

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Sonora, CA — While the trees across the Mother Lode may be regaining vigor from this past season’s heavy rains, experts caution landowners to remain vigilant.

During a Mother Lode tree mortality tour as reported here, Jodi Axelson, an attending cooperative extension specialist in forest health, stated last fall that plans were in the works for research and landowner extension support dealing with bark beetles.

Axelson, who is based out of the Department of Environmental Science, Policy and Management at the University of California at Berkeley, shares the latest on the bark beetle epidemic with Clarke Broadcasting, along with details of what property owners should be watching for in their pines now — as we are entering the insects’ most active time of the year.

While Regaining Vigor Trees Still Under Attack

Asked if this past winter has made a dent in dissuading the critters, particularly the western pine beetle, which is responsible for decimating ponderosa and Coulter pines across the Sierra Nevada, Axelson couches her reply. While the extraordinarily heavy precipitation did help the trees, she says realistically — and typically — we should still anticipate a lag of a few years from the time they start to regain more vigor before the bark beetle outbreak finally collapses.

“I am really curious to see how quickly or slowly the outbreak does that…bark beetle outbreaks do always end — and tree vigor can be a big part of that — so it is fantastic that, at least this year, the trees will not be stressed but they also do not recover immediately,” Axelson reemphasizes.

In fact, Axelson reports that her department is busily ramping into multi-agency research projects that, as the summer progresses, will help gain a better understanding of the current bark beetle population. One study will utilize student teams, who will spend the summer in the Sierra, charting the outbreak across a latitudinal gradient and within it from the south to the north at different elevations. Along with other UC-Berkeley professors, the collaborators include a team of scientists from the US Forest Service, USGS, National Parks and State Forest services.

Summer Study Will Gauge Beetle Population  

“What is going to be good about this project is we are not only going to be able to get a sense of how many trees are dead in any given location, in a plot that we work in, but how active the beetle is,” Axelson states. This will help determine what kinds of trees are currently being attacked, what is already dead and what no longer has any beetle in it.

She expects this will help gauge the risk of bark beetle pressure staying high, provide a snapshot at what the future forest is going to look like — as well as address the amount of carbon that has been lost and kinds of fuel loads that are building from the dead trees on the landscape.

“Collaborating with so many other scientists…not only are we able to answer a whole lot of different questions, both science and somewhat management-related, but we can also make sure that, with the work others are doing we can get a good cross-section,” Axelson maintains.

Landowner Tips, Resources

As for landowners, Axelson points to extension programs doing outreach in the harder-hit counties, like Tuolumne, which have turned to providing reforestation education. Experts are now sharing with property owners about what will likely grow after dead trees are removed as well as best practices for removing freshly attacked trees. For the county’s resource page, click here.

“I say the most useful thing for landowners will be to check their property for trees that…have a red crown or are turning yellow,” Axelson advises. “In red trees, the beetles are gone and so those trees do not really pose a forest health risk, although they can to buildings or an accumulation of fuels. Bark beetles tend to be lazy, so look at nearby green pine trees….for evidence of [new] attack.”

The most telling hallmarks are pitch tubes, which Axelson describes as creamy blobs of pitch on the trees, high up on the crown; also froth mixed with the fine yellow-orange sawdust that beetles create as they bore into a tree. She stresses, “So, if [owners] have a totally green tree that is exhibiting some of these symptoms, they could have a brand new attack on their hands — and those are trees you want to remove.” After felling, these trees should be shredded and or chipped to break down the bark, and burned to ensure that all the beetles within them are killed.

How To Get Ahead Of New Outbreaks

Western pine beetles are particularly tricky and defy treatment, especially when populations are high, according to Axelson. “Throughout the season, keep checking [even apparently healthy pines], and if possible, get them down when there are still beetles under the bark. When a tree is mass-attacked or just starting to turn yellow…there is no coming back for that tree,” she states. “If we can get ahead of [the outbreaks] instead of chasing the dead trees where the beetles are already gone…there is a chance of kind of dampening down of the population at small spatial scales.”

Now is the best time to remove dead and bark beetle infested trees as, through the summer, the insects are on the move. Since fresh wood attracts them, try not to damage remaining trees on your property while clearing out the problem ones. To view CAL Fire’s bark beetle checklist, click here.

Axelson also points to the University of California Forest Research and Outreach tree mortality replanting and reforestation resources, available online by clicking here.

For those in replanting mode, on Sunday, April 23 from 11 a.m. until 3 p.m. the Calaveras County Tree Mortality Task Force is giving away 5,000 pine seedlings to anyone interested. For details, click here.