Drought, Bark Beetles, and Tree Mortality in the Sierras

Drought, Bark Beetles, and Tree Mortality in the Sierras

If you like learning about the natural world, be sure to check out our free seminars. Come to the park to learn in the morning, picnic at noon, and hike in the afternoon. It makes for a great day!

On May 13, 2017, our special guest was Dr. Christopher Fettig, Research Entomologist and Team Leader for the Forest Service. He spoke on climate change, the drought, this past wet and cold winter, and the effects of all this on the bark beetles.

As explained by Dr. Fettig, bark beetles are a natural part of the ecosystem. Normally they act to thin out the forest by attacking the weakest trees – usually just one or two per acre. Healthy trees can stop an attack by secreting resin and expelling the pioneer female beetle. However, our forests have been severely weakened, because there simply hasn’t been enough water. The multi-year drought is partly to blame, but the suppression of fire has also led to vast overcrowding of trees.

How a bark beetle invasion begins

Lack of water can cause cavitation in the tree cells that pull up water. Cavitation acts like an air bubble in a straw, so the tree cells can’t function and can’t recover. Trees weakened this way can’t survive an initial attack by bark beetles.

  • A pioneer beetle that establishes itself in a tree sends out a chemical invitation for a mass attack.
  • Eventually, there are so many beetle larvae (usually over 8,000) in a tree that the chemical message is changed to “no room in the inn, go elsewhere”.
  • A tree full of beetle larvae can still be green, but it’s doomed and will suddenly turn brown.

There is intensive research into the second chemical message of “no room in the inn”, and there are some products on the market that attempt to replicate this message when applied to healthy trees.

What to expect in 2017 and beyond

The cold winter probably killed about 80% of the beetle larvae already in the trees, and the weakened trees can’t supply enough nourishment for healthy beetles to develop. Dr. Fettig expects the epidemic will diminish, but many more trees will continue to die.

The long-term solution is thinning the forest – which is occurring now because of both bark beetles and wildfires.

Interested in a follow-up seminar?

Based on questions from the audience after his talk, Dr. Fettig expressed a willingness to return and do a follow-up seminar on how to preserve your still-living trees. If you would like to attend such a presentation, please contact Vida Kenk at vidakenk@comcast.net  and she’ll try to arrange an additional seminar on that topic.

Here are three interesting publications provided by Dr. Fettig regarding management options for bark beetles.

Fettig2016-2-2-2016 FettigandHilszczanski-Ch14-1-15-2015 Fettigetal-1-30-2013

FettigandHilszczanski-Ch14-1-15-2015

Fettigetal-1-30-2013

More seminars to come in 2017

Be sure to mark your calendar for our upcoming seminars. We have great speakers who love to share their expertise and answer your questions.

Thank you Sanders LaMont and Vida Kenk for organizing our seminars!

2017-05-17T16:58:28+00:00