Recent drought causes weak trees that are more susceptible to attacks from bark beetles.

COURTESY: CHRISTINE BUHL, OREGON DEPARTMENT OF FORESTRY - Drought may result in a thinning canopy or stress cones. 
It rains a lot here, but lately it's not enough to meet the needs of thirsty trees.

Oregon's Department of Forestry expects more trees to die this year from drought and attacks by bark beetles. Last summer was warmer than normal, and the last winter was drier than usual. Both may contribute to the trees suffering in coming months.

According to Oregon Department of Forestry entomologist Christine Buhl, warm days in spring mean beetles start attacking earlier in the year. Bark beetles serve an important purpose in the forest ecosystem, picking off the weak trees, allowing the stronger ones to thrive.

However, when all trees in the forest become weak from things like drought, beetle populations can increase. The increased numbers give the beetles an upper-hand against the normally strong, healthy trees stressed out by drought. The result is more dead trees.

Oregon had only one good year of rain since the drought of 2012 to 2015, according to the Department of Forestry, and we're still feeling the effects from the lack of precipitation. Trees remain damaged, and may never fully recover if drought trends continue. Symptoms of damaged trees are typically not seen until the following spring, but the department says recent droughts have been severe enough to where we could see the result of drought by late summer to early fall the same year.

Climate change can directly affect these conditions, and contributes to the increase of bugs. Warmer winters allow more insects to survive that would normally die off, and a longer spring and summer mean more time for reproduction and new generations of insects. Dry weather during drought also means less bugs dying from disease and more to attack thirsty trees.

COURTESY: CHRISTINE BUHL, OREGON DEPARTMENT OF FORESTRY - Drought may result in flagged branches.Damage from drought affects trees on the edge of forests the most, or trees in shallow or rocky soil. "Trees growing near roads, ditches, pastures, or in areas of soil disturbance or abundant competing vegetation are most frequently affected," according to the Department of Forestry.

Beetles are considered secondary agents in attack, since the tree is already damaged and they can't kill healthy trees on their own. Healthy trees are able to defend themselves, but when weakened from drought, their means of defense are weakened.

The Mountain Pine Beetle is the most destructive bark beetle in the West. According to foresters, between 2007 and 2016 it is estimated that 380,000 acres per year contained dead trees due to the pine beetle. The trees it affects the most are lodgepole, ponderosa, western white, sugar and white bark pine.

Other beetles are also very damaging during drought conditions, like the fir engraver and ips beetle.

The forestry department advises tree and forest owners to plan ahead and consult with an arborist or forester to help healthy trees survive, despite lower precipitation. This can include removing some trees or competing weeds to allow the remaining trees to get enough food and water during dry spells. Avoid fertilizing and planting less drought-tolerant trees such as Douglas fir in areas historically dominated by more drought-tolerant trees such as oak and pine.

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