Why are more conifer trees looking shabby? It might be damage from the drought of 2015

Douglas Fir trees are showing drought damage around Washington state. Photo Glenn Kohler/DNR
Douglas Fir trees are showing drought damage around Washington state. Photo Glenn Kohler/DNR

Damage caused by last year’s severe drought is starting to show up in conifer trees across Washington state. As it does, DNR is receiving more reports of dead or damaged conifers , especially in lowland areas and sites with well-drained soils. DNR’s forest health experts say that in all likelihood, the signs of damage — entirely red crowns, red tops, or scattered red branches  — are the result of stress to the trees caused by last year’s extended drought. According to the U.S. Drought Monitor, the entire state was under severe or extreme drought conditions from late July through early October, making 2015 the worst drought year in the state since the late 1990s.

Drought symptoms made a delayed appearance

True, drought damage was visible in many areas last summer, but many of the affected conifers remained green for several more months as the weather cooled over winter. With this year’s warmer-than-normal (so far) spring, delayed drought symptoms have become noticeable in more conifers as the affected needles dry and rapidly turn red. In some trees — notably, the western hemlock — the appearance of drought symptoms was delayed until spring when the affected trees began dropping still-green foliage. Other symptoms of drought damage in conifers include rapid needle loss, dried buds, wilted shoots, and root systems that appear abnormal.

Most of the damaged trees examined by DNR foresters do not show any indication that pathogens, insects, or other animals are responsible for the damage. While bark beetles and wood borers have been found in some trees, their presence is probably secondary to the drought damage. In other words, drought stresses may have compromised the trees’ defenses making them more susceptible to bark beetle attack. The situation is  expected to continue until soil moisture conditions improve.

On the west slopes of Snoqualmie Pass, unseasonably warm spring days and hot, dry east winds have caused noticeable browning of conifer branch tips. Large numbers of trees on the west side of Stevens Pass between Gold Bar and Skykomish are showing similar damage. These conditions caused rapid water loss from needles at a time when trees were unable to actively replace the lost water. Most of the damage has occurred to newer needles which gives a scorched appearance to the outer crowns of affected trees, sometimes only on the east side of the tree. This type of damage is sometimes called “red belt” or “parch blight” and typically does not harm unopened buds, so those trees are likely to recover with some needle loss.

What to do

Forest health experts do not recommend attempting to water trees on forestland because the trees may become dependent on getting that extra water and then fail to harden off — reduce their growing cycle — when the weather turns cool next winter. The exception would be for landowners managing small areas of seedlings that need extra water after planting to become established.

Otherwise, it’s best to monitor drought-damaged trees for signs of improvement after spring bud flush or to spot damage from bark beetles or disease. Drought-killed trees close to buildings or areas where people gather or work should be removed.

Dead tops and branches will eventually fall and trees can grow new tops but the overall shape of the tree may end up deformed. Before deciding whether to remove a damaged tree, look to see if a normal flush of green buds has emerged this spring: it’s a sign that the tree may continue to grow and survive. As long as the tree has not lost the majority of its foliage, it is likely to recover as weather conditions  improve. Western hemlock is less tolerant of lost foliage than other conifers and might not survive if more than half of its foliage is lost. Surviving trees should also be monitored for evidence of bark beetle attack.

For more information on Washington’s forest health, visit www.dnr.wa.gov/ForestHealth

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