Why Our Native Trees Are Dying—What YOU Need to Know

Many native forest trees are getting stressed and dying all around us. In more than fifty years of working with trees, I have never seen anything like this. What is going on?

The reason numerous native Douglas-firs, western redcedars, true firs, cottonwoods and other trees are looking so sickly and some are dying has to do with water—or the lack thereof. None of us can live very long without water, and we need a regular supply of it to survive. Without that…well, you know what happens. Trees are no different.

Yes, the reason many trees in our region are dying is because they are thirsty. As of the date of this blog post, all of the Willamette Valley in western Oregon is either in a moderate or severe drought (https://www.drought.gov/drought/regions and https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?West).

“Drought is a period with reduced precipitation and above average temperatures. Across all Oregon counties, 2013-2015 proved to be record drought years. Although these may be peaks in a drought cycle, trends show increasing average temperatures and decreasing average precipitation. In addition, winter snowpack has been disappearing earlier in the year and the duration of summer weather has been extended” according to the Oregon Department of Forestry’s article entitled “Drought Stress in Conifers” published in February 2019 (https://www.oregon.gov/ODF/Documents/ForestBenefits/Drought.pdf). The same article goes on to say that…

Drought conditions create water stress inside the tree and can reduce growth or cause mortality. Tree water stress is an internal shortage of water that occurs whenever water loss exceeds uptake long enough to cause plant damage or disturb physiological processes.

Drought damage in trees is due to one or all of the following factors:

  • Lack of available soil moisture due to reducedprecipitation, evaporation and/or runoff, poor water storage properties of soil (e.g., shallow soil, high rock or sand component) or competing vegetation.
  • Reduced uptake by roots and translocation throughout the tree due to damage to roots or water-conducting tissues from mechanical equipment, compaction, diseases, etc. Poorly aerated or waterlogged soils can starve roots of oxygen and also decrease water uptake.
  • Increased water loss due to exposure to wind (particularly easterly winds) and sun (particularly southern exposures), which increase transpiration and evaporation rates. (ibid.)

Not only this, but a region may have its regular amount of rainfall in a given season, but if the rainfall is erratic, this may cause stress and harm to some trees as well. As Dr. Christine Buhl, entomologist with the Oregon Department of Forestry, explained to me in a private conversation last year, imagine trying to survive on a glass or two of water every few days. Not possible. She told me that the same principle applies to trees. With our erratic weather patterns, in the nine months of the year when we used to get regular rains, the rainfall patterns are now erratic. Now it’s not uncommon to go for weeks with little or no rain causing the soil to dry out leaving trees with little or no water to take up. The result is stress on the tree due to thirst.

The reasons that the climate is so erratic is due to climate change, which is something that has been going on as long as life has been on the earth. Trees are continually having to adapt to changing climates. Only the fittest will survive. Weak species die out and those which are more adaptable win out. As the ODF fact sheet quoted earlier states,

Our changing climate can also directly increase the impact of native and non-native insect pests. Mild winters reduce mortality of overwintering insects, extended spring and summer conditions allow for faster insect development and more generations, drier weather reduces incidence of diseases in insect populations, changing conditions allow for range expansion (latitudinal and elevational), and synchrony with natural enemies may shift. Some of these changes, such as additional generations, are not instantaneous but occur over the course of several years or more.

Certain trees are more susceptible to stress than others. In March 2019, the U.S. Forest Service published a booklet entitled “Forest Health Highlights in Oregon, 2018” where it lists the trees that are that have the lowest tolerance to drought. Those with the lowest tolerance to drought include:

  • Western red cedar
  • Western hemlock
  • Some true firs
  • Several species of spruce
  • Red alder
  • Black cottonwood.

Those with the medium tolerance to drought include:

  • Douglas-fir
  • Bigleaf maple

So what can YOU do? First, identify that your tree is drought stressed. The main signs of this include:

  • The entire crown of the tree will begin to have a wilted or droopy look like any plant that is lacking water. Once the tree has a drink of water, the droopy look will leave and the tree’s foliage will look “perky” again.
  • After the wilty look occurs, pitch globules or droplets exuding from the trunk of tree through the bark will begin to appear.
  • The next stage of a tree exhibiting drought stress is an unusual and excessive needle drop.
  • As a result of on-going needle drop thinning of the tree’s crown begins to occur, so that you can easily see sunlight through it.
  • As the entire tree is beginning to show all of the above symptoms of drought stress, the needles then begin to lose their bright green color and begin turning yellow.
  • After turning yellow, the needles begin to turn brown. By this time, your battle is lost and it’s highly unlikely that you can pull your conifer back, even by extreme watering.
  • As needles begin to turn brown, whole branches will begin to die..
  • By this point, the tree is dying a slow death and it’s too late to do anything to save it.

After you have identified that your tree is stressed due to drought, give your tree regular drinks of water during warm and hot weather! This is easily accomplished with the help of a whirlybird or impulse sprinter or a soaker hose. Just make sure that the entire area under the tree’s foliage out to the drip zone (or edge of the branches) is thoroughly watered deeply (down at least six to twelve inches in the soil). Traditional lawn irrigations systems are designed to water grass whose roots are only an inch or two deep, and are thus inadequate for the deeper watering necessary to reach tree roots. During hot weather, I recommend watering your trees twice a week for several hours, and during warm weather at least once a week. With a shovel, dig down into the soil to ensure that the water is reaching the tree’s roots.

If you begin watering your tree during the early stages of drought stress, you can save easily save it. However, the longer you wait, the greater the chance of losing your tree.

Yes, if your trees dies, Good News Tree Service, Inc. of Wilsonville will be there to help you. But like your dentist whose focus is on prevention of tooth decay, our goal is to help you to preserve your tree. It’s not only the least expensive thing to do considering the cost of removal and replacement, but keeping trees healthy preserves property values, improves the quality of life of your living space, and it’s the right thing to do for the environment which benefits us all in too many ways to mention here, but which we have documented in previous articles on this blog.

If you’re in Wilsonville or the surrounding areas, and have concerns about your trees, don’t hesitate to call us. We give free advice over the phone, or will visit you and your tree either for free or for a minimal fee.

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