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Preparing Trees for Winter Storms

Autumn is a perfect time to walk our landscapes and inspect the trees in order to minimize or prevent possible damage which may occur from upcoming winter storms.

What you can do?

Learn to spot the eight warning signs of structural tree defects.

What a Collier Arbor Care Certified Arborist can do for you?

Depending on your tree care needs, a Collier Arborist might recommend to...

Trees are living organisms. Their integrity and stability change over time. Inspect your trees regularly to ensure their longevity and health.

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Western Red Cedar — natural foliage drop. Note tips are green.


Seiridium Canker disease causing un-natural whole branch dieback.


Interior foliage is turning brown — a normal occurrence.

Evergreen Foliage Drop (Natural Foliage Drop)

Every fall our office is inundated with client phone calls concerned with their evergreen trees turning brown and they are convinced they are dying. However in most cases, this is nothing to be concerned about. What is happening is commonly called evergreen foliage drop, a natural occurrence.

All trees and shrubs renew their foliage annually, producing new leaves in the spring and shedding the old leaves in the fall. The leaves of deciduous trees like maples and oaks live for just one growing season and then fall off usually in a blaze of color. Foliage of evergreen trees lives from one to several years old depending on the species. As new growth emerges in the spring the older growth becomes shaded and its role in photosynthesis is diminished. During the year this inner or older foliage dies, turns brown and is shed, especially in the fall.

In some species like pines, cedars, arborvitae and sequoia, this fall browning can take place rather suddenly. Sometimes this natural occurrence is hardly noticed but this year it is especially noticeable and people are concerned.

The natural foliage drop can be distinguished from disease by its uniform appearance over the whole tree and other neighboring trees of the same species having similar symptoms. It is confined to the innermost or oldest foliage or needles. The amount of foliage drop depends on the vigor of the tree, and of the preceding growing season especially in a drought year.

However, there are other serious disease problems that cause foliage browning, but the pattern of symptoms and dieback is different. For example, we are experiencing a canker disease called Seiridium in incense cedars that causes a scattered (not uniform) but severe branch dieback. Large branches will turn brown and die usually in the lower half of the tree. Diseased branches should be removed. If the new, terminal or current year’s growth is green and vigorous, the health of the tree is not in jeopardy from natural foliage drop in evergreens.

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The arboreal acrobat: Eastern fox squirrel.

Squirrels remove the bark to feed on the cambium layer causing branch die back.

Animal Damage to Trees: Signs & Solutions

Many animals such as beavers, sapsuckers, and deer can damage trees but the worst culprit in our area are those arboreal acrobats, the rats with busy tails — the squirrel. This year the squirrel damage was particularly severe. While many tree species are susceptible, the trees with the most damage are our native big leaf maples, and Oregon white oak. Damage appears as branch flagging; the foliage on the branch turns suddenly brown and dying. Although mature trees are not killed by squirrels, we have seen trees with up to 40% crown dieback from the branch girdling. The squirrels will chew the bark off a branch, thus girdling it, causing it to die from that point outward.

The main reasons for the damage:

The non-native Eastern fox squirrels are the most common squirrel in the Portland area. Fox squirrels are reddish brown in color with large bushy tails and tan undersides. Over population seems to be the main cause for the profusion of tree damage.

Ways to minimize tree damage:

Sapsuckers (a type of woodpecker) also damage trees. Typical damage observed on soft-wooded trees is neatly spaced horizontal or vertical rows of holes in the tree trunk or on the branches. The trees most often attacked by sapsuckers are pine, spruce, birch, and fruit and nut trees. Occasionally, other trees are damaged. Rarely do the sapsuckers kill a tree but we have seen small trees girdled from their damage. The sapsucker relies on tree sap for more than one half of its diet. Sapsuckers often attack the same trees year after year, feeding on the sap and insects associated with the tree wounding. Control of damage is difficult, but some success can be obtained using strips of shiny Mylar or balloons that startle and scare the birds. Wrapping the trunk with burlap will also prevent damage.

Deer damage to trees can be extensive in the urban rural interface. Recently, a newly planted magnolia suffered extensive damage from bucks rubbing antlers on the tree bark. Fencing off areas or spraying plants with a deer repellent can prevent damage.

If you live near a stream or lake beaver damage can be common. Walking along the Willamette River near OMSI, several young Oregon white oaks felled by beavers have been observed. Protect against beaver damage by double wrapping the lower trunk with chicken wire. Make sure to re-adjust the wire wrapping to allow for trunk growth.

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