How Do Western Hemlock Trees Adapt To Their Environment?

Every living organism changes and adapts over time, and hemlock trees are no exception. Western hemlocks, in particular, have adapted to a specific set of conditions common in the temperate rainforests of the northwest. So, how do western hemlock trees adapt to their environment? What has allowed them to become so tolerant of wet, shady conditions? Keep reading! In this article, we’ll answer these questions and more!

How Do Western Hemlock Trees Adapt to Their Environment?

how do western hemlock trees adapt to their environment

Western hemlocks are a type of evergreen. These beautiful, densely-needled trees are known for thriving in the temperate rainforests of the Pacific Northwest region of the United States.

So, what qualities have allowed them to adapt so well to this particular environment?

  • Shade tolerance: Western hemlocks do well in full and partial sun, but they also are able to thrive in full shade. This impressive quality allows them to grow in an environment where there is a lot of rain and cloud cover and where the young trees are often fully shaded by larger trees towering over them.
  • Soil moisture: Western hemlocks are shallow-growing trees, meaning the majority of their root system remains just below the surface throughout their lives. This allows them to tolerate a lot of watering since the surface soil drains well; their roots are also more resistant to rot than some types of trees.
  • Soil quality: Western hemlocks need loose, loamy, acidic soil to do well, but the soil doesn’t need to be particularly nutrient-dense. Studies have been done showing that hemlock can thrive even in nutrient-bare sand cultures; the important thing is that the soil is loose enough for its roots to stretch and spread out.
  • Drought resistance: Western hemlocks are not especially tolerant to long or severe droughts, but they do have a built-in method of conserving water that allows them to survive short periods of dry weather. Their stomata (pores in their needles that allow for the exchange of carbon dioxide and water vapor) are positioned on the undersides of their flat needles, where they are almost never exposed to direct sunlight.

The undersides of the needles tend to stay slightly cooler, which in turn prevents more water from escaping through the pores. 

How Are Western Hemlocks Adapted to Growing in the Shade?

As mentioned above, the high shade tolerance of western hemlocks is probably the most important factor in their adaptation to their environment. Most plants need full or at least partial sun for a good portion of the day; so what is it that allows western hemlocks to survive and thrive in the shade?

The answer is simple, really: the surface area of their needles is much greater than that of most evergreens. This allows trees that grow in full shade to make the most of the small amount of sunlight that reaches them.

Western hemlocks are known for having a very thick, feathery appearance. Their needles are fairly short, less than an inch long; but these needles are extremely broad relative to their length, and they are clustered thickly along the branches.

Because they are so broad, and because there are so many of them, they have a greater potential for taking in light and undergoing photosynthesis than most other evergreens. In other words, western hemlocks are highly efficient trees that are able to supply their own needs using far fewer resources than most other trees.

This benefits them in two ways:

  1. Hemlocks grow naturally in temperate rainforests, where it is rainy and overcast most of the time. Since there is little sunlight available in these regions, the hemlocks and other native trees and plants must be able to make do with what they get.
  2. Additionally, young hemlocks often get their start growing under larger hemlocks and other tall trees. These adult trees block out what little sunlight is available; therefore, the young trees have to survive and grow in nearly total shade.

Check out this video to learn more about this impressive evergreen tree:

What are the Best Tips For Maintaining Western Hemlock Trees?

Though western hemlocks are well-suited to growing in their natural environment, they sometimes struggle to thrive outside of this environment. If you are planning to plant this type of evergreen in your yard, there are some things to keep in mind to make sure it grows well.

Plant properly

Plant young saplings in the spring or early fall, and choose a location where they will not be exposed to harsh winds. The soil should be loose and full of organic matter such as compost or decaying wood chips. 

Dig a relatively shallow hole with a large diameter–at least five times the diameter of the root ball. Do not plant it any deeper than it was growing in its planter; remember, western hemlocks are shallow growers, so they don’t do well if they are planted too deeply.

If you live in an area with hot, sunny summers, you may want to plant your tree in an area where it will receive partial shade throughout the day. Though they thrive in full sun, they are used to coastal climates and will not do well in hot and dry conditions.

Water frequently

Western hemlocks are used to soil that drains well but never fully dries out. Unless you live in an area where these trees are native, you will want to water your hemlock often.

There is no need to soak the tree with every watering; in fact, it is better to give small amounts of water frequently than to flood the tree sparingly. Again, because the roots stay fairly close to the surface, it is important to keep the surface soil moist; but any excess water will simply drain away and go to waste.

Check for pests

Western hemlock appears to be more tolerant to pests than other types of hemlock, but it is still subject to infestation by the wooly adelgid and spider mites. Inspect your tree regularly for signs of insect damage, and if you spot a pending infestation, treat the tree with horticultural oil or insecticidal soap. 


Western hemlocks are well adapted to growing in the wet, shady conditions of the Pacific Northwest. They are highly efficient trees that are able to make use of what little light they receive, and their shallow root system allows them to tolerate the large amounts of rain common to their native rainforests. 

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