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Plant Answer Line Question

Keywords: Fraxinus latifolia, Plant longevity, Populus balsamifera ssp. trichocarpa

Do you know which type of cottonwood tree is growing along shores of Lake Sammamish, and the normal life expectancy is for these trees? Someone told me they are "blackheart cottonwoods." Is that true?

We also have Oregon swamp ash growing here. Are these trees really just indigenous to Oregon, and what is their life expectancy?


I could not find any reference to "blackheart cottonwood," but here is information about black cottonwood (I cannot be sure these are the trees you have around Lake Sammamish). Populus balsamifera ssp. trichocarpa (its botanical name) is native from southern Alaska to northwestern Mexico, according to Arthur Lee Jacobson's Trees of Seattle (2006). It has a relatively short life span (and probably shorter in urban and suburban settings than in the wild) of 100-250 years. These trees have brittle limbs, and sometimes fall prey to strong winds. Jacobson mentions several hybrid cottonwoods, one of which closely resembles the native species but is crossed with a northeast Asian species, P. maximowiczii.

Just to complicate things, there is another Populus whose common name is black poplar (Populus nigra) and it is native to northwest Africa, Europe, western Siberia, and the Caucasus. There are many varieties of this Populus as well.

The USDA and CalFlora have information about black cottonwood for you to compare with the trees around the lake. Compare and contrast with the USDA page on black poplar.

As for the longevity of these trees, see what Arthur Lee Jacobson says about old trees. Here is an excerpt:
"Frequently the oldest trees are not the largest, so it is not as simple as finding the biggest trunk. Cottonwoods grow gigantic in a hurry, then bust up, earning their nickname rottenwood."

Arthur Lee Jacobson has led tours of the trees on the Sammamish River Trail, and he is the best-versed person locally on what trees are growing in our area, so you may want to contact him directly.

As for Oregon swamp ash, there are trees called Oregon ash, and trees called swamp ash, but I could not find a tree called Oregon swamp ash. Oregon ash is Fraxinus latifolia, and is a Northwest native whose range also extends to southern California. According to Jacobson's book, it closely resembles green ash (Fraxinus pennsylvanica), except that the native species has bark which flakes easily from the trunk, leaflets of 7 (rather than 9) which are hairy, rounded and broad. Its seeds are broader than green ash.
The USDA Forest Service has detailed information as well. Below is an excerpt:
"Oregon ash has moderately rapid growth for 60 to 100 years and attains a height of 18 to 24 m (60 to 80 ft) and a d.b.h. of 40 to 75 cm (16 to 30 in) in 100 to 150 years on good sites. Individuals may grow twice as large and reach 200 to 250 years of age under favorable conditions, although they generally grow slowly after their first hundred years."

The website SelecTree says Oregon ash trees usually live over 150 years.

Swamp ash is also known as black ash, or Fraxinus nigra, and is native to the northeastern swampy woodland areas. They are not mentioned in Jacobson's book or in other local sources, so I suspect they are uncommon in our area. Here is a link to the Forest Service description of this tree.

Date 2018-03-07
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May 31 2018 13:14:08