That tree isn’t dead: it’s a western larch!

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Image from http://www.cnr.uidaho.edu/ietic/2programs.htmWestern larch is one of my favorite trees. It seems like every year at this time, someone points at a yellowing tree and says something like “that tree is dying!”

That tree is a western larch (Larix occidentalis), and it is not dying. It is simply losing its needles like it does every fall.

Western larch violates the rule we learned in school: deciduous trees have leaves and lose them in the fall, while coniferous trees have needles that stay on the tree through the winter. 

Fast growing, limited to the northwestern United States

Base map copyright Google MapsWhile there are many species of larch around the world, western larch is limited to the Rocky Mountain region of the northwestern United States. I became enamored with western larch while living in northeast Washington State where entire mountain hillsides turn flaming golden yellow in the fall, and in the spring the new growth is a bright lime-green color.

I was reminded of western larch this week as I drove west-to-east past Mt. Hood, Oregon, and passed through a larch population that exists in a narrow band on the eastern flank of the Cascade Range. A passenger in the truck said, “Those trees are dying!”

Western larch is a fast growing tree. It is one of the first trees to regenerate after a fire. It successfully competes against slower growing trees for sunlight. It often occurs in even-aged stands, so if you see lots of trees of about the same age, you may be looking at a forest that has regrown after a forest fire.

Why does western larch drop its needles?

Western larch is so interesting because it is a conifer that loses its needles in the fall. What was the evolutionary pressure that caused a needle-leaved tree to invest energy regrowing needles every year?

I suspect it is partly due to the relationship of western larch and fire. Western larch and ponderosa pine both grow heavy, thick bark that is resistant to fire. Occasional fires help these species compete with other plants.

For western larch, losing needles late in the season may be a response to late-season crown fires. A crown fire jumps from tree to tree, and dry trees at the end of a hot summer are much more susceptible to this kind of fire. Losing the resinous needles in the fall would help protect western larch trees from this kind of damaging fire.

Want more information?

Here are some links to good information about this unique and delightful tree species:

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