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First light on autumn larches. Photo by Andrew Bertino

The Science of Larches

Why they grow here, why they lose their needles and why they they turn such a glowing gold | by Melissa Ozbek

Larches are a pot of gold in the fall hiking season; their flaming yellow needles turn a Cascade landscape into something ethereal and otherworldly. The few short weeks when the larches’ needles turn golden—typically late September into early October—make them all the more precious to spot. It’s no wonder we call our annual search “Larch Madness.”

But what do we know about larches? Ask a hiker or a park ranger what a larch is, and you’ll likely hear “deciduous conifer.” But what does that really mean? Why can’t we find them (for the most part) in Western Washington? And why do their needles turn yellow? With the help of trusty field guides and local experts, I set out to answer these questions.

You may have heard larch in Washington called tamarack, but that is actually the name for a different species that grows on the East Coast. Photo bu Craig Smith.

I started with “Natural History of the Pacific Northwest Mountains” by Daniel Mathews and “Northwest Trees” by Stephen Arno and Ramona Hammerly. According to Mathews, there are two larches native to Washington state: the western larch (Larix occidentalis) and subalpine larch (Larix lyallii).

Western larches have a triangular shape with a narrow crown and grow up to 170 feet high on north-facing slopes between 2,000 and 5,500 feet in elevation. Their range stretches from Oregon to British Columbia and east through Idaho into northwestern Montana.

Subalpine larches, on the other hand, tend to have branches spreading out in different directions. They grow up to 70 feet high, typically in cold, snowy locations on bedrock or talus outcropping between 5,800 and 7,500 feet, according to Mathews. Their range extends north from the Wenatchee Mountains to British Columbia and Alberta, and east to northern Idaho and western Montana.

In Washington state, both species grow on the sunny, eastern slopes of the Cascades, although western larch can be found a bit west of the Cascade Crest.

Larch needles grow in small clumps. In the fall, they turn a brilliant gold before falling off for the winter. Photo by Megan Kirkpatrick.

Next, I called up naturalist Stewart Wechsler to understand the “deciduous conifer” bit. I recalled from Mathews’ book that western and subalpine larches had tufts of “deciduous” needles radiating from woody pegs—15 to 30 needles per peg for the western larch, 30 to 40 needles on a subalpine larch—almost like tiny, electric-shocked ponytails peppering their branches.

Larches grow new, yellow-green needles in spring that turn a show-stopping yellow-amber in the fall. Then the needles drop, leaving the tree branches bare in the wintertime. And that, according to Stewart, is what “deciduous” is all about: the annual cycle of growing and shedding leaves. Evergreen trees, on the other hand, have needles (yes, needles count as leaves) all winter.

Keeping and losing needles are adaptations that work to each tree’s advantage where it grows.

Why do evergreens keep their leaves while larches lose theirs? According to Kevin Zobrist, associate professor at Washington State University, keeping and losing needles are adaptations that work to each tree’s advantage where it grows. Evergreen conifers can use their needles for photosynthesis in the fall and winter when conditions are warm enough, enabling them to grow throughout the year. The temperatures that larches grow in tend to get too cold for winter photosynthesis, so larches can save resources by not producing leaves in the fall and winter. Additionally, losing needles is an advantage because it makes the larches more resilient to defoliating insects and fires.

Hiking during larch season will allow to to see your favorite trails in a whole new light. Photo by Bobby Olsen.

What about the yellow color that larch needles are known for? Why do they turn yellow in the fall, and not red or orange like other deciduous trees? Stewart explained that the green color of chlorophyll masks the other pigments in a leaf during most of the year. In the fall, though, when temperatures cool and daylight grows shorter, the chlorophyll is drawn into the tree, leaving behind the other colors in the leaf. In the case of larches, it’s predominantly yellow.


How about the conifer part of the larch description? Stewart explained that a conifer is a plant with cones and either “needle-shaped” leaves (like Douglas-fir) or scales (like western redcedar). Trees that have “needle-shaped” leaves and cones belong in the pine family, a part of the larger conifer division. Western and subalpine larches are members of the pine family: They have deciduous needles and conspicuous cones with “bracts” that stick out like a porcupine’s quills between the cones’ scales.

What about where they grow, I wondered. Why are they found on the eastern side of the Cascades? David Giblin, a botanist and the collections manager at the University of Washington Herbarium, explained.

“Larches are not well adapted to the climatic conditions west of the Cascade Crest,” he said. “Larches are very shade-intolerant and as a result grow in open, often fairly young forests. Not coincidentally, they occur in fire-prone areas. West-side climate conditions result in far less fire frequency, and as a result less forest disturbance or openings.”

So, if you don’t happen to live where larches grow, you’ll need to take a trip to the east side of the Cascades. For the glory of larches in full color, however, it’s worth the effort.

Cutthroat Pass is a popular destination for larch viewing. Photo by Victor Chinn.

See them yourself

So now that you know about larches, where can you see them? And when? Tyler Chisolm, an interpretive ranger at the North Cascades National Park Service Complex, offered some suggestions (below) on where to find larches. She also explained that larches usually stay yellow for just a few weeks. Tyler recommends calling a ranger station or—if you’re heading out on Highway 20—the North Cascades Visitor Center for more information during larch season. Here are some ideas for your next larch hike:

Stay until sunset for an even more impressive color display. Photo by Victor Chinn.
This article originally appeared in the Sept+Oct 2017 issue of Washington Trails Magazine. Support trails as a member of WTA to get your one-year subscription to the magazine.