This is a blog about the native conifers of the Pacific Northwest. It is a companion to the Northwest Conifers site. The blog will focus on timely and interesting details about our conifers, their connections to the rest of the environment, and our connection to them.

Wednesday, September 2, 2020

Alpine Conifers

The timberline in the mountains is a special place for conifers. Below the timberline, the trees grow tall. Visitors walk among the large trunks in deep shade under the canopy high above. However, at the timberline, the conifers are transformed into a completely different form. The timberline is often a park-like area that conifers share with grasses, shrubs and wildflowers. If the towering trees in the forests below remind us of the pillars of a great cathedral, the trees at the timberline elicit visions of heaven. Indeed, when the wildflowers bloom in summer, the streets there are paved with gold, as well as blue, red, and white wildflowers.
McNeil Point
McNeil Point on Mount Hood
Mountain hemlock

Yet, the beauty of these trees is forged in adversity. It is a wonder that conifers can survive at these high elevations where they can be completely covered in deep snow, where they can be blasted with ice crystals in fierce winds, and where their branches and even their roots can be frozen by severe winter temperatures. To survive here they must adapt. The short branches of subalpine fir and Pacific silver fir keep them from breaking when covered in snow. Mountain hemlock branches are bendable and small trees that are covered with snow bend to the ground and pop back up in summer. The drooping branches of Alaska cedar just don’t collect much snow. On the other hand, many species depend on deep snow to protect their roots from freezing. The snow also protects trees from high winds that would blast them with ice crystals.
Subalpine fir
The conifers that can survive these harsh conditions often grow in small clumps with just one or two larger trees, surrounded by a thicket of small trees. At the highest elevations, these conifers may grow in a stunted, krummholz form, often unrecognizable from their tall relatives below.
Mountain hemlock and whitebark pine

Whitebark pine
In his book, Timberline, Stephen Arno explains how these alpine conifers survive the extreme conditions at the timberline. Curiously, the winter conditions are not the limiting factor for these trees. Summer is the critical time when conifers must prepare for the winter. They must have enough time in the brief summer to put on new growth and for the new growth to become mature. Arno describes this maturation process as “hardening off of shoots.” This hardening enables the new growth to survive the winter. (Arno, p. 57)

Contrary to common sense, it is not only the cold of winter that is destructive to alpine conifers. It is also … wait for it … heat. Conifers prepare for cold weather in the fall when temperatures begin to drop below freezing. If needles do not mature in the summer, they can be damaged by frost. But warm weather can dry out the new growth in winter, especially when it is windy or sunny. This drying or “winter desiccation” can be fatal to needles that have not had a chance to mature in summer. This hardening protects the needles, enabling them to retain their moisture. You can look at damaged needles and tell whether they were damaged by frost or winter desiccation. Frost damaged needles shrivel and then turn black. Needles damaged by winter desiccation turn orange-brown. (Arno, p. 58)
Mount Rainier
The factor that determines the upper elevation limit for conifers is not how cold the winters are. Rather, it is how cold the summers are. Summer must be warm enough and long enough for new growth to become hardened to survive both frost and desiccation.

Late summer is a great time to visit alpine areas. The snows have melted, and wildflowers are taking advantage of their brief summer and blooming in abundance. These parklands of life living on the edge are unmatched in stunning beauty themselves. Also, the view there is often framed by picturesque, snow-capped mountain peaks.
Mount Hood
The most common conifers at the timberline are mountain hemlock, subalpine fir and whitebark pine. Look closely on the ground, too. You may see a mat of common juniper. To identify all the trees you find at the timberline, print this page: Alpine Conifers
Common juniper

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