Treeline at a glance
- Olympic Mountains
- 5,000 to 6,000 ft
- Sierra Nevada
- Above 10,000 ft
- Rocky Mountain NP
- Subalpine forest to 11,000 ft
- The zone just below treeline, per the park
- Alaska
- Can be at sea level
Why does treeline sit at different heights?
Mostly temperature. Olympic National Park's explanation is that average temperature drops as you climb, or as you travel far enough north, until it is too cold for trees. That is why treeline sits between 5,000 and 6,000 feet in the Olympics and above 10,000 feet in the Sierra, and why in Alaska it can reach sea level.
Local conditions move it further. In the maritime Pacific Northwest, heavy snow breaks branches, avalanches snap trunks, and snow that lingers into summer stops seedlings getting started. In Rocky Mountain National Park, the subalpine forest just below treeline runs from 9,000 to 11,000 feet.
What does treeline look like on the ground?
A thinning, not a wall. The Park Service describes it as a zone where trees get gradually smaller and more stunted until they cannot grow at all. Near the top, the low, dense growth is called krummholz, and Rocky Mountain National Park notes that well-established krummholz trees can be several hundred to a thousand years old.
Above it is alpine ground, and in the Northeast that zone is small and fragile. The Adirondack Mountain Club counts 173 acres of alpine plant community across twenty-one of New York's highest summits, and asks hikers to walk on bare rock because the mosses, sedges and dwarf shrubs up there cannot survive footsteps.
Why does going above treeline change a hike?
You lose all shelter. Above treeline nothing breaks the wind, and on an open ridge there is nothing taller than you. The National Weather Service advises avoiding hilltops and ridges in a thunderstorm, and notes that in mountainous areas storms typically develop in the early afternoon, so it recommends hiking early and being down the mountain by noon.
That is why above-treeline days start early and carry a real shell and an insulating layer even when the forecast at the trailhead is mild. It also rules out a hammock, which needs trees, and means sleeping on the ground if you camp up there.
What this means when you're choosing
- A wind-resistant shell and an insulating layer, since there is no forest to break the wind
- An early start, so you are off exposed ground before afternoon storms build
- A ground shelter rather than a hammock for any camp above the trees
- Footwear that grips bare rock, which is much of what you walk on up there
The common mistake
Planning the summit for the afternoon
In the mountains, thunderstorms typically build in the early afternoon, and above treeline there is no sheltered ground within easy reach. The National Weather Service's advice is to hike early and be down by noon. A summit you reach after lunch on a day when clouds are building is one you should have turned back from.
Common questions
Is treeline the same as timberline?
Yes. In hiking use they mean the same thing: the point on a mountain above which trees stop growing. Tree line, treeline and timberline all turn up on maps and in trail descriptions.
What elevation is treeline?
It depends on where you are. Olympic National Park puts it between 5,000 and 6,000 feet there and above 10,000 feet in the Sierra, and in Alaska it can reach sea level. Latitude, snow and exposure all move it.
Where this is defined
- Subalpine Forests, National Park Service, Olympic National Park
- Subalpine Ecosystem, National Park Service, Rocky Mountain National Park
- When a Safe Building or Vehicle is Nearby, National Weather Service
- Alpine Stewardship, Adirondack Mountain Club