Key takeaways
- The treeline is the elevation above which it's too harsh for trees to grow.
- It's set by cold, wind, and a short growing season; its altitude varies with latitude and local conditions.
- Above treeline is the alpine zone — low plants, tundra, and bare rock — with no shelter.
- Crossing treeline means big views but full exposure to wind, weather, and lightning.
What the treeline is
The treeline — also called the timberline — is the elevation above which the climate becomes too harsh for trees to survive. Below it grows forest; above it lies the alpine zone of stunted shrubs, tundra, grasses, and bare rock. It’s a visible boundary on most mountains where the trees thin out and stop.
What causes it
The treeline is set chiefly by cold, wind, and a short growing season, all of which intensify with elevation. Its actual altitude varies a lot: higher near the equator, lower toward the poles, and shifted up or down by local aspect, moisture, and wind exposure.
Planning a peak, a hiker notes where the trail breaks above treeline and aims to be back below it before afternoon thunderstorms — knowing the exposed alpine stretch offers no shelter from wind or lightning.
Why it matters
Crossing above treeline trades forest shelter for open terrain: huge views, but full exposure to wind, sun, rapidly changing weather, and lightning with nowhere to hide. Above treeline, trails are often marked by cairns rather than blazes, and carrying the Ten Essentials and extra layers becomes especially important.
The bottom line
The treeline marks the boundary between sheltered forest and the exposed alpine world above. Knowing where it is — and that it varies with latitude and local conditions — helps hikers plan for the dramatic increase in wind, weather, and lightning exposure that comes with climbing above the trees, where there's no shelter to retreat to.
Frequently asked questions
What is the treeline?
The treeline, or timberline, is the elevation (or latitude) beyond which trees cannot grow because the climate is too harsh — too cold, too windy, and with too short a growing season. Below it is forest; above it is the open alpine zone of stunted shrubs, tundra, grasses, and rock.
What determines the elevation of the treeline?
Mainly temperature, wind, and growing-season length, all of which worsen with elevation. The treeline's actual altitude varies widely: it's higher near the equator and lower toward the poles, and local factors like aspect, moisture, and wind exposure shift it up or down on a given mountain.
Why does the treeline matter to hikers?
Crossing above treeline means leaving the shelter of the forest for fully exposed terrain — bigger views, but also wind, sun, fast-changing weather, and serious lightning risk with nowhere to hide. Many hikers plan to be below treeline before afternoon storms and carry extra layers for the exposure above it.
Sources
- Mountain ecology & zones — National Park Service
- Alpine environments — The Mountaineers