How high ground shapes the plants

The treeline is the height on a mountain above which trees do not grow as a closed forest. Above it, the ground is open, exposed and often rocky. The plants that grow there are not simply small versions of lowland plants. Their form, timing and structure respond to the conditions around them.

The treeline and what lies above it

Trees need a long enough warm season to build wood and set seed. Above the treeline that season is short, and the air is colder on average than it is lower down. Growth happens in a brief window once the snow has melted, and that window sets the pace for everything else that lives there.

Cold and the short season

A plant with a short season has to finish its work quickly. Many high plants store energy from one year to the next in roots or in a compact crown, so their flowers appear early in the warm period. Some keep their leaves through winter under the snow and begin to grow as soon as the snow lifts.

Cold also limits height. A short plant sits in the layer of air nearest the ground, which is often warmer on a sunny day than the air higher up. This is one reason many alpine plants stay close to the soil.

Wind and exposure

Wind on exposed ground removes moisture and cools leaves. A plant that grows low, tightly packed or with its leaves held close to the stem presents less surface to the wind. The effect is visible. On a ridge, plants are often flattened, while in a sheltered hollow the same kinds of plant grow taller and looser.

Snow as cover

Snow protects plants from the coldest air and from wind-driven ice. Where snow lies deep and late, the ground beneath stays close to freezing and the growing season starts late. Such places, called snowbeds, carry a different set of plants from an open ridge a short walk away.

Thin soil and stony ground

Much high ground has thin soil over rock, or broken stone with little fine material. Water drains quickly and nutrients are scarce. Plants on these sites tend to have deep or spreading roots, and many grow in cracks or wedged between stones.

What to see in the field

Condition	Effect on the plant	What to notice
Wind on a ridge	Low, flattened or tightly packed growth	Plants lying close to the stones
Late snow	Late start and a short flowering window	Plants flowering while the ground around them is still wet with melt
Thin, stony soil	Spreading or deep roots, growth in cracks	Plants wedged between blocks
Sheltered hollow	Taller, looser growth	The same kind of plant standing higher than on the crest
Strong sun	Hairy or waxy leaf surfaces	Pale hairs or a grey sheen on the leaves

The table is a guide, not a rule. A single plant can show several of these features at once, and the features can vary within one slope. Compare plants of one kind in different positions to see which feature belongs to the site and which to the plant.