Trees grow all over the world, in many different types of weather. But above certain elevations, trees just cant grow. Think of it like this: someone draws a horizontal line on a mountainside; above that line, there are no trees. This imaginary line on the Earth is called the timberline, or the tree line. The timberline is usually a point where there isnt enough air, heat, or water to keep trees alive.

Although the timberline often seems abrupt from a distance, on the ground you can observe a gradual change from big, tall trees to stumpy ones. For example, trees at the timberline start to look more like low bushes than trees. Small trees need less moisture and less oxygen. The trees will get shorter and shorter until the weather is too harsh for any trees, large or small, to grow.

Sometimes, the timberline can be lowered by natural causes such as fire. Other times, the timberline can be lowered by human activity. Development can lower the timberline when land is used for commercial activity, agriculture, or housing. Even hiking, over a long period of time, can trample saplings or prevent new ones from taking root. This means trees stop growing a lot sooner than they would have otherwise, lowering the timberline.

Pollution can also lower the timberline. Trees need air, water, and soil to survive. If one of those elements is contaminated, entire groves of trees can die. The copper and nickel smelter on the Kola Peninsula in Russia is one of the largest producers of heavy metals in Europe. Trees in the area have large amounts of copper, nickel, lead, and sulfur. These heavy metals have prevented many trees from growing in the cold climate of the natural timberline. The timberline in northwest Russia is lower as a result.

Timberline can climb up as well as climb down. Due to the effects of global warming, the timberline in Canadas Arctic is much higher than it was in the past. Warmer temperatures and greater precipitation have improved growing conditions in the area. The provinces of Yukon and Labrador now have trees such as white spruce and balsam fir growing past what used to be the natural timberline.

Types of Timberlines

The alpine timberline marks the point where the elevation is too high, and usually too cold, for tree growth. The city of Vail, Colorado, is located near an alpine timberline in the Rocky Mountains. Trees along the Vail timberline include quaking aspen and lodgepole pine.

The desert timberline marks the point where the soil is too dry for tree growth. Youll find this kind of timberline at very low elevations, usually below 1,500 meters (5,000 feet). The desert timberline in the Sonoran Desert of the United States and Mexico features cactus as well as trees like palo verde.

A desert-alpine timberline is the point where the elevation is too high and the soil is too dry for tree growth. Some places, like the slopes of the Mauna Loa volcano in the U.S. state of Hawaii, are very high up but have low rainfall and a lot of exposure to the sun. The conditions are too dry for tree growth.

timberline
The timberline is sometimes called the tree line.

Tree Line USA
Tree Line USA, a program from the Arbor Day Foundation, supports urban forests.

No Timberline
The timberline in Antarctica is purely theoretical: there are no actual trees on the entire continent.

Noun

the art and science of cultivating the land for growing crops (farming) or raising livestock (ranching).

Noun

layer of gases surrounding Earth.

alpine timberline
Noun

area with high elevation where trees will not grow.

balsam fir
Noun

tree native to North America.

bush
Noun

low-lying plant with many branches.

cactus
Noun

type of plant native to dry regions.

Noun

all weather conditions for a given location over a period of time.

commercial
Adjective

having to do with the buying and selling of goods and services.

copper
Noun

chemical element with the symbol Cu.

desert-alpine timberline
Noun

area with high elevation and low moisture where trees will not grow.

desert timberline
Noun

dry area where trees will not grow.

development
Noun

construction or preparation of land for housing, industry, or agriculture.

Noun

height above or below sea level.

fire
Noun

a chemical process that releases heat and light due to burning.

Noun

increase in the average temperature of the Earth's air and oceans.

gradual
Adjective

rising or falling by a small amount.

grove
Noun

group of trees.

heavy metal
Noun

chemical substance with a specific gravity of at least 5.0.

horizontal
Adjective

left-right direction or parallel to the Earth and the horizon.

housing
Noun

shelters where people live.

Noun

the geographic features of a region.

lead
Noun

chemical element with the symbol Pb.

lodgepole pine
Noun

tree native to North America.

moisture
Noun

wetness.

nickel
Noun

chemical element with the symbol Ni.

oxygen
Noun

chemical element with the symbol O, whose gas form is 21% of the Earth's atmosphere.

palo verde
Noun

tree native to the Americas.

Noun

introduction of harmful materials into the environment.

Noun

all forms in which water falls to Earth from the atmosphere.

prevent
Verb

to keep something from happening.

quaking aspen
Noun

tree native to North America.

rainfall
Noun

amount of precipitation that falls in a specific area during a specific time.

sapling
Noun

young tree.

ski resort
Noun

facility where people can ski for recreation or sport.

slope
Noun

foothills or gently rising base of mountains.

smelter
Noun

industrial plant or machinery that melts large amounts of ore to extract metal.

soil
Noun

top layer of the Earth's surface where plants can grow.

stumpy
Adjective

short and thick.

sulfur
Noun

chemical element with the symbol S.

survive
Verb

to live.

Noun

elevation above which trees and other forest vegetation will not grow.

tree
Noun

type of large plant with a thick trunk and branches.

Noun

an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

water
Noun

chemical compound that is necessary for all forms of life.

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

white spruce
Noun

tree native to North America.