• 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.

    The timberline is sometimes called the tree line.

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

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

  • Term Part of Speech Definition Encyclopedic Entry
    agriculture Noun

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

    Encyclopedic Entry: agriculture
    air Noun

    layer of gases surrounding Earth.

    Encyclopedic Entry: air
    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.

    climate Noun

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

    Encyclopedic Entry: climate
    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.

    elevation Noun

    height above or below sea level.

    Encyclopedic Entry: elevation
    fire Noun

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

    global warming Noun

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

    Encyclopedic Entry: The Greenhouse Effect and our Planet
    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.

    landscape Noun

    the geographic features of a region.

    Encyclopedic Entry: landscape
    lead Noun

    chemical element with the symbol Pb.

    lodgepole pine Noun

    tree native to North America.

    moisture Noun


    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.

    pollution Noun

    introduction of harmful materials into the environment.

    Encyclopedic Entry: pollution
    precipitation Noun

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

    Encyclopedic Entry: precipitation
    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.

    timberline Noun

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

    Encyclopedic Entry: timberline
    tree Noun

    type of large plant with a thick trunk and branches.

    volcano Noun

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

    Encyclopedic Entry: Plate Tectonics and Volcanic Activity
    water Noun

    chemical compound that is necessary for all forms of life.

    weather Noun

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

    Encyclopedic Entry: weather
    white spruce Noun

    tree native to North America.