Effects of Climate

Trees are genetically programmed to grow within certain climatic conditions. The length of the frost-free growing season, temperature extremes, precipitation amounts, and the duration of droughts are a few elements of climate that influence tree growth. A single tree species also varies in its climatic requirements across its natural range. For example, quaking aspen naturally occurs from northern Alaska to northern Illinois, but a quaking aspen transplanted from Illinois will not flourish in Alaska.

Native trees have evolved and adapted to a specific climate. When tree seeds or seedlings in the Northern Hemisphere are moved a short distance northward for planting, they may grow faster than local trees because they are genetically programmed to begin growth earlier in the spring and to extend their growth longer in the fall. But when trees are moved too far north, they often cannot survive the winters, are damaged by late spring or early fall frosts, or find the growing season too short to consistently produce viable seed. Trees growing on the northern limits of their natural range usually should not be moved more than 50 miles north.

When planting stock is moved southward in the Northern Hemisphere, it often grows more slowly than native trees because such introduced trees are genetically programmed to begin growth later in the spring and end growth sooner in the fall. They also may not tolerate the higher temperatures and greater water demands of a warmer climate.

Plant hardiness zone maps have been created to show where tree species typically can be grown in North America based on the average annual minimum temperature. Search online to find a plant hardiness zone map. Zone boundaries have changed in recent years because of climate changes. Trees and tree seeds usually should not be moved from one zone to another. Plant hardiness zones should not be your only criteria for tree selection since they do not take into account other climatic factors affecting tree survival, such as summer temperatures, precipitation, number of frost-free growing days, humidity, and snow cover.

In the Lake States much of our winter snowfall runs off in the spring, summer rainfall is not evenly distributed over the growing season, and prolonged summer droughts occur periodically. Our native trees have adapted to this precipitation pattern. Where the prairie meets the forest, evaporation may exceed precipitation, greatly reducing tree survival. Some tree species will grow in droughty prairie regions, but may need supplemental watering, mulching, or weed control, especially when young.

Trees also influence the climate on a global scale. Since individual trees are composed mainly of carbon, woodlands are great reservoirs of carbon, a greenhouse gas. Carbon storage is becoming a recognized value for woodlands to help offset the impact of burning coal, oil, natural gas, which releases carbon into the atmosphere, leading to global warming. Trees remove carbon from the atmosphere and store it in their woody tissues.