Deciduous forests

DEFINITION: Natural areas consisting of diverse plant species that lose their leaves annually at the end of each growing season

Deciduous forests are important ecosystems that support multiple life cycles and provide habitat for native populations and wildlife. Located in the most heavily populated areas throughout the globe, these forests are declining because of human activity, including overuse and environmental pollution.

Deciduous forests did not exist until the end of the last ice age, which was some 20,000 years ago, as the plant species associated with this forest type were unable to adapt to the glacial climate. The word “deciduous” is derived from the Latin word decidere, which means “fall off.” Deciduous forests are located mainly in the temperate forest biome, which has very seasonal weather patterns consisting of four seasons with warm summers and cold winters and precipitation in the form of rain and snow throughout the year.

In the fall season the leaves of deciduous trees change from green to brilliant yellow, orange, red, and brown because of a lack of the green pigment chlorophyll, which they can no longer produce as daylight wanes. Eventually the leaves fall off as they go into dormancy at the end of the growing cycle, and most trees in the temperate deciduous forests remain bare during the winter months.

The temperate forest is located in the middle latitudes of the earth, and temperate or deciduous forests can be found in eastern North America, eastern Asia, and western Europe. Parts of Australia and New Zealand also contain deciduous forests. Less prominent are the tropical and subtropical deciduous forestbiomes that exist in South America and Southern Africa. Plants in these biomes are dependent on seasonal temperatures and rainfall. Most of the trees in these forests, such as teak and ebony, drop their leaves in the dry season in order to conserve water, but new leaves sprout once the rainy season begins.

Forest Zones and Plant Associations

Temperate deciduous forests consist of five distinct zones or strata. The first is the tree stratum. Trees in this zone, including maple, oak, beech, hickory, walnut, chestnut, basswood, linden, elm, and sweet gum species, average from 18 to 30 meters (60 to 100 feet) in height. The second stratum, the small tree and sapling zone, is made up of younger trees found in the tree stratum. The third stratum consists of shrubs, including such species as azaleas, rhododendrons, mountain laurels, and huckleberries. The herbal or fourth zone consists of short herbal plants, and the rich soils of the forest floor make up the ground stratum, the fifth zone, which includes lichens, mushrooms, and mosses.

E. Lucy Braun, an important botanist and plant ecologist of the early twentieth century, spent much of her life studying and cataloging the deciduous forests of eastern North America in order to preserve them at a time when humans were involved in random and logging. Braun and others created deciduous forest subcategories known as forest regions based mainly on the regions’ natural vegetation composition, but also on physiognomy. These regions vary from ones that are made up mainly of deciduous plants, such as the oak-hickory and beech-maple regions, to forest communities that include coniferous species, which do not shed their leaves in the winter, including the oak-pine and hemlock-white pine-northern hardwood regions. Braun named one of the major deciduous forest communities in eastern North America the “mixed mesophytic.” Unlike most forest communities, which have only two or three dominant species, the mixed mesophytic deciduous forest is made up of more than eighty plant species.

Animal Species

Temperate deciduous forests flourish with a variety of fauna. Mammals include deer, elk, bears, squirrels, skunks, raccoons, rabbits, opossums, foxes, and porcupines. Other diverse species found in these forests include many varieties of salamanders, frogs, snakes, and spiders. Small and large birds, such as wild turkeys, owls, hawks, and the bald eagle, depend on deciduous forests for habitat. During winter months some of the deciduous forest animals, especially birds, migrate to warmer climates where food is plentiful, while animals such as squirrels slow their metabolisms and store nuts and seeds in the hollows of trees to survive the winter months. Bears are among the animals that hibernate during winters in temperate deciduous forests.

Many animals associated with temperate deciduous forests have long been on the decline, such as bobcats, mountain lions, and timber wolves. Loss of and human slaughter have led to decreases in the populations of several of these species to the extent that they have been recognized as endangered or threatened and in need of protection from extinction. The continual loss of deciduous forests caused by logging, blights, plagues, depletion owing to pollution, and climate change has exacerbated negative effects on all of the species that make their homes in these forests.

Bibliography

Braun, E. Lucy. Deciduous Forests of Eastern North America. 1950. Reprint, Blackburn Press, 2001.

Delcourt, Hazel R. Forests in Peril: Tracking Deciduous Trees from Ice-Age Refuges into the Greenhouse World. McDonald & Woodward, 2002.

Frelich, Lee E. Forest Dynamics and Disturbance Regimes: Studies from Temperate Evergreen-Deciduous Forests. Cambridge University Press, 2008.

"Temperate Deciduous Forest." Earth Observatory, NASA, earthobservatory.nasa.gov/biome/biotemperate.php. Accessed 27 Jan. 2025.

Yetman, David A. A Tropical Deciduous Forest of Alamos: Biodiversity of a Threatened Ecosystem in Mexico. University of Arizona Press, 2000.