Shrublands

Introduction

Shrublands refer to regions whose main plant life are woody shrubs—low-lying plants that have several stems instead of a single trunk protruding from the base. Woody shrubs are also known as bushes. Woody shrubs are perennial (they bloom every year without the need of planting of new seeds).

Shrublands are located in various regions of the world. They can be permanent or temporary. Temporary shrublands can arise after an event such as a forest fire or clear-cut logging, and represent a transition between the former environment and the re-established mature environment. Other shrublands are created by the overuse of an environment by humans.

The barren appearance of a shrubland can be deceiving, as the environment can support a variety of life. However, the barren appearance can lead to misuse and overexploitation of the land for other purposes, which can result in the encroachment of nearby desert areas (one form of desertification).

The loss of shrubland plant cover may increase the nighttime radiation of heat back to the atmosphere, further fueling atmospheric warming.

Historical Background and Scientific Foundations

The plants that occupy shrubland are small bushes that grow up to a maximum of about 20 ft (6 m) in height. Most often, shrubland plants are lower than 10 ft (3 m) in height. Shrublands are extensive in regions of the globe near the equator (between 32° and 40° north and south of the equator) that do not receive extensive rainfall. This territory includes southwestern regions of North America such as Arizona, New Mexico, and Texas, and the Mediterranean, the central area of Chile, portions of Brazil, the Cape area of South Africa, and regions of Australia.

These regions are characterized by hot, dry summers and cool, moist winters, or by distinct seasons that are very wet and very dry. The shrubs tend to be evergreen plants that are hardy, and able to tolerate fire and sparse nutrients, or non-evergreens that shed their leaves during the dry time of the year. Examples of plants are the chaparral (Mediterranean), caatinga (Brazil), mallee (Australia), and sagebrush (North America).

These naturally occurring shrublands tend to be stable and long lasting. Other shrubland that also persists over time can result from the excessive lumbering of trees and the overgrazing of cattle. An example is the moors of Scotland, which at one time were pine forests. Excessive lumbering altered the ecosystem so drastically that the re-establishment of forests was hindered. Instead, the bushy moor plants became dominant.

Other shrubland is not permanent, but represents a stage between the former environment and the similar environment that will develop over time. This is known as successional shrubland; the shrubland is one of a number of stages (successions) between the original and ultimate environments. Most shrublands in temperate regions of the globe tend to be successional systems, and are an indication of the extensive land use that has occurred in the past.

Although shrublands can appear desolate, they are actually ecosystems that support many species of plant and animal life. The parts of the plant that are above the ground are slower growing that the roots, which can grow far down into the soil to reach water. The soil is stabilized by the roots. The low-lying and dense plants provide protection for birds and animals.

Impacts and Issues

Some shrubs can produce and secrete compounds that are toxic to herbs in the vicinity. This helps the shrub compete for the available nutrients by eliminating some of its competitors. These compounds may be an exploitable source of natural herbicides. Thus, the destruction of shrublands may be depriving scientists of valuable compounds that could reduce the use of synthetic herbicides.

The barren and dull-colored appearance of shrub-lands can lead to their disregard. Use of the land for other purposes destroys the groundcover that birds and animals rely on for protection and habitat. Furthermore, the absence of soil stabilizing roots can lead to use of soil through wind and water erosion, and the loss of the fire-tolerant bushes can increase the tendency of fires to spread and cause more extensive destruction.

The extensive areas of arid, semi-arid, and temperate regions of Earth that are covered by shrubland make the plants an influential contributor to climate modification. Experiments have shown that the absence of shrubs increases the radiation of heat to the atmosphere, especially at night. The influence of extensive loss of shrub-land on the global climate is unclear, as is the effect of global warming on shrublands.

See Also Desertification; Ecosystems; Grasslands; Tundra

WORDS TO KNOW

CLEAR-CUT: A parcel of forest that has been denuded of trees. Clear-cutting can be destructive of forests, particularly when the cycle of reforestation is slow and the processes of wind and water erosion of deforested land make it inhospitable to reforestation. However it can also be a tool for increasing the biodiversity of forests that have been protected from forest fires for many years.

DESERTIFICATION: Transformation of arid or semiarid productive land into desert.

ECOSYSTEM: The community of individuals and the physical components of the environment in a certain area.

SAVANNA: One of Earth’s biomes characterized by an extensive cover of grasses with scattered trees. The savanna biome is a transitional biome between those dominated by forests and those dominated by grasses and is associated with climates having seasonal precipitation accompanied with a seasonal drought.

TUNDRA: A type of ecosystem dominated by lichens, mosses, grasses, and woody plants. It is found at high latitudes (arctic tundra) and high altitudes (alpine tundra). Arctic tundra is underlain by permafrost and usually very wet.

BIBLIOGRAPHY

Books

Burnie, David. Shrublands. New York: Raintree, 2003.

Kump, Lee R., James F. Kasting, and Robert G. Crane. The Earth System. New York: Prentice-Hall, 2003.

Parker, Gary. Exploring the World Around You: A Look at Nature from Tropics to Tundra. Green Forest, AR: Master Books, 2003.

Web Sites

World Resources Institute. “Ecosystem Area: Open Shrublands.” http://earthtrends.wri.org/searchable_db/index.php?theme=9&variable_ID=756&action=select_countries (accessed April 28,2008).