Land-Use Change
(Michael Pidwirny, Tracy Gow and Cindy Thiessen)

1. Introduction

Humans have been altering the abiotic and biotic character of the Earth's land surface since the beginning of human civilization. Land-use/cover change can take on two forms:

• Conversion of a land-cover type to another type (e.g., forest/woodland to farmland).
• Modification of a land-cover type (e.g., animal grazing).

Since the Industrial Revolution humans have rapidly become the most influential species on the surface of the Earth. Some scientists estimate that humans now directly or indirectly influence 40 % of the planet's terrestrial biological productivity. Much of this influence is due to the conversion of natural ecosystem types into modified habitats that supply humans with some type of resource commodity. In general, humans convert natural biomes for the purpose of agriculture, aquaculture, forestry, transportation, and urban settlement.

More than 10 % of the world's terrestrial surface is now used to grow crops. About 6 to 8 % of the Earth's surface has now been converted into rangeland for livestock. Over the last thousand years the amount of land under cultivation has increased by about 1800 %. Cropland development has come at the expense of natural forest, shrubland, woodland, and grassland land-use types. Continued expansion of the human population to over 10 billion individuals by the year 2050 will result in more natural ecosystems being converted into cropland.

Forest and woodland have been greatly influenced by land-use conversion and habitat modification. Of the forest remaining about 4 % are intensively harvested plantations and about 14 % are actively used for a variety of goods and services. Humans continue to increase their use and conversion of forests into cropland. Some estimates suggest that agriculture has caused the conversion of about a third of the Earth's forest land-use type since the rise of agriculture-based civilization. Annual harvesting of forests for fuel and wood is currently about 5 billion cubic meters and is increasing by about 1.5 % per year.

The clearing of most forests is the result of factors external to this habitat. In most of the world, the resource value of forests has been grossly undervalued. As a result, royalties, purchase prices, or stumpage fees have been set too low to recover sufficient capital for the proper management of this renewable resource. Many forest habitats have also been replaced with agricultural systems because they yield quicker financial returns.

Humans have also greatly altered the grasslands. The world's major grassland habitats are found in the Great Plains of North America, the Serengeti plains of Africa, the pampa of South America, the veldt of South Africa, the steppes of Central Eurasia, and surrounding the deserts in Australia. Natural vegetation of this biome consists of many different species of grass, herbs, and shrubs. Tree are uncommon because of the effects of fire and herbivore damage. Most of the natural grasslands have been replaced by monocultures of various types of cereal crops and introduced grasses that have been planted as pasture for sheep and cattle. The conversion of grassland into agricultural land-cover has resulted in a decline in the numbers of natural grazing animals and grassland bird species.

Table of Contents   Next