The Threat Posed by Habitat Loss and Degradation
Habitat loss is the primary cause of species loss at local, regional and global scales. Urban development, water development, road building, recreation, fire-raising, fire-suppresion, agriculture and tree logging all destroy and degrade natural habitats. It is estimated that habitat destruction from human activity is the primary cause of risk for 83% of endangered plant species. Rates of destruction of tropical rain forest (a particularly species rich habitat) vary between places, but some studies have calculated an average 1% per year (an alarming figure - consider the cumulative effect over 50 years), whilst Laurance et al (2001) suggested that recent deforestation had proceeded at the rate of 2 million hectares per year.
Habitat loss is harmful not only to a single species, but to whole communities and ecosystems. There are few parts of the world that have not been altered, damaged or destroyed, and modern technology is speeding up the process. It has been estimated that by the year 2032, more than 70% of the land's surface will have been destroyed or disturbed.
Habitat loss is also a problem because it fragments the remaining habitat. This is because edges of habitats are strongly affected by their surrounding matrix. To return to the example of tropical rain forest, the edges of forest fragments have micro-climates that are markedly warmer, drier and lighter, leading to higher adult tree mortality, overall decreased biomass and greater gap formation. In other habitats this is also an important factor. For example, in Europe any land near conventional intensive agriculture receives drift and runoff containing fertilisers and herbicides meant for the farmed area. The natural land becomes nutrient rich, which leads to a far less diverse mix of plants (nutrient poor soils support a greater variety and non-dominated mix of species) whilst the chemical agents decrease the viability of some plant types.