By Alexander Gillespie
According to the Convention on Biological Diversity, ‘habitat’ means the place or type of site where an organism or population naturally occurs. Tomorrow is World Habitat Day. The obvious question is, why do we need a day devoted just to habitat? The short answer is that loss of habitat is now the foremost conservation concern of the 21st century. If you want to know more, read on.
Historically, habitat loss was the second most important reason for species loss: the first reason being species introduction. This is no longer the case. Globally in the 21st century, and particularly in some regions such as Europe, habitat loss is the primary cause of species extinction. Habitat destruction is caused by numerous factors, but the most important is exponential human population growth. The mid-term projection for 2050 is 9.1 billion people, this being considerably higher than the 6.5 billion who currently exist. Expanding human populations have already profoundly changed the global landscape over the past few centuries. It is estimated that between 1700 and 1980 the world’s forested woodlands declined by nearly 20 percent from 6.2 billion to 5.1 billion hectares. The degree of human disturbance of vegetated land varies widely from continent to continent. In Europe less than 12 percent of land has only low disturbance whereas other regions, such as South America, have 75 percent with low levels of disturbance. On a global level, 26 percent of all land surfaces are highly disturbed, 27 percent are subject to medium disturbance, and 47 percent are experiencing low disturbance. In some countries, very little natural vegetation remains. For example, in Bangladesh a mere 6 percent of original vegetation is left; and in the United Kingdom and the Netherlands all but 4 percent of lowland bogs have been undamaged.
Although there are many important habitats being lost, one of the best examples is the removal of the Earth’s tropical forests, which are probably the premier areas for species habitat on the planet. In the last 8,000 years about 45 percent of the Earth’s original forest cover has disappeared, mostly during the past century. The present area of the world’s forest is 3.9 billion hectares. This area is the equivalent to North, Central, and South America combined. The Earth lost 450 million hectares of its tropical forest cover between 1960 and 1990. Asia lost almost one-third of its tropical forest cover during this period, whereas Africa and Latin America each lost about 18 percent. Between 1990 and 2005 the world lost a further 3 percent of its total forest area, with an average decrease of some 0.2 percent per year. Deforestation in the Brazilian Amazonia surged from 14,000 square kilometres per year in the early-1990s to consistently over 20,000 square kilometers per year between 1995 and 2005. Forty percent of the Amazon could be gone by 2050 if present trends continue. Likewise Papua New Guinea, which had a deforestation rate of close to 1.7 percent per year in 2007, was projected to have lost more than half of its forests by 2021.
Other habitats of particular note with regard to oceanic species are coastal zones. These habitats are valuable in every sense of the word. These are the areas where the oceanic upwelling systems collide as the cold, nutrient-rich, deep water currents run up against continental margins. They are centres for social and economic wealth, hotbeds for marine biodiversity, filters for marine pollution, and form part of a number of intricate ecological webs. They are the core habitats of the marine world and the critical habitats typically manifest themselves as coral reefs and/or habitats of seagrass or mangroves. With regards to mangroves, estimates in 2010 suggested that more than one in six mangrove species worldwide are in danger of extinction due to coastal development and other factors, including climatic change, logging and agriculture. Similarly, despite their clear importance, both warm water and cold water coral reefs and their dependent species are increasingly under threat and the current rate of loss of coral reefs is estimated to be 1,000 to 10,000 times the background rate without human interference. The first global surveys on coral reefs began to appear in the late-1990s, from where it was apparent that these ecosystems, both warm and cold, were already highly damaged from multiple sources including overfishing, indiscriminate fishing methods such as deep sea or bottom trawling, land-based pollution, and even climate change. Episodes of coral bleaching over the past 20 years have been associated with several causes including increased ocean temperatures.
Habitat loss impacts upon 86 percent of all threatened mammals. In West Africa it has been shown that during the 20th century approximately ninety percent of the original range of the African elephant was lost. More than 70 percent of the habitat of each of the African Great Apes has been negatively affected by infrastructure development. For the orangutan, which is often threatened by the development of palm oil plantations, the figure is 64 percent. By 2030, it is expected that less than 10 percent of Great Ape habitats in Africa will be free from the impacts of infrastructure development, and for the orangutan, the figure is 1 percent. Habitat loss impacts upon 86 percent of all threatened birds. Of this figure, 87 percent are at risk because of habitat loss due to agricultural practices while habitat change as a result of inappropriate forestry extraction is responsible for 55 percent (668) of all bird species being at risk of extinction. Habitat loss has also been identified as a primary threat to species of Lynx, leopard, tiger, and lions. It is also a threat to some species of rhinoceros and was a concern for certain types of bear such as the panda. Habitat loss is also identified as having a significant impact on 87 percent of all threatened amphibians, as well as bats and habitat dependent insects such as butterflies. With regard to butterflies alone, Europe has lost 15 percent of its critical habitats between 1990 and 2006. Habitat loss is also primarily responsible for 91 percent of all threatened plants.
Habitat loss in the oceanic environment is a very direct concern for all species that are dependent upon such areas. Numerous examples of this range include, inter alia, sea turtles, dugongs, and cetaceans. Episodic losses of seagrass have also be associated with extreme weather events and bad management regimes allowing excess nutrient run-off, oil spills, sewage, and other pollutants. A 2009 study suggested that that the total area of known seagrass meadows decreased by 29 percent between 1879 and 2006, and that this rate was increasing to such a degree that a football-pitch size of seagrass was lost every thirty minutes. A number of highly endangered whales, especially small cetaceans such as Mexico’s Vaquita, are threatened by loss of habitat. It was the loss of habitat that drove the Baiji to extinction in China. Similar threats now challenge the highly endangered Western Pacific Grey whales, foraging in oil exploration grounds off Russia.
Convinced now, that a day to consider habitat is a serious enough issue?
Alexander Gillespie is Professor of Law at the University of Waikato, New Zealand and is the author of International Environmental Law, Policy, and Ethics, published by Oxford University Press.
Image credit: Jungle burned for agriculture in southern Mexico by Jami Dwyer, via Wikimedia Commons.
Image credit: Coral Reef in Florida by Jerry Reid (U.S. Fish and Wildlife Service WO-3540-CD42A) [Public domain], via Wikimedia Commons.