Habitat destruction

Uploaded on Mar 30, 2010
Murray Gell-Mann, the 2004-2005 Pardee Visiting Professor of Future Studies, argues that global problems cannot be considered in isolation, and he wonders about the best ways to separate environmental issues from those involving population growth.Run time 1:27

Hosted by Pardee Center for the Study of the Longer-Range Future on September 27, 2005.

News coverage of environmental issues can be difficult, in part, because those who are affected—whether the effect is economic or environmental—routinely exaggerate their claims. Non-governmental organization advocates pull “facts” in one direction; big
business tugs them in another, and sometimes neither leaves the cushy offices in the northwest section of Washington, D.C. Truth resides in a place somewhere in between.

Preventing illness is the best way to get health-care costs down. So why aren’t governments doing more to protect the environment? We’ve long known that environmental factors contribute to disease, especially contamination of air, water, and soil. Scientists are now learning the connection is stronger than we realized.

New research shows that 60 per cent of emerging infectious diseases affecting humans — those that rapidly increase in incidence or geographic range — start with animals, two thirds from wild animals. Lyme disease, West Nile virus, Ebola, SARS, AIDS… these are just a few of the hundreds of epidemics that have spread from animals to people. A study by the International Livestock Research Institute concludes that more than two-million people a year are killed by diseases that originated with wild and domestic animals. Many more become ill.

Habitat destruction is the process in which natural habitat is rendered functionally unable to support the species present. In this process, the organisms that previously used the site are displaced or destroyed, reducing biodiversity.[1] Habitat destruction by human activity is mainly for the purpose of harvesting natural resources for industry production andurbanization. Clearing habitats for agriculture is the principal cause of habitat destruction. Other important causes of habitat destruction include miningloggingtrawling and urban sprawl. Habitat destruction is currently ranked as the primary cause of species extinction worldwide.[2] It is a process of natural environmental change that may be caused byhabitat fragmentation, geological processes, climate change[1] or by human activities such as the introduction of invasive species, ecosystem nutrient depletion, and other human activities mentioned below.

The terms “habitat loss” and “habitat reduction” are also used in a wider sense, including loss of habitat from other factors, such as water and noise pollution.

Tropical rainforests have received most of the attention concerning the destruction of habitat. From the approximately 16 million square kilometers of tropical rainforest habitat that originally existed worldwide, less than 9 million square kilometers remain today.[8] The current rate of deforestation is 160,000 square kilometers per year, which equates to a loss of approximately 1% of original forest habitat each year.[10]

Other forest ecosystems have suffered as much or more destruction as tropical rainforestsFarming and logging have severely disturbed at least 94% of temperate broadleaf forests; many old growth forest stands have lost more than 98% of their previous area because of human activities.[8] Tropical deciduous dry forests are easier to clear and burn and are more suitable for agriculture and cattle ranchingthan tropical rainforests; consequently, less than 0.1% of dry forests in Central America’s Pacific Coast and less than 8% in Madagascarremain from their original extents.

Habitat destruction caused by humans includes conversion of land to agricultureurban sprawlinfrastructure development, and other anthropogenic changes to the characteristics of land. Habitat degradation, fragmentation, and pollution are aspects of habitat destruction caused by humans that do not necessarily involve overt destruction of habitat, yet result in habitat collapse. Desertificationdeforestation, and coral reef degradation are specific types of habitat destruction for those areas (desertsforestscoral reefs).

Geist and Lambin (2002) assessed 152 case studies of net losses of tropical forest cover to determine any patterns in the proximate and underlying causes of tropical deforestation. Their results, yielded as percentages of the case studies in which each parameter was a significant factor, provide a quantitative prioritization of which proximate and underlying causes were the most significant. The proximate causes were clustered into broad categories of agricultural expansion (96%), infrastructure expansion (72%), and wood extraction (67%). Therefore, according to this study, forest conversion to agriculture is the main land use change responsible for tropical deforestation. The specific categories reveal further insight into the specific causes of tropical deforestation: transport extension (64%), commercial wood extraction (52%), permanent cultivation (48%), cattle ranching (46%), shifting (slash and burn) cultivation (41%), subsistence agriculture(40%), and fuel wood extraction for domestic use (28%). One result is that shifting cultivation is not the primary cause of deforestation in all world regions, while transport extension (including the construction of new roads) is the largest single proximate factor responsible for deforestation.[16]


Nanjing Road in Shanghai

While the above-mentioned activities are the proximal or direct causes of habitat destruction in that they actually destroy habitat, this still does not identify why humans destroy habitat. The forces that cause humans to destroy habitat are known as drivers of habitat destruction.Demographic, economic, sociopolitical, scientific and technological, and cultural drivers all contribute to habitat destruction.[15]

Demographic drivers include the expanding human population; rate of population increase over time; spatial distribution of people in a given area (urban versus rural), ecosystem type, and country; and the combined effects of poverty, age, family planning, gender, and education status of people in certain areas.[15] Most of the exponential human population growth worldwide is occurring in or close tobiodiversity hotspots.[7] This may explain why human population density accounts for 87.9% of the variation in numbers of threatened species across 114 countries, providing indisputable evidence that people play the largest role in decreasing biodiversity.[17] The boom in human population and migration of people into such species-rich regions are making conservation efforts not only more urgent but also more likely to conflict with local human interests.[7] The high local population density in such areas is directly correlated to the poverty status of the local people, most of whom lacking an education and family planning.[16]

From the Geist and Lambin (2002) study described in the previous section, the underlying driving forces were prioritized as follows (with the percent of the 152 cases the factor played a significant role in): economic factors (81%), institutional or policy factors (78%), technological factors (70%), cultural or socio-political factors (66%), and demographic factors (61%). The main economic factors included commercialization and growth of timber markets (68%), which are driven by national and international demands; urban industrial growth (38%); low domestic costs for land, labor, fuel, and timber (32%); and increases in product prices mainly for cash crops (25%). Institutional and policy factors included formal pro-deforestation policies on land development (40%), economic growth including colonization and infrastructure improvement (34%), and subsidies for land-based activities (26%); property rights and land-tenure insecurity (44%); and policy failures such as corruption, lawlessness, or mismanagement (42%). The main technological factor was the poor application of technology in the wood industry (45%), which leads to wasteful logging practices. Within the broad category of cultural and sociopolitical factors are public attitudes and values (63%), individual/household behavior (53%), public unconcern toward forest environments (43%), missing basic values (36%), and unconcern by individuals (32%). Demographic factors were the in-migration of colonizing settlers into sparsely populated forest areas (38%) and growing population density — a result of the first factor — in those areas (25%).

There are also feedbacks and interactions among the proximate and underlying causes of deforestation that can amplify the process. Road construction has the largest feedback effect, because it interacts with—and leads to—the establishment of new settlements and more people, which causes a growth in wood (logging) and food markets.[16] Growth in these markets, in turn, progresses the commercialization of agriculture and logging industries. When these industries become commercialized, they must become more efficient by utilizing larger or more modern machinery that often are worse on the habitat than traditional farming and logging methods. Either way, more land is cleared more rapidly for commercial markets. This common feedback example manifests just how closely related the proximate and underlying causes are to each other.

The rapid expansion of the global human population is increasing the world’s food requirement substantially. Simple logic instructs that more people will require more food. In fact, as the world’s population increases dramatically, agricultural output will need to increase by at least 50%, over the next 30 years.[19] In the past, continually moving to new land and soils provided a boost in food production to appease the global food demand. That easy fix will no longer be available, however, as more than 98% of all land suitable for agriculture is already in use or degraded beyond repair.[20]

The impending global food crisis will be a major source of habitat destruction. Commercial farmers are going to become desperate to produce more food from the same amount of land, so they will use more fertilizers and less concern for the environment to meet the market demand. Others will seek out new land or will convert other land-uses to agriculture. Agricultural intensification will become widespread at the cost of the environment and its inhabitants. Species will be pushed out of their habitat either directly by habitat destruction or indirectly by fragmentation, degradation, or pollution. Any efforts to protect the world’s remaining natural habitat and biodiversity will compete directly with humans’ growing demand for natural resources, especially new agricultural lands.


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