As humans, we rely on nature to provide us with the resources to keep us fed, clothed and housed, not to mention raw materials for medicines, fuels, and luxury items. But our ever-increasing numbers are taking a huge toll on the habitats of other species.   

At a glance
As we focus on our own development in the short term, we often fail to recognise the sustainability of that development, and how it will affect not only other species, but also further generations of human beings. This leads to the degradation, fragmentation and even the complete destruction of habitats.  

Deforestation and logging are main contributors to this destruction, but urban sprawl, mining, pollution, dam building, farming, forest fires, ocean-bed trawling and many other human activities also have detrimental effects on the environment.

Urban sprawl
There's a worldwide trend for people to relocate from rural areas to towns and cities, which causes urban areas to expand rapidly. This trend is acknowledged by many governments, who set limits on how far into rural areas this expansion can go in order to preserve ‘green belts’. Schemes which encourage highly concentrated building within city centres are another solution to the problem. But these processes are often politically sensitive and difficult to manage, and, as a result, large areas of wildlife habitat are constantly being displaced. 

In addition, car use among suburban settlements contributes directly and significantly to carbon emissions, more so than the use of cars in city centres. And when those cars are taken into open land for recreation, the effect on local wildlife through pollution and destruction is direct and often brutal.  

Agriculture
Before the Second World War, the world's agriculture started a slow change towards industrial methods: machinery replaced animals and manpower, and high-yield crop varieties were planted to feed a booming population. These changes certainly succeeded in producing more food (grain production across the world doubled between 1945 and 1980) but these intensive methods had a big knock-on effect in terms of habitat destruction. And not just in terms of land lost to agriculture; also the associated use of fertilisers, pesticides, irrigation methods and increased fuel consumption by agricultural machinery. 

'It's estimated by the US Environmental Protection Agency that ten billion kilos of pesticides are used across the world every year. And the more this gets used, resistance to these chemicals develops, and even more needs to be used to have the desired effect.’

Similarly, the huge quantities of fertiliser we use have been shown to reduce the amount of oxygen in local rivers, leading to the death of various species of fish and plants. Irrigation also affects life in our rivers, with over 70 per cent of our freshwater consumption used for agriculture. All these intensive methods combined lead to a far smaller range of crops being produced; in India there were once 30,000 varieties of rice grown, but by 2015 it's estimated that there will be only 50.  

Dams and water development
Dams, along with other man-made constructions which affect water flow such as canals and flood barriers, can give many benefits to the local human population. They can regulate water supply, help with irrigating agricultural land, generate power, aid transport and navigation and protect against flood damage. Today, nearly all the world's major rivers are dammed in some way but the ecological cost of creating these structures is far greater that you might imagine. Not only does it directly affect wildlife at the site where the construction takes place, it can also spoil habitats that lie downstream.  

The flooding of vast areas to create reservoirs has an immediate impact on the local wildlife, with whole habitats that were once land-based now completely submerged. Dam construction can change the temperature and salinity of the water downstream, radically altering the habitat and making it unsuitable for the fish and plant life that had made it their home. In addition, any form of damming blocks migration routes that fish have used for centuries, and despite the use of ‘fish ladders’ to help them navigate, many fail to make it. This has been a particular problem with salmon in the Pacific northwest of America - and of course, their disappearance goes on to affect other species which depend on their existence for food: bears, otters, birds, and even humans.  

Forest fire
Some forested areas are cleared deliberately by humans using fire, in a process known as ‘slash and burn’. The process involves the vegetation being cut back, left to dry, and then torched in order to free up land for agriculture. Initially, when fire is used to clear an area of forest, it can release nutrients within the soil and get rid of large numbers of pests, making it ideal to plant new crops. However, repeating the ‘slash and burn’ process too frequently can leave land infertile. Slash and burn techniques can, in theory, be done sustainably, but it depends on leaving land fallow for enough time to regenerate. However, pressure to produce food stops us from exercising much patience. Also, when land is cleared in this way, rainfall can wash straight through the rootless soil, taking many of the nutrients away with it.  

Conversely, some ecosystems depend on naturally occurring fire, and our attempts to suppress it can also have a damaging effect on the environment. Wildfire can help keep a balance of plants within an area and avoid more serious fires in the future. Some plants even depend on fire in order to release their seeds. Fire can be an integral part of an ecosystem but when we use it for our own ends, the results can often be highly destructive. 

Facts and figures

• An area of unspoilt land larger than North America is likely to be damaged by human activity in the next 30 years.  
• The spread of human activity threatens a quarter of the world's mammals with extinction.  
  
• Logging affects approximately 14-17 per cent of endangered species; grazing 19-22 per cent, water development 29-33 per cent; recreation 23-26 per cent, and mining impacts on 14-21 per cent.   
  
• Habitat destruction from human activity is the primary cause of risk for 83 per cent of endangered plant species.
  
• For migrant bird populations, a decline of close to 40 per cent is directly linked to habitat destruction.   
  
• For amphibians, declining populations are linked to habitat destruction, introduction of exotic species, water pollution and ozone depletion.   
  
• Habitat destruction was also a contributing factor in the extinction of at least 73 per cent of freshwater fish in North America and is the leading threat to fish species considered threatened, endangered or of special concern (see also marine).