Land Use

Changes in how the land is used is probably the principal contributor to habitat disruption. Approximately one-quarter of all the land surface is converted to agricultural use. It is estimated that we are now utilising directly or indirectly about 40 percent of what biologists call the primary production of the Earth's biota (the products of photosynthesis on which all other life depends). In addition land acquisition, especially for agriculture and forestry, occurs initially in areas with the most fertile soils and equable climates, which are often also the areas of greatest biological diversity.

The current trend of most concern with respect to tree-cover in for example the U.S.A is a shift to smaller parcel sizes. Where there used to be continuous forest there are now small patches of trees, crossed by roads, agricultural tracts, and a variety of different land-uses and land-covers. The average size of these areas is smaller than at any other time over the last 20 years, as a result the landscape is highly fragmented and partitioned.

The known consequences of these changes are reduced numbers of both plants and animals and a greater possibility of the total loss of some of them. The mixing of favourable and unfavourable habitats also reduces the ability of species to move between areas and makes re-colonisation of distant areas more difficult.

In agricultural areas the impacts of intensive farming methods also gives cause for concern. Heavy applications of fertilisers and pesticides affects the abundance and viability of the other plants and animals and microorganisms in the same or adjoining areas. The adverse effects of non-point-source pollution due to the run-off of pesticides and herbicides from intensively used fields are well known. (Unit 3)

In addition, when agricultural use expands into the less fertile areas heavier applications of chemicals tend to be required to bring the land into "productive" use. The typical result is increased chemical run-off to the landscape. This damages the land further and increases the need to expand and bring other areas into use and so on creating a dangerous cycle.