The spatial configuration of ecosystems at a landscape scale plays a major part in determining how they function and the composition of their plant and animal populations. Fragmentation is the subdivision of a habitat or ecosystem either by a natural disturbance (e.g., fires, storms) or by human activities (e.g. roads, agriculture). The main impacts of changes in the size and connectivity of land (particularly forest) ecosystems include:
• changes in patch size (impacts through species/area relationships)
• edge effects (biophysical impacts, sometimes increasing access for other uses)
• isolation effects (distance from core area increases vulnerability of predation and disease impacts and decreases ability of species to recolonise)
In freshwater habitats (particularly rivers) the main impacts of fragmentation (eg from dam-building) are:
• changes in sedimentation patterns
• changes in water flow/oxygenation rates/temperature regimes
• effects of physical barriers obstructing migratory movements of species
Major ecosystem changes can also occur when connectivity is increased, that is, when previously existing barriers between systems are broken down. Increased connectivity may facilitate the spread of alien invasive species or change predation rates, for example.
Indicators of terrestrial ecosystem fragmentation often measure patterns of patch size and change in time of average patch size. Such indicators are usually calculated using a geographical information system (GIS), and measures of edge and isolation effects can also be produced. Challenges in producing such indicators include problems of defining and mapping ecosystems and that measures highly dependent on the scale of analysis, from local to national and regional. The biodiversity significance of a measure of fragmentation will depend on the species of interest, such as a small, terrestrial insect or a mobile large mammal. A habitat that might be considered highly fragmented from one perspective might be regarded as contiguous from another. On the whole, is considered that less fragmented ecosystems are better for biodiversity, although many ecosystems are probably mosaics in an undisturbed state and ecotones often increase species diversity. It is Important therefore to consider whole landscapes.
Indicators on connectivity and fragmentation of ecosystems complement information on trends in extent of selected biomes, ecosystems, and habitats. Because of the varying sensitivity of species to fragmentation, the indicator provides supplementary information to the indicators on trends in abundance and distribution of selected species and on change in status of threatened species. To avoid unnecessary fragmentation of ecosystems and habitats is a key aspect of national and regional land use plans and other relevant instruments such as environmental impact assessment at the project and the strategic levels and cumulative impact assessment. Therefore, at regional and national scales the definition of this headline indicator is the vital importance to know the state and the capacity of ecosystems to provide goods and services.