The term 'wildlife corridor' is used to refer to any linear feature in the landscape that can be used for migration or dispersal of wildlife. Wildlife corridors offer the possibility of linking habitats and reducing the isolation of populations. Linear features vary considerably in size (in terms of width and length), they may not be continuous, for example, a hedgerow may have a gate in it or an opening to a field. The extent to which a linear feature is broken by gaps has implications in terms of its function as a corridor. Patches of natural features or a particular habitat type can also enable wildlife to disperse / migrate - the term 'stepping stones' has occasionally been applied to them. In a countryside that is becoming increasingly fragmented, the role of wildlife corridors has assumed greater importance.
All of the following may function as a corridor to a greater or lesser extent :
- hedgerows (fences
- road and motorways 'verges'
- railway tracks
- tunnels and underpasses
- avenues of trees
- urban gardens
- field margins
- rivers and river sides
- irrigation channels
- remnant woodland
- urban green belt areas
Some linear features have additional benefits - trees and hedgerows can ameliorate the effects of pollutants in towns and cities, some offer amenity value / recreational value. Whilst these 'corridors' offer opportunities for plants and animals to disperse, allow for mixing of gene pools, it should also been borne in mind that pests and pathogens can also spread along such 'pathways'.
Hedgerows have featured in a number of woodlands blogs - they are generally narrow bands of woody vegetation and associated organisms that separate fields / stock / pasture. Hedgerows often interconnect with one another, forming a network or 'bocage'. Some 500 / 600 plant species have been recorded in English hedgerows (which says something about their importance to our wildlife) and would seem to be obvious candidates to act as corridors .
Trapping studies have shown that mice and voles move freely along hedgerows, as do carabid beetles (moving out of woodlands along hedgerows); the seasonal migration of adders (from hibernation areas) is assisted by hedgerows, banks and ditches. Badgers, when dispersing, are also known to use hedgerows.
Railway cuttings and embankments often support a diverse flora (hence leaves on the line!) which afford a number of niches and habitats and it is thought that foxes and deer move along these from rural areas into major cities e.g. roe deer entering Bristol by means of railway lines and river banks.
Rivers themselves are used by animals such as otters, and have been 'used' by a number of invasive aquatic species. One such species is the water primrose. It is a highly invasive freshwater weed from South America. It has already become a serious problem in France where it blocks water ways and overgrows ponds and lakes. It has recently been found in Britain. Key features of the water primrose include
- it grows on the banks of rivers and lakes and floating on the surface of the water
- it has a flower with 5 bright yellow petals and distinctive seed pods
- it has a thick fleshy stem
- has leaves which range from long and thin to almost completely round
- it leaves brown hay-like stems protruding from the water over winter
The Image of water primrose (Ludwigia grandiflora) above is courtesy of the gallery at http://www.nonnativespecies.org/
Further information on this plant available here (note link downloads a PDF file).