9
HOW USEFUL ARE WILDLIFE CORRIDORS?
My thoughts and reservations on wildlife corridors are based on my knowledge of
invertebrate populations and the restriction of many species to very small areas within sites.
Invertebrates often have very specific habitat requirements, e.g. bees may need south-
facing slopes to provide a warm microclimate, areas of bare ground for nesting, flower-
rich areas for foraging and many species even need specific plants to provide pollen.
Solitary wasp species also have different requirements, for example nesting habits may
demand different kinds of dead wood or various sandy, chalky or clay substrates. Spiders
often have very specific habitat requirements, ranging from pioneer habitat such as open
ground to scrub, ancient woodland, leaf litter, old grassland, heathland, etc. Many
invertebrates have particular prey requirements and so will only be found where these
occur. The unfolding of the ecological requirements of the Large Blue butterfly (too late
to save it from extinction in Britain) illustrates the complex needs of many invertebrates,
yet in most cases we know very little about these needs.
Many of the scarcer and more restricted invertebrate populations do not seem to be able
to move from one site to another easily. For example we have in Essex examples of
species of spider which are widespread in some southern counties but which survive in
our county apparently as relic populations. This seems to be a result of the extent of
habitat loss and fragmentation that has taken place, particularly to old grassland and heathland.
It seems logical to me that a wildlife corridor will only be useful to those invertebrates
that can find their habitat requirements within it. Migration along the corridor will
depend on these habitat requirements being available at a number of places along the
corridor close enough to allow natural movement. This is evidently particularly important
when suitable habitats are not available outside the corridor because the surroundings are
developed for industry, housing or intensive agriculture. The value of wildlife corridors
is therefore likely to be limited by the habitats available within it. A variety of habitats
will help species to survive and move on as natural succession makes one part of the
corridor unsuitable. But even when the corridor contains a variety of habitats, succession
will inevitably take place and open areas will soon disappear. Grassland areas will scrub
up, their flowers will disappear and open sunny areas will become shaded out. Once this
happens 1 would suggest the value of the corridor to many invertebrates is lost. The
problem is compounded because wildlife corridors are usually very narrow strips of land
and open areas will disappear much more quickly than in most other wildlife sites.
Management will be needed to maintain the variety of habitats and this has far-reaching
implications for wildlife trusts and local authorities. Maintaining the value of many corridors is
likely to be difficult because the rate of succession will make frequent management work
necessary and access along the length of the corridor may well be difficult.
1 therefore believe that it is very important to be realistic about the value of wildlife
corridors. We should not assign too much importance to them in wildlife planning and
Local Plans without careful assessment and a recognition of their limited value and
dependence on management. The future of nature conservation within the county
depends not only on the identification and protection of sites of nature conservation
importance but also on the survival and adequate management of inteivening habitats to
maintain variety.
Wildlife corridors demand just as much ecological understanding as any wildlife site and
should be the subject of detailed survey work for invertebrates and other kinds of
wildlife. I would welcome further comments and discussion on the value of wildlife
corridors in the Newsletter.
Essex Field Club Newsletter No. 20, February 1997