Habitat fragmentation

When wild land is broken-up by human developments such as roads, infrastructure and community expansion, it is referred to as being fragmented.  When wilderness becomes fragmented, it loses the qualities that define it as wilderness, and loses the capacity to support species such as brown bears, grey wolves, wolverine and lynx that rely on large areas of undisturbed wild land for their populations to remain viable.  Few regions in the world today have not been fragmented to some degree or another, and in many cases, conservationists and land managers have to work with systems that are damaged to some extent.  Fragments of wild land are only useful as habitat for large mammals if they are connected to one another by corridors of land that permit movement between them by the species they support.  The smaller the fragments, the more important this is.  The term 'connectivity' describes connections between isolated fragments of land, permitting movement of wildlife between them.  Many reserves, such as national, provincial and state parks, are too small to function as stand-alone habitats for large mammals, and are only viable if they are linked to one another through protected movement corridors.  Connectivity facilitates the breadth of movement essential to meet range requirements and maintain genetic diversity in populations of wildlife.

Roads and towns and many other features of human development tend to "cut" viable bear habitat up, reinforcing the impression of isolated areas that, inevitably, are too small to fulfill their intended purpose. Certain roads can be very difficult for wildlife to cross, and the problem they present is compounded by the potential for mortalities due to traffic. In the Bow Valley, in Alberta, Canada, for example, Banff National Park is literally bisected by the Trans-Canada Highway, which also bisects the whole Rocky Mountain ecosystem. The Trans-Canada is a four-lane road which is fenced to reduce the potential for wildlife to be hit by vehicles. This precaution, however, is also very effective in preventing wildlife from moving freely across the park, with the net result that species on each side of the Bow Valley are developing separately from one another, implying a significantly reduced gene pool. The Bow Valley is also divided by a smaller road, the Bow River and the Canadian Pacific Railway.

In extending the example of the Bow Valley, which is one of many areas similarly affected by development, Canada Highway 3 also bisects the Rockies 300 kilometres to the south. South of that, in Montana, the Burlington Northern/Santa Fe Railway does the same, as again US Interstates 80 and 90 do to the south of it. Towns like Banff, Alberta, and Missoula, Montana, which have both grown significantly in recent years, sit like plugs along these linear disturbances, blocking valleys that used to be wildlife migration routes, further fragmenting habitat. The pattern of recession of grizzly bear habitat from including all of the west of the US and Canada at the beginning of the last century, to their range today, has been manifest through a process of development, marginalisation, fragmentation and finally impoverishment that leads to redundancy. With the islands of intact habitat that remain, and with the preserves that are scattered within them, it is essential that as much connectivity be restored as possible. Without it, such islands will be inadequate as habitat for grizzly bears and the recession of the last 80 years will continue.