One consequence of
clear-cutting is habitat fragmentation.
Fragmentation can be defined as the subdivision of once contiguous habitats and ecosystems into patches of various sizes and shapes. This type of fragmentation
in a forested ecosystem is seen as a patchwork of treed areas and
clearings. Timber harvesting may increase or decrease fragmentation,
depending on the block size compared to the natural patch size. For example,
harvesting within a large, even-aged stand increases fragmentation, whereas
harvesting a large, patchy area may later produce a more uniform forest
Fragmentation decreases habitat effectiveness for many
forest-dwelling species. Species requiring large tracts of undisturbed forest
for food, cover and reproduction may be less successful in areas where this
habitat type remains as patches only. On the other hand, other species of plants
and animals will benefit from the large clearings and more forest edge.
During the past couple of decades, the forest industry has
tended to use smaller-sized cutblocks in most harvest areas. More recently, a
wider range of cutblock sizes and shapes have been employed. Although smaller
blocks are more aesthetic and beneficial for regeneration of some tree species,
they also effectively increase the degree of habitat fragmentation. Between 1966
and 1996, there were 51,700 coniferous and 4,500 deciduous blocks cut in Alberta
over an area totalling one million hectares. These numbers represent a certain
amount of habitat fragmentation in harvest areas with associated cutblocks and
leave blocks. However, there are other factors that contribute to fragmentation
in forested areas, including clearing for agriculture, energy exploration,
building roads, urban expansion, and so on. Habitat fragmentation is a complex
issue, and the forest industry is continuing to experiment with different types
of cutting methods that will reduce the effects of fragmentation.
Department of the Environment. State of the Environment Report, Terrestrial Ecosystems. Edmonton: n.p., 2001. With permission from Alberta Environment.