Habitat Fragmentation

The Yarra River : Fragmentation of Habitat and The Riparian Corridor. The Problem of Large-Scale Developments on the River’s Edge.
by M. Bancroft and P. Herman

Fragmented habitats are habitats that were once contiguous but are now separated into smaller, isolated areas.

Habitat fragmentation usually occurs because of human activities such as new roads, parking lots and housing developments. Organisms need their specific habitat for survival, and fragmentation is a leading threat to many terrestrial animals.

To frame it in “human” terms, imagine if you lived happily in your house, with a surrounding community, where friends and family also lived, with grocery stores, restaurants, places to meet other people with whom you could start your own family. Then, suddenly, your community is destroyed by being dug up, crushed, and built over by a large alien species. Now you have no access to any of your previous resources and your family is dead. Where can you go, and what can you do?

Habitat fragmentation almost invariably occurs as a result of human activity. Fragmented habitats may be subject to the edge effect. The edges of habitats are important parts of the landscape and are so unique that they have their own sets of physical conditions and communities of organisms. When habitats become fragmented, their edges often become more abrupt and transition less smoothly than they would naturally. Edges usually have less diversity and are dominated by a small number of species specially adapted to those areas. When more edges are created, the species inhabiting edges expand into areas where they wouldn’t normally be found. This creates new competition for the species native to the fragmented habitats. Habitat fragmentation is a significant cause of biodiversity destruction. Fragmentation characteristically reduces species richness not only because it reduces the amount of functional habitat, but it may isolate a species population into sub populations, that may be sufficiently near the minimum viable population size to risk local extinction.

Habitat fragmentation invariably involves some amount of habitat destruction. Plants and other sessile organisms in these areas are usually directly destroyed. Micro-climatic changes in light, temperature and wind can alter the ecology around the fragment, and in the interior and exterior portions of the fragment. Fires become more likely in the area as humidity drops and temperature and wind levels rise. Exotic and pest species may establish themselves easily in such disturbed environments, and the proximity of domestic animals often upsets the natural ecology.

Environmental corridors are areas in the landscape that contain and connect natural areas, open space, and scenic or other resources. They often lie along streams, rivers, or other natural features. These corridors protect environmentally sensitive areas by providing linkages in the landscape and potential buffers between natural and/or human communities.

Environmental corridors are complex ecosystems that provide an avenue for wildlife movement, protection of natural resources, and green space buffers for humans. The practice of breaking up larger blocks of land, or fragmentation, has further reduced native habitat areas and their environmental corridor linkages.

Putting it in “human” terms once again, environmental corridors are like hallways in a building which connect different rooms, and allow movement between rooms like the kitchen, bedroom or living room. If people were confined to only one room with no access to food or resources they probably wouldn’t survive for very long.

Over 70% of all terrestrial wildlife species use riparian corridors. The Yarra River is a riparian corridor. Riparian areas provide habitat for wildlife, including migratory birds, mammals, reptiles, and insects.  Woody debris and shading provided by riparian areas create ideal in stream habitat for fish and other aquatic organisms.  Food and water for wildlife are provided by these areas and dense vegetation serves as a high forage area, while the canopy acts as a windbreak and thermal cover.  Riparian areas are an important breeding ground for birds.

A riparian buffer is a vegetated area (a “buffer strip”) near a stream, usually forested, which helps shade and partially protect a stream from the impact of adjacent land uses. It plays a key role in increasing water quality in associated streams, rivers, and lakes, thus providing environmental benefits. Riparian buffers also serve to provide habitat and wildlife corridors, and to reduce erosion by providing stream bank stabilization.  The habitat provided by the buffers also double as corridors for species that have had their habitat fragmented by various land uses.
Large trees in the first zone of the riparian buffer provide shade and therefore cooling for the water, increasing productivity and increasing habitat quality for aquatic species.

Building enormous developments which fragment habitat, destroy vegetation, have absolutely no riparian buffer zone, and encroach on the river corridor with height, bulk and 24 hour human activity, noise and light pollution, are an absolute crime against the river environment, especially the fast disappearing remnants in our inner city environment. We need to safeguard the river and its wildlife.

We do not need shops and apartments right on the river bank. We need the river to continue to provide habitat for our native birds, animals, insects and reptiles.

 

We would like to thank local residents and concerned river users for these contributions. If you have more environmental information about the area, please contact us. We will publish your information, with attribution, or you may remain anonymous if you wish.

Residents and river users have valuable insights and information to share and these deserve to be heard by our politicians and the wider community.