Designing with Habitat Fragmentation in Mind

Habitat fragmentation is when habitats are broken up into smaller habitat fragments. This can be caused by natural occurrences, such as wildfires and floods. Where we typically see it is in areas that have been disturbed by humans.

What is Habitat Fragmentation and Why is it Bad?

Habitat fragmentation is not classified as habitat loss. A habitat can be fragmented without significantly decreasing the habitat area. We see it when a road is constructed through a habitat – effectively cutting the habitat in half. We also see it when human development in the middle of a habitat creates holes within the habitat. Those holes of human development typically expand as the human population grows and the fragmentation gets worse.

Habitat fragmentation is generally thought to have a negative effect on an ecosystem. Ecological effects like increased “edge” phenomenon (when an ecosystem is impacted along a boundary with a different ecosystem), reduced interior area, increased isolation of patches, increased number of patches and decreased average patch size are all consequences of habitat fragmentation. These can all cause fewer native plants and animal species, more invasive species, more soil erosion, and reduced water quality.

How to Lessen its Impacts?

Landscape developers and city planners can lessen the impact by paying attention to and eliminating or lessening the factors that make habitat fragmentation detrimental to an ecosystem. The size, connectivity, shape, context, and heterogeneity of the fragments all play a role in dictating how much habitat fragmentation will impact an ecosystem.

When a fragment decreases in size, the edge or boundary of the fragment says the same width while the interior of the fragment decreases in size. What this means is the edge, which is the impacted part of a fragment, is a higher percentage of the total area that the interior, which is not heavily impacted. Developers should focus on fewer, larger fragments instead of many, smaller fragments. Communities can be planned in a way that lessens the total number of street intersections – increasing the size of fragments.

If the fragments can be connected through a corridor, the impacts to the ecosystem will be lessened. The reduction of Island Biogeography typically seen in habitat fragments by constructing corridors increases biodiversity. Developers can incorporate wooded corridors through planned parks and developments or include highway crossings for wildlife.

Fragments that are longer rectangles versus a square shape will be more impacted. This is, again, related to the “edge” phenomenon. Long rectangles will have edge boundaries be a higher percentage of the total area than squares. Fragments should be designed to have a square shape and not a long rectangle.

The fragment context – how the fragment relates to the environment surrounding the fragment – has a large impact on the biodiversity. Fragments that are heterogeneous – varying soil types, varying terrain, and varying vegetation – have more biodiversity than fragments that are more homogenous. These factors are not easily influenced. What developers and planners can do is adjust the factors they can influence, like fragment size and shape, while being aware of the fragment context and heterogeneity.