Ecological Impacts by Town
Measuring the Ecological Impacts of Development
We estimated the ecological impacts of development by running a model designed to assess the ecological integrity of lands and waters across relatively large geographic extents (e.g., all of Massachusetts). Ecological integrity can be thought of as the ability of an area to support plants and animals and the natural processes necessary to sustain them over the long term. The model is called the Conservation and Assessment Prioritization System or CAPS and it presumes that by conserving intact areas of high ecological integrity, we can conserve most (but not necessarily all) species and ecological processes.
The 'index of ecological integrity' (IEI) was calculated for all areas of the state in 1971, 1985, 1999, and 2005. It takes into account eight factors when generating results: habitat loss; microclimate alterations; impacts from domestic predators such as cats and dogs; impacts from edge predators such as raccoons, blue jays, and cowbirds; non-native invasive plants; non-native invasive earthworms; connectedness of the landscape; and similarity of each point to the surrounding landscape. The result is that each cell (30 x 30 meters) in the state is given a score between zero and one, zero being a low score while one is the highest score possible.
The Index of Ecological Integrity (IEI) depicts the value of a given point on the landscape relative to others based on its ability to support plants, animals, and the natural processes that sustain them. To facilitate this comparison of one area with another, units called IEI-acres are used throughout CAPS analysis. One IEI-acre is equivalent to an acre of cells-roughly five cells-with a perfect score of 1. One IEI-acre can also be comprised of 2 acres of cells each with a score of 0.5.
For example, consider the town of Townsend with a total land area of 21,100 acres. In 1971, Townsend had an IEI score of 12,000, i.e., the sum of the cells in the town's 21,100 acres added up to 12,000 IEI-acres. By 2005, Townsend's score had dropped to 8,700 IEI-acres, which can be thought of as a loss of 3,300 acres of land with high ecological integrity. This loss occurred throughout the entire acreage of the town rather than on just 3,300 acres; but it enables comparison of Townsend with other towns and allows calculation of the change in IEI over time.
Direct vs Indirect Loss in Ecological Integrity
The direct impacts of development can be thought of as the impact that the building footprint has on the ecological integrity of an area. In a previously forested area, the IEI score will be dropped to zero directly under the home or building footprint. In contrast, the indirect impacts of development can be measured by examining the IEI scores in all places that remain in a natural state. The forests that surround a new subdivision, for instance, are still present, and will have scores that are greater than zero. However, their ecological integrity has been diminished. Invasive species such as multiflora rose and bittersweet will likely be introduced via humans. Domestic pets, primarily cats and dogs, will impact the surrounding woodland as they venture into the forest. Other wild predators that 'follow' humans such as cowbirds, skunks, and raccoons will also have impacts on species that were previously present. Fragmentation is another example of an indirect impact of development. Interior forest dwelling species, such as the Scarlet Tanager, will no longer be found adjacent to newly built homes.
The CAPS model allows us to tease apart the direct impacts of development from the indirect impacts.