Natural Areas Attribute
Our analysis attempted to measure the size and abundance of Madison’s natural areas, which were defined as forest fragments, water impoundments, and conservation parks. Forest fragments were identified using aerial photography. As with open spaces, only those forested patches of 1.5 acres or greater were mapped. Using data from the City of Madison, they were then divided into two subsets: publicly-owned land and privately-owned land. This distinction is important because land that is publicly owned may be easier to secure for conservation purposes. Water impoundments were defined as inland lakes or ponds exceeding 1.5 acres in size, and they were identified using the aerial photographs and digitized manually. Finally, data on conservation parks was provided by the City’s Parks Department and added to our database.
Because of the range of ecological services they provide, natural areas relate to all four sustainability goals. In order to constitute effective habitat for viable wildlife populations (Natural Areas), however, a natural area must be sufficiently large. Research has shown that at least 25 acres of compact forested area are needed to sustain a diversity of bird populations, and at least 250 acres are needed for populations of small to medium-sized mammals. Whether or not it is practical or even feasible for a particular urban area to provide such habitat remains somewhat of a value judgment.
The standards we used, therefore, are derived partly from scientific literature and partly from our own analysis of Madison (described in the next section). Our GIS analysis revealed six 25-acre patches of natural space and at least two additional potential 25-acre sites. With Madison's population of 208,000, eight 25-acre sites citywide translates into 25 acres per 25,000 residents. The 1,200-acre University of Wisconsin Arboretum is currently the only natural area in Madison that is larger than 250 acres. One additional area encompassing the Cherokee Marsh conservation park and adjacent lands could be expanded to meet this standard as well. A "no net loss" recommendation has also been included in our district level recommendations to protect existing natural areas from development pressures.
- Eight natural area sites of 25 acres or more on a citywide basis
- One additional site exceeding 250 acres
- No net loss of existing natural space.