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Editor’s note: This research was conducted as part
of a Doctoral Dissertation by Yale student Richard Karty, with
support provided by the Connecticut Sea Grant College Program.
When his thesis is turned into a journal article, we will provide
the paper
on the Literature portion of this site.
The amount of impervious surface in a region can serve as a shorthand
or surrogate measure not only of water quality, but of other aspects
of ecosystem health as well. For example, a study in New Haven
County showed that weedy, invasive and non-native plant species
are mostly restricted to places having a high proportion of impervious
surface, and conversely, that plants typical of relatively undisturbed
forest interiors are restricted to areas with little impervious
surface. This is something that everyone knows intuitively—dandelions
aren’t found deep inside state parks, and orchids don’t
grow in parking lots—but until now it hadn’t actually
been measured with respect to impervious surface area.
The threshold level of impervious surface above which the forest
interior species become rare was found to be around ten percent.
This is remarkably similar to the threshold of impervious surface
for water quality degradation,
as indicated by a number of national studies. And above a mere seventeen
percent impervious surface area, weedy plants are predominant to
the exclusion of the more sensitive species. This can be seen in
the graph below, which shows the average amount of impervious surface
in which each species was found.
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