Tree Ordinances Protect Canopy, Lower A/C Bills, UF Study Shows
July 6, 2000
GAINESVILLE, Fla. — Municipal ordinances are a good way to preserve urban tree canopies and likely lower city residents’ summer electricity bills, a University of Florida study suggests.
The study by UF geography researchers used a new method to compare the tree canopy in Gainesville, which has a strict tree ordinance, with nearby Ocala, which has a looser law. It concluded Gainesville’s canopy is more than twice as thick as Ocala’s — and that the canopy’s added shade is likely the reason Gainesville residents spend an average of $126 less than their Ocala counterparts for power bills annually.
“This study justifies in economic terms the existence of a tree ordinance,” said Michael Binford, a UF associate professor of geography.
The study compared the tree canopies in both cities through satellite- and land-based observations combined with computer analysis. Where past studies tended to measure only the top surface of the canopy, the UF method measured the top leaf coverage as well as leaves beneath. To do that, researchers combined images of the cities’ tree canopies from a satellite with ground-based light measurements and analyzed the data with an “artificial neural network,” an analytical computing technique that mimics the action of biological nerve systems.
The analysis generated a number for the leaf area index, or square meters of leaves per square meter of ground, for each city. Gainesville’s index was 4.61, while Ocala’s was 2.13, meaning Gainesville has more than twice the leaf coverage of Ocala.
Ryan Jensen, who did the study for his doctoral research, said a prominent reason for the difference is that Gainesville has far stricter rules than Ocala regarding tree removal.
A couple of examples: In Gainesville, anyone who wants to cut down a tree with a trunk diameter greater than 30 inches in a residential area must apply for a permit. In Ocala, no permit is required, as long as the lot is less than three acres, according to a comparison of the rules in Jensen’s thesis. Gainesville residents caught removing a tree without a required permit, meanwhile, must replace the trees on an inch-per-inch basis, meaning if they illegally cut down a large tree they face the expensive proposition of replacing it with an equally large tree. In Ocala, illegally cut large trees can be replaced with multiple smaller trees, as long as the smaller trees have trunks at least 3 inches in diameter.
“The Ocala ordinance just doesn’t have the teeth of the Gainesville ordinance, and the consequences are fairly significant,” said Jensen, who earned his doctorate in May and is now an assistant professor of geography at Indiana State University in Terra Haute.
Jensen also compared household energy bills in Ocala and Gainesville, discovering Ocala residents pay an average of $126.40 more per year for electricity than Gainesville residents. He said the likely culprit is Ocala’s thinner tree canopy and resulting sparser shade.
Binford said the UF satellite-computer method could be applied in other cities or regions as well as for related projects. For example, one of his graduate students is using a similar method to map productive cattle range land in South Florida.
“The method may have to be recalibrated, but it can be used for any vegetation.”