Throughout this page you will find information about the urban forest of the Madison Area. This information is a compilation of data acquired by the Urban Tree Alliance independently and through research collaboration with the University of Wisconsin-Madison. Our goal is to understand the urban forest as a whole (including public and private lands) so that we can make better decisions about how to manage it. Information is divided into four categories: Canopy Cover, Species Diversity, Urban Forest Benefits, and Current Actions. If you have further questions about this information or are interested in acquiring similar data for your property, neighborhood, or city please contact us.
Canopy Cover is a measurement of the amount of the ground surface that has a tree canopy over it. As urban foresters we are interested in this for several reasons. Mainly, it is a measure of how much of our community is covered by trees. From this we can make estimates about the services provided by the urban forest, the potential for expanding the number of trees, and the costs of maintaining them. These maps were generated in a GIS using LIDAR data.
To the right you’ll see various images of our computer generated canopy overlayed onto aerial photos to give an idea of what is being represented. Click here to see the whole image in .pdf format.
Above you saw what the forest canopy looks like in the digital world. If we start to measure and quantify the amount of canopy, we can figure out how much canopy exists in a city, a neighborhood, a block, or even a single parcel. The photos in the slideshow on the right show canopy calculations for each parcel at a few locations in Madison. This can be viewed closely to see the amount of tree canopy on an individual homeowner’s parcel, or, when zoomed-out, gives a more regional context. You can download the whole image in .pdf format here. From a wider angle you can start to see trends in the amount of canopy cover. More highly developed areas such as the downtown area, or West Town Mall clearly have lower canopy cover, while residential areas are typically more densely covered. There are, of course, naturally forested areas like the Arboretum, Picnic Point, or Olin Turville Park where there is almost a complete cover of tree canopy.
Images of canopy cover in Madison (red is least, dark green is most). Click here for the full image.
If canopy cover tells us where we have trees and how abundant they are in our community, the next question is what kind of trees are there? There are some pretty cool ways to identify and map trees in a similar manner to what we showed you in the canopy cover section, but usually this involves on-the-ground tree inventories. Of course, it is very difficult to map every tree in the Madison area (there are hundreds of thousands) but we can get a good estimate in other ways. The program i-Tree Eco (developed by the U.S. Forest Service) was created to do just that. We completed such an inventory of the Madison Urban Area. This is a census-defined geographical area so it looks a little crazy, but we used it because it follows a recognized definition of “urban”. The inventory used 200 sample plots to determine the number and species of trees in the whole study area as well as the benefits they provide (see the next section for more on this). Of the estimate 1 million total trees in the area, there were 53 species identified (surely there are more, but these are the most common). Here were their relative abundances:
To give an idea of what this means, the institutionalized rule is to have no more than 10% of one species, 20% of a genus, or 30% of a family present in an urban forest. Another, more progressive, guideline is to limit this to 5, 10, or 20%. We believe strongly in greater urban forest diversity. When many trees of few species are planted, a large amount of resources are susceptible to loss. For example, presently 9 % of the Madison Area Urban Forest is either green or white ash. If the Emerald Ash Borer reaches the area–as expected–all of those trees will be lost. If a greater diversity of species had been planted, there would be fewer losses.
Urban Forest Benefits
In the Benefits of Trees section of this website you’ll find more information about the benefits trees provide. Here we’ll document the results of a study of tree benefits in the Madison Area. These results were derived from a study of the Madison Urban Area using the computer modeling program i-Tree Eco, which was developed by the U.S. Forest Service to assess the benefits urban trees provide to their communities.
If you’ve read the last three sections you know what the current status is of the Madison Area Urban Forest. The next question is where is it going? Is canopy increasing? Is species diversity increasing? Are we growing the benefits from our urban forest or losing them? Not all of these questions can be answered (yet) but we do have some insight. One part of our collaboration with the University of Wisconsin-Madison was to study what species of trees are currently being planted in the Madison Area. We surveyed arborists, landscape contractors, landscape architects, urban foresters, and nursery salespeople to find out what they are planting, selling, and recommending. What we found is that although the species we’re using today are different than what we used in the past, the frequency at which we use them is nearly identical. Here are the 20 most common trees in the relative abundances they are currently being planted in the Madison Area:
So what can be done about this? At the Urban Tree Alliance we believe the best option is to plant more trees (to increase canopy cover and urban forest benefits) and to use a wide variety of species. If you are choosing to plant a tree we recommend not picking a species from the top 10 most abundant or most planted species documented here.