By Dan Buckler, DNR Urban Forest Assessment Specialist
Daniel.Buckler@wisconsin.gov or 608-445-4578

Much of what we know about our urban forests is limited to publicly maintained spaces such as in parks or along streets. However, the curtain covering other urban lands is rising, starting in Milwaukee and Madison.

The Urban Forest Inventory and Analysis (UFIA) program, a partnership between the USDA Forest Service and the DNR, has established 1,300 permanent plots in urban areas across Wisconsin. Project foresters captured loads of information on each plot, such as tree species and sizes, land ownership, tree damages, and wood volume. The data were extrapolated from those plots and made into estimates for each city. The data were also incorporated into i-Tree to calculate ecosystem services.

Though statewide results will have to wait until 2026, baseline results for the cities of Milwaukee and Madison, stemming from about 400 plots across the two places, are now available.

There are many ways you can access the UFIA results:

• Milwaukee’s Urban Forest in a Nutshell [pdf] – an infographic summarizing results for Milwaukee.
• Madison’s Urban Forest in a Nutshell [pdf] – an infographic summarizing results for Madison.
• My City’s Trees [exit DNR] – a tool which summarizes UFIA data by theme (e.g., watersheds, building age or population density).
• Urban Forest Stats [exit DNR] – a tool which allows customized searches and summaries.
• Urban FIA DataMart [exit DNR] – a platform where raw data can be downloaded.

It is estimated that Milwaukee has 3.7 million trees at least 1-inch in diameter. Norway maple, boxelder and honeylocust are the most common trees at least 15 inches in diameter, while the smaller size ranges are dominated by invasive common buckthorn. It’s a similar story in Madison which has 2.9 million trees, many small buckthorn and large trees led by Norway maple, honeylocust and white oak. Milwaukee and Madison’s species and size distributions are below.

A summary of Milwaukee’s trees, from the Milwaukee Urban Forest in a Nutshell document.

A summary of Madison’s trees, from the Madison Urban Forest in a Nutshell document.

Results also show that although larger trees make up a smaller portion of our urban forests, their significance is much greater. Leaf area is what drives many benefits of urban forests, such as air pollution reduction or stormwater mitigation, and large trees play an outsized role in providing these services. For example, trees at least 15 inches in diameter make up 10% of Madison’s trees, but 53% of the urban forest’s leaf area (see below).

The population and leaf area of trees by size class in Madison, from the Madison Urban Forest in a Nutshell document.

UFIA data can inform long-term management plans and policies to sustain a healthy urban tree population. While these results capture attributes of the current urban forest and associated ecosystem services, future monitoring will identify how the forest is changing over time. The plots in each location will be remeasured on a seven-year cycle as part of the continuing UFIA program.

Stay tuned for more articles stemming from these exciting UFIA results. For questions or data requests, please contact Dan Buckler at Daniel.buckler@wisconsin.gov.