Can’t see the forest for the trees? Accounting for the urban forest


One day in 2011, I came home from work to discover a neon orange ring around the giant elm tree in my front boulevard. I had seen the ring on other trees on the block and watched them be taken down the previous year so I knew that it was only a matter of time. Dutch elm disease is a fungus that is spread by the elm bark beetle and leads to branch die off and the eventual death of the root system. There are treatments for Dutch Elm Disease, but they are expensive and generally don’t work in the long term. The preferred treatment is prompt eradication of the infected specimens. The following spring, the Minneapolis Parks and Recreation Board cut it down and ground out the stump. In its place, they planted a Hackberry, a weedy and tough urban survivor not known for its looks.

This article is reposted from TCDP media partner Streets.MN. Check out the links below for other recent Streets.MN stories:

Like most American Elms, mine was a beautiful specimen. It had a dense trunk that split to gracefully arch over the street, creating a cathedral effect over the right of way. Elms are the perfect street tree. They grow fast, they can handle nearly any soil conditions, and don’t drop a lot of litter. They also became the poster child for why urban forests can’t be a simple cut and paste operation, but instead must be thoughtfully planned systems that are diverse and resilient. Despite this story repeating itself with the arrival of the emerald ash borer and the impending destruction of the Green Ash, most people still have little understanding of the challenges facing our urban forest and the beneficial roles that urban forests play in our lives as a living green infrastructure. The benefits of a healthy urban forest are somewhat well known, but understood mainly as broad platitudes. People are aware of the improved property values that come from mature tree canopy as well as the benefits that they provide towards cooling urban environments. The purpose of this series will be to build a more nuanced conception of how our urban forests function from the roots up. There is a lot of fascinating research being conducted at the University of Minnesota as well as interesting pilot projects and initiatives happening within local governments. This series will highlight a variety of projects and research related to street trees and the urban forest. What follows are a few of the broad topics that we will address in the series.

The Missouri Gravel Bed Cultivation System

Soil and Water in the Life of a Street Tree: This post will document the challenging nature of establishing and maintaining a healthy urban forest, by considering the pathetically short shelf life of most trees and the new cultivation and planting techniques that urban foresters are using to improve the longevity of these trees.

Right: The omnipresent stock photograph of the Emerald Ash Borer

Pests, Fungus, and Disease: Most people are aware of the impending epidemic of the Emerald Ash Borer that is estimated to decimate the Green Ash population, but are not aware of the details of how it spreads, how it is treated, and the diverse array of strategies that cities and tree services are employing to contain it and plan for its eventual culmination. This post will present key information and will discuss the implications for future blights.

Biodiversity: In light of the mass die off of key tree species (potentially maple trees in the future), the need to build a more diverse urban forest is critical. This post will consider the historic impact of mass die offs, consider what level of species diversity is desirable and consider the different approaches that local governments are taking to restore balance to their tree inventories.

Stormwater Pollution and Runoff: Street trees are responsible for intercepting large volumes of stormwater runoff with their canopy that otherwise would fall on pavement and end up as stormwater runoff. Many exciting and interesting projects are underway that are pushing this further by using engineered structural soil mixes and drainage systems to use trees as Bioretention and filtration systems for urban stormwater pollution. Likewise, street trees are also responsible for the export of massive quantities of phosphorus and organic nutrients to our waterways when they drop their leaves in the fall. This post will examine some of the interesting research underway to account for the stormwater benefits of urban tree canopies and intelligent street sweeping regimes.

Livability and Property Value Improvements: This post will go into more depth about the benefits to health and wellness that trees provide in the urban landscape as well as documenting the positive impacts mature trees have on property values and improving the fiscal performance of retail districts.

Carbon Sequestration and the Urban Heat Island Effect: This post will examine some of the interactive models and tools that purport to model the overall benefits that trees provide in terms of carbon sequestration, air quality, cooling, and energy savings. Likewise, it will examine work being done by the University of Minnesota and metro area cities to model their urban tree canopy and its estimated impacts.

So while this post was more of a fluffy and broad introduction to the series, I hope that it will generate interest for the posts to follow. On each of these topics, I will be writing a focused piece that conveys the most up to date research and local examples that we can identify and I will be reaching out to local experts to provide guest contributions relevant to each post topic. So if you have any other thoughts about what would make an interesting additional topic or some cool work being done in your community, please shout it out.