The benefits of trees in the urban environment are both qualitative and quantitative. Trees offer an aesthetic enhancement to the urban environment. There is something magical about driving, biking, or walking down a street lined with mature trees. There is a connection to the past – with the people who planted those trees and all the residents that have consciously or unconsciously enjoyed their presence. But in today’s society money talks. Lucky for trees – it turns out they have an economic voice – and its pretty loud.
Researchers at the USDA Forest Service, Northern Research Station have developed a tool for discovering, among other things, the economic impact that trees have in the urban environment. Its called the Urban Forest Effects (UFORE) model. This model is able to estimate the economic value of various ecosystem services provided by urban trees. For example, would you have guessed that the urban forest of Minneapolis removes around 384/tons of pollution each year? And the value of this service? $1.9 million/year. How about the current ‘hot-topic’ – carbon. Well, Minneapolis trees sequester around 8,900 tons/year – worth around $164,000/year according to the UFORE model. Urban trees also happily store this sequestered carbon for us. The Minneapolis urban forest is estimated to store 250,000 tons of carbon – a value of $4.9 million. (For more information visit http://www.nrs.fs.fed.us/tools/ufore/).
rban citizens live in highly developed and altered landscapes. We have houses connected to gas lines, sewer lines, electric lines, cable lines, phone lines, paved roads, sidewalks, and parking lots. In many cases our urban trees must coexist with these structures in close proximity. Furthermore, trees need to deal with all the construction and renovations that must be done to keep these urban systems going. Now, no one is suggesting we get rid of our modern conveniences to make room for growing bigger and better trees…well, some probably do! So we need to understand how our construction activities effect the nearby trees.
This is the goal of a 20 year study undertaken by University of Minnesota Urban and Community Forestry Professor, Gary R. Johnson. In 1993-1994 the Kenwood neighborhood of Minneapolis underwent a complete utility and infrastructure renovation. New utility lines (sewer, electric, water and gas) were run, streets were widened, curbs were lowered, new sidewalks installed, and the boulevard was regraded. The goal of the study was to see how trees planted in the area between the sidewalk and street – also known as the boulevard – performed when subjected to intensive construction activities. For comparison, a control group of boulevard trees that did not experience any construction activity was also established nearby. Five different genera of trees were looked at including maple (Acer spp.), American elm (Ulmus americana), ash (Fraxinus spp.), hackberry (Celtis occidentalis), and linden (Tilia spp.). Stem diameter (DBH) and condition ratings were taken for each tree in the study three times over the course of 20 years. Survival was also noted.
A complete statistical analysis is still forth coming but several trends are appearing from the data. For example – elm and maple trees experienced a greater percentage of loss in the construction group compared to the control group. Ash and linden on the other hand had a smaller percentage of loss in the construction group compared to the control group. Causes of tree loss are unknown. Elms by far had the greatest percentage of loss over all genera with 57% loss in the construction group and 45% loss in the control group. Average increase in DBH was not significantly different between construction and control groups among the various genera.
This represents a case study of boulevard trees in one neighborhood of Minneapolis. More studies are needed to form any definitive answer on the effect of construction on our boulevard trees. A complete report of this study is forthcoming. Stay tuned.
by Luke Midura
Armed with Shovels, Sharpies and scientific-grade Ziploc bags, Team Tree continued its intrepid adventures in urban forestry this week. Charged with the mission of soil data collection, the team took soil density ratings at depths of six and twelve inches, and collected a pint of soil for analysis from a series of random sites located within the study site.
“Can I help you?” Is probably the most common question you can expect to get from homeowners if you are using a penetrometer in a residential area. A penetrometer is a tool used to measure soil density, useful in determining compaction. It is similar in shape and execution of a soil probe, except no soil core is removed, and a pressure gauge on the top of the unit indicates the level of force required to penetrate the soil to a desired depth. The process of taking penetrometer readings and removing a soil sample from each location looks just unusual enough to raise concern from vigilant homeowners, leading the conscientious scientists of Team Tree to recommend that similar expeditions be carried out in classic lab coat attire using vehicles clearly marked with the University of Minnesota Department of Forest Resources logo.
While some may argue that nothing is more exciting than collecting soil data, the summer data collection portion of this project proved to be among the highlights of Team Tree’s year. Procuring data during visits to each of over 1800 trees that failed during the storms of June 20th and 21st, 2013 provided opportunities for close examination of some extremely large trees and their root systems. Included among those trees were those which failed due to tip over and those that broke off above the ground line. Experience and teamwork aided the crew as they assiduously compiled information on boulevard, sidewalk and street conditions amidst what evidence remained of the dendronomic destruction dealt by the astonishing summer storms.
by Chad Giblin
As the growing season of 2013 was drawing to a close, we teamed up with Scott Alsleben and his Forestry Occupation students at Great River School (GRS) to wrap up the reNewell project and prepare it for the long winter.
During our first meeting we introduced the site and project to the 6th and 7th grade students from GRS and discussed some of the inspiration and challenges faced when maintaining urban tree canopy. During the next few sessions students helped mulch all the new trees and shrubs on the site had a chance to get to know these native species a little better.
We wrapped up the 12-week session with a few weeks of survey and mapping training. Students worked in teams to survey and map all of the new oaks planted on the reNewell site. On our last session together I joined Scott and his class at GRS and created a web map at ArcGIS.com.
We also teamed up with the students to plant a new crop of oak seeds that they collected at Newell Park in hopes that they will become part of ongoing efforts to regenerate oak canopy throughout the City of Saint Paul.
As we get ready for the long winter – thanks again to everyone who made reNewell 2013 a great success!
- Saint Paul Garden Club
- Hamline-Midway Coalition
- City of Saint Paul Parks & Recreation
- Great River School
Two USDA Zone 5 hardy tree species – the London Plane Tree (Platanus x acerifolia) and Yoshino Cherry Tree (Prunus x yedoensis)– are making their way into the Twin Cities. These two trees have shown they may just have what it takes to make it through the Minnesota winters – bringing greater diversity to both public and private landscapes.
The Yoshino Cherry Tree is a spring blooming ornamental hybrid cherry tree found naturally in Japan. Its very name comes from Yoshino, Japan – a city known for its 30,000 cherry trees and, as you might imagine, an incredible destination during the spring bloom. The flowers emerge before the leaves providing a splash of color after the winter months. These cherry trees have been bred for their flower fragrance as opposed to their fruit. The fruit is a great wildlife food source for various bird and mammal species, however is less sweet than what many humans would expect from a cherry. At maturity the Yoshino Cherry grows 40-50 feet in height with a 25-40 foot spread.
The London Plane Tree is a tall deciduous shade tree growing to a mature height of 70 feet. At our research nursery on the University of Minnesota St. Paul Campus we have three varieties of London Plane Tree: Exclamation!™, Columbia, and Bloodgood. The London Plane is a tough tree. It has the ability to withstand high soil compaction and atmospheric pollution. These attributes along with its height and shady canopy make it a desirable street tree. With the loss of many of our beloved ash and American elm street trees to emerald ash borer and Dutch elm disease, species such as the London Plane may play a role in a diversified street tree canopy moving into the future.
To the right you can see Carl at our research nursery holding a Yoshino Cherry and London Plane that made it through their first winter here in the Twin Cities. While we don’t suggest planting these trees on a broad scale quite yet, the future is looking leafy for these two trees here in the Twin Cities.
By: Jonathan Fillmore
On Saturday June 8th, around 30 volunteers helped plant baby oak seedlings that will hopefully take the place of their parents as they slowing start to decline from age.
Designated as a park in 1908, Newell Park is one of the oldest parks in St. Paul. One of the most notable features that separates it from other parks in St. Paul are the pre-settlement mature Bur Oaks that create a dense canopy over the entire park. Unlike in a natural system, regeneration of new oak trees from fallen seeds does not occur due to the heavy use as an urban park. In efforts to regenerate oak trees in Newell Park, we teamed up with the City of St. Paul Forestry to plant baby oak seedlings germinated in our greenhouse from Bur Oak acorns collected in the park. For now, only a small wooded area located in the northeast corner of the park was planted with baby seedlings (shown bellow). In addition to the oak seedlings, bare root Carpinus and two different varieties of Amelanchier (Serviceberry), both native understory species, were planted on the reNewell site to further restore the park.
The first oak tree being planted!
The image bellow shows the site after all the oaks were planted. Inside each of the white tubes seen in the image are baby oak seedlings. Tree tubes are commonly placed on seedling trees to protect them from the getting eaten by animals or stepped on by humans. Additionally, the tube acts as a mini greenhouse that encourages the seedling to grow faster and straighter. The tube is removed shortly after the tree grows out the top of the tube.
Instead of using a truck to transport the bare root Carpinus and Amelanchier and flat of oaks, we carried the trees down to Newell Park from the nursery using our bicycle trailers!! Bellow is a team shot taken before we started our ride to Newell Park.