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Thumbnail image for London Plane 3.JPGThis week's tree of the week is the London Plane Tree (Platanus x acerifolia). The London Plane Tree is a stately shade tree growing to a height of 70 feet tall. The mature bark is a stunning pale grey with exfoliating brown bark. The leaves resemble the look of a maple having a palmately lobed leaf. However, unlike a maple leaf, the London Plane Tree has a fussy back, giving it a unique character.

Being a zone 5 tree, The London Plane Tree is not commonly seen in Minnesota as it is not hardy to the northern climate. However, there are a few London Plane Trees scattered throughout St. Paul and Minneapolis. The slightly warmer temperature of the cities is often just enough for the London Plane Tree to survive the harsh Minnesota winter.

London Plane 2.JPGIn the team tree fields, we have three varieties of London Plane Tree, Exclamation!™, Columbia, and Bloodgood. All three varieties grew extremely well this season! It was exciting to see the trees grow from small 4-6 foot whips to a sizable 1" caliper trees (left image). This fall, we dug out most the London Plane Trees to prepare to plant in root trapper containers next spring!

The image bellow shows two of the four rows of London Plane Tree at the nursery. The lush, 12 foot strips of grass like plants growing in between the rows of trees are cover crop that team tree uses in all fields to keep the soil as healthy as our trees. The cover crop is a mixture of millet and buckwheat, both fast growing plants. The cover crop is used to maintain moisture in soil, reduce weed population, prevent wind erosion, and finally, increase soil organic matter. Often times, nurseries keep the soil bare by continuously spraying for weeds throughout the season to reduce the competition for resources. However, the benefit cover crop provides for the soil far out weights the marginal decreased caliper growth.
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The vigorous growth of the London Plane Tree is quite typical for the tree. The London Plane Tree is often used as street trees in warmer climates due to the vigorous growth and ability to withstand high compaction and atmospheric pollution. The number of tough tree species for urban situations is becoming less with the loss of American elm to Dutch elm disease and the more recent loss of Ash species to emerald ash borer. Both American elm and ash trees were extremely common street trees due to similar tough qualities the London Plane Tree has. With fewer and fewer street trees to withstand the tough street conditions, it is important to test the winter hardiness of different tough trees like team tree is doing with the London Plane Tree.

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Across the United States there are pockets of land in our urban environments that have been made inhospitable for the growth of most trees and other desirable plants.

These areas, while once comprised of native soil and vegetation, have become "brownfields", generally only supporting less desirable plants like thistle, nutsedge, knotweed, and crabgrass.

Brownfields are generally created over a long period of time by various human activities (construction, development, chemical pollutants, etc.).  The soil in this are is altered in such a way that many trees have a difficult time establishing.  These sites are used by urban foresters to identify tree species and varieties that will adapt to even the harshest of urban conditions. 

The following map (created with ArcGIS) gives an overview of the recently planted brownfield site in Saint Paul.  Located on the southwest corner of Phalen Blvd. and Payne Ave., this site is a collaborative research project between the Saint Paul Park & Recreation's Forestry Division and the University of Minnesota's Urban Forestry & Horticulture Research Institute.

 

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Many of the species planted at this site are of interest in other areas of Saint Paul and Minneapolis, representing possible replacements for threatened trees like ash. 

Others are tried-and-true species that have worked on other locations but never put to the test in a place like this!

If trees survive (and thrive!) in this location they become prime candidates for use throughout the city, especially on tough disturbed sites.

Watch this site for updates as the project progresses!

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2010 marks the fifth year that researchers at the Urban Forestry & Horticulture ResearchMiller Park - Comp.JPG Institute have been collecting, cloning, and screening Minnesota-native elm trees for Dutch Elm Disease (DED) resistance. Mature trees that have survived - and thrived - in areas where DED is rampant are prime candidates for this screening work.

Researchers in Robert Blanchette's Forest Pathology Lab at the University of Minnesota have been working side-by-side with our scientists to inoculate selections with the DED fungus.

Outstanding specimens like this American elm located in Eden Prairie, MN may offer new options for trees in our increasingly threatened urban forests.

Photograph courtesy of Jeff Cordes - City Forester, Eden Prairie, MN
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Gravel bed production continues in 2010 focusing on producing tough nursery stock suitable for replacing ash trees.





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