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We have been running a research project for the past 7 years on the Olson Memorial Highway median in North Minneapolis. This is a true proving ground for urban trees. There are multiple lanes of traffic on either side, lots of salt spray from cars, large mowers on small spaces, and 

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compacted soil to name a few challenges. This is not a friendly environment for trees, but it is just the place to do an evaluation on which trees work best in difficult urban environments.

There are 147 trees going down the boulevard, almost a mile and a half of them in a line. There have been a few necessary replacements, and most trees show signs of wear, but beyond all the salt damage and mower slashes, there are quite a few trees showing promise of high, wide crowns and stable trunks. On the right, Chad is holding a long (7 ft.!!) basal sprout coming from a Cathedral elm, (Ulmus davidiana var. japonica). Basal sprouts can cause trouble for urban foresters and arborists.  Nonetheless it is a good demonstration of the vigorous growth of elms and why they continue to be a popular tree in our urban forests.


The data collection took a whole day, starting and ending with a nice bike along the cedar lake trail (team tree gives it two thumbs up). Thankfully the weather cooperated and wasn't blazingly hot, or extremely windy. It was the most pleasant trip we have had to that site, and that is saying a lot for 6 hours between traffic.

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Elm trees on the research plot begin life as a cutting from an older elm tree. To get material to make new trees, we prune the old ones. Jonathan, myself, and Lara our volunteer cut off all of the lower branches from one plot of the elms. After taking the branches off, we took them to be processed.

Jonathan, Lara and I are all working our pruning technique. It is as much science as an art form, and to get material to make cuttings from, we are able to practice our cuts. We made a  red permanent marker marking to outline the cut. When removing a limb, the aim is a cut that is perpendicular to the branch. The cut should be as close as possible to the collar of the branch without breaching it. The collar provides a physical and chemical barrier to disease entering the main stem of the tree, and nicking it or the trunk of the tree with a saw is the sure sign of a beginner.

During processing, we removed the new growth from the woody growth from last year. The newer the cutting, the more likely it will sprout roots. We cut the new growth into sections of around 6 inches, or the distance between an extended pinky and thumb (think "hang loose").

After they are in 6 inch pieces, we remove all but two or three leaves from the very top of the cutting. The bottoms of the cuttings are then dipped in a hormone solution that causes the cutting to sprout roots.

Fast forwarding 10 years, the elm trees in the plot are inoculated with Dutch elm disease. This disease wiped out much of the elm population, and now we are working to propagate the most resistant varieties. The trees that prove resistant to the disease are then trimmed down again, and another generation of elm trees is produced.

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Urban forestry and arboriculture has changed quite a bit over the last 100 years.

Many old practices like cavity filling and wound painting are gone for good. Oftentimes, though, we can learn from the old-timers, like Theodore Wirth.

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Wirth was appointed Superintendent of Parks in Minneapolis in 1906 and was instrumental in creating this "City of Parks".

In this photo we see Wirth (far left) and other Park Board Commissioners, posing with bare-root American elms.

Fast-forward 100 years to 2010 and we are applying pruning practices from this bygone era to trees in the 21st Century.

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Craig Pinkalla, arborist with the Minneapolis Park & Recreation board, stands next to a Princeton American elm he's just finished pruning at Fort Snelling. 

Since his days maintaining the urban forest in the City of Milwaukee, Craig has been a strong advocate of giving young trees a chance to become mature, productive shade trees. 

In a sense, we've gone "back to the future."



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Sean Peterson is the newest member of the Urban Forestry & Horticulture Research Institute.

Sean is a Forestry Technician based in Green Hall at the University of Minnesota.

When he's not helping manage our research nursery, Sean specializes in producing and directing a new line of "how to" videos featuring outreach, research, and teaching work of Institute professors and scientists.

Join Sean at the 48th annual Minnesota Shade Tree Short Course at Bethel University in Arden Hills, MN on 16 & 17 March 2010, to discuss some of his work.

Watch this site for videos to complement the Pruning Young Elms book recently published by fellow scientist, Chad P. Giblin.

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Chad - Smiley.JPGChad Giblin will be at the 48th annual Minnesota Shade Tree Short Course at Bethel University in Arden Hills, MN on 16 & 17 March 2010 signing his new book Pruning Young Elms and discussing structural pruning techniques for young elms and other popular trees in the urban forest.

Stop by for some great continuing education for arborists, urban foresters, and tree advocates.  A copy of Chad's book is included in the registration price for the Short Course.







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