Check out this neat time-lapse video of our elm grafting process! Created by our very own J.W. Fillmore...and featuring American elm roostocks from our friends at Three Rivers Parks District Nursery.
Recently in RESEARCH Category
Last fall I had the opportunity to join Mr. Don Willeke in observing the removal of a large 'Iowa State' American elm at his neighbor's house in the Dean Park area of Minneapolis. This large tree was planted in 1978, shortly after Don grafted it onto a wild American elm seedling. Unfortunately, the tree had developed major defects over the years (it had already been cabled and braced) and required removal for safety purposes.
Don is a local elm aficionado and has been "speaking for the trees" since the 1970s. He has been my host on many visits to the forest of elm trees (amongst other species) in and around his Dean Park home.
'Iowa State' was discovered and screened by Prof. Sandy McNabb at Iowa State
University from the late 1960s to early 1970s where it proved to be quite resistant to Dutch elm disease (DED) when inoculated with the fungus.
While not widely released (at least to my knowledge) this tree remains
an important reminder of those lucky escapes - native American elms with
high tolerance to DED. Unfortunately, the structure of this tree is less than ideal as it has a tendency to form weak branch unions due to inclusions and very acute angles of attachment.
In my ongoing efforts to make-lemonade-outta-lemons I worked with Don and Jay Linn from Log and Limbs Company (who was performing the removal) to collect some prime cuttings material for cloning of this now rare tree.
By the end of the removal process Don and I were able to collect some vigorous vegetative shoots from the very top of the tree, which I brought back to the University for propagation and inclusion into our elm program.
Now, weeks later, I transplanted some of the first rooted cuttings of 'Iowa State' and can now add this tree to the growing collection of elms at the University of Minnesota.
Plants are also slated for distribution to the USDA National Arboretum in Maryland for inclusion into their continuing work on the American elm.
Many of my friends assume that I am out of the job now that the snow has fallen, and the
days are short and cold. Although we don't get outside as much anymore, there is still a lot of work for team tree over the winter months. Recently, we drove out to St. Paul to take data on the High Bridge dog park. There is an earlier article that talks about the dog park in more detail, but it is basically a remidation site where we planted groups of 1 1/2" caliper trees on the site of a former rail yard for a coal plant. The site is a difficult place for trees, with poor soil conditions, and of course, lots of dogs, who may or may not be nice to the trees we planted. We have been taking data for awhile on how well they are growing to see what varieties do well in the adverse conditions.
During our check up on the trees, we were going to collect data on caliper and take photos of
Sadly, many of the trees have lost all their cambium at some points, which will most likely kill the trees. Chad said that when he originally checked the site out, the trees in the surrounding area showed signs of damage from critters, and there was probably a lot of them living in the area.
The remaining trees that survive the winter will make it to the 2" caliper mark, where the bark usually will become hard and inedible. Also, there was generally less damage on Catalpa, Birch, and Alder than other varieties.
Team Tree met up with some Saint Paul Forestry after our initial visit and wrapped the stems, so some of the trees will make it to spring!
There is a lot of work we have to do around the nursery to get ready for winter. The trees we
grow expect, and rely on winter to come, but they are also used to being under the ground, away from the harsh temperatures of the surface during winter. They are also vunerable to animals who will nibble away their cambium, which, if it gets bad enough, will kill the trees. If a tree is small enough, animals will leave you with only a frayed stump.
When planning to keep trees alive over winter, you need to keep these concerns in mind: to keep them protected from animals, and also to keep them in enough mass that the roots don't freeze and kill the plant. In planning for this, you need to take into account the amount of snow you will get. If you put a 6 inch wrap on a tree and there is 2 feet of snow, the wrap is going to be a foot and a half under, leaving the tree exposed. For our nursery stock, we placed as many as we could in the pot-in-pot section, and for the rest, we packed them in with mulch and then wrapped the stems.
This 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.
In 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.
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.
At the beginning of the summer we began two European-style pruning experiments, Les Trognes, and Der Dachplatane. The trees will take quite a few seasons to develop, but the end results will be very interesting.
For some background, Les Trognes is a very common practice in European cities. We chose a non traditional species for it (poplar), so it will be interesting to see how it reacts. Les Trognes, also known as "pollarding," is the yearly pruning of a tree down to one point. This, over time, develops a nubby club of scar tissue with a large amounts of yearly sprouts.The large quantity of callus (woundwood) tissue allows pruning off all of the sprouts without having as much danger for decay and infection. Les Trognes should not be confused with topping, which is where important sections of the main trunk are removed at the top to satisfy height requirements. Les Trognes is a pruning method that requires annual care and does not remove important parts of the tree, topping is a dangerous method of making trees fit that removes important natural defenses. As the photo on the left shows, pollarding can produce old, healthy, trees, that are also quite small. This one is from my friend Andrea in Oslo.
The method was said to of originated in France, where a king, to control deforestation,
decreed a maximum diameter on available firewood. Les Trognes then developed out of this, with people trimming trees down to a certain diameter every year for firewood and animal food. Eventually this became a very common sight. In the US, this is very unusual, and, outside of San Francisco, it isn't seen in urban environments. In a few seasons, hopefully ours can develop the Les Trognes look, right now it hasn't had time to develop sprouts (there one of them is on the right).
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
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.
At the nursery we have almost finished a job that has been a standing order since last fall. This is our pot-in-pot system. It is basically a field of plastic pots dug into the ground. there are 168 15 gallon pots, and room for two more rows (28 per row) of larger 30 gallon pots. The pot in pot field sits in the southeast corner of the nursery, going along the fence.
The system is used to help trees survive the winter. All of the trees in our nursery need winter to maintain their life cycles, but they also need to maintain certain temperatures. If their roots were in the ground, they would be much warmer than when they are potted above ground, without insulation from the soil. The pot-in-pot system allows us to have trees in the ground, but also keep them mobile for fall and spring plantings.
After we finish the pot-in-pots, the new ones will start to look like the olds ones, the next steps being turf, wraps, and irrigation. We cover up the patches in between with grass, spaced so that a mower can ride between the rows, and lay an irrigation line with drippers for every tree. Out of the trees that were in there last winter, only a few died, and the system is working very well. We hope that it will still be there in 10 years.
A special thanks to Matt, Jonathan, Charlie, Chad, and the Nicks.
This week's tree is the Chinese catalpa (Catalpa ovata). They are easily recognized by their long thin pods and their heart shaped leaves. They differ from the native variety by having longer pods, and
purple tinted leaves. Just recently we planted a few flats of them in one of our fields, replacing the winter kill from last year.
Chinese catalpa is obviously not native plants, but they work well in Minnesota, and have been successful in urban environments. A good example is still flourishing next to the stone arch bridge - 10 years after transplanting from our research nursery here at the U of MN. They grow in the USDA Hardiness Zones of 5-9, going to -20 or -30 F. The Chinese catalpa is a little squatter than the southern catalpa, growing to 20-30 feet. It was a special tree in china because its wood was used to make the bottom of the qin, a traditional Chinese instrument.
A full grown Chinese catalpa, down near the Stone Arch Bridge in SE Minneapolis
Team Tree under the same, a tree that left our nursery 10 years ago
One of the trees, a former champion from the year 2010 nominated by MPRB arborist Kevin O'Connor, comes from our very own Hennepin
County. It was a Black Willow, Salix Nigra, with a circumference of 384", 64' tall, and a 73'
The tree died, and had to be cut down, but it was an amazing specimen. Chad had time to get some cuttings from the tree before it died. They took root, and just like willows are know to do, they are growing quick and wild. With some structural pruning, they are looking great so far. These trees have some very large shoes to fill, but hopefully they can join the ranks of some of Americas largest trees. Pictures of the new champion willows coming soon!
Link to the American Forests Big Tree page, a must for anyone who wants to see some amazing trees: