Vol. 10, No. 3
Seed Bed Bob T COMMUNITY FOREST PROFILE
Fall 2008
By Gail Soens he story of Johnny Appleseed, a legendary man who wandered around planting apple seeds, is one that most of us have heard growing up. Anyone who has ever really looked at an apple probably wonders: Where did Johnny get all those apple seeds? There are only about five seeds per apple and they are inside the fruit, so you have to somehow get them out of the apple to plant them. How did Johnny Appleseed get enough seed to plant apple trees for 40 some years? The answer is wonderfully simple. Johnny got all of his seed from the cider mills. The mills pressed the apples to make cider and Johnny collected the seed as it flowed out into the river. The cider mills let him have the seed for free because planting more apple trees would hopefully bring more apples to the mills. Johnny Appleseed wasn’t just a wandering seed caster. He was a nursery man. He bought tracks of land, fenced them with log fences, planted his seed and paid those who lived nearby to tend the trees for him. Then he moved on to plant more trees in the next plot.
Inside This Issue
So where do trees come from today? The guy to ask is Bob Arntzen, fondly known as “Seed Bed Bob”. Bob Arntzen plants tree and shrub seeds for Bailey Nursery; and has done so for 35 years. He is a shy encyclopedia of growing knowledge (pun intended). Bob is the modern day version of “Johnny Appleseed”.
3 Mystery Tree 4 Invasice Garlic Mustard
Seed Bed Bob continued on p. 2
7 If you build it ... 8 Emerald Ash Borer 10 Maples for Minnesota
Photo by Gail Soens
Bob Arntzen grew up in St. Paul Park and took a summer job with Bailey Nursery when he was only 13 years old. Like Johnny Appleseed, he loves to work outside. At first, he was busy hand planting in the field, weeding, pruning trees and “budding” pru-
14 MnSTAC Awards 14 Firewood Correction 15 Calendar
Visit MnSTAC on the Web at www.mnstac.org
The Minnesota Shade Tree Advisory Committee’s mission is to advance Minnesota’s commitment to the health, care and future of all community forests. ADVOCATE • Fall 2008
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Seed Bed Bob from p. 1 nus, apple and ash trees. Eventually Bob started accompanying Pat Perkins, who was a neighbor and foreman at Bailey Nursery, to collect seeds for trees and shrubs. They studied tree and shrub forms and picked characteristics for the best plants and then collected the seed from those trees and shrubs.
How long is a seed viable? That’s a great question and it depends on the seed. Oak acorns rot fairly easily, whereas apple seed is easier to store. Populus seed needs to be planted fresh, whereas Kentucky Coffee tree, without any help, can take years to germinate. The science of seed storage and germination is fascinating and complex.
After high school, Bob Arntzen attended the University of Minnesota. He started out in the Forestry Program, but at the time, there were more opportunities in Nursery Management, so he switched majors. After graduation, he spent two years in the U. S. Army. When he returned home, the fall of 1970, he went back to Bailey’s. He started in Green House Propagation. Back in those days, he worked in glass green houses, with sand benches. He produced hard and soft woods and evergreens.
Bob Arntzen started out in the seed beds in Hastings, Minnesota. In 1981, new seed beds were created at the Nord Farm in Cottage Grove. Each seed has a “best time to plant” which varies from spring to fall. Bob scatters between 50-60% of these seeds by hand. Each seed has a different depth it needs for optimal germination. Each seedling needs to be protected from late frosts. Each tree needs water, fertilizer and the correct soil conditions to thrive.
For 35 years, Bob Arntzen has been collecting and storing seed; giving seed treatments; preparing the beds and planting; warding off spring freezes that can damage emerging seedlings; growing the trees and shrubs and then harvesting and grading them. He grows nearly 100 varieties of trees and shrubs for Bailey Nursery from seed. He collects most of the seed from the Twin Cities area, although some seed is collected from farther away. Bob Arntzen knows the characteristics of trees and seed quality and amounts. He knows how many seeds of each variety make a pound. The smallest seed he works with is the size of a pencil dot. Can you guess what it is? It is an aspen seed, and yes, there are 3.6 million aspen seeds per pound. The largest seed he works with is a black walnut. This seed is roughly between the size of a quarter or a half dollar. There are 40 black walnut seeds per pound.
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In his 35 years of planting trees and shrubs for Bailey Nursery, Bob Arntzen has planted between 90-100 million seedlings. Not even Johnny Appleseed can hold a candle to Bob Arntzen. Bob was recently given the JV Bailey award for his many contributions to the nursery. You could say that Bob has always been outstanding in his field!
Gail Soens is a Grower and a New Variety Coordinator at Bailey Nursery. She is also a Minnesota Tree Care Advisor.
Photo by Gail Soens
Even though he enjoyed his work, Bob Arntzen needed to follow his sense of adventure, and he took off four months to see Europe. When he returned, he settled back at Bailey’s, this time with Don Nordine, in the seed beds. Arntzen spent three years assisting Nordine with tree and shrub production. In 1973, when Nordine retired, Bob Arntzen stepped into his boots.
There are long days spent collecting, preparing (for example, the wings on the maple seeds need to be removed), storing seed; then preparing the fields; sowing the seeds; covering them; monitoring moisture; weeding, frost protecting. When asked to name his favorite part of growing trees and shrubs, Bob Arntzen says he enjoys collecting and preparing the seed; but to watch the miracle of new seedlings emerging from the soil makes all the hard work worth it.
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Mystery Tree... This small tree or large shrub is native to Minnesota and is found throughout the state. The white flowers, containing 5 petals, bloom in early spring before the leaves are out. This tree is found along forest edges and forms a thicket because of its suckering habit. An easy identifier of this species is the green to yellow to red drupe that forms in the mid to late summer. Other identifiers include the dark green and glabrous leaves that are alternately arranged and that have a finely serrated margin with a pointed tip. No glands are found on this leaf base or petiole; however, pubescent midribs and petioles can be seen.
Photos: University of Minnesota
The furrowed mature bark of this species is dark brown and contains horizontal lenticels in its juvenile years. The thorn-like spur shoots found on the branches, along with its bark characteristics, result in this species often being confused with the invasive Rhamnus cathartica.
Answer on page 14 ADVOCATE • Fall 2008
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URBAN FOREST HEALTH
Invasive Garlic Mustard in Forest Understories By Laura Van Riper Garlic mustard (Alliaria petiolata, mustard family) is a biennial herb that is native to Europe, but has become abundant in forested regions of the United States. Garlic mustard can form dense patches in the forest understory and crowd out native plants. Garlic mustard also exudes allelopathic chemicals that can harm plant seedlings and mycorrhizal soil fungi. Spring wild flowers and tree seedlings appear to be most vulnerable to the changes caused by a garlic mustard invasion. The first report of garlic mustard in the United States was in New York in 1879. It was likely planted purposefully as a medicinal and food plant. By 1950, garlic mustard was present in 14 states; today it is found in 37 states. Garlic mustard is most commonly found in deciduous forests, but it can also be found in coniferous forests, forest edges, roadsides, and river banks. As a biennial, garlic mustard goes through several life stages. In the spring, garlic mustard seeds germinate and the forest floor can become a carpet of garlic mustard seedlings. By the fall of the first year, seedlings have grown into a basal rosette, which then over-winters. The next spring, the rosette bolts and forms the adult flowering stalk. Adult plants flower in the spring, set seed in mid-summer, and then die. Identification of garlic mustard can be aided by its distinct smell: crushing the leaves releases the odor of garlic. Garlic mustard seedlings and rosettes grow low to the ground and have rounded leaves. Flowering garlic mustard has small, white, 4-petaled flowers and triangular, toothed leaves (Fig. 1). At some sites in Minnesota, either rosettes or flowering plants clearly dominate in any given year. This pattern is demonstrated in Figure 2 with photos from Baker Park.
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Garlic mustard thrives in disturbed forests; however it can invade relatively undisturbed forests as well. Garlic mustard begins growing early in the spring and can form a dense cover which can crowd out native species (Fig. 3). The impact of garlic mustard on spring wild flowers is of particular concern. Native butterflies may also be affected by garlic mustard. White butterfly species (Pieris sp.) lay their eggs on toothworts (Cardamine spp.), native plants in the mustard family. Toothwort leaves contain chemicals that stimulate female butterflies to lay eggs. Garlic mustard plants contain similar chemicals which encourage female butterflies to lay eggs on garlic mustard rather than the native toothwort plants. The confused females lay their eggs on garlic mustard and the larvae are unable to develop. Thus, high numbers of garlic mustard plants may result in reduced populations of the native butterflies. Recent research has focused on the impacts of garlic mustard on native soil microorganisms. Garlic mustard’s allelopathic root exudates have been found to be detrimental to mycorrhizal fungi in the soil. Many native species are dependent on mycorrhizae and grow poorly when mycorrhizae populations are suppressed. Seedlings of tree species, such as sugar maples, have been found to have difficulty growing in soils that have been invaded by garlic mustard. Garlic mustard itself is non-mycorrhizal and so is not impacted by the decline in mycorrhizae. Once garlic mustard populations have established they are difficult to control. In smaller populations, hand-pulling adult plants is an option for targeted control. However, plants must be collected, bagged, and removed from the site because adult plants are still able to set seed after being
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Due to the limited success of conventional control methods (pulling, herbicides, fire), a search for suitable biological control agents was initiated in 1998. Several European weevil species (Ceutorhynchus sp.) were selected for further study due to their impact on garlic mustard and their limited host-range. It is crucial that biocontrol insects do not complete development on nontarget and economically important plant species. Therefore, the weevils were tested to determine whether they would feed, lay eggs, and develop on species other than garlic mustard. Testing was carried out at CABI Bioscience Centre in Switzerland and in quarantine at the University of Minnesota. The root-mining weevil Ceutorhynchus scrobicollis was found to reduce survival of garlic mustard plants as well as have a high preference for garlic mustard. A proposal to approve the release of C. scrobicollis was submitted to the USDA-APHIS Technical Advisory Group this year. They will review the studies and determine if C. scrobicollis can be released in the field to control garlic mustard. Research continues on the suitability of two shoot-mining weevils (C. alliariae and C. roberti) as additional biological control agents. In anticipation of biological control agents becoming available, a project to monitor garlic mustard in Minnesota was initiated in 2005. Permanent monitoring plots were established at 12 sites throughout Minnesota. At the sites, garlic mustard population density, cover, plant heights, silique (seed pod) production, and amount of insect damage are monitored in addition to the cover and diversity of the other plant species growing with garlic mustard. From these sites we can monitor changes in garlic mustard populations from year to year as well as the changes in the
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native plant population. By collecting pre-release data we will be able to determine the effectiveness of biocontrol. We can see if garlic mustard populations decrease and if native species are able to recover. Currently, garlic mustard is experiencing very little herbivory in Minnesota. On average, garlic mustard plants had less than 2% of their leaf area removed by herbivores. A biological control insect could greatly increase the amount of damage to garlic mustard plants in Minnesota. Increased herbivory could reduce reproductive output and population density. Biological control would not eradicate garlic mustard, but could change garlic mustard from the dominant plant in the forest understory to one species of many that are present in lower numbers. Photo: Luke Skinner, Minnesota Department of Natural Resources
pulled from the ground. Herbicides, such as glyphosate, applied in the fall can help reduce garlic mustard populations and minimize nontarget impacts to native species. Garlic mustard seeds have been found to remain viable for more than 10 years, so control must be repeated for many years to keep the garlic mustard population low.
Figure 1. Adult garlic mustard plant in flower.
The Minnesota monitoring sites can guide management decisions on garlic mustard. If garlic mustard is reduced, we want to know if native species can reestablish. If garlic mustard has changed soils (by killing native mycorrhizal fungi) then reestablishment of some native species may be difficult. Some species may be able to recover more quickly than others. In some cases additional restoration action may be necessary. Preventing garlic mustard populations from becoming established is the best way to protect a site. Garlic mustard seeds can easily be carried into a site in the mud stuck to a person’s shoes, equipment, or vehicle. Aggressive action on small populations is the priority. If a site has a large garlic mustard population and several small satel-
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lite populations, management efforts should focus on controlling the satellite populations so they don’t continue to grow. Then management can turn to the larger population. In the future, biocontrol may be an additional option for managing established populations.
Photo: Laura Van Riper, University of Minnesota
Laura Van Riper is a post-doctoral research associate at the University of Minnesota.
Photo: Minnesota Department of Agriculture Biocontrol
Figure 2. Photos of a single garlic mustard monitoring plot over time. This plot at Baker Park, MN shows the dominance of different garlic mustard life stages from 2005-2006. The adult flowering plants were dominant in spring 2005 with few seedlings present. By fall 2005, the adults senesced and there was little other vegetation present. In spring 2006 there was a carpet of garlic mustard seedlings. By fall 2006, the surviving seedlings had grown into rosettes. Note that there are few species besides garlic mustard present within this plot.
Figure 3. Garlic mustard growing abundantly in the forest understory at Prairie Creek Scientific and Natural Area (next to Nerstrand-Big Woods State Park).
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DISPEL-A-MYTH
“If you build it… the trees will die!”
the trees will die!
By Gary Johnson
The question of whether or not a tree will die following site development or construction activities evokes polarized opinions and emotions. One side is convinced that rarely do construction activities cause damage and if trees die, it’s generally due to something else like a disease. The other side is convinced that pointing a tractor in the direction of a tree causes enough trauma to kill it. Both opinions are emotional; contractors and engineers are trying to defend their actions, while tree lovers are angry that trees are dead or dying and are trying to find the culprit.
Who to believe? Both opinions are functions of ignorance, and that’s not stated in a disparaging manner. They are based on an ignorance of tree and forest biology, of activities that affect tree health, and risk assessment. Builders, contractors, architects and engineers are not experts in tree and forest health issues or trained in risk assessment. Likewise, homeowners, horticulturists and foresters are not experts in engineering, architecture and construction. Trusting a builder for tree advice or an arborist for septic field construction specifications is like asking your dentist to tune up a motorcycle. None are good moves.
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Construction and development activities are ongoing events, but the loss of trees due to these actions is not a fait accompli
Too many opinions are based on anecdotal observations or information. “I’ve built homes for 30 years and have never lost a tree!” How long was data recorded? How long was the health of the trees monitored after the construction was completed? “I know the excavator killed the trees because they died shortly after the house was built and the back-hoe cut lots of roots.” What was the health of the trees going into the construction season? Was a new landscape installed, including
trenching for lighting and irrigation after the construction was completed? Construction and development activities are ongoing events and are necessary, but the loss of trees due to these actions is not a fait accompli as some may believe. Woodlands can be developed and streets can be widened without causing mass destruction of urban and peri-urban forests. The key to dispelling this myth is to stop the damage, not the construction or development. Waiting until the construction or development activities are over before anything is done to save the trees or help them recover is not nearly as effective as predicting and preventing the damage.
Hits and misses…what kills trees? What activities do kill trees and forests? Simply stated, anything that kills or causes the death of a significant portion of a tree’s root system. Occasionally, killer diseases are spread by construction activities (e.g., oak wilt) or trees are wounded so severely that they no longer add to the beauty of the landscape, but those types of damage are the exceptions. Root death is the damage to stop. That seems simple enough, but root death is rarely obvious, it’s often progressive and by the time it’s noticeable, hard to turn around. Not all construction activities kill roots or cause their death and not all trees that suffer root loss die. A professional experienced in mitigating construction damage to trees can predict which activities are likely to result in significant damage. Likewise, that experienced professional can evaluate a tree’s or woodland’s potential to tolerate damage. When these two factors are considered together, a protection plan can be implemented and if followed, most trees will survive the assaults on the land. Many good publications and books have been written on tree preservation during construction and provide the technical information necessary to minimize the loss of trees. Despite these resources, trees in boulevards, woodlands and If you build it ... continued on back
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In the Wake of
Emerald Ash Borer: Managing our Trees for Long Term Success Photo: Mark Stennes
By Mark Stennes Having been to ground zero of the initial emerald ash borer (EAB) infestation in suburban Detroit, Michigan, in the summer of 2007, I can witness to the overwhelming destructive capacity of this invasive Asian insect. EAB pays no mind to vitality, taking out perfectly healthy trees bursting with normally sufficient defensive energy reserves. No indigenous ash tree within a generally infested area has a chance of escaping or ever making it to reproductive maturity. While EAB may prefer green Ash (Fraxinus pennsylvanica), it takes no prisoners and shows no mercy on white (F. americana) or black ash (F. nigra) (Anulewicz et al. 2007). All three species are native to North America and commonly used as ornamental shade trees in communities and on rural homesteads across Minnesota. Black ash dominates vast tracts of forest in the northeast third of the state, and green ash has been planted as an ornamental shade tree in numbers and proportions far greater than would occur naturally. And the news has not been improving. On 4 September, 2008, I attended an EAB field day in Chenoa, a rural town in central Illinois. The field day was sponsored by the Illinois DNR, but also contributing was the Illinois DOA and DOT, the University of Illinois, USDA/APHIS/PPQ, and local municipal officials. I have never been in a room with more long faces. There had been some ash mortality in the community in the recent past, but little or no awareness of EAB until it was positively identified and the extent of the infestation recognized. Over a period of years, the trees had been taken down, cut into firewood, and distributed far and wide. At the time of the field day there were no dead ash in Chenoa, so we went to the local park and took branches from living trees. Peeler knives revealed living EAB larvae. With the likelihood of a general infestation in Illinois,
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what can we make of the established infestations just north of Milwaukee, Wisconsin? There are several components to the EAB problem, and none of them will accept a sugar coating. As unfortunate as this reality is, we cannot make it go away. There are, however, several action items we can engage in right now to ameliorate to some extent the damage this insect is destined to inflict on the urban and rural forests of Minnesota. Buy firewood locally. This is perhaps the single most effective thing we can do individually at this point. We will try, but cannot with any assurance, prevent this insect from taking a 70 mile per hour hitchhike in the back of someone’s pickup. We do not, however, have to be the ones that open the box. I have photos of Dutch elm disease burning through the camp grounds at Itasca State Park in the early 1970’s just as we were beginning to pay attention to it in the Metro area. How do you suppose it got there? Build awareness and watch intently. Learn everything you can about what to look for, and if you are genuinely suspicious about a dying/declining ash tree or trees, call the Arrest the Pest Hotline 651-201-6684 or 1-888-545-6684. www.mda.state. mn.us/keyword: ash borer. Manage prudently. There does not appear to be a consensus among the most knowledgeable experts about just what prudent management is. It does seem to be clear that once an infestation is discovered, complete eradication is not a reasonable possibility. It seems obvious enough, however, that the principals of good hygiene probably apply: find infested material that cannot or will not be treated and destroy it as soon as possible. Keeping the population of fertile adults as low as possible should have the effect of slowing the rate of mortality among untreated trees (Poland & McCullough, 2006). While there will certainly be effective preventive treatments, no one is argu-
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Stop planting ash trees. Removing such dependable work horses from our list of ornamental shade trees will not be easy, and not everyone is willing to go that far, but one could argue that we should stop planting ash trees if only because we have depended on them too heavily and have an unsustainably large number of them already. Be more thoughtful when selecting the species we do plant. From the perspective of this old arborist, plant community ecologist and shade tree pathologist, we should be planting more of what we cut down and named some of the streets after when we got here, particularly in my view, our indigenous oak trees. We are in no danger of having planted too many white oak, bur oak, bicolor oak (also known by the unfortunate name of swamp white oak), Northern red oak or Northern pin oak. If they had been planted in proportions reflective of what occurs naturally there would be far less use for tree health care professionals like me. There is an indigenous oak tree for almost any site in Minnesota that is not under water. The bur oak pictured here sheltering statues of Theodore Wirth and some frolicking children was on the site when the park was created. It has not just survived; it has prospered. And it has prospered and delivered the amenities we want from our shade trees in spite of us and not at all because of us. For a thoughtful observer, there is an invaluable lesson in that. It is not unreasonable to argue that bur oak is perhaps the single most important ornamental shade tree in Minnesota if only because of shade and shelter it provides to homes, parks, parkways, parking lots and businesses in almost all parts of the state except the arrowhead. And it has done so by virtue of its own ability to become established, survive and render service under the most difficult of circumstances. But what about the twin boogiemen: oak wilt and slow growth? It is difficult to tell the homeowner whose invaluable Northern pin or Northern red oak trees are dying of oak wilt that oak wilt is a manageable disease. But in a larger sense it is
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true. Oak wilt appears to be an indigenous disease of an indigenous group of trees, so if it was going to kill them all it would have done so by now. If the trees did not comply with the needs of the pathogen by forming root grafts with other trees of the same species nearby, it would probably have failed as a pathogen altogether. With intelligent management of the trees we plant we can avoid setting up such circumstances. Oak wilt is especially a problem in areas like the Anoka Sand Plain where Northern pin oak competes well and wins against everything else.
Photo: Mark Stennes
ing that treatment at least every two years will be required, possibly forever. Accordingly, preventive treatment will of necessity be reserved for the most valuable landscape ornaments only, and cannot be a significant component of our EAB management plans.
The myth of slow growth is among the most discouraging of all, because it is in fact a myth. I would not be one to argue that bur oak is a fast growing tree, but it is nowhere near as slow as reputation would have it. If you really need “fast” growth, plant Northern red or Northern pin oak and then make sure their needs are met. I planted two Northern red oak trees on the south and west sides of my house when I was in my early to mid 30’s, and once established they took off like scalded dogs. I am now 57 and the trees are 17 inches plus in diameter and shade my home to the extent that we get by without air conditioning. In addition, they are truly attractive ornamental landscape plants that are completely free of meaningful pests. Mark Stennes is a Plant Pathologist and ISA Board Certified Master Arborist #MN-0147B with S&S Tree Specialists. References: Anulewicz, A.C., D.G. McCullough and D.L. Cappaert. 2007. Emerald Ash Borer Density and Canopy Dieback in Three North American Ash Species. Arboriculture & Urban Forestry 33(5): 338-349. Poland, T. M. and D. G. McCullough. 2006. Emerald Ash Borer: Invasion of the Urban Forest and the Threat to North America’s Ash Resource. Journal of Forestry 104(3): 118-124.
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Maples for Minnesota Susan Wiegrefe
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ndividuals tend to fall into two camps when discussing maples – those who are unaware that maples exist beyond “hard”, “soft”, and Norway, and those that are completely bewildered, intimidated, or enthralled by the vast array of species found in the genus. For the purposes of this article, I will be tailoring my comments more towards the latter group and helping them to determine which of the many possible non-native species might bear testing under their conditions - and which to steer clear of.
Twin Cities area (usually red-leaved selections), we are well north of the area where these plants can be grown reliably (USDA zone 5-6). Close relatives of the Japanese maple may provide better success. The Korean maple (A. pseudosieboldianum) (Fig. 1), fullmoon maple (A. japonicum), A. pubipalmatum, and A. shirasawanum (no English common names that I am aware of) each appears to have somewhat better potential, though poor availability and lack of controlled testing limit our understanding. Marginal hardiness is accompanied, or at least complicated, by susceptibility to canker(s) that seriously limits the use of the group (Hokanson, 2003; Wiegrefe and Bonnewell, 2004). Photo: Susan Wiegrefe
To orient budding “maple-ologists” to the great diversity in the group, it is helpful to know Another group that may that the most recent be familiar to individuals comprehensive study who visit arboreta during of the maples (de their travels outside the Jong, 2002) placregion, is the trifoliate es the number of Figure 1: Acer pseudosieboldianum leaves maples (Section Trifoliata). species at over 150 The best known species in and has grouped this section is the paperbark maple, aptly named those species into 19 clusters (a.k.a. taxonomic Zimtahorn, or cinnamon maple, in German (Pirc, sections) of more closely related species. With 1994). Although paperbark maple is hardy only maples of various types growing from 62ºN to USDA zone 5, the three-flowered maple (A. latitude in Finland to northern Africa and triflorum) from Manchuria is hardy to USDA zone from seashores to far up mountain sides, there 3 (Dirr, 1998). A couple of sizable specimens can is great variability in their adaptations as well be found at the Minnesota Landscape Arboretum as their physical appearances. (Fig. 2) showcasing the species’ attractive tan exfoliating bark and reliably bright fall color. In The non-native species most promising of some circumstances, there can also be issues with good performance under Minnesota condicankering on this species ( J. Carlson, pers. comm.) tions tend to come from northeastern Asia, that merits study into the genetics of resistance including the northern Japanese island of and the means of inoculum dispersal. Two other Hokkaido, and eastern Europe. There are at members of this section, Nikko maple (A. maximoleast six sections that have species with potenwiczianum) and Manchurian maple (A. mandshuritial for our conditions. cum) are less promising due to insufficient midwinter hardiness and overly-rapid dehardening in One of the most popular and diverse species spring respectively. of maples is the Japanese maple (Acer palmatum). Although some individuals have been documented to reach significant size in the
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Photo: Susan Wiegrefe
A specimen of the lesser-known A. tschonoskii spp. koreanum that I transplanted from northern Illinois to River Falls in 2006 has gotten smaller each year due to canker infections. I have it planted to the northeast of my garage and protected by a
Figure 2: Acer triflorum specimen in fall color
white pine to the west. It is naturally small-statured and has reddish twigs that transition to the mature light tan more quickly than occurs with many snakebark maples. Due to the non-professional manner of its transplanting and the drought experienced during its subsequent establishment, I expect it will take a couple years for it to readjust its root to shoot ratio and show its true colors (Fig. 3). If this species were found to be adapted, it would add a delightful option for shade gardens (Fig. 4). When Piet de Jong, the maple taxonomy guru lists it as one of his top two favorite maples, you know it is something special!
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Photo: Susan Wiegrefe
Although the snakebark maples (Section Macrantha) have beautiful, longitudinally striped bark in greens, white, and even maroon, in some cases, they are problematic in our area. They prefer evenly moist, acidic soils, and protection from direct sun. Exposure to direct sun on the smooth bark results in sunscald and the creation of opportunities for canker organisms to enter. The native moosewood (A. pensylvanicum) and the Manchu-striped maple (A. tegmentosum) appear to have sufficient midwinter hardiness, but suffer unless provided just the right protected site.
Figure 3: Acer tschonoskii ssp. koreanum fall color leaves
The members of the Norway maple section (Sect. Platanoidea) are unified, in part, by the presence of a milky sap in their leaves and petioles. Most of you are aware of the invasive tendency of Norway maple. Although various studies have been conducted on what life history traits contribute to its success, they have concentrated on measuring seed production and germination. My impression is that it is its ability to out compete rivals with its extensive shallow roots system, superior shade tolerance, and dense canopy that enable it to eliminate even our most shade tolerant native, sugar maple, in its natural settings. Although I would not recommend planting Norway maple, I am excited about the potential of one of its Asian relatives, Shantung maple (A. truncatum). This species has an extensive native range, however, and seed sources vary considerably in their hardiness. Some of our understanding of the species is further clouded by its confusion in botanical literature with A. mono. Oddly enough, the efforts to control the Asian Longhorn Beetle introductions in eastern U.S. may be bringing some research funding to play on resolving the identities and characteristics of each. The beetles favor A. mono but are less attracted to Shantung maple (Smith, 2007). Appropriate selections of Shantung maple have a less shallow and less profuse root system, cast less intense shade, and enter dormancy at a time not too different from native species. In addition, it can have very attractive reddish fall color. (though I’ve heard Swedish populations of A. platanoides also can exhibit good fall color. I suspect the day length differences between our
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Photo: Susan Wiegrefe
tatter, hardy to USDA zone 4, tolerant of a wide range of soil conditions, and more drought and heat tolerant than Norway maple (Chicagoland Grows, Inc., 2000).
Figure 4: Acer tschonoskii ssp. koreanum specimen
region (~45°N) and Sweden (>55°N) play a major role in the expression of this trait.) Shantung maple also has attractive light yellow flowers that bloom at the time the leaves are expanding – often with a reddish cast (Fig. 5). In addition to testing the species’ invasive potential more extensively and the cold hardiness of the specific seed source, the presence of a strong central leader is a characteristic that might be improved through selection that would eliminate the need or desirability of hybridizing it with A. platanoides in order to produce an acceptable nursery product. Another member of section Platanoidea that shows great promise is a more distantly related species, the Miyabe maple, (A. miyabei). The main distribution of this species is in northern Japan, including the island of Hokkaido. Material from a separate population on the Asian mainland, A. miyabei ssp. maiotaiensis is being tested by Mark Krautman and others at Heritage Seedlings (Salem, OR), which will hopefully provide information as to whether it is more or less tolerant of our continental climatic extremes. The species is a very stately small tree, with beautiful bark and potential for golden fall color. Unlike the previous two species, it has rounded leaf lobes and greenish petals. This species is somewhat difficult to propagate so is sometimes grafted onto its more easily-rooted European counterpart, the hedge maple, A. campestre. The hedge maple is not hardy in this region and graft compatibility between the two is tenuous (van Gelderen, et al., 1994). A selection of Miyabe maple, ‘Morton’ or State Street® has been well received by members of the nursery industry since its introduction in 2000. It is resistant to leaf
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Members of the section Ginnala are beautiful and cold hardy, but their use is contentious because of their prolific production of viable seeds. Whether you separate them into A. tataricum and A. ginnala or consider the latter to be merely a subspecies of the former, i.e., A. tataricum ssp. ginnala, they are very similar in their traits. The Tatarian maple’s distribution reaches from Austria in the west to the Caucasus in the east, whereas the Amur maple occurs in northern and northeastern Asia (van Gelderen et al., 1994). The Tatarian maple tends towards tree-form, less distinct lobing of the leaves, and less attractive fall color. Amur maple can be densely shrub-like and has earned itself a common name of Feuerahorn (Pirc, 1994), or fire maple, by its intense, orange to red fall color. The Amur maple has been more widely available and has been used extensively due to its cold hardiness (USDA zone 3; Dirr, 1998), small stature, the fall color of its leaves and summer color of the red immature fruits. It is also reported to be the one maple vigorous enough to outgrow a Verticillium infection and recover its aesthetic appeal (K. Bachtell, pers. comm.). Canadian researchers were endeavoring to make selections for even greater tolerance of high soil pH before Ag Canada’s funding was decimated. It is such a useful plant/complex for this region that I hope the programs of Alan Smith, Steve Strauss, Tom Ranney and others working to create sterile selections of landscape plants gives this species high priority. I’ve seen seedlings of it deep in the center of Afton State Park - evidence that even though the seeds are dispersed by non-avian means, their winged fruits enable them to travel significant distances. The adventurous among you might be tempted to grow A. ukurunduense, a relative of our native mountain maple (A. spicatum) that is native to northeast Asia. My observations of specimens at the Morton Arboretum (Lisle, IL) were that it is susceptible to frost injury from pre-mature dehard-
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ening in spring and foliar diseases in the summer. Fall color was sometimes good but short-lived and the trees did not form a well-branched crown.
tain landscape plantings capable of withstanding the challenging growing conditions they will face during their (hopefully) long lifetimes.
A few additional species that are just a hardiness zone (or 2) too tender, are the Montpelier maple (A. monspessulanum), Devil’s maple (A. diabolicum), and sycamore maple (A. pseudoplatanus). These species may contribute tolerances to drought, high soil pH, and salt through interspecific hybridizations even though they may not be useful as direct introductions. However, as with many of the others – a superior seed source or individual may be discovered on the very next seed collection expedition.
Susan Wiegrefe is an Assistant Professor of Horticulture, Department of Plant and Earth Science, at the University of Wisconsin – River Falls. She is also the incorporator, and currently, the Secretary/Treasurer of The Maple Society’s North American branch. She can be reached at susan.wiegrefe@uwrf.edu
I encourage green industry professionals with an interest in plant materials research to support your local arboretum/university and efforts to increase funding for the USDA National Plant Germplasm System through advocacy through your professional organizations and directly with your congressional representatives. The University of Minnesota is a member of the Midwest Plant Collecting Consortium, a group of arboreta located in the center of the country that conducts cooperative seed collecting expeditions. Drs. Harold Pellett and Jim Luby have both participated in
Cited works: Chicagoland Grows, Inc. 2000. Plant Release Bulletin #10 State Street® Miyabe Maple http://www.chicagolandgrows.org/ downloads/miyabe.pdf Dirr, M.A. 1998. Manual of Woody Landscape Plants. Stipes Publishing: Champaign, IL. Jong, P.C., de. 2002. Worldwide maple diversity. In: Wiegrefe, S. et al. (eds.) Proceedings of the 2002 International Maple Symposium. Westonbirt Arboretum, Tetbury, Glou., UK.
Photo: Susan Wiegrefe
Gelderen, D.M. van, P.C. de Jong, H.J. Oterdoom. 1994. Maples of the World. Timber Press: Portland, OR.
Figure 5: Acer truncatum flowers and new leaves
expeditions to Eurasia. With continued support, Dr. Stan Hokanson, or others, will be able to participate as well. For our latitude and hardiness zone, North America is relatively species-poor compared to Asia. Especially with the increasing urbanization and erratic rainfall patterns that are part of the climate change forecast, having a diversity of genetic resources to draw from will be essential for ensuring we are able to main-
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Hokanson, S. 2003. Acer pseudosieboldianum - A Japanese-like maple for the North? Yard & Garden Line News 5 (15): 1 http:// www.extension.umn.edu/yardandgarden/ YGLNews/YGLN-Sept1503.html Pirc, H. 1994. Ahorne. Eugen Ulmer GmgH. & Co.: Stuttgart. Smith, M. 2007. The Asian Longhorned Beetle. (Presentation) The 2007 Annual Gathering of The Maple Society, North American Branch, October 11-13, Atlanta, GA. Wiegrefe, S.J. and V.A. Bonnewell. 2004. Serendipitous science: The case of the cankered maple. Landscape Plant News 15(3): 11-15. (Also reprinted in The Maple Society Newsletter 14(4): 9-11.)
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Congratulations MnSTAC Award Winners Outstanding Volunteer of 2007 Award Jane Klein for her passionate contribution of over 550 hours as a Minnesota Tree Care Advisor and as a founding member of the Oakdale Tree Board.
Outstanding Partnership Award Hutchison Utilities Commission & City of Hutchinson for the Energy Tree Planting Project which shows Hutchinson Utilities commitment to the community’s forest through cooperation with the City of Hutchinson Forestry Department.
Sponsorship Award Ann G. Salovich for sponsoring and supporting TRE (Teaching, Research, Education) Tree Production Research Nursery at the University of Minnesota.
Outstanding Arbor Day Celebration Award Minneapolis Park & Recreation Board for “Branching Out to Our Community”, bringing together multiple partners of diverse interests to plant 200 trees in Powderhorn Park.
Outstanding Community Forestry Maintenance Award State of Minnesota, Department of Administration, Grounds Services for management of Princeton elm at the World War II Memorial on the State Capitol Grounds.
Innovation Award Bonestroo & Tree Trust for City Tree Sustainability and Best Practices.
Stewardship Award The City of Red Wing for Urban Forest Asset Management Program building capacity through education, tree management and systematic tree maintenance.
Media Award Austin Daily Herald for ongoing support of Spruce Up Austin with monthly articles, annual Arbor Day Tabloid, promotion of programs and news coverage of events.
Firewood Correction In the Minnesota Shade Tree Advocate, Spring 2008, page 9, we recommended the purchase of wood that has been inspected and given a seal of approval from the Minnesota Department of Natural Resources (DNR). In fact, the DNR does not inspect firewood. The firewood sold by vendors must meet specific DNR criteria to be considered approved firewood. In most cases, there is no packaging and no “seal of approval”. The DNR does provide a page of tickets/receipts with the DNR logo that the vendor can use if desired, or the vendor may use their own labels. The consumer who purchases firewood then shows the ticket, label or cash register receipt to the staff at Minnesota state parks and campgrounds. The staff will confirm that the vendor is approved to sell firewood that can be brought into state parks and campgrounds.
Mystery Tree Answer: Wild or American plum (Prunus americana)
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STAC INFO & NEWS
About MnSTAC The Minnesota Shade Tree Advisory Committee (MnSTAC) was established in 1974 by a group of concerned citizens to address the health and well being of community forests. MnSTAC is recognized throughout Minnesota and the country for its expertise, advice, coordination and support for community trees. It is an organization of diverse individuals who represent a broad spectrum of tree-related interests. It fosters and supports local community tree programs across the state so healthy community forests are fully integrated into community development, infrastructure, education and management. MnSTAC Board of Directors President: Ken Simons—763/355-8694 Emily Barbeau, City of Minnetonka—952/988-8421 Ken Holman, MN Dept. of Natural Resources/Forestry— 651/259-5269 Tina Markeson, MN Dept. of Transportation—651/366-3619 Steve Nicholson, Kunde Company—651/484-0114 Gary R. Johnson, U of M/Forest Resources—612/625-3765 Kameron Kytonen, City of Andover—763/767-5137
Calendar Events
October 26-29, 2008, Minnesota Invasive Species Conference, Duluth, Minnesota. Contact Bob Koch at 651-201-6549 or robert.koch@state.mn.us November 5-9, 2008, Society of American Foresters 2008 National Convention, Reno-Tahoe, Nevada. www.safnet.org November 18-20, 2008, Partners in Community Forestry National Conference, Atlanta, Georgia. www.arborday.org December 3-6, 2008, American Society of Consulting Arborists Annual Conference, Tucson, Arizona. www.asca-consultants.org January 7-9, 2009, Minnesota Green Expo, Minneapolis, Minnesota. www.minnesotagreenexpo.com January 14-16, 2009, Mid-America Horticultural Trade Show, Chicago, Illinois. www.midam.org
Plant-Driven Design: Creating Gardens That Honor Plants, Place and Spirit. Scott Ogden and Lauren Springer Ogden . 2008. Timber Press The New Encyclopedia of Daylilies. Ted L. Petit and John P. Peat. 2008. Timber Press Timber Press Pocket Guide to Water Garden Plants. Greg Speichert. 2008. Timber Press Trees and Shrubs of Minnesota. Welby Smith. 2008. University of Minnesota Press
Websites Great River Greening www.greatrivergreening.org International Society of Arboriculture www.isa-arbor.com Minnesota Landscape Arboretum www.arboretum.umn.edu Minnesota Nursery and Landscape Association www.mnla.biz Minnesota Society of Arboriculture www.msa-live.org
New Publications
Minnesota Turf and Grounds Foundation www.mtgf.org
A Natural History of Conifers. Aljos Farjon. 2008. Timber Press
Tree Link www.treelink.org
Lichen Biology. Thomas Nash. 2008. Cambridge University Press
Tree Trust www.treetrust.org
Living with Fire: Fire Ecology and Policy for the Twenty-First Century. Sara Jensen. 2008. University of California Press For handy up-to-date links to Web sites of interest, be sure to visit
www.mnstac.org
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Minnesota Shade Tree Advocate A quarterly newsletter published by the Minnesota Shade Tree Advisory Committee. Managing Editorial Group: MnSTAC Education Committee (Emily Barbeau, James Burks, Ken Holman, Gary R. Johnson, Rebecca Koetter, Lara Newberger, Jeff Rick, Jacob Ryg, Stephen Schott, Mark Stennes, and Patrick Weicherding) Editor-in-Chief: Judy Slater Design: Creative Services Unit, MNDNR Material in this newsletter is not copyrighted. Reproduction for educational purposes is encouraged. Subscriptions are free. Articles, news items, photos and videos are welcome. This publication was produced with the support of the USDA Forest Service, Northeastern Area; State and Private Forestry. Address inquiries to: Minnesota DNR Division of Forestry 500 Lafayette Road St. Paul, MN 55155
If you build it ... from p. 7 back yards continue to die from construction related damages. The most common reasons for these unacceptable losses can be summarized by three common errors: 1. Too often tree preservation practices are afterthoughts often made by unqualified people that don’t understand the relationship between actions and biological reactions. 2. There is a general unwillingness to alter construction or development plans in order to save existing trees from damage. 3. The wrong trees were selected for preservation.
Five Steps to Keeping Trees and Woodlands: 1. Hire an experienced tree care consultant the same day that you hire an architect and a contractor. 2. Understand the resource. Determine the relative tolerance of the trees and/or the woodland to changes. 3. Predict the potential damage and reduce or eliminate it without eliminating the construction or development activities. 4. Save the best (trees) and chip the rest. Don’t fight for trees that don’t deserve protection efforts. 5. Maintain the health of the trees and/or woodland before, during and after construction activities. In the next issue of the Minnesota Shade Tree Advocate, Steps 1 and 2 will be addressed in more useful detail. Gary Johnson is an Extension Professor of Urban Forestry in the Department of Forest Resources, University of Minnesota.
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