Vol. 10, No. 1
Winter 2008 COMMUNITY FOREST PROFILE
UP at the TRE Nursery?
WHAT’S *
By Chad P. Giblin, Jeff Gillman, and Gary Johnson Since the presentation and publication of our original work on root pruning extremely pot-bound container stock, we’ve received a lot of requests and questions regarding further work. One of the biggest concerns was the time length of the original study and the number of species used. To broaden our understanding, we planted a new study in the autumn of 2005. This new research includes four different species: Techny white cedar (Thuja occidentalis), Red Splendor crabapple (Malus ‘Red Splendor’), Sienna Glen Freeman maple (Acer x freemanii ‘Sienna’), and Deborah Norway maple (Acer platanoides ‘Deborah’). Now in the second full year of study, many observations are being made.
Chad Giblin
Square Roots for Round Holes
Photo 1: pot-bound control sample.
The results from our first study showed that root pruning techniques had no positive or negative effect on rooting out. Indeed, doing nothing was as effective as cutting, scoring and teasing roots. Even cutting the container in half in the often-recommended “butterfly-cut” had no positive effect. Therefore, in this new study, we decided to get a little more aggressive with root disruption techniques. Again, we maintained a control treatment that was planted as-is directly out of the container (see photo 1). Next, we modified the root-scoring treatment used before, this time cutting a little deeper into the root system, both on the sides and bottom of the root ball (see photo 2). Finally, we added a new treatment, dubbed “The Box-Cut” where all visible portions of circling roots were removed using a pruning saw (see photos 3, 4, and 5). Even though this treatment appears extremely aggressive, consider that amount of root loss when transplanting a typical B&B or bare-root tree; this method probably retains even more roots! *Teaching, Research, Education
WHAT’S UP continued on p. 4
Inside This Issue 2 Perspectives Column 3 Mystery Tree 6 Trees and Ice Storms 10 Cold Temperature Tolerance and Dormancy in Woody Plants 12 What Happened to the Oaks this Summer? 15 Calendar 16 Important MNSTAC Updates
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 • Winter 2008
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PERSPECTIVES COLUMN
Ode to Grandpa and Grandma By Bruce Allen
When I was asked to write this column regarding why I became a Tree Care Advisor (TCA) and what motivates me to be a volunteer, I was flattered and began thinking about what to write. Then I realized that I have held most of the same values since grade school. I will spare you my life story and begin in the very early 1980s. When I was in my mid-twenties, I started to feel that life was no longer just about me, there had to be something bigger than myself that I could and should expend time, energy and resources on. About the same time, I began to take note of my grandmother’s life and how she had always been an active volunteer and that she had always been happy and healthy. I began to realize that parents and grandparents not only teach in conventional methods, but also have a profound effect on what children and grandchildren learn by proxy. I had the same intent and values as my grandmother and was just now realizing it. My children, April and Rebecca, were born in 1983 and 1986, and as any parent desires: I wanted them to grow happy and healthy. So I started to incorporate volunteering into my life in various ways. I instantly felt the intrinsic value, psychological reward and social benefits as a result and felt a positive connection with my fellow volunteers. The world no longer seemed so big and unfamiliar when I realized I was taking an active role in my community as a goodwill ambassador. People seemed friendlier to me and I was making more friends that had the same values as I had. I wanted my children to be exposed to this in the hope that they might pick up some of the same lifestyle characteristics and receive the same intrinsic rewards and gifts that volunteering has brought to me.
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So I have been volunteering ever since and have led a cheerful and healthier life as a result. It certainly helped me to be a better parent. My girls have volunteered in various ways and will more than likely incorporate it into their lives as well. I have a memory from the mid-1960s of walking around my uncle’s property in northern Minnesota where my grandfather would often take me. One day I was walking through a natural prairie area that seemed as if it had not been walked on or disturbed for many decades. I smelled the most earthly aroma. It was so alluring that I wished I could take it home to share with others. It was fall and I now know that the aroma was wet leaves beginning to decompose. That is my earliest memory of loving trees, botany and good old Mother Earth. My grandparents bought a farm in Glencoe, Minnesota in the early 1970s that had a few groves of trees. There was also a swampy slough area with low growing trees and shrubs bordering it. My grandfather had an excavator come in and dig out a very large zero, or mote, in the middle of the slough making it a perfectly protected refuge for waterfowl. Needless to say, my favorite aroma was abundant and I spent a lot of time out there. Grandpa and I would clear selected trees from time to time that may have failed or been at risk of failing. I began to develop a working relationship with trees. One may ask: “Can someone have a meaningful relationship with trees”? As far as I’m concerned, it is an essential part of my spirituality.
Perspectives continued on p. 11
Winter 2008 • ADVOCATE
Figure 1: Brown pointed buds typical of this species. Let us start off with the biggest clue... all three of these species are susceptible to Dutch elm disease to some varying degree and have been identified as housing bark beetles that can carry the deadly fungus.
Photo: Virginia Tech
Other pieces to put this puzzle together:
Species #1 This species is native to Minnesota and is prized for its history as a majestic landscape tree. Leaves are alternately arranged with doubly serrate margins that range in size from 3-6” long and 1-3” wide with leaf bases that are oblique. Buds of this species are brown and pointed (Fig 1). The other telltale identification clue is the “bacon-strip” bark that is seen in cross section (Fig 2).
Figure 2: Bacon strips found in bark cross-section of this species. Note: not all individual trees show such distinct stripping. Photo: Peter Gillitzer, University of Minnesota
Species #2 This species is native to Minnesota but is not regarded as a valuable tree. Leaves are also alternately arranged with doubly serrate margins that range in size from 4-6” long and 2-3” wide with leaf bases that are oblique (Fig 3). Buds of this species are nearly black (Fig 4) but unlike Species #1, the bark is not nearly as diamond-shaped. Also, unlike Species #1, the leaf surface is usually very scabrous and “baconstrip” bark is NOT present in cross section.
Figure 3: Example of leaf shape for Species #1 & #2-oblique base, doubly serrate margin. Photo: Dave Hanson, University of Minnesota
Figure 4: Black pointy buds typical of this species. Photo: Virginia Tech
Species #3 This species is not native to Minnesota or the United States and is mostly considered a dispensable, weedy tree wherever it grows. Leaves are alternately arranged with single serrate margins that range in size from 3/4-3” long and 1/3-1” wide with leaf bases nearly equal. The leaves (Fig 5) unlike Species #1 and #2, are generally much smaller, and the “baconstrip” bark is NOT present in cross section.
Answer on page 11
Figure 5: Leaves of Species #3 have singly serrate margins and equal base. Photo: Virginia Tech
Figure 6: Reddish round buds typical of species #3. ADVOCATE • Winter 2008
Mystery Tree
Do you know these trees?
Photo: Virginia Tech
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Chad Giblin
What’s Up continued from p. 1
Photo 2: modified root-scoring treatment.
While growth data from 2006-2007 is yet to be analyzed, there was no initial mortality in any of the treatments. Observations and condition ratings in 2006 and 2007 also provided valuable insight into how well these trees are surviving transplant stress. Many of the box-cut trees showed smaller leaf size and reduced leaf density from an untreated control in the first season. In the second season, only a slight decrease was evident. The other treatments showed no significant trends at this point. We hope to continue this research for at least two more growing seasons, allowing the trees to fully recover from the stresses of the root pruning treatments. At that point, we should have a much clearer understanding of how these particular species respond to root pruning.
Chad Giblin
A New University Acronym: StemGirdling Suckers (SGSs)?
Chad Giblin
Photo 3: box-cut phase 1.
Chad Giblin
Photo 4: box-cut phase 2.
Photo 5: box-cut phase 3.
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We’ve just finished the seventh year in our longterm planting depth study at the TRE Nursery, and I’m sure most of you are aware of the stemgirdling root data so far. However, a new bit of information, one that’s really adding weight to the advice of proper planting depth, is the effect of root suckers and stem sprouting on tree health. The littleleaf linden in Photo 6 has showed signs of decline for about two full growing seasons. Early in 2007, we saw a marked decrease in crown vigor, new growth, and leaf size, shortly followed by death. Initial data on trees like this seems to suggest that stem constriction due to excessive suckering and/or sprouting may be girdling the aboveground stem tissue. Our data so far suggests that this may be all or in part due to stem tissue which is buried too deeply, producing suckers and/or sprouts which occur in such extreme numbers that they compress the stem. Sometimes, suckers and sprouts are associated with stem-girdling roots (SGRs) (see photo 7) but they often occur without this association. SGRs are insidious enough, but these trees are being girdled by new branches; what’s next?! Again, just one more reason to get root depth right at planting time!
Little Elms = Big Maintenance For the last eight years, we’ve been taking a close look at many of the Dutch elm disease Winter 2008 • ADVOCATE
Photo 7: with lindens, suckers and sprouts are associated with deep planting. (DED) resistant hybrid and American elms available in the nursery trade. One recurring question we’ve heard asks: how do we prune these trees for long-term structural health during the juvenile life stages? Due to the constraints of many municipal pruning schedules, a tree is often planted on a street or a park and then left untouched for as long as seven years. While this may be fine for some tree species, both hybrid ADVOCATE • Winter 2008
While the customer (and in our case, the tax-payer) may always be right, they often lack the knowledge needed to make educated decisions that ensure long-term tree health. Take a Photo 10 look at how elms looked at planting around 1909 (see photo 12). This appears to be typical of all elms planted at that time. So, if our glorious, mature elms (see photo 13) are a product of that kind of nursery WHAT’S UP continued on p. 9
Dave Hanson Dave Hanson Chad Giblin
Gary Johnson Gary Johnson
Photo 6: littleleaf linden shows signs of decline.
and American elms are particularly susceptible to a number of structural problems that need to be addressed within two years of planting. Unlike typically excurrent species like ash, Norway maple, and upright lindens, which often develop decent branch structure with little maintenance, Photo 8 elms require almost constant attention to spot co-dominant leaders and to remove heavy, included, side branches (see photos 8, 9, and 10). Currently, juvenile elms are often treated like other trees and indiscriminately limbed-up and “opened-up” to make them look nice. However, it may be that many of the problematic issues are Photo 9 a result of consumer demands for “pretty” stock off the flatbed, on the sales floor, or in the boulevard (see photo 11).
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URBAN FOREST HEALTH
Trees and Ice Storms:
Developing Ice Storm Resistance in Urban Tree Populations
By Richard J. Hauer
Introduction Every year we read or hear in the popular press that an ice storm struck some part of the United States. Is the recent December 2007 ice storm across the central and southern United States a regular event or are ice storms infrequent? The answer is that ice storms occur annually somewhere in the United States, regularly shaping forest ecosystems across rural and urban landscapes. For a kid, they are a great excuse for school to be canceled and to fire the toboggan down the sledding hill. For adults, we tend to see the potential of causing significant damage to trees and property and the likewise death and injury to people. Annual losses from ice storms exceed $225 million in total damage to trees and property. A major multistate ice storm, such as the 1997 northeastern North America storm, can exceed several billion dollars in losses. Whether localized or widespread, damage to electric distribution systems, blocked roadways, and property damage from fallen trees and limbs pose safety concerns and disrupt normal community functions. Ice storms visit Minnesota annually with major events occurring on a regular near-annual basis.
For example, 25 severe Minnesotan ice storms have been documented between 1896 and 1953. (State Climatology Office “Severe Local Storms� and anecdotal reports). Areas near Duluth and Lake Benton on the Buffalo Ridge are especially at risk for more frequent and damaging ice storms as a result of their elevation differences with the neighboring areas. A March 4, 1935 Duluth ice storm caused a documented halfmillion dollars of tree and shrub damage. A 1991 Rochester storm resulted in 16 million dollars in total damage. Ice storms in the 1996/1997 winter were unfortunate precursors to the 1997 spring flooding in western Minnesota. A late 2007 winter storm with ice accumulation and winds followed by snow damaged many trees and utility systems in southeastern Minnesota. What can you do as an urban forest manager, arborist, horticulturist, elected official, university professor, or concerned citizen? Read on and learn how planting a diverse urban forest that includes trees resistant to ice storms and performing regular tree maintenance to avoid or remove structural weaknesses will reduce damage caused by severe ice storms. Management plans
Figure 1. Forms of precipitation resulting from a warm air mass advancing over a cold air mass.
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Illustration: Lynn Hawkinson Smith
Winter 2008 • ADVOCATE
Figure 2. Tree characteristics that increase the susceptibility of trees to ice storm damage. for urban trees should incorporate information on the ice storm susceptibility of trees in order to limit potential ice damage; to reduce hazards resulting from ice damage; and to restore urban tree populations following ice storms.
How do Ice Storms Form? Ice storms by definition occur when a 1/4 inch or more accumulation of freezing rain on surfaces such as tree branches and electrical wires develops. Most ice storms develop when a moist winter warm front passes over a colder surface-air layer (Figure 1). Rain falls from a warmer layer above freezing through cooler air that’s below freezing without freezing, becoming supercooled. Ice accumulates when supercooled rain freezes on contact with surfaces that are at or below the freezing point. Ice storms may occur over several days and large areas, most storms usually last only a few hours. Ninety percent of these storms occur between December and March, most occur in January. The relative likelihood of ice storms that are most prevalent in the central, northeastern, and southeastern parts of the United States is illustrated in Hauer et al. (2006). ADVOCATE • Winter 2008
Illustration: Lynn Hawkinson Smith
Why Trees Fail From Ice Storms and Accumulation Trees are damaged during ice storms for a number of reasons. Severity of tree damage depends on three factors: amount of accumulated ice, exposure to wind, and duration of the storm. An increased susceptibility of tree species also involves tree characteristics: weak branch junctures indicated by included bark, decaying or dead branches, tree height and diameter, increased surface area of lateral branches, broad crowns, unbalanced crowns, restricted and unbalanced root systems, and shallow rooting habit (Figure 2). Included bark results from in-grown bark in branch junctures and it enhances a tree’s susceptibility to breakage under ice-loading. The ‘Bradford’ pear, for example, has branches that often break during ice storms where there is included bark in branch junctures. Already weak, advanced decay or dead branches have a high probability of breaking when loaded with ice. Tree branch length, horizontal branching, and inflexibility of the stem, in general, lead to greater susceptibility. Trees and Ice Storms continued on p. 8
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Trees and Ice Storms continued from p. 7 Tree architecture plays an important role in ice storm susceptibility. As the surface area of lateral branches increases, more ice can accumulate on lateral branches and greater ice loading results in greater branch failure. Contrary to popular belief, the wood strength of sound branches matters less than the ability of a tree to withstand breakage at branch junctures and the presence of fine branching or a broad crown that enhances ice accumulation. Many broad-leafed tree species, when grown in the open, form broad crowns (decurrent branching), that increase their susceptibility to ice storms. Examples include Siberian elm, American elm, hackberry, green ash, and honey locust. Trees with unbalanced crowns (such as at forest edges) are more susceptible to ice damage and increased bending through greater ice accumulation on the side with more branches. In contrast, trees with a conical form (excurrent branching) tend to be resistant to ice storms. Finally, small stature trees such as ironwood, blue beech, service berry, and hawthorn also are infrequently damaged.
Ice Storm Management and Prevention Urban tree populations in areas subjected to ice storms should have management plans to incorporate ice storm resistance. Regular maintenance of tree populations to develop greater resistance should occur. Removing structurally defective branches, training trees from a younger age, and proper branch removal will go far in developing ice storm resistance in the urban forest. The old adage you can pay me now or you can pay me latter is true with tree maintenance. Regular and budgeted infusions of money into an annual tree care budget is better than an unbudgeted and often large expenditure to recover from an ice storm. See Burban and Andresen (1994) for more information on storm damage planning. Tree species vary in their susceptibility to ice storms (Table 1). Planting a diverse financial portfolio is a wise investment strategy. Planting a diverse urban forest is a likewise sound investment to increase your odds of long-term benefits that urban trees provide communities. Rather than avoiding susceptible tree species to ice storms, avoid creating the majority of your tree population with susceptible species. Also, minimize
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planting susceptible species near locations that damage to property and infrastructure would occur if a tree failed from an ice storm.
Conclusion Ice storm frequency and severity within the eastern United States necessitates the incorporation of ice storm information into the urban forestry planning process. While we cannot stop ice storms from occurring, we can take steps to reduce the impact of this major forest disturbance on urban forests and the interface between forests, buildings, and infrastructure. Richard J. Hauer is an Assistant Professor of Urban Forestry at the University of Wisconsin – Stevens Point. You can reach him at rhauer@uwsp.edu or 715-346-3642.
TABLE 1
Ice storm susceptibility of tree species found growing in urban areas.
Susceptible Intermediate American basswood American beech American elm Boxelder Bigtooth aspen Chestnut oak Black ash Choke cherry Black cherry Douglas-fir Black locust Eastern white pine Black oak Gray birch Bradford pear Green ash Butternut Japanese larch Common hackberry Loblolly pine Eastern cottonwood Northern red oak Honey locust Paper birch Jack pine Pin oak Pin cherry Red maple Pitch pine Red pine Quaking aspen Scarlet oak Red elm Scotch pine River birch Slash pine Siberian elm Sourwood Silver maple Sugar maple Virginia pine Sycamore Willow Tamarack Tulip poplar White ash Yellow birch Table: Richard J. Hauer
Resistant Amur maple Baldcypress Balsam fir Bitternut hickory Black walnut Blackgum Blue beech Bur oak Catalpa Colorado blue spruce Crabapple Eastern hemlock Eastern redcedar European larch Ginkgo Hophornbeam Horsechestnut Kentucky coffeetree Littleleaf linden Mountain ash Northern white cedar Norway maple Norway spruce Ohio buckeye Pignut hickory Shagbark hickory Swamp white oak Sweetgum White oak White spruce Witch-hazel Yellow buckeye
Additional information on next page Winter 2008 • ADVOCATE
Chad Giblin
What’s Up continued from p. 5
Photo 11: “pretty” stock.
Hauer, R.J., J.O. Dawson, and L.P. Werner. 2006. Trees and Ice Storms: The Development of Ice Storm-Resistant Urban Tree Populations, Second Edition. Joint Publication 06-1, College of Natural Resources, University of Wisconsin-Stevens Point and the Department of Natural Resources and Environmental Sciences and the Office of Continuing Education, University of Illinois at Urbana–Champaign 20 pp. http://web.extension.uiuc. edu/forestry/publications/pdf/ urban_community_forestry/ trees_and_ice_storms_2006.pdf
ADVOCATE • Winter 2008
Photo 12: an elm at planting in 1909.
For more information about the TRE Nursery, visit their website at www.tre.umn.edu Chad Giblin
Burban, L.L. and J.W Andresen. 1994. Storms over the Urban Forest: Planning, Responding, and Regreening - A Community Guide to Natural Disaster Relief. Second Edition. USDA Forest Service, Northeastern Area. 152 pp. http://www.na.fs.fed.us/ spfo/pubs/uf/sotuf/sotuf.htm
Photographer unknown
For Additional Information on Ice Storms and Trees:
stock, why did we stop growing and planting them as such? I doubt that any modern urban forester, arborist, or nursery grower could get away with planting, maintaining, or selling trees that look like that! As stewards and advocates of urban and community forests, we are obliged to educate people about the changing face of arboriculture and tree health. In the case of elms, a compromise between aesthetics and structural success must be reached. To that end, replicated research is underway at the University of Minnesota and several off-campus locations to take a close look at how different pruning practices affect these trees long-term. We’ll keep you posted.
Photo 13: a mature elm.
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Chad P. Giblin is a Scientist in the Department of Horticultural Science and a Graduate Student in the Department of Forest Resources at the University of Minnesota. Jeff Gillman is an Associate Professor in the Department of Horticultural Science, University of Minnesota, where he specializes in nursery management and production. Gary Johnson is an Extension Professor of Urban Forestry in the Department of Forest Resources, University of Minnesota.
COLD TEMPERATURE TOLERANCE and DORMANCY in WOODY PLANTS By Gary Johnson
hy do some trees and shrubs seemingly shrug off the winds and chills of winter in the upper Midwest while others fail to flower, chronically suffer twig dieback or in some instances, die? The answer in part depends on three factors: the plant’s ability to tolerate cold temperatures and fully develop bud dormancy, the character of the late summer/autumn weather, and the spring temperatures as plants resume growth activities. Most tree and shrub buds, both vegetative and floral, require a period of dormancy to both survive the winter and emerge as healthy, growing, embryonic tissues. Dormancy usually begins as a short-day response. That is, as the daylight hours decline, dormancy begins. In late summer (mid- to late August in the upper Midwest), cambial activities begin to slow down, leaf photosynthesis begins to decline, and the process of leaf drop begins. This change in metabolism is the chemical signal for the buds to begin their journey to dormancy. Once buds become fully dormant, a period of “chilling” is required before this rest period can be “broken.” The chilling period varies for different plants, from a few weeks to 3 months for others. Likewise, the minimum chilling temperature varies somewhat, but most of the time, for our
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trees and shrubs, temperatures well below freezing must be maintained for that time period. If the buds are not subjected to their genetically required chilling period, then no amount of light or temperature will stimulate the spring growth of the buds and the buds eventually die. Once the chilling period has been satisfied, a period of a few to several weeks of temperatures near or slightly above freezing will effectively “break” the dormancy and stir the buds into active growth (cell division and expansion). Once buds have fully emerged from dormancy, they are no longer “cold hardy,” and temperatures only slightly below freezing will kill or damage them. Roots and cambial tissues do not undergo a period of dormancy; rather, they simply enter a state of reduced metabolism. All winter long, albeit unnoticed, roots and cambial tissues are actively respiring (using stored energy), moving moisture at least at the cellular level, and in some cases, photosynthesizing. The bark of young plants or thin-barked plants photosynthesizes throughout the winter at very low rates, even when temperatures are brutally cold! Not all plants, but many of those with photosynthetic bark, such as Winter King hawthorn and big-toothed aspen, are manufacturing sugars in January.
Winter 2008 • ADVOCATE
PERSPECTIVES COLUMN
Plant tissues are prepared for the extreme cold weeks via a process of “super-cooling” and “deep super-cooling.” The product of this chemical preparation courtesy of acclimation is functioning, water-containing cells that can withstand temperatures of -38 degrees C to as cold as -47 degrees C! As marvelous as this little piece of botanical trivia is, the third phase of acclimation is just as interesting. As temperatures begin warming up in the late winter - those few to several weeks of temperatures ranging from just above freezing to warmer that brought the buds out of dormancy – all winter hardiness is essentially lost. Plant tissues that 2-3 months earlier were tolerant of brutally cold temperatures are now damaged or killed by temperatures just below freezing!
Gary Johnson is an Extension Professor of Urban Forestry in the Department of Forest Resources, University of Minnesota.
ADVOCATE • Winter 2008
I felt as if I had hit the mother load! I emailed and ask if there was still space for me in the 2007 winter class. Dave Hanson at the Tree Biology Lab emailed and offered me a spot in the class. I registered and completed the class. I took the optional test at the end of the course to become a certified tree inspector and passed. I have been volunteering as a TCA throughout 2007 with enthusiasm, and have made some new friends and have learned a great deal. I live in Cannon Falls and would like to be of some assistance to this community’s arbor needs at some point. Gary Johnson and Dave Hanson have assembled and developed a nurturing and caring community of TCA’s at the University, which are indicative of what Minnesota stands for. I am proud to have taken their course. Bruce Allen is a Tree Care Advisor in Cannon Falls, Minnesota.
Mystery Tree
Environmentally, the most common situations that damage plant materials either at the beginning or near the end of acclimation and dormancy would be unseasonable freezing temperatures. Late summer/early autumn frosts or late spring frosts can undo all of the good things that time, day lengths, temperatures and growth regulators patiently put together.
In the fall of 2006, I was surfing the Internet when I came across the University of Minnesota website about tree care and becoming a Tree Care Advisor. I found a winter class was offered and held on Saturdays at the Saint Paul campus. The tuition was quite reasonable along with being required to volunteer a certain amount of hours each year moving forward to pay for it.
Mystery Tree Answers: #1= Ulmus americana, American elm #2= Ulmus rubra, red/slippery elm #3= Ulmus pumila, Siberian elm
Although roots and cambial tissues do not enter a state of dormancy like buds enter, they still must chemically prepare for winter. Again, beginning during the waning daylight hours of late summer, the functioning tissues begin the transition to winter-hardy tissues. During this first step of winterizing – botanically referred to as acclimation – chemical and growth regulator signals begin the transition to slower growth rates, and more cold-tolerant plant cells. By the time of the first frost – late September to mid-October in the upper Midwest – most perennial tissues are now tolerant of freezing temperatures, although not nearly ready for minus-zero weather. The second phase of acclimation is triggered by a combination of even more waning daylight hours and progressively colder temperatures. This period of approximately two months, prepares the functioning plant tissues for the extremely cold temperatures of hardiness zones 4, 3 and 2.
continued from page 2
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DISPEL-A-MYTH By Ben Johnson
What Happened to the Oaks this Summer? It’s been a tough year for the private consulting arborist. Late frosts, Emerald Ash Borer (EAB) scares, and a severe drought have sent us on some mysterious visits for the concerned homeowner. In particular, oaks have required a little extra attention. With the obvious (and not so obvious) disease and insect problems, surfacing construction damage, winter/spring storm damage, and plenty of drought stressed trees, it has been difficult to differentiate some of the issues. In many cases, we’re looking at many symptoms and need to separate them, and then add them up for a care program.
So you have a mix of symptoms and you need to separate them.
I’m often asked to put our common tools and practices in real terms from the private consultant’s perspective. Perfect historical data, aerial infrared photography, the ability to collect and test multiple trees samples - this isn’t always possible when working with a homeowner and needing to come to a relatively fast and economic resolution. In the perfect world, we would spare no expense and have every resource to come to a solution immediately.
Thus begins the job of the consulting arborist. The examination starts with a lot of questions for the homeowner and some borderline psychic observations. Construction damage, grade changes, sprinkler system installations, and compression from girdling roots are just a few of the damages that may have occurred. These damages will show up in the canopy and can complicate diagnosis. In the case of two-lined chestnut borer, these stresses will actually encourage infestation. This is where things become complicated and the breakdown of symptoms begins. Leaf and canopy symptoms from oak wilt are quite noticeable at the right time of year. Leaf necrosis will occur from the edges in, usually covering 1/3 to 2/3 of the leaf area before falling. There will be a clear line between the green and necrotic portion of the leaf area. In the red oak family, rapid leaf loss from the top
Some of these issues are pretty clear from the beginning. Oak anthracnose (Apiognomonia quercina) will occur in the spring and has telltale leaf symptoms. Right symptoms, right timing and you can put together a spray plan for next spring if the infection is bad enough. My story for today will focus on the big two, along with this year’s unwelcome guest. We’re talking about oak wilt (Ceratocystis fagacearum), two-lined chestnut borer (Agrilus bilineatus), and of course, this year’s massive summer/fall drought. As if oaks didn’t have it hard enough, nature threw in the drought stress that is not only directly damaging to oaks, but complicates the diagnosis of wilt and borer damage.
Oak wilt dieback in canopy.
Credit: Joseph O’Brien, USDA Forest Service, Bugwood.org
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Winter 2008 • ADVOCATE
dryness. This is one of the reasons this year’s drought complicated matters. Symptoms of both problems, along with drought symptoms, all started showing up at about the same time. With drought, you should notice wilting, curling at the edges, and yellowing and browning of the leaf margins. You’ll find these symptoms scattered over the leaf and between the veins. So you have a mix of symptoms and you need to separate them. As mentioned before, begin by examining the site and questioning the tree owner. The recent (or not so recent) activities around the tree may explain a lot of what you’re seeing and will likely guide, determine, and design your health program. Any damage to the root system, changes in grade, changes in available water (including a drought), and changes to the nutrient levels should be considered. Ask the same question several different ways and you’ll likely get some real answers. Twolined chestnut borer damage throughout canopy. Note completely dead sections near green areas. (For better photo clarity, view online publication.) Credit: Steven Katovich, USDA Forest Service, Bugwood.org
down is a very clear indicator. In the white oak family, leaf symptoms can begin in isolated sections of the canopy, and in severe cases, defoliate and kill a tree within a year or two. Two-lined chestnut borer (TLCB) symptoms can be very similar to oak wilt (especially considering that the tree may have both), but can be distinguished from it with some careful examination. With TLCB, symptoms are a result of the larval feeding and begin with the death of a single limb or a section of the tree beyond the infestation. Subsequent feedings will result in large portions of the canopy or entire trees dying. Key differences from oak wilt are the sudden and uniform browning of the leaves that usually persist in the tree. If limbs are accessible, peeling the bark and finding larval tunnels will confirm borer presence. Symptoms of both oak wilt and TLCB overlap in timing. Oak wilt will usually start showing up in early to mid-summer depending on the amount of rain received and TLCB will start showing up mid to late summer in conjunction with summer
ADVOCATE • Winter 2008
The obvious next step is to confirm your suspicions and get some samples. This sounds easy, but can become difficult and costly. With symptoms occurring in the canopy and often upper canopy of the tree, getting a sample from the ground without mechanical equipment can be difficult. Also, with the drought symptoms of this year, finding quality samples for oak wilt can be extremely difficult (see a really nice how-to at www.na.fs.fed.us/ spfo/pubs/howtos/ht_oaklab/sample.htm). Grace Anderson, University of Minnesota Plant Disease Clinic Technician, advises the collection of oak wilt samples earlier in the What Happened... continued on p. 14
Oak wilt leaf symptoms.
Credit: Fred Baker, Utah State University, Bugwood.org
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DISPEL-A-MYTH
continued from p. 13 history from the client should allow you to make an educated decision. Having samples within reach will allow you to confirm or eliminate some disease, insect, or abiotic symptoms. When you have an assessment, you can weigh the options of a treatment program based on educated data collection versus a thorough (ideal, but potentially costly) examination. Ultimately, the homeowner is the decision maker for where this process goes.
Anthracnose throughout canopy. Note healthier tufts in upper canopy and healthy oaks in background. Credit: Russell Kennedy, Rainbow Treecare.
season as the symptoms become “obvious”. The samples are usable throughout the summer, but the quality will deteriorate as the season progresses. Anderson emphasizes the need to obtain samples from at least two or three branches throughout the canopy and keep the samples a workable size: one-half to one inch in diameter. Also, it can be dangerous for homeowners trying to obtain samples, it is often necessary to hire a professional to get to the right parts of the canopy and collect quality samples. This is where things can become a little tricky when a consulting arborist wants to get samples but costs get in the way. Using climbers or bucket trucks to obtain quality samples can quickly become expensive. It can be hard to justify those costs to a homeowner with one ill tree when obtaining and examining samples approaches the cost of treatment.
If making assessments only from visual observations, consider your sources for more information. Talking to the homeowner, neighbors, and city foresters can help put together a history of the area. Even using aerial photo sources could give you an idea of trees or structures that were or weren’t in the area before. Seeing a photo without the now-present garage and driveway can really answer some questions! Put together all this information (fairly easy, actually) and you can formulate a pretty accurate assessment of what issues are at hand and what the tree needs. In the end, we may find ourselves relying on our knowledge and ability to adapt. We can take advantage of the educational opportunities offered throughout the year to sharpen our skills and further develop the tools available. It often comes down to working with what you have, so it’s up to you to have the best and be the best. Good luck next summer.
Ben Johnson is a Consulting Arborist with Rainbow Treecare in St. Louis Park and is an ISA BoardCertified Master Arborist.
Here is where the skill of the arborist, the collection of data for the surrounding area, and a firm grasp on the differentiation of disease and insect problems is most important. Knowing the history of an area (if possible) or obtaining a
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Winter 2008 • ADVOCATE
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—763/717-9366 Emily Barbeau, City of Minnetonka—952/988-8421 Ken Holman, MN Dept. of Natural Resources/Forestry— 651/259-5269 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
Regional MnSTAC Committees Southeast STAC
Chair: Henry Sorensen—651/388-3625 or 651/385-3674 Sec./Treas.: Katie Himanga, Heartwood Forestry, Lake City —651/380-9680
Northeast STAC
Chair: Kelly Morris, City Forester, City of Grand Rapids —218/326-7481 Secretary/Treasurer/Technical Advisor: Dan Jordan, IRRRA Mineland Reclamation—218/254-7967
Calendar Events
March 11-12, 2008, Iowa Shade Tree Short Course, Ames, Iowa. www.ucs.iastate.edu/mnet/shadetree/home.html March 12, 2008, Northwest Minnesota Urban Forestry Workshop and New Tree Inspector Certification, University of MinnesotaCrookston, Crookston, Minnesota. Contact Jennifer Severinson at 800-862-6466 ext. 8681. http://cal.umcrookston.edu/ Conferences/UrbanForestry.htm March 25-26, 2008, Minnesota Shade Tree Short Course, Bethel University, Saint Paul, Minnesota. www.cce.umn.edu/ shadetree April 24, 2008, MnSTAC and Tree City USA Awards, University of Minnesota Landscape Arboretum, Chanhassen, Minnesota. www. mnstac.org May 13-14, 2008, Hazard Tree Workshop, Minneapolis, Minnesota. www.arborday.org May 14, 2008, Northeast Minnesota Urban Forestry Workshop and New Tree Inspector Certification, Cloquet, Minnesota. Contact Rebecca Koetter at 612-624-4261. www.dnr.state.mn.us/forestry/ urban/certifiedtreeprogram/ index/html May 21, 2008, New Tree Inspector Certification Workshop, Saint Paul, Minnesota. www.dnr. state.mn.us/forestry/urban/certifiedtreeprogram/index/html June 23-25, 2008, Crisis or Opportunity? Sustaining and Strengthening Forest-Based Industries in the Great Lakes Region, Madison, Wisconsin. Contact: 608-442-1255. www. greatforests.org July 26-30, 2008, International Society of Arboriculture 84th Annual Conference & Trade Show, Saint Louis, Missouri. www.isa-arbor.com/conference October 6-8, 2008, The Landscape Below Ground III Conference, Morton Arboretum, Lisle, Illinois. www.landscapebelowground.org
ADVOCATE • Winter 2008
October 10, 2008, Minnesota Society of Arboriculture Fall Conference, University of Minnesota Landscape Arboretum, Chanhassen, Minnesota. www.msa-live.org November 5-9, 2008, Society of American Foresters 2008 National Convention, RenoTahoe, Nevada. www.safnet. org
Websites American Society of Consulting Arborists www.asca-consultants.org Great Lakes Forest Alliance www.greatforests.org ISA’s Multilingual Arboriculture Dictionary www.isa-arbor.com/ Dictionary Minnesota Arbor Month www.dnr.state.mn.us/arbormonth/index.html Minnesota Certified Tree Inspectors www.dnr.state.mn.us/forestry/urban/certifiedtreeprogram/index.html Minnesota Green Roofs Council www.mngreenroofs.org Minnesota Landscape Arboretum www.arboretum.umn.edu Minnesota Society of Arboriculture www.msa-live.org National Arbor Day Foundation www.arborday.org Tree Link www.treelink.org University of Minnesota, Department of Forest Resources Extension and Outreach. www.forestry.umn.edu/ extension Urban Parks www.pps.org For handy up-to-date links to Web sites of interest, be sure to visit
www.mnstac.org 15
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 Printed on recycled paper using soy-based inks.
Important Updates If You Missed the December MNSTAC Forum MnSTAC Reorganization
Thank you to those members who mailed in your vote on MnSTAC’s reorganization. The majority of the votes were in favor of the proposed shift in structure. Two of the most dramatic changes will include expanding the number of board members to build broader support for community forestry and omitting business items from the informational forums. We hope the changes will benefit members and strengthen MnSTAC’s role as a state tree board and advisory body to the state forester. There will be more information available in the next few months as we implement the changes.
State Representative briefs MnSTAC members on Minnesota’s Forest Protection Plan Representative Diane Loeffler attended the meeting to communicate the progress of the Minnesota Forest Protection Plan Task Force. The task force was formed when the 2007 Legislature directed the Minnesota Forest Resources Council to create a task force to examine and create a state-wide plan of action for emerging invasive forest pests. The plan will assign responsibilities and provide direction on how agencies will work together on forest pest issues. One of the twelve recommendations in the report, as communicated by Rep. Loeffler, is the need for a “clear front door”. This means there must be a clear place for homeowners, city officials, arborists, or other interested parties to start if they need to report an invasive pest or have other forest health inquiries. The report will be published later this year.
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Winter 2008 • ADVOCATE