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Norway Maple

November 28, 2010 by
Categories: Midd Blogosphere

I’ve been thinking a lot lately about one of the more contentious trees in our urban forest, the Norway maple. Late this fall, while the leaves were still turning, I recently closely inspected over ⅔ of our campus trees, looking for problems, and Norway Maple kept appearing in the problem lists, with similar patterns of failure.

Norway Maple-healthy young tree

Some would say this is to be expected. Norway maple has been an extremely overused plant in the North American landscape, a victim of its own success. 100’s of cultivars have appeared over the years, including one of the most popular shade trees, Crimson King Maple-what most former customers of mine would simply call “Red Maple”, for its dark red leaves all summer long.
John Bartram, one of the fathers of early American botany, introduced the Norway maple in 1756, after receiving seedlings from Philip Miller in England, and started selling them in 1762. The trees remarkable adaptability to varying site conditions, including a broad tolerance of soil texture and pH, made it a popular tree among early arborists and gardeners. And a knack for sending out sports made it one of the first trees to get cultivars selected from it.

Norway Maple,  Acer platinoides,  flowers attractively in the early spring, late April here, with clusters of yellowish green flowers appearing before the leaves, each flower about ⅓” in size, but held in large clusters called corymbs, completely covering the tree. Norways are actually one of the most attractive early flowering trees. Bright yellow fall color can frequently be seen, in years when Tar spot doesn’t decimate the crown foliage.

The flowers turn into large seed pods called samaras, with a pair of seeds held in the center, and large flat wings spreading to each side. Split in half, and each side will helicopter towards the ground slowly, or alight in a breeze and fly for some distance. The wings of the helicopter extend around the seed, and can be opened like a book, where the milky white sap inside can act like a glue, allowing the samara to be attached to one’s nose, where it can stay stuck until nap time.

This milky white sap is a great way for the confused to identify Norway maples, as the similar sized Sugar and Red (Swamp) maples have a clear sap when broken. Spend some time with them, though, and identification becomes easier. The bark is a dark gray, and is ridged and furrowed, unlike any native maple. The leaves are large and dark green, larger than any other maple around, and while similar to Sugar maple, are flatter at the base.

It’s the leaves that cause many of the problems of the species, a victim of their own success. The size of the leaves create a super dense shade, making growth for grass underneath nearly impossible, but also for any interior growth on the tree itself. All the leaves on a Norway maple, and therefore all the growth, is on the outside of the tree. This is a red flag in the tree structure world, where all the end weight of the tree, and all of the wind load, is not shared throughout the tree, but, being held at the ends of the branches, and can be prone to breakage. Fortunately, the wood is fairly strong, and failure is more often seen in bad branch angles. The bare interior of a Norway, though, to me, is as distinctive an identifying characteristic as anything else.

Trunk Failure from Bad Branch Attachments

The dark dense canopy from the leaves also aid in the invasiveness of the species. Norway maple has been outlawed for sale in southern New England, and will become so in Vermont in a couple of years. The shade tolerance, in addition to its own dense shade, and its shallow root system makes the tree a fierce invader in the forest ecosystem, out-competing native maples in the understory, and inhibiting native seedlings (Galbraith-Kent, S. L. and Handel, S. N. (2008), Invasive Acer platanoides inhibits native sapling growth in forest understorey communities. Journal of Ecology, 96: 293–302. doi: 10.1111/j.1365-2745.2007.01337.x) . The shallow roots also hinder the growth and development of native forest flower species.The tree itself hosts less native caterpillars than other native maples, and North American mammals don’t recognize the seeds as a food source.

Norway maple gets its name from the northern end of its native range, and the population extends through the Caucasus and Turkey. There, the tree flowers 3-4 weeks earlier than the similar Sycamore maple, and is thereby kept in check, as both trees are insect pollinated, but the earlier flowering means only 5-15% of the seedling forest population seems to be Norways. Normal longevity for the species only seems to be 100-150  years, although trees in it’s preferred habitat, the Balkan peninsula, lives to about 200.

Our campus trees seem to be failing all at about 100 years as well, for a variety of causes. As mentioned above, Norways seem to be prone to bad branch angles, where cavities form and cause holes in the branches and trunk. Another problem with the tree seems to be a propensity towards girdling roots-roots that circle around the trunk underneath the ground, choking itself off. Norways make up about 10% of our tree population, but account for more than that in shade canopy, so, while they are invasive, we clearly can’t actively remove them. Some younger trees are in front of Forest Hall along Route 125, as well as in front of Emma Willard. The largest specimen is on the north side of the Axinn Center, a tree held together by a jungle of cables up in the crown.

Over-Mature Norway Maple at Axinn

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Some Late Fall Color

October 30, 2010 by
Categories: Midd Blogosphere

We’re in the bitter end of fall here, at least in terms of foliage. To me, this is when trees really start to shine. Maybe it’s all the bare trees nearby, or the perpetually cloudy skies, but the remaining foliage seems to take on an extra glow, or maybe urgency. Foliage colors that wouldn’t have turned a head 2 weeks ago now looks spectacular in the dying season, like the russet brown of the Star Magnolia behind Voter Hall. Sunlight breaking through the clouds acts like a highlighter pen. The wet cold makes any color seem all the more special. Here’s a little slideshow of trees and some shrubs that turned my head late last week.

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Strange Fruit Falling from the Moon

October 25, 2010 by
Categories: Midd Blogosphere

Osage Orange-fruit

Every year, people working in Facilities start bringing me these tennis ball sized fruit. Last year, I decided to have some fun, and started freaking people out, acting incredulous they were actually touching them, and insisting they go wash their hands immediately, or terrible things would happen. This year I’m pretending they fell off the moon, and just happened to roll down to the front of the auto shop.

The truth is almost as strange. Middlebury College is in posecession of Vermont’s largest Osage Orange tree, Maclura pomifera. The circumference of the trunk is only 40″, nowhere near the record tree in Virginia of 321″. Ours is under the shade of a large sugar maple, and sits at the top of Stewart Hill, where its tennis ball sized fruit promptly roll downhill, over the speed dip, and end up near all the equipment.

Originally native only to southern Oklahoma and northern Texas, the Osage Orange was introduced far out of it’s range by using it as fencing, as it’s thorns and brushy nature made great hedges to keep out cattle.   It met the demand of a hedge in the wild west , “horse high, bull strong, and pig tight.” I’ve chased a loose pig before. Pig tight is saying quite a bit.

Alas, it was not hedge clippers, but barbed wire that won the west, replacing Osage Orange in the 1880’s.  The edible (?) fruit is cherished by squirrels, but more commonly used as holiday decorations.  Some have described the fruit as “brain-like”. If my brain were only that large…Chemical compounds in the fruit repel insects, although the whole fruit itself does not. The fruit is anachronistic. Usually large fruit is a method of seed dispersal, but squirrels are notoriously finicky on that front. Some theorists state that an extinct Ground Sloth used to aid in the spread of the plant. Indeed, the fossil record shows a  much larger range to the genus than what we see now.

The wood itself is remarkably able to resist rot and decay-and has been used as railroad ties and pavement blocks, as well as a superior wood for bows (archery, not violins). A bright yellow dye can be extracted from the bark.

Osage Orange Bark

Horticulturists like some parts of the Osage Orange. It’s yellow gold fall color can frequently rate spectacular, and it also boasts a pretty orange brown older bark. Michael Dirr, expert on all landscape plants, says the fruit is “effective in September, and lethal in October if one is sitting under the tree” and states that one should “select male trees; the large fruits are a nuisance and a problem around public areas as people will invariably use them for ammunition”. Male trees are being selected, and cultivars developed for use as a street tree. The species is remarkably tough, able to grow nearly anywhere. One last thought-Osage Orange is dioecious. Male and female flowers appear on separate plants, and of course you need both to pollinate. So, while our clearly female tree still sets fruit, they are sterile. Large, but sterile nonetheless.

So ours sits, unremarkable most of the year, until the fruit starts rolling. I don’t know how it ended up planted there, or even where it was grown. I’ve never even seen one for sale.

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New School Year, New Vandalism

October 15, 2010 by
Categories: Midd Blogosphere

Personally, I was hoping we were done with this. I’m as tired of writing of it as you are of reading.

Since the school year started, our landscape department has seen an additional 4 incidents of tree vandalism. One, a newly planted tree was broken in what appeared to be a climbing attempt (no, we’re sure it wasn’t a squirrel of exceptional size). An arborvitae was snapped in half in front of a dorm, and a random branch broken off a a large sugar maple in front of Johnson.

This is only half the tree!

The final straw, though, and the reason for the quick post on a lunch hour, was the near total destruction of a little red oak by the Davis Family Library. Nearly every single branch on this street tree was broken or bent downward, leaving only the very top branches. This wasn’t just a random “lets grab a branch and break as we walk by”, this was intentionally standing in front of a tree, breaking as many branches as you can reach. Cruel, senseless, disheartening, and more than a little bewildering. What can we do as  a community?

Just the other day a crew chief and I were interrupted by a student walking to class, and he’d mentioned how he had joined us tree planting on Arbor Day. He pointed to the tree he did, and said he can’t wait to bring his kids to see it in 30 years. So we keep planting, and keep pruning broken branches.

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Leaf Color

October 7, 2010 by
Categories: Midd Blogosphere

I’ve been reading quite a bit this fall in various newspapers, web sites, etc. about the science of leaf change, and I thought, well, heck, there goes another blog post. I don’t see the sense to retread ground others are covering.

By now, you’ve probably read that leaf color changes by the shortening of day-length light triggers the tree to begin shutting down the leaves, and that chlorophyll breaks down, and sugar is absorbing into the tree. In a nutshell, the veins connecting the leaf to the tree are closed (abscission layer), and once this is complete the leaf falls.

Weather does play a part in leaf color, and in the color you see in the hills as you visit your children on parent’s weekend here (Hi parents! Your kids are doing fine. They want more money.) Many articles have talked about warm weather delaying fall, cool nights are good, drought bad. It’s easy to understand, though, if you think of it in terms of plant health.

A happy, healthy tree in a good growing season will more than likely have pretty spectacular colors. The factors responsible for bad fall color aren’t good for the tree health either. Drought is bad for fall color, and also bad for the trees. Southern Vermont this year had a pretty bad late summer drought, and when I was on route 4 a week or so ago near Woodstock the leaves were terrible, turning brown and falling off, rather than turning nice colors. Here at Middlebury it’s been a dry September, and then the recent rain storms came at just the right time, and the leaves held on long enough to turn well. Warm fall days and cool nights? Good for sugar production, and the breaking down of chlorophyll in the active leaf. A late spring or a severe summer drought can delay fall color-the tree holding on to it’s leaves as long as possible, storing as much energy as it can before winter.

Another leaf color fact plant geeks have probably noticed is called the Leaf Wave Model. An article at the University of Georgia discusses this: Peak color is an opinion. Different trees turn at different times, and in differing colors. Yellows dominate early, then oranges as both later trees turn, as well as some yellow leaves becoming more orange. Finally reds dominate the landscape, with accompanying orange. Browns come last, generally in oaks. The leaves in Vermont are spectacular because of the forest cover types found here, yellow Ash, orange and red maples, along with splashes of green from Pine and Spruce. By paying careful attention to the mountains in the fall you can watch this leaf color wave happen.

Some other reading I’ve been doing this fall was about the color red, something I’ve never thought about. An interesting question for botanists has been “Why red?”.  As chlorophyll disappears from the leaf, the other colors emerge, such as yellows and oranges provided by Carotenoids. Red, though, is expressed through Anthocyanin, but is not found in a leaf, and must be produced. The question, therefore, becomes why would a plant be producing a compound, expending energy, at a time in it’s life cycle when it is trying to store and conserve? There are two schools of thought, and probably both are correct, some for some plants, some for others.

One theory is that anthocyanin is produced in trees in nitrogen poor soils. In some varieties of trees, as the green chlorophyll breaks down, the leaves are vulnerable to bright sunlight, and this sunlight breaks down the produced sugars, thereby not being absorbed back into the tree as energy storage. The red pigmentation acts like a barrier from the sunlight, allowing the tree to absorb more of the sugars it has produced. Nitrogen poor soils means the tree would have produced less sugars, being weaker growing, so more red pigmentation would conserve more of the valuable food.

The other theory is one of coevolution, that red leaves are a signal to insects as a repellent, a red warning signal to the insects attempting to use the tree as an overwintering site. A study has shown this in aphids and apple trees, that wild apple leaves turn red in the fall, and suffer less aphid predation.

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Tree Planting 2010

September 22, 2010 by
Categories: Midd Blogosphere

Of all the work we do here in the landscape department, some of the best is the tree planting.

Think of our landscape at Middlebury as a living organism, changing and evolving. Trees have a lifespan, like us, only measured not in decades but hopefully in centuries, for the best and strongest. Site vagaries not withstanding, most species live for a similar amount of time.  A mad rush of planting one year will mean that down the road a large hole may develop in the landscape, as the same aged trees all need replacing at the same time. Take, for instance, some work being done at Utah State University.

The main quad at Utah State is lined with 80 year old Norway maples, which in Utah live about 60-80 years. Plans are underway to replant the green, and to remove the Norways before they fail. This has met with some resistance, probably based more on disappointment, as the look of a beloved quad radically changes in the space of a couple short years.

We started our tree planting this year on Arbor Day, thanks to Hilary Platt and Chelsea Ward-Waller, two of my students from Winter Term, and the driving force behind getting Middlebury to become a Tree Campus. Many students helped plant trees around Bi-Hall, and near Coffrin. The focus for this area was to help define some of the space around Bi-Hall Park, as well as planting in between Coffrin and Bi-Hall to help with storm water abatement. We used Sweet Gum there, Nyssa sylvatica, and a variety of other native trees nearby, such as Hop Hornbeam, Scarlet Oak, Red Oak, and Ohio Buckeye.

Chelsea and Friends planting

More friends planting

The second focus of tree planting this year happened later, after the rush of commencement and reunion. I enjoy this so much so I almost don’t want to tell of it.

Part of a happy and sustainable campus landscape involves diversity. Having as many different species of trees as possible ensures that should the next insect (Asian Longhorn Beetle, Emerald Ash Borer) or disease come to campus, large sections of our tree population won’t get wiped out, like the aging Norway maples at Utah State.

So I prowl nurseries and garden centers, looking for healthy plants that will do well on our campus. With such a varied landscape, it isn’t difficult to find a spot to tuck in some type of tree somewhere. We focused this year on areas of the campus lacking in tree color, and used ornamental flowering varieties of trees to liven up otherwise very static green locations. An example of this is a small section of lawn right to the north of Painter Hall.

While not a large area, comparatively, it was large enough for three small flowering trees, set in a triangle. One was a Butterflies Magnolia, small yellow flowers in early spring. Later in June will come flowers from the Yellowwood nearby, followed by a small tree in bloom now, a Heptacodium, Seven Sons Flower. More on that species in a later post-it’s spectacular.

Other areas planted include North of Warner Science, where many over-mature Sugar maples are slowly showing the effects of time, as well as along the east side of Hepburn Road, and North of Gifford.

Hoopsii Blue Spruce north of Gifford

Paperbark Maple north of Gifford

Maackia amurensis north of Stewart

Other fun varieties planted were a “Discovery” hybird Elm, Red Obelisk Beech, “Katsura” Japanese Maple, Kousa Dogwood, and Yellow Birch (the kind they make Birch Beer from). 4 Different varieties of Magnolia were planted, one red, one pink, and two yellow. In all, 32 trees have been planted so far, and a couple more are still on the way. The Tree Karma count? Not exactly sure, with all the storm damage, but I’m thinking it’s still holding at 3.5 to 1 or so.

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Big Huge Icky Giant Tar Spot

September 19, 2010 by
Categories: Midd Blogosphere

Giant Tar Spot

The study of plant diseases made me terribly depressed in school, but also made me laugh on occasion. I imagined two plant pathologists walking around, looking at sick leaves. Of course, each of them wouldn’t admit to the other that they didn’t know or recognize some strange disease, so they’re making up names as they go along. Strange fungal spores on a cherry tree? Well, it looks like Black Knot, and the disease is named.

A fall arrival on campus (and occasionally in my inbox as a question) is always the blatetenly named Giant Tar Spot. (“Hey, what’s this?” “You don’t know that? Any idiot knows thats, um, Giant Tar Spot. Yeah, that’s it. Giant Tar Spot”) You guessed it, huge jet black spots on the leaves of primarily Norway Maple.  This, too, is a fungus, Rhytisma acerinum for you latinally inclined. It infected the leaves way back in early summer, but they don’t really show up until now. When it’s too late to treat.

Not that you need to. Late diseases and insects like this look terrible but, let’s face it, the leaves are only around for a couple of more weeks anyway. It’s not a bad year for it this year on campus, we’ve had it much worse. If you’re looking to get rid of it on your tree at home, rake and dispose of the trees at your neighbors…

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