Saturday, December 29, 2007

Tulip Trees

Tulip trees reserve their charms for those who seek them out. Demure in all seasons, tulip trees are now discreetly displaying their unusual fruits.

The fruits hang on into the winter even after dispersing their winged seeds into the wind. Spring brings the "tulips", pale yellow blooms tinged with orange and green. Their unassertive colors can blend into the foliage and fail to catch your eye. But when you spot the flowers unexpectedly you are rewarded with the feeling of having discovered a secret.

Once you have seen a tulip tree leaf, you will never mistake it for that of another species. The distinctive shape has been described as that of a maple leaf with its tip cut off. The leaves turn a handsome yellow in the fall.

There is a massive and beautiful tulip tree at 443 Stelle Avenue near the corner of Field.

A tulip tree at 1001 Central Avenue illustrates two of the species' most typical features: a long, straight, slightly tapered trunk with no branches near the ground and a rather narrow crown. The form is distinctive enough that tulip trees can be recognized from a distance even when they are leafless.

970 Hillside Avenue provides another example of a mature tulip tree.

Tulip trees are also called tulip poplars or yellow poplars. In fact, they're neither true poplars nor closely related to the poplars (genus Populus). In the lumberyard, however, tulip tree wood is called poplar and is commonly sold for use as interior trim. The wood is among the lightest in weight of the hardwoods and is not particularly strong.

Tulip trees grow fast and become huge. In a favorable environment they can grow to 200 feet tall with ten foot diameter trunks.(1) Their massive size and weak wood make them susceptible to damage by high winds. For that reason tulip trees are not often used as street trees.

Light and easily worked wood can have advantages, however. Tulip tree trunks were hollowed out by several native American tribes to make canoes. It is said that Daniel Boone took his family and belongings down the Ohio River in a sixty-foot tulip tree canoe, abandoning Kentucky for the Spanish Territory in the late 1700s. (2)

(1) Trees of Pennsylvania and the Northeast, Charles Fergus. Stackpole Books 2002, p. 148.

(2) A Natural History of North American Trees, Donald Culross Peattie. Houghton Mifflin 2007, p. 260.

Copyright Gregory Palermo

Sunday, December 16, 2007

Elm envy

The devastation wrought by Dutch elm disease in the middle of the last century left Americans largely bereft of our favorite street tree. We lost no time in trying to find substitutes that could reproduce the look of American elm and resist Dutch elm disease. Japanese Zelkova, Zelkova serrata, was seized upon as a tree that could replace American elms along roadways.

Zelkova was little known until a few decades ago. It is rare to encounter a mature one. In the last few decades the tree has become a very popular elm substitute. The tree shares the American elm's vase-like habit, but Zelkova's vase is typically squatter. The habit is also stiffer. American elm limbs undulate as they ascend. Not so the limbs of Zelkova, which lacks the elm's sinuous grace.

The tree has a handsome and distinctive bark. The young bark has very prominent lenticels(1), horizontal striations, that are reminiscent of the bark of some cherry trees. Older bark is rough and peeling.

The unusual bark and vase-like habit make this species easily recognizable even when it is leafless.

One peculiarity of Zelkova that has the potential to cause trouble as the tree matures is the density of its branching pattern. An entire forest of limbs emerges from the trunk a short distance above ground level. The Central Avenue tree pictured above illustrates the tremendous branching density. The Putnam Avenue Zelkova pictured below shows how numerous limbs typically originate in a bunch.

One wonders what is going to happen to all those limbs when they get large. You would have to bet that some will be crowded out and will drop to the street. Professor Edward. F. Gilman of the University of Florida (formerly of Rutgers) has drawn attention to this problem. In a presentation at the New Jersey Shade Tree Federation meeting in 2006, Professor Gilman spoke of Zelkova as a special case among shade trees in that it needs careful pruning for the first two or three decades of its life in order to develop a healthy form. Is he being overly pessimistic? Hard to know. There just aren't that many mature Zelkovas around on which to base a judgment. If he is right, the enormous vogue that Zelkova now enjoys is going to lead to large maintenance expenses for the municipalities planting them in great numbers. The only mature Zelkova I know is at 9 Remington Avenue in Edison (off Park Avenue). That tree has a diameter at breast height of about three feet and is quite a beautiful specimen. Pruning history? I haven't a clue.

Another American elm substitute that is growing in popularity, but still a rarity, is lacebark elm, Ulmus parvifolia. Like Zelkova, lacebark elm is resistant to Dutch elm disease. Kathryn Uhrich and Jeff Holmes recently planted two lacebark elms in the curbside strip in front of their house at 1441 Evergreen Avenue. They are the only lacebark elms I know in Plainfield. The peeling bark of this species is exceptionally beautiful. These two elms are an exciting addition to Plainfield's urban forest.

Siberian elm, Ulmus pumila, is yet another elm with resistance to Dutch elm disease. There is an example of this species near the Muhlenberg Hospital Park Avenue parking lot. The first tree on your right as you turn off of Park Avenue onto Laramie is a mature Siberian elm.

Michael Dirr's Manual of Woody Landscape Plants, the Bible for many gardeners, calls this species "one of...the world's worst trees" because of its susceptibility to damage by wind and insects.(2) I think Dirr is exaggerating. I have seen many attractive Siberian elms (not in Plainfield, where it is uncommon), and I find the coarse, chaotic bark quite attractive.

Finally, some people are still planting American elms. Dutch elm disease-resistant varieties include 'Princeton', 'Liberty', and others.
(1) Lenticels are loosely bundled groups of cells that permit gas exchange, allowing the tree to "breathe" through its bark.

(2) Manual of Woody Landscape Plants, fifth edition, Michael A. Dirr, Stipes Publishing 1998, p. 1048.

Copyright Gregory Palermo

Sunday, December 2, 2007

Norway maple

"Norway maples should be banned from the United States." Bill Nierstedt, Plainfield tree guru and head of the City's Planning Division, made this xenophobic comment three years ago. I have waited in vain since then for him to be invited to repeat this hate speech for a national audience on Lou Dobbs' television program. Despairing after three years of ever seeing Bill on television, I decided to reprint his words here.

Bill is too late. The genie is out of the bottle. The horse is out of the barn. Norway maples are here. Norway maples are among the most common street trees in Plainfield. These European imports are perhaps the most numerous street trees in the eastern United States.

It has to be admitted that their bright yellow autumn foliage is quite attractive.

Some varieties have maroon foliage all season.

They're handsome trees. Arthur Plotnik's The Urban Tree Book describes their regular, lollipop form as looking like a tree drawn by a child.(1)

So what's the problem? Norway maples cast an inky shade in which very little can grow. They make a dense network of subsurface roots that quickly suck every bit of moisture from the soil and that lift sidewalks. Any gardener knows that to dig a hole near a Norway maple is to dig a hole in wood. Tight-angle crotches make the trees more susceptible than most to storm damage. Drive around Plainfield after a storm and take note of what kinds of limbs you see blocking the road. Mostly maples, many Norways.

But Norway maples' most egregious offense is that they breed faster than the natives (and I'm sure that it's this fact that most distresses Mr. Nierstedt). Norway maples are the most sucessful reproducers that I know. They put dandelions to shame. In a hospitable habitat like Plainfield, each tree manages to produce thousands of seedlings each year. The seedlings carpet the ground and are difficult to uproot. Those that grow in a lawn eventually succumb to repeated mowing, but what about the rest? They're extremely shade-tolerant and so have no trouble at all growing up in the middle of a mature hedge. They also have no trouble growing up in the middle of a mature forest. They leaf out earlier than most plants and hold their leaves later into the fall, giving them a longer growing season.(2) Norway maples are crowding native species out of our parks and forests.(3)

They're taking over the urban landscape as well. How many hedges have you seen that started out as privet and ended up as maple? Homeowners tire of struggling to uproot the very tenacious maple invaders and instead just shear the maples along with their hedging plants.

What happens if the maple seedlings are left to their own devices for a few years? They make a Norway maple jungle. Such jungles are easily found in Plainfield. The maple jungle pictured below is on Belvidere Avenue near Berkeley.

Don't mix up Norway maples with sugar maples. Although the leaves of the two species are quite similar, the trees are easily distinguished by their bark. Norway maple bark is brownish grey with shallow furrows.

Sugar maple bark is silvery grey and shaggy.

Found: a big, beautiful ginkgo.

955 Woodland Avenue has a mature ginkgo as beautiful as the hacked Netherwood Station ginkgo used to be.(4) It's worth a visit.

Dan Damon sent photographs of a handsome ginkgo in the 900 block of Central Avenue. His photographs are below. Dan made the ultimate ginkgo sacrifice. He got up close and personal with the stinking ginkgo fruits and tracked some of them into his car. For his efforts he got great photographs of fruits that are adapted to fend off even dinosaurs with their odor.

(1) The Urban Tree Book, Arthur Plotnik, Three Rivers Press 2000, p. 95.

(3) To make the threat quite local, Professor Thomas Ombrello of Union County College observes that "There are numerous parks in our area where Norway Maples are displacing the native tree species." The Trees of Union County College, 2nd edition, Thomas M. Ombrello, Union County College 1997, p. 43.
An Overview of Nonindigenous Plant Species in New Jersey, ( published by the state Department of Environmental Protection in 2004, cites Norway maple among 29 "invasive nonindigenous plant species documented to aggressively invade...natural plant communities in New Jersey."
The Invasive Plant Council of New York State includes Norway maple on its list of the "Top 20 Invasive Plants in NYS" (
The Pennsylvania Dept. of Conservation and Natural Resources lists Norway maple among "serious threats to our native ecosystems" (

(4) See April 19 Plainfield Trees post on Ginkgo biloba.

Copyright Gregory Palermo