Maples

SHADES OF MAPLE: DEATH BY NORWAY

 

A Norway maple has three effective ways of destroying your lawn: dense summer shade, a smothering blanket of fall leaves, and a choking network of surface roots. There are mosses that will survive this onslaught, so treasure them. The prolific Norway seedlings also wreck havoc in the yard and surrounding garden.

No one doubts that Norway maples are beautiful: delicate lime-green flowers in spring, handsome leaves in summer, butter yellow, or sometimes red or orange in fall, graceful branches and trunks for the winter. The Norway maples hold their leaves longer in the fall than our native maples, providing late-season yellow accents for bare tree branches and winter evergreens. (FYI: Order of leaf turning: sugars, reds, Norway, silvers, then Japanese)

Norway maples aren’t so bad in Norway because it’s too cold for them in most of the country but they have become one of the most widespread trees in Europe, as well as being a major pest in North America. Since the way we nurture our lawns in the USA tends to be worse for the environment than Norways are for our lawns (see Issue 60), Norways wouldn’t be so bad except for their winged seeds (called “samaras”) that float off into our woodlands and wreck havoc there. What kills your lawn is also doing in our treasured woodland wildflowers.

Norways were introduced to North America in the late 1700’s. George Washington is said to have bought two from a Philadelphia importer. They became widespread around World War II when many were planted to replace elms stricken by the Dutch Elm disease. It seemed like a good idea at the time because Norways are one of the faster growing hardwoods that do well as street trees (handle pollution, live a long time, have strong branches). The problems didn’t show up until decades later when the mature trees and their grown-up, escaped decedents proved themselves to be lawn and forest killers.

So many, many Norway maples were planted along streets and in yards. Years later, the average home owner sees the trees gracing the neighbor’s yard and thinks: “nice tree, but why don’t they take better care of their lawn? They should put lime on the moss and re-seed under the tree.” The same person goes hiking in the woods, and wonders about the lack of wildflowers. The Norway maple’s culpability only becomes clear once it’s been pointed out.

Recently, a reader wondered why garden and landscaping professionals continue to recommend environmentally-unsafe plants like Norway maples. Equally intriguing is: why do homeowners buy them? Of course, every person acts for his or her own complicated set of reasons. But there are some identifiable trends. In this area, I suspect ignorance is a big one.

Plant nurseries and landscapers are no different than other retailers: their first concern is to make a living; not save the planet. They stock what they think people will buy. And they have to consider price. Fast growing, hardy plants are easiest to mass produce, cheapest to sell, and have the fewest returns and complaints. However, if they’re aliens, they also have the best chance of overwhelming the more delicate local flora.

The plant retailers know that most homeowners aren’t expert horticulturists and are more comfortable in choosing already familiar plants. Just think of the overuse of Impatiens. Since baby trees are relatively expensive long-term investments, people are even more likely to want to stick to the “tried and true”. So, popularity begets popularity, regardless of actual wisdom. This tends most pronounced with trees because the problems often don’t show up for 20 to 50 years. Sort of like smoking.

What we need to do is to demonstrate to our local retailers ever chance we get that we want sustainable agriculture and are willing to pay for it. That means buying the organic, local-grown produce in the store and farmers’ market, and planting non-invasive, low-chemical and water using, wildlife-nurturing plants in the garden.

So how do you tell the Norways from our lovely native sugar, red and silver maples? This is tougher than you’d think because maples interbreed and “cross-dress”. For example, red maples are supposed to have red stems but sometimes so do Norways, sugars and sycamore maples. See Issue 134 (coming October 17, 2004).

Conifers

ODE TO THE WHITE PINE WEEVIL

 

When we talk about preserving biodiversity by preserving our native plants, part of the reason is so that our native insects with specialized diets will have something to eat. This statement may puzzle the gardener who thinks that bites out of the roses are a bad thing. After all, who needs bugs? Yeah, some of the “bugs” pollinate the flowers so that we have fruits and vegetables, some till the soil, some make the honey, some spin the silk, and some break dead things down into their original components for re-use, but…well, who cares about the rest of them?

Our small creepy-crawlies actually come from several families. There are the eight-legged spiders and mites, the six-legged the insects, the zero-legged worms, the centipedes and millipedes with too many legs to count, the armor-plated pill-bugs (related to shrimp), and a whole host of microscopic guys. For our purposes, they are all “bugs”, even if to a biologist “bug” means just one kind of “insect” and “spiders” aren’t “insects”…

The white pine weevil (Pissodes strobe) seems as good a candidate as any to start The Monday Garden native bug-appreciation day movement. Chances are you’ll be much more likely to see this critter’s work than the critter, which may be a good thing seeing that the bug is an ugly as an orc. You can tell all weevils by their long, downward curving snouts, good for poking holes in plant tissue. The white pine weevils are small beetle-types with splotchy, hard shells and the characteristic long snouts. Their children are pasty white legless grubs. Yuk.

However, this little bug’s whole job is to go around topping out our native eastern white pine trees. According to the Ohio State University Extension these little guys “prefer” eastern white pine and various spruces, but, it is said, that in a pinch they’ll also attack about 20 other pines, including, on rare occasion, a Douglas-fir or two. In other parts of the country, due to a difference in diet, the white pine weevil is called “Sitka spruce weevil” and “Engelmann spruce weevil”.

What the white pine weevil does, as a larva and adult, is feed on the new soft leaders at the top of the tree. They seldom kill a tree but can significantly change its shape.

Left to their own devices, eastern white pines grow tall and straight. When they loose their top leader, due to while pine weevils, utility companies, severe weather or other cause, they usually develop the soft, wind-swept shapes with which the trees grace many a New England sky-line.

If you look around the Northeast, here and there, you’ll see a white pine grown to adulthood tall and straight, but most have developed multiple leaders and wonderful individualized shapes. There’s no way to say for sure that a particular pine got its shape from a weevil rather than other cause but the weevils do a lot of the work.

Interesting, sources pretty much agree that the only white pines likely to be killed by weevils are the under 4-footers growing in full sun, particularly if a bit over-watered (that means in a tree farm, tree nursery or front yard, rather than in natural part-shade understory conditions).

Equally interesting, they say that if the weevil population is in balance, usually only one weevil per tree will lay her eggs in the holes she makes right under the white pine’s top bud cluster. In this case, most of the grubby larva will get smothered by the white pine’s thick, plentiful resin, provided for exactly this purpose, and the tree’s leader is likely to survive even if gets a bit (artistically) bent.

If there are too many adult weevils, multiple females will compete for egg-laying space on the same tree. If simultaneously attacked by several weevil broods, the tree is sure to loss its terminal (top) leader and possibly also the next rung down, which will change is its shape and stunt its growth, making it ugly for a year or two while it sheds the dead top and makes new leaders. (If this happened to your tree, prune out the dead parts.)

The weevil population is kept in balance naturally through the white pine’s own defenses, predators, weather conditions, and the like. The weevil population will increase in monocultures (one-kind-of-plant places) of its chosen food plant, especially if any of the trees are unhealthy. The weevil population will also increase when the predators have been killed off by chemicals, unusual weather conditions, destruction of habitat or some other ecological disturbance.

Tree nurseries, of course, hate white pine weevils, because the nurseries are trying to sell “prefect” little trees, grown quickly, packed together in full sun, and the weevils are actually taking a bite out of the cashier register’s contents. The lumber folk don’t like the weevils either because a severely bent tree is worthless for lumber.

Once white pines were dominant in northeast forests but they lost significant population due to lumbering over the past 200 years. So to the extent that the white pine weevil prevents the trees from being cut down by their worse predator, lumbering humans, this is so bad? While the weevils make life difficult for the (non-organic?) tree farmers (according to the growers’ way of thinking), for the rest of us, though, the white pine weevil is one of nature’s great pruners, toiling hard to beautify the roadsides and hilltops. Who knew?

Catalpa

CATALPA: GREAT AMERICAN and INVADER?

The northern catalpa (Catalpa speciosa) is a beautiful, tropical-looking North American native shade tree with a mysterious past. At one time, its range was confined to part of the Mississippi Valley but sources are admittedly fuzzy about which part. Likewise, the name is definitely Native American in origin but there’s a big disagreement over which tribal language is the source.

RANGE AND FAMILY: Today, the northern catalpa (Bignonia family) is found through out the U.S.A. and southern Canada, as well as in other countries where it has been imported as a combat-ready urban tree. Also found in temperate urban areas are the northern catalpa’s southern Appalachian kin, the southern catalpa (Catalpa bignioides), and its Asian kin – particularly the clearly invasive empress tree (Paulownia tomentosa). Those of you from the southwest might know the southwestern native cousin, desert willow (Chilopsis linearis). Many gardeners are familiar with the lovely orange-flowered native trumpet vine, which is the family’s signature member. The Chinese catalpa (Catalpa ovata) is also sold for landscaping.

INVADER OR RETURNING ALUMNI? Some say that outside of its native range, the northern catalpa is an invader. My home state of Connecticut has labeled the northern catalpa as having “demonstrated invasive tendencies”, which is a no-no of the third degree. (The first degree has been reserved for the worst of the worst, like ailanthus). Being “invasive” means that the plant doesn’t come from the area, can escape cultivation and survive on its own, can spread widely, and can out-compete local native plants.

There is no question that the northern catalpa does not stay where it is planted. My own Hoyt Street Alley hosts numerous northern catalpa specimens both large and small. The northern catalpa’s spread, however, is limited by its natural fussiness as to location – it likes rich, moist, slightly acid soil and just a touch of shade. In other words, it is an edge-of-forest tree that won’t survive in deep forest, and which does well in the open meadow and lawn only with plenty of water, as in the Alley.

But is an invader? How come the northern catalpa is built to withstand the -30F temperatures in Montreal, if its original range was only in the southern Mississippi Valley? The black locust may be similarly situated. Many say the black locust an invader in the Northeast, but geologists have found that black locust was here before the Ice Age. So, the black locust is only reclaiming its original territory. Is the same true of the catalpa? Oddly, it is hard to come by popular-level research publications on the catalpa. The northern catalpa has even been neglected by the U.S. Forest Service, whose web site is normally the source of much good information.

Does it play nicely with others? To me, this is the more important question. Regardless of whether the northern catalpa has a pre-Ice Age “green card” permitting it to be outside of the Mississippi Valley, does it add or detract from bio-diversity? Again, popular-level research is hard to come by. Anecdotally, in my area, I have not observed it taking over. It is weedy in that it makes lots of seedling-babies.. However, I don’t see pure stands of catalpa where it has crowded out the competition. (I wish that could say the same for certain others such as the ailanthus and Norway maples). In Hoyt Street Alley, the northern catalpa shares space with a variety of trees including the box elder and Norway maples, American elm, eastern cottonwood, red oak, shaggy bark hickory, American sycamore, chokecherry, white mulberry, ailanthus, and native crab apple. The catalpa saplings are hardier than those of most of the other trees (as hardy as the ailanthus in fact), but even the big catalpa trees are being smothered in places by that dreaded invader porcelain vine.

Allelopathic: There is authority that both the southern and northern catalpas are “allelopaths”, in that they emit chemicals from their roots that prevent other plants’ seeds from germinating. The work done on the southern catalpa indicates that the allelopathic properties only become a problem when the tree is allowed to grow in large, pure stands.