Posts filed under ‘Trees’

American Chestnut

You’d have a hard time finding today’s plant on a walk through the city. In most cases it has been completely wiped out, or it’s just a shadow of its former self. But its story is so monumentally tragic, and has so much to say about our interaction with plants, that it’s worth telling. Plus, it has a sci-fi ending!

The American Chestnut (Castanea dentata) was once one of the most common trees in eastern North America. It took up a quarter of the hardwood canopy, and could reach a height of 100 feet. Its nuts were an invaluable food for animals, as well as the inspiration for the lyric “Chestnuts roasting on an open fire…”.

In 1904, a forester noticed that some of the Chestnut trees in the New York Zoological Garden were suffering from an unusual disease. Called the Chestnut blight, it likely originated from Asian chestnut trees that were sold in nurseries. The American Chestnut had no immunity to the foreign pathogen. It traveled rapidly outward from the New York area, and by the early 1950s most of the great American Chestnut trees were gone.

When we walk through lush eastern forests today, it’s hard to imagine that one of the most important trees is missing. You can still find American Chestnut wood fences and cabins that stand incongruously in a Chestnut-free forest. Even more strangely, you can sometimes find a small shrubby Chestnut just a few feet high, as in this photo (right) — doomed little sprouts growing from a trunk that was destroyed by disease.

We almost completely destroyed the American Chestnut, and strangely, we’re now engineering its return. Scientists are creating a blight-resistant American Chestnut. Here’s the plan: first they cross some of the few remaining healthy trees with Asian trees, and then they breed them until they’re mostly American Chestnut. Like so many other plants, this tree’s future is now inseparable from our own.

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July 21, 2010 at 1:55 am 1 comment

Ginkgo biloba

I’ve moved to a new city and started a new job, so I’m going to cut the number of posts down to one a week. I’ll update on Mondays, barring extenuating circumstances. Thanks for reading!

You might be more familiar with today’s plant when it’s found in products like energy drinks and traditional medicines. Believe it or not, many of our city streets are lined with Gingko biloba trees, and they have a peculiar history.

The Ginkgo is a living fossil. It might look like any other tree from far away, but take a close look at those weird clusters of wedge-shaped leaves — they were a familiar sight to ancient reptiles that walked the Earth long before dinosaurs.

For a time, the Ginkgo tree spread throughout the globe. Eventually, however, this tree could no longer compete in a world filled with modern plants. About two million years ago there were so few Ginkgos that they no longer showed up in the fossil record. The Ginkgo tree still hung on in some parts of China, but times looked tough. Fortunately, it was about to see another international resurgence.

At some mysterious point in history, a few humans decided that the Ginkgo tree was useful and attractive. They began to cultivate it far outside of its native range. Eventually, people carried this tree outside of Asia and spread it to urban areas around the globe.

Nowadays there is no unquestionably native population of Ginkgo trees — that is, there is no population that wasn’t planted by people. But once again this species flourishes internationally. The future of the Ginkgo tree is now inextricably connected with the future of the human species, like so many other plants in the urban jungle.

July 7, 2010 at 1:46 am Leave a comment

Norway Maple

There may be an imposter living in your backyard.

Full disclaimer: I grew up in Canada, and I’ve always been a sucker for the Sugar Maple tree. Its leaf is found on our flag and everything else that is patriotic. But people in the US Northeast also love this tree because it provides the sap for maple syrup. (This sweet quality is reflected in its Latin name, Acer saccharum.)

So I was surprised to learn that many of the “Sugar Maples” lining Canadian and American streets aren’t Sugar Maples at all. They’re members of a look-alike species from Europe called the Norway Maple, Acer platanoides.

The Norway Maple was brought to North America in the mid-1700s. It was a popular garden tree; even George Washington was thrilled to score himself a couple of Norway Maples for his yard. In urban areas, it proved to be the ultimate secret replacement for the beloved Sugar Maple because it was much more tolerant of pollution, road salt and denuded soil.

Unfortunately, the success of the Norway Maple came at a price. It spread into natural areas and displaced native plants (including the Sugar Maple). Its leaves were just a smidgen bigger, and its foliage just a touch thicker, and native seedlings couldn’t grow in its thick shade.

Nowadays it’s considered a dangerous invasive species. Some states have even banned people from planting them.

How can you tell that Norway Maple from the Sugar Maple? There are several subtle clues, but my favorite way to distinguish them is to pick a leaf and snap the stem. Only Norway Maple will exude a milky white sap. Of course, you could always just compare its leaf to the one on a handy bottle of ice cold Molson Canadian beer. Cheers!

June 19, 2010 at 2:52 am Leave a comment


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