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Posts Tagged ‘natural history’

Since moving to St. Paul I’ve been exploring a lot on my bike, but a couple weeks ago (before the snow blew in) I got a history lesson in my own yard. And it was putrid. Rancid, even. But enlightening.

I love fall. I love the colors, the crispness in the air, the sound of leaves blowing around on the ground and crunching underfoot, their distinctive smell. It was a brisk fall day and I though it would be a good idea to rake all the leaves that had dropped. Not only would I be doing a good deed, I would get fresh air and exercise. It would only take an hour or so.

The house sits on the corner of the block and there isn’t much lawn. I quickly worked my way across the backyard, where the leaves were thickest, along the boulevard to the front, and then got to work on the front yard and boulevard. I had left them till the end because they are small and a cursory glance indicated that they didn’t have many leaves. Two small apricot trees stand on the front lawn, a maple stands close to the corner on the side boulevard, and a medium-sized tree graces the front boulevard. It would be a snap.

Ginkgo tree that has lost its leaves in the fall.

Mysterious tree on the front boulevard.

Once I got within ten feet of that tree on the front boulevard, my idyllic autumn interlude came to an unpleasant, malodorous end. I don’t have the greatest sense of smell in the world, but it took no time for me to discern the scent of vomit and dog poo. I remembered what my friend had said:

Beware of the stink fruit!

There were so many questions:

  • Why does this tree produce noxious but innocent-looking fruit and the one in front of the neighbor’s house with the same kind of leaves doesn’t?

    A single ginkgo fruit lying in the grass.

    Who would expect such a harmless-looking fruit to emit such a rancid odor?

  • Why would anyone choose to plant a tree that produces stink bombs in the fall that fall to the sidewalk and street and get smashed by feet and tires, thus releasing the disgusting fumes into the air and contaminating shoes with toxic waste?

    Ginkgo 'fruit' smashed on the pavement.

    And yet if you value your shoes, don't step here!

  • While we’re at it, why is this street lined with just ginkgo trees while the cross street is lined with some kind of maple?

You may already have guessed that the unassuming tree on the front boulevard is no ordinary tree; it is a ginkgo tree. A female ginkgo. And here is where the history comes in, not to mention a little biology. It turns out that ginkgo trees are dioecious, which means that the male and female flowers appear on separate plants. The females fruit while the males do not. Ash, boxelder, juniper, cedar, and holly are all dioecious, but it is only the female ginkgo that produces such an objectionable but benign-looking fruit.

Ginkgo 'fruit' left on the tree after all the leaves had fallen.

Ginkgo 'fruit' left on the tree after all the leaves had fallen.

Given this substantial drawback, why did the city plant this female ginkgo tree (and several others along the same street)? It turns out that ginkgoes have several things going for them. They do well in urban environments with disturbed soils, they tolerate air pollution, and they aren’t prone to problems with pests or disease. Furthermore, the ginkgo will eventually develop into an attractive shade tree, although ours hasn’t made it to that height yet. Ginkgo leaves are a unique fan shape and turn a brilliant golden color in the fall. These were all probably important considerations.

A neighbor told my friend several years ago that this street used to be lined with large elm trees that formed a leafy cathedral ceiling above the street. When they were decimated by disease in the 1970s, apparently the city decided to replant the boulevards using a different species for each street. That way if one species were hit with a new disease, only one street would be affected, not all the streets in the neighborhood. This street hit the jackpot with its ginkgoes!

Today most ginkgo trees are grown from cuttings from a male tree grafted onto a seedling rootstock so that the resulting tree will be male and will not produce offensive stink bombs in the fall. If grown from seed, the sex of the tree might not be distinguishable for ten to twenty years, when the tree is finally capable of flowering. So either the City of St. Paul wasn’t concerned about the sex of the trees or this tree was too young for its sex to be determined when it was planted.

Much as I hate to admit it after an afternoon cleaning up ginkgo fallout, the ginkgo is a fascinating species. It is often called a living fossil (although I believe this is a misnomer, since as far as I’m concerned fossils should be unscented) and has been around for over 270 million years. It lived through the age of the dinosaurs and survived down to the present day in a small area of central China where Buddhist monks apparently kept ginkgoes alive near their monasteries for more than a thousand years.

The ginkgo has no living relatives. What we think of as the fruit of the female ginkgo is really a seed surrounded a hard shell and then by soft and fleshy section. The nasty stench comes from butyric acid in the ‘fruit.’ The fan-shaped leaves are unique as well. If you look closely, you can see fused needles in the leaf. Ginkgoes represent a link between needled evergreens and broadleaf deciduous trees.

Golden ginkgo leaf

Ginkgo leaves turn a beautiful golden color in the fall.

As I looked into the history of the ginkgo, I also discovered that its survival capabilities are downright impressive. Forget standard American urban air pollution: several trees survived the 1945 atomic bomb blast at Hiroshima when all other life was destroyed. These trees are still alive today. No wonder the Japanese call them the “bearers of hope.”

I vaguely remembered learning about the gingko in a college biology class, but this was my first close encounter with one. I appreciate the chance to learn something new about my community and the outdoors, but I’m hoping the next lesson won’t be quite so … um … fragrant.

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