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Stuff I shoulda known
Just heard a snippet of a Robert Krulwich piece on NPR that made me dash to the computer to check out the full story.
One of the guaranteed species on an Urban Nature Walk is the honey locust. It's a widely planted, pollution tolerant tree, with tiny leaflets that blow away in the fall requiring little clean-up. Most of the honey locusts found in cities are cultivated varieties that have done away with their two most interesting features. First, their huge seed pods, and second, their array of large sharp thorns:
I'd been walking around with the misapprehension that this tree was native to the hills south and west of here, but apparently that applies only to black locust. Honey locust is considered native, and for the purposes of Krulwich's piece, was known to be growing on Manhattan Island 13,000 years ago. Also on Manhattan at that time, were elephants, specifically mastodons. Now for the honey locust tree to evolve these big, sharp, and expensive (from a biological point of view--that's a lot of energy to devote to a decoration) thorns, there had to be some animal that the tree wanted to deter. I always assumed that the thorns were there to slow down raccoons and bears from climbing the tree to eat the seed pods before they were ready. Krulwich proposes that the thorns, which come out of the bark of the trunk as well as the branches, evolved to keep some herbivore from stripping the bark. He points out that the acacia tree of Africa, which famously still has elephants, bears similar thorns. He also mentions that until someone studies mastodon droppings or coprolites and finds honey locust parts therein, there is no proof that mastodons ate from the honey locust.
Pretty cool. Of course my contrary side would quickly like to mention that there are other bark-eating animals in Northeastern North America that haven't gone extinct. Moose and white-tailed deer come to mind, not to mention the cottontails. But it's so fun to picture mastodons in New York and New England that I'll play along for a while.
One of the guaranteed species on an Urban Nature Walk is the honey locust. It's a widely planted, pollution tolerant tree, with tiny leaflets that blow away in the fall requiring little clean-up. Most of the honey locusts found in cities are cultivated varieties that have done away with their two most interesting features. First, their huge seed pods, and second, their array of large sharp thorns:
I'd been walking around with the misapprehension that this tree was native to the hills south and west of here, but apparently that applies only to black locust. Honey locust is considered native, and for the purposes of Krulwich's piece, was known to be growing on Manhattan Island 13,000 years ago. Also on Manhattan at that time, were elephants, specifically mastodons. Now for the honey locust tree to evolve these big, sharp, and expensive (from a biological point of view--that's a lot of energy to devote to a decoration) thorns, there had to be some animal that the tree wanted to deter. I always assumed that the thorns were there to slow down raccoons and bears from climbing the tree to eat the seed pods before they were ready. Krulwich proposes that the thorns, which come out of the bark of the trunk as well as the branches, evolved to keep some herbivore from stripping the bark. He points out that the acacia tree of Africa, which famously still has elephants, bears similar thorns. He also mentions that until someone studies mastodon droppings or coprolites and finds honey locust parts therein, there is no proof that mastodons ate from the honey locust.
Pretty cool. Of course my contrary side would quickly like to mention that there are other bark-eating animals in Northeastern North America that haven't gone extinct. Moose and white-tailed deer come to mind, not to mention the cottontails. But it's so fun to picture mastodons in New York and New England that I'll play along for a while.
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http://en.wikipedia.org/wiki/Megalonyx