Tuesday, November 06, 2007

Autumn leaves

Autumn has come to New York at last. For a reason that is as yet unknown, the City’s trees change color far later than the surrounding areas. Generally, while leaves in Vermont or South ’Jersey turn all sorts of colors, here in Manhattan they generally just turn yellow then brown before falling off and mucking up the sidewalk.

I’ve always felt cheated by this, for this time of year is the Plant kingdom’s chance to party, and the riot of color can be truly breathtaking. The damn problem is that one has to get all the way to the outer suburbs to even get a really good view. But there’s really no choice in the matter. All we get to look forward to is the decorative cabbage around the end of December.

If done right, leaf watching can be as a rewarding experience as amateur astronomy, except the travel expenses are greater. They start turning in Hudson Bay near the Arctic in the middle of August and end during Christmas time in mid-Florida. Peak color is a difficult proposition to predict due to global warming, but if you manage to hit it just right, the rewards are amazing.
Nature’s artists: Autumn leaves in New York

By eric lurio

The reason this happens is that trees have feelings. Not feelings as we know them, but they can sense changes in temperature and the like, and when the water in the ground or the air reaches a certain temperature for a certain length of time, then they know it’s time to stop drinking the sunlight and get ready for bed. How they figure this out will probably remain a mystery for decades to come.

Each tree is an individual, and they start pulling the chloroplasts, that’s how they feed themselves, out of their leaves at different rates depending on whether they’re lazy or hungry or their roots are too dry. Light and shade have their effect too, sometimes a tree would pull the chloroplasts out of just the areas of the leaves that are shaded by other trees and leave the rest green for a bit longer to drink more sun while it lasts. That requires some really detailed control, which is pretty amazing for something that doesn’t have the semblance of a brain or nervous system!

Color depends on the species and how individual trees are feeling at any given moment. Evergreens, obviously don’t shed their leaves at any particular time, and when they do, they just gulp the green stuff and sugar down quickly into their trunks and let the things turn quickly brown while new needles grow in to replace them. Ginkgoes, those bizarre living fossils descended from the ancestors of Pine clan, turn yellow from the edges inward, and for the most part just abandon the chlorophyll in the leaves when they fall to the ground. Oaks generally turn lighter, but the star of the show is the sugar maple.

Maple trees produce prodigious amounts of sugar, which, if the tree decides to leave it there after it drinks up it’s chlorophyll first turns the leaves bright red. Empty leaves are yellow, thanks to a pigment called from xanthophyll so as the tree drinks up the sugar the leaves turn lighter and lighter shades of orange (some species have carotene, which makes carrots orange in their leave, too). Sometimes a single Maple will be a rainbow of color, going through two thirds of the spectrum. Sumac Ivy acts this way too, and White Ash turns purple, which is kind of perverse but adds to the effect.

Unfortunately, the only places the Native New Yorker can see get a good look are in Central, Inwood and Prospect Parks and the best views are limited, timewise. But now seems to be the time, so go for it.

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