October 19, 2012

Fall Leaves

Lately a couple of people have remarked to me that the fall color this year is disappointing and speculated that this might be because of the summer drought and high temperatures. Personally, I think the color this year has been just fine, and in some cases, spectacular. I suppose it just depends on where you are, and fortunately we have been exploring in places where the color has been lovely.

I have a major job ahead raking lots of those lovely leaves, some perhaps for the second time thanks to the high winds we had over the weekend. Just as I was contemplating that chore yesterday I happened to see a beautifully written and illustrated essay by Rob Dunn in the October 2012 issue of National Geographic entitled "The Glory of Leaves".

The article delves into the evolution of leaves from the beginning, when a cyanobacterium entered a living cell and began to capture energy from the sun, giving rise to the amazing and varied world of plants. It muses about how natural selection has produced such a variety of leaf shapes and sizes, all contributing to intense competition for sunlight. 

In most cases we can't begin to imagine the selective advantage one leaf type might have over another in a temperate deciduous forest, whether they are rough, smooth, toothed, lobed, simple, compound, or a host of other descriptive attributes.

And why would leaves with different shapes occur on the same tree, as in sassafras and mulberry? What selective advantage might this characteristic, called polymorphism, offer to the plant?

The relationship between the shape and texture of leaves and their function is a fascinating topic for discussion but few definitive answers are available. The constantly changing mix of climate, competition for water and nutrients, and the need for defense mechanisms ensures that natural selection will continue and the plants upon which it acts will continue to slowly change in response.

So much is going on all the time in the plant world, most of it quite subtle by our standards, and that will give me lots to think about as I rake all these fallen leaves!

No comments:

Post a Comment