Friday, May 25, 2007

Succession = Diversity

When Lava Flows And Glaciers Recede, Predicting How Species Take Over
Whenever an event such as a fire, clear cut, or lava flow creates an empty habitat, species arrive, interact, and assemble to form a new ecological community--a process known as "succession." How quickly does succession proceed" Most ecologists might expect change to be rapid at first and then decline as the community ages, but there was no systematic analysis of this idea until recently.

It’s only a “disaster” if you want it to be. Otherwise, it’s a natural process that is clearly poorly understood in some ways. Change (succession) is natural and necessary for diversity. It does end in mature ecosystems that are devoid of the diversity succession experiences. Luckily there are man-made and natural events that can bring things full cycle back to the beginning (or nearly so).
Anderson's study provides a framework to understand why communities mature at different rates. According to the author, "Understanding how quickly new ecological communities develop is fundamental to numerous ecological questions ranging from, 'How often should fires or clear cuts be allowed on landscapes?" to 'What determines how many species are found on an island?" yet we were unable to make many generalizations about succession rate. That is what motivated this study."

The “forever wild” clause in the creation of the Adirondack Park and various national parks has created an environment in which little change takes place and, therefore, reduced the diversity of the forested park lands owned by the state of New York and the United States. Succession has seen to it that the forest will grow to large trees that mature, die and rot where they stand or fall. The gap created by the fallen giant may make for a temporary tiny hole in the forest that undergoes some form of succession, but it’s not much on the grand scale of things. Thank goodness for the few large timber companies still operating within the Blue Line, the occasional wildfire, and the beaver, nature’s little diversity machine (chop it, dam it, flood it, abandon it once it fills in).

If you want examples, go look at the explosion of life in the forests of Yellowstone that burned in the late 80s, or at the burgeoning growth on the flanks of Mount St. Helens, or at the Hawaiian Islands once formed (and still forming) from molten rock.

When we see film of forest fires or volcanic lava and ash burying a forest, we mourn the loss of all those stately trees. We forget that in a few years time, the land will sprout anew with different species of plants and animals often far more diverse than the monoculture forest that was lost. It all takes time. And patience. Something that we humans seem to have in short supply.

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