All things come to those who wait … unfortunately
Hidden in the soil beneath our feet is a ?seed bank,? a zillion-plus seeds deposited by plants that have flowered this year, last year … and years and decades before that. The older seeds haven?t germinated yet; they?re waiting to sense that conditions are right ? that they won?t be shaded out, dried out, or out-competed for nutrients.
And so they remain in suspended animation, barely ?breathing,? waiting.
Some are waiting for an indication that something drastic has happened in the world above ? a flood, windstorm or fire. Some sort of disturbance creating an opening in which to grow.
Roads are disturbances par excellence, and roadsides abound with ?disturbance species? ? moth mullein (whose seed capsules look like small brown marbles), woolly mullein, star thistle; all have yellow flowers, all are common along our roads.
Our planet is home to myriad species that provide food and shelter, medicine and delight. As genes mutate and nature selects which combinations of genes will survive, new species appear, and others go extinct.
One of the prime forces driving plants and animals into extinction is the invasion of their habitat by nonnative species ? plants and animals from other parts of the world taking up residence here (and, to be fair, plants and animals from here taking up residence in other parts of the world).
Plants have evolved wondrous ways of getting animals to haul their seeds about ? the invention of Velcro was inspired by the seed-burs that grasp an animal?s fur (or a hiker?s socks) and don?t let go.
Today?s transportation has amplified these means of dispersal.
Carried in the feed hay and feces of livestock or in the mud on cars, trucks, logging equipment and off-road vehicles, plants send their seeds to other parts of the state, the continent, the world. Deposited in the seed bank, they wait, days or years or decades for a disturbance.
Today?s ever-larger, ever-hotter forest fires stem from the way we?ve managed our forests, from the suppression of fire (which allows fuel to buildup), to the way we?ve harvested trees (taking the large, fire-resistant, trees and leaving the smaller ones, along with the shrubs and slash that can both kindle a fire and carry it through the woods).
Building fire-breaks and setting ?prescribed burns? seem logical responses, and, in some cases, they are. But at the annual meeting of the Ecological Society of America in Tucson. Ariz., this month, one researcher after another demonstrated how nature is never as simple as we might naively imagine.
To an invasive species, a fire-break looks a lot like a road ? a means of penetrating deep into the forest. And a prescribed burn could be just the sort of disturbance an invader?s seeds have been waiting for.
Many of our invaders are new arrivals from the Old World, where they?ve been evolving with humans for tens, even hundreds of thousands of years longer than have plants of the New World. They are survivors of intense selection, a process that included frequent fires, employed to replace shrubs with more-nutritious grasses.
Having evolved with frequent fire, the invaders can actually change the ecology ? the set of interrelationships ? of the site they?ve invaded. Drying out faster than the perennials they?ve replaced, the newcomers are a wildfire waiting to happen. Many western plants, such as sagebrush, have evolved with fire, but not such frequent fire. Once the process starts, it?s hard to stop and, all too often, the result is extinction.
Alan Stahler trained as a biologist and is a local amateur astronomer.
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