Grey clouds hang off the sky like a wet overcoat dripping more water onto the already saturated world, the drip-drop drip-drop of beads of rainwater forming and falling off the deep oxygenated green of the mosses, grasses, herbaceous shrubs and trees; the every magnificently green hills and hollers of central Tennessee.
Greenest state in the land of the free…
Nature is more than a visionary experience. It fills all the senses, from the cold jolt of a raindrop on ones head to the shades of green contrasting with the grey of the sky massaging the rods and cones of the eyeball to the heady scent of the privet in bloom, vicious invasive plant that it is, the nose can hardly face reason, that this plant should be eradicated from the landscape, when it offers such a seductive appeal to the olfactory senses. Who are we humans to be the judge of what should live or die when the process of natural selection, fitness in biological terms, has already asserted that this privet (Ligustrum sinensis) is a survivor, a thriver, a builder of empires in any temperate landscape it invades?
Or do we have a right, a responsibility to destroy all that is invasive, alien, not of this place? Is some fanatical racism at hand telling us that this illegal immigrant of a plant, brought over solely for the utilitarian purpose of landscaping the unnatural assault on nature that we call a lawn, has gotten out of hand when it left the manicured artificial habitat of city lots, escaping into the countryside and surrounding woods to compete and destroy any chance of life for our native population of similar shrubs and small trees?
I have spent summers employed by the Federal gov’ment walking through woods with loppers, machete, and brush blade cutting this privet then applying a lethal dose of Garlon, a vile smelling poison, the vapors of which burn as if they would eat away the lining of the nasal cavity, all in an effort to ensure that particular plant would never more raise a leafy green arm toward the sky. Usually the application worked, nut often it didn’t. Weeks later little sprouts would spring up from the base of the plant I had meant to kill but in actuality had only severely pruned.
What does it mean when a plant or an animal creeping in from some other local, or a race of people moves in and outcompetes native populations? In a not so veiled metaphor, what would it mean if the privet moved in and outcompeted the bush honeysuckle, itself an invasive shrub, to the point that the bush honeysuckle disappeared under the assault of the new invader?
There is a philosophy to be found in botany, a philosophy of what grows where and why it is there. There are questions to answer regarding what plants should be fought for and preserved and which ones should be left to the forces of fate to slip quietly into extinction, having left a dead end in the evolutionary line, not through any lack of adaption to the landscape but through an inherent weakness in the DNA that Nature so specifically chose for that plant to pass on through hundreds of thousands, perhaps millions of generations.
All these musings lead me to an observation at once perfectly sensible and utterly contradictory. In Nature that which is too highly specialized is often the most susceptible to extinction. To give an example, there is the star orchid (Angraecum sesquipedale) in the Amazon whose corolla tube is so long that when the plant was first discovered Charles Darwin predicted that a moth would eventually be discovered with a proboscis of sufficient length to pollinate the plant. It would likely be the only creature on Earth that could perform this service. Several years later a moth was discovered that fit this description, and was fittingly named Darwin’s hawk moth (Xanthopan morgani praedicta). Study found that this moth with the twenty-five centimeter proboscis was the only pollinator for the star orchid and the plant was the only nourishment sought out by the moth. For millennia the co-evolutionary arrangement has worked. But if for some unforeseen the reason, be it a peculiar disease or loss of habitat, the moth or the orchid should become extinct the other would soon follow.
Now for an example of specialization keeping a plant from fading into the oblivion of the millions of species that have come before but are no more. The cedar glades of central Tennessee are harsh landscapes where standing water can be present from December through March or April, followed by a few weeks of pleasant dampness. During this period of April and May the cedar glades burst with color as prairie larkspur, glade mustard, Nashville breadroot, Sunnybells, glade sandwort, and Pyne’s groundplum, push forth an explosion of color in the age old story of growth, flowering, seed production, then decay. By the middle of June the sun had dried up all water and the glades are dry as a bone, the mud between the limestone hardened like a brick. The flowering plants of a few weeks ago have withered and blown away leaving only a hopeful seedbank as a as yet unfulfilled promise of continuation next year. In their place are poverty grass and little bluestem grass, thinly leaved angiosperms such as Gattinger’s prairie clover and the thorny prickly pear cactus.
Hardly any exotics encroach onto this landscape. The promise that the glade will continue indefinitely into the future seems assured as long as no developer comes along and pours an asphalt parking lot on top of it. Since the glades have been recognized as unique habitats and gained some protection from state and federal governments the only serious threat of utter annihilation has come from the flooding of the Percy Priest Dam in the late 1960’s when the waters of the Stones River backed up over thousands of square acres of pristine habitat in the heart of glade country. But for the efforts of a few botanists the Tennessee coneflower (Echinacea tennesseensis) would have likely been lost in the name of civic water supply and recreational opportunities for boaters.
Is saving one rare, endemic wildflower worth scraping plans for a dam that will benefit many more people than would ever care to walk out in the hot landscape to look at a rather scraggly plant? The answer to that is above my paygrade. But in defense of saving plants and their habitats, an array of medicinal benefits have been garnered from members of the genus Echinacea.
As for the privet, it stops dead in it’s tracks at the edge of the glades, as if unable to take that one step each year, that, when multiplied by increments each year, would allow it to colonize the glades. The privet can’t quite master the landscape enough to enter it, much less work incrementally toward colonizing it. Instead it stands on the unmoving fringe, competing with the native privet (Forysteria lugustrina) and the redcedars and the winged elm. But they too have mastered this environment at the edge of adversity. And in doing so they have stopped the invader in its tracks. Adversity leads to diversity.
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