Invader, Pioneer, a Bit of Both?

Invader, Pioneer, a Bit of Both?    —by Jinny Batterson

Over a decade ago, I was introduced to the notion of “invasive species.”  My ecologically minded sister got me involved in an effort to reduce the spread of a plant by the popular name of “garlic mustard” in a state park near the Maryland home where we both grew up. This plant, with the scientific name Alliaria petiolata, was introduced from Europe as a kitchen and medicinal herb during the 19th century. Over time, it naturalized and began to crowd out more established plants in temperate woodlands in the eastern U.S., where the natural controls that kept garlic mustard in check in its native range were missing. My sister for several years helped organize a spring event to uproot the shoots of the biennial plant so that the native understory plants it was outstripping would have a better chance for survival. Prizes were given for the heaviest quantities of mustard harvested; area amateur and professional chefs were enlisted to compete at serving up their best recipes using the somewhat tasty, if overreaching, plant. 

I’ve not been back to the Maryland park recently, so I don’t know whether garlic mustard is on the wane.  Where I now live in North Carolina, the most visible invasive plant is kudzu (Pueraria lobata), the “plant that ate the South.”  This legume native to Asia was first used in the U.S. as a source of livestock forage. More widely propagated during the 1930’s for erosion control, kudzu has since invaded vast stretches of untended land, choking trees, fouling utility lines, overgrowing abandoned structures and vehicles. Under favorable conditions, a kudzu vine can grow up to 60 feet in a single season. Control and mitigation efforts related to invasive species such as kudzu cost an estimated $137 billion in the U.S. each year.

Classifying a species as invasive can be complicated. Both English ivy (Hedera helix), another imported ground cover, and the Norway maple (Acer platanoides), which graced my grandmother’s front yard and provided shade and climbing branches when I was a kid, are considered invasive in some U.S. localities. On a recent visit to New Zealand, I learned that a tree native to the western U.S., the Lodgepole pine (Pinus contorta), has become a serious invasive threat in parts of New Zealand’s South Island. What distinguishes a species as invasive has to do with the characteristics of the invader, along with the resilience, hardiness, and biodiversity of the ecosystems into which the new species is inserted.   

In a biology course I took in school, I was also introduced to the concept of “pioneer species.”  These are generally defined as the earliest plants to colonize a previously barren landscape, or a landscape that has suffered a catastrophic event such as a forest fire or volcanic eruption. Pioneer plants (and later, animals) are the earliest of a succession of species that eventually combine to form a more stable, mature, diverse ecosystem.

We humans have traveled increasing distances at increasing speeds. We’ve often brought colonies of other species in our wake, either intentionally or unintentionally. Even as we marvel at the regenerative capacity of damaged ecosystems, we’ve continued to upset the ecological balance of previously more stable ones. At present, we probably constitute our planet’s premier invasive species. Absent a catastrophic die-off of humans (which I would prefer not happen), what can we do to reduce our impact? 

We can learn to be more careful of the “exotics” we are tempted to introduce where they previously did not grow. We can be conscientious about observing quarantine and decontamination restrictions. We can relearn more of the qualities of pioneers—ability to withstand hardships, adaptability, wise use of available resources. We can realize that all natural systems eventually reach new balances. We can remind ourselves frequently that, whatever our engineering or innovative prowess, we remain imbedded in an ever evolving natural world.

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