So much has been said and written about climate change and global warming that there’s not much I can add that hasn’t already been covered. However, personally, I’ve failed to see much attention given to the global impact of all the exotic and invasive species that have been relocated and introduced into ecosystems, thousands of miles from their home range.
This planet has experienced many climate changes over its lifetime, ranging from uninhabitable to tropical to ice ages. Species have appeared, prospered and then disappeared when climates adversely changed. So in many ways what we’re witnessing now isn’t all that new, albeit fodder for debate. What is new is the rapid global relocation of so many species, thanks to a globally mobile economy that results in a potential witches brew of assorted alien species to be leapfrogged all over the planet.
Last week this column covered the many new invasive insects that are threatening to decimate many of our indigenous tree species that comprise the majority of our nation’s forests. We already know the impact exotic species can have on their new ecosystems, thanks to what has occurred in the Great Lakes and the Mississippi River system where exotics have gained firm footholds and are negatively impacting indigenous species. But with the accelerated pace of alien introductions, what will be the long and short term impacts on our outdoor ecosystems? With few or no natural enemies present in their new environment, alien species normally thrive, at the expense of the indigenous ones.
And while we may be concerned over climate changes that could negatively impact us and our accustomed environment, few seem to also consider the potential damages that are resulting from literally tens of thousands of area-specific species being relocated all over the globe. The domino effect of this “alienation of environments” could be just as damaging as climate change, by affecting agriculture, public health and the abilities of the areas’ natural ecosystems to sustain themselves. Recent studies by the Environmental Protection Agency show that as the Earth's climate heats up, invasive species will hold the advantage over native plant species in spreading across the countryside.
A Princeton University study concluded that in many cases, a warming climate will provide more welcoming conditions for invasive plants to get a foothold, spread quickly and crowd out native species. Of course not all our alien species are recent arrivals. Many have been here since European settlers spread across the continent and nonnative weeds and plants followed them, sometimes literally. Even one of the West's most famous symbols, the tumbleweed (also known as Russian thistle) isn't a native plant. It was brought from Russia generations ago. In addition to the large variety of alien flora, many of our more common fauna came from other parts of the planet -- pigeons, English sparrows, startlings, black and Norway rats, feral hogs, burros and horses, gypsy moths, and several other long-term non-native species.
Although some non-native fauna species are less destructive than others, precious few have demeaning characteristics, ecosystem-wise. Feral hogs, for example, are now estimated to number more than 52 million nationally, and their destructive impact on native and agricultural environments and ecosystems is alarming. A breeding age sow can produce1,000-plus feral swine in just a 5 year period. They degrade wildlife habitat and private property, compete with native wildlife for food, and can pose a threat to humans, pets and domestic livestock through the spread of diseases such as swine brucellosis, pseudo-rabies, trichinosis and leptospirosis.. Their rooting and wallowing accelerates erosion, destroys emerging flora and helps contaminate watersheds.
But the single largest and expanding threat is habitat destruction caused by human actions, and that includes introduction of alien species that destroy native habitat. No species can continue to exist when its ecosystem—its very home—is destroyed. There are between 5 and 40 million species alive today. Approximately 1.7 million have been identified and cataloged. We know that millions of unidentified species also still exist. No one is certain of how many. So what happens to the earth’s various ecosystems when species from one part of the planet get relocated to another ecosystem thousands of miles away? Obviously there’s an impact …usually a negative one
A good example is purple loosestrife, a herbaceous perennial of Eurasian origin that became established in the estuaries of northeastern North America by the early 1800's. Loosestrife's strong competition with and replacement of other, more desirable aquatic emergents has led to a decline in wildlife food and cover values in many wetlands of our nation, including New York. Nothing will eat it and annually cutting or burning will not permanently remove it
In the late 1950's, a large percentage of 23 small wetland impoundments that had been created in the lower Hudson area of New York had become almost pure stands of purple loosestrife. As of 1980, these stands were still more or less unchanged. In 1956, several years of experimental control of purple loosestrife on the Howland Island Game Management Area in central New York was undertaken. Working in the same area about 20 years later, proposed water level manipulations (to enhance waterfowl habitat) had been hindered because of the threat of continued purple loosestrife infestation. So basically many of our once productive wetlands that supported a variety of fauna are gone, thanks to an alien species.
Now that studies indicate climate change will generally be more beneficial to invasive species than native species, the combination of the two seem to hint very strongly this old earth could again be entering a major extinction episode with unknown global consequences.