Collision of Worlds

Online First The Local Climate

Invasive species are a problem with no easy solution, and, in my experience, are so often misunderstood by the general public, so if you’ll bear with me, I’ll start from the top.

We live in a time of unprecedented biodiversity, so much so that we clever apes have failed to identify even half of this planet’s species. The reason for this diversity of life is the diversity of available habitats – deserts, forests, grasslands, lakes, rivers and oceans, barren, swamp, heath, glacier, meadow and alpine, each molding their native flora and fauna into unique and interesting shapes by way of natural selection, over time building ecosystems which are stable, prolific and resilient.

Were it not for this diversity of habitats and the barriers separating them – mountains, oceans or inhospitable climes – we would not have our present global biodiversity. The only reason human beings evolved separately from our great ape relatives is because we became geologically and reproductively separated, forced to adapt to open savanna while they remained in trees, allowing us to become something wholly new. Separation and adversity allows one species to become two, or three, or more. Separation allowed Europe and North America to start off with many of the same species, transmuted by time and the splitting of continents into wonderfully novel worlds, the old and the new. The cedar trees of Canada’s east and west coasts can hardly be recognized as cousins, ours adapting to harsh wind by remaining short and hardy, theirs to perpetual warmth and moisture by becoming giants.

Now, if you were to take a species exquisitely adapted to one particular biological community and introduce it somewhere else, odds are it won’t do very well; take the American chestnut, native to the mixed deciduous forests of the eastern United States, and plant it on PEI, its seeds wouldn’t survive our harsh winters and so couldn’t reproduce without human intervention. Every now and again, however, a species can do well outside its native range. Take a Norway spruce or Scots pine and plant it in Nova Scotia, it’ll do just fine, perhaps complicating local ecology in ways which are difficult to appreciate, but by all appearances, innocuous. All of these – the American chestnut, Norway spruce and Scots pine – we would called “non-native” or “exotic” species, originating elsewhere, yet quietly enduring.

But of course there’s another scenario – that an introduced species is a destructive mismatch for its new home, finding an abundance of defenceless prey and few, if any, predators. It multiplies, spreads, and begins a messy conquest of native ecology, crowding out, competing with or outright assaulting resident species. When this happens, we call the species “invasive,” causing spectacular ecological or economic damage because it doesn’t belong.

Examples include the European Green crab and several species of invasive tunicate devastating Maritime bays, the smallmouth bass and chain pickerel swallowing whole the freshwater ecosystems of Nova Scotia, the European starlings flooding our skies and leaving slim pickings for our resident birds; in fact there are more European starlings in North America than there are in Europe.

A common rebuttal I hear is that the movement of species from one ecosystem to another is an entirely natural process, that it happened before human beings showed up and therefore isn’t of serious concern. First I’ll point out that, yes, species did move from one ecosystem to another without our help, but the ecosystems in question tended to be adjacent. The collision of radically different ecosystems a world apart – Asian carp invading the Great Lakes, for example – would be comically implausible without our intervention. As for the frequency of these “natural” introductions, I direct you to Hawaii, the ultimate case study.

Before the arrival of human beings to the Hawaiian archipelago 1,600 years ago, these islands were a marvel, lacking completely in mosquitoes, ants, stinging wasps, venomous snakes or venomous spiders. There were also few plants with thorns or poisons, because such hostile adaptations were largely unnecessary. It was home to as many as 145 endemic (found nowhere else) species of bird, including eagles, long-legged owls and an array of spectacular honeycreepers. In fact there were thousands of species endemic to these islands, a shining example of the evolutionary process.

In order to become a member of Hawaiian ecology, a species needed to first cross the Pacific Ocean, arrive safely, avoid potential predators, find food, find a mate who survived the same journey, and build for itself a new niche, which became harder and harder as these islands filled up. Birds, plants and insects dominated here thanks strong winds blowing them off course or driftwood carrying them with exceptional luck to these lost shores. It’s estimated a new species arrived once every thousand years, cold, hungry, disoriented and immediately subjected to the ultimate audition. For Hawaii, this was a “natural” pace of introduction, one which we sped up to the extreme.

In 400 CE, Polynesians brought pigs, rats, domestic plants and other consequential organisms which promptly wreaked havoc on the pre-existing balance, while the settlers themselves began clearing land for agriculture and hunting to extinction several species of flightless bird. Then came Europeans in 1778, setting into motion unapologetic centuries of exotic importation. Today Hawaii’s truly native species are relegated to the least hospitable stretches of the archipelago after a blitz of extinction, the majority of its landmass now held by introduced species. It’s 145 endemic birds have been reduced to 35, 24 of whom are critically endangered. We human beings broke the rules of isolation, and the natural capital of our planet dropped.

To my knowledge, we have no grasp of the “natural” rate of exotic introductions to Atlantic Canada, but I feel confident we have accelerated the process a hundred times or more. Into Halifax harbour came the Beech scale in 1890, an invasive insect which devastated the American beech tree. At this very moment the Emerald Ash Borer is raging eastward across the Maritimes while the Hemlock Woolly Adelgid comes from the south, two invasive insects killing billions of trees between them.

It might be that Maritime ecology could handle a few invasives, eventually bringing them into the fold by way of evolution, but we’ve imported too many at once, threatening an upheaval we can’t now afford.

Solutions do exist for invasive species, but they must be specific to the species in question, some intended to eradicate the invaders, other to contain them, but none will work if we do not take invasives seriously, and do everything in our power to respect the natural barriers we have so thoughtlessly overcome.

Zack Metcalfe is a freelance journalist, columnist and author active across the Maritimes.


One of countless Eastern hemlocks in the path of the invasive Hemlock Woolly Adelgid. (Zack Metcalfe photo)