So, Non-Native Plants are Good Now?

So, Non-Native Plants are Good Now?
By Sue Reed
There’s a big tempest going on these days in the world of conservation biology. I suppose a certain amount of controversy among scientists isn’t too unusual, but this one directly affects us native plant advocates, so it has gotten my attention.


Should we learn to love this sort of landscape?

Here’s the thing: a few respected biologists have recently been proposing that we should stop worrying about the question of native vs. non-native plants. Basically, their message seems to be that invasive plants are no big deal, the world is changing, and we should just get over it. Move on. Embrace what they call “novel ecosystems.” Accept the new reality.

Maybe this debate isn’t even so big, in the scope of things. Imagine questioning whether the Earth is flat or round. Do human bodies consist of four humours or something else (like maybe a hundred trillion cells)? I’m pretty sure everybody now agrees that the Earth revolves around the sun, but in 1633 poor old Galileo was convicted of heresy and placed under house arrest (for the rest of his life!) for following that damned new Copernican doctrine. You get the point. Scientific argument goes on and on, while we regular folks listen in and try to make sense of it all, until some sort of truth comes into focus.


The ferns and spring wildflowers that once grew here may not be officially extinct, but Japanese Stiltgrass has effectively taken over the entire forest floor.

So, back to the current controversy. “Recent analyses suggest that invaders do not represent a major extinction threat to most species in most environments.” So writes Mark Davis, author of Invasion Biology and one of the leading voices for this new point of view. This particular statement is from his article “Don’t Judge Species on Their Origins,” in Nature (June 2011, Vol. 474). Some respected biologists do agree with his conclusions and many disagree with him, but more on that later.

I myself am troubled by this “non-natives are no big deal” message, for several reasons.

First, the authors of this literature frequently use the terms “non-native” and “invasive” interchangeably. In paraphrasing their message just above, I did it too. Did you notice? Well, we all know that this is wrong. So when Mark Davis begins his article by writing, “Over the past few decades, ‘non-native’ species have been vilified for driving beloved ‘native’ species to extinction,” he’s mis-stating the issue, right at the start. Worse, by implying that all non-native plants are necessarily invasive, he’s misinforming the public.

Here’s my second concern: why focus on extinction as the only evidence of harm? New data may well show that “extinctions due to competition” are rare, but, really, extinction isn’t the big problem for most of the world. The big issues are species displacement, loss of biological complexity and a weakened food web. Even without evidence of lots of extinctions (and I suspect that with further study we will discover more losses than are evident now), non-native species can powerfully diminish the vitality and resilience of any landscape.


Who's got the upper hand here... the native blue-flag or the European yellow iris?


They say invasive species help heal the planet. Did this riverbank ecosystem need any help before the multiflora rose thicket took over?

A third problem involves media coverage. This idea is getting a lot of attention in the form of reviews, op-eds and blogs that extract and condense their message from scientific literature that originally contained numerous caveats and exceptions. Unfortunately, much of this subtle detail is getting lost along the way. What most people hear, as a result, is that we really don’t need to be so concerned about non-natives. For some, especially those who are predisposed to automatically dismiss all environmental concerns, this message can so easily translate into not being concerned at all. The true message is increasingly getting blurred and lost to the public.


A little-known dispersal vector: holiday decorations.

I say this as a member of the public myself. For quite a while now, I’ve been hearing about these guys who preach that invasive plants are good. Whaat?! I suppose I’m as likely as the next person to cling to my cherished beliefs, but I’m chagrined to admit that, in my knee-jerk reaction against these “invasive-plant lovers,” I’ve waited until now to explore their facts. And, as it turns out, the message I’ve gotten is not accurate. Despite their sometimes rather extreme language, what I’ve discovered is that these scientists are trying to convey a more nuanced message: the native-alien story is more complex than we’ve thought, and in the face of new data we all ought to look at the situation objectively, without attachment to familiar dogma.

Now, I’m fairly well informed about plants and landscape design, but I know I’m not qualified to evaluate their data. So at times like this I look to other authorities to guide me. At a recent conference that I attended, Doug Tallamy (entomologist and author of Bringing Nature Home) helped me out: he listed the current arguments in favor of re-thinking non-native plants, and he then proceeded to discredit all of these points with his usual clarity and quiet certainty backed up by simple facts. When he spoke, I sat up and noticed. His is a voice I trust.


Purple Trillium at the base of a Musclewood tree: who needs 'em?

Which brings me to trouble number four: respected experts who dispute the conclusions reached by Mark Davis and his colleagues don’t get much media coverage. Is this just the media’s natural tendency to focus on the new and controversial? Perhaps.

Here’s Mr. Davis again, instructing us: “It is time for scientists, land managers and policy makers to ditch this preoccupation with the native-alien dichotomy and embrace more dynamic and pragmatic approaches to the conservation and management of species – approaches better-suited to our fast-changing planet.” With some trepidation, I wonder out loud: does this new, less-gentle and less kind point of view represent an attitude that’s becoming more prevalent in society as a whole? Maybe, maybe not. But how different his tone is from Doug Tallamy’s: “You can be indifferent about non-natives onlyif you don’t understand, and even love, the complexity and necessity of the ecosystems being displaced.”

So, with due respect for those who propose a new way of thinking about non-native species, I’ll continue to believe as I have up until now: that we need to be careful of the Earth and protect it from our hubris and mistakes. To do this, I will still give preferential treatment to native plants, and avoid using non-natives if possible, in every situation. And, as an advocate for rich, diverse and healthy landscapes everywhere, I will also keep my eyes and mind open, to see what kind of truth eventually emerges from the current controversy.