Invasive Plants, Are They Really That Bad?

Garlic mustard (Alliaria petiolata), an European herb, is one of the most sought-after "villains" on the East Coast of the U.S. 

Some people when first faced with the overwhelming task of removing invasive plants get an internal twinge of suspicion about the true effectiveness of such an enterprise. A sense of questioning rises within you. That's when you ask yourself skeptical questions like, is this right? Are we ever gonna win this battle? Don't these plants come back like crazy a month or less after you remove them? Is this gardening, or, restoration? Does this make any sense? Even when you know you are doing something that is supposed to be right you can't really help wondering. Well, at least I did, and still do...

I'm not going to say that invasive species are not a problem because it is clear that some nonnative species have really become invasive and caused enormous ecological and economical damages. But, it is also clear that they are a minority of all the introduced species. All I'm trying to do here is just bring up the other side of the story, and foster some critical thinking. There's a very interesting "counter-invasion biology school of thought" going on that is refuting the lack of scientific substance of many of the claims insisted on by invasion biologists and conservationists for at least the last two decades. These invasion biology mavericks are not some senseless fools, they are renowned scientists that really know what they are talking about. They just want to bring back disinterested science to the table and steer away from the black and white assumptions predominant in the invasion biology world.

Last year I attended an interesting symposium at the Annual Meeting of the AAA here in DC, that's when I first heard of Mark Davis (Macalester College, Saint Paul, Minnesota). Davis is one of the main critics of invasion biology, I thought his lecture had really good points and he didn't reduce his speech to accusatory "invasion biologists are Nazis", like other opponents do. Since then, I've been reading some of his stuff, and, I'm really liking it, I think his assertions are genuinely science-based! The bias of some invasive species people is sometimes preposterous, from biologist with high academic credentials to the go native gardeners and backyard weed pullers. One of Davis' main points is that the negative impacts of invasive species have been largely overgeneralized and exaggerated. He also points out that ecosystems change,thus, we are witnessing rapidly changing ecosystems and not necessarily ecosystems "harmed" by invasive species as it is often claimed without any scientific evidence. The highly subjective and value-based premise that all nonnatives are bad and natives are good is also anything but scientific. Unfortunately an awful lot of people take that stance very literally and all too often with a zeal that borders on fanaticism. Native species like the Pine bark beetle or the Colorado potato beetle have become invasive and caused a lot of trouble, according to Davis. Also think about the abundant Poison ivy here on the east coast, so loved by birds and so hated by many people even knowing that it is a native species. At the end they are all species, they are nature, some are old locals and others are newcomers.

Wineberry (Rubus phoenicolasius) is an Asian shrub whose edible raspberries are heavily dispersed by birds and mammals. It is considered invasive in the north half of the East Coast of the U.S.  

 So, the question is: have we gone too far? Are we being eco-bigots? Whether in the tropical forests or the temperate woodlands of North America many conservationists feel strongly about our pristine, pre-colonial ecosystems and the natural heritage represented by what we call native species. That's fine and we should definitely encourage the use of native plants for landscaping and restoration. But, are we gonna be able to bring ecosystems back to what they were 70, 100, 300 or 600 years ago? Are we really going to be able to reverse the course of the seemingly fast expanding novel ecosystems by pulling invasive plants?  Are we gonna be able to create invasive species-free ecosystems? I really don't think so.  

Another important question is: Do we want to protect species diversity or ecosystem services? Perhaps, many ecosystems are disturbed enough and are so deeply modified that they have reached a point of no return. Maybe we should just leave the highly adaptable invasive species alone in those places and let them provide important ecosystems services such as carbon sequestration, reduction of heat island effect in the cities, etc. We are, without a doubt, facing novel ecosystems here --well, at least in the DC area. These are ecosystems with a significant component of nonnative species. Rather than being the game changers, invasive species are moving in to fill in new niches and to take advantage of habitat conditions that have occurred as a result of a greater change. Climate change, for instance, is modifying habitats and shifting species distributions altitudinally and latitudinally and at anastonishingly fast pace. Also, changes in the nitrogen cycle around the globe are modifying aquatic and terrestrial ecosystems in extremely complex ways, perhaps faster than we can humanely understand.

At my work I still do invasive plant management work, but after reading about new opinions, scientific evidence and other perspectives I have a different mindset. Now I look at invasives with different eyes and have even taken some management decisions along the lines of refocusing and prioritizing on what's really harmful. Or at least on the worst actors where there is some sort of evidence of their real environmental impacts, not just based on their nativity. I think that the field of invasion biology will change in the next decade or so, not only that, even the discipline of ecological restoration will change since it is based on bringing back ecosystems to that 'historical natural stage' which is, veritably, determined by us and our values.

I have to admit, the loss of our native species will always be something worrisome and frankly sad for many of us, but in some instances it responds to extremely complex factors that we might not even be able to tackle. But people should at least listen to other opinions and leave the religious-like vehemence and subjectivity to the chapels and art studios. New research and fresh brains working in these fields will bring some adaptive change to redirect the scarce resources available into more sound and realistic conservation and restoration actions.

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