Last week was National Invasive Species Week, noted by our friends at Beautiful Wildlife Garden and also at this post at Andrew Revkin's New York Times DotEarth blog. And honestly, I thought enlightened gardener agreed. I thought we welcomed both well-behaved natives and exotic plants, and we'd deal sternly with invasive exotics. When exotics spread into the wild, they displace natives, offering less optional habitat for native bugs, which are preferred by native birds and so on up the food chain.
Then I came across this post on Garden Rant (one of my favorite garden blogs, actually), where Amy Stewart interviews Jeff Gillman about his new book. Amy started the interview with this summary/quote from Jeff's book:
You quoted someone as saying that no plant species in the United States has ever been driven to extinction by an invasive plant.
And Jeff proceeds to explain that we're lacking data.
Well, if a plant is doing well in a location then the perception is that it is pushing other plants out. If we see what appears to be a monoculture of what we know to be an alien plant then we tend to just assume that plant is displacing natives – often without much data.
And he continues to bemoan the fact that we really don't have enough data. The ecosystem is disturbed, but we don't know what that really means.
Thinking of the problem with pampas grass we have in California -- it's costing tax payers a pretty penny, here are some articles -- I almost left a snide comment on the post. "Interesting, but hardly relevant". But I did not. Instead, let me pose some questions:
- How can we know which plants have been driven to extinction? The statement that "no single plant species has been pushed to extinction by invasive plants" should be, instead, we cannot scientifically prove that a species has been pushed to extinction. The first settlers did not keep careful records? Yep. we lack data, but that doesn't mean it hasn't happened. And it certainly doesn't mean it can't happen soon. Is the only acceptable proof that a species has gone extinct? Doesn't close enough count?
- Can a one-dimensional analysis fit a system? The whole thread of the interview, with its emphasis on SCIENCE and DATA reminded me a lot of the scientific studies about nutrition that Michael Pollen so eloquently disassembles in his book In Defense of Food. In my mind, California meadows as they once were have been driven to extinction by non-native grasses (and also by food crops, and suburban developments).
- Do you really think the battle is plant against plant? Dare I say American chestnut? Sure, the European chestnut has not driven out the American chestnut, it just so happened that the fungus that drove them out came from the European chestnut. It's also highly likely that the Sudden Oak Death fungus California oaks are succumbing to in alarming numbers came in with shipments of rhododendron from China, and that the oaks are more susceptible because of the invasive annual grasses surrounding them that hold water differently than native bunch grasses.
Here's how the interview ends:
AMY: And yet, as you point out in the book, it continues to be an ecosystem that functions in some way. I mean, England is obviously capable of supporting life -- plant life, human life, animal life.
JEFF: But what they have is completely different from what they would have had if humans had never entered the scene. Nature has a way of finding its own balance. New plants change the balance, but that doesn’t mean that the balance ceases to exist.
And sure, England is capable of supporting life, but a limited palette. A diverse ecosystem is, for many reasons, preferable to an ecosystem with a limited number of species. For me, it's been a revelation and a joy to come from the quite impoverished ecosystems in Europe to much richer systems in America. I've truly enjoyed the wild places that still exist here. And I don't believe nature is in balance if high percentages of native plants (such as the native oaks) are dying. I applaud nurseries that do not sell invasive species, and I wish the government did more to prevent their import and sale.
I still believe that as gardeners, we can make things worse if we plant invasives. And I believe that we can make a difference for the better if use a diverse plant palette, if we include well-behaved exotics and natives, if we care.