Learning Lessons from Invaded Forests

In 1946, North American beavers were introduced to the archipelago of Tierra del Fuego at the tip of South America in an attempt to start an industry based on beaver fur. Although this industry has not thrived, beavers have multiplied enormously. By cutting trees and building dams, they have transformed forests into meadows and also fostered the spread of introduced ground cover plants. Now numbering in the tens of thousands in both Chilean and Argentinian parts of the archipelago, beavers are the target of a binational campaign to prevent them from spreading to the mainland of these two nations. — Invasive Species: What Everyone Should Know by Daniel Simberloff

Beavers in South America are just one example of the series of effects a species can have when it is placed in a new environment. Prior to the arrival of beavers, there were no species in the area that were functionally equivalent. Thus, through their felling of trees and damning of streams, the beavers introduced novel disturbances that have, among other things, aided the spread of non-native plant species. Ecologists call this an invasional meltdown, wherein invasion by one organism aids the invasion of another, making restoration that much more difficult.

Complicated interactions like this are explored by David Wardle and Duane Peltzer in a paper published last month in Biological Invasions. Organisms from all walks of life have been introduced to forests around the world, and while many introductions have had no discernable impact, others have had significant effects both above and below ground.

The authors selected forest ecosystems for their investigation because “the imprint of different invaders on long-lived tree species can often be observed directly,” even when the invading organisms are doing their work below ground. Moreover, a greater understanding of “the causes and consequences of invasions is essential for reliably predicting large-scale and long-term changes” in forest ecosystems. Forests do not regenerate quickly, so protecting them from major disturbances is important. Learning how forests respond to invasions can teach us how best to address the situation when it occurs.

The authors begin by introducing the various groups of organisms that invade forests and the potential impacts they can have. This is summarized in the graphic below. One main takeaway is that the effects of introduced species vary dramatically depending on their specific attributes or traits and where they fall within the food chain. If, like the beaver, a novel trait is introduced, “interactions between the various aboveground and belowground components, and ultimately the functioning of the ecosystem” can be significantly altered.

Wardle, D.A., and D.A. Peltzer. Impacts of invasive biota in forest ecosystems in an aboveground-belowground context. Biological Invasions (2017).  doi:10.1007/s10530-017-1372-x

After highlighting some of the impacts that invasive species can have above and below ground, the authors discuss basic tenets of invasion biology as they relate to forest ecosystems. Certain ecosystems are more vulnerable to invasions than others, and it is important to understand why. One hypothesis is that ecosystems with a high level of species diversity are more resistant to invasion than those with low species diversity. This is called biotic resistance.  When it comes to introduced plants, soil properties and other environmental factors come in to play. One species of plant may be highly invasive in one forested ecosystem, but completely unsuccessful in another. The combination of factors that help determine this are worth further exploration.

When it comes to restoring invaded forests, simply eliminating invasive species is not always enough. Because of the ecological impacts they can have above and below ground, “invader legacy effects” may persist. As the authors write, this requires “additional interventions to reduce or remove [an invader’s] legacy.” Care also has to be taken to avoid secondary invasions, because as one invasive species is removed another can take its place.

Nitrogen-fixing plants (which, as the authors explain, “feature disproportionately in invasive floras”) offer a prime example of invader legacy effects. Introducing them to forest ecosystems that lack plants with nitrogen fixing capabilities “leads to substantially greater inputs of nitrogen … and enhanced soil fertility.” Native organisms – decomposer and producer alike – are affected. Simply removing the nitrogen fixing plants does not at once remove the legacy they have left. Examples include Morella faya invasions of forest understories in Hawaii and invasions by Acacia species in South Africa and beyond.

“It has been shown that co-invasion by earthworms enhances the effects that the invasive nitrogen fixing shrub Morella faya has on nitrogen accretion and cycling in a Hawaiian forest, by enhancing burial of nitrogen-rich litter.” – D.A. Wardle and D.A. Peltzer (2017) – photo credit: wikimedia commons

The authors conclude with a list of “unresolved issues” for future research. A common theme among at least a couple of their issues is the need for observing invasive species and invaded environments over a long period. Impacts of invasive species tend to “vary across both time and space,” and it is important to be able to predict “whether impacts are likely to amplify or dampen over time.” In short, “focus should shift from resolving the effects of individual invasive species to a broader consideration of their longer term ecosystem effects.”

This paper does not introduce new findings, but it is a decent overview of invasion biology and is worth reading if you are interested in familiarizing yourself with some of the general concepts and hypotheses. It’s also open access, which is a plus. One thing that is clear after reading this is that despite our growing awareness of the impacts of invasive species, there is still much to be learned, particularly regarding how best to respond to them.

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Eating the Invasives

Happy National Invasive Species Awareness Week! It’s a fine time to get educated about invasive species, and perhaps even play a role in mitigating them. Opportunities for getting involved are myriad and include volunteering with local conservation groups, replacing invasive plants in your yard with non-invasive alternatives, and being mindful when you visit natural areas not to bring along weed seeds and other pests and diseases. Another strategy in the battle against invasive species is to eat them, which is precisely what I plan on doing. If you are interested in doing the same, this revised post (originally published in November 2013) will help get you started.

Invasivore: One Who Consumes Invasive Species

Invasive species are a major ecological concern, and considerable effort is spent controlling them. The ultimate goal  – albeit a lofty one in many cases – is to eradicate them and to prevent future outbreaks. The term “invasive species” describes plants, animals, and microorganisms that have been intentionally or unintentionally introduced into an environment outside of their native range. They are “invasive” because they have established themselves and are causing adverse effects in their non-native habitats. Some introduced species cause no discernible adverse effects and so are not considered invasive. Species that are native to a specific habitat and exhibit adverse effects following a disturbance can also be considered invasive. (White-tailed deer are an example of this in areas where human activity and development have reduced or eliminated their natural predators resulting in considerably larger deer populations than would otherwise be expected.) Defining and describing invasive species is a challenging task, and so it will continue to be a topic of debate among ecologists and conservation biologists for the foreseeable future.

The adverse effects of invasive species are also not always straightforward. Typical examples include outcompeting native flora and fauna, disrupting nutrient cycles, shifting the functions of ecosystems, altering fire regimes, and causing genetic pollution. Countless hours of research and observation are required in order to determine the real effects of invaders. The cases are too numerous and the details are too extensive to explore in this post; however, I’m sure I will cover this topic more thoroughly in the future.

There are many approaches to eradicating invasive species, but one fairly unconventional method is to simply eat them. Why not, right? Historically, the voracious appetite of humans has helped drive several species to extinction, so why not employ our stomachs in the removal of introduced species from their non-native habitats? The folks at Invasivore are suggesting just that. By encouraging people to consume invasive species, they are also promoting awareness about them – an awareness they hope “will lead to decreasing the impacts of invasive species by preventing introductions, reducing spread, and encouraging informed management policies.”

“If you can’t beat ’em, eat ’em!” And so they provide recipes in order to encourage people to harvest, prepare, and consume the invasive species in their areas. Some of the invasive plant species they recommend eating are Autumn Olive (Autumn Olive Jam), garlic mustard (Garlic Mustard Ice Cream), Japanese honeysuckle (Honeysuckle Simple Syrup), purslane (Purslane Relish), and Canada goldenrod (Strawberry-Goldenrod Pesto). And that’s just a sampling. One might ask if we are encouraged to eat invasive species and ultimately find them palatable, won’t our demand result in the increased production of these species? The Invasivores have considered this, and that is why their ultimate goal is raising awareness about the deleterious effects of invasive species. In the end, we should expect to see our native habitats restored. Our craving for Burdock Chips on the other hand will have to be satisfied by some other means.

lonicera japonica

Japanese honeysuckle (Lonicera japonica) – photo credit: wikimedia commons

More about eating invasive species:

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What are you doing to celebrate National Invasive Species Awareness Week? Let us know in the comment section below.

What Shall We Do About Invasive Species?

I think about invasive species a lot. This blog doesn’t really reflect that though. I have been avoiding a deep dive into the subject mainly because there is so much to say about it and I don’t really want this to become “the invasive species blog.” Admittedly, I’m also trying to avoid controversy. Some people have very strong opinions about invasive species, and I don’t always agree. But then an article entitled Taking the long view on the ecological effects of plant invasions appeared in the June 2015 issue of American Journal of Botany. Intrigued by the idea of “taking the long view,” I read the article and decided that now is as good a time as any to start exploring this topic in greater depth.

However, before getting into the article, we should define our terms. “Invasive species” is often used inappropriately to refer to any species that is found outside of its historic native range (i.e. the area in which it evolved to its present form). More appropriate terms for such species are “introduced,” “alien,” “exotic,” “non-native,” and “nonindigenous.” The legal definition of an invasive species (according to the US government) is “an alien species that does or is likely to cause economic or environmental harm or harm to human health.” Even though this definition specifically refers to “alien species,” it is possible for native species to behave invasively.

These terms refer not just to plants but to all living organisms. The term “noxious weed,” on the other hand, is specific to plants. A noxious weed is a plant species that has been designated by a Federal, State, or county government as “injurious to public health, agriculture, recreation, wildlife, or property.” A “weed” is simply a plant that, from a human perspective, is growing in the wrong place, and any plant at any point could be determined to be a weed if a human says so. (I’ll have more to say about human arrogance later in the post.)

Rush skeletonweed (Chondrilla juncea) - labeled a noxious weed in Idaho

Rush skeletonweed (Chondrilla juncea) – labeled a noxious weed in Idaho

The authors of the AJB article (S. Luke Flory and Carla M. D’Antonio) begin by clarifying that “most introduced species are not problematic.” Those that are, however, can “cause significant ecological and economic damage.” This damage is well documented, and it is the reason why billions of dollars are spent every year in the battle against invasive species. But there is a dearth in our research: “less is known about how ecological effects of invasions change over time.” The effects of invasive species could “increase, decrease, or be maintained over decades,” and “multiple community and ecosystem factors” will determine this. For this reason, the authors are calling for “concentrated efforts to quantify the ecological effects of plant invasions over time and the mechanisms that underlie shifting dynamics and impacts.” Armed with this kind of information, managers can better direct their efforts towards invasive species determined to be “the most problematic.”

The authors go on to briefly explain with examples why an invasive species population may decline or be maintained over time, highlighting selected research that demonstrates these phenomena. Research must continue with the aim of improving our understanding of the long term effects of plant invasions. The authors acknowledge that this “will require carefully designed experiments,” “patient and persistent research efforts,” and significant amounts of money. However, they are convinced that through a widespread collaborative effort it can be done. They encourage researchers to deposit data obtained from their research in open source online repositories so that future meta-analyses can be conducted. The information available in these online repositories can be used to develop management plans and help predict “future problematic invasions.”

Considering the amount of time and resources currently spent on confronting invasive species, the approach proposed by the authors of this article is quite reasonable. It seems absurd to continue to battle a problematic species that will ultimately be brought down to more manageable levels by natural causes. It also seems absurd to battle against a species that is essentially here to stay.

Field bindweed (Convulvulus arvensis) - labeled a noxious weed in Idaho

Field bindweed (Convulvulus arvensis) – labeled a noxious weed in Idaho

And that brings me to the point in which I make enemies. Take a look at the terms defined earlier. When we talk about introduced species, we are referring to introductions by humans, whether purposeful or accidental. An “alien” species introduced to a new location by wind, water, or animal (other than human) would be considered a natural introduction, right? If that species becomes established in its new location, it would simply be expanding its range. If a human brought it there, again whether purposefully or accidentally, it would be considered an exotic indefinitely.

Humans have been moving species around since long before we became the humans we are today in the same way that a migratory bird might move a species from one continent to another. At what point during our evolution did our act of moving species around become such a terrible thing?

I will concede that our species has become an incredibly widespread species, able to move about the planet in ways that no other species can. We also have technological advances that no other species comes close to matching. In the time that our species has become truly cosmopolitan, the amount of species introductions that we have participated in has increased exponentially. Leaving ecological destruction in our wake is kind of our modus operandi. I don’t want to make excuses for that, but I also don’t see it unfolding any other way. Give any other species the opportunities we had, and they probably would have proceeded in the same manner. Just consider any of the most notorious invasive species today – “opportunist” is their middle name.

More and more, as we are able to see what we have done, we are making efforts to “fix it.” But how de we rewind time? And if we could, when do we rewind back to? And how do we not “ruin it” again? The earth does not have a set baseline or a condition that it is supposed to be in at any given time. The earth just is. It is operating in a state of randomness, just like everything else in the universe. Any idea of how the earth must look at any given time is purely philosophical – conceived of by humans. I’m not saying that we shouldn’t try to repair the damage, but we should acknowledge that the repairs we’re trying to make are largely for the perpetuation of our own species. Yeah, we’ve developed a soft spot for other species along the way (thankfully), but ultimately we’re just trying to maintain. The earth, on the other hand, would be fine without us.

So, what shall we do about invasive species? I’m not entirely sure. The only thing I’m certain of is that I will continue to ruminate on them and potentially bore you with more blog posts in the future. Until next time…

Puncturevine (Tribulus terrestris) - labeled a noxious weed in Idaho

Puncturevine (Tribulus terrestris) – labeled a noxious weed in Idaho

Book Review: Rambunctious Garden

Last month in a post entitled Making the Case for Saving Species, I reviewed an article written by Emma Marris about doing all we can to prevent species from going extinct, even when the approach is not a popular one – like introducing rust resistant genes into native whitebark pine populations. Intrigued by Marris’ words, I decided to finally read her book, Rambunctious Garden: Saving Nature in a Post-Wild Word, which had been sitting on my bookshelf for several months and had been on my list of books to read for at least a couple of years before that. At only 171 pages, Marris’ book is a quick read and comes across as an introduction to some sort of revolution. Its brevity demands future volumes, which are hopefully on their way.

rambunctious garden

The general topic that Marris addresses is how to do conservation work in a world that is riddled with human fingerprints, especially coming from a perspective that human influence is and has been largely negative. What should our goals be? The traditional approach has been to restore natural areas to a historical baseline. In North America, that baseline is usually pre-European colonization. So, we remove introduced species and we use whatever records we have and data we can gather to make natural areas look and function as they did several hundred years ago.

But there are some concerns with this approach. Rewinding time requires massive amounts of money, labor, and time, and if that historical baseline is ever achieved, it will require great effort to keep it there. Also, a number of species have gone extinct and there is no way of replacing them (unless we introduce similar species as proxies), and some species require large areas to roam that even our most spacious parks cannot accommodate. And then there is the challenge of continual change. Anthropogenic climate change aside (which complicates conservation and restoration efforts in serious ways), the earth’s ecosystems are in a constant state of flux, so holding a site to a pre-determined baseline makes little sense when viewed from a geological timescale.

There is another issue – which is in part a semantic one – and that is, we seem to have a distorted view of nature. We like to think of it as being apart from us, away from us, somewhere wild and pristine. Marris writes: “We imagine a place, somewhere distant, wild and free, a place with no people and no roads and no fences and no power lines, untouched by humanity’s great grubby hands, unchanging except for the season’s turn. This dream of pristine wilderness haunts us. It blinds us.”

We are blinded because “pristine” is a myth. Every inch of the globe has been altered in some way by humans – some areas more than others – and disconnecting ourselves from nature in a way that makes it unattainable deters us from the perception that nature can be all around us. Nature is not found only in national parks, nature preserves, and other protected areas, but in our backyards, on our rooftops, along roadsides, in the cracks of concrete, and in farm fields. Nature is everywhere. And if nature is everywhere, then conservation can happen everywhere.

After a brief overview of how we (Americans specifically) arrived at our current approach to conservation and restoration, Marris dives into some new approaches, visiting sites around the world and talking with biologists and ecologists about their work.  She explores rewilding (Pleistocene rewilding even), assisted migration, embracing exotic species, novel ecosystems, and designer ecosystems. The subject matter of each chapter in Marris’ book is worthy of a post or two of its own, but I’ll spare you that and suggest that you read the book. The controversy that surrounds these novel approaches is also worth noting. A few searches and clicks on the internet will lead you to some fairly heated debates about the ideas that Marris puts forth in her book, as well as some criticisms of Marris herself.

Florida torreya (Torreya taxifolia) - a critically endangered tree species native to a tiny corner in the southeastern United States that is not likely to survive the coming decades in the wild without assisted migration.

Florida torreya (Torreya taxifolia) – a critically endangered tree species native to a tiny corner in the southeastern United States that is not likely to survive the coming decades in the wild without assisted migration. (photo credit: www.eol.org)

My view as an outsider – that is, one without a high level degree in ecology and lacking years of experience working in the field – is that the tools and methods outlined in Marris’ book are worth exploring further. Certainly, each natural area must be approached differently depending on the conditions of the site and the goals of the managers. [Marris offers a great overview of some goals to consider in her last chapter.] Ultimately it is up to people much smarter and more experienced than I to sort it all out. But I heartily encourage thinking outside of the box…for whatever it’s worth.

And that brings me to what I loved most about the book. Controversy aside, Marris’ clarion call for a paradigm shift is a welcome one. Nature is all around us, and regardless of what land managers and the powers that be decide to do with large tracts of land “out there,” every individual can find purpose and beauty in the nature that surrounds them, whether it be the street trees that line our neighborhoods or the vacant lot growing wild with weeds down the street. We can decide to let our yards go a little feral, to plant some native plants, to encourage wildlife in urban areas, and to even do a little assisted migration of our own by planting things from nearby regions just to see how they will do in our changing climate. In short, we can garden a bit more rambunctiously. And we should.

This is how Marris puts it:

If we fight to preserve only things that look like pristine wilderness, such as those places currently enclosed in national parks and similar refuges, our best efforts can only retard their destruction and delay the day we lose. If we fight to preserve and enhance nature as we have newly defined it, as the living background to human lives, we may be able to win. We may be able to grow nature larger than it currently is. This will not only require a change in our values but a change in our very aesthetics, as we learn to accept both nature that looks a little more lived-in than we are used to and working spaces that look a little more wild than we are used to.

Read a short interview with Marris about her book here, and listen to a discussion with her on a recent episode of Out There podcast.

Making the Case for Saving Species

It is no question that the human species has had a dramatic impact on the planet. As our population has grown and we have spread ourselves across the globe, our presence has altered every ecosystem we have come into contact with. Our footprints can be detected even in areas of the planet uninhabited by humans. As awareness of our impact has increased, we have made efforts to reduce it. However, much of the damage we have caused is irreversible – we can’t bring species back from extinction and we can’t replace mountaintops. Furthermore, for better or for worse our continued existence – despite efforts to minimize our negative influence – will continue to be impactful. This is the nature of being human. It is the nature of all living things, really. As John Muir said, “when we try to pick out anything by itself, we find it hitched to everything else in the Universe.” That we are cognizant of that fact puts us at a crossroads – do we make a concerted effort to protect and save other species from the negative aspects of our presence or do we simply go on with our lives and let come what may?

The quandary isn’t that black and white, obviously. For one thing, cleaning up polluted air, water, and soil is beneficial to humans and has the side benefit of improving the lives of other species. Protecting biodiversity is also in our best interest, because who knows what medicine, food, fiber, or other resource is out there in some living thing yet to be discovered that might be useful to us. On the other hand, putting our own interests aside, what about protecting other species and habitats just to protect them? Purely altruistically. That seems to be the question at the crux of an article by Emma Marris in the May/June 2015 issue of Orion entitled, “Handle with Care: The Case for Doing All We Can to Save Threatened Species.” [Listen to a brief discussion with Marris about the article here.]

The main character in Marris’ article is the whitebark pine (Pinus albicaulis), a species whose native habitat is high in mountain ranges of western United States and Canada. Whitebark pines thrive in areas few other trees can, living to ages greater than 1,000 years. Here is how Marris describes them:

Whitebark pine’s ecological niche is the edge of existence. The trees are found on the highest, driest, coldest, rockiest, and windiest slopes. While lodgepole and ponderosa pine grow in vast stands of tall, healthy-looking trees, slow-growing whitebarks are tortured by extremes into individualized, flayed forms, swollen with massive boles from frost damage. Their suffering makes them beautiful.

photo credit: www.eol.org

photo credit: www.eol.org

But in recent years they have been suffering more than usual. White pine blister rust, an introduced pathogen, is killing the trees. The native mountain pine beetle is also taking them out. Additional threats include climate change and an increased number, extent, and intensity of wildfires. Combined, these threats have been impactful enough that the species is listed as endangered on the IUCN Red List where it is described as “experiencing serious decline.”

So people are taking action. In Oregon’s Crater Lake National Park, botanist Jen Beck is part of an effort to select blister rust resistant trees and plant them in their native habitats within the park. Hundreds have been planted, and more are on their way. Great effort is taken to minimize human impact and to plant the trees as nature would, with the vision being that blister rust resistant trees will replace those that are dying and that trees with rust resistant genes will dominate the population.

But Beck faces opposition, and not just from challenges like seedlings being trampled by visitors or a warming climate inviting mountain hemlocks and other trees into whitebark pine’s native range, but by people who argue that the trees shouldn’t be planted there in the first place – that what is “wild” should be left alone. Marris specifically calls out a group called Wilderness Watch. They and other groups like them profess a “leave-it alone ethic.” Rather than be arrogant enough to assume that we can “control or fix disrupted nature,” we should respect the “self-willed spirit of the wild world.” Proponents of nonintervention criticize what they call “new environmentalism” and its efforts to engineer or manage landscapes, fearing that these actions are “morally empty” and that “rearranging bits of the natural world” lacks soul and will ultimately serve to benefit humans.

In her article, Marris argues against this approach. First off, the human footprint is too large, and for natural areas to “continue to look and function the way they did hundreds of years ago” will require “lots of human help.” Additionally, nonintervention environmentalism “perpetuates a false premise that humans don’t belong in nature,” and if we decide not to work to protect, save, or restore species and habitats that have been negatively affected by our actions simply because we are “in thrall to wildness”, we will be withdrawing with “blood on our hands.” Marris sums up her position succinctly in the following statement:

We have to do whatever it takes to keep ecosystems robust and species from extinction in the face of things like climate change. And if that means that some ecosystems aren’t going to be as pretty to our eyes, or as wild, or won’t hew to some historical baseline that seems important to us, then so be it. We should put the continued existence of other species before our ideas of where or how they should live.

Marris acknowledges that there are risks to this approach. “Our meddling” may save species, but it could also backfire. But that doesn’t mean the effort wasn’t worth it. We can learn from our mistakes and we can make improvements to our methods. Some sites can even be cordoned off as areas of nonintervention simply so that we can learn from them. The ultimate goal, however, should be to save as many species and to keep as much of their habitat intact as possible. Putting “other species first, and our relationship with them second” is what Marris considers to be a “truly humble” stance in our role as part of nature.

Cones of whitebark pine, Pinus albicaulis (photo credit: wikimedia commons)

Cones of whitebark pine, Pinus albicaulis (photo credit: wikimedia commons)

The dichotomy presented in this article is a tough one, and one that will be debated (in my mind particularly) long into the future. If you would like to share your thoughts with me about this issue, do so in the comment section below or by sending me a private message through the contact page.

Other article reviews on Awkward Botany