“The discussion about native plants encompasses a remarkable mixture of sound biology, invalid ideas, false extensions, ethical implications, and political usages.”
Steven Jay Gould, evolutionary biologist, writer, Harvard University, Natural History Museum NYC
An Evolutionary Perspective on Strengths, Fallacies, and Confusions in the Concept of Native Plants. S.J. Gould. Arnoldia, Spring 1998. (Quarterly magazine of Arnold Arboretum, Harvard University)
“There is no biological criterion on which to judge a priori the smaller or greater value of one species against that of another.” Lugo, in Biodiversity, E.O. Wilson ed.
You walk through the wood edge of the local park, farm, or neighborhood trail. You see the rampant undergrowth of shrubs with spiny stems and small red berries. Many people have taken an instinctive reaction to these barberry bushes and liken them to invaders on the land that are harming the native species there.
We’ve been hearing for many years about the danger of invasive species. They’re everywhere and causing widespread harm to the environment. And yet, we understand that nature is hugely complex and its hard to grasp all that’s going on with species interactions and besides…everything is changing with all the damage humans are causing to the environment…
The issue of invasive species has permeated our society to where many people fervently believe there are species taking over, causing widespread harm, and that should be eradicated. But many scientists don’t subscribe to these notions but believe that these complex systems are constantly in flux and adapting to the ever present changes. There is no perfection or stability in nature. As they explore the novel ecosystems around us, they ask questions about how they came to be, how they function, and how do they respond to the intense ecosystem changes occurring.
I first came to this issue through my work doing habitat restoration for The Nature Conservancy in the 1990’s. Much of what we did was amazing; replanting forests in flood-prone agricultural land along the Sacramento River in the Central Valley of California. We planted thousands of trees and shrubs. We had a large staff, hundreds of volunteers, and an ecosystem restoration education program. But we also used techniques that continued to disturb the system even as we tried to repair it. We sprayed Roundup with tractor boom sprayers across many acres. We used heavy equipment, brush hogs, and tractors and tilled the soil, increasing the soil disturbance.
I started to have misgivings about the approaches we used and the war we waged with the ecosystem– to save it. I’ve come to believe the process of restoration and land management is as important as the result. It turns out that the ends don’t justify the means. I look at techniques being used in current land management, farming, and landscape work through that lens. In the work I do on residential properties, community land, farms, campuses, and in urban areas, I look to heal the land, reduce the ongoing disturbance, and to reconnect people to the land and their place on it.
There are many questions that need to be asked about invasion biology and “invasive species” (see sidebar). We need to go into our land work, farming, gardening, with an openness to these questions and a desire to reach new understandings.
There are currently inadequate definitions for many terms used in the native-invasive debate. A simple definition for Native that gets used often is “A plant or animal that lived in a given area before European colonization”. This is a very arbitrary definition. Here’s another. “A plant that is a part of the balance of nature that has developed over hundreds or thousands of years in a particular region or ecosystem. “
These definitions are problematic in their ambiguous use of time frames, locations, and vague terms such as “balance of nature” to determine “belonging”. The nature of species is to move into new areas. This is part of evolution and what creates diverse ecosystems. These not-measurable definitions do not try to measure anything of direct ecological importance. Why is range/geography in and of itself ecologically essential? Why is a time period of being in a place a definition of nativeness?
So the question arises: which period of time are we talking about as the basis for the snapshot which defines nativity? Why should we choose one time period over another for that snapshot? Shouldn’t the definition of “native” apply to all species in all ecosystems if the concept or definition is to be valid, and not apply only to the unique circumstances of the Western hemisphere and its history of European arrival 500 years ago? And how do we know what that species range is or was in 1492, or 1500, or 1600? We have a better idea what ranges were in 1950, when E. Lucy Braun published her findings of the first, most comprehensive look at the plant communities of the eastern half of North America. But that is far too late a date, isn’t it, by the definition of native now in use? Are the range maps we refer to compiled using multiple time periods and multiple sources? I have looked at many range maps, and there has never been a date given for when the species was in that range, even though we know that species move far and wide in response to past climate changes.
Some of those movements continue today in response to the melting of the glaciers 15,000 years ago, not to mention our current climate changes. In his excellent book Where Do Camels Belong? Ken Thompson uses the evolution of camels as a query about defining nativeness.
The media has taken hold of the invasive species issue and run with it. There are many books, articles, fliers, fact sheets, websites, speakers, conferences, journal articles espousing the dangers of invasive species and how to get rid of them. Words like “taking over”, “biological pollution”, “invaders”, “planet of weeds” and “overrunning” are used to describe these newcomer species and what is happening. There is the use of fear to motivate action. A “culture of fear” has developed that even leads people to fear going outside, lest they come into contact with a dangerous invasive species.
Short Time Frames
Ecosystems develop and evolve over hundreds and thousands of years. Trees can live for hundreds of years. Our human time frame of years, decades, and a human lifespan is often too short to really grasp the long timelines of natural systems. Researchers trying to understand invasive species often do studies based on a graduate program or funding cycle of months to several years.
The field of Biogeography is the study of species and ecosystems changes through geologic time and geographic space. Species ranges are a tool to understand where species are located in a given time. A range map is often used to define whether it is native or not. But without a reference to time the idea of range is useless. Species ranges change over very short time frames; sometimes thousands of years and sometimes over hundreds or tens of years. Should we presume that a given species’ native range is that of where it was when European settlers came and no more and no less forevermore? Could any ecologist stand by this concept where species ranges don’t change over time?
Since the retreat of the most recent glacier in New England, about 15,000 years ago, there have been huge changes to the regional climate as species began colonizing this raw, scraped land. By 10,000 years ago temperatures were close to todays and by 8,000 and 5,000 years ago the climate was even warmer. The northeast region was tundra and boreal forest for thousands of years after the glacial maximum. Pollen studies have revealed an intricate process of plant migration into the region that has changed our understanding of plant community timelines and formation. It is no longer believed (by many ecologists) that plants move as whole ecologies, tightly knit together. Instead organisms migrate at different rates using different routes. Spruce (Picea spp.) were in the region 12,000 years ago. 3,000 years later hardwood forests were assembling with oak, maple, elm, and other species. Hickory arrived only 5,000 years ago and the latecomer Chestnut arrived to New England only 2,000 years ago and came to dominate an already assembled ecosystem. 5,000 years ago hemlock (Tsuga Canadensis) experienced a sudden decline in abundance in the region, possibly from a disease outbreak. In 2,000 years it recovered its previous abundance.
Ecological Fitting vs. Coevolution
Many ecologists learned in school that when two species are in cooperation, sharing or utilizing each other in some way that this is a form of “mutualism” or co-evolution; i.e. these species have evolved together over time to develop a connection. An insect utilizing a specific flower, or a fungi-plant interaction are examples of this kind of co-evolved behavior. And thus many people have come to see the ecosystem as a tightly fitting interconnected and interdependent web. The result of this idea is believing that ecosystems are set combinations of specific species and thus brittle and liable to break apart when disturbed.
It turns out that though there are some co-evolved and tightly dependent relations in nature, in the last decades ecologists and researchers have begun to understand ecosystems as much more fluid and adaptable. One researcher who pioneered this understanding is Daniel Jantzen who coined the term “ecological fitting” in 1980, for “the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition.” In this view, nature is a fluid system constantly changing, mixing, and adapting. Species come. Species go. Often in largely random ways over short and long periods of time.
Janzen came to his idea of ecological fitting while working in Santa Rosa National Park, Guanacaste province, Costa Rica. He observed that the Guanacaste tree, the national tree of CR and vitally important to the tropical drylands, was not reproducing. The seeds would pile up and there was limited reproduction due to the lack of seed dispersers; herbivores that could eat and spread the seed. The previous dispersers were the ground sloths, camels, ancient horses and others that disappeared during the megafauna dieoff approximately 10,000-15,000 years ago (probably from climate change, human overkill- or a combination of both). Janzen surmised that the ecosystem lacked a seed dispersal herbivore to replace the lost megafauna. His solution was to reintroduce the modern horse into Santa Rosa National Park, a controversial approach in conservation circles where purity of species introductions is paramount. Bringing in a domesticated and non-native species (though originally evolved on the continent) was ecological heresy. It turns out that the European horse was a perfect surrogate for eating the fruit pulp without chewing the seeds and depositing them on the landscape where they could establish.
In Janzen and other researchers’ and conservationists’ view, species combinations are constantly under change, there’s no fixed formula. Across a landscape there’s often a gradation of species mix with no break between combinations. The idea of a climax forest or ecosystem has been debunked as it’s become clear there’s no settled arrangement, often there’s a large dose of chance of which seedling is there when a storm takes down a large tree, or the seed mix in the soil after a fire comes through.
Relatedly, the idea of ecosystems as complete and full is just as erroneous. New species often find space within an ecosystem and there is no “one species in—one species out” kind of trade off. Study of island biogeography and ecosystem dynamics has shown that many more species can arrive and find niches without the loss of other species.
These new combinations of species have been given the name novel ecosystems. They are a hallmark of the Anthropocene; ecosystems altered in some way by humans and they now cover as much as a third of the planet, In nature there is no judgement of the players as good or bad, belonging or not…everyone finds their way, their place, or moves on. The study of novel ecosystems is increasing as scientists try to understand these new ecologies and how they adapt and evolve. There is growing evidence that the increase in new species combinations will lead to a burst in evolution, hybridization, and speciation. It is a brave new world that we’re headed into.
“Sure, species move and the ecosystem is changing… but some super aggressive species are “taking over”, pushing out other species, and causing a lot of damage to the environment”
And here we get to the crux of the issue. We don’t mind some of the plants and animals coming in, but its those few that are really causing the problem; bittersweet, Japanese knotweed, mile-a minute vine, barberry, black locust, and the list goes on. The claim is harm and taking over by these newcomers, but is there evidence? Is there more than the anecdotal idea we get when we see a species growing aggressively and expanding into our yard, woodland, or field? Is a species causing harm by this expansive growth? Is it causing harm by existing in a place and taking up space?
Idea of Harm
Much of the harm that many people experience is a very subjective and arbitrary one. Where people have decided they don’t like a plant or animal, “it’s invasive” is a reason to dislike and remove it. Its mere presence is seen as causing harm. Wild nature, out of our control, is not something modern human society has allowed. Sometimes it doesn’t even need to be a newly arrived species. Poison ivy, grapes, sumac, dandelions, and others can be considered invasive as well. A sad offshoot of this is that children and many people see nature as dangerous; a place where there are bad plants and animals hurting the environment and they may hurt you or your children. We are moving into a period where people are losing their nature connection, and casting some nature as good, and some nature as bad is just feeding this nature disconnect.
One commonly used statistic of invasive species harm is “invasive species are the 2nd leading cause of species extinctions”. This is a factoid from a scientific paper by David Wilcove “Quantifying Threats to Imperiled Species in the United States” printed in the journal BioScience in 1998. This widely cited paper was in fact based on anecdotal and observational accounts by land managers, using limited data. It also included Hawaii, which is a very distinct situation, being an island with species evolved in isolation and then centuries of introductions by humans. The authors expressed the limitations of the data and yet the idea that “invasive species are the 2nd leading cause of extinctions” has gained a life of its own and is repeated often without reference to the source or limitations. A Canadian assessment in 2006 found that invasive species were the least of all factors considered. The biggest factor? Disturbance and removal of habitat by humans.
Harm can also be quantified monetarily. One widely quoted amount comes from a study done by David Pimental, a Cornell professor, in a paper published in 2005. He calculated that invasive species cost the US $120 billion dollars a year. This number is large enough to move federal bureaucracies and research institutions to fund removal campaigns, research, and a massive education campaign against these invaders. Unfortunately when one looks closely at the calculations to get to $120 billion per year it stretches reason and heads quickly towards the absurd and misleading. It includes:
– Crop losses in agriculture (mostly nonnative crops) from weeds ($24 billion/yr).
– Herbicides used in U.S. agriculture ($4 billion/yr).
– Control of species in lawns, gardens and golf courses including pesticides and herbicide use. ($1.5 billion/yr)
– Forage losses and “weed” control on overgrazed range and pasture ($6 billion/yr).
– Cost of domestic cats in damage to U.S. bird population. ($17 billion/yr).
Many of the costs are to industry, including the cost to companies to keep waste outlet pipes heading into waterbodies from getting clogged by zebra mussels. The benefits of these newcomer species aren’t part of the calculation. For instance those zebra mussels clogging the industrial pipes also have been cleaning the Great Lakes and other waterways of human-caused pollution, leading to cleaned up waters (they are filter feeders) and a return of many sport fishing species and commensurate return in the sport fisheries industry.
Scientific literature — what are scientists saying?
The conservation and research community is slowly coming around to question the dominant ideas around invasive species. There are reviews looking at bias in scientific studies of invasives, studies of the “real” impact of invasives, and studies of the benefits of these new arrivals. One particular thread is to tease apart whether invasives are the “drivers” or “passengers” of change in ecosystems. Several of these studies have identified, among the complex interactions going on, that invasives often ride in on the changes in ecosystems that we humans have initiated. Its not surprising, but for several decades now, scientists have worked from the presumption of harm, and research has looked to confirm that and focus on methods to remove species.
Reassessing Specific Cases/Species
Its coming to light that many of the species accused of egregious harm are guiltless and even are bring benefits to landscapes they are in.
A classic case of this is tamarisk (Tamarix spp.), a shrub introduced into arid southeastern landscapes in the 19th century. They were initially welcomed as an ornamental, and a drought-resistant shade tree. In the 1930’s as drought swept through Arizona, Central New Mexico, and West Texas and they were branded as “water thieves” and then after WWII as nonnative invaders salting the water. For 70 years they were the object of an intensive removal campaign using bulldozers, chains, herbicides at the cost of tens of millions of public dollars. In the last few years ecologists have found that they utilize water at the same rate as other riparian species and do not add additional salt. (Stromberg, 2009) They are also the preferential nesting habitat of the endangered Southwestern willow flycatcher. This species is surviving and thriving under the vastly changed water regimes in the altered southwestern landscapes. Shouldn’t we recognize that tamarisk has a place as part of restoring those places?
Closer to home, black locust (Robinia pseudoacacia) is accused of being a non-native invader. This suckering, nitrogen-fixing tree was certainly here in the region before the last glaciation pushed it out, and was moving steadily northward. Range maps from mid 20th century show it as being in present day Pennsylvania, but unfortunately not within the borders of Massachusetts and so suspect as a problem newcomer. The label non-native invader comes from its propensity, primarily in the sandy soils of Southeast MA and Cape Cod, to spread readily, utilizing its ability to fix nitrogen to colonize the depleted soils; depleted from the land clearing, grazing, and farming activities of people since the earlier human colonists came some 500 years ago. Black locust trees repair the land and bring back fertility through their tenacious growth and nitrogen fixation. They are one of the most resilient and multi-functional trees in the region, providing rot resistant post wood, pollinator support, fodder, high btu firewood etc — but they are outlawed for sale or distribution in Massachusetts. Earlier settlers through much of the last century relied on these regional resources. The USDA Silvics Manual Vol 2 (1990) outlines the many current and historic uses for black locust: “It is used for fence posts, mine timbers, poles, railroad ties, insulator pins, ship timber, wooden ship construction, boxes, crates, pegs, stakes, and novelties…. Black locust is widely planted…for erosion control, reclamation of drastically disturbed sites, windbreaks, nurse crops, amelioration of sites, honey production, and ornamental use.” Society has changed and so has our preferences for the plants around us, but this tree is certainly high on my “best trees” list.
What do we do? How can we change our relationship with the world around us and not be drawn into fighting nature itself? In the work I do with landowners we look for ways to meet their goals while restoring and regenerating the land. Each person is different and can try out different practices like tree planting, selective thinning in woodlands, changes to mowing management and rebuilding soil with compost, microbial inoculation, and encouraging pollinator support plants.
• Incorporate change- Don’t stop the flow
Our work on the land needs to work with ecological processes. In the martial art aikido, incoming energy is transformed and redirected, not blocked. The work we do must be earth aikido. There is a temptation to begin fighting the species that arrive with herbicides or pesticides and causing further disturbance and disruption.
Understand the current patterns and flows on the land and adapt your practices to be more in line with that. i.e. change your vegetation management (mowing, weeding, clearing), water and soil management.
• Learn to Live with Them
These new species, naturalized and in many cases already here for centuries, aren’t leaving. We can learn to live with them. When taking a walk or working on the land, notice your reaction to plants; do you feel anger towards these new arrivals? What is coming up inside you like concern for the environment, or concern for the future? And how are these plants and animals part of that concern? How can we transition from anger and pain to healing and forgiveness?
These new combinations of species, our “novel ecosystems,” are responding to ecosystems changes. Long-standing species are behaving differently with new conditions. Lets explore them. Celebrate the new connections being made.
• Understand the context of where you’re working
Wherever we live and work we need to deeply investigate the history of the land. We need to understand past disturbances, like fire or storm events, successional changes, species arrival, changes to hydrology, terrain and air flows. Human changes are often intertwined with the ecological trajectory, particularly the disturbance history. What kind of changes have humans made and how has the land been managed, altered, or disrupted?
Here in New England, there have been centuries of human disturbance. Layers of land clearing, acid rain, fire suppression, forestry, grazing, farming, and more recently development and urbanization have left an utterly changed ecosystem. On a landscape scale, the activities that have left places degraded can sometimes be used to reverse the damage. For instance overgrazed land might be restored by intensive mob grazing. Thinning woods, managing brush, and tree planting can reverse high grading or clear cut management.
More Plants with Multiple Values
Many “invasive species” are actually super beneficial for habitat, ecosystem functions, and food or medicine. Here are two examples:
Autumn Olive, Russian Olive, Goumi (Eleagnus spp.)
• Introduced for soil stabilization, ornamental, wildlife value.
• Fixes nitrogen, hardy, drought tolerant, few pests/diseases, disturbance adapted.
• Used to reclaim strip-mined land, wildlife habitat.
• Delectable fruit high in lycopenes (cancer reducing compounds: 6-20x the levels in tomatoes; Fordham, 2001). High in vitamins A, C, E, flavonoids, and essential fatty acids.
Japanese Knotweed (Polygonum cuspidatum)
• Introduced as an ornamental in late 1800’s.
• 2,000 year medicinal history in Asia.
• Edible shoots, high in resveratrol, anti-Lyme, anti-cancer, anti-bacterial compounds.
(Buhner, Healing Lyme, 2005)
“ Man (sic) is part of nature, and his war against nature is, inevitably, a war against himself.”
Rachel Carson, Silent Spring, 1962
Reducing the ongoing disturbance should be a priority.
• Urban environments — altered and not going back
Urbanized environments have special conditions to be considered. These environments have long histories of change with altered hydrology, soils, and air. Nothing is like it was in the past and the idea of bringing it back to some past condition is a nostalgic notion and unrealistic. A vacant lot in downtown Lowell, MA will not become the floodplain forest that it once was several hundred years ago before the Merrimack River was channeled and urbanized. What is the best use of the urban Lowell land? What are the ecological functions it can serve where it is, now? How might it serve the residents of the neighborhood and reduce their demands for food, water or other goods from far away? Put the lens of an earth healer and food grower on and a whole world of possibility opens up.
• A sensible policy on native and naturalized species
We need a sensible policy on naturalized species that allows us to pull back from trying to control everywhere. It may be part “learn to live with them” and it may be selective management and removal, recognizing there are specific vulnerable habitats and species that need our intervention, allowing some areas to go through succession, as messy as it looks, and focusing on stabilizing and reducing disturbance.
• Protect and restore diverse, rare, and sensitive ecosystems. Refugia!
There are places that need to be protected and carefully managed. These are locations with rare species, specialized and unique habitats, genetic diversity hotspots, and places where research and conservation is ongoing.
• Create and expand habitat corridors
Connect isolated habitats through corridors that allow dispersal and movement of species. This is essential as climate change requires movement of plants and animals into new areas.
• Restore ecological function
Focus on function and not the name or original location of a species. In this time of stressed ecosystems we need species that are resilient and adaptable. We can assist in development of these resilient and productive ecosystems and communities. Utilize deep sustainability, regenerative approaches, and permaculture design.
• Human-assisted species dispersal in response to habitat loss and climate change
We will need to be active participants in helping species that have become isolated or whose movement can’t possibly keep up with the ecosystem changes we’re dealing with.
In 2010 my wife Kemper and my young son visited the California restoration project that we worked on in the early 1990’s. The forests had grown tall, deer watched us from the brush and woodlands we planted. The Sacramento River flowing nearby had breached its banks and flooded through the fields, cutting side channels and depositing woody debris. It was an affirmation that we can get on the right side of nature and become part of the solution. My son walked those fields with us and, I hope, saw a vision for the future where we can help repair the world around us.
It would be far better to teach people about the rich biodiversity and ecology around them, and to foster an appreciation for all living things, than to hide behind science while pushing pest control agendas that contribute to more loss of habitat and declining biodiversity.
And surely the most insidious and destructive outcome to be avoided is the fostering of human alienation with nature, or a feeling that we are surrounded by an alien and therefore, unnatural, environment.
Fostering a worldview that some species are good while others are bad sets the stage for a nihilistic society that can never be at ease in, or nurtured by, the natural world.
Vivian Parker, California Indian Basketweaver’s Association (2002)
Jono Neiger has thirty years experience in conservation, restoration, land stewardship, permaculture, agroforestry and landscape design and planning. Jono was the Land Steward at Lost Valley Educational Center, Oregon, Restoration Ecologist with the Nature Conservancy of California, and Lost Creek Watershed Council Founder and Coordinator. He was faculty at the Conway School of Landscape Design, founding board president of the Permaculture Association of the Northeast, and is a founding partner of the Regenerative Design Group in Greenfield, Massachusetts. He operates Big River Chestnuts, an emerging chestnut agro-forestry in Sunderland, MA.