Exotic and Invasive Species

Besides the dangers presented by bulldozers and developers, there are other significant threats to the prairie. Various exotic plant species mount one of the most persistent assaults at Stone Prairie Farm. These invaders from around the world make me tense and angry, since they often present serious risks to the health of the local ecosystem. The alien species that thrive often dominate native plants and animals, depleting both soil stability and biological diversity, the very things I've struggled to heal. They use a variety of tactics, such as the chemical warfare described earlier, or growing faster than the natives and thus stealing their sunlight. One would think that such a lush green wall of vegetation would benefit soil stability, but often the reverse is true. The successful invasives tend to have shallower root systems that don't hold the soil well. As the deep-rooted natives decline, the soil becomes subject to easy erosion. I have to work quickly to counterattack and weed out these invaders that deprive the indigenous plants of their soil nutrients and light or they will take hold and overwhelm the prairie.

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The migration of aggressive, invasive species is accelerating worldwide as the demands of global trade and an expanding international commerce system facilitate the unintentional spread of seeds and insects. In addition, the nutrient enrichment of the landscape from airborne and land-applied fertilizers has elevated levels of nitrogen and phosphorus, which tend to favor invasive plants. Stone Prairie Farm is a representative microcosm of this global phenomenon, which has serious implications for human and ecosystem health, implications that promise diminishing returns for world economies, particularly in the agricultural sector.

We have developed tactics to deal with this dynamic on our patch of land. Realistically it is impossible to prevent invasion, but I make informed decisions that help neutralize unwanted change, and sometimes manipulate it to my advantage. To do so I must consider many elements when fighting back against exotic or invasive species.

At daybreak, one mid-May morning I awoke to the melodious call of an oriole beckoning me to come watch the sunrise. I stumbled into the front yard just as the uppermost branches were igniting in the glow of golden morning light. The first oriole of spring, orange and black against the tattered bark, always gets my attention, even when I'm sound asleep. Max heard me and made it known that he was ready for his morning romp, so I let him out. Startled, the orioles took wing, landing some distance away in the branches of the weeping willow tree by the spring.

We followed, and soon I stood marveling at the spooky dead branches hanging from the willow tree's scarred, spire-shaped trunk. The former main section of the trunk was practically a cadaver, yet the tree still stood, splendid in the sun. A downy woodpecker poked out from one of many holes in the barkless trunk to warm itself in the morning sunlight. A few feet below the woodpecker, the head of a chickadee appeared from a silver-

dollar-sized hole that was partly concealed by the young lime green leaves of a willow branch. Squawking grackles flew into the upper branches, chasing the orioles off for good. The grack-les jostled the branches, staging for a short glide down to the nearby blue spruce that housed their nests. Blue jays rolled in next, addressing all assembled with their raucous clatter.

The willow is an introduced species that has become invasive in some locations of the country, and my general response would be to cut it down and plant a native. But this tree is so beautiful, and such a hub of animal activity, that I've let it stay, year after year. Originally it was a cutting that the previous owners of the farm had planted. They'd stopped at a garage sale on their way up from Chicago sometime in the early 1970s, and along with a couple of cast-iron skillets they'd been given a willow shoot. They'd dug a shallow hole and stuck it in the ground where it now stands. Artesian springs run a few feet beneath its root system; otherwise it's well drained and dry at the surface. A looping gravel driveway meanders beneath its outermost branches, and Susan and I must be careful to park well beyond the distance that a respectable wind might carry falling limbs.

Death has often seemed imminent for the willow. It is constantly shedding parts of itself, a branch here, a limb there— once a twenty-foot section of the main trunk crashed down in a fierce windstorm. I can't remember how many times I've dragged away the wreckage chained behind the tractor, thinking that this time it was surely a goner. On the cusp of death, however, the tree always revives, with green buds sprouting new branches. This persistence has reinforced my compassion for the willow, and I have allowed it to grow amidst native plants because I feel as if it has earned the right to be there—and, most important, it lives in peace among the other species on the farm.

Scarred where limbs have fallen off, it is not a perfect specimen by any means, but from our porch it complements the landscape. Susan and I relish its organic twisted form, comparing it to a nonagenarian with a teenager's flowing mane because once the numerous new branches grow, a supple curtain of young, elongated yellow-green leaves hides the gnarled and stalwart hulk. Beneath all that virgin growth, it's amazing to see how long dead rotted limbs remain on the trunk, especially as willows are not known for the strength or durability of their wood. I often wonder if it's immortal, able to continue this cycle of decline and regeneration indefinitely. It falls into the category of "living dead" that I assign to places or things that are hovering in the shadow of death.

Overall, I have been a reluctant lumberjack because the farm had few trees to start with, and they are important resting spots for migratory birds. They also shade the house on hot summer days and protect the woodland wildflowers that grow beneath it, such as phlox, jack-in-the-pulpit, and bloodroot.

Some exotic plants, such as this willow, remain innocuous and are content to stay put. Others become invasive, and it is still possible the willow might someday begin to spread. Though I have accepted this individual tree, I remain wary of making hasty decisions on other loners and misfits trying to call the prairie their home. Once they cross the line and start to colonize, all sentimentalism is vanquished because of the harm they are able to inflict on the ecosystem and the economic damage they might cause. I meet the challenge head on, with whatever tools are called for—shovel, herbicide, or chainsaw.

The possibility of exotic species developing aggressive habitats is a real threat. Because of this unpredictability, I can get terribly distraught by the appearance of exotics, regardless of how charmed I am by their beauty. And since continual waves of exotic plant and animal species are still intentionally circulated, there are ongoing invasions on the land.

The pioneers started the process, introducing many species and their corresponding diseases, which tested the limits of the adopted environments. The common English plantain, or "pio neer footstep"—an oval-leaved plant that looks like a smaller-leaved, flattened hosta—is an introduced plant from Europe that has been found growing in former canoe portages as far away as the most remote North American wilderness and in pathways around log cabins and the few remaining prairie sod houses. This European perennial is only mildly invasive. Many other exotic plants are nearly untamable. As a result some native plant communities once thought to be impenetrable because of their dense and long-established root systems are now being overrun. One of the new threats on our farm is reed canary grass, which as an invader is the equivalent of a malignant cancer. When it first appears in moist floodplain soils along the spring brook, it initially seems harmless, establishing itself only in small isolated colonies. Then, in a sudden rampage, these disparate patches coalesce, and the native sedges and wildflowers are consumed.

Not only have we brought in invasive species, we have also inadvertently laid the groundwork for the invasion in many ways. Before the exotic species even arrive, many native plant communities have been weakened through livestock grazing and the particularly devastating effects of agricultural runoff, which infiltrates the soil with high levels of herbicide, fertilizer, and sedimentation. Natural immunities are thus undermined, and sadly there are no effective antibiotics for the plant and animal communities in developed, agricultural, or other altered landscapes. (On the positive side, it is worth noting that some native plants resemble exotic species in their propensity to fight back, invasively counterattacking after environmental disturbances. Black-eyed Susan and evening primrose, for instance, are biennials that cannot be controlled with fire. Like garlic mustard, they effortlessly reseed themselves and persist despite focused management and against all odds. Transported to another ecosystem these might be dreaded invaders we would fear. On their home turf we cheer their resilience.)

What is the process of invasion? Reed canary grass provides a good example on prairie land. Recognizable by its broad leaves and coarse growth, reed canary grass is unlike any native plant. Once established it disregards environmental gradients and habitat distinctions and establishes itself easily everywhere it can reach. It manages this rapid spread in a number of ways, reproducing with rhizomes—underground root systems—as well as seeds. Its growth pattern generally follows nutrient-enriched surface waters and sediments, but it will also invade well-drained soils. We have even witnessed canary grass invading from downstream into the upper reaches of our spring brook and into adjacent uplands. This unusually diffuse pattern led me to ponder its mechanisms for seed dispersal. Wind seemed unlikely, and the stream ran in the wrong direction. Then one day I saw Max tromp through a patch of ripe reed canary grass. The following week the house was littered with the shiny grayish-black seeds that he had scattered everywhere: in our bedsheets, rugs, couches, anything covered with cloth. And adorning all my clothing, of course—a couple weeks later I had a project interview with the City of New York. I became so irritated by a prickly object in my shirt that I couldn't focus on my notes until I excused myself and retrieved a seed fragment with a strand of Max's hair. All of this gives me a much clearer understanding of how important raccoons, opossums, foxes, coyotes, and deer are in disseminating the canary grass, as well as other exotic plants.

None of the fields of Stone Prairie Farm, or the neighboring farms on this side of the drainage divide, contained any canary grass when we arrived. However, an isolated individual plant, perhaps seeded by birds or coyotes, will occasionally sprout along game trails that parallel the stream margins and spread radially from the nexus. I'm hypervigilant in combating this invader as soon as I notice it. First I'll pull the plants up by hand, or mow the patch if it's large enough. This prevents it from re-seeding but doesn't kill it. To do so I'll return at the right time of year and spot spray or brush the intruder with herbicide.

One spring morning Susan and I drove to a farm a few miles to the north where we thought there might still be some patches of wild prairie, with the concomitant profusion of native species. We'd spotted this land from the road some time before, intrigued by the prominent bedrock cliffs we could see cradled back in the dark recesses of the valley. When a chance encounter with the landowner allowed us to ask if we could hike the land, his "yes" was a welcome invitation to explore. We began our hike at a sandstone outcropping faced with draping ferns. On the ridge top we discovered a tall, dense planting of crown vetch, a purple flowering species commonly seeded along highway embankments. It grew in a dense dark-green profusion, spreading out over longer distances than most other plants with running root systems do. This plant forms billowing green foliage with telltale purple flowers, sometimes looking like soft, cushy, gently-mounded green snow drifts.

We walked along the ridge for about a mile, stopping to peer through the occasional breaks in the monotonous wall of crown vetch. On the other side we hoped to locate patches of the dry prairie community that historically grew on similar south- and west-facing bedrock bluffs. We spotted numerous plants there— remnants of little bluestem grass, clumps of northern dropseed grass, and Indian grass—the seeds of which we had in abundance back at AES. Then, unexpectedly, we spied something remarkable, a lone birdfoot violet plant, peeking out between a few clumps of grass. It was a marvelous and bittersweet discovery, as this plant was the sole survivor of a species that had likely been prevalent across this shallow bedrock landscape many generations ago. The crown vetch, it turns out, had been intentionally planted by the farmer in the 1970s to help stabilize fields in areas where heavy cattle grazing had resulted in serious erosion. But now the vetch had completely overrun that patch of prairie and choked out the violets altogether.

Federal agencies have routinely introduced plants like canary grass and crown vetch, European brome, multiflora rose, pine plantations, and numerous others—with utter indifference to their effect on the diverse native plant communities. And as we had seen countless times, the exotics had flourished, mercilessly dominating the native flora. Susan and I realized that if we left the violet in place it too would be overrun, so we dug it up and moved it to Stone Prairie, where it could be assured a more certain future. The decision to dig it out of its natural environs was difficult, but we felt it was the only choice in such a hopeless situation.

Even exotic plant species that are introduced inadvertently can sweep across the land with ease. Popping up sporadically, individual plants such as wild parsnips have steadily marched down road margins as their small waferlike seeds are carried forward by the whirl of passing cars and trucks, spawning thousands upon thousands of siblings. In addition to animals, the wind acts as carriers, allowing the plant to invade neighboring hayfields. Only the annual soil cultivation in corn and soybean fields and the shade of dense woodland environments has foiled the parsnip.

Other than the garden vegetables and orchard plants, and a few cover crops such as winter rye or barley, we've reduced avenues for invasion by exotic plant species on the farm. This cuts down significantly on the proliferation of species like white mulberry, multiflora rose, and tartarian honeysuckle, which were originally introduced to North America as cultivated ornamental plants.

When multiflora rose and honeysuckle shrubs display their telltale red fruits, it's a signal that they're going to spread across the land, since the birds are only too eager to comply by ingesting the fruit and dropping the seeds far afield. One October afternoon I found a large honeysuckle bush and two multiflora rose shrubs laden with bright red fruit growing in the middle of the prairie. I returned immediately to the barn for the tractor, my leather gloves, a lopper, and paper bags. Using the front-end loader on the tractor, I hooked the bucket onto the base of the honeysuckle's thick main stem at the soil surface and pulled the six-foot-tall plant and its entire root system out of the ground. After the fruit was removed from the rose shrubs, these too were yanked from the ground, roots and all. It took a few hours to collect the ripe rose hips in paper bags, but Susan and I enjoyed burning them in the woodstove along with the honeysuckle. It takes great vigilance to repel the invaders, and one must celebrate every victory!

The economic impact of exotic species in the United States totals hundreds of billions of dollars annually. If you want to find a career with excellent job security and an opportunity to be outstanding in your field, take on invasive species management. Most restoration projects require large investments for the control, reduction, and management of invasive species. The costs for this service are rising rapidly and expected to skyrocket in some parts of the world, where invasive species management may require Herculean efforts for decades to keep land available, even for economic uses such as farming.

In part this is because we as a society have ignored and underestimated the global impact of invasive plants, bacteria, and certain viruses, so we have been slow to guard against them. Many invasive species are even welcomed in, with no thought of their potential threat. They lie low as their populations grow and spread until reaching a point of critical mass, when they are capable of exploding over the landscape. For example, reed canary grass was widely distributed to farm owners by U.S. farm agencies without consideration for the consequences. Rather than turning to local native species, they simply provided this nonnative species to stabilize waterways. For a few decades the stream courses looked stable at first glance. But where the rubber meets the road is at and below the soil surface. There reed canary grass is problematic. Its shallow roots bind only the top couple inches of soil rather than extending down for many feet. It also has very few stems per square foot compared to native grasses and sedges, which have much denser growth patterns. So the land looks lush and green from above while soil is actually being swept away beneath the stems.

Managers of natural areas eventually began to recognize that this species was lying in wait, multiplying, and ready to explode. In the mid-1980s I published the first detailed account of the ecology and management of the grass, predicting that it would become a serious threat to biodiversity in nature preserves, national parks, and private lands. Reed canary grass has since invaded sensitive alpine meadows in Washington State's Olympic National Park and elsewhere. Waterfowl and other birds and wildlife are declining in national wildlife refuges and other public and private lands in direct proportion to increases in this invasive grass. I now receive over a hundred pleas for help with this problem from farmers and land managers each year. I have made countless phone calls offering to provide the results from our studies on how to manage this rampant species. I've copied and forwarded a barrage of the letters and e-mails I've received with people's personal stories of exasperation. Still the agencies are slow to react.

Restoration has its critics. Many question our ethics and even accuse us of "playing God" by determining which plants and animals are desirable. But as we study in detail the effects of ignorance, it is clear to us that we have to make intentional decisions to restore plant and animal communities and reduce invasive plants and animals. Any decision about land use and crop selection favors one species or set of species over another. But bringing in an exotic set of crops always entails the risk that they will become invasive and have a major negative impact economically. So our definition of ecosystem health clearly prioritizes ecological settings with a prevalence of native plants and animals, both because it seems right to be in tune with nature and because it has long-term economic benefits.

Not long ago, I participated in a tour to educate corporate executives and municipal officials on the ecological changes they could make in their communities with regard to property management. When the buses parked in front of the corporate headquarters of a Chicago-based concern, everyone got out to admire a new project that replaced lawns with wildflowers, which has become the rage for so-called trendsetting corporations trying to revamp their images.

Instead of an expansive lawn, we stood before a 20-acre planting dominated by dame's rocket, a European import in the mustard plant family, which was blooming in shades of purple, pink, white, lavender, and blue. Very colorful indeed, but I became quietly furious as I stood there among the assembled group listening to their exclamations of approval for the "lovely wild-flowers" and the pitch of the representative from an esteemed local landscape architecture firm responsible for the design. True, this was a remarkable turnaround—the planting replaced expanses of expensive lawn that had required ongoing care and management to deal with environmental impacts ranging from fertilizer runoff to air pollution generated from weekly summer mowing. But while I was pleased to see this attempt to change direction and adopt progressive policies, they had failed in the details. Dame's rocket was a horrible choice that wouldn't fit the environmental intent of the design.

I didn't want to say anything negative in that setting, where environmentally conscious and civic-minded citizens were trying to demonstrate how concerned corporations could be leaders in ecological stewardship. But it's not always easy for me to withhold my thoughts when I'm impassioned about something, and I couldn't manage to keep quiet.

"I really don't intend to chastise or embarrass anyone, but beautiful as this all seems, it raises real concerns for me."

Things got very quiet. There was a sense of brows furrowing.

I'd opened my mouth and there was nothing to do but continue in a steady, friendly manner.

"This is a wonderful redirection we are witnessing here, to switch out unsustainable lawn for lower-maintenance flowers. But the details are seriously wrong. You've planted dame's rocket, which is beautiful, and appears to be a healthy wildflower that fits the environment. In fact it is an exotic plant that has invaded state reserves and critical conservation areas around the Midwest. There's an inherent conflict here. While huge efforts are ongoing to control its rapid proliferation, projects such as this one are encouraging its use by getting people to like the way it looks."

Dead silence ensued. Finally a businesswoman broke the silence, and a productive discussion began.

"So you are saying this successful planting may have used the wrong species?"

"Exactly. And I'm sorry if I seem aggressive, but I've just spent the last three weekends surgically removing each and every dame's rocket plant in a southern Wisconsin scientific area, where its invasion is associated with the steady decline of rare plants. It's agonizing work! So I'm a little riled up."

"I'm not sure I understand the problem," ventured another one of the spectators.

"This plant has been a traditional farmstead garden flower for over a hundred years, which is why it probably looks familiar to you all," I said. "Just in the last decade or so it has become unruly, even ambitious. It has begun invading our most precious and important midwestern natural areas."

"Why would it suddenly start spreading if it's been around all this time?"

"We're not entirely sure why this happens, but it does. So a species may seem sedate and well behaved for decades. Then all of a sudden, within a few years really, it seeds into adjacent landscapes. Presto, it's coming up everywhere. My best guess is that nutrient levels of nitrogen in the soils finally reach a tipping point that favor this plant."

"And they kill the native species, Mr. Apfelbaum?" the businesswoman asked.

"Let's take garlic mustard, for instance, which is a common invasive relative of the dame's rocket here. The mustard family produces a number of compounds that act as what we call bio-fumigants, killing off many organisms in the soil and altering its microbial communities. Once the soil chemistry shifts on a large enough scale, the native plants species begin to decline and the invasive mustard takes over. This is clearly contributing to the decline of native plant diversity."

"I'm not alone in thinking this is a problem," I continued, scanning the crowd for skeptical expressions. I looked to the representative on hand from the U.S. Fish and Wildlife Service, which was a co-sponsor of these corporate efforts. "Many scientists believe that this is just the beginning of a greater assault on our ecological systems. I hate to be so blunt, but the truth is that this planting is a clear example of good ideas and bad details."

The government official nodded in agreement with my concern over the invasive species issue. But he clearly had a more political agenda. He told the group how pleased the Fish and Wildlife Service was to have this level of corporate commitment to this project and reiterated his organization's intention to make it successful. Perhaps he was simply being more tactful than me by portraying this corporate shift as setting a good precedent. To him, it seemed, the invasiveness issue was a secondary consideration in this preliminary stage of the project, and he may have simply assumed that in due course the details of the process would be refined as things moved forward.

Conversations broke out on the side. One between an executive from the host corporation and their designer was a bit tricky, with the corporate executive commenting on the apparent beauty being undermined by the larger problem. "What can you do to fix this situation?" the executive asked.

I didn't hear the designer's answer, but his body language looked very defensive.

I was somewhat sorry that my lecture had embarrassed well-meaning people trying to create beautiful landscapes in a well-intentioned project. But I didn't really mind opening that can of worms. It would have been unconscionable to remain silent. This was another clear example of decisions being made with little thought as to the obvious consequences. And what made it all the more infuriating for me was that design professionals had initiated this, and they should have known better.

Susan and I seized on an opportunity to convert a monocultural landscape into a small paradise teaming with hundreds of native plants and animal species. It took vision and a great investment of time and hard work. But once aided, nature itself joined in the effort—for instance prairie ants have returned and they help in the restoration process by transporting the seeds of the violets across the landscape, so we are beginning to see the greater landscape bobbing with the spring blooms of thousands of birdfoot violets.

But nature can't undo all of our devastation alone. We must act, helping it regain the ability to take care of itself.

Like other parts of the world, North America has experienced many invasions of animals, molds, and viruses as well as plants: the European earwig, the West Nile virus, chronic wasting disease in deer, and canine distemper in indigenous gray and introduced red foxes, and in timber wolves. Starlings have displaced red-headed woodpeckers and other cavity nesters, and carp have muddled the waters once used only by native fishes. There are countless nonnative earthworms in the soil. The list goes on and on: houseflies and house mice, the voracious European green crab, and the Chinese mitten crab. And let us not forget the ironically named Norway rat, originally from China, which has spread throughout the contiguous forty-eight states since its unintentional introduction as a ship stowaway in 1775.

Both these invaders and exotic plant species, brought in by the world's incessantly mobilizing and globalizing societies, have had profound effects on our native ecosystems. How can the land withstand the invasion or ever recover from the resulting changes? According to fundamental ecological and population dynamics theories, it cannot. If societies don't show vigilance against exotics, nature won't get a second chance.

chapter 14

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