Chris Standley

Invasive species have garnered a lot of media attention, and it's no surprise when you consider examples such as the infamous emerald ash borer, accountable for nearly 100 percent ash mortality within infested stands; hemlock wooly adelgid, which is sucking the life from large tracts of hemlock stands in the Northeast; and Japanese stiltgrass, which carpets the forest understory depriving native plants the light they need to survive.

As a wildlife ecologist, I appreciate the utility of this coverage. It informs people about invasives that are having large effects on our ecosystems, but I think we need to start looking at this issue with a broader perspective and deeper understanding to reduce the rate of future introductions. The continued crash-course model of discovering and managing invaders post-arrival has frightening implications for the long-term viability of our ecosystems, which is the basis of our survival.

The fossil record indicates we are living in one of the Earth's most biologically diverse periods. Roughly 200 million years ago, the super-continent of Pangaea began diverging into separate landmasses, fragmenting ancestral species assemblages that led to a cornucopia of unique life forms across the continents. Over millennia, species arose, either persisting or going extinct. They interacted and adapted not only to their environment, but to one another in a process known as co-evolution.

Modern technology has allowed nations to exchange visitors and natural resources in a global-market economy. Tourists have the ability to purchase agricultural goods on one continent and, upon return to their native continent, introduce pests and pathogens responsible for billions of dollars in damage annually. Natural resource sectors, such as lumber, have been responsible for introducing invasive wood-boring insects and fungi throughout the globe, resulting in losses of forest species. Even horticultural plants from exotic locations are sold at local nurseries only to escape people's landscaping and invade native systems. We are currently undergoing the sixth-largest extinction spasm known over geologic time, and invasive species are one of the primary contributors. Our inadvertent bridging of oceanic divides is resulting in rapid, intercontinental species exchange at the expense of endemic ecosystems.

Swapping species is a dangerous business because exotic species may be released from predators and natural enemies, competitors, and co-evolved host defenses that regulate their populations. The emerald ash borer is an excellent example of this. This beetle feeds on the living tissues of trees known as the phloem. The ash trees of Asia co-evolved with this beetle and launch chemical and mechanical defenses in response to the beetle's attack. Additionally a number of parasitoids attack and kill the eggs and larvae of the emerald ash borer in its native range. However, ash trees in North America have not co-evolved with the insect, limiting their abilities to launch an effective defense. Nor do our ecosystems possess a native suite of parasitoids to combat emerald ash borer larvae, leaving our ash trees extremely vulnerable to the impending onslaught by this pesky beetle.

In some cases, scientists have introduced natural enemies in an effort to control a new invader. This tactic, known as "classical biological control," has yielded mixed success. In 1869, Etienne Leopold Trouvelot introduced the gypsy moth, Lymantria dispar, as a potential source for silk production. The moth escaped his confines and has been one of the most destructive defoliators of hardwood forests. In response, scientists released a tachinid fly, Compsilura cocinnata, a natural enemy of the gypsy moth in its native range. Unfortunately, the introduction of C. cocinnata backfired, and the fly has been documented feeding on more than 200 non-target, native moth species in North America. When used alone, classical biological control employs an over-simplified logic that disregards the complex, multifaceted regulatory parameters species face in their native range. When improperly executed, it often results in poor regulation of invaders while posing great risks to native species.

Does this mean we should not manage invasive species? Should invaders be granted their ecological visas and evolutionary time needed to facilitate their integration into the system? I struggle to answer this, and it's a question I frequently face. Often my answer is "I don't know … it depends on your perspective." What I do know is that species assemblages drive ecosystem function, which is the interaction of organisms and their physical environment to produce ecosystem services such as water budgeting and filtration, nutrient cycling and soil viability.

We don't currently understand how each individual species contributes, but one of the earliest ecologists, Aldo Leopold, noted, "To keep every cog and wheel is the first precaution of intelligent tinkering." Keeping species assemblages ensures a functioning ecosystem that provides the services we need to survive. By managing invasive species, we seek to maintain native ecosystem function and, ultimately, our survival.

In a perfect world, we'd be able to detect invaders soon after they arrive and eradicate them before they become problematic. In reality, we often aren't aware of an invasive species until they are well-established and causing major issues. Few management efforts have led to eradication, because detection rates are so delayed that populations are widespread, making elimination from the landscape economically and operationally unfeasible. The obvious and simplest solution is to avoid species introductions in the first place, no doubt a tall order, but measures can be taken to reduce the rapid rates of spread. Educating consumers and tightening up natural resource and horticultural regulations are a couple that come to mind.

Our global exchange of species is reducing the biological diversity on the planet and threatening functional native ecosystems. As a result, we need to manage for the invasive species we do have and prevent future invasions from occurring. The issue transcends political and national borders but there are steps we can all take as individuals. Support the movement for local economies, be mindful of the items your return with in your carry-on, and leave exotic plants from the nursery out of your garden. Investing in long-term integrity of native ecosystems ensures we are moving in the right direction and that will take a conscious effort from local to international scales.

Chris Standley is the Applied Conservation Coordinator at Daniel Smiley Research Center at Mohonk Preserve in Gardiner.