The weather outside is icy, or balmy, or foggy or brilliantly sunny. Our roller-coaster winter continues, here and throughout the country. This time of year we all enjoy both the profiles of towering trees and wildlife in the winterscape, and some “not a fit night out for man nor beast” time to ponder perspectives of the natural world.
Winter is also a time that I do tons of programs throughout Ohio, the U.S. and even Canada as college students, landscapers, nursery growers and other green industry practitioners have time away from outdoor work to share in book learning.
One topic increasingly urgent for plant and nature lovers is the issue of invasive species. Here are a few topics on invasives I shared with my Sustainable Landscape Maintenance class at Ohio State University in Columbus this past week.
Invasive species issues are nothing if not diverse. These include woodland and urban forest insect pests such as emerald ash borer and Asian longhorned beetle and out west, the Mountain pine beetle as its range moves ever northward.
Invasive plant disease-causing pathogens threatening Ohio include impatiens downy mildew in landscapes and thousand cankers disease of black walnut, a complex disease involving the Geosmithia fungus intimately involved with the walnut twig beetle insect.
Invasives also include plants, such as exotic bush honeysuckle species in woodlands, garlic mustard invading gardens, and hogweed causing serious dermatological problems to humans contacting it along roadsides. There are invasive zebra mussels befouling Lake Erie, purple loosestrife in Midwest wetlands, and even fungal pathogens that cause white-nose syndrome on mosquito-eating bats.
Exotic, non-native species also make up much of what we typically consider positive additions to nature: European earthworms, European honeybees, and much of what we eat, from tomatoes and corn to peaches and plums.
One fascinating story of invasives is that of a dock that drifted onto the shores of the Oregon coast this past June. The dock was unlodged during a destructive tsunami in Japan in March of 2011. Despite more than 15 months on the open sea of the Pacific Ocean, separated from their usual lifestyle, life on the 150-ton dock included more than 90 species of marine organisms. These included the wakame kelp alga, considered one of the 100 worst invasive species on Earth. A common foodstuff in sushi cuisine, it is nevertheless a problem as it invades and thrives in new habitats. Ridding the dock of these organisms upon arrival was difficult but important.
Estimates of damage from invasive species vary, but one from the National Center of Environmental Economics cites up to $138 billion in losses annually in the United States. By any estimate, invasives are a problem, and the number of issues appears to be increasing as commerce becomes ever more mobile, from accidental introductions such as the arrival of the emerald ash borer from Asia into the port of Detroit, to deliberate introductions, such as when the multicolored Asian ladybeetle was brought to the U.S. as a biocontrol for pecan aphids in the South many decades ago.
One of the perspectives shared with students is the puzzle of trying to determine which introduced species will become problem invasives. Obviously we are glad that tomatoes and potatoes and peaches and plums were added to our culture. On the other hand, those Asian ladybeetles, though they did not work out so well as biocontrols, behaved for many decades until suddenly their populations swelled in the 1990s and tainted everything from the flavor of Ohio wines to enjoyment of our houses where the cute but stinky beetles were most unwanted home invaders.
This time component with invasives is important. Bush honeysuckles imported to Europe did not pose a problem for more than 100 years, but at some tipping point, their numbers exploded and caused problems in forested areas, crowding out native vegetation.
What is it about these honeysuckles that made them problem invasives after all those years? These are the kinds of issues that are addressed by a diverse group — the Ohio Invasive Plants Council (OIPC). The OIPC has developed a new science-based protocol to look at which introduced plants pose problems.
The 22-question protocol and an assessment team are designed to better define current invasives and evaluate potential invasive plant species in Ohio.
“OIPC is not a regulating group,” said Theresa Culley, University of Cincinnati professor and chairperson of the OIPC assessment team. “Our mission is to develop a new list of invasive plants for Ohio. We also intend to play a primary role in education, research and early detection.”
The group includes public garden horticulturists, natural area conservationists, nursery growers and university researchers in an attempt to improve our understanding and response to invasive issues.
And these issues are by no means simple. Even those exotic bush honeysuckles, introduced originally for land reclamation projects and as ornamentals, then banned in many areas, are now seen through some recent research as leading to an increase in bird species diversity, though other research suggests that the fruits they produce are of poor nutrition and nesting habitat for certain bird species.
Nature is complex and of an interwoven fabric that is tested, at least initially, by new introductions.
Ecologist Mark Davis of MacAlester College and 18 colleagues put it this way in a 2011 paper in the journal Nature:
“We are not suggesting that conservationists abandon their efforts to mitigate serious problems caused by some introduced species, or that governments should stop trying to prevent potentially harmful species from entering their countries. But we urge conservationists and land managers to organize priorities around whether species are producing benefits or harm to biodiversity, human health, ecological services and economies. Nearly two centuries on from the introduction of the concept of nativeness, it is time for conservationists to focus much more on the functions of species, and much less on where they originated.”
No simple task, but without question the best approach is to keep learning and applying diverse knowledge to solve problems and enhance the balance of the nurture of nature and the nature of nurture. In the words of journalist and author Michael Pollan: “Up with multihorticulturalism!”
Jim Chatfield is a horticultural educator with Ohio State University Extension. If you have questions about caring for your garden, write: Jim Chatfield, Plant Lovers’ Almanac, Ohio State University Extension, 1680 Madison Ave., Wooster, OH 44691. Send email to firstname.lastname@example.org or call 330-466-0270. Please include your phone number if you write.