The Deep Wounds of Forest Invasive Species

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Adam Janke
Assistant Professor - Natural Resource and Ecology Management
Iowa State University

ajanke@iastate.edu

One my favorite quotes from Iowa native and conservation icon Aldo Leopold goes like this:

 “One of the penalties of an ecological education is that one lives alone in a world of wounds.”

I think about that quote often this time of year because every fall, after the grand finale of summer recedes to the grays and browns of our dormant winter landscapes, those of us with an ecological education are stuck with a constant reminder of one of our deepest wounds.

It is this time of year that our native trees and shrubs downshift into dormancy during cold fall days, first trading the greens of photosynthesis for the brilliant colors of fall and then, in a synchronous ritual formed through millennia of adaptation to Iowa’s climate, drop their leaves and settle in for winter. 

It’s also this time of year when plants from the opposite side of the world, innocently introduced into Iowa for landscaping or poorly-conceived ideas of land-improvement, ignore those thousands-of-year-old traditions shared by our native plants. Rather, these exotic plants, including bush honeysuckle, Tartarian honeysuckle, and European buckthorn, take a different route into winter.

invasive speciesThese plants, which have escaped the grasps of the pests that once burdened them in their natural Eurasian habitats, grow rampantly in forests and old fields across the state. Then, as if being freed entirely from the burdens of specialized pests to limit their growth is not a suitable advantage, their internal clock, the same one that gives us the annual show of brilliance from our native plants over a short sequence of days each fall, yields additional advantages. While the native plants that have called Iowa home for thousands of years drop their leaves and surrender to the cold, these exotic plants stay green, taking advantage of shortened days to continue to store nutrients until the bitter cold of December sets in and finally calls their leaves to the ground.

It’s through this asynchronous timing each fall that the deep ecological wound they’ve created is ripped open for all to see.  

Invaded woodlands and roadsides throughout the state are lined with a layer of green from one to eight feet above the forest floor. This time of year, exotic highly invasive shrubs take advantage of all the sunlight released from the canopy of trees over head to continue to assert their dominance in the forest. They put all those extra reserves stored during fall to good use in spring, breaking buds well in advance of most native plants, monopolizing sunlight that should have reached the forest floor where native flowers and the next generation of trees need it.

Through these advantages –pest free growth coupled with their ability to use the latest and earliest days of the growing season—these invaders have completely changed the composition of Midwestern forests. Scientists across the Midwest have been tracking the impacts of exotic shrubs on our native flora and fauna and found drastic impacts. They alter soil conditions to promote their own growth. They display a behavior called allelopathy that chemically suppresses growth and survival of other species of plants in their presence. They shade the ground in ways that further inhibits growth of herbaceous plants, trees, and shrubs. The combined influence of these growth characteristics is a gradual but comprehensive shift in the composition of the forest from the canopy to the ground cover. Their impacts extend beyond plants too. Birds perceive their branches and berries to be suitable substitutes for native plants but end up suffering from reduced nutrition, increased susceptibility to predators while nesting, and, living up to the axiom “you are what you eat”, male birds of some species have altered feather coloration after eating a diet of exotic berries.

invasive speciesDirect control is the only option to fight back against the wide-ranging negative consequences invasion by honeysuckle, buckthorn, and other isolated cases of problematic invasive species present in our timber stands and other natural areas. Research and experimentation is ongoing across the Midwest to find scalable solutions to fight woodland invasives. Everything from helicopter applications of herbicide to hand-pulling is on the table. For small land owners or those with only an emerging infestation, cutting, treating, and pulling are still viable options. One character common to many invasive species is that their biomass tends to be above ground. That means they have shallow root systems, preferring to invest their energy towards growing up into spaces that take up sunlight, rather than down to compete for nutrients and water. So that makes them easy targets for hand pulling, particularly among first-year shoots. For older stems or more established stands, herbicide applications, often in concert with cutting are merited. The publication at the end of this article from Iowa State University Extension and Outreach is a useful resource for finding the right herbicide for the job. Some applications will involve cutting the stem and then painting the cut surface with an herbicide, while another approach is to apply a basal application, which surrounds the stem of the plant with an herbicide that can be translocated from the bark into the growing tissue where it can kill the plant. For larger-scale infestations, like those in large timber stands, more drastic methods are merited. Two practices being employed by County Conservation Boards and the Iowa Department of Natural Resources among others are precisely timed aerial applications of herbicide and targeted grazing combined with prescribed fire.

Fall is high-time to mount a defense against these unwelcome invaders. Not only are these exotic species easy to spot this time of year thanks to their late-season leaf growth, but they are also in the process of moving nutrients down to their root systems for the winter, making them particularly vulnerable to herbicide. There is cost-share available for landowners to mount a defense against invasions as part of state or federal programs designed to improve forests for timber production and wildlife habitat. A meeting with a local NRCS office or District Forester from the Iowa DNR can provide access to those resources.

The necessary first step in addressing the challenge these invasive shrubs, and all other invasive plants, pests, and pathogens pose to our natural ecosystems, is to develop that fundamental ecological education Aldo Leopold advocated nearly a century ago. With an eye for the wounds in our modern landscapes, we can start to work to find ways to help them heal.

Resources

Find contact information for local NRCS or Iowa DNR district foresters and private lands biologists that can help improve forest habitats for wildlife on private lands with the following link. https://www.nrem.iastate.edu/wildlife/contacts/Wildlife-Habitat-Programs-and-Consultation

Chemical Control of Unwanted Shrub and Tree Vegetation, ISUEO Publication on herbicides to control problematic woody plants, including those discussed in this article. https://www.extension.iastate.edu/forestry/publications/PDF_files/F-341.pdf

More information on identification and control of the most problematic exotic invasive shrubs in Iowa’s woodlands:

European Buckthorn : https://www.invasiveplantatlas.org/subject.html?sub=3070

Tartarian Honeysuckle: https://www.invasiveplantatlas.org/subject.html?sub=3043

Bush Honeysuckle: https://www.invasiveplantatlas.org/subject.html?sub=3040

Morrow’s honeysuckle: https://www.invasiveplantatlas.org/subject.html?sub=3041

Bell’s honeysuckle: https://www.invasiveplantatlas.org/subject.html?sub=5948

Date of Publication: 
November, 2017