Michael DeRosa: Zoo animals vs. invasive plants

BY MICHAEL DeROSA, for ecoRI News

Invasive plants tend to be fast-growing species found throughout New England's abandoned landscapes, along roadsides and stream banks, and in neglected gardens. These plants are effective in occupying areas otherwise controlled by native species. As the range of non-native, invasive species expands, they displace native species and can have a profound effect on insect populations, which have evolved and adapted to native plant communities.

Removing invasive species from the local landscape is important. More important , though, is the re-establishment of these vacated areas with native plants; thereby reclaiming the landscape and creating habitat for native insect species, which form the basis of the food web and in turn serve as food for higher-level vertebrate species. This all leads to a more stable and healthier ecosystem.

Japanese knotweed, for example, is a highly aggressive and invasive plant that appears on federal and state prohibited plant lists. The plant is a large herbaceous perennial with spreading rhizomes. The plant originated in Asia and is a member of the buckwheat family. It was introduced to the United States as an ornamental plant and used as hedge plantings and to control erosion.

Like most invasives, though, Japanese knotweed is resilient and can grow almost anywhere. The notion of the permanent removal of knotweed or other invasive species is a noble but naïve endeavor. The local control and eradication of an invasive species, however, is achievable with adequate aftercare and re-establishment of a native plant community.

Japanese knotweed, however, is particularly troublesome. Cutting and removing standing vegetation is a beginning, but without removing the root ball completely, the plant will re-colonize the area within the same growing season. Moreover, the plant will regenerate into an entirely new plant from broken stems, leaves and root parts.

Over the years, we have established two different protocols for the removal and disposal of knotweed — each with its own set of costs and benefits.

Beau, a 14-year-old male giraffe, and many of the other herbivorous residents of the Franklin Park Zoo in Boston, enjoy snacking on Japanese knotweed.

Photo by Franklin Park Zoo

The first is the harvesting of the plant. The knotweed is manually cut at the stem base and used as natural forage for particular herbivores at Zoo New England’s Franklin Park Zoo. The roots are then harvested with the assistance of a machine or backhoe and either stockpiled and burned or buried at a depth greater than 10 feet. This eliminates the possibility of a successful re-colonization of the area.

The second option includes the harvesting of the plant and use as forage for zoo animals, but it doesn’t include root removal. Oftentimes, sites are in areas that preclude the use of heavy equipment. In these situations, we will continually harvest the knotweed on a routine basis, typically every three to four weeks. We are continually stressing the plant and forcing it to use stored energy in the root system to produce more stems and leaves without getting much energy in return. These new shoots are excellent forage for the zoo animals, and contribute to their winter and summer supply of forage plants.

Over time, we have seen interesting morphological changes in the plant’s reaction to the continued stress. The roots seem to be sending information to the stems to produce many more shoots than it otherwise would; presumably in the hopes of sending out more leaves to gather more energy and store more energy resources.

Our thought is that by continually stressing the root mass and not allowing the plants to transfer additional energy to the root system, it will ultimately force the plant to shut down. Without sunlight and the ability to photosynthesize, the hypothesis is that the plant will not be able to grow and will ultimately die.

Establishing a liaison with Zoo New England has been paramount to our continuing sustainability efforts with our invasive-species-management program. In this way, we are re-thinking our disposal options and utilizing a former waste as a resource.

Michael DeRosa is the principal at DeRosa Environmental Consulting, in Ipswich, Mass. This story originally appeared in the July 2015 Ecological Landscaping Association newsletter.