Background and History:
Public gardens and arboreta (gardens that focus on the display of shrubs and trees) have a unique role to play when it comes to keeping an eye out for potential invasive species. On one hand, these institutions' missions focus on the collection and display of plants from around the world, so gardens and arboreta are continually assessing and importing exotic plants to the United States, some of which may potentially be invasive here. On the other hand, the vast majority of public gardens also incorporate an environmental ethic into their missions, and work very had to conserve regional or global biodiversity and/or to maintain naturalized areas on their grounds.
Along with several other industries and interests, public gardens have, in the past, inadvertently introduced and spread invasive plants. For example, in the late 1800's, Japanese barberry (Berberis thunbergii) was first planted in the U.S. at an East Coast botanical garden. After those first specimens were successful, it was widely promoted as a replacement for the garden shrub European barberry (Berberis vulgaris), which was known to carry a disease that affected wheat crops. Japanese barberry has become an extremely popular landscape shrub over the last 100 years, and while it doesn't harm wheat crops, it causes all manner of ecological problems due to its tendency to escape cultivation due to birds depositing seeds in natural areas.
Awareness of invasive plant issues, particularly among botanists and horticulturalists, has grown a great deal over the last several decades, and many public gardens have taken steps to define their roles and positions. For example, in 2001, ecologists and horticulturalists representing multiple sectors gathered in St. Louis and developed a set of voluntary guidelines aimed at reducing the risk of invasive plant introduction and spread for several sectors, including public gardens. These guidelines are collectively known as the St. Louis Declaration. Many public gardens and arboreta integrated the Declaration commitments into their strategic plans and operating procedures.
Plants on the Move attendees observe an Amur Corktree (Phelloodendron amurense), a plant that escapes cultivation and is listed as invasive by certain Midwestern states.
MIPN joined with The Morton Arboretum (Chicago-area, IL) and the Ohio Invasive Plants Council to bring public garden stakeholders back together to discuss invasive plant issues, building on the foundation established in St. Louis. In November of 2016, we hosted an event called the Plants on the Move Summit. This meeting was focused on discussing advancements in thinking and practice on invasive plant issues over the last 15 years, new methodologies and tools for evaluating the potential invasiveness of plant species, and how the public garden community can better share and communicate observations of plants escaping cultivation with each other, with their visitors, and with the general public.
Key findings of the summit were that among the 26 U.S. and Canadian institutions represented, there was a high level of interest in continuing to discuss and refine practices to prevent invasive species introduction and spread. Participants embraced the potential for public gardens to become leaders on this issue, potentially even acting as sentinels against new invaders by choosing not to import exotic species evaluated as high-risk and by sharing observations about plants that escape cultivation both inside and outside of the public garden sector. However, communication on "plants on the move" must be done carefully because not all plants that grow outside of their intended confines are capable of naturalizing or causing the ecological, economic, or human health impacts that would qualify them as invasive. A report summarizing the summit proceedings, discussions, and findings is available in a pdf document.
For the organizing partners, our next steps will be engaging more members of the public garden community on this issue by sharing our findings and actively soliciting interest with the help of professional organizations like the American Public Garden Association (APGA). We will also continue to explore potential venues and communications tools for public garden staff and volunteers to share observations about plant movement easily and consistently. If you would like to be part of our continued conversation, please get in touch!