Our Approach to Invasives

For all the resources that are (rightfully) dedicated to climate change, much less consideration is given to its parallel relationship with Biodiversity. Biodiversity is the central organizing principle that creates resilience in habitats and ecosystems worldwide. For those not familiar with the concept of biodiversity, simply put it is used to define the “variety of living organisms” found in a defined ecosystem or habitat. Ecosystems and habitats with high biodiversity have a higher resilience to change while those with low biodiversity are more likely to see major breakdowns in ecosystem functioning with the addition of stressors such as climate change, disease and invasive species.  

A symptom of a highly globalized world;  plants, pathogens, and insects can now find their way across continents rapidly, introducing novel and highly invasive organisms to environments with little to no local competition. Plants are finding themselves rapidly transported across the globe for ornamental or agricultural purposes, caterpillars are hitchhiking on camping gear and infectious blights and bacteria are touring the world on lumber. In just a few short hours a species which has spent millions of years existing within the confines of geographic limitations can be dropped off at a new frontier on the other side of the world. While movement of species is a natural process, high-speed global transportation has allowed species to travel long distances at unprecedented rates. Some of these misplaced species have adaptations that allow them to rapidly outcompete the native species, creating a situation which might be comparable to what dropping a modern day tank into a medieval village might look like… those knights don't stand a chance. While chainmail is an effective defensive strategy against maces and swords, it isn’t going to provide much defense against 21st century technologies. Had the medieval village seen the tank off in the distance they might’ve taken a different approach. Returning to the world of plants, species which have had millions of years to grow  alongside one another usually develop defensive or growth strategies that allow them to develop a sort of balance. Introduction of species to new areas can upset this balance, often resulting in one species greatly outcompeting the other(s). 

Just because a species is added to an ecosystem where it has not existed historically, doesn't mean it will become invasive. Non-native species can typically be classified into three groups; cultivated, naturalized or invasive. Typically, cultivated species are limited to the area where they are planted and require extensive care to ensure their survival in their planted location. Examples of cultivated species include many landscape plants such as tulips and hydrangea, or edible crops such as tomatoes. Species like this are not considered to be at a high risk of escaping cultivation. Naturalized species include those which are growing and reproducing outside of a cultivated environment but are not causing a negative impact on the ecosystem to which they were introduced. Some species which are originally classified as naturalized may have the potential to become invasive. Dandelions are classified as naturalized by most states as they originate from Europe and therefore are not native, but are not causing any immediate harm to the habitats in which they are found. Changing climate and precipitation patterns may cause some naturalized species to become invasive. Invasive species are specifically non-native species that are causing immediate harm to an ecosystem in one way or another. Asiatic bittersweet, a plant classified as invasive in the State of Maine, is considered damaging due to its ability to completely outcompete most native understory plants due to smothering. When left unchecked this species of bittersweet can create large monocultures where it becomes the dominant species found in a stand. This can be seen along the I95 interstate here in Maine where bittersweet grows in large, tangled piles. These invasive species monocultures are effectively useless to native wildlife and insects, creating a space that is a virtual deadzone that is serving little to no ecosystem function. 

If you’ve spent any time here at the Arboretum, and you have even a casual understanding of plants, you’ll see a variety of invasive plants everywhere on our grounds. Some of the more common offenders found here include honeysuckle, asiatic bittersweet, Japanese knotweed, burning bush, buckthorn and Japanese barberry. All of the species listed above were intentionally planted as ornamental plants for many years before they escaped cultivation and found immense success in the wilds of North America. Some features that give these species a leg-up over our native plants include their ability to leaf out rapidly in the spring and high seed yield starting at a young age. Some species including Japanese knotweed, Asiatic bittersweet and burning bush have the ability to sprout from pieces of cut stems allowing them to grow back even more aggressively once they have been disturbed or cut. While cutting and bagging these plants can be an effective strategy for removal in small scales, here at the Arboretum we are faced with thousands of pounds of invasive plant matter in areas as small as an acre. 

And while we’ve been caring for these lands for over 40 years, we’ve only recently been able to take invasive plant management more seriously; recognizing the threat these plants pose to our varied habitats and botanical collections. 

The most effective methodology to manage pests (insects, plants, diseases) is the utilization of an Integrated Pest Management approach. This philosophy is widely used in land management across a variety of disciplines, and emphasizes an ongoing combination of (1) monitoring, (2) action thresholds, and a variety of (3) control methodologies which range from mechanical to chemical. In Maine, Integrated Pest Management is required practice in schools, municipalities, state-owned public lands, and by commercial (for-hire) pesticide applicators. 

We utilize the same (IPM) approach here at the Arboretum, and our Land Management Team has worked with Maine Bureau of Parks and Lands, the Maine Forest Service, the Maine Natural Areas Program, and the Natural Resource Conservation Service, to develop a comprehensive plan for invasive management on this property. It’s a strategic approach which, over the next 3 years, will increase the ecological value of our lands and give native plants an opportunity to thrive. As we implement this plan, volunteers and staff will be working tirelessly to remove invasive plants by hand, with assistance from our licensed applicators using Glyphosate and Triclopyr herbicides to selectively control species that cannot be effectively controlled mechanically.

No matter the circumstance, the consideration to use any pesticide should not be taken lightly, and the decision to move forward with an application should  consider the target pest, the application site, and the product being used; carefully reviewing the manufacturer's recommendations.  By utilizing this approach, we can reduce the unnecessary use of harmful pesticides in our community, while doing our part to restore Maine’s habitats and prevent rapid biodiversity loss.