Invasion Dynamics, Aldo Leopold, and the Penalties of an Ecological Education

by Chad Hammer


I am a first-year master’s student with the Natural Resources department at UNH. My research is assessing the invasion patterns and impacts of terrestrial invasive plants in New England riparian forests (forests typically found along streams and rivers). I have always been very fascinated by nature since I was a young boy, always playing in the streams and forests near my house in western New York. Even into my adult life, whenever I would pass by different ecosystems in the car (e.g., wetlands, forests, vernal pools) I would always ask myself, “what sort of organisms would live there?” When I found myself considering a career change, I knew exactly what I wanted to pursue. After closing my business in Buffalo, N.Y. in 2013, I moved to the Adirondacks (northern New York) to study ecology and biology at Plattsburgh State University. I learned about terrestrial and aquatic invasive species through my coursework and during my time with the Lake Champlain Research Institute as a research technician, although I did not have a lot of hands-on experience with terrestrial invasive plants. My experience was limited mostly to the dense patches of invasive phragmites (also known as common reed, native to Europe) along roadsides and on the shores of Lake Champlain and the invasive common and glossy buckthorn (native to Eurasia) in many of the wildlife management areas towards the perimeter of the 6.1 million-acre state park. Buckthorn was often intentionally planted in the eastern United States for bird and other wildlife habitat before realizing its invasive potential. I was very fortunate to live in the Adirondacks and spend all my free time hiking near the High Peaks region, where terrestrial invasive plants are not a major issue.  

Shortly after arriving to New Hampshire, my mentor Dr. John Gunn gifted me a book, “A Sand County Almanac” by Aldo Leopold. John wrote on the back of the cover, “This is essential reading for any ecologist.” Aldo Leopold (1887-1948) among other things was an American author, philosopher, ecologist, forester, and conservationist. He helped to develop many of our modern wildlife management practices, environmental ethics, and much of our wilderness conservation ideology. As I read the first line of the book, “There are some who can live without wild things, and some who cannot, these essays are the delights and dilemmas of one who cannot,” (Aldo Leopold) I knew that John was right and this was going to be one of my new favorites. 

A few months ago, my father visited me from western New York. I wanted to take him for a nature walk, so I decided to take him to Odiorne Point State Park (Rye, NH). I knew that he would love the remains of Fort Dearborn from World War II and the views of the ocean, so I decided this is where we would go. Typically, when I get time to enjoy nature I head right to the mountains or a mature forest. These forested ecosystems are often believed to be very resistant to invasive plants, as they have high species diversity and biomass. These plant communities would be taking up all the available niche spaces and limit available resources to potential invaders, therefore increasing their resistance to invasion; this is known as the biotic resistance hypothesis. Upon arrival, we went to the Seacoast Science Center, which was fantastic, and we even got to go birding! We then began our journey through the nature trails. In addition to typically hiking in the mountains, I was new to this area and not prepared for the level of invasion in some parts of the New England region. I was completely shocked by the amount of oriental bittersweet at Odiorne State Park. Oriental bittersweet is native to Asia and was introduced to the United States as an ornamental vine circa 1860.  Bittersweet’s climbing vines grow over the top of shrubs and trees, weighing down branches and blocking sunlight. This greatly reduces photosynthesis and the health to the overtopped vegetation.  Oriental bittersweet has attractive fruits and seeds that can be a winter food source to birds, which facilitate the spread of bittersweet into new areas. The seedlings are shade tolerant, fast growing, and can exploit open areas very quickly. 


It was clear that there was a lot of restoration work taking place here and that they definitely had their work cut out for them. I know my father could not see what was obvious to me and most likely saw thriving green plants, but just because it’s green it doesn’t mean it’s good. What I saw was a serious attack on the native vegetation by the climbing oriental bittersweet. This was causing mortality to the native vegetation. As Leopold said, “A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community.  It is wrong when it tends otherwise.”  Many native trees were being strangled to death and there where large areas where oriental bittersweet had formed dense monocultures that completely choked out all other vegetation. Bittersweet was outcompeting the native plants for valuable resources such as sunlight, space, and nutrients and causing their slow death. This brings me back to another one of Aldo Leopold quotes that John and I had previously discussed.  It states, “One of the penalties of an ecological education is that one lives alone in a world of wounds, much of the damage inflicted on land is quite invisible to laymen.  An ecologist must either harden his shell and make believe that the consequences of science are none of his business, or he must be the doctor who sees the marks of death in a community that believes itself well and does not want to be told otherwise.”


As we continued down the trail, I kept asking myself how the degree of invasion got to be so bad here. About a half mile further down the trail we arrived at the remains of Fort Dearborn, from WWII (1939-1945). After seeing the remains of the fort, I believed I had found my answer! This is just my theory but seeing how these massive concrete bunkers were built and then buried with an enormous amount of soil to create large hills (probably to protect and camouflage the fort and gun towers) I couldn’t help but visualize the massive excavation project and disturbance that would have taken place here in the mid-1930s. This is about 75 years after oriental bittersweet’s introduction, which would have given it time to establish in many areas and wait for openings to invade and exploit. Human modifications (bridges, culverts, dams), human disturbance (timber harvests, development) and natural disturbance events (hurricanes, fire, floods) all play a large role in invasion dynamics and often introduce invasive species to an area. These open areas with newly available resources (space, sunlight, nutrients) are easily colonized by invasive plants that are often fast growing and highly competitive. They can spread to new habitats by dispersal of their seeds and other plant propagules (via birds, animals, wind, moving water, transporting fill and soil) into recipient habitats. Once invasive plants are established, they begin to outcompete native vegetation through a suite of mechanisms such as rigorous growth early in the growing season, altering soil chemistry to benefit the invaders, aggressive rhizomes and root systems, and increased allocation of nutrients.  Many of these traits allow the invaders to grow in dense monocultures (single species) with a thick canopy and often shade out everything below them and greatly reduce regeneration of native plants that would grow above them.  This has many negative impacts to local biodiversity.


These complex and highly competitive life history strategies, in addition to the role of disturbance and historical land use at Odiorne Point State Park has most likely contributed to the high levels of invasion found here. My research will assess the impacts of invasive plant invasions and assist conservation efforts to further understand the distribution of invasive plants in riparian forests.  In addition, my work will help identify which areas may be at risk of invasion, how to minimize this risk, and mitigate the effects on ecosystem services. My hope, in the words of Leopold, is that even “laymen” will someday be better stewards of nature and recognize the many ecological “marks of death” and care enough to restore habitats and let nature begin to recover. 

About Chad

If you are interested in hands-on opportunities to eradicate invasive plants in New Hampshire, check out Nature Groupies.