September 4th- It is a warm morning, with the wind blowing and the sun shining down on the beautiful northern half of Bard College. Cold weather has yet to come, so the bees are happily buzzing around, moving from flower to flower gathering nectar and pollen. The birds are active too, as I can hear them singing different songs all around me. I walk into the grassy field, still soggy from rain days before, where I will study a one by one meter plot assigned to me for the semester. Upon entering the field, my eyes are drawn to the different species of flowers and grasses spread unevenly throughout the field. I walk to my assigned plot, where I immediately notice the arrangement of purple and yellow flowers. Both flower species, purple loosestrife and goldenrod, tower over the grasses, weeds, and other flower species.
As I observe my one meter plot closely, I notice the heavy presence of bird’s foot trefoil and tall grasses. However, they are no match for the showy goldenrods and purple loosestrife that tower over them. The purple loosestrife and goldenrods in my plot reach heights of three feet, which allow them to better compete for light. While observing these two flower species, I notice that they have more visitors than the other flower species. Bees, beetles, butterflies and flies all swarm the various flowering stems of the purple loosestrife and goldenrod. Both species, however, seem to get pollination visits primarily from the bees in the area. Both of these flower species are known for their dominance, due to their height and showy flowers, however both of them have a dark secret.
The truth is, purple loosestrife is an invasive species, non-native to upstate New York (and to the Bard College campus), which dominate wetland areas (or areas where soil is more water-saturated than average). Purple loosestrife, like other invasive species, takes over non-native regions because of a lack of non-native insect predators. Purple loosestrife is able to disrupt various ecosystems, including rice farms, whose growth and production is hindered. Invasive species cause a domino effect, because when they successfully establish a population in a non-native area and their presence disrupts the native community, it leads to a chain of events that negatively affect the native community. Invasive species negatively impact an ecosystem by causing habitat loss and alteration, and by causing species to go extinct. Purple loosestrife can contribute to the extinction of a species, as well as habitat alteration, because of its abilities to act as a strong competitor. Purple loosestrife is like a race car driver who wins most of the races they enter, because of their skill and strength as a competitor, and because they have the best car before the race. Purple loosestrife, like the race car driver who is swimming in a pool of money after winning all the races, is rich with nutrients, because it has the advantage of being a tall plant that is a dominant competitor.
The field in which I am conducting observations is haphazardly filled with purple loosestrife. I notice, however, that in our field, goldenrods are of equal, if not greater abundance than purple loosestrife. If invasive species normally take control of a community because of a lack of a predator, why are goldenrods of equal if not greater abundance than purple loosestrife? Should purple loosestrife not be everywhere?
To answer this question, I looked at my plot as well as the surrounding field. One morning, while observing the plots, something caught my eye that provided me with a potential answer for my question. I noticed that the goldenrods in the field were not randomly distributed, but could be found in clusters throughout. On the other hand, purple loosestrife tended to grow in an arrangement that was more randomly distributed. The characteristic that makes goldenrods so special, is that they are a clonal species, meaning that each individual flower can reproduce by itself, allowing for identical flowers to appear. The cloning of purple loosestrife is rare, and so these purple flowers rely more heavily on pollinator visits than goldenrods do. The cloning of goldenrods allows many clonal plants to appear near the parent plant more rapidly than the plants that rely on pollinators for reproduction. Cloning, as well as plant physiological features like height and vibrant flowers, allow goldenrods to dominate their native ecosystems.
The invasive purple loosestrife is the parasite of the wetland habitat, as it scrounges soil nutrients, water, and sunlight from the community in which it invades. Purple loosestrife, similar to parasites, causes harm to its host, the community, while providing no direct benefits (Purple loosestrife does, however, provide pollen and nectar to bees, butterflies, beetles and flies). Additionally, although purple loosestrife primarily reproduce sexually (which takes more time because it relies on pollinators to move pollen to another plant), it is able to produce between 100,000 and 2.5 million seeds per plant (which is alot), depending on age. When purple loosestrife produces millions of seeds, it allows the species to overpopulate, and take over the space and resources in the community. In contrast, goldenrods produce a mere 3000 seeds per plant (which is only 0.1-3% of the seeds that purple loosestrife produce), meaning they are less likely to populate a community at the same scale that purple loosestrife can. Although goldenrods may seem like a harmless species compared to purple loosestrife, the yellow flowers actually have their own dark secret.
Goldenrods release harmful chemicals through their roots or leaves that are absorbed by the roots or leaves of other plants. This chemical process is known as allelopathy, and it can have an array of negative effects on other plants. The effects of allelopathy can be compared to a broken bridge, preventing semi-trucks from carrying goods from a facility to a distributor. For plants affected by these chemicals, the process of germination (or seeds becoming plants) can be halted, and the process that turns sunlight, carbon dioxide, and water into sugar for the plant, with oxygen as the byproduct, can be slowed or stopped altogether (this is formally known as photosynthesis). In a sense, these chemicals break the bridge that allows plants to move from one stage in growth to another stage, or slow the chemical processes of a plant. If a plant is affected by the enemy chemicals, the plant will not be able to produce the sugars that it needs via the process of photosynthesis. In terms of our goldenrods, these tall yellow flowers can negatively affect the growth of plant species including woody plants like Sugar maple trees.
Next time you walk through the fields of upstate New York you will likely notice the vibrant purple loosestrife and goldenrod. Despite the natural beauty that the two species provide, both the purple loosestrife and goldenrods negatively impact the communities in which they live. Purple loosestrife is the uninvited guest that overstays its welcome, and goldenrods are the bullies of their native communities.