Could Climate Change Affect Your Local Forest?

 Author: Audrey Kaiser, Edited By: Autumn Berlied

            Climate change and invasive species are two concepts you have probably heard of, even if you are not an ecologist. In fact, you don’t have to be a scientist at all to be familiar with either of these issues- they’re occurring in your own backyard.

Invasive Species

Invasive species are plants or animals that are not native to an area and pose a threat to native biodiversity. All organisms have a niche that allows them to survive in their respective environment based on their physical tolerance of several biotic factors. These factors include (but are not limited to) climate, habitat suitability, available resources, and competition for those resources. These factors determine the distribution of most organisms, and changes in any of these factors have the potential to alter their future distribution.

When invasive species are introduced to a new ecosystem with biotic factors similar to its home range, they can establish and spread rapidly. Additionally, the absence of a native predator in these new habitats enable them to further increase their population density, as they are not being naturally controlled. Invasive plants are generalist species- meaning they have broad niches, and there is little stopping them from easily growing in foreign habitats. This is what eventually allows them to outcompete native species and overtake their habitat.

Glossy buckthorn

European barberry

Oriental bittersweet

Photos: (From top to bottom) Glossy buckthorn, European barberry, and Oriental bittersweet. These photos were taken by conservation interns for the Harris Center for Conservation Education during an invasive monitoring project in Hancock, NH.

Invasive Plants and Climate Change

 In recent years, the world has seen a rising number of invasive plants. In New England, some primary species of concern are Glossy buckthorn, Japanese barberry, and Oriental bittersweet (pictured above.) These plants are naturally aggressive competitors and can overtake native habitat on their own accord. Additionally, invasive species tend to do especially well in less desirable conditions and can easily adapt to changing environmental factors (6). This is only one piece of evidence that invasive plant communities may be facilitated by predicted future climate conditions (6). Paring invasion mechanisms with climate change, we may be seeing significant shifts in forest communities in the near future. 

Climate change is and will continue to alter the distributions of both native and invasive plants in New England (1). As the climate warms, the distribution of native plants in New England will most likely become smaller, and the distribution and spread of invasive species will most likely become larger and more rapid (1). A 2017 study predicted that both Japanese barberry and garlic mustard will continue to move Northeast as global temperatures rise. If this is true, as distribution of invasive species continue to spread, it may also broaden their niches. For instance, garlic mustard is typically found on forest edges, but is beginning to move into the New England forests, threatening native communities (1). 

Garlic Mustard and New England Forests

Garlic Mustard in the first season rosette stage, Source: Audrey Kaiser (5).

Garlic Mustard in the Second season Mature stage. Source; Pixabay

Invasive Species of Garlic Mustard

One concerning but lesser-known invasive species in New England is the garlic mustard (Alliaria petiolata). Garlic mustard is a noxious weed that stays alive for two growing seasons (biennial) (3). It can self-pollinate, meaning that there only needs to be one to reproduce, making seed distribution relatively easy. As shown in the diagram below, it starts from seed (A) and spends the first growing season in the juvenile rosette stage (B). In the second growing season, it matures to a seed-producing adult (C)(3). Its unique life cycle is one of its many invasive advantages. Due to such heightened reproductive potential, it is considered a threat to native New England Forests.

Figure 1. The life cycle of Garlic Mustard (5). Source: Argetsinger 2018.

The Spread of Garlic Mustard

Garlic mustard is already making its way into New England forests. Its home range extends from Italy at the southernmost point, and Sweden at the northernmost point (3). In this native habitat, it thrives in partially shaded areas such as those on forest edges, or in riparian ecosystems (3). This plant was introduced to the U.S from Europe by early colonists for food and medicinal purposes (3). After its introduction, it was it first seen growing amongst a native community in Long Island New York in 1868 (3). Since then, its expansion rate has increased to 6400km2 per year as of 1991 (3). It has since spread to many states in the U.S, according to data gathered by EDDMAPS.

Figure 2: Current distribution of garlic mustard in the U.S.  

Source: EDDMapS. 2020. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health.

Noxious Compounds

Garlic mustard is considered noxious due to its fascinating ability to use secondary compounds to manipulate the relationship between native plants and their symbiotic fungus (mycorrhiza) (3). These fungal relationships are commonplace in most vascular plants and are needed in order to complete many important biological processes including water uptake and nutrient cycling from the roots (3). These secondary compounds have been also been shown to negatively impact native seed germination (3). It also has negative effects on native pollinators by preventing the maturation of native butterfly larvae, therefore decreasing survival rates (3). Additionally, the secondary compounds make garlic mustard extremely unpalatable to native herbivores, making them even more competitive in a foreign habitat (5). If garlic mustard’s distribution continues to extend from edges into forests, this could cause a multitude of challenges for New England natives.

Future Directions

There is still relatively little known about how garlic mustard’s secondary compounds affect native plants in the long term, or post-removal. There is also still a lack of research on whether climate change will cause this particular invasive plant to become more aggressively competitive or not. Another question to consider is how it will compete and interact with other invasive plants compared to native plants. Additionally, studying how this plant reacts to global climate change in its native range may help for us to predict its future distributions in NE. As climate change progresses, more research must be done on invasion ecology to really be able to predict how NE forests will shift in the future, and what garlic mustard’s role will be.

Citations

(1)  Garlic mustard identification and control: Alliaria petiolata

(2)  Leishman, M., & Gallagher, R. (2015). Will there be a shift to alien-dominated vegetation assemblages under climate change? Diversity and Distributions, 21(7/8), 848-852. Retrieved March 5, 2020, from www.jstor.org/stable/24817369

(3)  Merow, C., Bois, S., Allen, J., Xie, Y., & Silander, J. (2017). Climate change both facilitates and inhibits invasive plant ranges in New England. Proceedings of the National Academy of Sciences of the United States of America, 114(16), E3276-E3284. doi:10.2307/26480457

(3) Kristina Stinson, Sylvan Kaufman, Luke Durbin, & Lowenstein, F. (2007). Impacts of Garlic Mustard Invasion on a Forest Understory Community. Northeastern Naturalist, 14(1), 73-88. Retrieved February 13, 2020, from www.jstor.org/stable/4499897

(4) Rodgers, V., Stinson, K., & Finzi, A. (2008). Ready or Not, Garlic Mustard Is Moving In: Alliaria petiolata as a Member of Eastern North American Forests. BioScience, 58(5), 426-436. doi:10.1641/b580510

(5) Stinson, Kristina A.; Argetsinger, Sophie; Jackson, Michelle R.; Coates-Connor, Erin; and Meadows-McDonnell, Madeleine, "Here's the Dirt: The Newest Recommendations for Garlic Mustard Management" (2018). Environmental Conservation Educational Materials. 4.

(6) Wilcove, David S.; Oppenheimer, Michael. (2009). Climate change increases the risk of plant invasion in the Eastern United States. Biological Invasions, 12(6):1855-1872. Springer International Publishing 2010.

(7) Leishman, M., & Gallagher, R. (2015). Will there be a shift to alien-dominated vegetation assemblages under climate change? Diversity and Distributions, 21(7/8), 848-852. Retrieved March 5, 2020, from www.jstor.org/stable/24817369