The Invasive Rosa multiflora
Nothing is more peaceful and refreshing than a walk through the woods on a brisk fall day…except when you find your path engulfed by thorny thickets with no escape except through. Unfortunately, this is becoming the reality for vast amounts of woodland in the northeastern United States, including Pennsylvania. The thorny culprit goes by the common name Multiflora rose but is scientifically known as Rosa multiflora. Growing up in western Pennsylvania, in a 6a hardiness zone, I have witnessed R. multiflora steadily take over much of my family’s land as well as the neighboring McConnells Mill State Park. The land was farmed during the early 20th century and was easily passable when my parents acquired it 40 years ago. Yet now, one must be prepared for a prickly battle to pass through the woods. While I have always been able to excuse the occasional scratch from a black raspberry bush or other native thorny plants, the same is not said for the invasive R. multiflora.
Native to Japan, Korea, and eastern China, R. multiflora was first brought to the United States around 1860 to be used as rootstock for ornamental roses and by the 1940s was promoted as a living fence and ground cover (Jessie et al., 2013). Today, R. multiflora has taken over around 45 million acres in the northeastern United States (Jessie et al., 2013). It is likely the dense population of R. multiflora on my family’s land is the result of the plant being used as a living fence during the land’s farm days and later the promotion of R. multiflora to increase game populations.
Each stem on an R. multiflora plant grows up to 15 feet long and arcs toward the ground where it once again takes root, known as layering. This forms dense thickets up to 10 feet tall (PennState Extension, 2020). The northeastern U.S. is also home to many thorny plants with similar characteristics such as black raspberries (Rubus occidentalis) and Allegheny blackberries (Rubus allegheniensis). However, R. multiflora can be differentiated from these native species by its year-round olive-green stems, although new growth can appear red, and a fringed stipule at the base of each pinnately compound leaf. Additionally, R. multiflora bears small, shiny, red hips (fruit) that darken over time and persist over the winter (PennState Extension, 2020). Therefore, the hips are eaten by birds year-round, increasing the dispersal of R. multiflora seeds.
Because the invasive species can tolerate a large range of moisture, pH, and salinity, it thrives in poor growing sties (PennState Extension, 2020). Even more, native browsers and invertebrates prefer not to eat R. multiflora, leaving extremely cold temperatures, below -28 degrees Fahrenheit, to limit its range (PennState Extension, 2020). Nonetheless, the species prefers ample light but can be found growing in low-light conditions such as dense forests. I recently made the interesting observation that many of the R. multiflora plants on my family’s property retained leaves even at the end of November when nearly all other plants had died or entered dormancy. Because R. multiflora is semi-evergreen, it retains some leaves during winter and can continue photosynthesizing (Banasiak & Meiners, 2009). Dlugos et. al (2015) explain that R. multiflora plants begin spring growth before other vegetation and hold on to their leaves much longer than other vegetation in autumn. In densely wooded areas, the plants tend to hold on to their leaves even longer than plants in less shaded fields (Dlugos et. al, 2015). Therefore, R. multiflora is able to grow in low-light forests. However, Dlugos et. al (2015) concluded that R. multiflora is not shade-tolerant and that seedlings have difficulty developing biomass in shaded areas. This has important implications for managing this invasive species.
In Pennsylvania, R. multiflora is considered a Class B noxious weed, meaning that the sale of the plant is prohibited and that measures are in place to address the infestation (PennState Extension, 2020). Because R. multiflora spreads through seed dispersal, layering, and root sprouting, its successful invasion has negatively affected the richness of native species and is particularly difficult to combat (Banasiak & Meiners, 2009). According to PennState Extension (2020), the best plan to address the R. multiflora infestation is to “save the best” and treat the least invaded areas first through a mix of physically pulling out plants and applying herbicides. Densely populated areas must be cut with a brush mower or other mechanical method followed by herbicide application (PennState Extension, 2020). However, this also kills many native plants. It is important to note that as temperatures increase and winters in the northeastern U.S. become milder, it is likely that the range of R. multiflora will expand North. Therefore, monitoring and treatment of these northern areas must begin now in order to prevent further R. multiflora infestations in the face of climate change.
Identification Resources
References
Banasiak, S., & Meiners, S. (2009). Long term dynamics of Rosa multiflora in a successional system. Biological Invasions, 11(2), 215–224. https://doi.org/10.1007/s10530-008-9226-1
Cornell University Cooperative Extension. (2019). Multiflora rose. http://nyis.info/invasive_species/multiflora-rose/
Dlugos, D., Collins, H., Bartelme, E., & Drenovsky, R. (2015). The non‐native plant Rosa multiflora expresses shade avoidance traits under low light availability. American Journal of Botany, 102(8), 1323–1331. https://doi.org/10.3732/ajb.1500115
Herndon Environmental Network. (2014, Janurary). How to identify and remove multiflora rose. [Video]. YouTube. https://www.youtube.com/watch?v=qRAOptB_e50
Jesse, L., Cllyer, M., Moloney, K., & Obrycki, J. (2013). Distribution of Megastigmus aculeatus (Hymenoptera: Torymidae) and the levels of seed predation of Rosa multiflora (Rosaceae). Weed Biology and Management, 13(3), 79–88. https://doi.org/10.1111/wbm.12013
PennState Extension. (2020, February). Multiflora rose. https://extension.psu.edu/multiflora-rose
