The Wild Parsnip Problem: How This Invasive Species Impacts Iowa's Tallgrass Ecosystem
One of the most biodiverse ecosystems in North America faces numerous challenges, not least among them the encroachment of invasive species. One particularly concerning invader in this precious Tallgrass Prairie ecosystem is the wild parsnip (Pastinaca sativa).
While this species may be aesthetically pleasing might remind you of the native Golden Alexanders with its delicate yellow flowers, its impacts on native flora and fauna are anything but benign.
Pastinaca sativa
What Is Wild Parsnip?
Wild parsnip is a Eurasian plant introduced to North America in the 19th century, likely as a food crop. Over time, it escaped cultivation and established itself in various ecosystems, including Iowa's tallgrass prairie. Wild parsnip thrives in disturbed soils, such as roadsides, agricultural margins, and even within prairie remnants under management lapses.
Wild parsnip contains chemicals called furanocoumarins, which can make your skin blister when exposed to sunlight after touching the plant. The burns can be severe — and you’ll just have to take my word for it. I go out of my way to avoid ever having skin contact with this plant, similar to poison ivy, but I think I’d take the poison ivy itch over this any day. These burns hurt!
Direct Competition with Native Plants
One of wild parsnip's primary impacts is its ability to outcompete native vegetation. Its broad leaves form a dense canopy that shades out native species, particularly those with lower stature or rosette growth forms, such as prairie violets (Viola pedatifida) and shooting stars (Dodecatheon meadia). To get science—this shading reduces photosynthetic rates in native plants, leading to diminished growth and reproductive success. Parsnip grows fast and dense in prairies, and prairies want that full sun! I’ve seen it time and time again, where parsnip fills in around large grasses leaving no room for other forbs. I will say, the established older grasses do pretty good holding their own, as their root systems are deeper. But this isn’t always the case, and certainly not for a first or second-year prairie.
Dodecatheon meadia
Wild parsnip’s rapid growth and prolific seed production give it a true competitive edge over slower-growing native perennials. For example, compass plant (Silphium laciniatum), a keystone species in the tallgrass prairie, often struggles to establish in areas where wild parsnip dominates, as its seedlings are outcompeted for sunlight and resources. Some plants move at a slower pace— and they’ll never be able to catch up if parsnip is already established.
Silphium laciniatum
Disruption of Pollination Networks
Wild parsnip’s flowers attract a variety of generalist pollinators like bees, flies, and wasps. While this might seem beneficial, these interactions can disrupt native pollination networks. Generalist pollinators often prioritize wild parsnip over native species due to its abundant nectar and pollen.
This diversion reduces visitation rates to native flowering plants like milkweeds (Asclepias spp.) and black-eyed Susans (Rudbeckia hirta), potentially leading to lower seed set and reproductive success in these critical prairie plants.
Toxicity and Herbivore Impacts
As mentioned earlier, wild parsnip produces furanocoumarins, chemical compounds that are toxic and cause phytophotodermatitis—a severe skin reaction triggered by exposure to sunlight after contact with the plant. These toxins deter many herbivores, further aiding wild parsnip's spread.
Grassland birds such as the bobolink (Dolichonyx oryzivorus) may also suffer. These birds, which forage and nest in tallgrass habitats, might avoid areas heavily invaded by wild parsnip due to reduced prey availability and physical obstructions created by dense parsnip stands.
Female Dolichonyx oryzivorus by Andrew Cannizzaro
Management Challenges
Managing wild parsnip is a complex task requiring a multifaceted approach.
Mechanical removal methods, such as mowing, must be timed to prevent seed production but can inadvertently harm native species.
Chemical treatments like spot-spraying with herbicides can be effective but pose risks to non-target plants.
Fire management, a cornerstone of prairie restoration, may even exacerbate the problem by stimulating wild parsnip seed germination if not carefully managed.
The Path Forward
Combatting wild parsnip’s spread necessitates an integrated strategy. Early detection and rapid response are critical, as is educating landowners and managers about the importance of controlling this invasive species. Restoring a diverse native plant community can also help outcompete wild parsnip over time, as a robust native seed bank and established perennials can resist invasion more effectively.
Pastinaca sativa
