Invasive plants: If we can't beat 'em...

Scientists, people with yards, and nature lovers generally all agree that invasive plants are the worst. Mention buckthorn or multiflora rose at a party and I bet you won’t hear anyone say how much they like them.  Before we go on, check out Christopher Wells’ post, Why Study Invasive Species?

So, does anyone have a reason to like invasive plants? I’m looking for a silver lining, to help me sleep at night. I have nightmares of Japanese knotweed gradually covering the New England area, such that wildflowers and trees are merely a memory.

Japanese knotweed. Photo credit: Gav, wikimedia commons

Japanese knotweed. Photo credit: Gav, wikimedia commons

Well I’ve done some research, I’ve been out scrambling around in invasive shrubs, I’ve talked to a few people, and I have some thoughts. While I won’t be singing the praises of invasive plants any time soon, I do think investigating their ecological effects—positive, negative, or neutral—is a fascinating topic.

For my research, I climb/crawl/smash my way through very dense shrubbery, and one of the first things I noticed was the growth patterns of different species. Dogwood, raspberry, blueberry, and rhododendrons are all native shrubs that I have seen frequently, and they all have more or less one main stem and a few branches per plant. These plants have important ecological roles, including providing food for wildlife.

Raspberry. Image credit C.A.M. Lindman

Raspberry. Image credit C.A.M. Lindman

Underneath honeysuckle

Underneath honeysuckle

For better or for worse, many invasive shrubs have growth forms that differ from natives.  Autumn olive and honeysuckle produce many stems that grow up and bend over in all directions, creating arches with many branches off of each one, such that it is close to impossible to walk or crawl through. My advisor mentioned that honeysuckles create “igloos” when they are covered in snow, possibly providing shelter for small mammals in the winter. I’d like to investigate this. Mostly because I think a photo of bunnies in an igloo could make me famous.

Multiflora rose and Japanese barberry create tangled messes of thorns, and the vegetation is so dense that under a thicket of these plants that the ground is dark and damp, with perhaps some moss but no other plants, and don’t even think about trying to walk through them. This seems terrible for biodiversity, but as promised a silver lining: A thicket of barberry or rose provides protection from predators for small animals, and many animals that use these types of habitats are in decline, such as the woodcock and the New England cottontail. The main problem that I see is that there doesn’t seem to be anything for them to eat under the thickets.

There are some native thicket-forming plants such as hawthorn, so don’t go out planting invasive rose bushes just yet.

Oriental bittersweet fruits. Photo credit: Alpsdake, wikimedia commons

Oriental bittersweet fruits. Photo credit: Alpsdake, wikimedia commons

Many invasive plants have fruits that persist through the winter. You might have noticed the red berries of Japanese barberry, or the orange fruits of bittersweet that look rather lovely against the snow. Throw in a cardinal and you have yourself a Christmas card. It’s a bit complicated and the jury is still out on whether this is a benefit, but studies have shown that birds will eat these berries and they might help improve winter survival rates [1]. This is a nice bonus considering that many songbirds suffer from habitat loss.

The bottom line is that invasive plants are different physically and ecologically, and these differences might have surprising effects, ranging from devastating to useful.

Again, I’m not promoting invasive plants, but it’s an interesting perspective and I’d love to hear what you think about it! And if you’re interested, here’s an article about this topic written by someone smarter than me.

References

1. Kwit, C., Levey, D. J., Greenberg, C. H., Pearson, S. F., McCarty, J. P., & Sargent, S. (2004). Cold Temperature Increases Winter Fruit Removal Rate of a Bird-Dispersed Shrub. Oecologia, (1), 30. doi:10.2307/40006408

Check out more posts on introduced species