Sunday, February 20, 2011

Invasive species in Ann Arbor

Alliaria petiolata--garlic mustard. Highly invasive, allelopathic, makes a tasty pesto, produces cyanide upon digestion.

Despite the impending icepocalypse, spring will be springing soon. Ducks and geese have begun flying north. Soon plants will emerge from their winter stasis and send their leaves above ground. This also means it's prime time to start thinking about invasive species. On Damn Arbor, we have discussed some invasive animal species: mute swan and Asian carp. Over the next few weeks I will be writing a series of articles focusing on invasive plant species in the Ann Arbor area. I will cover the the major invasive species, how to identify them and the best ways to remove them. Why invasive plant species? Well, they say write what you know, and I know plants.

Organisms and and populations are capable of colonizing new areas. Indeed, the history of life on Earth has been marked by important colonization events: plants colonized land 450 million years ago. Insects soon followed plants emerging on land just over 400 million years ago. In short, colonization is a natural process. More recently, tree species have recolonized Michigan after the last glaciation. Humans action has greatly increased the frequency of colonization events. Settlers and immigrants brought with them plants and animals from their home countries. In recent decades, global commerce has given rise to ever more frequent species introductions. It is important to keep in mind that not all introduced species become invasive species.

In classifying invasive species some gray area exists. Nonetheless, here are some definitions to keep in mind:

Native species: Native species are species that have arrived in an area or habitat without human intervention. In Michigan (and North America) we generally consider species that were present before European colonization to be native.

Non-native species: Non-native species, or introduced species are species that have arrived in an area due to human actions. It is important to note that not all non-native species become invasive. For example, in Michigan Malus pumila (common apple), and Prunus avium (sweet cherry) are two introduced species that have become naturalized but not invasive.

Invasive species: Invasive species are species outside of their natural range that threaten biodiversity and disrupt relationships between native species and ecosystem processes. We can consider species that adversely impact native species and have been introduced by human action to be invasive, i.e. the emerald ash borer. Things get a little grayer when we think about species that have moved out of their native habitats due to indirect human actions. Species moving northward with climate change and species moving out of their traditional habitats due to forest fire suppression could be considered invasive if they prove sufficiently threatening to species in the habitats they are entering. More on this later.

Once invasive species become established in an area, removal and mitigation of damage can be incredibly costly and tremendously difficult. An informed population, actively engaged in helping to remove invasive species, whether found on their property or encountered on public land, can help to reduce the spread of these pests and assist professionals in restoring natural areas.

Ann Arbor has an interesting history with invasive plant species. Many of the areas more prevalent invasive species (i.e. Rhamnus cathartica, common buckthorn) were originally planted in Nichols Arboretum as ornamental plants in the early 20th century.

Up next: Ailanthus altissams, tree of heaven

Photo via Phyzome's Wikimedia page


  1. Do you know the worst thing about invasive species?

  2. Is this some sort of joke? I would say the worst thing is that they reduce biodiversity and negatively impact ecosystem services humans depend on. But I'll bite: what's the worst thing about invasive species?

  3. Listening to you jabber on about them.

  4. Whoa, and here I am, a Chris who posts on here sometimes, coming to say that weed you pictured creeps from our neighbor's yard into our flowerbeds. I thought it was informative. Maybe I need a different identity.

  5. Yeah, you probably do. This blog ain't big enough for two Chrises, and since I've known Ben for over eleven years, I got dibs. This is also why I can get away with needling him about his dendrophilia from time to time.

  6. Wow, this is confusing. My dendrophilia notwithstanding, I think there is plenty of room for two people named Chris in the comment section of Damn Arbor.

  7. There, i fixed it. My smarm shant go uncredited.