Sunday, April 17, 2022

Garlic mustard -- a uniquely troublesome invasive



In the woods near the Cloister at Three Creeks today, I came across an example of Garlic Mustard (Alliaria petiolata) growing in an apparently undisturbed forest area, and concentrated directly under a large dead oak, with only young red maples surviving in the area.

Could Garlic Mustard be contributing to the pervasive 'oak decline' we are observing at the Cloister and in the east coast deciduous forests in general?

I discuss this quote, retrieved today, 17 April 2022, from the Wikipedia article entitled 'Garlic Mustard as an invasive species':

"Garlic mustard produces allelochemicals, mainly in the form of the compounds allyl isothiocyanate and benzyl isothiocyanate,[9] which suppress mycorrhizal fungi that most plants, including native forest trees, require for optimum growth.[10] However, allelochemicals produced by garlic mustard do not affect mycorrhizal fungi from garlic mustard's native range, indicating that this "novel weapon" in the invaded range explains garlic mustard's success in North America.[11]"

Garlic Mustard is a spice that was used by my north German ancestors at least as far back as 6000 years ago. The remnants found in 'Funnelbeaker Culture' pottery is, in fact, the oldest known documented evidence of the use of spice by humans. It was brought to the US by European Colonists to grow in their gardens as a cooking spice, and escaped into the wild, just as so many other problem invasives here have.

But in this unique case, the damage is much more complex than simply physically out-competing native forest ground cover species. It acts chemically, to suppress growth of its competitors and to weaken the forest trees in its vicinity.

All natural woodland ecosystems are highly complex, involving a tapestry of biological and chemical interactions between species that we're only just beginning to notice and identify.  The disruption that Garlic Mustard wields on the balance of our eastern deciduous forests is just one example of the sort of subtle, indirect effects that our forests are struggling, and largely failing, to adapt to.

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