Earthworms in the National Parks

 

By: Mac Callaham, USDA Forest Service Southern Research Station, Georgia, USA


 Photo from George Washington Memorial Parkway.

Photo from George Washington Memorial Parkway.

 

I plop down into my seat as I board the flight.  I give a brief nod of greeting to my neighbor, and notice that he is (like me) of an age which might indicate that he could expect to pass the flight time in conversation, rather than totally absorbed in a liquid crystal display.

I start with a standard question, “Are you headed out, or headed home?” And we’re off!

When it’s my turn, I tell him that I’m headed out to a conference where I’ll give a presentation on my research on earthworms.  I know this is a topic that will keep the conversation rolling all the way from Atlanta to New York… fortunately, we have refreshments!

It’s generally true that people are interested in earthworms, and even more so when I tell them that I study invasive earthworms.  People are also quite interested – and protective – of their National Parks, so I find that I usually have an attentive audience when I talk about my work on earthworms in the Parks.

“Invasive earthworms?!?” they exclaim. “There’s more than one kind?” they gasp. Then in rapid succession: “Where do they come from?  What do they do? How do you know they’re invasive?” and more.  I do my best to answer them, and eventually get around to describing the work that my colleagues and I have been doing at the Great Smoky Mountains National Park (GSMNP) in Tennessee, and the George Washington Memorial Parkway (GWMP) in Virginia and Washington, DC.

In the GSMNP it’s an introduced Asian worm that’s moving into the Park from the edges.  This worm is one that’s sold as bait, and goes by the trade name of “Alabama Jumper.”  It’s aptly named, because (although not technically from Alabama) they definitely jump. When molested these worms can flip and twist and throw themselves up off the ground, sometimes catching several inches of air in the process.  This species is a cause for concern because where it becomes established, it can reach very high densities, and it consumes much of the fallen leaves on the forest floor.  These leaves are habitat for lots of other invertebrates, as well as some larger animals like salamanders.  It’s no surprise that the GSMNP is considered a hotspot of biodiversity for forest floor creatures like millipedes and salamanders considering the rugged, inaccessible terrain, the lush vegetation, and the warm and wet conditions that predominate.  On the other hand, it is a bit surprising, and alarming that one introduced earthworm species can outcompete these other forest floor dwellers, and impact their numbers and diversity, but this is exactly what our team has documented in recent years.

At the George Washington Memorial Parkway (GWMP) in Washington DC, we sampled earthworms and other soil invertebrates to help catalog the existing biodiversity of the Parkway and its constituent Parks (including Great Falls NP).  We were also interested in whether the past history of human uses of the land could be detected in the soil animal community.  There’s evidence that major disturbances can contribute to the establishment of non-native earthworm species, and the GWMP provided a great opportunity to examine this relationship with well documented history of soil disturbances ranging from the canal-building activities at Great Falls Park in the 1780s, through the Civil War entrenchments, and on into contemporary disturbances.  We’ve uncovered good news and bad news with this work.  On the one hand we’ve found what we believe to be an undescribed native species of millipede at one of the GWMP network parks (Turkey Run Park), but on the other hand, we found several individuals of a European earthworm species that has never been reported in North America before our sampling. 

 Alabama Jumper.  Photo © Susan Day / UW Madison Arboretum

Alabama Jumper.

Photo © Susan Day / UW Madison Arboretum

All this brings up a couple of important points.  First, we still don’t seem to have a good handle on the species diversity that we have native to the soils of North America, and second, there are new species introductions happening all the time, and we don’t have a good handle on what these introductions will mean for the native species.  Will this latest introduced species become invasive?  Will it choke out some native species, or otherwise decrease our native biodiversity?  Is there any way to control these invasive species?

Out the window, our flight from Atlanta to New York has skirted the eastern slope of the Smoky Mountains, and passed within sight of the National Mall in DC.  My new friend leans over and looks down on these landscapes.  He is reflective.

“Wow, there’s a lot going on down there that I never thought about before…”

I nod knowingly.  I tell him that few people ever really think about what’s going on right under their feet, but I tell him that now he’s one of the lucky ones.