Tuesday, October 26, 2010

River Terrace Forest - Landforms of the Chesapeake

Olmsted Island, Great Falls of the Potomac
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This is a tough one. It doesn't involve any of my well known havens of the coastal plain - mud, sand, gravel, tidal water. None of those. Instead, let's pop up the fall line of the Potomac (and the Susquehanna, to name another) and look at a rare piedmont landform within the Chesapeake Bay watershed - which after all, extends into central West Virginia and southwest New York. River Terrace Forests - or Bedrock Terrace Forests, as they're sometimes known, are harsh, semi-permanent habitats that exist within the floodplains of certain rivers. The plant and animal communities continued within are pretty unique.


River oats, Poverty Grass, Red-cedar, and Virginia Pine
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River Terrace Forest, or International Vegetation Classification Group CEGL006209 (helpful, huh?), is dominated by a variety of plant species, namely oak, hickory, and pine species that can withstand winter flooding and incredibly shallow and poor soils. Some of the Potomac islands immediately above Great Falls are incredible showcases of this rare habitat type. Basically, the large granite islands act like clay pans that prevent drainage or penetration by tree roots - a far more common habitat type called "Piedmont Hardpan Forests."

Possumhaw Viburnum and River Oats
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In this unique habitat, soils develop as soils do - from the collapse and weathering of bedrock and the deposition of organic and mineral matter on the surface. Unlike most other areas, the islands will get overtopped by high velocity river flows every few decades, stripping the young soil and returning the islands to bedrock and whatever plants held on through the storm. As a result, these areas never really progress through a normal plant succession model. You'll notice that all of the trees are less than 6" diameter.
Pretty diverse system - and few invasive species
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According to Wikipedia, the entire island's plants and wildlife were completely wiped off the map in the floods that followed Hurricane Agnes in 1972. And apparently picnicking around the island's rocks was popular through the 1940s. It was chilly on the day of our trip, so the wildlife sightings were really minimal. I hope to return on a warmer day and see what I'm pretty sure will be a good diversity of reptiles and migratory songbirds using the island.
Thanks for stopping by.

3 comments:

Leigh said...

Very interesting post. I have to admit it bums me out bit when the critters are hiding. :)

Rick Kratzke said...

Don't those blueberries make a pretty picture.

Whitetail Woods Blog / Deer Hunting and Blackpowder Shooting at it’s best.

Swamp Thing said...

You are both mountainfolk! Thought you'd enjoy seeing some boulders on my blog for a change!

Thanks for stopping by as always!