Looks like a grassland at the edge of the boreal forest, doesn’t it?  Actually, it’s a slope fen; there’s water flowing very, very slowly under there.  You can’t walk across it, but there is a boardwalk around it.  There are a few open pools of water within.

So you might be wondering, as I did, what distinguishes a fen from a bog, or from any other type of wetland?  And what exactly is a wetland?

According to Lewis Cowardin of the US Fish and Wildlife Service, “wetlands are lands where saturation with water is the dominant factor determining the nature of soil development and the types of plant and animal communities living in the soil and on its surface (December 1979).”

There are four main types of wetlands: marshes, swamps, bogs, and fens.

Marshes are wetlands dominated by herbaceous vegetation.  Most of the water in marshes comes from the surface, but in many cases groundwater is also a source.

Swamps are wetlands dominated by woody vegetation.  There are a few swamps on the Maryland side of the Potomac gorge.  Long-tube valerian, winged monkey flower, and lizard’s tail are some of the wildflowers I’ve found there.

Bogs are wetlands formed by the growth of sphagnum moss either over a pond, filling it in, or over land, preventing water from evaporating.  Either process results in a wetland characterized by very acidic water and a low amount of nutrients.  Not many plants are well adapted to these conditions.  Regardless, the bottom of a bog is generally impermeable, so most of a bog’s water comes from precipitation.

A fen is basically a bog that receives some groundwater; as a result, fens have more nutrients and less acidic water.  They support a broader range of plants than bogs do.

Bogs and fens are found mostly in the higher latitudes of the northern hemisphere, and in some alpine areas in the middle latitudes.  There are no bogs or fens in the Potomac gorge.

A slope fen is exactly what you’d think it is: a fen situated on  gently sloping land. Sadly I did not learn the names of most of the plants I found here, though I believe the area is dominated by rushes, not grasses.  (Hmm, now I have an idea for another blog post.)

If you click on the first picture and zoom in, you’ll see some goldenrods and a northern pitcher plant.

In case you were wondering, the sevenangle pipewort featured on November 26 was found in the shallows of a very large pond, not in this slope fen.