WEBVTT

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Dr. Swarzenski: We are only about 15 miles away

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from New Orleans and the Mississippi River in a

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beautiful example of a floating marsh that has been

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pretty much unmanaged for many, many years---decades.

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There’s fire that comes through here, and that may be

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about the only disturbance. It’s a continuous, almost prairie-like

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expanse of a marsh, a freshwater marsh, without any

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interruptions by little waterways or ponds or lakes.

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This is just a solid, solid meadow of a freshwater marsh.

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Narrator: Extensive floating marshes occur in a few

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locations around the world. Papyrus swamps of tropical

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Africa occur along the White Nile, the Okavango and Niger

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deltas, and along the shoreline of Lake Victoria. There

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are extensive Phragmites swamps in the Danube Delta in Romania.

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Seasonal and permanent floating meadows are found in the middle

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Amazon flood plain. And in the Mississippi River

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Delta Plain, there are large expanses of floating

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marsh, which are the focus of this video. This

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unique ecosystem is dominated by a variety of

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grasses and forbs, which can create a buoyant

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mat that floats on a layer of water. Different

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terms are used to describe floating marshes

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and reflect the country of origin. In Louisiana,

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they are often referred to as flotant or prairie tremblant.

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The best way to get around floating marshes is by airboat.

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Dr. Swarzenski: If you stay in one place for any

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length of time, eventually the water...your ankles

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will start being inundated with water, but this kind

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of marsh pretty much never on its own, never gets

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flooded. It’s always dry, and there’s always one or

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two inches of unsaturated zone near the, near the top,

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and then it’s almost always saturated below that.

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Narrator: Floating marsh, or flotant, forms a

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buoyant mat of air-filled roots and rhizomes, which

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allows the marsh to float up and down as water levels change.

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Over time, the marsh mat may thicken, becoming

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strong enough to support woody plants such as

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wax myrtle. Periodic fires, however, keep the woody

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growth in check, allowing the herbaceous plants

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to continue to dominate the marsh.

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[laughter]

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Dr. Swarzenski: There’s some buoyancy to this marsh.

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This is what we would call about a five on a scale

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of one to five in terms of buoyancy. You can see the

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water’s going around my ankles because I’ve been

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standing here for a while. And I’m going to walk

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away from here, and then everything will rebound.

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Narrator: Peat buoyancy varies among marsh types.

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From most to least buoyant, are maidencane, bulltongue, and wiregrass.

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Dr. Swarzenski: This area gets burned regularly..uhm.. so

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there’s nothing crowds out other species.

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Nobody really takes over….no one species takes over,

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and there’s a huge diversity of plants and grasses

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and forbs and orchids. There’s four to five species of

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orchid that we’ve seen out here. This is

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Calopogon tuberosus right here. There’s two

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different kinds of ferns….Thelypteris palustris

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and Osmunda regalis. This is Thelypteris. Wax myrtle

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would start invading this area, if it was not burned

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every year and eventually there would be 10, 15 feet

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tall wax myrtle thickets out here.

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In Nova Scotia, there’s these areas of wet meadows,

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wet bogs, called red orchid bogs. And they have

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the Calopogon; they have the Pogonia that we see

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out here, The, the Junonia, the buckeye… common

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buckeye. Here’s an example of an orchid. And then just a lot of ferns.

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Ah..it’s also common in Nova Scotia. So this is all

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northern temperate environment with very harsh

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winters. And yet here we are in Louisiana a few miles

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away from New Orleans and we see a very similar kind

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of a peat system. The soils here are highly organic;

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there’s almost no clay or silt. Even though the

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Mississippi River is close; it of course is kept from

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coming in here by the flood control levees.

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Narrator: Floating marshes form when an attached

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marsh forms an organic mat that later detaches

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from the underlying mineral soil. They may also

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form through infilling as floating fragments expand

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and as vegetation extends from an adjacent marsh

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forming a floating mat over a body of water.

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Dr. Urbatsch: They’re usually pretty early bloomers…

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Dr. Swarzenski: OK so you already have.. what you..

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I mean, it’s worth.. going and looking for.

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Dr. Urbatsch: Well, yeah, I’d like to find one in flower.

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Dr. Swarzenski: A few weeks ago in that same area

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there were a lot of them, and now I just saw one.

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Right here is Habenaria nivea, which is a very good name for it.

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Dr. Urbatsch: It’s a winner, It’s been reported for

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Louisiana, we actually don’t have a specimen of it.

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Dr. McKee: OK.

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Dr. Urbatsch: So it’s that rare.

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[laughter]

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Dr. Swarzenski: Right. We’re in the subtropics at 29

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degrees and there’s these half a foot to 12 inch tall

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peat mounds that may be as much as 10, 15 yards in

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diameter and they just cover this whole area where

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we’re at. They grow..Panicum grows through it uhm..

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it survives burning. It seems to have come in recently…

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since about 2000. Before that I didn’t notice…

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any of these…I saw some small mounds, but

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nothing of the scale that we see now.

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Somebody from Quebec ended up with two samples

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of Sphagnum from the national park, which is about

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five miles to the east here. And he identified two separate

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species of Sphagnum moss down here. And he,

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working up in Canada, was kind of surprised to

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see these two species in the sub-tropics.

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[distant voices]