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A forested floodplain: Lousiana bayou along the Pearl River. Photo: <a href="http://www.flickr.com/photos/99012321@N00/3499802982/">Josh Kellogg</a>, Creative Commons, some rights reserved
A forested floodplain: Lousiana bayou along the Pearl River. Photo: Josh Kellogg, Creative Commons, some rights reserved

Natural Selections: Flood-plain forest restoration

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Trying to put nature back the way we found it can be more complicated than just leaving things alone. Dr. Curt Stager talks with Martha Foley about attempts to restore "green tree reservoirs," flood-plain forests that have been reduced 80 percent in size by human encroachment.

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Martha Foley: I’m interested in our movement to restore the landscape to what it was before we came in and changed it all. Like wetland restoration, all those rivers in the South that were dammed up. There is definitely a movement to bring things back to the way they were, but I wonder how good we are at accomplishing that.

Dr. Curt Stager: There are some really interesting cases now, where people are not just trying to restore an ecosystem, but actually get multiple benefits out of it and figure out ways to manage this resource by also taking into account ecological principles.

MF: You can’t just let the Mississippi run wild again. You can’t do that. So we have to do something else. What are we doing, and does it work?

CS: One of the neat examples of that is something called “green tree reservoirs,” which are a kind of a wetland floodplain sort of a forest that people are trying to restore down in the southern U.S., especially places like the Mississippi Delta. Dr. Jim Allen in the forestry division at Paul Smiths College has done a lot of work on this, and filled me in on this. I had never even heard of these, but it’s really fascinating.

MF: It’s like where the river would flood and flood the woods every year, or whatever.

CS: Right. So they call them “green tree reservoirs”, as opposed to “dead tree” things, where the woods are actually flooded permanently, and the trees all die. These are seasonally flooded forests that, in the old days before there was big development there, you’d have these. During the wintertime and spring, the Mississippi and other rivers would rise from all the melt water and the storm water and they’d flood their banks and they’d go into these forests. And it would only stay submerged for a few months a year, so it wouldn’t kill the trees.

As soon as the floodwaters retreated, the seedlings would come up, and stuff like that. But now, 80 percent of those are gone, because of the dams and the levees, and also farms have encroached on them. So the goal is to restore those. But like you said, you can’t just let the river go, so now people have to consciously try to reconstruct this flood region.

MF: I bet it’s a little more complicated than just letting it flood every spring.

CS: Yeah. It turned out that even just the randomness of it was important. You have El Niño years--there’s more of a flood, let’s say. It turns out if you just control the levees and flood them the same amount every year, then certain species get to take over. And you don’t have the biodiversity you want.

MF: So you have to have some dry years, you have to have some wet years, you have to – so they’re figuring it out, I bet.

CS: Yeah, I mean even to the point of how deep should it be flooded. There are actual manuals coming out now based on the mistakes folks have made, saying you don’t want it to be more than 18 inches deep for a long period, for a couple of reasons: one is it will overtop the red oak seedlings, let’s say, and if it stays that way for a long time they drown. And also, if you have that much of a depth of the water but not too much, you can have several kinds of migratory water fowl in there.

We have to remember in the northern winter, a lot of birds head south. The redwing blackbirds and all, but also wood ducks and mallard ducks, and all this, too. Mallards will dabble and feed kind of down deep, and the wood ducks will sort of peck around in the shallows. If you have a relatively deep (but not too deep) flood, then you can have both kinds of ducks in there.

MF: I’m also thinking that two branches of the science have to come together. You have these people who’ve been damming the rivers--the management people--then you’ve got these people who are on the ecological side or something--the natural, wild-earth side. So are they cooperating to do this?

CS: Well, I’m not sure about the social dynamics, but certainly the information and the attitudes are mingling in here. Because in order to end up with this result, where you have a good diversity of kinds of tree species in there, and wildlife, you have to mimic the natural system--kind of the way it was. So you really have to consider ecological principles in the process.

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