Floods and Trees

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Published on: Aug. 2, 1995

Last revision: Oct. 20, 2010

Floods and similar disturbances act as "reset buttons" for tree succession and growth. Carpets of silver maple, cottonwood and green ash were visible the summer following the flood, thanks to the favorable conditions created for these pioneer species. Silt deposited by the flood provides a perfect seed bed.

Most competing understory plants were killed, and light now penetrates to the forest floor through the dead overstory trees. Seeds cast in the fall and spring by these colonizing plants sprouted with ease and took hold. This is the way forests work.

One good result from the floods is that the acreage of bottomland forest will increase in Missouri. Bottomland hardwood is the only forest type showing a decline over the last 15 years, according to forest survey statistics. The decline is attributed to increasing development in flood plains, including farming, industrial and residential uses.

Levees allowed these uses with protection from flood waters. However, the levees really only provided a false sense of security. Floods of this magnitude have happened before and they will happen again. Realizing this, some flood plain land will be allowed to revert to bottomland forests, thus increasing their overall total acreage.

We will continue to monitor the effects of floods on trees to increase our management skills. The point to remember is that our native bottomland habitats and the species that live there are the ones that tolerate flooding best and recover from flooding the quickest. When trying to determine the best uses for your riverside land, keep in mind the resiliency of bottomland forests.

Bottomland Forests and the Flood

by Phil Covington

Walking in the woods on a windy day can be dangerous at the Ted Shanks Conservation Area. Most of the trees in the floodplain here were killed by the 1993 floods and are now breaking off at what was the high water line of the flood.

This 7,636-acre wetland is located in the northeast corner of Pike County, near Louisiana. It lies at the confluence of the Salt and Mississippi rivers. Seventeen miles of exterior levee keep both rivers at bay, while 23 miles of interior levees separate the wetland into 19 manageable pools. The 2,920 acre bottomland forest here is the largest found along the Mississippi River between Rock Island, Ill. and Reelfoot Lake, Tenn.

On July 1, 1993, Mississippi flood waters overtopped our levee, and by July 4th the entire wetland area was under 15 to 17 feet of water. Our primary concern was for the bottomland forest. Mature pin oaks were obviously stressed. Leaves were small and light green, branch tips were dying back and dead limbs appeared in the crowns.

These trees shunted their remaining energy into producing a tremendous mast crop and then died. This might have been our greatest loss, because mature pin oaks made up over 80 percent of the trees in the forest. Mast crops are important as a food source for the migrating waterfowl and other wildlife this area was created for.

The prolonged 1993 floods, occurring just at the peak of the growing season, took a terrible toll: 90 percent of the bottomland trees at the Ted Shanks Conservation Area were dead. The same was true for nearby islands. In fact, a large island heron rookery went unused because nest-bearing sycamore trees had died.

Dead hickory, oak, hackberry, hawthorn, dogwood, holly, persimmon, sassafras and wild plum were among the trees that stood starkly against the spring sky in 1994. The few mast producing trees that survived included pecan, green ash, silver maple and button bush.

In the spring of 1994 we found young pin oak seedlings sprouting from the acorn crop of the previous fall. They were nestled close to the earth beneath a carpet of spanish needle, smartweed and ragweed. The process of renewal had begun.

Change is what wetlands do best. Long term static water levels lead to stagnation and a reduction in species diversity. Dynamic changes, like those at the Ted Shanks Conservation Area, ensure that wildlife will continue to find food and shelter in years to come.

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