Renewed Muck, Stuck

Nobody said it was going to be easy – and they were right. A landmark effort to restore a huge swath of Florida’s wetlands isn’t bringing native plants back to some areas, a new study finds. And to add insult to injury, an invasive exotic shrub appears to be gaining ground due to the restoration.

The Kissimmee River restoration project is one of the world’s largest. In 1992, after decades of controversy, the U.S. Congress approved a sweeping plan to undo some of the damage done by the C-38 Canal, a 50-mile long ditch feeding into Lake Okeechobee that destroyed some 200 square kilometers of wetlands. Since 1997, engineers have been systematically filling and rechanneling 22 miles of the canal, in a bid to restore original water flows and flooding patterns.

Ecologists had hoped that the resculpting would help resurrect the Kissimmee’s once dominant “broadleaf marsh” plant community. In particular, they predicted that restoring traditional flood patterns would, within a few years, enable two important wetland plants – duck potato (Sagittaria lancifolia) and pickerelweed (Pontederia cordata) – to recolonize areas that had been “moderately drained.” Researchers also expected that the better-adapted native plants would hold their own against invasive species.

But things haven’t quite gone as planned, Louis A. Toth of the South Florida Water Management District reports in the current issue of Restoration Ecology. Surveys at 22 study sites, done between 1998 and 2008, show that the native plants are struggling to gain a foothold, while the invasive Peruvian primrose willow (Ludwigia Peruviana) is flourishing. Overall, researchers found duck potato and pickerelweed covered from 0.9% to 6.1% of the plots, while the invasive willow covered 17% to 19%.

Why has the project “diverged from the predicted temporal trajectory for ecosystem restoration”? Toth speculates that the native plants may be having trouble due to nuanced changes in water flows, a severe flood early in the restoration that may have killed colonizing plants, and roots and other material left behind in the soil by shrubs that once grew on the drained land. To help the natives – and kill off the invasive willow – he says restorationists may need to use herbicides, more aggressively manage water flows, and even hand-plant seedlings. As a result, it appears that restoration “may require a longer time period than hypothesized.” David Malakoff

Source: Toth, L. (2010). Unrealized Expectations for Restoration of a Floodplain Plant Community. Restoration Ecology DOI: 10.1111/j.1526-100X.2010.00731.x

Image © John Anderson