Louis A. Toth

Hydrologic Manipulations of the Channelized Kissimmee River Implications for restoration

H istorically, much of 50uthcentral Florida was dominated by a contiguous wetland system that extended from the headwater lakes of the Kissimmee River basin to Florida Bay. During the past half century, this wetland landscape has been compartmentalized with a network of canals, levees, and water-control structures (gated spillways; Figure 1). This network is used to manage hydrologic regimes of the regional hydrosystem, primarily for flood-control purposes (Light and Dineen 1994, Toth and Aumen 1994). Modifications of the physical configuration and hydrology of the South Florida. landscape have affected the Everglades, Lake Okeechobee, and the 7800 km2 Kissimmee River basin, where an extensive flood-control project was constructed from 1962 to 1971. Lakes in the rivers headwater basin were connected by canals and partitioned into floodstorage reservoirs; a 90 km long, 9 m deep, and 100 m wide drainage canal

RESTORATION OF WETLAND VEGETATION ON THE KISSIMMEE RIVER FLOODPLAIN: POTENTIAL ROLE OF SEED BANKS

The composition of seed banks of areas on the drained Kissimmee River floodplain (Florida, USA) that are currently pasture and formerly had been wet prairie, broadleaf marsh, and wetland shrub communities was compared to that of seed banks of areas that have extant stands of these communities. The species composition of the seed banks of existing wet prairie and former wet prairie sites were the most similar, with a Jaccard index of similarity of 55. Existing and former broadleaf marsh and wetland shrub communities had Jaccard indices of 38 and 19, respectively. Although existing and former wet prairie seed banks had nearly the same species richness, species richness at former broadleaf marsh and wetland shrub sites was higher than at existing sites. Mean total seed densities were similar in existing and former wet prairies (700 to 800 seeds m2). However, seed densities in former broadleaf marsh and wetland shrub sites were significantly greater than in comparable existing communities (>4,900 seeds m2 at former sites versus 200 to 300 in existing communities). The higher seed densities in former broadleaf marsh and wetland shrub sites was due to over 4,000 seeds m2 of Juncus effusus in their seed banks. Half of the species that characterize wet prairies were found in the seed banks at former and existing wet prairie sites. At existing broadleaf marsh and wetland shrub sites, most of the characteristic species were found in their seed banks. However, only one characteristic broadleaf species was found in the seed banks of the former broadleaf marsh sites, and no characteristic wetland shrub species were found in the seed banks of the former wetland shrub sites. The seeds of only two non-indigenous species were found in the seed banks of former wetland communities at very low densities. For all three vegetation types, but particularly for the broadleaf marsh and wetland shrub sites, re-establishment of the former vegetation on the restored floodplain will require propagule dispersal from off-site sources.

Effects of rooting by feral hogsSus scrofa L. on the structure of a floodplain vegetation assemblage

We evaluated effects of rooting by feral hogs (Sus scrofa) on total emergent vegetation cover, vegetation species richness, and diversity of plant-defined microhabitat types in an impounded floodplain marsh in central Florida. Data were collected in 6 split-plots (rooted and control) over 10 post-rooting, monthly sampling periods. Hog rooting led to reduced plant cover in broadleaf marsh habitats and to significantly higher microhabitat diversity and species richness. Although feral hogs can have detrimental effects on native biota and community structure, our data suggest that hog rooting is a disturbance that can enhance plant species richness and associated microhabitat diversity in wetland habitats.

Drainage-basin–scale geomorphic analysis to determine reference conditions for ecologic restoration—Kissimmee River, Florida

Major controls on the retention, distribution, and discharge of surface water in the historic (precanal) Kissimmee drainage basin and river were investigated to determine reference conditions for ecosystem restoration. Precanal Kissimmee drainage-basin hydrology was largely controlled by landforms derived from relict, coastal ridge, lagoon, and shallow-shelf features; widespread carbonate solution depressions; and a poorly developed fluvial drainage network. Prior to channelization for flood control, the Kissimmee River was a very low gradient, moderately meandering river that flowed from Lake Kissimmee to Lake Okeechobee through the lower drainage basin. We infer that during normal wet seasons, river discharge rapidly exceeded Lake Okeechobee outflow capacity, and excess surface water backed up into the low-gradient Kissimmee River. This backwater effect induced bankfull and peak discharge early in the flood cycle and transformed the flood plain into a shallow aquatic system with both lacustrine and riverine characteristics. The large volumes of surface water retained in the lakes and wetlands of the upper basin maintained overbank flow conditions for several months after peak discharge. Analysis indicates that most of the geomorphic work on the channel and flood plain occurred during the frequently recurring extended periods of overbank discharge and that discharge volume may have been significant in determining channel dimensions. Comparison of hydrogeomorphic relationships with other river systems identified links between geomorphology and hydrology of the precanal Kissimmee River. However, drainage-basin and hydraulic geometry models derived solely from general populations of river systems may produce spurious reference conditions for restoration design criteria.

Predictability of flood pulse driven assembly rules for restoration of a floodplain plant community

Community assembly rules were formulated to evaluate the restoration of wet prairie along the periphery of the floodplain of the Kissimmee River in central Florida. Restoration of this plant community is expected to be driven by the reestablishment of flood pulse hydrology following the ongoing dechannelization of the river. Assembly rules were assessed with plant species composition and cover data from 15 permanent plots on the restored floodplain and 6 control plots on the channelized floodplain. These sites were sampled biannually from 1998 to 2010. Mean annual hydroperiods and depths confirmed that the frequency, duration and amplitude of post-restoration flood pulses at study sites were similar to historic reference locations. Elimination of pasture grasses (primarily Paspalum notatum Flüggé) following restoration of the flood pulse validated the hypothesized deletion rule for initial transformation of the wet prairie zone. Predicted increased dominance of obligate and facultative wetland species, a “community addition rule”, also was confirmed. An index of weighted averages of wetland indicator taxa showed significant short-term responses to antecedent hydroperiods and depths, and a restoration trajectory for wetland plant species. As predicted, recruitment of wet prairie indicator species from the extant seed bank correlated with reestablishment of the flood pulse, but was greatest when inundation extended from the wet season into the dry season. Restoration of a wetland plant community did not result in the predicted increase in species richness and diversity. Colonization and expansion of the exotic grass, Hemarthria altissima (Poir.) Stapf & C.E. Hubb., disrupted community reassembly processes. By summer 2007, mean cover of this species and several other exotic grasses increased to 24%, and necessitated herbicide treatments. Assembly rules provided useful predictions for the initial restoration of wet prairie vegetation, but were eventually confounded by the spread of an exotic species that was new to the regional flora.

Potential propagule sources for reestablishing vegetation on the floodplain of the Kissimmee River, Florida, USA

After channellization of the Kissimmee River, the primary land use of the drained floodplain was cattle pasture but included sod farms. A project to restore the river began in 1999. One of its goals is to reestablish the three dominant, pre-channelization vegetation types (wetland shrub, broadleaf marsh, and wet prairie) in areas where they previously were found. We investigated whether indicator species of these three vegetation types were present in 53 permanent quadrats on the drained floodplain. All seven indicator species were found in the permanent quadrats. We also examined three potential sources of propagules (relict wetlands, seed banks, and several surrogates of hydrochory) for these indicator species. All seven species were found in adjacent relict wetlands; and six were found in the seed banks of permanent quadrats. Based on binomial logistic regressions, the presence of relict wetlands and surrogates for flooding (relative elevation, total days flooded) can predict the presence or absence of most of these indicator species. Sod farming reduced the presence of wet-prairie and broadleaf marsh indicator species in permanent quadrats, in adjacent relict wetlands and in the seed bank. The potential importance of relict wetlands for the re-vegetation of the floodplain was our most important finding.