Terrestrial Plant and Wildlife Communities on Phosphate-mined Lands in Central Florida

Abstract

A study of plant and animal communities documented the recovery of phosphate-mined land in central Florida. Hypotheses about community structure were tested in two sets of treatments. One set consisted of the relatively stable end results of post-mining land use. These treatments were: consolidated waste clay soil; late successional forest on unreclaimed overburden spoil piles with and without interspersed lakes; and grazed and ungrazed pastures on reclaimed overburden soil. The other set of treatments tested for differences in community structure among several seral stages on unreclaimed overburden spoil piles with interspersed lakes. The responses of biological communities were measured as the identity, diversity, and abundance of plants, mammals, birds, reptiles and amphibians, and insects. Major findings include:

1) Succession on clay waste areas was slow, resulting in senescent forest and a depauperate animal community.

2) Unreclaimed spoil piles underwent a rapid primary succession culminating in xeric or mesic oak forest with rich animal communities. The faunas were different on treatments with and without lakes, but both had moderate-to-high wildlife value, high aesthetic quality, and much potential for enhancing animal populations.

3) Succession on reclaimed sites was arrested by grazing or mowing. Both treatments provided relatively poor wildlife habitat, though animal diversity and abundance generally were higher on ungrazed sites. However, stocking with cows resulted in high livestock biomass and slightly more diverse vegetation.

4) Aboveground lenses of hardening clay appear to be properly characterized as wastelands, so implementing optimal reclamation procedures for clay wastes should be a top priority.

5) By contrast, both unreclaimed sites and the type of reclaimed sites examined here are valuable land with a variety of potential uses. The advantage these have in common is the presence of overburden soil.

6) The biological factors underlying the value of reclaimed land are the abundant, balanced nutrients in overburden soil and the free services provided by colonizing biota, notably creation of topsoil through symbiotic nitrogen-fixation by Frankia and Myrica, seed dispersal by wind and later by migratory birds, and possibly by introduction of mycorrhizal fungi spores by rodents. Operation of these processes should be built into plans for managing reclamation.

7) Succession on overburden soil was to mesic oak forest. Because its soil hardpan is destroyed during mining, restoration of pine flatwoods is not possible without new engineering designs for soil reclamation.

8) The study supports reclamation to rangeland as a legitimate post-mining land use, even though its wildlife value is low. However, the current trend of maintaining improved pasture on nearly all reclaimed land will result in a region-wide decline of wildlife resources in comparison to both pre-mining conditions and the present transitional habitats. The impending losses could be reduced by including modifications in reclamation plans that will provide wildlife habitat or by directing some reclamation projects specifically at wildlife values.

9) A second trend, toward the use of sand tailings as the major surface soil in reclamation, has the potential to diminish post-mining land quality on a large scale. Because the nature of reclaimed soil is a key variable, regulations should address soil quality and depth.

10) Evaluating the productivity of mined lands would be enhanced by closing information gaps including succession on sand tailings, wildlife communities in pre-mining habitats, socioeconomic value of the wildlife resources lost, field trials of game and vegetation management techniques, habitats restorable on soils that combine sand tailings with consolidated clay, and agronomic and forestry potential of reclaimed soils.