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Accelerating Natural Processes for Wetland Restoration After Phosphate Mining


Study was made of post-mining restoration of wetlands vegetation cover and soils by natural seeding accelerated with planted seedlings. Abundant evidence in this and other studies suggests that augmented natural succession can be the quickest cheap way to restore lands to future uses for forestry, agriculture, water conservation, or wildlife-wilderness. In other words, the prior self organizational processes of nature in the phosphate districts provided a set of species that are good at rapid restoration. Within clay settling ponds marshes and willow ecosystems were found similar to marshes and early swamp succession in unmined areas. Bottomland hardwoods found developing within old settling areas correspond to trees of lower floodplains. Mixed hardwoods coming in on drier parts of the basins correspond to mesic upland forest. Studies show that wetland restoration and the type of wetland depends on an appropriate water regime and adequate seeding. Marshes and shrubby vegetation with water-dispersed seeds develop readily with high productivities due to high phosphorus in soils aided by nitrogen fixing plants. Succession often stops with willows and maples because the larger seeds of the forested wetlands are not easily transported to isolated reclamation basins. Birds, animals, and floodwaters are principal means of rapid restoration where seed source vegetation is nearby and abundant and not isolated from stream courses by earthen barriers.

In this study the severe limits to rapid successional restoration due to inadequate seeding were readily overcome by planting seedlings of the mature species after the initial succession was well started. These trees then become the seed trees for more general restoration of areas not planted. By planting at the appropriate stage in succession, mortalities were low except where land managers forgot their promises and released cattle that ate the seedlings. Fire destroyed one experimental wetland because ground water levels were not maintained during drought.

As recounted in the chapter summaries that follow, microcomputer simulation models were part of each phase of work, clarifying concepts by checking numerical consistency between measurements in the field and the ideas of how things work. These models are quantitative statements of concept, quantitative hypotheses, showing consequences of alternative management over time.