Interactions of Wetlands with the Phosphate Industry
Field studies of 13 little-disturbed (control) wetland sites and of others influenced by nearby, mining through changes in water quantities, qualities, silting, and drainage showed dominant tree species’ with even age-class distributions. Apparently, self-organizational processes were maintaining considerable variety and forest canopy. Whether even age mode of growth was the natural one in Florida wetlands or whether the present wetlands are even aged because of past episodes of lumbering is not yet evident and will remain unknown until historical records can be correlated with tree rings. The vegetation first developing on floodplain wetlands whose hydrologic functions are adequately restored after mining may be expected to be similar with regard to an even age-class distribution of dominant trees. Using cypress tree ring analysis as a general site index and as a standard measure, growth on the study sites was found to be similar to that on undisturbed
sites of similar type. Growth was sometimes more rapid, as if the sites were fertilized. Computer programs were developed for generating basal area growth rate graphs and statistics of growth. Mean curves of basal area increment by year defined characteristic growth rates for trees of each age. Growth was usually in pulses of several years separated by, periods of lesser growth. Tree growth measurements at undisturbed sites and comparative data of other investigators provided baselines for evaluating future impacts and the success of reclamation. Growth of cypress on stream banks with roots reaching the main stream was usually more rapid than that of those on floodplains away from the channels. One area of former phosphatic clay deposition had lesser growth rate. The considerable amount of data on cypress tree rings assembled by other investigators working on other sites needs to be converted to these standard measures and graphs using the new computer programs in order to strengthen the confidence with which characteristic, growth rates are assigned as typical of the various kinds of undisturbed and disturbed sites. Study of case histories of natural succession on wet clay settling areas following mining identified some sites with rapid re-establishment of wetlands vegetation comparable to succession on disturbed soils without mining. In some sites with long hydroperiods, succession to willows was fast, but further succession was arrested apparently for lack of adequate seeding of cypress, gum, or other species adapted to the long flooding regimes.
Where the accidental distribution of dikes, spoils, and clays had developed in low places with a short hydroperiod of a few weeks or less with the balance of water draining in or percolating out, typical wetland hardwoods were found developing in 30 years. A preliminary analysis of available theory and data on seed dispersal and germination of normal plant succession showed that the distances now involved between vegetated areas that serve as seed sources and the clay settling areas in Florida’s mining areas may be limiting plant succession. Formerly when mined areas were smaller and dispersed within vegetated areas, the seeding was better. Preliminary experiments transplanting living soil blocks from areas in advanced succession to areas of early wetland succession following mining showed accelerated appearance of later successional species. Concepts of hydroperiod and seeding as determinants of the type and rate of wetland rehabilitation were made quantitative by expressing as a computer model. Preliminary runs using assumed but plausible values for parameters suggest that when calibrated with real site data, a model of this class can generate nomograms for implementing, wetland rehabilitation after mining in Florida. Ecological engineering of the restoration work of ecological succession, by improving seeding at appropriate stages and controlling hydroperiod through initial landscaping may be the fastest way found so far to restore wetlands in Florida. The next step is proving these concepts with direct experimental tests.
Suggestions are made for experimental testing of the ecological engineering of wetland reclamation with natural succession by transplant seeding of the areas in arrested state. Also suggested is the experimental verification of the means of rapid hardwood restoration by control of drainage area and percolation of low-ground swales in the final landscaping after mining.