Austin, Daniel F.

The object of this study was to investigate various physical
and botanical parameters of doming in stands of cypress
trees (Taxodium distichum (L.) L. C. Richard) in southeastern
Florida and to develop basic data about these
small swamps. Analysis of doming was made in relation to
topography, substrate, microclimate, soil moisture, soil
acidity, soil nutrients, vegetation, size and distribution
of cypress, and cypress ages, growth rates, and fire
traumas. Study results were compared with competing
theories of doming and it was concluded that the theory
of differential marginal fire promulgated by Kurz and
Wagner best fits the data set.

Epiphyte richness and abundance were observed in 18 cypress domes spanning two regions in South Florida that were classified by annual low temperature differences of 4.05°C. Using the Preston model of island biogeography and linear regression, the following hypotheses were tested: (1) Larger domes have greater epiphyte diversity because they moderate temperature extremes better than smaller domes. (2) The effect of cypress dome size is reduced in subtropical compared to more temperate regions. (3) A measurable temperature gradient exists within cypress domes. The analyses indicated that epiphyte distribution in cypress domes fits the Preston model. In addition to an increase in diversity with area, there were regional differences that were correlated to temperature, however, these differences diminished as dome size increased. Within the domes, an increase in diversity was correlated to significant differences between dome edge and center temperatures, indicating the occurrence of factors that were influenced by area.

The Wetland Rapid Assessment Procedure (WRAP) is a process developed to assist the regulatory evaluation of mitigation sites (created, restored, enhanced or preserved). These areas are permitted through the South Florida Water Management District's Management and Storage of Surface Waters or Environmental Resource Permit Process. WRAP evaluation is designed for the limited timeframes of the regulatory process. The objectives of WRAP are: (1) to establish an accurate, consistent, and timely regulatory tool; (2) to track changes in wetland sites over time (i.e., baseline data); and (3) to offer guidance for environmental site plan development. Test results of the WRAP procedure showed it to be a repeatable and effective training tool for biologists. Although some general trends were observed regarding land use and variable scores, additional data will need to be collected to establish more conclusive relationships between land use and wetland function.

The position of the cactus family, Cactaceae, within the order Caryophyllales was examined by outgroup analysis of chloroplast rbcL gene sequence data. Comparative data came from 28 outgroup species in 15 families and six ingroup species. Phylogenetic Analysis with PAUP 3.1 produced twelve equally parsimonious trees; these were used to generate a strict consensus tree. MacClade 3.06 was used to refine the polytomies in the consensus tree. Analysis indicates that the Cactaceae is a monophyletic clade; moreover, these results support the work of other analyses that the sister family to Cactaceae is the Portulacaceae. Other relationships within the order are not completely consistent with previous studies. For example Molluginaceae and Caryophyllaceae occupy a central position in the cladogram; Achatocarpaceae aligns with the Amaranthaceae and Chenopodiaceae; and Basellaceae is presented as the basal family within the order. Lastly, the Jamaican cactus Opuntia spinosissima was derived from a common ancestor with the Florida Keys endemic, Opuntia corallicola.

The oak hammock within the Flamingo Road ESL in Broward County, Florida has been disturbed by a number of factors. Twenty-one permanent plots were established to characterize the vegetation of the site and to determine the impact of non-natives on diversity and stability of the hammock. Non-native species may reduce species diversity and stability of communities. Point quarter sampling was compared to quadrat sampling. High percentages of non-native species in hammock sampling plots reduced Sorensen index of community similarity values below the 50% minimum used to define intact communities. Hammock plots were placed in the same clade as non-native plots by average linkage cluster analysis. Additional analysis separated the hammock plots from the non-native plots. The percent of non-natives (individuals and species) did not reduce diversity in the hammock. The hammock remains intact despite disturbances and invasions by non-natives.

The invasive exotic wetland tree, Melaleuca quinquenervia, continues to rapidly expand throughout seasonally wet areas of southern Florida. Water managers are concerned that lowering the water levels of Lake Okeechobee, part of the Everglades ecosystem, while benefitting various natural resources, would stimulate the Melaleuca population. Saplings and seven-week old seedlings were subjected to various hydroperiod treatments, based on a simulation of historical water level variations. Saplings grew taller, increased shoot number, and increased root biomass under longer hydroperiods with fluctuating water levels, including short periods of submersion. Age affected seedling response--those submersed at seven weeks grew slower and had less biomass than submersed 12-week old seedlings, yet mortality was low at both ages. While Melaleuca's plasticity allows it to adapt to hypoxic, aquatic conditions by means of aquatic heterophylly and adventitious roots, like other wetland trees, Melaleuca has limited flood tolerance. Algae and drought also increase mortality.

Three plots were chosen on the Florida Atlantic University Nature Preserve (FAUNP) to study the effect of the exotic Brazilian pepper trees, on the burrow site selection and foraging range of the native gopher tortoise. The home range of tortoises was not statistically different among plots. Proximity of burrows to tree, size of tree and nearest neighbor distance exhibited no effect on burrow site selection or foraging range. Tortoise burrows in all plots exhibited a random dispersion. Current coverage by Brazilian pepper trees and the size of the trees present on the FAUNP has no significant effect on the burrow site selection, or burrow status of the gopher tortoises.

Home owners and local and regional governments in Florida desire low maintenance ground covers. Therefore four xerophytic turfgrasses were evaluated for persistence. Turfgrasses were grown since late July 1990, along an access road to a public park and Interstate 95 in West Palm Beach, Florida. Percent cover, leaf water potential, and quantitative chlorophyll levels were determined for commercial Argentine Bahiagrass (Paspalum notatum) and three experimental grasses: Bahiagrass cv. Rapid Cover Polycross (RCP-2) (Paspalum notatum); St. Augustinegrass cv. FX-10 (Stenotaphyrum secundatum); and Buffalograss cv. Prairie (Buchloe dactyloides) after 12 months of biweekly irrigation and natural rainfall. Argentine Bahiagrass and St. Augustinegrass cv. FX-10 were the best performers while Buffalograss cv. prairie and RCP-2 were poor performers in this study.

Environmental parameters were quantified to develop a physiognomically-based system for describing and predicting gopher tortoise (Gopherus polyphemus) habitat on the Florida Atlantic University Nature Preserve. There were significant correlations among gopher tortoise densities and all physiognomic features except saw palmettos. The only feature with predictive usefulness was bare ground as indicated by a multiple regression. Burrows were regularly dispersed and the highest densities occurred in wet prairie associations. Tortoises located burrows in areas with less canopy and shrub cover but greater herbaceous cover and more extensive bare ground. This physiognomically-based system for predicting location of gopher tortoise habitats should prove useful in the relocation of displaced tortoises as required by the Florida Game and Fresh Water Fish Commission.

The distribution of plant communities along a water level gradient was examined, in light of recent logging and fire history, in Fakahatchee Strand State Preserve. The dominance values of trees and shrub were used in cluster analysis to delineate plant communities. Qualitative data on logging and fire history was obtained by inspecting aerial photographs and surveillance in the field. Local water regime, as a function of topography, appears to be the most important factor associated with the distribution of plant communities in Fakahatchee Strand. Logging of cypress and subsequent dominance of hardwoods has altered the species composition of most communities so that community types have become more distinct from one another. The species composition of plant communities has apparently been altered even more when severe fire followed logging.