Austin, Daniel F.

Sixty-two coastal and inland tree islands (hammocks) in Martin and Palm Beach Counties were mapped. Species composition was determined for 36 sites and used to test several hypotheses. The hypothesis was tested and supported that the percentage of tropical species inhabiting a tree island increases on north to south and west to east gradients. A linear regression was run to determine patterns in percent composition of tropical species and whether low hammocks were separable from high hammocks. Data suggested that a range from 70 to 80 percent tropical species composition might be used to define "tropical" hammocks. Since hammocks in southern Florida are considered habitat islands, the MacArthur and Wilson concept was tested. An obtained slope (z value) of 0.18 compares well with the slope of 0.17 predicted by the MacArthur and Wilson model. A cluster analysis showed similarities of 36 sites based on 83 tree and shrub species present.

The insular nature of southern Florida's floristic community
and unique contact with tropical systems have produced plant
communities that are exceptional to the continent. This
uniqueness provides an ideal situation for a localized
palynological study. Pollen from seventy-five species of
angiosperms, each representing a family extant in southern
Florida, is analyzed morphologically and systematically to
provide information for related studies. Families are
selected on the basis of phylogenetic or economic
importance, or uniqueness of occurrence on this continent.

A characterization of successional vegetation patterns on abandoned
farmland in the Hole-in-the-Donut area of Everglades National Park
was performed. Vegetative community composition and structure were
examined in detail in twenty-one study plots located throughout the
study site. Successional assemblages are described qualitatively and
quantitatively. Distinct community types are defined using methods
that emphasize site-to-site comparisons. The relationship between
vegetation and substrate, farming history, hydroperiod, and spatial
arrangement was examined. Results were used to summarize and predict
trends of old field succession on abandoned farmland in southern
Florida. Post-farming vegetation patterns do not resemble prefarming
conditions. Successional forest, frequently dominated by exotic
species, is a relatively new community in southern Florida. It is
likely a final stage in secondary succession on abandoned farmland.

The object of this study was to determine habitat preference (seedlings)
and adults) and the population status of the Florida Royal Palm
(Roystonea elata (Bartram) F. Harper], in the Fakahatchee Strand State
Preserve. Associated species, seedling establishment and germination,
growth rates, size class ratios and elevation of establishment
(epiphytic nature) were examined. The palm showed a preference for high
ground as indicated by the increasing colonization of elevated logging
tramways. Seeds germinated under low light conditions in 17-22 days.
Seedlings had an escalating growth rate from 4.2 em/year for seedlings
to approximately 50 em/year for adults. Each size class was well represented
in the Fakahatchee Strand, suggesting that reproduction was not
being hindered by changes in water level, cold and area urbanization.
Elevation of seedling establishment was a function of water level during
that particular year and did not correlate year to year. These data
indicate a stabilization of the Royal Palm population in the Fakahatchee
Strand.

Populations of Guzmania monostachia, Catopsis berteroniana, C. floribunda
and C. nutans were studied in the Fakahatchee Strand State Preserve,
located in southwestern Florida in Collier County. The habitat preference,
within habitat distributions and quantitative estimates of rarity were
determined for each of the bromeliads. Catopsis and Guzmania are found
primarily in swamp communities, especially in Fraxinus caroliniana-Annona
glabra sloughs. Fraxinus carolihiana is the most comroon host for these
bromeliads. On a host, these species are distributed along a vertical
gradient probably in relationship to light intensities. Guzmania monostachia
is found at the lowest height (Y = 2.5 +- 0.5 m) while Catopsis
berteroniana is found at the greatest height (Y = 5.2 +- 0.2 m). Catopsis
berteroniana occurs in the lowest densities and Guzmania in the highest.
Specific ecological requirements, habitat destruction and the existence
at the extremes of their ranges are responsible for the rarity of Catopsis
and Guzmania in Florida.

Several characteristics of butterfly communities were evaluated in seven pine flatwoods units that differed in time since the last prescribed burn (time-since-burn). Abundance, species richness and species diversity of common butterflies were dependent on plant diversity. These butterfly community characteristics and plant species diversity declined with time-since-burn. Atrytonopsis Manna loammii , a rare butterfly, was found during three different flight seasons in a unit that had been burned in July 1997, as well as a unit burned in February 1999, indicating that early recovery of recently burned units can provided suitable habitat for this rare species. Proper burn rotations and invertebrate surveys are recommended for the conservation of rare species.

Reconstructive aging techniques were used to construct the age frequency distributions of T. testudinum short shoots in the Salt Ponds of Key West, FL. Median short shoot age was approximately two years. No evidence of sexual reproductive effort was found. A site-specific leaf emergence rate was not used, which may have contributed error in the reconstructive technique. Gradients in salinity, phosphorous availability, community composition, and leaf width were observed along the water flow pathway through the ponds. Populations of short shoots more distal from the tidal source exhibited an older age structure reflecting higher salinity, temperature, and dissolved oxygen stresses. Populations closest to apparent sources of nutrient enrichment were skewed toward young individuals. A significant positive relationship between increasing short shoot mortality and recruitment was identified. A significant correlation between low phosphorous availability and narrow leaf width was observed, and a positive relationship between phosphorous availability and recruitment was suggested.