BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 38 PT. I(3)


and leaf growth forms or growth phases depending on soil moisture conditions.
Others (for example, Hypericum fasciculatum) had a needle-like leaf form typical
of many stress tolerant species (Grime 1979). Other species responded in the same
way to a particular stage in the hydrologic cycle. This can be seen in ponds where
drawdown had been recent. Some plants represented species that colonize the bare
mud which becomes available after drawdown. Rapid plant growth was supported
by the nutrient-rich, moist soil present in a temporary pond at this time. The
period available for growth may be relatively short, and, thus, these species were
annuals with a high potential growth-rate or short-lived perennials that were
adapted to exploit this intermittently favorable environment (Grime 1979).
Panicum verrucosum (an annual) is an example of this type of strategy. It had the
highest percent cover on the 1989 transects in BP and GP and had set seed at the
time of sampling. In 1990, the species was not found in either BP or GP. It is
likely that its disappearance reflects the declining level of soil moisture between
sampling events (LaClaire 1992) and that continued drought conditions did not
favor seed germination. Another example of a drawdown species is the annual or
short-lived perennial, Cyperus odoratus. It shared the highest percent cover with
P. hemitomon on transects in OS. It occurred at the lowest elevation in the pond
center and disappeared shortly after it set seed (LaClaire unpubl. data). This result
fits a pattern where the deep area of a pond or marsh changes community
composition seasonally depending on drying conditions (Botts and Cowell 1988).
A perennial species, Eupatorium leptophyllum, was co-dominant in BP (1990), HP,
and ANF-3. This ruderal species is also adapted to exploit the bare soil exposed
after the pond dries. However, it requires less soil moisture, as indicated by its
FAC+ status, and so moves into the pond basin later in the pond drying cycle than
P. verrucosum or C. odoratus. It occurred throughout the pond basins when soil
was exposed and moisture conditions were appropriate.
 Some differences between ponds can be explained by differences in the
 surrounding habitat. Low similarity between the WREC ponds and other study
 ponds can be explained partly by the association of flatwoods vegetation with the
 WREC ponds and not the other study sites. Another explanation may relate to the
 selection of these ponds for study. None of the ponds at WREC has been verified
 as breeding ponds for the Florida gopher frog or the striped newt. If they are not,
 in fact, breeding sites, this may relate to differences in the pond plant communities.
 The higher similarities that resulted when ponds were compared within study sites
 suggests other unknown habitat variables.
 Panicum hemitomon was the only species present in every pond sampled. The
 distribution of this species was a good indicator of the extent of previous flooding
 in the pond basin, and its highest elevation in each pond roughly corresponded to
 the average high water mark (Abrahamson et al. 1984; Lowe 1986; LaClaire
 unpubl. data). Panicum hemitomon cannot tolerate long-term flooding, and, thus,
 its absence in flooded pond centers demonstrated a persistent flooding event. The
 above-ground growth of P. hemitomon tends to be fibrous and resistant to