The Ecology of Hydric Hammocks - USGS National Wetlands ...

(a)swamplaureloakSweet-Florodared horn -maple beam bald shrubsWFigi~re 25. Species composition of common trees (>I0 cm dbh; hatched bars) and shrubs andsaplings (2.5-10 dbh; open bars) in two hydric hammocks: (a) Seminole County (data from G. R. Bestand P. Wallace, Center for Wetlands, University of Florida); (b) northern gulf coastal hammock(Thompson 1980). Importance values (defined in Table 5) were calculated for each size-class withina hammock. Species with importance values of 5 or less in both tree and sapling classes wereomitted.Tree saplings dominated the 2.5-10cm dbh :izc class in hydric hammocksof Seminole County and the northerngulf coast (Figure 25); shrubs accountedfor less than 20% of the basalarea. With the exception of cabbagepalm, a1 1 tree species were representedin the smaller-sized category.The converse was not true: red maplesapl ings were abundant in the SeminoleCounty hammock, but mature trees ofthat species were absent. In the sameforest, swamp 1 accrel oak, sweetgum,and loblolly pine had higher importancevalues as sapl ings than astrees. Apparently the canopy containedgaps that promoted colonizationof these shade-intolerant species(Putnam et a7. 1960).Hornbeam and swampbay were more importantas "sapl ings" than as "trees,"because they attain maturity at asmall size (Figure 25). Hornbeam wasan abundant member of the subcanopy ofthe Seminole County hammock, the OrangeLakc palm hammock, and the inlandreach of Gulf Hammock, and it musthave dominated this stratum in theHi1 1 sborough River hydric hammock(Table 5). However, this species wasscarce in the northern gulf coastalhammock (Thompson 1980) and non-existentin many of the hydric hammocksthat we visited, including SilverSprings, Wekiva Springs, Myakka River,and Sanchez Prairie (in San FelascoHammock State Preserve). Hornbeam'sabsence from the last forest is puzzling,since the species is common insurrounding mesic hammock.Yaupon, wax-myrtle, and dahoon werethe most common shrubs on the northerngulf coast (Thompson 1980), whereasswamp dogwood and wax-myrtle were theonly shrubs sampled in the SeminoleCounty hydric hammock (G. R. Best andP. Wall ace, pers. comm. ). Wax-myrtle