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

frequent fires, a1 though timber harvesting(evident from stumps of southernred-cedar) also may be signifi -cant. It is likely that sites (a) and(b) are more diverse not only becauseof less frequent fire, but because ofless extreme hydrological regimes--their soils probably are kept moreconstantly saturated. The low diversityat sites (c) and (d) may also result,in part, from higher salt concentrationsthat exclude sal t-intolerantspecies.The boundaries of hydri c hammocks,as well as their species composition,may be affected by fire. When fire issuppressed in an adjoining communi ty,often by human actions, hydric hammockmay expand. In the Alafia River systemof west-central Florida, Clewel 1et al. (1982) documented the movementof wetland hardwoods (live oak, swamplaurel oak, water oak, and sweetgum)into pine flatwoods. They attributedthe extension to a reduction in firefrequency brought about by agri culturalactivities in the uplands.Though the expansion of hydric hammockinto freshwater marsh in Myakka RiverState Park is related partly tochanges in the hydro1 ogi cal regime(see section 3.32), fire suppressionalso may be responsible. Fire suppressionwithin the park has accompaniedincreased recreational use; frequencyalso has decreased in the watersheddue to land-use changes.3.3.5 Other DisturbancesHydric hammocks have a long historyof human use and disturbance that ischronicled in the accompanying managementhandbook (Simons et a7. 1989).Probably few areas have remained untouchedby human activities. Timberharvesting and 1 ivestock grazing probablyhave had the greatest influenceon the plant composition of contemporaryhydric hammocks.Logging of hydric-hammock forestshas greatly varied in intensity andscale, from selective cuts of scatteredindividual s to clearcutting ofhundreds of acres. Until the twentiethcentury, the cuts generally wereselective; the chosen species changedwith m2rket dz~:c?. I, :.,-highly valued in the era of woodenships, especially in the early andmid-1800's when the United Statesbuilt its navy. Pencil production inthe late 1800's was dominated bysouthern red-cedar, resul ti nq in theover-exploitation of this species inGulf Hammock. The large stumps thathave endured in the hydric hammocksshow that regenerated southern redcedarshave no+ yet reached their f:rmer size. In the 1800's and 1900's,sweetgum and some other hardwoods ofhydric hammocks were cut selectivelyfor manufacture of furniture andcrates, and these harvests too aremanifested in present size distri butions.Sweetgum trees between 50 and75 cm dbh are common in the TigerCreek hydri c hammock, 1 ong protectedfrom harvesting, and in remote areasof the gulf coastal hammocks, butelsewhere the trees are rarely greaterthan 50 cm dbh. Where past harvestingis particularly evident, for examplein the Orange Lake palm/oak hammock(Tab1 e 5), sweetgirms are less than 25cm dbh. Highgrading, the practice ofharvesting all merchantable treeswhile leaving species and individualtrees of low value, became popular inthe twentieth century. This type of1 oggi ng in hydri c hammocks general 1 yretains all cabbage palm, live oak,and an assortment of crooked and decayedtrees. The dominance of cabbagepalm and live oak in some hydric hammocks,for example the Orange Lakeforest, must in part be due to highgradingand selective harvesting practicesthat bypassed these species.Clearcutting became the predominantmode of harvest in hydric hammock inthe past 20 years. Sometimes thecl earcuts are a1 1 owed to regeneratenaturally, but more often, and particularly in the gulf coastal hammocks,they are planted with loblolly pine.uc; ;ak ~;l;Spanish explorers brought cattle andhogs to Florida in the sixteenth century,and wild hogs have roamed hydrichammocks and many other habitats eversince. Cattle still are grazed insome hydric hammocks where ground vegetationis relatively lush, such asthe inland reaches of the gulf coastal