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

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cabbage palm and live oak adjoins themarshes of the Myakka River. We followthe examples of R. Harper (1927)and Davis (1943) in differentiatingthe temperate-subtropical hydric hammocksfrom the tropical hammocks ortree islands common to southernFlorida. The tropical hammocks featurea diverse assemblage of West Indian,flood-intolerant plants (Olmstedand Loope 1984). They also may inhabitslight mounds within marsh,prairie, and mangrove vegetation,physiographic settings different fromthose of most hydric hammocks. TheFakahatchee strand in southwesternFlorida is difficult to classify becauseit contains stands of cabbagepalm and swamp laurel oak that resemblehydric hammock. However, theseforests most likely are transientstages resulting from the harvestingof cypress.Hydric hammocks seem to be rare outsideof Florida. Wharton (1977) notedonly small patches of comparable forestin Georgia, mainly in the coastal1 owl ands near Savannah. Reviews ofthe vegetation of South Carolina(Barry 1980) and the lowland forestsof its northern coa'stal pl ain (Jones1981) included no descriptions offorests similar in vegetation and hydrologyto hydric hammocks. A1 thoughHarper (1905) reported that hammocksranged from North Carolina to Floridaand Mississippi, the vegetation surveysof Georgia and South Carolinasuggest that, beyond Florida, the hammocksare mainly of the drier mesicand xeric types.A1 1 wet1 ands--forested and nonforested,saltwater and freshwater--covered more than 8.3 n~i 71 ion acres ofFlorida, about 22% of its land area,1472-73 i;' ---a- '""A'la1t1paVat A J u Y j . Fur eskdwetlands accounted for about 2.1 millionha; of that amount, hydric hammockprobably compri sed 120,000 to140,000 ha. Hydric hammock is estimatedto cover 80,000 to 100,000 ha atpresent (Simons et a7. 1988). A precisedetermination is not availablebecause the boundaries of hydric hammocksare difficult to delineate onaeri a1 photographs. Neither can dataon its extent be exlrd,td from theperiodic inventories of southeasternforests (e.g., Bechtold and Knight1982), because hydric hammock does notcorrespond to a U.S. Forest Serviceforest type or physiographic class.However, it is evident that the areaof hydric hammock has significantlydeclined in modern times, due primarilyto clearing for agriculture, realestate development, and, especi a1 ly inthe past 20 years, for pine plantations.The management guide that accompaniesthis profile details thevarious uses of hydric hammocks, bothdel i berate and inadvertent a1 terati onsof this community, and the impacts onforest structure, wild1 ife habitat,and hydrology (Simons et al. 1988),This community profile summarizes whatis known of the ecology of hydric hammocksand includes new data on thevariation of plant composition amongstands. Since hydric hammocks havebeen 1 i ttle studied, many inferencesare made from similar communities.The scarce scientific attention affordedhydric hammocks in no way reflectstheir value. The beauty of hydric-hammockforests and their provi -sion of wildlife habitat, timber, andflood control argue for their preservationand sound management.
CHAPTER 2. PHYSICAL SElTiNG2.3 CLIMATEFlorida boasts a subtropical climate,but that is technically correctonly for the southernmost and coastalportions of the state (Dohrenwend andHarris 1975). Winter temperatures innorthern Florida are much lower thanin the southern part of the State:mean minimum values are 5 and 16 OC,respectively (Jordan 1984), and extremesin the north range well belowfreezing. Low-temperature extremes inwinter require many plants and animalsto overwinter in typical temperatezonemanner. Summer temperatures, influencedby warm, moist air from theGulf of Mexico and the Atlantic Ocean,are re1 atively uniform throughout thestate. In July the mean daily maximumis about 31 to 33 OC and the meandaily minimum ranges from 22 to 24 OC.The average growing season is 270 daysin the north and more than 320 days inthe south (Tanner and Smith 1981).Rai nfall is plentiful everywhere inFlorida, averaging between 122 and 152cm annually (Jordan 1984), but itsdistribution is highly uneven over theyear (Figure 2). Rainfall is at amaximum in summer and a minimum inspring (Apri 1 -May) and fa1 1 (October-November), when condi ti ans becomedroughty in some years. SouthernFlorida receives most of its rain inthe period from June through September,and its hydric hammocks may floodthen. Northern Florida receives anadditional pulse of rain in late winter.Because of 1 ewer evapotranspi rationrates, winterprobablycontributes as much or more thansummer rain to surface- and groundwatersupplies. Hydric hammocks innorthern Florida often are flooded atFigure 2. Seasonal distribution of rainfall at threelocations in Florida, 1941-70 average (from Jordan1984).the beginning of the growing seasondue to the late winter rains. Especiallyalong the gulf coast, hydrichammocks also may flood from hurricanesin late summer and early fall.Thunderstorms prevail on 70 or moredays each year in Florida (Jordan1984) and bring 1 ightning as well asrain. Bolts of 1 ightning can strikeand kill individual trees and ignitefires. Fires are re1 atively uncommonin hydric hammocks, but their frequentoccurrence in some adjacent communitiesaffects the extent and compositionof hydric hammocks. Before humansactively Suppressed fires andbuilt roads and other barriers totheir spread, fires must have burned
Page 2 and 3: Copies of this publication may be o
Page 4 and 5: DISCLAIMERThe opinions and recommen
Page 6 and 7: CONVERSION TABLEMetric to U.S. Cust
Page 8 and 9: FIGURESNumber1AL...............Dist
Page 10 and 11: NumberTABLESPaqeClassifications of
Page 13 and 14: CHAPTER 1. INTRODUCTION"Hammock, ho
Page 15: whereas hydric hammock is a still-w
Page 19 and 20: Recent and PIe~sIoLene sands clay m
Page 21 and 22: ern vegetation associations formed-
Page 23 and 24: Table 3. Comparison of surface soil
Page 25 and 26: throughout the year in Florida, and
Page 27 and 28: Figure 13. Flooding and drydown of
Page 29 and 30: +southari:magnolla+-------cabbage p
Page 31 and 32: frequency may be once per year in f
Page 33 and 34: Table 4. Plants occurring in hydric
Page 35 and 36: Table 4. (Continued).Scientific nam
Page 37 and 38: of the subcanopy and shrub layers i
Page 39 and 40: sites were not chosen randomly;rath
Page 41 and 42: When present in a hydric hammock,ca
Page 43 and 44: hydric harriniock forests. These sp
Page 45 and 46: was the most frequent shrub in the
Page 47 and 48: Gulf Hammock is rep1 aced abruptly
Page 49 and 50: A sequence of changes in plantmat a
Page 51 and 52: I ~ U mapleswamp laurel oak 3:1100b
Page 53 and 54: The salt concentration of hydricham
Page 55 and 56: Cabbage palm is the most fire-toler
Page 57 and 58: frequent fires, a1 though timber ha
Page 59: Figure 38. Tree blowdowns due to hu
Page 62 and 63: locally collected litter lost 85% o
Page 64 and 65: Table 7. Occurrence of reptiles and
Page 66 and 67:
Table 8. Occurrence of reptiles and
Page 68 and 69:
4.3 BIRDS4.3.1 Community StructureM
Page 70 and 71:
Table 11. (Concluded).- ----Variabl
Page 72 and 73:
and cerambyci d beet1 es) . Unl i k
Page 74 and 75:
no specific habitat preference; it
Page 76 and 77:
not take place in years of mast fai
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Graves 1977). These observations su
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Consumption of fleshy fruits by res
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CHAPTER 6. LINKAGES WITH OTHER ECOS
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R Amerlcan swallow-tailed kite b. t
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Conner, W.H., and J.W. Day, Jr. 197
Page 90 and 91:
Duck foods in managed tidalimpoundm
Page 92 and 93:
Puri, M,S., 3.W, Yon, and W.R.Ogles
Page 94 and 95:
Wharton, C.H. 1977. The naturalenvi
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