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

More documents

Recommendations

Info

trees for many years because they donot slough off the trunks (iaessle1942). P!G 63~bt hydric ha:ccck: Szrnmuch less often than fire-adapted communiti es such as pine fl atwoods, butwe propose that fires are sufficientlyfrequent and intense in some stands toinfl uence plant composi tion (Figure34).The effects of fire on hydric-hammockvegetation are mediated by differencesin suscepti bi 1 i ty among theplants. Seedl ings and sap1 ing-sizedtrees are more 1 i kely to be killed byfire than larger trees, because thebark tends to be less thick and thecrowns can be reached by the flames.However, even large trees of some hydric-hammockspecies, especially hardwoods,can be injured by fire, makingthem subject to attacks by fungi andinsects (Fowell s 1965). Bark thick-ness varies among species, accountingfor some, but not all, of the differnncszin firp C I I C C P ibil ~ ~ i t,y (Tab1 P6). When bark thickness was held constant,fourteen species of southerntrees still varied in fire resistance,presumably due to differences in thestructure, composition, density, andmoisture content of the bark (Hare1965). Generally, conifers were moreresistant than hardwoods, and fieldobservations support these findings.Pine fl atwoods (and planted pine plantations) are maintained by regularfires that kill hardwood reproduction.Two severely burned cypress swamps experienced18% and 23% declines in theabundance of the dominant tree, pondcypress (Taxodium distichum var.nutans, a conifer), but 98% and 83%decreases in the hardwoods (mainlyswamp tupelo, sweetgum, and sweetbay)(Ewe1 and Mitsch 1978). Loblolly pineis among the most fire-tolerantspecies in hydric hammocks, and almostall the hardwoods are susceptible tofire. However, one conifer, southernred-cedar, is quite fire-suscepti ble(Putnam et a7. 1960).Table 6. Fire sensitivity in five tree species commonto hydric hammocks. A standardized flamewas applied to living bark and the mean time inseconds for cambium to reach a lethal temperatureof 60 "C was recorded (from Hare 1965).Bark thickness (cm)Species 0.5 0.8 1.0Sweetgum 25.6 48.6 101.8Red map1 e 29.0 56.8 117.6Water oak 30.2 61.0 136.0Figure 34. Fire in the cabbage palm edge Ofhydric hammock, Seminole Ranch, BrevardCounty; top, June 1977, bottom, May 1978 (photoat top by G. Kenneth Scudder).Sweetbay 30.8 67.0 152.0Loblolly pine 35.6 84.2 179.2
Cabbage palm is the most fire-toleranttree in hydric hammocks, survivingeven htlvrr r r; 1 ii. Aii f lii~fi~lbui-ii iiia cabbage pal m/l i ve oak/southern redcedarstand in Tosohatchee State Reservekilled all trees except cabbagepalms (Randall E. Hester, Florida Departmentof Natural Resources; pers.comm. ) . Harlow (1959) ascri bed nearlymonospecific stands of cabbage palm tofrequent fires (every 2-3 years).Fires favor cabbage palm, and theirproduction of flammable 1 i tter in turn~)-c;,;;i?tes f i I-e. Less frequent and intensefires probably favor 1 ive oak inaddition to cabbage palm. Though manyauthors (e.g., Putnam et a1. 1960;Fowell s 1965) have claimed that 1 iveoak is fire-suscepti ble, Laessle andMonk (1961) observed signs of fire ina1 1 eight of the 1 ive-oak-dominatedforests they examined in northeasternFlorida. Because coastal and in1 andstands featured similar vegetation andfire scars, Laessle and Mank (1961)concluded that salt spray was less importantthan occasional fire, coupledwith the tenacity and longevity oflive oak, in maintaining live oak forest.More frequent and intense firesresulted, in coastal areas, in a lowthicket of vegetation containing sawpalmetto and dwarfed forms of severaloak species (Laessle and Monk 1961).Some of the variation in speciescomposi ti on among hydri c hammocks(Table 5) also may result from difFerencesin fire frequency and intensity.The domination of loblolly pine in hydrichammocks a1 ong Si 1 ver Springs runprobably is favored by occasionallight fires as well as soil conditions.If fire (and cattle grazing)were prevented, the forest would convergetoward more "typical" hydri chammock with an abundance of cabbagepalm, oaks, and sweetgum (Florida Gameand Fresh Water Fish Commission 1976).Hydric hammocks highly dominated bycabbage palm, and some live oak, arefound in the Myakka and St. JohnsRiver basins (Table 5). In these areas,hammocks often are bounded bothup- and down-slope by communitiescharacterized by frequent fire--pineflaiwoods and freshwater marsh. Geographicallocation plays a role in thelow diversity of hydric hammock in theMyakka region (see section 3.31), butother factors also may be important.Figure 35 contrasts the tree speciescomposition of two hydric hammockswithin Myakka River State Park. The0 Shep's IslandDeer Prairie SloughswampFloridaFigure 35. Tree-species composition of two hydric hammocks in Myakka River State Park: Shep'sisland, adjacent to Upper Myakka Lake and Deer Prairie Slough, about 20 km to the east.43
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 and 16: whereas hydric hammock is a still-w
Page 17 and 18: CHAPTER 2. PHYSICAL SElTiNG2.3 CLIM
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: The salt concentration of hydricham
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
Page 78 and 79: Graves 1977). These observations su
Page 80 and 81: Consumption of fleshy fruits by res
Page 82 and 83: CHAPTER 6. LINKAGES WITH OTHER ECOS
Page 84: R Amerlcan swallow-tailed kite b. t
Page 87: 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
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?