Wildlife, Animals, and Plants
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KUCHLER TYPE
KUCHLER TYPE: Cypress savanna
KUCHLER-TYPE-NUMBER :
K091
PHYSIOGNOMY :
Open forest to savanna with needleleaf deciduous trees, some broadleaf
evergreen trees or shrubs. Trees and shrubs also in groves surrounded
by open grasslands [31].
OCCURRENCE :
Kuchler's description of cypress savanna is similar to Davis'
description [7] of cypress swamps in southern Florida. Davis classified
southern Florida by physiographic regions and recognized four vegetation
types containing baldcypress (Taxodium distichum) or pondcypress (T. d.
var. nutans) in southern Florida. Three of these correspond to
generally recognized types of stillwater cypress swamps in southern
Florida: dwarf cypress savanna, cypress domes (also called cypress
heads or cypress ponds), and cypress strands [6,7,17]. In addition,
mixed swamps (also called mixed hardwood swamps or mixed swamp forests)
contain cypress, although cypress is usually not dominant [7,17].
Kuchler's description and species list for cypress savanna appears to
include the three cypress-dominated types. Throughout this writeup,
where information pertains to all three types the term cypress swamp
will be used. Where information is specific to a particular type, the
abovementioned type names will be used.
Kuchler's definition of cypress savanna appears to include cypress
domes, strands, and dwarf cypress savanna that occurs in southern
Florida in Big Cypress Swamp, Fakahatchee State Preserve, Corkscrew
Swamp Sanctuary, and Everglades National Park. Cypress domes also occur
in Okefenokee Swamp and within pine flatwoods in northern Florida.
These domes are not on Kuchler's map of cypress savanna; whether this is
because of size or because he did not include them in the definition is
unknown. This writeup will focus on cypress domes, strands, and dwarf
cypress savanna occurring in southern Florida. The cypress domes
occuring in northern Florida and in Okefenokee Swamp are slightly
different from those described by Kuchler, but they contain many of the
same species and have similar ecological processes and are thus included
in this writeup [8,31]. Information derived from cypress domes
elsewhere will be included where it is deemed relevant since many of the
species and ecological processes appear to be similar. This writeup
does not include cypress swamps on alluvial soils which occur over the
southeastern Atlantic Coastal Plain from the Carolinas to Louisiana.
STATES:
FL
COMPILED BY AND DATE :
Janet Sullivan, November 1994
LAST REVISED BY AND DATE :
NO-ENTRY
AUTHORSHIP AND CITATION :
Sullivan, Janet. 1994. Cypress savanna. In: Remainder of Citation
Kuchler Type Index
FEIS Home
KUCHLER TYPE DESCRIPTION
PHYSIOGRAPHY :
Big Cypress Swamp is a large, basin-like area, with low limestone
outcrops, numerous sloughs, shallow ponds, and prairies on sand or marl
(unconsolidated calcitic clay). It forms a discrete hydrological unit
[6,11]. Big Cypress Swamp drains south and west through sloughs,
strands, and culverts under the Tamiami Trail. During periods of low
water levels, water is impounded in numerous ponds [6]. Elevation
ranges from 12 to 40 feet (3.6-12 m) above mean sea level in the
northern part of Big Cypress to sea level where it grades into mangrove
(Rhizophora mangle, Avicennia germinans, or Laguncularia racemosa)
swamps [6].
The formation of cypress domes, strands, and dwarf cypress savannas is
driven primarily by hydrology. Cypress domes develop in depressions
within large watersheds. The characteristic circular shape is probably
created by the slow dissolution of the underlying limestone over years
of acid water percolation [19]. The water level in cypress domes
normally fluctuates dramatically once or twice during the year [17]. In
Big Cypress Swamp and in the Everglades, cypress domes are underlain by
marl and limestone bedrock [8].
Cypress strands form where high water level and sufficient flow generate
a depression channel. At low water there may be no discernible flow
[17]. Corkscrew Swamp, a cypress strand, is an elongate depression in
the mineral soil with very little relief (less than 4 inches/mile
[6cm/km]). The ground surface in Corkscrew Swamp is more irregular in
the deeper parts of the strand due to mounds formed by stumps, logs,
litter, burned-out holes in peat, and root wells [9].
Dwarf cypress savannas are open stands of stunted cypresses (also called
hatrack cypress) with an understory of grasses. They occur on sites
with a medium-length hydroperiod (6-9 months). Rainfall is the most
important source of water for dwarf cypress savannas [6,17].
CLIMATE :
The climate of southern Florida is moist and mild; it is frost-free
nearly all year. Mean annual precipitation is around 60 inches (1,524
mm), 80 percent of which falls from May to October, creating distinct
wet and dry seasons [3]. Precipitation received in 1 year ranges from
30 to 100 inches (762-2,540 mm) [3]. Occasionally, drought in summer
(normally the wet season) can result in complete cypress defoliation
which normally does not occur until fall [17].
SOILS :
In southern Florida, cypresses are found on a variety of soils including
organics, sands, marls, and rock lands [7], with pH usually in the range
of 6 to 8. Cypress swamp soils are characterized by Coultas and Duever
[43].
Soils in Big Cypress Swamp are mostly derived from Tamiami limestone and
quartz sands. The soils are usually pure sand, marl, or mixtures,
ranging from 2 to 24 inches (5-61 cm) deep on limestone bedrock. Dwarf
cypress savanna occurs on thin marl, 3 to 6 inches (7.6-15 cm) deep [6]
Outcrops of dense, fine-grained limestone are scattered within the
cypress savanna ecosystem [6,23].
VEGETATION :
There is no standard nomenclature for the vegetation associations of
southern Florida [42]. Cypress swamps occur in the oak-gum-cypress
Forest and Range Ecosystem. Garrison and others [23] described the
alternating wetlands and drylands west of the Everglades as cypress
savanna. Craighead [6] defined a number of physiographic provinces for
southern Florida. His descriptions include cypress domes, strands, and
dwarf cypress and are similar to those of Davis [7]. Wade and others
[42] listed 10 vegetation associations for southern Florida and
included cypress as a single type. Long and Lakela [32] described five
physiographic provinces for southern Florida, listing Big Cypress as a
single province. The Florida Natural Areas Inventory [22] included
three natural community types that correspond to cypress swamps.
Baldcypress dominates alluvial floodplain forests, and pondcypress is
dominant in cypress domes [37]. It has been indicated by some authors,
however, that both species occur in cypress domes and strands [6,9,17,].
It is thought that distributional differences may be due differences in
tolerance to acidity [34], or because pondcypress is more drought
tolerant than baldcypress [1]. Many authors do not attempt to
discriminate between the two taxa, partly because of controversy over
their taxonomic status and partly because of the difficulty of
distinguishing them in the field. Throughout this writeup, where
baldcypress and pondcypress have not been differentiated by the authors
or where the information is applicable to both taxa, the term cypress
will be used.
Plant associates in cypress swamps vary with depth, duration, and
frequency of flooding, soil type, geographic location, and stand density [17].
Cypress domes and strands have few associates in the center; most of
those present are shade-tolerant species of epiphytic bromeliads,
orchids, ferns, and nettles, many of which do not occur in the United
States outside of Florida [6,17,42], or aquatic macrophytes such as tall
flag (Thalia geniculata) and arrowhead (Sagittaria spp.) [7,42]. Ground
cover is sparse in the center [42]. On the perimeter of cypress domes
and strands, associates include buttonbush (Cephalanthus occidentalis),
redbay (Persea borbonia), sweetbay (Magnolia virginiana), magnolia
(Magnolia spp.), cocoplum (Chrysobalanus icaco), dahoon (Ilex cassine),
myrsine (Myrsine florida), southern bayberry (Myrica cerifera), Coastal
Plain willow (Salix caroliniana), and Florida poisontree (Metopium
toxiferum) [6]. Slash pine (Pinus elliottii) is occasionally present in
cypress domes, particularly in northern Florida [17,19,20]. Water
tupelo (Nyssa sylvatica var. biflora) is also present in northern
cypress domes [10,20]. Red maple (Acer rubrum), pond apple (Annona
glabra), strangler fig (Ficus aureus), water ash (Fraxinus caroliniana),
swamp bay (Persea palustris), and paurotis palm (Paurotis wrightii) are
frequent in cypress domes and strands [6,7,17,44]. Spanish moss
(Tillandsia usneoides) is common in more northerly cypress domes. Other
species of Tillandsia are more common in central and southern Florida.
Resurrection fern (Polypodium polypodioides) is another common epiphyte
[5].
In open stands grading to dwarf cypress savanna, sawgrass (Cladium
jamaicense) may be an important component on the higher layers of peat.
Occasionally palmettos (Sabal palmetto or Serenoa spp.) are present, and
greenbriars (Smilax spp.) are conspicuous. Herbs present in cypress
domes and strands include sweet rush (Cyperus haspan), maidencane
(Panicum hemitomon), beakrushes (Rhynchospora spp.), spikerushes
(Eleocharis spp.), arrowweeds (Pluchea spp.), eupatorium (Eupatorium
spp.), fingergrasses (Chloris spp.), swamp fern (Blechnum serrulatum),
small yellow bladderwort (Utricularia juncea), and leather ferns
(Achrostichum spp.) [6,7,31,42]. Algal mats often cover the soil
surface in the wet season [42].
WILDLIFE :
Cypress swamps play a unique role in animal ecology. They do do not
have a distinct fauna, sharing many species with adjacent plant
comunities. Most species and individuals spend only part of their lives
in the swamp [17,23,28].
Benthic invertebrates form the base of the food chain. A high diversity
of invertebrates has been recorded for cypress domes and dwarf cypress
savannas. In cypress domes, immature chironomids (Diptera) dominate the
benthic fauna [21]. Wild turkeys (Meleagris gallopavo) and other
predators feed on crayfish in cypress swamps [17]
In summer, reptiles and amphibians dominate cypress swamp vertebrate
communities; in winter the vertebrate fauna is dominated by birds. High
temperatures allow herpetiles to remain active through the winter [28].
Jetter and Harris [45] trapped 23 species of reptiles and amphibians in
three cypress domes from 1974 to 1976. The most numerous group was
ranid frogs, particularly southern leopard frog (Rana utricularia).
Other common species included cricket frogs (Acris spp.), oak toad (Bufo
quercicus), green treefrog (Hyla cinerea), and cottonmouths (Agkistrodon
spp.). Undisturbed cypress domes in Bradford County, Florida, contained
(in addition to southern leopard frog) little grass frog (Pseudacris
ocularis), central newt (Notophthalmus viridescens louisianensis), pine
woods treefrog (Hyla femoralis), striped mud turtle (Kinosternon
baurii), and slender dwarf siren (Pseudobranchus striatus spheniscus).
Amphibian species outnumbered reptiles [28].
Bird densities are higher in cypress swamps in winter than during
breeding season, largely due to the presence of wintering birds that
breed elsewhere. Birds using cypress swamps include wild turkey, ibis
(Plegadis spp.), double-crested cormorant (Phalacrocorax auritus),
herons (Ardea herodias, Butorides striatus, Egretta caerulea, Nycticorax
nyticorax, and Nyctorax violaceus), snowy egret (Egretta thula), great
egret (Casmerodius albius), anhinga (Anhinga anhinga), and belted
kingfisher (Ceryle alcyon) [23]. The limpkin (Aramus guarauna) is a
characteristic occupant of cypress swamps due to the availability of
snails. Canopy-feeding passerines are common, but there are usually
only a few mid-story species such as red-bellied woodpecker (Melanerpes
carolinus), red-headed woodpecker (M. erythrocephalus), pileated
woodpecker (Drycopus pileatus), tufted titmouse (Parus bicolor), and
great crested flycatcher (Myiarchus crinitus). The wood duck (Aix
sponsa) is common in the larger cypress domes that contain sufficiently
large trees [28]. Swainson's warbler (Limnothlypis swainsonii) and
prothonotary warbler (Protonotaria citrea) are also typical members of
the cypress swamp avian community. Endangered bird species occurring in
cypress swamps include Bachman's warbler (Vermivora bachmanii) and
southern bald eagle (Halieetus leucocephalus leucocephalus).
Mississippi kite (Ictinia mississippiensis) and American swallow-tailed
kite (Elanoides forficatus) breed only in swamps, including cypress
swamps [17]. The globally endangered (extinct in the United States)
ivory-billed woodpecker (Campephilus principalis) once inhabited cypress
swamps [23,28].
Most mammals occurring in cypress swamps occupy ecotones. Mammals
include white-tailed deer (Odocoileus virginiana), gray fox (Urocyon
cinereoargenteus), fox squirrel (Sciurus niger), raccoon (Procyon
lotor), Virginia opossum (Didelphis marsupialis), striped skunk
(Mephitis mephitis), eastern cottontail (Silvilagus floridana), and
swamp rabbit (S. aquaticus) [23,28]. River otter (Lutra canadensis) and
bobcat (Lynx rufus) are common residents of large cypress domes [28].
There are many rodents and shrews [23] including southeastern shrew
(Sorex longirostris), short-tailed shrew (Blarina brevicauda), cotton
mouse (Peromyscus gossypirus), hispid cotton rat (Sigmodon hispidus),
and golden mouse (Ochrotomys nutalli). The latter nests in trees to
avoid floodwaters [17,28]. Away from the center of cypress domes small
mammals include marsh rabbit (Silvilagus palustris) and wood rats
(Neotoma spp.) in addition to species mentioned previously. Arboreal
mammals include southern flying squirrel (Glaucomys volans), eastern
gray squirrel (Sciurus carolinensis), and several species of bats [28].
Rare and endangered species, and species whose ranges formerly included
cypress swamps, include mangrove fox squirrel (Sciurus niger avicenna),
elk (Cervus canadensis), black bear (Ursus americanus), Florida panther
(Felis concolor), mink (Mustela vison), and gray wolf (Canis lupus)
[17,23,28].
ECOLOGICAL RELATIONSHIPS :
Successional Processes: Cypresses are dependent on regular water level
fluctuation for successful germination and establishment [17]. Cypress
stands become established on open sites during periods of drought
[27,42,44]. Conditions that exist following crown-killing fires that do
not consume the surface peat layer are conducive to cypress
establishment [27]. In the absence of fire, cypresses are succeeded by
hardwoods. Cypresses are not the most rapidly growing trees in swamps;
hardwoods, particularly water ash and red maple, produce more wood
(basal area) relative to their biomass than cypresses [9].
Cypress dome establishment within sawgrass marshes (i.e., the
Everglades) can proceed on batteries of peat: peat masses that float
loose from the substrate and provide a relatively dry site suitable for
colonization. Peat batteries may be initially colonized by buttonbush,
hurrahbush (Lyonia lucida), or dahoon. These shrubs stabilize the mass
and increase the rate of peat formation, favoring subsequent invasion by
bays (Persea spp.) and cypresses. The resulting community is similar to
that found in cypress domes in closed depressions. These communities
are usually referred to as tree islands or cypress islands and usually
succeed to hardwoods in a short period of time [5].
Community Structure: Distinct seasonal communities dominate cypress
swamps. The wet season flora dominants include species adapted to
growing under flooded conditions; a different group of species grows
during periods when there is no standing water [9].
Dwarf cypress savannas do not usually have standing water in late
winter, but are wet the remainder of the year [6]. Duever and others
[11] reported a hydroperiod for dwarf cypress savanna of 120 days, with
a maximum water depth of 6 to 8 inches (15-20 cm). On a dwarf cypress
savanna study site in Big Cypress Swamp, the water table was above
ground level for approximately 4 months between July and November.
Maximum depth of surface water was 4 inches (10 cm). In March of the
dry season, maximum depth to the water table was 40 inches (103 cm) [3].
In dwarf cypress savannas, cypress seedlings become established in wet
years but grow very slowly [6]. Trees are usually less than 12 feet
(3.4 m) tall and have disproportionately large buttressed trunks. Many
of these small trees are over 100 years old; trees the same size in
nearby cypress domes may be only 25 years old. Trees are often 50 to 65
feet (15-20 m) apart [6].
Cypress domes are small, roughly circular, forested wetlands that occur
in poorly drained depressions [5,7,17,42]. In cypress domes and
strands, decomposition rates are slow and peat accumulates [17]. In
some cypress domes the peat layer is up to 20 feet (6 m) deep; a record
depth of 96 feet (29 m) was reported for one cypress dome [7,11]. Most
of the cypress domes in southern Florida have a central pond, surrounded by
the tallest trees [6].
The cypress canopy may be up to 60 feet tall (18 m) around the central
pond with almost complete crown closure [42]. Further away from the
pond, the trees are shorter. Some authors report that the shorter trees
are younger [7]. However, Craighead [6] stated that the trees in the
middle are not much older than the trees on the periphery; in some
cases, the trees on the shallow soil of the periphery are older. This
occurs for two reasons: the lower fertility of the soil on the
periphery and the lower likelihood of severe fire due to a smaller
quantity of fuel. Trees are killed in the center during peat-consuming
fires. The higher fertility in the center contributes to relatively
rapid growth rates for new trees established after the fire. Further
discussion of fire and community structure is in FIRE EFFECTS ON
VEGETATION [6,9,42]. Cypress domes sometimes expand and grow together
to form meandering cypress strands [11].
Cypress strands are found along major drainageways, mostly oriented
north-south. Cypress strands have a well developed layer of peat, up to
6 feet (2 m) deep [11]. Cypress strands have a hydroperiod of 8 months
or more [10], and are sometimes flooded year-round [42]. Normal wet
season water levels in Corkscrew Swamp may fluctuate from 1.6 to 5 feet
(0.5 to 1.5 m) deep and there is usually a measurable but slow flow
rate. Water level may be relatively stable in a wet year (with dry
season rainfall) but may drop as much as 6.6 feet (2 m) in a drought
year [9].
The trees in the middle of cypress strands are larger than those in
domes and may be 100 to 115 feet (30-35 m) tall and 6 feet (1.8 m) in
diameter above the butt swell. Strands intergrade with dwarf cypress
savanna on the edge. Trees near the periphery of the strand are usually
smaller than trees in the center, probably for reasons similar to those
for similar structure in cypress domes. The best correlation between
tree size and environmental factors was found to occur with peat depth;
larger trees tended to be found on deeper peat [9]. The relationship of
tree size and fire is discussed further in FIRE EFFECTS ON VEGETATION.
In Gordon Swamp (a small strand on the edge of Corkscrew Swamp
Sanctuary), cypresses near the center of the strand grew 50 percent
faster than trees near the edge for the first 50 years of growth. Trees
over 150 years old had ring widths that were similar in all parts of the
strand. It was hypothesized that young trees were better able to take
advantage of improved site quality in the center of the strand than
older trees [9].
In cypress domes and strands hardwood species contribute to the
formation of a thick layer of peat. With the gradual reduction of
cypress in older stands due to lack of regeneration, hardwoods increase
in dominance, and the stand becomes a mixed swamp (a transitional
stand), and then a bay head (hardwood swamp stand dominated by bays
[Persea spp.]) [6].
Nutrient Status and Community Productivity: Nutrient inflow to dwarf
cypress savanna is extremely low. For example, total phosphorus inflow,
which is solely via rainfall, is approximately 0.1 g/sq m/year [1].
Nutrient concentrations in dwarf cypress savanna surface water were
reported: Nitrate nitrogen ranged from 0.07-0.18 mg/L and total
phosphorus ranged from 0.005-0.013 mg/L [3]. An increase in nutrient
flow can occur when lower water levels allow more rapid decomposition
and nutrient mineralization [17]. Spanish moss extracts nutrients from
incident rainfall and may play an important role in nutrient cycling
[5]. There is not an appreciable contribution by nitrogen-fixation [17].
Gross primary productivity and net primary productivity are low in
cypress swamps, which are supplied with nutrients primarily by rainfall
and have little nutrient storing capacity. Dwarf cypress savanna is
rated the lowest in productivity, and cypress domes and strands are
slightly higher. Estimated gross primary productivity for southern
Florida cypress strands is approximately 6.74 g of carbon/sq m/day; and
for southern Florida dwarf cypress savanna gross primary productivity is
1.82 to 2.41 g of carbon/sq m/day. Aboveground biomass productivity is
also low: 0.5 kg/sq m/year [17]. Mean basal area increment for dwarf
cypress savanna trees ranged from 7.2 to 12.7 sq cm/year [3]. Biomass,
productivity, and water relations were discussed for Fakahatchee Strand
[4].
KUCHLER TYPE VALUE AND USE
KUCHLER TYPE: Cypress savanna
FORESTRY VALUES :
Most old-growth cypress swamps (and other swamps) in Florida were logged
by 1950. The most valuable product was the old-growth baldcypress which
contained large volumes of very durable hardwood. Current logging is in
second-growth, relatively young cypress, which is less durable. It is
primarily used for chipping; until recently cypress was primarily used
for specialty items such as crab traps and ladders. [17,33].
RANGE VALUES :
WILDLIFE VALUES :
Cypress swamps provide food, nesting sites, hibernation sites, and cover
for a variety of species. Rare and endangered birds and mammals are
more likely to be found in cypress swamps and mixed hardwood swamps than
in other kinds of swamps. Cypress swamps are amoung the few areas not
colonized by humans in southern Florida [17]. In Big Cypress Swamp, 6
of 19 bird species listed as rare, endangered, or threatened use cypress
swamps for breeding and feeding [8].
Cypress swamps commonly contain rookeries of wood storks (Mycteria
americana), herons (nine species and subspecies), and double-crested
cormorants [17]. The wood stork is dependent on Florida wetlands. It
nests in cypress stands or mangrove stands, and its range is now largely
restricted to Florida [15]. Other rare birds found in cypress swamps
include short-tailed hawk (Buteo brachyurus), southern bald eagle [36],
and osprey (Pandion haliaetus). The roseate spoonbill (Ajaja ajaja) is
found in dwarf cypress savannas [17].
The Florida panther, which is endangered, is restricted to Big Cypress
Swamp and the Everglades [15].
Ewel [17] subjectively rated the contributions of various cypress swamp
parameters to bird and mammal habitat. All three types of cypress
swamps were rated low in canopy insect production, low in edible seed
and fruit production, and low in vegetative density. Cypress domes and
strands were rated high in cavity density, but dwarf cypress savannas
were rated low. All three types were rated high for presence of water.
Dwarf cypress savannas are important for their sparse cover; this
community provides perching sites for raptors and wading birds that
search for small organisms in an open environment [17].
OTHER VALUES :
Cypress swamps recharge groundwater and play a role in regional flood
control. Cypress domes in northern Florida are under study for
wastewater treatment areas [18,19]. Nutrient enrichment from wastewater
dumping result in immediate response among floating aquatics and
herbaceous species. Net photosynthesis in cypresses growing in
sewage-treated domes increased over a 6-year study, but there was no net
increased tree growth [5,40]. Other uses of cypress swamps include
harvesting of peat and phosphate mining. Reclamation after phosphate
mining usually converts the site to planted grass pasture [17].
A detailed review of cypress swamp values has been published [18].
MANAGEMENT CONCERNS :
Currently, most of the extant cypress swamps in southern Florida are under
management or protection in Big Cypress National Preserve, a 920 square
mile (2,300 sq km) area. Other preserves in which cypress swamps occur
include Corkscrew Swamp Sanctuary, Fakahatchee State Preserve, and
Everglades National Park [19].
Southern Florida has the youngest flora of any area in the United
States; perhaps 3,000 to 5,000 years have passed since establishment of
vegetation on newly emerged land. It has been hypothesized that since
the flora is so young, there are many unfilled niches which therefore
facilitate invasion by exotic species [41]. Melaleuca (Melaleuca
quinquenervia) invasion affects groundwater levels in cypress swamps
through increased transpiration [17]. Other impacts of melaleuca
invasion are discussed in FIRE MANAGEMENT CONSIDERATIONS.
Many cypress swamps have been drained, logged, impounded, or experienced
other disturbances. Drainage allows invasion by species with low flood
tolerance, and often results in significant decrease in primary
productivity [17]. Drainage of cypress swamps causes a shift in the
frequency distribution of reptile and amphibian species but no
differences in abundance or richness [28]. Cypress swamps in northern
Florida had poor cypress regeneration, increased shrub density, hardwood
invasion, and increased fire potential after drainage [17]. Logging
activities change drainage patterns due to the construction of dikes,
roads and tramways, and the loss of trees (with concomitant lower
transpiration rates).
Regeneration after logging in cypress swamps is usually dominated by
hardwoods. Water level changes and lack of cypress seed are responsible
for the lack of cypress regeneration [17]. Structural characteristics
change with logging of large old-growth cypress and affect bark-gleaning
birds, reptiles, amphibians, and large arboreal mammals such as
raccoons. These changes include loss of nest sites for cavity nesting
species. Species that forage in open areas are temporarily benefited.
Logging slash favors certain species of herpetiles, small mammals (i.e.,
cotton mouse), and birds (i.e., rufous-sided towhee). Breeding birds
respond favorably to edges created by clearcutting pinelands that
surround cypress swamps. Individual density of animals, number of
species, species diversity and density are all higher in sharply defined
edges than in ecotones [28].
Alexander and Crook [46] documented vegetation changes in southern Florida
over the last 16 to 30 years, on 100 mile square (160 km square)
quadrats. They concluded that the natural ecosystem will continue to
lose its diversity and ability to maintain itself with any resemblance
to the pre-1940 condition unless ways are found to return and properly
distribute more water to wild habitats, control exotics, and manage
fire.
KUCHLER TYPE FIRE ECOLOGY AND MANAGEMENT
KUCHLER TYPE: Cypress savanna
FUELS, FLAMMABILITY, AND FIRE OCCURRENCE :
Fuels: On the driest sites, rapid decomposition and occasional flooding
prevent organic matter accumulation [17]. Most of Big Cypress Swamp,
however, is covered with sufficient fuel to carry fire. Occasional
freezes may influence fuel characteristics by killing back the
cold-sensitive vegetation and increasing litter [39]. Mean standing
stock of litter in a dwarf cypress savanna was 344 (+/- 94) grams per
square meter [3].
In years of average precipitation, fires may burn in grasslands and
dwarf cypress savanna, but will not burn very far into the middle of
cypress domes or strands. Conversely, in a drought year fire may be
more severe in the centers of domes and strands than on the edges. When
peat is dry enough to burn, the larger amount of litter and organic
material in the center will support a more severe fire than on the
edges. Fires that consume peat may kill trees due to root damage and
loss of structural support. Fires are rarely severe enough to kill
trees in dwarf cypress savanna because of sparse organic matter [3,6].
Flammability: In cypress swamps, ericaceous evergreen shrubs are
particularly flammable community members [17].
Cypress domes and strands and hardwood swamps probably constituted
natural barriers to the spread of wildfire in presettlement times; fire
burning in grasslands and savannas around cypress domes would burn into
the dome only as far as soil and vegetation moisture levels would
permit. Drainage of these wetlands has increased the flammability of
cypress domes [42].
Fire During Presettlement Human Occupation: Human occupation occurred
within a few hundred years of vegetation establishment in southern Florida
[39,24]. Most cypress swamps in southern Florida contain evidence of past
fires [42]. It is generally assumed that lightning fires have always
been an important factor in southern Florida fire regimes. Prior to
European settlement, human-caused fire may have substantially increased
fire frequency over the background frequency of lightning fires
[14,38,39]. It is likely that most Native American-caused fires were
set in the dry season, as soon as fuels could carry fire [39].
Fire in the Postsettlement Period: The frequency of fires increased
with European settlement of southern Florida. Fires were set for numerous
reasons and many fires were started through carelessness or accident.
Drainage of swamps increased the frequency and intensity of fires, with
concomitant severe damage to peat exposed by drainage [41].
Fire Frequency: The Everglades and Big Cypress National Preserve are
the most fire-prone ecosystems in the National Park Service system.
Southern Florida experiences 70 to 90 thunderstorm days per year, the
highest number of any area in the United States. The mean annual number
of ground strikes is from 4 to 12 per square kilometer. Most of the
cloud-to-ground strikes occur during the wet season and 87 to 93 percent
of lightning fires occur from May to August; lightning fires have been
recorded in all months except January and February. Fewer strikes but
more lightning fires occur in the Everglades than in Big Cypress Swamp
[39,41]. Taylor [41] estimated that the interval between extreme fire
years (years in which a very large number of fires or large number of
acres burned) in the Everglades is 5.8 to 7.5 years, and that there is a
moderate fire season every 3.2 years.
In southern Florida, widespread and severe fires occurred in more than
one-third of the years between 1900 and 1952. In very dry years,
organic soil fires occasionally burned from one dry season to the next,
through the normally wet summer months. Between 1948 and 1979, there
were 682 fire reports and 451,082 burned acres in the Everglades. For
the first 21 months of fire records for Big Cypress (starting in 1979),
there were 131 reported fires, which burned 40,370 acres (16,716 ha).
Many fires in Big Cypress burn out before discovery. Both Parks have
been disturbed by drainage, logging, farming, off-road vehicle use, and
invasion by exotic species, all of which affect fire frequency to some
extent. Other changes in fire intensity, frequency, and type have come
from fire suppression, prescribed fire programs, and incendiary fire.
Wildfires and incendiary fires are extinguished [41]. Wet-season
prescribed fires have replaced dry season lightning fires in many
grasslands. Drainage has decreased hydroperiods and increased
flammability of peat [5,41].
In Big Cypress Swamp, lightning-caused fire is minor relative to
human-caused wildfire and prescribed fire. Human-caused wildfires occur
in the dry season, and are strongly correlated with moisture conditions
[39]. Of the 1,068 fires recorded in Big Cypress Swamp from 1979 to
1988, about four-fifths were incendiary or accidental [39]. The number
of fires is positively correlated with peak backcountry use during wild
turkey season in March and concides with dry conditions. "Sunday is a
particularly popular day for starting fires" [39].
The average fire return interval for all community types in Big Cypress
is approximately 12 years [39]. Cypress in dwarf cypress savanna show
fire scars and may reveal fire frequency in the dwarf cypress type;
however, the slow growth of the trees makes interpretation of rings
difficult [41]. Snyder [39] estimated the fire return interval for
dwarf cypress savanna as 24 years. Wade and others [42] reported an
estimate of seven to nine fires per century in dwarf cypress savanna.
Cypress-mixed hardwood strands and cypress domes have a fire return
interval of 110 years according to Snyder [39], but Ewel [17] stated
that they experience three to five fires per century. Strands appear to
have longer fire rotations than domes or dwarf cypress savanna [42].
FIRE EFFECTS ON SITE :
Peat based habitats such as cypress domes and strands can support both
ground and surface fires. Fire may remove aboveground vegetation only
or may also consume peat.
FIRE EFFECTS ON VEGETATION :
The effects of fire on southern Florida ecosystems are compounded by
changing hydrologic relationships. Presettlement fires had different
effects than current fires due to human-caused changes in drainage
patterns, fire frequency, and the introduction of exotic species [42].
Cypresses survive surface fires better than competing hardwoods [20].
Low-severity surface fires therefore tend to maintain monospecific
cypress stands by suppressing hardwood regeneration and killing young
hardwoods [9,17]. For example, in Okefenokee Swamp, woody species
invade peat islands between fires but most are killed by fire [12].
Young cypress trees (less than 200 years old) may sprout after fire if
damage to roots is slight. Sprout production and viability decline with
tree age [5].
The characteristic rounded shape of cypress domes and strands appears to
be related to peat depth, fire frequency, and site conditions. In
Corkscrew Swamp, trees are generally larger and older on sites with deep
peat. The deeper peat is in contact with water for longer periods and
dries out more slowly. Fires are therefore more frequent and more
severe on the edges of domes and strands than in the center where peat
is deepest. The less frequent the fire on a microsite, the more likely
cypresses will survive to larger size. Outside the strand, hydrologic
conditions favor fire that is frequent enough to kill young cypress
trees before they can grow large enough to survive low-severity fire;
the community is therefore maintained as grassland. In Gordon Swamp, a
small cypress strand on the edge of Corkscrew Swamp Sanctuary, a
different pattern was recorded. Peat depth increased towards the center
of the strand, but tree size was uniform (rather than increasing in the
center) and trees were younger in the center of the strand. This
situation was probably caused when fire killed trees in the center but
not the edges. Following fire, newly established cypresses grew faster
than the trees on the edges of the strand. Better site conditions in
the center may have contributed to faster tree growth; relative sizes of
trees may be partly due to the poor condition of fire-damaged trees on
the strand edge. Strands and domes probably expand and contract in
response to fire occurrence and hydrologic conditions. During extreme
drought, even large strands and domes may experience stand-replacing
fire [12].
In a north-central Florida cypress dome, a wildfire killed most shrubs,
hardwoods and pines, but killed less than 50 percent of the dominant
cypress trees. By 3 years after the fire, the study site flora was
composed almost completely of cypress, but the site was being colonized
by hardwoods and shrubs [20].
Gunderson [25] proposed a conceptual succession model for southern
Florida swamps that shows the effects of logging and fire on cypress and
mixed hardwood swamps. After logging, mixed hardwoods and remnant
cypress are maintained in the absence of fire. With a severe fire,
willow (mostly Coastal Plain willow) colonizes open areas. Willows are
maintained by repeated fire, but in the absence of fire succeed to mixed
hardwoods. After logging, stands of mixed hardwoods and remnant cypress
may experience low-severity fires, which favor cypress over hardwoods,
and could return the stand to conditions approximating the prelogging
conditions. In the absence of fire, cypress regeneration returns the
stand to a mixed swamp (cypress and hardwoods, but with continued lack
of fire succession to mixed hardwoods occurs). Cypress and mixed
hardwood stands may be converted to monospecific cypress forests by
surface fires; in the absence of fire, monospecific cypress stands are
invaded by hardwoods. With severe fire, monospecific cypress stands and
cypress and mixed hardwood stands are converted to willow and remnant
cypress stands. Willow-remnant cypress stands may develop to
monospecific cypress stands with occasional surface fires, if cypress
regeneration occurs. More frequent or more severe fire that eliminates
cypress regeneration will maintain a willow-remnant cypress stand [25].
Since cypress seed dispersal in limited, recovery from severe fires that
consume peat may be very slow, particularly where water flow is slow to
negligible. In areas where severe fires have burned old-growth cypress
stands, there is little sign that communities are recovering to prefire
conditions [5].
FIRE EFFECTS ON RESOURCE MANAGEMENT :
Prescribed fire in and near cypress swamps is used mainly to enhance
wildlife habitat, particularly for endangered species [39].
FIRE USE CONSIDERATIONS :
Dye [13] reported on firing techniques in the Everglades and Big Cypress
Swamp. In the past, prescribed fire in Big Cypress was usually
conducted in the cooler months: November to April [39]. The current
trend is to conduct prescribed fire in May and June during the "natural"
lightning fire season, which fulfills the goal of approximating original
conditions. Most fires are set as headfires; burn plots are small
(600-1,000 ac [243-405 ha]); blacklines are wide; and multiple firing
patterns are employed. Dye [13] recommended staggered headfires after
the establishment of backing and single flankfires within zone
perimeters. Plowing lines and the use of firing patterns leading to
development of broad coalescing fire fronts are not recommended.
FIRE MANAGEMENT CONSIDERATIONS :
Low-severity fires do no apparent damage to dwarf cypress savannas and
prevent invasion by hardwood species. Fuel build-up could result in
crown scorch and cypress mortality. It is unlikely that wet season
lightning fires ever occurred with any regularity in presettlement
times; fuels were either inundated or too sparse to carry fire.
Lightning fires were probably common whenever the water table dropped.
Low-intensity, prescribed headfires are recommended for this type at
approximately 10-year intervals [42].
Fire management in cypress domes and strands will be an incidental
effect of prescribed fire in dwarf cypress savanna. Some domes will be
moist enough to prevent fire spread, while others (in the same year)
will carry fire. Prescribed fire in dwarf cypress savanna will,
therefore, create a patchwork of fire that burns into domes to some
extent. Because of reduced hydroperiods, however, some prescribed fires
may burn severely in cypress domes.
Fire management in cypress swamps must be "fine-tuned". Fire cannot be
excluded, but cypress is vulnerable to severe fire [42]. In northern
Florida, periodic fire in seasonally dry cypress domes will perpetuate
cypress at the expense of pine [20]. An intense fire every 2 or 3
decades kills most pine and hardwoods, but leaves cypress. The removal
of a thin layer of organic soil appears to be tolerated by cypresses and
other species. It is possible that more frequent, low-intensity fires
(every 2-3 years) could be used to achieve the same goal, although this
has not been demonstrated [42].
The nature of fires in both northern and southern Florida has changed
[17]. Drainage of southern Florida has resulted in soils that are dry
early in spring which contributes to wildfires that are more destructive
than fires that occurred before widescale drainage. Under current
conditions, fires consume large amounts of organic soil and kill the
roots of most fire-adapted plant species (as well as fire sensitive
species) [42]. Fire in logged cypress swamps is more severe than in
unlogged swamps due to remaining slash and the presence of dense
regrowth. Fires burn hotter, destroy cypress seeds and roots in the
soil, and eliminate cypress sprouts. This situation favors the
replacement of cypresses by willows which are followed by mixed
hardwoods [25]. The detrimental effects of severe fires in cypress
swamps include smoke production (hazardous to health), loss of organic
soils, loss of vegetation, damage to wildlife habitat, loss of esthetic
value, and scars and damage caused by suppression efforts [42].
Melaleuca invasion occurs on sites that have been drained and severely
burned. The flammability of melaleuca increases the probability of
crown fires in cypress stands, particularly where melaleuca has invaded
the ecotone between cypress stands and pine flatwoods [39,41].
Fire management programs in southern Florida will probably be designed
to bring about desired effects rather than recreate a specific fire
regime. Prescribed fire use is limited by public tolerance; visible
smoke is produced, and high intensity fires are feared [39].
REHABILITATION OF SITES FOLLOWING WILDFIRE :
NO-ENTRY
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