Vegetation of Shark Slough, Everglades National Park

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Vegetation of Shark Slough, Everglades National Park
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Olmsted, Ingrid
Armentano, Thomas V.
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SFNRC technical report 97-001

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NAT iRAL
IESE IJ ECES
CENTEll




NATIONAL PARK SERVICE
SVKEPAR SFNRC TECHNICAL REPORT 97-001
Vegetation of Shark Slough,
Everglades National Park
SI NRC. I \VLRCiL.- DI.S N.AI ION \L '.\RK. 40001t SI.Al R(.-\D )933. 1 .10\I S'l LAD f-I.. 33035-6733











VEGETATION OF SHARK SLOUGH,

EVERGLADES NATIONAL PARK







SFNRC Technical

Report 97-001








Ingrid Olmsted' and Thomas V. Armentano2

'Centro de Investigacion Cientifica de Yucatan
Merida, Mexico
2South Florida Natural Resources Center
Everglades National Park
Homestead, Florida


April 1997















TABLE OF CONTENTS



INTRODUCTION. ............ ..... ............ ........... I
BACKGROUND ......... ........ .......... 2
M ETHODS ............ ..... ............. 3
Vegetation Map ........... ....... .......... ................ 3
Vegetation Sampling ....................... .................. 5
Elrie on Surc.s ar.d Soil, Meaiurernents ............ ....... 5
Hydroperiod Calculations ..... . . ............... . ........... .... 7
RESULTS ....................... ........ ............. 7
Overview of Elevations, Hydroperiods and Soils ........................ 7
General Vegetation Patterns ... ............ ...... .. .......... 12
Marsh Communities .... ...... ........................... 16
Sparse sawgrass ........ ................ ............... 17
Tall sawgrass .......... .. ....... .... ................ 19
Tall sawgrass with trees ........... . ...... ..... ....... . 21
Typha islands .............. ........... ............. 21
Spikerush marsh .....................................22
M~ldencane-spikerush marsh ......... .. ............ 23
Spikerush-sawgrass mosaic ....... ...... .......... . .. 24
No.nheri Shark Slough Marshes ............. ................. 25
Tree Island \ egetanon ............................................ 25
Tropical hardwood hammock . .......... ........... . .. 26
Bayheads ................. ...... ...................... 27
Bayhead swamp forest ... ........... ...... ............ 28
Willowheads ............. ................ ........28
DISCUSSION ....................... ...... ............ 29
Comparison with Davis's map ................................. 30
Evidence for Disturbance Effects on Vegeirau on ......................... 31
Effects of Fire on sawgrass .................................... 31
CONCLUSIONS .................. .................. ............ 32
ACKNOWLEDGEMENTS .. ...... ............................ 33
LITERATURE CITED ...................... .................... 34
Appendik 1. Scils from >.11plIn >ites along the middle transect............. . .37
Appendix L Species ............................................ 38

VEGETATION MAP (Fig. 1) ................ ..................... .Back Cover


Olmsted, Ingrid C. and Thomas V. Armentano. 1997.
Vegetation of Shark Slough, Everglades National Park,
South Florida Natural Resources Center Report 97-001. 41 pp.















INTRODUCTION


Shark Slough drainage, the largest in Everglades National Park (ENP), forms the
southern portion of the greater Everglades system which, prior to agricultural development,
began just below Lake O',cechobee and extended to the Gulf of Mexico. This low-lying,
wide "river" comprises a mosaic of marsh communities, tree islands, ponds, and sloughs. In
addition, Shark Slough supports important populations of freshwater fishes, reptiles, and
birds, and influences the estuarine system of the Gulf of Mexico.
Before artificial drainage of the Everglades, which began in the late 19* century,
water depths, and periods of inundation (hydroperiods) in southern Shark Slough averaged
greater than at present. In addition, the timing and distribution of water flows was directly
linked to the natural hydrological cycle and surface waters moved entirely as sheet flow
down the Slough (Craighead 1971, Fennema et aL 1994). Although historically the Slough
was fed by direct rainfall and by surface water flows from Lake Okeechobee, surface waters
now originate entirely from diked impoundments immediately to the north of ENP. In
addition, water flow within Shark Slough is diverted away from its channel by L-67
extension, a levee which extends about 16 km south from Tamiami Trail, nearly bisecting
the Slough.
The imposition of artificial controls upon the natural system has led to important
changes in the hydrological regime of Shark Slough. Comparison of water levels from
gauging stations to computer simulations of surface water flows in the absence of the
present system of roads and water control structures shows that the altered system has lost
much of its dry season flows. Furthermore, the Slough has experienced larger peak wet
season flows than would have occurred under ailiural cord ions i Fe niena e at 1994).
Water management practice. over thc pait several decades also have diverted large water
volumes to the west side of Shark Slough, significantly reducing the proportion of the flows
passing through the main channel of the Slough.
Thus, depending on their distribution within the Slough, plant communities have
been exposed to wetter or drier conditions o'.er the past half-century than would be expected
in a natural rainfall-driven system. AihouiLgh as discussed below, several authors have
attempted to determine the effects of hydrological alterations on the plant communities of
Everglades National Park, relatively little is known of the extent that the current structure
and distribution of vegetation within ENP has departed from pre-disturbance conditions.
As a first step in investigating vegetation patterns in Shark Slough within Everglades
National Park, data were collected from field plots in 1980-81 under the direction of the
senior author in order to establish a quantitative base-line suitable for evaluation in plant
community c )mrpoition and structure. The base-line was needed both to increase basic
understanding of the dynamics of Everglades vegetation and to provide the information
essential to evaluate the effects of managed freshwater inflows upon ENP ecosystems.
Circumstances prevented the completion of the data analysis and report-writing phases of the
project although a vegetation map (Fig. 1) was produced. Because of the continuing need
for an accessible base-line of data on Shark Slough vegetation, particularly given the steps















current) underway to restore Ihe Everglade the junior author, cooperatively with the senior
author, ha.% .:umpleled and updared the Luninistied report
Specifically, the objectives of this report are to: 1) describe the patterns of plant
communities within the Shark Slough portion of Everglades National Park as they existed
in 1980; 2) describe quantitatively the composition of the marsh communities; 3) describe
qualitatively the composition of selected Shark Slough tree communities; 4) provide
supporting data on elevation, hydroperiods and soils for sampled areas, and 5) infer, within
the limits of available data, the changes in vegetation that may have occurred in Shark
Slough.

BACKGROUND

The area of Shark Slough considered in this report is restricted to the portion south
of the Tamiami Trail, northeast of the estuarine areas, west of the Levee 67 extension, and
east of the western Slough boundary as indicated in Figures 1 and 2. All of this area,
estimated a: 57,725 ha (Kushlan et al. 1975) lies within ENP. Northeast Shark Slough,
located east of L-67 eens. ion. a.ihough directly connect led to the study area and authorized
for addition to ENP, is not covered in this report.
Shark Slough is a shallow, natural basin oriented along a longitudinal northeast-
southwest axis. Slough widths vary from 9-17 miles (northeast to southwest) and hydraulic
gradients are 2-3 inches (5-7.5 cm) per mile, producing extremely small velocity vectors
characteristic of sheet flow. Water quality, which had been monitored for about 25 years as
of 1980 (Flora and Rosendahl 1981), had not been iLgnmlicariilv degraded throughout most
of the ENP portion of Shark Slough at the time that the vegetation inventories were
conducted.
The Slough orifer, in ,'erial aspects th-'oughout its eUcent %ithin ENP. The northern
portion of the Slh:ugr is righer in elevation and consequently supports somewhat different
plant communities than elsewhere in the Slough, particularly in its main channel. In
addition, although the tree islands in most of the Slough as ar. apparent etfeci of the strongly
directional flow, are distinctly elongate or teardrop-shaped, the higher hammocks in the
northern portion lack the characteristic "tails" of the tree islands in the lower Slough. In
contrast, the southernmost portion of the Slough intergrades into a broad transitional area that
increasingly supports plants adapted to marine influences, In this zone, the water traversing
the Slough gradually becomes distributed as a complex of small streams that coalesce
within mangrove forest into the Harney, Shark and Broad Rivers. Thus in this region about
20 km inland from the Gulf of Mexico, the Slough as it is configured further north, comes
to an end. The area of the current study stops short of the transition zone although even
within the area we cover, coastal influences can be discerned in the vegetation, particularly
within tree islands.
The soils of hI Slough dIe of t oa maj..- types: organic muck and calcareous marl.
The thickest organic soils (up to 1.5 m deep) occur in the central Slough towards the
southern end. The higher flank? of the Slough are rockier and overlain with marl. The marl
is intermixed on with sand on the western side.


Both Eerpiades peat. derived principally from tall sawgrass marshes, and
Loxahatchee peat. derived mostly from deep water communities characterized by white
water lily ( Nymphaea odorata) are found within the Slough. the latter predominating within
ENP (Cohen and Spackman 1984). Deposition of organic sediments in the southern
Everglades began about 5000 years ago (Gleason et al. 1984).
Marl deposits, formed through the precipitation of calcite crystals by periphyton, are
usually found where mean annual hydroperiods allow for annual decline of the water table
below the soil surface for protracted periods (Browder et al. 1994). In addition, in some
Shark Slough areas, current hydrological conditions in the open marshes favor both marl
formation and organic soil accumulation, resulting in a mixture of muck and marl in the
surface layers. Fires, particularly during droughts, often have destroyed peat soils, leaving
rock or marl surfaces (Craighead, 1971, Wade et al 1980). While southern Shark Slough
may be relatively free from the consequences of such intervention_ compared to areas To ihe
north and east, the northeastern portions of the Slough probably have experienced
alterations of peat depuosi. as a result of overdrainage and fire (Craighead 1971).



METHODS


Vegetation Map

The ,egetauon nup documented by this report (Fig. 1) was developed in association
with a copy of a color infrared photograph taken in January 1973 by a NASA U2 flight.
A copy of this photograph is available for inspection at the junior author's institution. The
vegetation map presents communities encountered along three trarsects established across
Shark Slough. An enlargement of the infrared ptiotgraph i. I 166'61).i was used in the field.
Plant communities were identified from the photograph and verified on the ground on the
basis of dominant species. Plant community characterization was further accomplished by
deierm-ininag ppccie- co.:mpo:.iiion and irwucure. of the vegetation types. Field checking of
infrared signatures and of final vegetation units on the transect maps was carried out
extensively by helicopter and on foot.
Several sources of error can result from shortcomings in interpretation of infrared
photographs although the errors are believed to have been kept acceptably small through
intensive ground-truthing and the quantitative ploi samrplng The greatest risk of errors in
map interpretation were associated with differentiating the many color variations on the
photograph. In particular, in the open spikerush (Eleocharis cellulosa) and sawgrass
marshes, delineation was difficult because of the variable reflection of periphyton. This
difficulty necessitated the establishment of a pLKenruJh/sawgrass" vegetation unit.
The presence or absence of small, scattered trees in the tall sawgrass stands could
not aliL ,,s be senfied becau c cLf rtei canil inalure Cattail ( T lha d&mnge-nsis stands,
rypic.div small and dil, fl.e, could not be seen from the infrared photograph and are only















indicatedd when they were identified on the ground. Willowheads were identified from the
ground or when ponds were visible on the infrared photograph. On the photograph, only
largee willowheads without ponds could be identified. Many of the willowheads on the
northern transect were verified from ground-truthing work conducted in an unrelated study
Figure 2: Map of Shcrk Slough within Everglades National Park Kushlan. unpub. data),
showing hydrologicol gouges mentioned in the text. Panther
Mound (found along the middle transsct) and Johnny Buck tree vegetation sampling
island (found near the north transe:c) are also shown.
/The plant communities described represent the main types found in Shark Slough
within ENP. Over the years, many terms have been reported in the literature to represent
SS the same or very similar community types. Table 1 compares the terminology used in this
.. report with the synonyms used by other researchers, dating back to Harshberger in 1914.
S lu Three transescts from six to 12 km long were established in 1980 across Shark
Slough (Fig. 1). The graminoid (sedge, grass, rush) communities in Shark Slough were
l .. ... analyzed quantitatively, using sets of five I m' quadrats, arranged linearly. Five or six of
S / / these quadrant sets were sampled in each marsh community, yielding a sample of 25 or 30 m'.
/ Locations for the plots were selected to represent communities typical of Shlik Slough as
S / determined from field inspection and review of aerial photographs. Percent cover was
S/visually determined for each species in each quadrat. Periphyton cover was indicated when
encountered. Height of dominant graminoids was measured. Species composition and
/ / structure of bayheads, bayhead swamp forests, tropical hardwood hammocks, and
J o- Wk w t a > / willowheads also were cualitatively described.

-/ U-. Elevation Surveys and Soils Measurements

/ / Relative elevation, soil type and soil depth across the Slough were determined in
/ / jNovember 1980 at points along the south and middle transects, the latter just north of
archerr Mound. a large r-ce island in cen'ral Shark Slough Elevations, taken with a Dumpy
/ Level, were related to water levels at staff gauges E-8 (Panther Mound) and E-17 (for the
southern transect) on the d, S the survey was taken. See Figure 2 for gauge locations, The
S/ gauges had been surveyed to mean sea level in 1977. Elevation was determined at intervals
,m ranging from 100 to 400 m. The first two km of the middle transect were walked to take
/ adings at intervals of 100 m or less. An elevation survey was not made for the north
Str|ansect, but the soil-substrate relationships of Rose and Rosendahl (1979) were used.
S / 1At each survey point along the two transects, water level and soil depth
/ / measurements were taken and the soil collected. Along all three transects, soil samples were
taken in each plant community. Soils were identified to color and texture by the Soil
A R Conservation Service (Lake Worth. Florida). Results are presented in Appendix I for sparse
IRE sawgrass, spikerush marsh, tall sawgrass and maiden-cane communities.
ENLARGED. To better understand the relationship of changing elevation on community type,
-ransects were established at 2-5 m intervals across plant community boundaries, especially
tree islands. Elevations were taken on foot, using either water depth or a Dumpy Level; the



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transects were between 20 and 100 m long. On these short transects water-levels were
determined relative to the particular plant community rather than surveyed to absolute mean
sea level.
Hydroperiod Calculations
In 1981, elevation and water-level measurements were taken in all communities.
Water-level correlation equations (Probst and Rosendahl 1981) relating water depth
measurements to gauge data were used for gauges P-33 and E-4 on the northern transect, P-
33 and E-8 on the middle transect, and NP-204 and E- 17 for the southern transect Probst and
Rosendahl (1981) found that water level data from the continuous stations in Shark Slough
correlated very highly (r= 0.95) with nearby staff gauges. Gauge locations are given in Fig
2. Data were available for P-33 over the period 1953-1980, and for NP-204 from 1973 to
1980. Since E-17 and P-33 were far apart, the correlation coefficient was too low to be
accepted for the calculation of hydroperiods in the southern transect. Thus the available data
on the southern transect cover a shorter time period than those available for the middle and
northern transects. Hydroperiods for the different plant communities were calculated from
water levels at P-33 and NP-204 and elevations were measured for the plant communities.
Water depths were calculated from water levels and ground elevation for years except for
1981, when water depths were measured directly.

RESULTS

Overview I letjiorvkU~diopedjo cjl dni Soi%,
Within the marsh communities, elevation declined from about 1.5 m in the north
transect to about 0.4 m along the south transect, a difference of 1.1 m (Table 2). The
difference in elevation across the three transects was remarkably similar, about 0.26 m,
(range= 0.19-0.33) from the highest point in the tall sawgrass marshes to the low point in
spikerush marsh Such a small difference underscores the significance of subtle topographic
vanatjor.s in Iniluercimg plainlc ionunALmr developmrni As Table 2 indicates, the elevation
differences, though small, have hydrological consequences as seen in associated hydroperiod
and water depths. The relative hydrological differences are maintained across the range of
annual precipitation experienced in the Everglades. In Figure 3, the elevation differences in
three marsh community types are superimposed on water level data for years with dry,wet
and average rainaIl The extent of inundation clearly depends on elevation.
As indicated m Fig. 3, elevation varies within each community by about 0.2-0.6 ft
(5 to 20 cm) with the greatest range in bayheads and hammocks.
Fig. 3 (next page). Elevation of Shark Slough plant romm.nities along three transeets superimposed
on water levels during a wet (1969-70), average (1977-78) and dry year (1964-65).


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Table 2. Hydrological parameters in three community types found in the central portion of transects.



erth Middk Sant
Low Hmgh Low High Low
Elevation Elevation Elevation Elevation Elevation
5.0 ft 5.3 ft 4.3 ft 4.5 ft 1.2 ft
MSL MSL MSL MSL MSL


High
Elevation
1.6ft
MSL


1977-78 Water levels (ft) 5.6-6.8 5.6-6.8 4.8-5.8 4.8-5.8 1.3-2.6 1.3-2.6
1977-78 Water depths (ft) 0.6-1.8 0.3-1.5 0.5-1.5 0.3-1.3 0.1-1.4 0-1.0
1977-78 Water depths 18-54 8.5-45 15-46 9-40 3-42 0-31
(cm)
Highest record 1967-79
water depth (ft) 2.7 2.4 2.3 2.1 1.4 1.0
water depth (cm) 82 73 57 52 42 31
Hydroperiods (dayM/yr
1953-1980 mean 338 323 343 335 321 260
Range 242-366 183-306 262-366 228-365 261-365 188-365

5.5 ft 5.6 ft 4.6 ft 5.0 ft 1.5 ft 1.7 ft
MSL PSL MSL MSL PML MSL

Tall Swgr 5.6-6.8 5.-6.8 4.8-5,8 4.8-5.8 1.3 -2.6 1.S-2.6
1977-78 Water levels (ft]
1977-78 Water depths (ft) 0.1-1.3 0-1.2 0.22-1.22 0-0.8 0-1.1 0-0.9
1977-78 Water depths (cam) 3-39 0-36 7-37 0-25 0-33 0-28
Highest record 1967-79
water depth (ft) 2.2 2.1 1.71 1.3 1.1 0.9
water depth (cm) 68 64 52 33 33 28
Hydrogerioda (dayalvrl
1953-1980 mean 304 280 328 255 323 276
Range 136-366 106-365 208-366 0-365 194-365 160-365

















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The 1969-70 hydrological year was wet with protracted high water and hardwood ham-
mocks along the north and middle transect, except in the highest portions, were inundated
for over two months. In the the dry year of 1964-65, even the lowest elevation spikerush
communities were free of surface water for about three months, and the sawgrass areas for
about five months. Figure 3 also illustrates that hammocks in Shark Slough are found on
outcrops extending above surrounding marshes by 0.45 m (1.5 ft) or more and that the two
other forest types found in Shark Slough tree islands, bayhead and bay swamp forest, are
clearly found at lower elevations than hammocks.
Interannual rainfall patterns, along with water management practices, have led to
marked shifts in the annual durations of soil surface flooding Sawgrass marshes in central
Shark Slough were continuously inundated for periods of two or more years three times
within the 1953 to 1980 period (Fig. 4). During dry years, however, there have been dry
ground surfaces for three or more months.

Fig. 4. Number of days per year from 1953 to 1980 that the soil surface in sawgrass marshes of central Shark
Slough were free of surface water.



SAWGRASS CENTRAL PORTION MIDDLE TRANSECT
1SO DRY DAYS DURING 195)- 1980 (FANThtR I' UND)





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53 4 5 56 57 5S S9 60 61 6 61 6+ 65 66 67 68 69 70 71 72 71 70 75 76 77 78 79 80
YEAR












Northern ransect. The 6 km wide northern transect was coincident with the area sampled
by Rose and Rosendahl (1979). These workers found that soil surface elevations varied less
than 0.3 m in the marshes, but that the bedrock was highly dissected, indicating that soil
depths fluctuated widely. A slight elevation gradient from tall sawgrass to the open marsh
was observed. The highly variable surface and sub-surface elevations are characteristic of
the general Shark Slough area sampled in this study.
Middle transectl The lowest point along the 10 km long middle transect was only 25 cm
below the highest point on the west end although surface elevation rises steeply with
increasing drsiance from ihe Slough itself (Fig. 5). Overall, like along the northern transect,
the relatively level soil surfaces contrasted with the dissected limestone substrate, The
surface of the limestone substrate underlying the soils of the middle transect forms a trough
differing by 1.2 m between the highest and the lowest point across the trough.
The major soil type in the slough is muck, but towards the sides of the trough.
calcareous marl deposits increase in depth, replacing the muck (Fig. 5). Towards the east
portion of the central slough, marl is sometimes found beneath large areas of open marsh
despite hydroperiods apparently long enough to promote peat formation. In many surface
samples of the middle transect, a mixture of muck and marl occurred.
Southern transect. The transect was located just north of the estuarine zone and
extended 12 km reflecting the greater width of the Slough here than at the level of the
middle tran.&eci A gun, the relatively level soil surface and dissected bedrock contrast (Fig.
6). The central portion of the southern transect was between 80 and 100 cm lower than the
marsh near Panther Mound in the central portion of the middle transect. The lowest points
of bedrock along the southern transect are below mean sea level.The soil patterns in the
Slough are influenced by the location of the transects relative to the configuration of the
Slough. Thus the soil depths in the eastern portion of the southern transect exceed those of
the middle transect because the main channel of the Slough swings westward at the level of
the southern transect. In addition, limestone outcrops characterize the easternmost 2 km of
the middle transect, reducing soil accumulation. The easterly portion of the southern
transect also passes across a shallow basin towards the Watson, Lane, and North River
estuaries to the south. In contrast, the western side of the southern transect rises more
towards the side of the trough and is covered more by marl.


General Vegetation Patterns
Shark Slough vegetation is distinctive and clearly different from any other plant
community in North America and perhaps the world. Even though the total area of sawgrass
marsh is large, the apparent uniformity is interrupted by hundreds of tree islands and over
large areas masks a mosaic of marsh commuriuei diffenng in dominant species and aspect.
Although over large tracts periphyton dominates the ground (or water) surface, often
mantling the stems and leaves of the macrophytes, its importance is not well represented in
this report. The floating penphyron m.fr usually envelop and combine with well developed
Utricularia (usually U.foliosa and U. purpurea) thalli and other hydrophytes to the extent-

Fig. (tnet page). Elevation, soils, and bedrock surface along the middle transect of Shark Slough, from s v wau
west (top) to east (bottom). The numbers along the top indicate the loc dions of transect sampling poles.












that the floating complex dominates the visual aspect of extensive marsh areas.
As noted, the three mapped transects are 6, 10, and 12 lan wide from east tc west and
about 2 km from north to south. Each transect delineates 11 community types: four tree
communities, four grarninoid communities, two mixed-dominance graminoid communities
(spikerush/sawgrass and spikerush/maidencane), and one tree/graminoid mixture (tall
sawgrass/bayhead species).
The total area mapped amounts to 5,873 ha, almost 10 percent of the Slough as
defined by Kushlan e al. (1975). Appendix Ul includes all species encountered including
those found outside of transects.
The three transects cross the same community types but the relative importance of
each community diffe-s with transect (Table 3). For example. uopical hardwond h.unmocks
are abundant along the northern and middle transects but hardly present on the southern
transect. Elongate, high-bedrock bayheads are abundant on the southern portion of the
southern transect, but more typical circular peat-based bayheads occur in the rest of the
slough.
Because the northern transect is relatively short, it excludes sparse sawgrass marsh
found further east and west of the central slough. The longer middle and southern transects,
however, do incorporate significant areas of sparse sawgrass.
IThe ravo of sawgras marsh to spikerush marsh varied from transect to transect. A
large area on the west side of the southern transect was comprised of solid "sparse sawgrass
marsh" as on the southeastern side. The distribution of sawgrass and spikerush marsh on
the east and west side of the middle transect and along the entire northern transect was more
patchy for the two communities. The largest percentage of spikerush/maidencane and the
spikerushisawgrass mosaic was encountered in the northern transect, probably because this

Table 3. Distribution of community types along mapped transects.'

Percent of Transect Area
North Middle South

Sawgrass 39 43 52
Splkerush 16 7 7
Spikerush/Maidencane 2 15 3
Splkerlsh. Sawgrass 19 11 13
Tall Sawgrass 13 15 11
Tall Sawgrass with Trees 4 5 9
Bayhead 2 2 3
Bayhead Swamp Forest 3 2 0.1
Willowheads 0.1 0.09 0,2
Tropical Hardwood Hammock 0.08 0.04
'Total Slough area equals 142,479 acres (57,725ha).


Fig. 6(next pages). A profile of soils, elevation and plant community type across the southern
transect in Shark Slough from the west (top diagram), through the central and eastern segments
(continuation page). The numbers across the upper horizontal Une are transect pole locations, in-
creasing in number from west to eastL Segment lengths are 4.8km, 1.9km and 4.2km,west to east


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Fig. 6. (conL). Easte rn segment, southern transact.

area had the largest body cf deep after iTable 31 The percentage cover of tall sawgrass and
of tree islands was similar on all transects,

Mash Com:uniuies
The sedge C'J!un jamameen,-ie was the dominant species in the sawgrass communities,
Its biology ha. bern descnued by Alexander (1971), Steward and Ornes (1975, 19,3.. Davs.
(1991), Herndon et al (1991) and others. In this report, sawgrass communities were
classified into spa.'sc sawgrass community with sparse cover and heights up to 2 m, and tall
sawgrass with dense cover and heights in excess of 2 m. In many areas, the distribution of
















Fig. 7. Soils, relative elevation and prevalent vegetation across 32 m of Shark Slough near the middle
transect from west (left) to east


sawgrass density arnd heights suggeQr the possibility of defining an intermediate category as
has been suggested by some authors but in this study, such a distinction could be made in
only a few sites. The relative elevations associated with the three sawgrass types is generally
consistent with Figs. 6 and 7.

Sparse sawgrass
The sparse sawgrass community was the most extensive in the Slough. In spite of its
apparent uniforrnny in aspect, the sparse sawgrass community varied greatly in percent
cover, height, soil type, periphyton, and associated macrophyte species. Most typically, the
sparse sawgrass community included extensive, very sparse marshes over marl with low
cover (usually well under 50%, sometimes as low as 10%) in which the sawgrass was shorter
than I m. Denser stands also occur on muck in the center of the Slough with 50% cover and
heights up to 2 m.
The extensive sparse sawgrass marshes found toward the sides of the Slough, usually
over marl, were lowest in species diversity and plant cover, While sawgrass was associated
with Rhynchospora tracyi, on the west and east borders of the transects, this species became
less common towards the center, where aquatic species became more abundant. Pontederia
cordata and Peltandra virginica are common associates here The common spikerush.
Sleocharis cellulosa, was the most constant associate in the sawgrass marshes. Utricularia
species were present in all but the densest marshes. The forbs, Justicia angusta, Crinum
americanum, and Bacopa caroliniana, as well as grasses of the genera Panicum (e.g. P.
hemitomon and P. tenerwn) and Paspalidium geminatum atso occurred here.
The elevation of sparse sawgrass marshes was usually 10-15 cm higher than the adjacent
spikerush/maidencane marsh and 10-1S cm lower than the sawgrass strand. In some
instances, pure maidencane (P. hemitomum) occupied areas between spLkerust and tall
sawgrass. The sawgrass communities found on muck has conspicuously greater cover.
density, and height thxn d.:. those found on marl. Periphyton was characteristic of nearly
all sawgrass marshes mantling the soil and water surface and many plant stems. Ontlv in the
densest marsh is the algal mat absent. In the sparse sawgrass community, the average
macrophyte plant cover ranged from 11% on the southern transect to 15% on the cuiddle
transect.
In the sparse sawgrasi community, the as erage macrophbvte plan cover ranged from 11%
on the southern transect to 16% on the middle transect, Sawgrass frequency was 100%
throughout the community. Spikerush frequencies were high but frequencies of other
species were low (Table 4). The sparse marshes were more extensive than intermediate
sawgrass stands which most often skirted tall sawgrass strands and were narrow in extent.
About 90% of the plant cover was sawgrass. Other species contributed little cover.
Spikerush contributed more than a trace in only a few instances, as did Rhynchcspora
traceyi, Pontederia cordata, and Bacopa caroliniana.
The total number of species encountered in the sample plots in all transects was 17; the
average number of species per m2 was between four and six, and the number per transect
varied from 10 to 15. Mean sawgrass height varied from 130 cm on the middle transect to
145 cm in the northern transect with small standard deviations in both cases.














The soil depths beneath sparse sawgrass ranged from an average of 34 cm on the middle
transect to an average of 69 cm along the southern transect (Table 5).

Table 4. Cover and frequency of occurrence by species in sparse sawgrass community. Data
summarized by transect.*


species


10
2


Cladlumrjamalcense
Eleocharis celulosa
Panicum hemitomon
P. tenerum
Paspalidlum geminiatum
Rhynchospora microcarpa
R. tracyt
Aeschenomene pratensis
Aster tenuffollus
Bacopa caroliniana
Crinum arnericanum
Jusultca angusta
Agaltnis harper
Pluchea rose
Pontcderia cordata
Sagittaria lancifoUa


Mean % cover EuCn(%)
N M S N M
.7513.5 15.449.9 9.26110 100 100
15a.98 0.44 0.93 100 68
0.04 0.27 55 4
T T 4
T T 20
T T 12
016 T
T 10
T
T 0.93 30
0.12 T 35
T T T 10 24
T T -


T 0.16


T

T


UL.utianar bitter 7 T 4 7

Mean Plant Cover (%) 13.1 16.2 11.4
Total # Species 10 8 15
Mean # Species/m 5.6 4.2 5.7
Mean height (cm) 145 130 135
sawgrass

Table Footnotes: T = Trace; -=absence" N = North. M = Middle, S = South

Water depths for sawgrass communities varied over the year from north to south.
Measurements made between December 1980 and February 1981 varied from 31 to 38
cm. Water depths calculated for the period 1967 to 1979, varied from 82 cm above the soil
surface during wet months to unspecified levels below surface during the dry months. Water
levels exceeded I m only for short and infrequent periods. More often, the water depths in
this community fell to within 20 and 50 cm during the wet season. The emergent portion
of sawgrass generally rose 70-100 cm above the water surface. Between 1953 and 1980, the
mean hydroperiod was 330 days (range 183-366) along the northern transect and 339 days
on average (range 295-365) along the middle transect. On the southern transect, the mean
was 290 days (range 188-365) over the period 1973 to 19&,S0 (Table 2 Hydroperiods varied
more towards the sides of the Slough. On the middle and southern transects, drier conditions
occurred on the west side of the slough sooner than on the eastern portion because of the
steeper ground-surface slope.
Where soil was especially shallow, rock outcrops and deep solution holes on the middle
transect produced patches of sawgrass between unvegetated areas and rock outcrops. On


------ mj


the southeast portion of the southern transect, the soil was deeper, and sawgrass more
evenly distributed.

Tall sawgrass
In addition to the distinctively shaped tree islands, elongate strands of tall sawgrass
form characteristic landscape features of Shark Slough. Sawgrass strands occur where there
is very little other plant cover and in the tails of tree islands. Tall sawgrass often surrounds
bayhead swamp forest and other tree islands. Tall sawgrass strands are conspicuous by
virtue of their great height and density. Heights reach at least 2 m above the soil surface and
may reach 3 m. Stands are very dense; consequently they often bum in the summer even
in water depths reaching 50 cm. Falling between bayheads and intermediate sawgrass in
elevation and hydroperiod, tall sawgrass communities contain species of both adjacent
communities. Thus its species richness exceeds that of other marsh communities.
Sawgrass frequency reached 100% within the community, far greater than any other
spees (Table 6b In contrast to the sparse sawgrass community, sawgrass cover approached
almost 100% on all transects. Secondary species occurring in at least 10% of the quadrats
along the three transects were spikerush, Blechnum serrulatum, Bacopa caroliniana and
Justicia angusta. More than in any other community, tall sawgrass was most constant in
cover, with a low standard deviation. Even in this community, spikerush was a frequent


Table 5. Site analysis by conuninity. Sumnnary for three transects. Water and soil depths recorded in plots at
lime of vegetation sampling.
Tal, SQawp,, Spine',j MldaienCiqe Sp'kerh

Average Soil Depth (cm) 48 12 53 21 41:t + 30 9
Average Wilei De ph, cm'i 24 8 31 t 4.6 40 3.6 43 2.8
Average Plant Cover (%) 96_ .6 13 13 6 2.5 6 3.6
Average Open (%) 4 87 94 95
Total # Species 14 10 8 1
Average # Species/m2 6 5.6 4.5 4

Average Soil Depth (cm) 79 +50 34_t26 60 26.4 34.2_ 19
Average Water Depth (cm) 23.6.t 6 3375 43.9 6.9 42A + 11.4
Average Plant Cover (%) 96 10 16t 10 3.5 1 8 2.3 .85
Average Open (%) 4 84 96.3 97.6
Total # Species 14 11 11 12
Average # Species/mi 5 4.2 5.5 4.6

Avera Soil Depth (cm) 82.7 44 6913 64.4. 40.3 48 6_t23
Average Waer Depth (cm) 26.8 388.3 51.5t 6 383 4.7
Average Plant Cover l) 964.5 llt i1 72.4 2'.,9
Average Open (%) 4 89 93 98
Total# Species 13 15 6 6
Averae # Speciesni' 4 5.7 5.4 2.8
















associate, but much less so than in the sparse sawgrass community. A species not found in
any quadrats but often encountered in ccotenes between tall sawgrass and edges of small
bayheads was Polygonum hydropiperoides.


Table 6. Plant cover and frequency of occurrence by
community. Data summarized by transect.

Mean % Cover/mi


SAw-ies


Cladlum Jamaicense
Eleocha.-s cellulosa
Panicum hemntomon
Typha dominguenalsi
Annona glabra
Cephalanthus occidentalls
Myrica cerifera
Persea borbonta
Blechnum serrulaturn
Bacopa carolintana
Erlocaulon compressum
HyruenocallUs paimert
Justicia angusta
Ipomoea sagittata
LudwAiga alata
L microcarpa
Peltandra virginica
Pluchea rosea
Pontederia cordata
Sagtttaria lanclfolla


species in the tall sawgrass


Frequency %)l


N M S N M S


95.16 + 8.59
0.36
T

T


T
T
0.20

T
T
T


94.90 + 10
0.90

T


T
T
T
T


T

T

020
T
R
T


96.00 100
T 23
13


Utriculanta blora I s10
Community
Mean Plant Cover (%: 95.7 96.0 96.2
Total # Species 14 14 13
Mean # Spedces/m' 6 5 4
Mean height (cm) 212 225 242
sawgrass

T = Trace
- = absence
* N = North. M = Middle. S = South


Soil depths varied between transects (Table 5), particularly going from the central portion
along each transect of the Slough to the flanks. Since soit depths were averaged for all plots
along one transect, regardless of position, they varied significantly. Even though in the


sample plots muck depth varied from 48 to 83 cm, the muck layer often exceeded I m deep
elsewhere near Panther Mound.
Alligators often seek tall sawgrass strands to build nests; the decreased bydroperiod
associated with relatively high elevation and availability of nest material may contribute to
that choice. While soil surface elevations of the tall sawgrass stands exceed those of other
marsh communities in most of the Slough, on the west and east sides of the Slough where
water depths are shallower, tall sawgrass grows at lower elevations than the surrounding
spikerush or sparse sawgrass. On the west side of the middle transact, tall sawgrass islands
are located in bedrock troughs filled with muck and surrounded by marl soils supporting
sparse sawgrass or spikerush. The marl sites often experience hydroperiods of 6 months,
while the lower elevation tall sawgrass stands often are inundated for 8 months. This
situation is common also in Taylor Slough (Olmsted et at. 1980) where extensive marl
communities surround a narrow channel overlain with muck or peat that support tall
sawgrass.
Hydroperiods and water depths in the three main marsh community types over the
period of record in the central portions of the three transects were shorter than for the other
marsh community types, reflecting the relatively high elevation of the tall sawgrass (Table
2). The southern transect, especially the western side, shows the reverse. The highest water
depths over the period of record (1967-1979) vary substantially among the three transects,
with the greatest maximum depths along the northern transect and lowest along the southern
transect.
The apparent successional relationship between tall sawgrass strands and baybead
swamp forest sometimes results in their interspersion. Also, tall sawgrass is often succeeded
by willow or by Typha when fires bum the organic soil and destroy 'the awgrais rtjz.rmea
Then sawgrass may gradually replace these species by rhizomatous ingrowth from
surrounding areas.

Tall sawgrass with trees
The southern tails of tree islands, downstream of the bayhead swamp forest, often
comprise a mixture of sawgrass and woody species, with tall sawgrass dominant. When a
fire bums through such a stand, the established species generally persist, the sawgrass from
rhizomes andl regrowth of burned culms, and the trees and shrubs as sprouts from stem
bases. Specific dynamics of the tall sawgrass-swamp forest relationship, however, have not
been adequately studied. The tree species in this community type are the same as those
found in the tall sawgrass community (Table 6), although they are more abundant here.
Pond apple (4ionna glabra i and huiionbsh I Cephal.vthus occidentalis) sometimes are the
commonest woody species.
The elevations, soil depths and hydroperiods of tall saI gra.s strnds. imlar Inr Ihat
of bayhead swamp forest, seems to be conducive to tree establishment. The two community
types often intermingle, usually over small areas. The trees have open crowns and often are
interspersed among thick stands of swamp fern (Blechnum serrulatum), occasional Typha,
and varying concentrations of the aquatic plants Peltandra virginica, Pontederia cordata,
and Sagittaria lancifolia These associations may represent incipient bayheads or degraded
willowheads,













Typha islands
This is one of the least understood unit mapped. The species present in ENP is
regarded as T. dominguensis. It appears to be successional to sawgrass after fire in some
places. In some areas of the southern Big Cypress National Preserve, Typha became
established in areas where sawgrass was burned out (Hofstetter and Alexander, 1979).
Recruitment from surrounding sawgrass rhizomes occurred after several years. The status of
Typha in Shark Slough in 1980 was not well understood. Some dying Typha had been
observed along the northern transect. Tilmant (1975) recognized Typha marsh as a small
component of his study site mosaic in Shark Slough. Typha was found mostly on deeper
soils than was tall sawgrass. Invasion of sawgrass marshes by scattered Typha near Rookery
Branch in lower Shark Slough also has been observed.

Spikerush marsh
In Shark Slough, the spikerush marsh was the second most extensive community
after sparse sawgrass. Generally, this community occurs at lower elevations than other marsh
communities The dominant species is the sedge Eleocharis cellilosa ,pikerush'. with a
scattering of other grasses and sedges, particularly species of the genera Panicum and
Rhynchospora. Aquatic plants like Peltandra virginica, SagJiraria lancifotia Bacopa
caroliniana and species of Ufricularia are also found here. The substrate can be either
muck or marl.
With an average macrophyte cover of 2.8% (range 1.6-4.6%), this community had
the lowest plant cover of any association analyzed (Table 7). The low cover favors the
abundanit owth ofpcriphyiorn. The average number of species was low, between 2,8 and
4.6/m', with a touJt ot I per transect. species. Eleocharis was the dominant species with a
100% frequency and a cover of 1.5-3.9%, while Panicum henitomon and Sagittaria
lancifolia follow with less than 1% cover and variable frequencies on the transects (Table
7 ). In the open marsh of sawgrass and slikerush, the most common vascular plants are
various submerged species of Utricularia. The importance of these species was
underestimated bv our data, however, because cover or frequency was considered only
if the emergent flower stalks were present. The white water lily, Nymphaea odorata, an
indicator species of deep water sloughs (McPherson, 197 3i is a scattered member of this
community. In contrast, this water lily dominates large areas of th. slough communiT) of
Conservation Area 3A north o1 Snark Slough and appears to have supplanted spikerush
marshes in the southern portion of that water storage basin.
Average marl and muck soil depths of the spikerush community varied from 30 cm
to 49 cm with iathe- large siandird deviations. Water depths in the spikerush marsh at the
time of sampling (38-43 cm) and for previous years were the greatest of all communities as
expected from the elevation surveys (Tables 2 and 5). The shallowest water depths in the
spikerush marsh were found in the southern transect.The spikerush marsh community was
found in areas with the longest hydroperiods in Shark Slough (Table 2). Mean annual
hydroperiods for the period of record varied from 315 to 352 days.
However, the ranges varied from 241 to 366 days in the northern transect and 143 to 365
days in the middle Transect.


Maidencane-spikerush marsh
This community type, distinctive because of the importance of maidencane, always
occurs adjacent to spikernsh marsh. Though it differs in aspect from spikerush marsh, this
community had only lightly higher species richness (4.5-5.5/ m2; Table 8).

Table 7. Plant cover and frequency of occurrence by species In sptkerush marsh. Data summarized
by transect.1


Mean % cover/ Im


Species N M S N M S
Eleochari cellulosa 3.90 1.55 1.88 .86 1.5 .97 100 100 100
Rhychospora microcarpa T 4
R. tracyi T T T 16 44 57
Panicum hemrnitomon 0.20 0.12 T 48 24 7
P. tenerum T T 4 -
Paspalidium geminatum T T T 28 20 20
Justica angusta T 4
Bacopa carolniana T T 28 10
Nymphea odorata 0 40 8
Oxypolls fllformis T 8.
Peltandra virginlca T 12
Sagittaria lan ifolla 0,12 0-28 0.13 12 48 43
Utricularia bulora T -
U. purpurea T T 4 8
U. resupinata T .
U. cornuta T 4

Mean total plant cover 4.6 + 3.6 2.3 ,.85 1,6_+ .9
Mean # species/m2 4.0 4.6 2.8
Total # species 12 11 6
Mean plant height cm
tspcerushl 76 75 70

T Trace
- = absence
* N = North, M = Middle. S = South



On infrared photographs, maidencane-spikerush stands were not as easily recognized as
the spikerush community and therefore, the area of maidencane community could be
somewhat underestimated.
The cover of this unit (3.5-6.5%) was slightly higher than for spikerush. Maidercane
and spikerush occurred in all plots. Paspalidium geminaitm is more frequent in this
community than in the spikerush marsh. Maidencane cover was highest along the middle
and southern transect, and spikerush is dominant on the northern transect.


F&quemn fImi















Table. 8 Plant cover and frequency of occurrence by species in maidencane spikerush community.


Meanenver/lmrn


species N M S N M S
Cladium jamalcensc 0.50 25
Eleochanrs cellulosa 3.50 + 2.3 .80 + 5 2.00 + .7 100 100 100
Panicum hemitomon 2.56 + 18 1.47 + 1.17 3,40 + 1.8 100 100 100
Paspalldium geminaturn 0,23 T 0,28 50 15 58
Rhynchospora microcarpa T--3--
R. tracyl T 0.16 10 28
Bacopa carollnlana T 0.15 0.28 30 35 32
Crinum americanum T 3 -
Justicla angusta T 5
Nymphea odorata 0,60 5
Peltandra virglnica T 3 -
Saglttarla lancffolla T T 0,28 30 45 40
Utricularia biflora T 10
U. pupurea T 10
U. radiata .2 28

Mean plant cover (%) 6.3 3.5 6.5
Mean # species/m* 4.5 5.5 5.4
Total species 8 11 6
Mean plant height cm
imafjidncanel 97 94 92

T Trace
- absence
*N = North. M = Middle. S = South

Soil depth varied more between transects than within them. [n Shark Slough,
maidencane communities occur on peat or muck but not on marl. The soils under
maidencane in the sampling sites averaged 16 cm deeper than under spikerush o TJolc 51
The latter seems to be the most obvious difference observed between the two mapped
units. In areas bordering tall sawgrass, maidencane grows densely, to the exclusion of
other species. This pattern is not reflected in the sampling data because plots felE in areas
of sparse nia.dencanc garomth adjacent to spikerush growth.

Spikerush-sawgrass mosaic
Delineation of this type is appropriate where sawgrass islands occurring within
spikerush marsh or spikerush marshes within sparse sawgrass are frequent at a scale too
small to distinguish separate communities. The ecotones between these two communities
are often indistinct. On the ground sawgrass appears to be invading the spikerush marsh in
many areas that cannot be recognized from the infrared photographs. These two
communities are successionally related through fire and other disturbance. Spikerush
becomes established in areas where the root system of sawgrass has been burned (Craighead


Emanias <


1971) or in areas where sawgrass has been damaged by airboats. The transition from
sawgrass to spikerush is very abrupt in areas where fires have burned. How long ii tke'
without disturbance for sawgrass to reinvade these marshes by rhizomes from the adjoining
sawgrass marsh is unknown but certainly is much slower than the establishment of
spikerush in burned sawgrass marsh.

Northwest Shark Slough Marshes

The northwestern flank of Shark Slough, on either side of Shark Valley Road, is
higher in elevation than the rest of the Slough. The soil here is shallower than elsewhere in
the Slough and is not a true marl, but rather a transitional deposit between marl and a
poorly drained Rockdale fine sandy loam. The marsh communities here are distinct,
partially because they have been slightly disturbed by the construction of the road. However,
the shallower soils and higher elevations also create difcnring ecological coniuonn, Many
of the tree islands here, for example, are principally hammocks, rather than bayheads as they
are in most of Shark Slough tree islands. The bayheads that are present sometimes are
surrounded by cypress. Cypress forms a few solid stands and is also scattered in the marsh,
the only place in Shark Slough where cypress communities occur.
The marsh or prairie communities of northwest Shark Slough differ from those
further south in hydroperiod and soil type as well as in species composition. The sparse
sawgrass marshes are interspersed with prairie and include Rhynchospora tracyi, Oxypolis
filiformis, and Pluchea rosea (Table 9). Unlike elsewhere in the Slough, there was no surface
water during sampling Thus both in terms of forested and marsh communities, these
northern sites bear considerable similarity to the communities of the higher elevation
Northeast Shark Slough and Rocky Glades to the east and southeast (Olmsted et al. 1980).
Total vascular cover for this community averaged 6%, more like a spikerush marsh
than a sawgrass marsh. The frequency of grasses, sedges, and forbs was high in this
community (Table 9). In sawgrass and spikerush marshes further south, usually just two
species are frequent, and the forbs seldom reach 30% frequency. Justicia angusta was as
often encountered here as was sawgrass. Aquatic plants such as Sagittraria and Pontederia
were absent; two terrestrial Utricularia species were present, but none of the floating ones.
Another distinctive feature of these communities is the presence of Myrica cerifera in
one-third of the plots. The spc ies wv as absent from the three southern transects.

Tree Island Vegetation

Tree islands develop on slightly elevated limestone outcrops or in bedrock
depressions within the marshes and are characteristic of Shark Slough. Four different tree-
dominated community types are described, of which three (tropical hardwood hammock,
willowhead, bayhead) were discussed by Davis (1943), Craighead (1971), and others. In
the present treatment, bayheads are sub-divided into bayheads and bayhead swamp forest.
The latter type has not been previously described before for Everglades National Park, but
can be delineated based on species composition. The swamp foreii type resembles the s&armp
forests of the Big Cypress National Preserve (Gunderson and Loope 1982). The community
types are described below and the species encountered are given in Appendix II.















Table 9. Mixed marsh. Tram Road.

Species Mean % Cover/im Frequency %
Cladlum jarmaicense 5.23 87
Panicumn tencrum 0.33 63
Panlcum henitomon 0.03 7
P. vlrgatunu T 3
Eleocharis cellulosa 0.64 87
Rhynchospora tracyt 0.30 67
Myrica cerifera T 33
AgalnlIs harper T 16.7
Justicia angusta 0.04 80
Oxypolls flifornli T 10
Pluchea rosea 0.07 20
Utricularia resupinat, T 37
U. subulata T 37
Open 93.4
Soil depth (cm) 12-t 7
Average water depth 0
Average plant cover/mr = 57%
Total # species = 13
Average # species/m' = 9
Soil type = marl


Tropical hardwood hammock
The upstream portions of the largest tree islands in Shark Slough often have small areas
of tropical hardwood hammock. The hammocks are found on bedrock highs rising as much
as one meter above the surrounding sawgrass marsh (Fig. 3). Consequently, during most
years, the hammocks are free of inundation but many if not all are flooded during wet years
such as 1969. In most portions of Shark Slough, the vegetation immediately adjoining
tropical hardwood hammocks on tree islands is usually bayhead swamp forest.
Since hammocks in the Slough are seldom more than 500 m2 in area, the number of
species in this tropical hardwood forest is rather low compared to other hammocks in the
pinelands or the prairies of Everglades National Park (Olmsted et al. 1981). Because
hammocks are the only dry places in the Slough during the rainy season, the Indians, and
later, whites settlers, used them as camping places and cultivated crops there as well. In
many hammocks, native trees have been cut and exotic species planted, however, all known
use of the tree islands by man ceased by, or soon after, 1947 when ENP was established.
Only by the presence of exotics is there any basis for concluding that the current tree
composition differs from pre-disturbance conditions. Some planted species such as Key
Lime (Citrus aurantifolia), sweet orange (C. sinensis ) and guava (Psidium guajava) persist
in some hammocks. Large trees of the exotic Brazilian pepper (Schinus rerebinthifolius)
are present on some tree islands as is the short-lived papaya (Carica papaya),. Although the
latter species may have been cultivated at one time it has now become naturalized and
appears throughout upland areas of south Florida following disturbances of forest canopies.


The presence in a few Shark Slough hammocks of the native coastal species Sapindus
saponaria and Ximenia americana suggests the influence of man but this has not been
confirmed. The soil depth in the hammocks that erie culumated iscomparauiely deep (up
to 40 cm), while soils are thinner in the northern hammocks (15 cm).
The major tree species of Shark Slough hammocks are Bursera simaruba (gumbo limbo),
Celis laevigata (hackberry), Eugenia axillaris (white stopper), Sabal palmetto saball palm),
Ficus aurea (strangler fig) and Mastichodendronfoetidissimum (mastic). As noted earlier.
in the southernmost reaches of Shark Slough, hammocks are poorly developed in tree islands.
On the southwest flanks of the Slough, however, within or near Big Cypress National
Preserve, small elevated outcrops of limestone support local patches of hammock species
within the bayhead-dorninated portions of the tree islands. Here, large trees of Lysiloma
latisiliqua and Quercus laurifolia, species absent elsewhere in the Slough, extend well
above the surrounding bayheads, but oth:r species more typical of the Slough are also often
present.
Each of these species, except the Eugenia is kcpable ufaitaning large izc and girth The
tallest trees in many hammocks reach heights of 10-14 m. However most if not all
hammocks were badly damaged by Hurricane Andrew, the first hurricane capable of
damaging Shark Slough hammocks in over thirty years. The eye of this Category 4 storm
passed directly over Shark Slough in August 1992 (Armentano et al 1995). But although
damage to the crowns of canopy trees was sometimes severe in the hammocks, mortality was
low (Jones et aL 1997). Typically, the understory of Sh.rk Slough hammocks is sparse and
reproduction of overstory trees is low, at least partially due to herbivory by deer. In wet
years, deer and feral hog destruction of the understory may be severe if high waters limit
animal movements for long periods (Jones et al. 1997).
In the northern portion of Shark Slough, on either side of the Tram Road, where the
highest ground in the Slough is found, the tropical hardwood hammocks are distinctive.
Topographic bedrock highs form plateaus that rise above the surrounding marsh prairie
vegetation by about 2 ft (0.61 m). Hydroperiods are shorter than further south in the Slough
and bayhead swamp forest is absent. These hammocks are more diverse in species than the
hammock portions of more southerly tree islands and do not seem to have been farmed.

Bayheads
Most of the hundreds of tree islands that dot Shark Slough are bayheads.
Compositionally Slough bayheads resemble those found elsewhere in ENP and in the water
conservation areas to the north. A mature bayhead is a closed canopy forest consisting
mainly of seven species. Five of these are temperate in distribution: red bay (Persea
borbonia), sweet bay (Magnolia virginiana), dahoon holly (llex cassine), willow (Salix
carohnlmiana), and wax myrtle (Myrica cerifera); cocoplum (Chrysobalanus icaco) and
pondapple (Annona glabra) are tropical.
In Shark Slough, bayheads are often surrounded by tall sawgrass. Because of the very
dense canopy cover, the ground layer is very sparse and consists mostly of swamp fern
(Blechnum serrulatum) and leather fern (Acrostichum danaelfolumn). C ir.i'p heigil rea. he.i
an average 8 L( m
Bayhead soils typically are mucks. Depths vary but in four bayheads probed in the
southern and middle areas, depths fell between 15 and 100 cm deep. In addition, several












bayheads were reconnoitered on the west and east ends of the middle transect. Since the
bedrock is slightly higher here than in the center of the Slough, the soil depths are shallower
aswell Soil deprhs varied between 5 and 25 cm on the west side and 40 cm on the east side,
near the E-26 gauge. The latter was on bedrock elevated above the general surroundings.
Typically bayheads are found in a predictable position within the elevational sequence of
Shark Slough ecosystems. Particularly in the northern and middle transect areas, the usual
pattern consists of a gradual increase in elevation from spikerush marsh, to intermediate
sawgrass, sometimes to tall sawgrass, and then to the bayheads. Additional community
relationships based on data from some of the same Shark Slough areas are discussed in
Olmsted and Loope (1984). The pattern is somewhat different on the east side of the
southern transect. Here elongated bayheads are found on slightly higher bedrock and unlike
bayheads in other areas in the Slough, are not surrounded by tall sawgrass. Here also
bayheads often are dominated by Chrysobalanus icaco, the only tree species. These are
probably the driest bayheads in the Slough with typical hydroperiods of only 2-3 months. In
contrast, most bayheads in the middle and northern areas of the Slough, depending on where
they are located relative to the topography of the Slough and whether they are on bedrock
highs or on accumulated muck, are inundated from 2 to 6 months.

Bayhead swamp forest
This community is very similar in spec ieA composition and physiognomy to bayheads,
but is not confined to relatively small circular stands as are most bayheads. Instead, the
bayhead swamp forest usually comprises the elongate downstream portion of a tree island
that has a tropical hardwood hammock at its northern end. The areal extent of bayhead
swamp forest on a tree island usually far exceeds that of the bayheads and hammocks.
While the bayhead "proper" has a closed canopy and is, therefore, shaded in the
understory, the bayhead swamp forest has a very open canopy. The understory has small
islands of sawgrass or cattails (Typha) and a number of aquatic plants like Utricularia spp.,
Sagittaria lancifolia. Pontederia cordata, Vallisneria americana and Bacopa caroliniana.
The soil is an organic muck sometimes exceeding I m in depth. The swamp forest is always
found in bedrock depressions and has a hydroperiod of up to 10 month/year. If there have
been no recent disturbances, tree heights decrease from upstream to downstream. Since
frequency of lightning fires and prescribed fires in these areas is fairly high, however, one
often finds a b3iding of differently aged swamp forest communities. These also vary in
dominance and mixture of graminoids. Pondapple (Annona glabra) and buttonbush
(Cephalanthus occidentalis) are frequent associates of the other typical bayhead tree species
with Annona sometimes codominiant with willow and cocoplum,
The elevation of the swamp forest varies and is sometimes the same as that of tall
sawgrass, but is always lower than that of the hardwood hammock. Even in the absence of
recent disturbance, the soil surface of the bay swamp forest is very uneven because of fallen
logs, stumps, and soil accumulation around tree bases. The difftrer ce n heigih b.:twen the
hammock trees and the shorter trees of the surrounding swamp forey is, quihe obh ioui and
can be as much as 3-5 m.

Willowheads
Willows (Salix caroliniana), besides being common tree island species, also often form


monotypic stands in willowheads. Many willowheads are actually ponds that are surrounded
by willows in bands of different widths. The ponds probably had their beginning in slight
soil depressions which were deepened by the work of alligators. Willowheads are most y
surrounded by tall sawgrass strands which are on equal or even 'lightly higher elevation.
Tall sawgrass and willows, both typically found on muck soils, are successionally related
communities. When fire consumes surface muck and thereby lowers the elevation in a tall
sawgrass strand, willows often invade. The position of the ecotone between tall sawgrass
and willowheads is relatively fluid. Willows are intolerant of shade and, therefore, mostly
successional or maintained by fire (Robertson 1955, Craighead 1971). Aquatic specie like
Sagitraria and Pontederia are often associated with willowheads as is Leersia hexandra, the
southern cut grass. Pontederia cordata, Sagararia lan jo'lia. and Peltandra virginica
stands are often found near willowheads on thick mucks,


DISCUSSION


A question of both scientific and resource management interest concerns whether the
present vegetation of Shark Slough represents a significant departure from the natural
pattern of the pre-drainage period. Unfortunately, pertinent information is quite limited,
dating back no further than the 1940s. Earlier observations, although made b% knowledgeable
scientists, were at best semi-quantitative and limited by accessibility. With a few limited
exceptions, noted below, previous observers left no field data or sampling locations that
could be re-analyzed. In addition, although it can be assumed that hydrology exerts an
important influence on wetlands e et.inm. deecunng plant Lcomunurti response at specific
locations can be obscured by hydropattern variability (Gunderson 1989). Another
complicating factor operating at specific sites can be intercession of fires that destroy
existing vegetiuon and een soiti. alterinng loal hydrnlugical regimes. Parucular!y where the
prevalent vegetation is herbaceous, detailed sampling at fixed sites over one or more time
intervals is essential unless changes are so great as to be unambiguously detectable by aerial
photography or more casual assessments.
It was not until the late 1950's, when major drainage canals in the Lake Okeechobee and
northern Everglades region had been in place for some 30 years, that more detailed work
appeared on the vegetation of Shark Slough, mainly north of ENP.These impounded water
conservation areas, separated from the Park by the Tamiami Trail and associated canals and
levees, once comprised major components of the greater pre-disturbance Shark Slough
system. The systematic observations of Loveless 11 5, and others make it c lear that radical
alteration of natural hydrology caused profound changes in the natural vegetation of the
water conservation areas. McPherson (1973), Goodrick (1974), and Volk et al. (1974)
reported further on the vegetation response to the protracted flooding in the water
conservation areas already manifested prior to the time of the present study.
The landscape-scale changes in the water conservation areas have been profound and
readily detectable at even a relatively coarse level of resolution (Alexander and Crook 1975,
Davis et al 1994, Rutchey and Vilchek 1994). Tree islands have changed character or
disappeared, and sawgrass and spikerush marshes have declined over large areas. A vast












deep-water slough community of mostly aquatic plants exists today in the impounded areas,
with Nymphea odorata as a widespread dominant.


Comparison with Davis's Map
One of the few sources of earlier information on Everglades vegetation is the monograph
and map produced by Davis (1943). The current vegetation of the water conservation areas
represents a strong departure from the vegetation described by Davis (1943) who based his
work on field work and on aerial photography of 1940. In contrast, departures from the
patterns observed by Davis in Shark Slough south of Tamiamni Trail are less obvious
primarily because the changes have been less profound Direct comparisons with Davis
(1943) are problematic, however, because Davis's analyses were not quantified or
documentable as to location. He assigned most or all of southern Shark Slough to the
category "slough and tree islands areas". Hit map (Davi, 1943) refers to the same area as
"sloughs, ponds and lakes (with aquatic plants)", but included tree islands and sawgrass
either as elongate extensions of the tree islands or separately as strands. The slightly higher
east and west flanks of Shark Slough were described as southern marshes and wet prairies.
The western and eastern ends of the middle and southern transects of the present study
approach areas designated by Davis as southern marshes and wet prairie without actually
extending into them. Note that Davis intended "wet prairie" to refer to marl areas dominated
by mixtures of forb and graminoid species but with dominance by sparse sawgrass and
pikerUih and mceresing admixtures of many other species associated with slightly higher
elevations and sometimes on rock outcrops.
Inspection of 1940 aerial photography suggests that, at the coarse scale level of
resolution, Shark Slough within ENP has remained essentially stable in its distribution of
nmaor plant corrnitnijei. But the "slough" community, an indicator of long-term inundation
by relatively deep water, may not have covered as large an area in 1940 as indicated by
Davis's map for Shark Slough. Aerial photography of 1940, 1954, 1965, 1971, and 1973
reinforce the impression that deep-water slough areas covered smaller areas thin vwggeSted
by Davis's map. Similarly, in 1980, unlike in adjacent water conservation areas, the slough
community occupied only small areas in Shark Slough within ENP. Instead, at least some
of the areas designated as slough on Davis's map appear to have been occupied by sawgrass
in 1980 while spikentsh and maidencane marshes occurred in the deepest areas instead of a
slough community dominated by aquatic species.
That water lily sloughs may have prevailed over more extensive areas in earlier times
is suggested by the predominance of Loxahatchee peat in Shark Slough (Cohen and
Spackman 1974). A plausible explanation for the apparent discrepancy between the
prevalence of Loxahatchee peat, known to be formed under essentially continuous deep
inundation, and the relative scarcity in 1980 of the Nymphaea dominated aquatic
communities that produce Loxahatchee peat, is that by the 1940's, uncontrolled drainage
may have already eliminated most Nymphea communities in Shark Slough. Further
investigation of hydrology-peat-vegetation relationships would help test the validity of this
tentative conclusion.
Davis's (1943) description of other graminoid plant communities also is somewhat
incompatible with 1980 patterns. The same species are present, but in different


combinations. Spikerush and maidencane marshes appear to resemble Davis's slough
communities except that he does not mention the two species in discussion of the slough
community. These discrepancies are not fully understandable and thus cannot be clearly
attributed to real changes in vegetation. But the fact that Davis does not mention the
currently abundani sawgrass marshes in Shark Slough, is further suggestive of a significant
shift in vegetation that may be explainable by artificial drainage.

Evidence for Disturbance Effects on Vegetation
More detailed observations also demonstrate that ftirther vegetation change has occurred.
Kolipinski and Higer (1969) show that community changes occurred from 1940 to 1967 in
several areas of Shark Slough within ENP that appear consistent with the effects of
hydroperiod reduction. They concluded that marsh once characterized by periphyton,
spikerush, Utricularia spp.. Saginaria lancifolia, and Rhynchospora spp. had declined since
1940. In sites near our northern transect, Kolopinski and Higer (1969) found that these
species were replaced by sawgrass communities. In lower Shark Slough, just south of the
southern transect, Rhizophora mangle (red mangrove), willow, cocoplum and pond apple,
all woody species, had expanded in place of aquatic species. The woody expansion originated
along the margins of tree islands and the banks of headwater streams which become common
in lower Shark Slough.
Further evidence of the expansion of woody species into herbaceous marsh during the
era of water management can be found in several papers (e.g., Johnson, 1958, Wade et al.
1980, and Alexander and Crook, 1975, 1984). It should be noted, however, that the spread
of "bushy vegetation" reported by Johnson (1958) could not be confirmed by the senior
author through inspection of aerial photographs.
Alexander and Crook (1975, 1984) descnbed %egetatzon changes from the 1940s to the
1970s of several kinds throughout south Florida based on field studies supplemented by
literature review and interpretation of aerial photographs, They concluded that the major
factors influencing overall south Florida vegetation (including, but extending far beyond
Shark Slough) were water management, increased fires, sea level rise and displacement by
exotic species.
Davis et al (1994) provide some confirming evidence of drainage-induced vegetation
c narge in S.ark Slough They examined aerial photographs from the mid- 1980s that covered
the square-mile field plots inventoried by Alexander and Crook (1975). Two of these plots
were located in the study area being reported on here. In both cases, decrease in wet prairie
(equivalent to Eleocharis and P. hemitomum stands in the present study) and increase in
sawgrass marsh was noted. In plot #61, located near the middle transect of the present study,
shrub cover also increased. Two other plots, located near Tamiami Trail also exhibited
declines in wet prairie and increases in sawgrass cover. In this area, various kinds of
disturbance have led to altered vegetation, including elevated soil phosphorous levels (Doren
et aL 1997). Overall, our information on the relative elevations and hydroperiods of these
community types indicate that reduced hydroperiod is a major contributory factor to the
observed effects as Alexander and Crook (1975) and Davis et al. (1994) have suggested.

Effects of Fire on Sawgrass
Fire has influenced the extent and composition of plant communities in the Slough for












a long time and continues to affect the succession.i relationships between ,panre sawgrass
communities and Eleocharis marshes, as well as between tall sawgrass strands and woody
vegetation. The natural fires that have occurred in south Florida have varied from light to
catastrophic, depending on water levels and fuel loads. Fire frequency has probably
increased during the last 50-60 years or more because of increasingly drier conditions during
the spring (Davis 1943, Robertson 1955, Craighead 1971). Taylor and Hemdon !' 98 1)
reported on the fire history of Everglades National Park, including lightning fires,
prescription fires, and man-set wildfires.
Sawgrass, a rhizomatous plant, is well adapted to fire and easily bums in dense stands,
even over water in the summer. Under continuously high water conditions, sawgrass forms
tussocks, a condition not often seen within the study area. But the rate at which marshes
are subject to rising water levels is important. Fire and deep flooding appear to be critical
co-factors explaining cases of sawgrass mortality. When fire bums back culms immediately
prior to rapid flooding which often follows storms, water levels can rise at rates sufficient
to inhibit sawgrass regrowth which normally follows burning (Herndon el al. 1991). A
sawgrass kill of about 40 ha occurred because of flooding following a fire in Taylor Slough
after Tropical Storm Dennis in 1981 (Hemdon et al. 1991). Therefore, proper timing of
burns is very important.
A different type of decline of sawgrass populations in patches has often been reported
within Shark Slough. This condition, designated as sawgrass decadence, and reported by
Wade et al (1980), Alexander and Crook (1984) and others, represents local areas of die-
back of sawgrass culms that sometimes are open to colonization by woody species.Causes
are seldom obvious. Lack of fire, nutritional problems, fungal infection in meristem, and
a boring larva (Scirpophaga perstrialis) have all been cited as possible causes (Hofstetter and
Parsons 1975). Of interest though is the observation that extensive areas of sawgrass
decadence that caused concern in the early 1970s could not be distinguished from healthy
(burned or unburned) sawgrass in 1980 (Wade et al. 1980). Thus the extent to which
episodic die-back of sawgrass related to fire and flooding interactions or to b:otic factors
contributes to shifting vegetation patterns is unclear except for specific areas and times.
However, because the area of sawgrass probably has expanded in Shark Slough in the past
half-century, episodic sawgrass die-back is unlikely to have been a primary factor in the
changing vegetation patterns.


woody communities, tropical hammock, bayhead, bayhead swamp forest and willow head,
were delineated and qualitatively described.
Sparse sawgrass is the predominant marsh community type in Shark Slough, covering
45% of the mapped area. Tall sawgrass covers another 13%, and spikerush-sawgrass
mixture 14%, totalling nearly three-quarters of the Slough occupied by sawgass-dominated
communities. The Shark Slough marsh communities are distinguished by their low species
diversity (3 to 6 species/ m '), single species dominance and low vascular plant cover (2-
16%) except for tall sawgrass stands where cover reaches 96%.
On the broadest scale, the structure and extent of plant communities in Shark Slough are
largely similar to the way they were in 1940, influenced mainly by hydrology and fire. On
a finer scale shifts in several community types appear related to alterations of the natural
hydrological regime.
One plaii c ommumni. the aqiatri "slough type", is uncommon at the present time, less
so than reported for 1940. At least some of the apparent reduction in slough area, however,
seems attributable to the limited characterization of Shark Slough vegetation presented in
the earlier work rather than to actual conversion to non-slough vegetation. But it is highly
probable that slough vegetation was more ubiquitous 100 years ago, before artificial
drainage (Johnson 1958, Kolipinski and Higer 1969, Craighead 1971, Alexander and Crook
i975, Hofstetter and Parsons 1975).
Many reports in the late 1960's and early 1970's and again in the 1990s mentioned the
deterioration or decline of sawgrass in the overall Everglades and the increase of woody
vegetation. As far as Shark Slough in Everglades National Park is concerned, reduction of
areas dominated by sawgrass communities over the past 50 years (as of 1980) has occurred
only locally, and it would be very difficult to say that sawgrass had diminished in extent.
Although the invasion of woody species into sawgrass communities has occurred, there is
a dynamic relationship between sawgrass and woody species that would allow for increase
or decrease of either comrunlt. dependir.g on fire and water level. Johnson's interpretation
, 195?i of increase of "brushy" vegetation was incorrect. However, the detailed, measured
change in woody %egetation by Kolipnlki and Higct (1969) along creekbeds was probably
accurate. The available evidence, however, supports the conclusion that sawgrass
communities have expanded in Shark Slough a. a response to reduction in hydroperiods.


ACKNOWLEDGEMENTS


CONCLUSIONS

Shark Slough is the southern portion of the greater Evergladre ma.shes tending from Lake
Okeechobee to Everglades National Park. This report provides baseline information on the
composition of the major vegetation types found in Shark River Slough with hierglades
National Park in relationship to environmental factors. In 1980-81, eleven vegetation
community types were ioeniified. including five herbaceous marsh communities. Each of
these, sparse and tall sawvra.s. spikeruih. and maidencane marsh, was analyzed for plant
cover, composition, and species frequency along three cross-Slough iransects. Four types of


The logistics of field work required perseverance and good humor from Vicki Dunevitz,
Lois Granskog and Jill Johnson. Dr. W.R. Robertson, Jr,. provided astute review of report
drafts in 1982 and in 1996. In addition valuable comments were provided in 1996 by David
Jones, Jim Snyder, and Mike Ross.















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patterns in south Florida: Part II: Final Report. South Florida Ecological Study.
827 pp.
Alexander, T.R. and A. G. Crook. 1984. Recent vegetational changes in South Florida
pp. 199-210 in P.J. Gleason (ed.) Environments of South Florida Past and Present II.
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Andrew on coastal and interior forests of southern Florida: overview and synthesis.
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35















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Appendix L Soil type nd texture from sampling sites along the middle uanwect.

9a=11,1 TRANTir


Community Pole Soil Type Sample Depth cim)

SO W-1 marl lop 10

SC W- mart 20
EL w-7 marl tol 10


El. W.7
EL W.ll
SG W.25
SO W-25
TS W-25
TS W-25
SG E-43

SG E.43
IMC E40
EL E-40

MC E-40


EL E-35

TS E-24

SG i6-


arla
muck
muck
muck
muck
muck
muck with marl
intermixed
muck
muck
muck
LauderhltI mucke
muck
mart

muck with marl
Intermnxed
Lauderhill muck


marl with some top 10
muck


Temxure and Color

small organic matter component, gray-brown,
numerous fine shell fragments
Light brownish gray light loamy marl
dark gray marl. mixed with organic matter,
numerous fine shell fragments
light, brownish gray, light louamry man
root fragments mixed in dark brown
<10%4 lber Ibrown)
brown, bit more friable than TS-W-25
very dark brown. a10% fiber
very dark brown, <10% fiber
very dark brown, very granular

brown, very little fiber
black muck. <10% fiber
black, very granular, some marl mixed in
pH 7. black
very granular. low fiber, friable, black
silt loamy. gray marl with organca, numerous fine
shell fragments
brown. very little fiber

black, slightly more fibrous than E-40. soil has <10%
aber
gray, silly marl with muck below. numerous fine
shell fragments


SO E-6 maril and muoK 15o-20u gnry man ana muc
91o1urM TRAnMaCT ANZD OTl lR ARAB
SO S-2 intermixed muck top 10 dark brown
and mal
SG SG-2 shell perlne snarl 20 grayJsh brown slt, loamy marl, numerous fine shell
fragrmenLs


SG S-19 muck 15 brown muck with 10% fiber intent
TS S-9 muck top 10 dark brown, fine roots mixed In
SO S-35 Penrre mart, 20 ughLt brownish gray. heavy LeMture. borderUli
shallow clay loam
SG S.-3 peat 10 helly sillt. loamy mnarI
SG Tram marl op t0 sandy loam. poorly drained. (gritty) trransail
Road Rockdale soil
Ow. paise sawgrass; T.stan swoal..; LetsE.ocEhars 0 etulosa domdinattd masu : MC. Fafriaun
hemaleomon domin ted manrh
*Pole" (column 21 refers to the nearest transeet pole: a map of pole locations Ia archived at the South Florida
Natural Resources Center
















37


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Appendix II Species found within the study area of this report by Shark Slough connunity type Species found along the Tram Road but not sewohere are found only
in Table s.
Tropical Bayhead Spikerush
Hardwood Swamp Tall Sawgiass Spaise Maldencane
Hacmtnock Forest Bayhead Willowhead Sawgrass Marsh


x (Wx


Annona glabra
Ardisia esalnoiides
Bumelia satlcifolia
Bursera siartuba
Carica papaya*
Caesta ligustrina
Cetus laevigata
Cephalanthua ocwdentalls
Chrysoba-lanus Icaco
Chbysophyllum olivaeforme
Citrus atranufoIla
C. aurantiumn
C. stnenlsl*
Coccoloba dwiverfolla
Eugenla axiJarts
Eugenia foctlda
Exothea paniculata
Ficu au rea
Ficus cirifolla
Guapira discolor
HameoJa patens
14 CAsssnte
Lysiloma latislllqua
Magnolia virginiana
Mastichodendron foetdivsAum
M"ica cerifera
Myraine flocldana
Nectandra coracea
Persea borbonia
Piscida piscipula
Psychotria nervosa
P, sultoer


x x


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x xs(x


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Blechnum serruatum x x x x x


AppendLx I, con't. T.oplcal kyh-lad Tall Sawgrass Sparse Spike sh
Hardwood Swamp Frest layhead Wllowheac Sawgrass Maidencane Typha
)1mm-, [t M r-


Boehmeria cyltndrlca
Caprarla blcoior
Crinum americanum
Cynanchum scoparlum
Ertocauto compressum
Gcrardia lnifolla
Hydroeotyte verticMata
Hydrolea corymbsu m
HymenocalUs palmier
JusUca angusta
Ludwigla peruvlana
T- alata
L. curtisli
L. repens
NephMolepls ,Aaltata
Nuphar lutea
Nymphea odorata
Nympholdes aquatic
Oxypolls (UifomIs
Parietaa floidana
Peltandra vTrgonica
Pluchea rose
Polygonum hydropiperoides
P+ puncLatum
Polypodium aureun
P. phyllitidil
Pontederia Cordata
Proseipinaca paiustris
Psllotum nudum
Rlvtna humults
Sagittarda lancifoua


K x


x x
x x


x X


x x


x x
X X
x
x x


x
x x
X

XX
x x
xx































































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