Structure of Mangrove Forests in Florida, Puerto Rico, Mexico, and

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Structure of Mangrove Forests in Florida, Puerto Rico, Mexico, and
Structureof Mangrove Forests in Florida, Puerto Rico,
Mexico, and Costa Rica
Douglas J. Pool
of PuertoRico,
Departmentof NaturalResources, Commonwealth
P.O. Box 5887, Puertade Tierra,San Juan,PuertoRico 00906
Samuel C. Snedakerl
Resource ManagementSystemsProgram,School of Forest Resources and Conservation,
IFAS-BIdg. 737, University
of Florida,Gainesville,Florida32611 U.S.A.
and
ArielE. Lugo
of PuertoRico, P.O. Box 5887, Puertade Tierra,
Departmentof NaturalResources, Commonwealth
San Juan,PuertoRico 00906, and Departmentof Botany,University
of Florida,Gainesville,Florida32611 U.S.A.
ABSTRACT
Structuralparametersof mangrove forestswere measured at seven geographical locations in Florida (U.S.A.), Puerto
Rico, Mexico, and Costa Rica. One-tenthhectare plots were subdividedinto twenty5 x 10 m plots where all individuals
greaterthan 2.5 cm DBH were measured and recorded. Height of the tallesttree in each plot was measured. The complexityindex developed by Holdridge (1967) as an integrativemeasure that combines floral characteristics(number of
species) (s), stand density (d), basal area (b), and height (h) was computed as follows: (s) (d) (b) (h) 10-3.
The riverineand basin mangrove forestsof the southwesterncoast of Florida had considerablytaller trees (6-9 m)
and largerbasal areas (20.3-38.5 m2/ha) than did scrubmangrovegrowingon the southeasternCoast of Florida where a
low canopy (1.0 m), a low basal area (6.0 m2/ha), and a correspondingly
low complexityindex (1.5) were measured.The
riverineforestsof the MarismasNacionales locatedon the Pacific coast of Mexico had high complexityindices (49.7-73.2)
due to the large basal areas (57.8-60.8 m2/ha), tall canopies (16-17 m) and a large numberof treesgreaterthan 10 cm diameter (103-145/ha). The entireestuarinesystemof the MarismasNacionales acts as a receivingbasin forlarge quantities
of freshwaterrunoffand nutrient-rich
sedimentsfrom surroundingupland watersheds.Except for local sportfishing,the
commercialfishingindustryof Florida, Puerto Rico, and Costa Rican mangrovewatersis not nearlyas active as thatobserved near Teacap'an, Mexico.
The structuralcharacteristics
of the north-and south-coastmangrovesof Puerto Rico are probably best describedby
the directand indirectinfluencesof the climate at each coastline. The basin mangroveforeston the humid northcoast
(annual rainfallof 1631 mm) has a basal area of 17.8 m2/ha,canopyheightof 13.6 m, and a complexityindex of 16.7.
The driestsite (rainfall of 860 mm/year) on the south coast of Puerto Rico was a red mangrove fringeforestwhich
had a complexityindex of 0.9, low canopy height (7 m), and low basal area (6.9 m2/ha). Here upland runoff,draining into the mangrovesthroughporous limestoneoutcrops,only occurs 1-2 monthsannually.
In Costa Rica, the riverinemangroves near Puerto Limon on the Caribbean coast (annual rainfall-of 3306 mm)
are more structurallydeveloped than either the riverineor fringemangrovesof the drier (1800 mm annual rainfall)
Pacific coast sites. A basal area of 96.4 m2/ha (primarilyPterocarpusofficinalisJacq.) and a tall canopy (16 m) gave
this forestthe largestcomplexityindex (84.5) of all forestsinventoried.The Pacific coast mangrovesof Costa Rica are
exposed to seasonal rainfall (six months dry season), and this drierenvironmentwas reflectedin a shortercanopy (9.510.0 m) and a lower basal area (23.2-32.9 m2/ha).
RESUMEN
El proposito de este papel es presentare interpretarresultadospreliminaresde los estudios de la estructurade los manglares en siete lugares en Florida, EE.UU., Puerto Rico, Mexico y Costa Rica.
Las areas de muestreode 0.1 ha. se subdividieronen veinteareas de 5 x 10 m, y se registrarontodos los individuosmayores de 2.5 cm de diametromedidos a altura del pecho. Luego se calculo el indice de complejidad desarrolladopor Holdridge (1967). Este es un medio integradoque combina las caracteristicas
floristicas(nuimerode especies) (s), densidad
de individuos (d), area basal (b), y la altura (h). Se calcula el indice de complejidad asi: (s) (d) (b) (h) 10-3.
Los manglares del suroeste de Florida, EE.UU. (clasificados como cuenca y ribefio) tenian 'arbolesmas altos (6.59.0 m), mayor 'area basal (20.3-38.5 m2/ha.) e indice de complejidad m'as alto (23.4-27.7) que los manglaresenanos
que crecen en la costa surestede Florida con una copa baja (1.0 m), area basal de 6.0 m2/ha y un indice de complejidad bajo (1.5)
Los manglares (clasificados como ribeniosy de borde) de las MarismasNacionales de la costa del Pacifico de Mexico
tenian un alto indice de complejidad (49.7-73.2) debido a su area basal grande (57.8-60.8 m2/ha), alta copa (16-17
m) y abundancia de arboles mayores de 10 cm de diametro (103-145/ha). El estuario de Marismas Nacionales sirve
como un almacen de grandes cantidadesde escorrentiay sedimentoscon nutrientesde las cuencas en el area. Este estuario sirve ademas como una base de la industriapesquera de Teacapan, Mexico y la actividad pesquera es impresionante
en comparacion con los sitios estudiados en Florida, Puerto Rico y Costa Rica.
Las caracteristicasestructuralesde los manglares en la costa nortey sur de Puerto Rico se explican mejor por las influenciasdirectase indirectasdel clima contrastanteen cada costa. En la huimedacosta norte (1631 mm precipitacion/
BIOTROPICA9(3): 195-212 1977
195
afio), los manglarestienen un aireabasal de 17.8 m/2ha,altura de copa de 13.6 m y un indice de complejidad de 16.7.
El sitio m'as airidoestudiado en la costa sur de Puerto Rico fue un manglarde Rhizophora (clasificadocomo tipo borde)
el cual tenia un indice de complejidad de 0.9 debido a la copa baja (7 m), un area basal baja (6.9 m2/ha) y pocos
arboles mayoresde 10 cm de diaimetro(26/ha). La escorrentiaprovenientede un aireade afloramientocalizo y ocurre
solo uno o dos meses al afio.
En Costa Rica, los manglarescerca de Puerto Lim6n (clasificado como ribefio) en la costa del Caribe (3300 mm
precipitacionanual) estainma's desarrolladosestructuralmente
que los manglares (clasificado como ribefioy de borde)
de la costa del Pacifico; la cual es mas seca (1800 mm precipitacionanual). El 'area basal de (96.4 m2/ha) (predominantementede Pterocarpus officinalisJacq.) y una altura de copa de 16 m resultanen un indice de complejidad de
84.5, siendo el mas alto en el estudio. Los manglaresde la costa del Pacifico de Costa Rica reciben lluvias estacionalmente (seis meses de sequia) y el ambientearido resultaen una copa mas baja (9.5-10.0 m) y un area basal de 23.232.9 m2/ha. Estos manglaresfueronclasificadoscomo ribeiio y de borde.
MANGROVE FORESTS area
ubiquitousfeature
of trop- in mangrovestructure
and function,
and variations
ical and subtropical
low-energy
coastlines.Compara- resulting
fromman-induced
perturbations.
tive studieshave emphasizedsuch characteristics
as
To date,we have evaluatedtechniquesformeaspeciesassemblages,
geographical
distribution
of spe- suringstructural
parameters
in thefieldat sitelocacies, probablesuccessionalpatterns,and otherde- tionsin Florida,PuertoRico,Mexico,and CostaRica
scriptivenotes (Walsh 1974). Althoughnumerous (fig. 1). Althoughthetechniqueand parameter
sesemi-quantitative
studieshavebeen made worldwide, lectionprocessis still underway,
much usefuldata
theircomparative
valueis diminished
as theresultof have been assembled.The purposeof thispaper is
differing
researchobjectivesand techniques.Quan- to presentand interpretthese preliminary
data.
titativestructural
studiesof mangroves
suggestthe Hopefully,
thesecomparative
data and techniquereexistenceof a large variationin survivalstrategies viewswill be of use to othersparticipating
in simiwhichare probablyrelatedto such forcingfunctions lar fieldresearchon mangroveecosystems.
as tidaldynamics,
waterquality,hurricane
frequency
and intensity,
geomorphological
processes,
soil salin- METHODS
ity,etc. These strategies,
or structural
and functional adaptations,
if betterunderstood,
could providea INDICES OF STRUCTURAL DEVELOPMENT
basis fordefiningthe commonprinciplesgoverning COMPLEXITY INDEX, as an expressionof the diand abundancewithinvarioustypesof forest
thebehaviorof mangroves
and othercoastalecosys- versity
has been testedfor Costa Rica and
communities,
tems.
elsewhere(Holdridgeet al. 1971). This index is
In 1973 a researcheffortwas initiatedto select
one integrative
measurethatcombinesfloralcharacthemostmeaningful
ecosystem
parameters
forrapid,
teristics(numberof species) (s), numberof indiquantitative
characterizations
of numerousdifferent
vidualswithDBH > 10 cm (stand density) (d),
mangrove
systems
overwidegeographical
areas (e.g.,
basal area (b), and height(h). The index results
circum-Caribbean)
duringtime-limited
studyperiods. in a quantitative
description
of the structural
comPossible correlations
betweenthese structural
and
plexityof tropicalvegetation.This methodhas not
functional
indicesand ourown intensive
research
rebeen used previously
to comparemangroveecosyssultson severalof theseecosystem
variantshave po- tems.
Field studieswere conductedin mangrove
tentialcomparative
valueparticularly
in thedevelopnaturalstandsnot disturbed
plots thatrepresented
mentof testablehypotheses.
Of specificinterestis
recently
by man or by hurricanes.
Site descriptions,
thequantitative
relationship
betweenthemagnitudes
including
uniquetopographical
features,
typeof subof themajorforcingfunctions
and thevariationsin
of
strate,linkageto upland watersheds,
frequency
the structure
and function
of distinctmangrove
ecofloodingare explainedbelow.
systemsunder "natural"conditions.FurtherinterOne-tenthhectareplots were subdividedinto
of the structure
and function
pretation
variationsin
twenty5 x 10 m plotswhereall individualsgreater
termsof thesystems
to maximizeenergy
adaptations
than2.5 cm DBH (diameterat breastheight)were
flow will continueto be developed.The time-cost
measured and recorded. Where red mangroves
constraint
for logistic
emphasizedthe requirement
(RhizophoramangleL.) were well developed,disimplicity
and universalapplicability
of techniques.
ameterwas measuredon themaintrunk(sometimes
Anotherlong-term
objective,of whichthisstudy
intersection
of theprop
3-5m) abovetheuppermost
is a part,is to distinguish
betweennaturalvariations
roots.Heightof thetallesttreein eachplotwas meaor a Haga altimeter.
suredwithan inclinometer
1 Present address: School of Marive and AtmosphericSciwas
index
The
complexity
computedfora 0.1 ha
ence, 4600 RickenbackerCauseway,Miami, Florida 33149
plotas theproductof s, d, b, h,and 10-3.
U.S.A.
196
Pool, Snedaker,and Lugo
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7r50
601
FIGURE 1. Location of mangrovesampling sites in Florida, Puerto Rico, Me'xlco,and Costa Rica.
SPECIES IMPORTANCE VALUE,
whichwas developedperaturesforall sitesrangedfromhigh of 28.1?C
byCurtisand McIntosh(1951), is an indexof strucof a treespecieswithina standof
turalimportance
a
mixedspecies.This is a relativevalue integrating
to stand
species influencethroughits contribution
This indexis calbasal area,and frequency.
density,
of basal
culatedby summingtherelativepercentages
each weightedequally,
and frequency,
area,density,
foreach speciesrelativeto the samedimensionsfor
theentirestand.
on thePacificCoastofCostaRica to a low of 23.5?C
at TurkeyPoint,Florida.
FLORIDA:The rainyseason (monthswith greater
than 100 mm precipitation)occursfromMay to
October(5-6 months)withNovemberand December as the only monthswhen evaporationmay be
Florida,there
In southern
greaterthanprecipitation.
in meanannualtemperais littlespatialdifference
althoughthe dry
tureand totalannualprecipitation,
longeron theGulfof Mexseasonmaybe somewhat
CLIMATE
Climaticdata foreach site weretakenfromnearby ico coast.
officialweatherstations.Samplingdates,seasonality PUERTORICO: Theseasonal
is approximately
rainfall
of wet and dryperiods,and thedate of themostre- the same for the north-and east-coast
sites with a
cent hurricaneare presentedin table 1. Climatic shortdryseasonin Februaryto April. Rainfallon
foreachsamplingsitearefoundin figure2. the southcoastis aboutone-third
diagrams
to one-halflower
The studysitesare locatedfromlatitude90 to thanrainfallon thenorthcoastand fallsmostlydurand October.
260 northof the equatorand thussituatedin what ing the monthsof May, September,
is commonlycalled a tropicaland subtropicalen- Nearly50 percentof the totalannualprecipitation
vironment.The mixed Pterocarpusofficinalisand fallsin thesethreemonths.
Rainfall(809 mm) on Mona Islandis moreunired mangroveriverineforestof the Caribbeancoast
the yearthanon the
throughout
of Costa Rica receivedthe highestannual rainfall formlydistributed
3336 mm) and theMarismasNacionalesin western island of Puerto Rico. Octoberis the monthof
peak
Mexico the lowest (775 mm). Mean annualtem- greatestrainfall(100 mm), witha secondary
Structure of Mangrove Forests
197
is the driestmonth
of (80 mm) in May; February
(25 mm).
MEXICO: In the mangroveforestof the westcoast
of Mexico onlythreemonths(July-September)
are
HOMESTEAD,
ELEV.Im
FLA
1643
mm
23.5
C
o
't
W
SAN JUAN, P.R.
ELEV.
4m
200_
r
100
80
80,
60-
30
60-
30
60-
30
40
20
40
20
40
20
tO1
20-
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P.R.
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ELEV.
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ENSENADA,P.R.
861
mm
ELEV.
25.1
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8 m
80-
80
80-
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CL
30
60
40
20
40
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I
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MAZATLAN,MEX.
18 m
ELEV.
I
i
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I
A
30
. 40.-. -20
I
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775
mm
24.5
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809mm
26.5
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M A M J
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PUNTARENAS,C.R.
ELEV.
60
30
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~~~~~~~~~~~~~0
I
(e)
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.
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200
200
60_
M J
MONA ISLAND,P.R.
56 m
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ELEV.
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100-
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1631mm
25.8 C
200_
100-
80
P
1346 mm
23.6C
FT.MYERS,FLA.
ELEV.
2m
E 200_
E 100-
z
consideredwet (over 80% of annualprecipitation
falls duringthis period), whereasthe rest of the
year(9 months)is excessively
dry.The annualprecipitation
is 775 mm.
4 m
1
_
SO
1
20 (f-)
).
'
N D
2150mm
28.1
0
*C
J
700
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'
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M A M J J
600
LIMON,
500
ELEV.
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C.R.
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3336mm
25.9C
400
300
200
100
u 300E 200100 -
z
300
200
I100
0
30
60Ov
w
40
O
.......:....
0
60 40
....30
----------
60-
30
4
..
FIGURE 2. Temperature-rainfall
diagrams for mangrove study sites. Diagrams represent (a) 29-year average values
for Homestead, Florida; (b) 80 years for Ft. Myers,Florida, (c) 25 years for San Juan, Puerto Rico; (d) 21 years
for Ceiba, Puerto Rico (e) 29 years for Ensenada, Puerto Rico; (f) 34 years for Mona Island, Puerto Rico; (g) 10
years for Mazatlan Mexico; and the year 1967 for both (h) Puntarenasand (i) Limn, Costa Rica. Solid areas represent the rainyseason, verticallines the period when rainfallexceeds evaporation,and the dotted area the period when
evaporationexceeds rainfall.
198
Pool, Snedaker, and Lugo
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Structure of Mangrove Forests
)-
199
COSTA RICA: On the Caribbean coast of Costa Rica,
there are only two months (September-October)
when monthlyrainfallis less than 100 mm. There
is no definitedry season. On the Pacific coast there
is a distinctsix-month(December-May) dry season
and a six-monthrainyseason. Besides the difference
in precipitationbetween the Pacific and Caribbean
coasts (1800 vs 3300 mm), the drainagearea of the
Caribbean coastal plain is several times larger (allowing for greaterfreshwaterflow) than is the area
of drycoastal hills borderingthe Pacific.
port occursprimarily
in the formof labile materials,products
of decomposition.
ROOKERY BAY: The mangrove forest evaluated at
Rookery Bay consistsof a fringezone of red mangroves facing the bay and a landward basin forest
with a stand of black mangroves (Avicennia germinans L. Stearn) interspersedwith individual red
and white mangroves (Laguncularia racemosa L.
Gaertn. f.). The buttonwood (Conocarpus erectus
L.) mangrovesoccupy the higher ridges above the
zone of normal tidal influence. Areas of regeneration occur where hurricanedamage has created opMANGROVE SITE DESCRIPTION2
enings in the otherwiseclosed canopy. The regenerFlorida, U.S.A.
ation under these openings is exclusivelyred manTEN THOUSAND ISLANDS: Overwash mangrovefor- grove, whereas red mangroveseedlings are not present beneath the closed canopy. Results of intensive
est of the Ten Thousand Islands (plots 3-7, 3-8)
occurs on small linear islands of fingerlikeprojec- ecological studies in this site are reportedby Lugo
tions that protrudeinto bays (fig. 3). This particu- et al. (1975) and Lugo and Snedaker (1974). They
lar site is situatedalmost perpendicularto the major recognize the fringeand basin types in this forest.
tidal flow patternand is overwashedwith each high We evaluatedthe basin forest.
tide. The velocities of the tidal waters are fast
enough to carryall loose surfacedebris into the in- TURKEY POINT: This site is characterizedby dwarf
ner bays on an incoming tide. As these materials or scrub mangrovesgrowingon the flat coastal plain
are not redeposited by retreatingtides, there is an of the southeasterntip of Florida (fig. 6). Red manobservable paucity of detritusin these foresttypes groves only 1.0 m tall dominate this forest,but
black, white, and buttonwood mangroves are also
and an inferredaccumulationin the inner bays.
in the dwarf form. Hammock forestson
present
Fringe forest (plots 5-11, 5-12, 5-13) is located
on one of the larger islands in the Ten Thousand slightlyelevated topographyare scatteredthroughout
Islands area. Since this fringe forest is exposed to the dwarf mangroves. Daily, tidal-inducedfluctuaan open bay (Fahka Union), it receives slight wave tions of surfacewaters influencethose fringestands
action. Fringe mangrove forest is best defined on growingalong the shorelineand the dwarf foreston
the larger island and shorelines whose elevations the topographic flats landward of it. During the
summer wet season, high water inundates the red
prevent daily overwashingby high tides (fig. 4).
mangrove
prop roots,whereas low water levels durTidal water movementis thus restrictedto an in-out
ing
the
winter
dry season leave most prop roots and
pattern which at any given point in the fringe is
soil
exposed.
The
soil consistsof a recentlydeveloped
manifestedas a rise and fall of the water level. Flow
velocities do not flush as much detrital debris into calcareous marl overlyingdiscontinuouspeat deposits. This site is presentlyseparated fromthe upland
the bays as theydo in overwashislands.
watershed
by canals and artificialwaterways.
Riverine forest (plots 6-14, 6-15 ) is located
along the Little Wood River which drains a large
mangrovearea and adjoining cypressstand and then Puerto Rico
empties into the numerousbays inland fromthe Ten
PINONES-VACIA TALEGA: The Pifiones basin manThousand Islands. Mangrovesgrowingon the banks
grove forestis dissected by several manmade canals
of Little Wood River are flushed by the daily rise
and connected to the ocean by a series of lagoons
and fall of the tides (fig. 5). The riverineforestis
(fig. 7). Daily tidal fluctuationsare slightbut measeparated from the river (or creek) channel by a
surable. The stand receives freshwaterfromrainfall,
shallow berm intersectedwith small drainage chanoverland drainage fromthe nearbyLofza River, and
nels. During the summer wet season, water levels
sheetflow from uplands and local drainage ways.
rise and salinitydrops. Flow velocities throughthis
Salt entersthe systemduring high tides, storms,and
riverineforestare very low: no significantscouring
througha salt wedge that moves inland throughrior redistributionof litter is apparent. Organic exvers and canals and then floods laterally.Soil sedi2 Plot identifications
based on foresttype correspondwith ments consistingof mud and clay, typical of tidal
swamps. support a mixed stand of red, black, and
those published by Lugo and Snedaker (1974).
200
Pool, Snedaker, and Lugo
iw
r~~~~
.
~~
U.
Structur
of.Manrov.Foest
.20
FIGURES 3-6. Figure3. Overwashred mangroveforestin Ten ThousandIslands. Note the top of the litterbasket
a thinbeltalongCardSound,
whichstandsaboutone meterabovethepeatysoil. Figure4. Fringeredmangroves
forming
and thetidalchannelsin TurkeyPoint,Florida.Figure5. Riverinemangroveforestin Ten ThousandIslands,Florida.
of TurkeyPoint,Florida. The forest
Dominantspeciesare the red and blackmangroves.Figure6. Scrubmangroves
all approximately
consistsof red mangroves,
1.0-l.5 m tall.
~~~~~~~~~~~~~~-
z.
44
L.
~ ~
~
~
~
~
~
4
-~~~~~~0.....
FIGURES 7-10. Figure7. A man-made
canal providesa transportation
routethrough
thebasinforest
of Piiiones,Puerto
Rico. Treesare blackmangroves.Figure8. A densestandof pneumatophores
coveringthe forestfloorof the largest
in
basinmangrove
left PuertoRico. The actualheightof the pneumatophores
indicatesthe highestlevel of flooding.
Figure9. Riverineforestof Vacia Talega dominated
by redmangroves
withwell-developed
proproots(3-5 m tall) and
abundantaerial rootsextending
downfromthe canopy.Lugo and Cintron(1975) measuredsoil and surfacewater
salinitiesin thissiteof 36.6 and 22.4 partsper thousand,
respectively.
Largetermitenestsare commonin this forest.
The termites
function
as decomposers
of dead wood. Figure10. Pellicierarhizophorae
withits buttressed
trunkgrowson
the Pacificcoastof CentralAmerica.
202
Pool, Snedaker,and Lugo
whitemangroves.The forestflooris coveredby a althoughtheblackmangroves
dominateoverthered
carpetof pneumatophores
(fig.8).
mangroves,
possiblydue to a contrast
in soil salinity;
Typicalof thePifionesbasinforestare thestands black mangroves
toleratea highersoil salinitythan
of whitemangrovesthat have been previouslycut do theredmangroves.
for charcoal,construction
material,and firewood.
Aftercutting,
whitemangroves
tendto coppiceand PUNTA GORDA: This is a fringemangrove forest,
formdensethickets
thatare believedto be veryfast- predominantlyred mangroves on a mud substrate.
It is usually inundatedby tidal water. The area regrowing.
ceives
less than 900 mm of annual rainfall. This
The riverinemangroveforestinventoried
near
Vacia Talega (fig. 9) formspartof the floodplain site receives some input fromthe conneatingupland
of the Loiza Riverand is in floodconditionseveral watershedwhich is primarilya porous limestonewith
monthsof the year. Here is wherered mangroves surface exposure. Xerophyticvegetation typical of
the subtropicaldry life zone is found on surroundpredominate.
CEIBA: This is a coastalfringemangrove
forestthat
ing limestonehills in the Guanica State Forest.
MONA ISLAND: Mona Island has a small basin mangrove forest (1 ha) located on the southwestcoast
near Punta Arenas. This is an essentiallypure stand
of red mangroveson a sandy substrate,with a nardow border of white mangroves growing on the
slightlyhigherelevations. A small man-made,brackish-waterpond adjacent to the mangrovesshows no
AGUIRRE: These are fringemangroves
thatare fre- evidence of daily tidal fluctuations.However, a sandquentlyfloodedand are composedpredominandystone hardpan,which was inperviousto water flow
of red mangroveson a sandysoil along the shore but not to mangrove roots (Cintron et al. 1975),
with white mangroveson the better-drained
soils was discovered approximately25 cm below the soil
furtherinland. There are no navigableriversor surface. The mangroves occupy a protected area
streamsin thearea. Anyfreshwater
inputwouldor- about 100 m inland between the shorewarddunes
diff. There is no eviiginatefromirrigation
runoffof agricultural
lands and a high southwest-facing
dence
of
recent
damage
by
either
hurricanesor exor directrainfall.Black mangroves
in
predominate
cessive
few
flooding;
dead
trees
are
present.
depressions
on the shoreward
side of the red man-
is frequently
flooded(5-10 cm) and composedpredominantly
of redmangroves
withareasof blackand
white mangrovesin shallowdepressions.Soil and
surface-water
salinitiesmeasuredwere47.7 and 45.2
partsper thousand,
respectively
(Lugo and Cintron
1975). A hurricane
destroyed
theforestin 1928.
grovezone. Therehas beenextensive
cutting,
mostly
of red mangroves,
and also somedamagedue to ex- Mexico (Teacapan Sinaloa)
cessive flooding.Of the six hurricanesthat have ROBLITOS: This riverine forest located inland on
passedoverPuertoRico since1893,fourpassedover Estero Puerta del Rio consistsof a mixtureof red,
the Aguirresite. The mostdestructive
and mostre- black, and white mangroves. Even though located
cent hurricaneto strikethis area was Hurricane some 20 km fromthe Pacific Ocean, daily tidal flucBetsy,on 13 August1956 (Calvesbert1970). The tuations flush these forests. Surroundingareas of
NaturalHistorySocietyof PuertoRico (1972) stu- mangroveshave been heavilylogged. The mangrove
died the mangroveareasdirectly
westof JobosBay wood is used locally for house construction,posts,
neartheAguirrePowerPlantcomplexand classified charcoal,and firewood.
mangrovesas high and low mangrovesdepending
ISLA LA PALMA: This large island located in the Eson theirtopographic
position.
tero de Agua Grande is characterizedby a tall (17
The high mangroves(plots 1-6) correspond
to
m) riverine mangrove forest dominated by white
theoverwash
forests,
whereastheinlandisland(plots
mangroves. The soil, primarilypeat, is compacted
7-11) and mainlandmangroves(plots 12-35) corand flooded infrequently.A dense forestcanopy alrelatewithfringemangrove
typeas describedin this
lows littlelight penetrationfor seedlingregeneration.
study.The low mangroves
have treesthatare selthis well-developedriverineforesthas been
dom tallerthan3.5 m and formmoreopen stands Recently,
selectivelylogged; however, plots were located in
in low basinsinlandfromthe coast. The structural
areas where minimumcuttinghad occurred.
differences
are apparently
due to highsoil salinities
or changesin waterlevel resulting
in shorterblack ISLA ROSCELLE: Daily tides completely inundate
Cintronet al. (1975) discussedtheeco- this overwash forestlocated on an island in the Esmangroves.
logy of thesemangroves.Structurally,
these corre- tero de Teacapan. Occasional high tides flood the
of SoutheastFlorida. entire island carrying off loose debris and litter.
spondto the dwarfmangroves
Structure of Mangrove Forests
203
Dense red mangroveprop roots and horizontal deep) releaseH2S on disturbance,
indicating
anaerobranchingnear the shoreforman almostimpene- bic sulfur-reducing
soil conditions.An unusually
trablebarrieralong the edgesof the island. Several largenumberof fiddlercrab(Uca spp.) holes (363/
birdrookeries(herons,egrets,
etc.) depositabundant mi2) wereobserved.A dailytidalfluctuation
of 3-4
whiteguanoon mangrove
leavesand branches.The m completely
inundatesthissite.
islandis uninhabited
and visitedonlyby local fishcharacterizes
SANTA ROSA: Daily tidal inundation
ermen.
thisfringemangroveforestwhichis dominatedby
EL CALON: Tidal channelsintersect
thisbasin for- red mangroves
growingon a stablesandysoil. The
est whichis locatedapproximately
41 km inlandat slightlyslopingshorelineis exposed to the ocean,
the edgeof Lagunade Agua Grandeand Esterode but receiveslittledirectwave action. Tidal water
Teacapain.A homogenous
standof blackmangroves movementis restricted
to an inlandmovementof
thissitewitha densegrowthof pneuma- only40-50 m bya naturalsandberm.A densestand
dominates
tophores(25-30 cm tall) coveringthe forestfloor. of red mangroveseedlingsand saplings(most less
A high standof tidal waterprobablyoccursonly than2.5 cm diameter)occupiesthe exposedfringe
duringspringhightidesand hurricanes.
Smallshal- next to the open waterwith largerred mangrove
low depressions
withcontinuously
standingwateroc- trees 2.5-10 cm diameter)growingfurther
inland.
cur throughout
the landscape.The soil consistsof A fewblackmangroves
are foundbehindthe berm,
shallow peat overlyingsand. This site is located but compositionof the vegetationquicklychanges
close to a singlelargeshellmound,Murexsp. (El to cactusand otherxerophytic
species.
Calon), wherearcheologists
artifacts
have discovered
and evidenceof earlyhumansettlement.
RESULTS AND DISCUSSION
RIO DE LAS CANAS: Daily tidesusuallyfloodthis In orderto understand
thatgovernthe
theprinciples
riverineforestdominatedby red mangroves
leaving physiognomic
it is
expressionof mangroveforests,
pools of standingwaterin shallowdepressions.On firstnecessary
in foreststructo definethevariations
severalof the tributaries
and narrowcreeks,confin- ture and to identifythose environmental
forcing
ing weirsare constructed
for seasonalshrimphar- functions
in controlwhichappear most important
vests.Rio de las Canfasis partof a watershedthat lingtheobservedvariation.This studywas designed
drainsa large agricultural
area inhabitedby small to searchforpossibleassociations
amongphysiognolandowners.
mic indicesand themoreobviousforcingfunctions
freshwater-seasuchas tidalamplitudeand flushing,
Costa Rica
waterinteractions,
and surficialgeology.The results
screeningare now interpreted
MOIN: Inlandfrom,
and parallelto,thecoastalplain of this preliminary
within
reported
or suggesthe
context
of
previously
on the inlandcoastalwaterwayis a riverineforest
a
ted
and
for
the
construction
as
basis
relationship
dominatedby Pterocarpus
and red manofficinalis
of testablehypotheses.
groves.This gallerytypeforestoccurson a large
of vegetation
The resultsof all measurements
floodplainwiththetallesttreesnearesttheriverand
of thecomand
and
calculation
structure
composition
treeheightsgenerally
withincreasing
disdecreasing
and
indices
are
compared
by geoplexity
presented
tance away fromthe river. River velocityis very
in
and
classification
location
graphic
topographic
slow withlittleor no scouring,
of
or redistribution
are
2
The
and
indices
reported
tables
3.
complexity
litter.Alluvialsedimentsare usuallyinundatedby
of treesgreaterthan2.5 cm DBH unless
1-15 cm of waterdailywithapparently
verylittle forgroups
stated
otherwise.
seasonalvariation.
BOCA BARRANCA: This riverineforestis located ap-
1 km upstreamfromthe Rio Barranca
proximately
thatemptiesintothe Gulfof Nicoya nearPuntarenas. The runofffromthe uplandwatershed
produces sufficient
riverdischargewithonlya slightdecreasein flowduringthe 5-6 monthdryseason.Pellicierarhizophorae
Planchon& Trianaaccountedfor
thelargestpercentage
on theplotwith
of individuals
redand blackmangroves
occurring
infrequently
(fig.
10). Verysoftalluvialsediments(sometimes0.5 m
204
Pool, Snedaker, and Lugo
GEOGRAPHICAL COMPARISON
OF MANGROVE STRUCTURE
Florida
The southwestern
areas of Florida
and southeastern
containall of themangrove
foresttypesdescribedin
thissurvey.The southwestern
coastof Florida,which
includesRookeryBay and theTen ThousandIslands,
had considerably
tallermangroves(6-9 m) thanthe
scrubmangroves(1.0 m) growingon thesoutheast-
00 IV
m
so, a-i>, r-
0o(
0
N Cst CN,
r--
t-C
Eo
<
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o,
o
tA
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PS
~~~~~~N
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_
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?
W
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C1
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fi
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A
j~~~~~~~~~~~~~~~~~~~~\
"'t>Fo?
oo
of
e~~~~~~~~~~C
bi
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ic
q\00
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i Ci
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- w
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a
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oo
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oo%o
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Cs
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C,,
FN
"M r-
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otm>o
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\0
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C1n
00
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C.,
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CC>00VNf-
rX
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I
E-C4
8
v4
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3
G
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2
5
c
;g
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XV
X }?
v
%Ic|&S
E
t8
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^|4
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2o34
{;
20 X ; ffi ;>6 2__;4
A23;0|
Structure of Mangrove Forests
205
TABLE 3. Summary
valuescalculatedfor mangrove
of importance
forests(all treeslargerthan2.5 cm DBH).
SITE
(Topography
classification)
Florida,U.S.A.
Ten ThousandIslands
Plots3-7,3-8 (overwash)
Relativevalue in percent
Taxon
Rhizophora
Laguncularia
Plots5-11,5-12,5-13 (fringe) Rhizophora
Laguncularia
Plots6-14,6-14 (riverine)
Rhizophora
RookeryBay (basin)
TurkeyPoint (scrub)
PuertoRico
PifionesI (basin)
PiiionesII (basin)
Piniones
III (basin)
IV (basin)
Piniones
Vacia Talega (riverine)
Avicennia
Rhizophora
Avicennia
Laguncularia
Other
Rhizophora
Rhizophora
Basalarea
Density
Frequency
70.0
89.0
67.0
68.5
31.5
49.8
87.7
12.3
75.0
60.0
40.0
50.0
50.8
42.4
3.7
3.1
100.0
31.3
31.3
25.0
12.4
100.0
30.0
50.2
31.3
67.4
1.0
0.3
100.0
5.3
11.0
25.0
19.3
24.7
50.0
41.7
33.3
44.4
28.9
Avicennia
Laguncularia
5.2
36.2
2.5
26.2
9.8
41.4
Avicennia
Laguncularia
0.4
68.0
0.4
68.0
2.6
51.2
Rhizophora
Avicennia
Laguncularia
Rhizophora
Rhizophora
Avicennia
50.3
58.6
15.6
81.2
3.2
31.6
0.2
16.6
51.8
71.3
37.7
44.2
18.1
31.6
1.1
9.0
75.3
33.0
Avicennia
Laguncularia
Rhizophora
Importance
value
33.3
72.1
27.9
58.3
37.8
47.0
9.9
5.3
100.0
19.3
35.5
33.4
48.8
45.2
59.6
42.5
45.0
12.5
46.2
31.9
56.8
11.3
36.5
5.5
38.9
5.8
34.6
1.1
62.4
2.3
21.5
Laguncularia
Rhizophora
Laguncularia
Rhizophora
Laguncularia
Rhizophora
83.2
99.2
0.8
90.0
10.0
81.6
89.9
99.1
0.9
87.0
13.0
80.1
55.6
95.2
4.8
50.0
50.0
57.1
76.2
97.8
2.2
75.7
24.3
72.9
Laguncularia
16.9
19.1
37.2
24.4
Plots7-11 (fringe)
Rhizophora
Avicennia
Laguncularia
Rhizophora
82.1
7.1
10.8
72.5
64.8
7.7
27.5
93.5
55.6
11.1
33.3
80.0
67.5
8.6
23.9
82.0
Plots12-35 (fringe)
Rhizophora
80.8
94.6
65.8
80.1
Rhizophora
100.0
100.0
100.0
100.0
Avicennia
Laguncularia
45.2
54.8
28.8
71.2
50.0
50.0
41.3
58.7
5.0
9.1
25.0
2.6
53.8
33.3
33.4
Ceiba (fringe)
Mona Island (basin)a
Aguirre(fringe)
JobosBayb
Plots 1-6 (overwash)
PuntaGorda (fringe)
Avicennia
Avicennia
Avicennia
Laguncudaria
1.5
27.5
3.6
16.6
0.8
6.5
2.2
3.2
5.7
20.0
17.1
17.1
2.7
18.0
7.6
12.3
Mexico
Roblitos (riverine)
Isla La Palma (riverine)
Isla Roscell(overwash)
El Calon (basin)
Rio de las Cafias(riverine)
206
Pool, Snedaker,and Lugo
Rhizophora
Avicennia
Laguncularia
Rhizophora
Avicennia
Laguncularia
Rhizophora
4.1
90.9
11.8
1.0
87.2
0.1
25.5
65.4
43.6
3.9
50.0
25.0
33.3
33.3
26.6
13.0
60.4
29.6
12.3
58.1
12.4
Avicennia
99.9
96.1
66.7
87.6
Avicennia
Laguncularia
5.5
93.0
12.8
55.3
20.0
40.0
12.8
62.7
Rhizophora
1.5
31.9
40.0
24.5
(continued)
TABLE 3 (continued)
Costa Rica
Moin (riverine)
Boca Barranca (riverine)
Santa Rosa (fringe)
Rhizophora
Avicennia
Laguncularia
Pterocarpus
Rhizophora
Avicennia
Pelliciera
Rhizophoza
Laguncularia
8.3
6.4
20.2
65.1
12.4
46.9
40.7
85.8
14.2
9.3
2.3
4.7
83.7
8.0
12.0
80.0
68.7
31.3
20.0
20.0
20.0
40.0
33.3
33.3
33.4
50.0
50.0
12.5
9.6
15.0
62.9
17.9
30.7
51.4
68.2
31.8
a Data fromRogers and Cintron 1974.
b
Data fromthe Natural HistorySocietyof Puerto Rico 1972.
ern coast near BiscayneBay (TurkeyPoint). The theuplandTabonucoforestnearEl Verde(elev. 425
red mangrovehad the highestimportancevalues m, and annualrainfallof 3760 mm) has 85 tree
andscrubman- speciesand a basal area of 40.1 m2/ha (Tschirley
fringe,
(72-100%) fortheoverwash,
grove forestswhile the riverineand basin forests et al. 1970).
of redand blackmangroves.
The driestsite on the southcoast was a fringe
showeda co-dominance
Of all mangrovetypessampledin Florida,the Ten forestin Punta Gorda dominatedby the red manThousandIslandsriverineforesthad thehighestba- grove (100% importance).The foresthad a comsal area (38.5 m2/ha),which is comparableto a plexityindexof 0.9 due to theshortcanopy(7 m),
from
NorthCentralFloridamixedhardwoodforest(33.0 andlow basalarea (6.9 m2/ha).Uplandrunoff
m2/ha) (Lugo et al. 1971). The scrubor dwarf a porouslimestonecap occursonly 1-2 monthsper
all less than year. Structural
of a subtropicaldry
characteristics
mangroveforesthad 25,000 stems/ha,
10 cm diameterand not morethan1-1.5m tall,re- forestat Guainicaadjacentto the PuntaGordamanbasal area (6.6 m2/
sultingin a low basalarea (6.0 m2/ha)and a corre- grovesiteindicatea comparable
index (1.5). The basin ha), and a greaternumberof species (16) which
low complexity
spondingly
indices givesa highercomplexity
index (14) (unpublished
and riverineforesthad thelargestcomplexity
of NaturalRe23.4-27.7) due to the tallercanopy (6.5-9.0 m) reportby J. L. Rogers,Department
and largerbasal areas (20.3-38.5m2/ha). The com- sources,1974).
plexityindicesof theoverwashand fringetypeswere
The fringeforestat Aguirrewas slightlymore
betweenthetwo extremes(3.4 and 9.6, developedwitha tallercanopy(12 m) and a larger
intermediate
table2).
respectively;
basal area (22.6 m2/ha) thaneitherthe fringeforests of JobosBay or Ceiba. The numberof stems
Puerto Rico
(11,000-47,000/ha)and a shortercanopy(4.6 m)
and
destruction
of pasthurricane
be indicative
might
mangrove
On the northcoast,the largestremaining
domithe
is
mangrove
Red
regeneration.
resultant
Talega forest,receivesthe
area, the Pifiones-Vacia
fromthe Rio Loiza. nantspeciesin theseforests(67-82% importance).
and floodwaters
overlandrunoff
of Ceiba are
Even thoughthe fringemangroves
has
The basinforestof Pitnones a basal area of 17.8
indexof 16.7. In two of locatedon theeast coastof PuertoRico, theirstrucm2/haand a complexity
are suggestiveof both the dry
the plots,the whitemangrovewas dominant(45- turalcharacteristics
and the morehumidnorthmangroves
south-coast
and in the othertwo,red (60%
60% importance),
The low canopy(8.5 m) of
forest.
mangrove
coast
were
importance)
importance)and black (57%
red mangroveforest(97%6 imthispredominantly
respectively.
dominant,
wheremangroves,
Four 0.1 ha plots of all treesgreaterthan 2.5 portance)is typicalof south-coast
basal
and
of
stems
(5690/ha)
the
number
large
as
cm diameteraveraged2350 trees/ha.An inventory
index
in
a
complexity
results
m2/ha)
16.7
area
(
of stemsgreaterthan10 cm diameterexcludesseedtypes.
of (16.2) similarto north-coast
lingsand smallertreesand is an underestimation
bya large
The Mona Islandforestis characterized
the total trees. In an unpublishedinventoryby
Wadsworth(pers. comm.), the numberof stems numberof treesgreaterthan10 cm diameter(1790/
tallerthan 1.5 m reportedin 1938 was 41.496/ha ha), whichgivesa largerbasal area (35.0 m2/ha)
in PuertoRico. Cintronet al.
with a basal area of 16 m2/ha;whereas,11 years thanthosemangroves
latertherewere30,398trees/hawitha basal area of (1975) reportedthatthe dilutionof sea waterby
foresttypes. freshwaterreducedsoil salinitiesto about 5 parts
to surrounding
35 m2/ha.In comparison
Structure of Mangrove Forests
207
perthousand.The low soil salinity
explainsthevigor
The entireestuarine
systemof theMarismasNaand dominanceof thezed mangroves(75% impor- cionalesacts as a receivingbasin forrunofffroma
tance) 15 m tall.
largeuplandwatershed
and supportsa largenumber
In additionto topographicclassification,
man- of local fishermen.
The mulletfishingindustry
and
grovesof PuertoRico can also be dividedinto two seasonalshrimpharvestsare evidenceof the probroadtypescorresponding
to northand southcoasts ductivity
of the estuarinesystem.Exceptfor local
(Lugo and Cintron1975). The structural
character-sportfishing,
the fishingindustry
of Florida,Puerto
isticsof the north-and south-coast
mangrovesare Rico,and Costa Ricanmangrovewatersis not nearprobablybestdescribedby directand indirectinflu- ly as activeas thatobservednearthemangrovearea
ences of dimate (i.e., rainfall,temperature,
runoff, on thewestcoastof MexiconearTeacap6n.
hurricanes,
etc.). The inventory
plotson the humid
northcoastreceiveapproximately
1630 mmof pre- Costa Rica
cipitationannuallywhereasthe southcoast is considerablydrier (861-1400 mm/yr).Likewisethis The Riverinemangrove(Moin) nearLim6non the
higherrainfallproducesmorerunoffand sediment Caribbeancoast (tropicalmoistlife zone) is more
developedthan eitherthe riverineor
forthe north-coast
mangroves,
whereasthe streams structurally
and riverson the south coast are dry for 10-11 fringemangroveson the drierPacific coast. The
Pterocarpus
monthsof the year. Of the totalestimatedannual largebasalarea (96.4 m2/ha),primarily
(65% of thetotalbasalarea), and thetall
runoffthatreachesthe ocean, the northcoast re- officinalis
indexof 84.5.
ceives45 percent,whereasthe southcoast receives canopy(16 m) resultin a complexity
Pterocarpus
had
a
high
species
importance
(63%)
than
less
10 percent(Departmentof NaturalRewiththethreespeciesof red,black,and whitemansources1974).
theremainder
of the speA second factorthat influencesthe structuralgroveequallycomprising
cies
The
importance.
life
tropical
zone
siteson
dry
of mangrovesin PuertoRico is the
development
the
coast
Pacific
of
Costa
Rica
rainhave
a
seasonal
frequency
of hurricanes.
Since 1893, 11 stormshave
dryseason), and thisdrierenvironproducedhurricane
winds (hurricanefrequency
ap- fall (six-month
in theshorter
canopies(9.5-10 m)
proximates
one everysix years); however,onlysix mentis reflected
and
lower
basal
areas (23.2-32.9 m2/ha) of the
hurricaneshave passed over the mangroveinvenThe fringemangrove
torysitesat Aguirre,
Ceiba,and Pifiones.
PuntaGor- fringeand riverinemangrove.
da and Mona Islandmangrove
forestsmaynot have forestwas dominatedby the red mangrove(68%
,beendisturbed
forceof hurricane importance)whereasPellicierarhizophoraedominby the destructive
ated (519% importance)the riverineforest.
winds.
Mexico
The riverineforests
of theMarismasNacionaleshad
highcomplexity
indices(49.7-73.2) due to thelarge
basal areas (57.8-60.8m2/ha),tall canopies(16-17
m), and a largenumberof individuals
greaterthan
10 cm diameter(103-145/ha). This foresttypeis
typicalof habitatsthat receivelarge quantitiesof
freshwater
runoffand nutrient-rich
sedimentsfrom
upland watersheds.Althoughthe basin foresthas
thelargestnumberof stems(3120/ha) of all types
thatwere sampledat this location,the treeswere
shorter(9 m) and smallerresulting
in a lowerbasal
area (15 2 m2/ha) and a lower complexity
index
(8.5). The blackmangroves
had thehighestimportancevalue (88%) in thebasin forestwheredense
stands of pneumatophores
covereda slightlydepressedforestfloorthatheld surfacewateruntilit
whitemanevaporated.In the two riverineforests,
groveswere the dominantspecies (59-63 importance) withredand blackmangrove
but less
present.
important
(table 3).
208
Pool, Snedaker,and Lugo
STRUCTURAL PARAMETERS
OF MANGROVE FORESTS
Expressed
as thesumof theindividual
cross-sectional
areas of tree stemsat breastheight,
basal area is used as an indicatorof timberresources whichis relatedto foreststructure.
all individualsgreaterthan 2.5 cm
Considering
thelargestbasalareaandprobably
diameter,
themost
structurally
developedmangroveforestswerethe riverineforestsof the Atlanticcoast of Costa Rica
(96.4 m2/ha) and the MarismasNacionaleslocated
nearTeacapa'n,Mexico (60.8 m2/ha). The smallest
basal areasweremeasuredforthe dwarfmangroves
in southeastern
Florida(6.0 m2/ha) and the fringe
on thedrysouthcoastof PuertoRico (6.9
mangrove
m2/ha;table 2). Table 4 comparesthe basal area,
stand density,height,and speciesdensityof other
single-species-dominated
tropicalforests.It is evident
thatmangrove
forests
developlessbasal area as comparedto forestecosystems
witha relatively
low numberof treespecies.
BASAL AREA:
I8
Basedonlyon mnasurements
of canopyheightas an indicator
of structu130
A
ral development,
the riverineand basin mangrove
A
typeshad tallercanopiesthanthe scrub,fringe,
and
12
A
overwash
types(fig. 11). Theseresultsare consistent
to
00
withthe rankingof theseforesttypesaccordingto O
litterfallproduction(Pool, et al. 1975). The implicationis thatthe factorsthatregulateprimary
pro0.~~~~~~~~
4
ductivity
mayalso regulatestandstructure.
Cintron 0z
et al. (1975) correlated
decreasing
standheightwith
2
O
increasing
soil salinityon the southcoastof Puerto
SCRUB
FRINGE
OVERWASH
BASIN
RIVERINE
Rico (r
0.79).
In Florida,all the mangroves
inventoried,
except
11. Canopy height of a varietyof mangroveforthe scrubtype,were growingundersimilarcondi- FIGURE
est types. The mangrovestypes are arranged in order of
tionsof dimate,nutrients,
and runoff.The overwash increasingfreshwaterturnover. The open circles represent
and basin typeshave slightlyshortercanopies. In Florida sites, the open trianglesthe site on the northcoast
of Puerto Rico, the shaded trianglesthe sites on the south
PuertoRico,thenorth-coast
mangroves
aretallerthan coast of Puerto Rico, the squares
the sites in Mexico, and
thesouth-coast
in partdue to rainfalland the shaded circles the Costa Rican sites.
mangroves,
runoffdifferences.
The basin mangroveof Pifnones
receivesabundantrunoffand overlandflow.
shortercanopy(Odum 1970) but a largernumber
Eventhoughthetallestmangroves
weremeasured of individualswithdiameters
less than10 cm (e.g,
in M6xico,the reasonsfor the variationsin tree mangroves
of southcoastof PuertoRico and South
heightsmaybe due to the differences
in size of the Florida,bothof whichlie in thehurricane
belt).
drainageareasand thequalityof the runoff.
In comparison,
thoseforests(i.e., Mexico,Costa
The mangroves
of thePacificcoastof CostaRica Rica) thatwere not affectedby hurricanes
had a
are structurally
similarto those mangrovesof the tallercanopy,less densestand,but a largernumber
southcoast of PuertoRico and Florida. However, of individuals
withdiameters
greaterthan10 cm and
the riverinemangrovesof the Caribbeancoast of consequently
were more structurally
developedas
Costa Rica (Moin site) wereamongthetallestmea- shownin a highercomplexity
indexthanthosemansured.The presenceof Pterocarpus
suggestslow soil grove foreststhat are periodicallyinfluencedby
salinities.In comparison,
the mangrovesof Mona strongwindsand hurricanes
(table 2). The shorterIslandarealsogrowingin a low-salinity
regime(Cin- canopiedforestshad a high standdensityas a retronet al. 1975) with treeheightscomparableto sult of extensiveseedlingestablishment
following
thosemeasuredin Moin site.
and strongwinds.
hurricanes
of
The structural
of othertropicalforHurricaneslimit the long-term
development
components
and forests.Such foreststendto have a estsof CostaRica are presented
in table4. Comparmangroves
HEIGHT OF MANGROVE FOREST:
14
0
TABLE 4. Structuralcomponentsof tropicalforestsin Costa Rica (afterHoldridge et al. 1971). Calculationsinclude only
trees greaterthan 10 cm diameter.
SITE
(foresttype)
Life
zone
Barranca (slope forest) Tropical
moist
Basal
Tree
Species
area
density
density
per 0.1 ha (m2/ha) (no./ha)
Stand
height
(m)
Complexity
index
13.3
46.7
506
45
141.4
Osa (Mora swamp)
Tropical
wet
4.5
35.0
235
26
9.6
Osa (mangrove
swamp)
Tropical
wet
1.0
12.5
360
34
1.5
Rio Colorado (cativo
swamp)
Tropical
wet
3.6
54.9
290
47
26.9
Rio Colorado (palm
swamp)
Tropical
wet
10.0
47.1
715
40
134.7
Dominant Species
Scheelea rostrata,Luehea
seemannii
Mora oleifera
Rhizophora mangle
Prioriacopaifera,Stemmadeniasp.
Astrocaryum
alatum, Pentaclethra
macroloba,Carapa guianensis
Structure of Mangrove Forests
209
spe- sizing the importance
ing data of treesgreaterthan 10 cm diameter,
of a large numberof small
cies densityand standheightare higherthanthose stems.The fringeforestat JobosBay,PuertoRico,
measuredin mangroveforestsand thushave a cor- and the scrubmangroveat TurkeyPoint,Florida,
index.
respondingly
indexof zero if only
highercomplexity
wouldeach have a complexity
of thoseindividuals
complexity
Anothermeasureof thestructural
greaterthan 10 cm diameterwere
tropicalforests
is thenumberof treestrataor layers. considered.All mangrove
studysiteshavebeenplota simplemethod ted on the Holdridgelife zone chartforeasyvisual
Holdridgeet al. (1971) suggested
the numberof treestrataby divid- comparison(fig. 12).
fordetermining
by two and finding
ing thestandheightsuccessively
Based on DBH greaterthan 10 cm the mean
the resultsgreaterthan5 m (consideredminimum complexityindex of 8.4 for all mangroveforests
heightfortrees). Most of the mangroveforestsin- classifiedin the subtropicaldrylife zone is somein thisstudyhaveonlyone storysinceun- what higherthanthe expectedvalue of 5.6 which
ventoried
derstory
seedlingsare too small to be considereda Holdridgeet al. (1971) projectfor"maturenatural
mangroveforests forestassociations
tree stratum.In the undisturbed
favorable
withoutany excessively
inventoried,
thisone treelayeris quite distinctex- or restrictive
growthfactors"(table 5). These pofernformedthe under- tentialvalues for complexity
cept wherethe Acrosticum
indicesare based on
story. In the Moin site, the Pterocarpusdominated extrapolation
or resultsobtainedin morehumidlife
the un- zonesand maynot be entirely
the canopywiththered mangroveforming
valid in drierareas.
derstory
or secondtreestratumwhichsupportsthe
indicesof both diComparisonof complexity
byHolddescribed
Holdridgetheory.The mangroves
and
> 10 cmDBH)
cm
DBH
(
>
2.5
classes
ameter
ridgeweretaller(34 m) thanthosereportedhere,
and tropical
moist,
tropical
moist,
subtropical
in
the
but had onlyone treestratum.However,the cativo
than
potential
lower
life
are
considerably
zones
dry
Griseb) withsimilartoposwamp(Prioriacopaifera
Howet
al.
(1971).
Holdridge
values
by
predicted
of theMoin site had 2-3 tree
graphiccharacteristics
predictions
between
Holdridge's
the
differences
ever,
strata.
indicesof mangroveforestsreand the complexity
a measureof stress.Two reamay
be
here
ported
STAND DENSITY OF MANGROVE FORESTS: The stand
discrepancy:1) the forest
this
explain
might
sons
densityin termsof number of individuals per land
damfromearliercouldstillbe recovering
area reflectsthe recent historyof the mangrovefor- vegetation
or impactof man; and 2) the
est. The numberof individual trees was greatestfor age by hurricanes
of certainmangroveforests
the fringeforestat Jobos Bay, Puerto Rico (47,300/ dry,salineenvironments
development.
structural
suppress
may
ha), and for the dwarfforestor scrub mangrovesat
Turkey Point, Florida (25,030/ha). No individual
treesgreaterthan 10 cm DBH are reportedforeither
of these sites. Hurricaneshave killed mangrovesin
southernFlorida (Hurricane Donna 1960) and Puerto Rico (1956) which in some situations may explain the lack of individual plants in the larger size
class (Wadsworth and Englerth 1959). There was
no visible evidence or data available which indicated
that the mangrove study sites of Mexico or Costa
Rica had ever been subjected to a hurricane.
The complexityindices (all
individuals greaterthan 2.5 cm diameter) for mangroves sampled in this studyrange from0.9 (Punta
Gorda, Puerto Rico) to 97.5 (Jobos Bay, Puerto
Rico). Holdridge considersonly those trees greater
than 10 cm diameterfor computationof complexity
index; however, mangrove forestshave a considerably largernumberof stemsin the diameterclass between 2.5 and 10 cm. Including these smaller individuals affectsthe total basal area very little, but
greatlyincreasesthe number of stems measured and
gives a betterrepresentationof the stand by emphaCOMPLEXITY INDICES:
210
Pool, Snedaker, and Lugo
INFLUENCE OF OTHER FACTORS
ON MANGROVE STRUCTURE
INFLUENCE OF EXTREME MANGROVE ENVIRONMENTS: The effectsof extreme environmentscan
also suppress the structuraldevelopment of mangroves and yield low complexityindices. Reduced
freshwaterflow througha mangroveforestprobably
not only reduces the nutrientinput from surrounding terrestrialareas, but also results in higher soil
salinities. The dry south coast of Puerto Rico is a
good example where high evaporation causes high
soil salinities,and these are reflectedin a shortcanopy, low basal area, and low complexity indices
(table 2). Cintron et al. (1975) lists several examples of mangrove foreststhat are under environmental stress due to high soil salinities. The structure of the scrub mangrove forestgrowing on the
limestone marl soils of southeasternFlorida is anotherexample of the effectsof an extrememangrove
environment.The relativelyflat topography,seasonal freshwaterflow, and low nutrientinputs result
/
Dry
Forest
Forest
Wet
/
\
/Moist
\
Forest
ht
T 0_P
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P
_SUBTROPICL
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oe
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r
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Tundro
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Tundra
A L P I N IE
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F
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ot
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-2
FIGURE 12. Diagram for the classificationof world life zones or plant formationsby L. R. Holdridge (1967). (Diagram courtesyof Tropical Science Center,San Jose, Costa Rica.) Enlargementshows mangrove study sites in the subtropical and tropical dry and moist life zones. For this diagram,life zones were determinedfromavailable climaticdata
that were only approximatefor the study sites. Note that life zones given in table 1 and the text are based on field
observationsand life zone maps prepared by Holdridge et al. (1971) and Ewel and Whitmore (1973). Numbers refer to specificmangrove forestsas follows: (1) Ten Thousand Islands, Florida, (2) TurkeyPoint, Florida, (3) North
Coast, Puerto Rico, (4) South Coast, Puerto Rico, (5) West Coast, Mexico, (6) Santa Rosa, Costa Rica, (7) Boca
Barranca,Costa Rica, and (8) Moin, Costa Rica.
maybe largelya function
of this forest mentand litterproduction
development
in suppressedstructural
and nutrients
of incomingfreshwater
of thequantity
(table 2).
in thatinput.
variation
and
the
time-dependent
Previousworkon litterproduction(Pool et al.
1975) at severalof the sitesevaluatedin thisstudy
indices of mangroves
of co-mplexity
has furthersuggesteda relationshipbetweenthe TABLE 5. Comparison
and upland subtropicaland tropical forests.
load) with
input (and potentialnutrient
freshwater
the productionof litterby foresttype. The rateof
Complexityindices
Upland forestsb
Mangroveforestsa
to productivity
uptakemaybe proportional
nutrient
>10 cmDBH >10cmDBH
Life zone
>2.5cmDBH
and to some extentrelatedwiththe subsequentacThe Subtropical dry 31.6
of livingbiomassas foreststructure.
cumulation
5.6
8.4
of leaflittermaybe used as an estimator Subtropicalmoist 14.8
production
90.0
2.3
45.0
4.8
7.6
and nutrientinput re- Tropical dry
of the relativefreshwater
270.0
72.0
84.5
and externalsources. Al- Tropical moist
ceived fromterrestrial
to a
are insufficient
thoughthe data on complexity
Complexityindices of mangrove forests(this study) caltheydo suggestsome cor- culated for two diameterclasses.
draw strongconclusions,
relationamong foresttype,litterproduction,and bHoldridge et al. (1971) predictionof complexityindices
(one diameterclass) for mature natural forestassociations
nutrientinputs. It appearsthat at the without
freshwater
any excessively favorable or restrictivegrowth
develop- factors.
optimumsalinityregimesboth structural
Structure of Mangrove Forests
211
ACKNOWLEDGEMENTS
Department of Interior, Bureau of Sport Fisheries and
Wildlife, Pittman Robertson and Dingle Johnson projects
This research efforthas been made possible through the 4-4-4, Study II and III; Mexico-National Institute of
supportand assistanceof many organizationsand individu- Anthropologyand History,and the State Universityof New
als to whom we expressour appreciation. By site location,
Rica-the Tropical Science Center.
the cooperatorsinclude: Florida-the U.S. Environmental York at Buffalo; Costa
Special thanks are due Ada Velazquez de Torres and Lucy
Protection Agency (grant number R-803340), the U.S.
Departmentof Interior (contractnumber 14-16-0004-426), Hernandez who typed the manuscriptand Nelson Cubano,
Jose Ortiz, and Diana Hernandez, who prepared the maps
and the Florida Power and Light Company; Puerto Ricoand graphs.
the CommonwealthDepartmentof Natural Resources,U.S.
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border region of WisconCURTIS, J. T., AND R. P. McINToSH. 1951. An upland forestcontinuumin the prairie-forest
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DEPARTMENT OF NATURAL RESOURCES. 1974. The 1973 Water Assessmentfor Puerto Rico. 160 pp.
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Pool, Snedaker,and Lugo

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