United States

Department of

Agriculture

Forest Service

Southern

Research Station

General Technical

Report SRS-13

An Old-Growth Definition for 

Tropical and Subtropical Forests

in Florida

Kenneth W. Outcalt

A Section of the Old-Growth Definition Series 
___________

The Author:

___________

Kenneth W. Outcalt, Research Plant Ecologist, Southern Research Station,

U.S. Department of Agriculture, Forest Service, Athens, GA 30602-2044.

Preface

Old growth is widely acknowledged today as an essential part of managed forests, particularly on public lands. However, this

concept is relatively new, evolving since the 1970's when a grassroots movement in the Pacific Northwest began in earnest to

define old growth. In response to changes in public attitude, the U.S. Department of Agriculture, Forest Service, began

reevaluating its policy regarding old-growth forests in the 1980's. Indeed, the ecological significance of old growth and its

contribution to biodiversity were apparent. It was also evident that definitions were needed to adequately assess and manage the

old-growth resource. However, definitions of old growth varied widely among scientists. To address this discrepancy and other

old-growth issues, the National Old-Growth Task Group was formed in 1988. At the recommendation of this committee, old

growth was officially recognized as a distinct resource by the Forest Service, greatly enhancing its status in forest management

planning. The committee devised “The Generic Definition and Description of Old-Growth Forests” to serve as a basis for

further work and to ensure uniformity among Forest Service Stations and Regions. Emphasis was placed on the quantification

of old-growth attributes.

At the urging of the Chief of the Forest Service, all Forest Service Stations and Regions began developing old-growth

definitions for specific forest types. Because the Southern and Eastern Regions share many forest communities (together they

encompass the entire Eastern United States), their efforts were combined, and a cooperative agreement was established with

The Nature Conservancy for technical support. The resulting project represents the first large-scale effort to define old growth

for all forests in the Eastern United States. This project helped bring the old-growth issue to public attention in the East.

Definitions will first be developed for broad forest types and based mainly on published information and so must be viewed

accordingly. Refinements will be made by the Forest Service as new information becomes available. This document represents

1 of 35 forest types for which old-growth definitions will be drafted.

In preparing individual old-growth definitions, authors followed National Old-Growth Task Group guidelines, which differ

from the standard General Technical Report format in two ways—the abstract (missing in this report) and the literature

citations (listed in Southern Journal of Applied Forestry style). Allowing for these deviations will ensure consistency across

organizational and geographic boundaries.

July 1997

Southern Research Station

P.O. Box 2680

Asheville, NC 28802
An Old-Growth Definition for Tropical

and Subtropical Forests in Florida

Kenneth W. Outcalt

Introduction

In the United States, tropical and subtropical forests are

found only in south Florida, covering the southern part of

the Floridian Coastal Plain and the Florida Keys. The

climate is typically hot and humid with abundant rainfall,

although droughts do occur. Soils range widely depending

on landform and parent material, and can be organic, finetextured silts, or coarse-textured sands. These forests

develop best on moist hammocks with organic soils. They

are the stable climax vegetation on the slightly higher

portions of the landscape where fire is infrequent. South

Florida slash pine (Pinus elliottii var. densa Little &

Dorman) dominates areas with more frequent fires with the

fire-sensitive subtropical and tropical hardwoods restricted

to subordinate positions. Lower wet areas are occupied by

cypress, saw grass, or wet prairie communities. 

Physical Environment

Geographic Distribution

Tropical and subtropical forests correspond to Society of

American Foresters cover type 105 (Eyre 1980). In the

United States, these forests grow only on the Florida section

of the coastal plain physiographic province (Fenneman

1938) and on the Florida Keys. They are most common in

Dade, Monroe, and Collier Counties (Woodall 1980) with

extensions farther north near the coast where ocean waters

mediate freezing temperatures (Simpson 1920). Within this

region, these forests occupy areas of the Miami rock ridge,

the Keys, the Everglades, the Florida Bay coast, and the

gulf coast. This community occupied about 25,000 acres

(ac) [10,000 hectares (ha)] in pre-Columbian times

(Woodall 1980).

Geologic Substratum

The Miami rock ridge, an outcropping of Miami oolite

limestone (Craighead 1971), extends down the Atlantic

coast through Miami south and west through Homestead to

the Long Pine Key area of the Everglades. Elevations range

from more than 23.0 feet [7 meters (m)] above sea level

near Miami to 13.0 feet (4.0 m) near Homestead and 6.5

feet (2.0 m) or less around Long Pine Key (Snyder et al.

1990). The upper Keys are islands of coral rock (Key Largo

limestone) formed during the Pleistocene age, while the

lower Keys are oolitic limestone (Craighead 1971). The

Everglades, often referred to as the river of grass, is a large

expanse of wetlands dominated by saw grass that stretches

south from Lake Okeechobee behind the Atlantic coast

ridge. The Florida Bay and gulf coasts are mostly low, wet

areas dominated by mangrove forest and coastal marsh. 

The Miami rock ridge has an extremely rough, irregular

surface pitted by solution holes. Pine lands, dominated by

south Florida slash pine, cover most of this area. Tropical

and subtropical hammocks generally occupy the higher

areas, but the difference in elevation is difficult to detect

because it is actually only a few inches (Alexander 1967).

A more prominent feature of tropical hammocks is the

presence of numerous solution holes, ranging in diameter

and depth from 1.5 to 8.0 feet (0.5 to 2.5 m) (Small 1909),

created by organic acids dissolving the limestone

(Craighead 1974). All the higher areas on the Keys north of

Bahia Honda were once covered by tropical hardwood

forests (Gifford 1911). In the Everglades, tropical and

subtropical forests form teardrop-shaped tree islands (Carr

1973). These tropical hardwood hammocks occur where

organic matter has accumulated on platforms of the

underlying limestone, which are slightly higher, 1 to 4 feet

(0.3 to 1.0 m), than the general area. Along the coast of

Florida Bay, tropical and subtropical hardwoods grow on

storm-deposited embankments and shell mounds (Olmsted

et al. 1981). In the gulf coast region, these forests occupy

the high ridges, outcrops of Tamiami limestone, which are

scattered throughout the area (Craighead 1971). Although

these communities are often surrounded by water, they are

rarely inundated (Schomer and Drew 1982). 

Soils

Because of fluctuations in sea level (most recently 5,000 to

8,000 years ago) soils for the entire area are of recent

origin. These soils are mostly calcareous muds or organic

deposits mixed with shell remains (Craighead 1971),

although some areas of the coast have soils derived from

storm-deposited sands. Soils are thin layers over the

irregular, porous, limestone rock, with hardwood hammock
2

soils being generally deeper and having a higher organic

matter content than those of adjoining pine lands (Wade et

al. 1980). Much of the actual soil material accumulates in

channels, fissures, and depressions in the bedrock. 

Climate

The region has a subtropical climate with about a 15 o

F (8 o

C) range between mean summer highs and winter lows

(Craighead 1971). Killing frosts occur as far south as

Miami about once every 5 years, while summer maximums

seldom exceed 94 o

F (34 oC) (Davis 1943). There is a

distinct summer, wet season from May to October, when 60

to 80 percent of the rainfall occurs, followed by a 6-month

winter, dry season. Annual rainfall is highest along the

Atlantic coast, averaging 60 inches [1524 millimeters (mm)]

from Miami to West Palm Beach. Inland precipitation drops

to 55 inches (1397 mm) over Lake Okeechobee and the

Everglades around Homestead. Mean annual rainfall

declines farther both south and west of Homestead,

averaging 50 inches (1270 mm) in the upper Keys and along

the southwest coast and about 40 inches (1016 mm) at Key

West. Wet-season rainfall comes from frequent, convective

thunderstorms accompanied by locally high winds and

lightning, while winter precipitation comes from the

passage of cold fronts (Schomer and Drew 1982). 

General Vegetation

Hammock Origin

Live oak (Quercus virginiana Mill.) is often a pioneer

species in hardwood hammock development on the Miami

rock ridge, commonly occurring near solution holes, which

provide water storage and fire protection (Sand 1971). As

other species invade, a closed canopy forms, dominated by

trees with crooked trunks, dense hardwood, and stiff

evergreen leaves (Harper 1927). These trees produce a

dense canopy that modifies the microclimate to a moister

and shadier environment (Carr 1973, Olmsted et al. 1983).

Other early successional species are wild-tamarind

[Lysiloma latisiliquum (L.) Benth.] and mahogany

(Swietenia mahagoni Jacq.), which do not reproduce in

shade but are prevalent in hammocks because of

disturbance from fire and storms (Robertson 1962).

Species Composition

Hammocks are dominated by mostly broad-leaved,

evergreen trees of West Indian origin and a few temperate

species (Craighead 1974). This is a diverse community

containing 150 to 170 native species of trees and shrubs

(Snyder et al. 1990). Species richness is greatest in the large

hammocks, such as those in the Long Pine Key area of

Everglades National Park. Because of landscape diversity

and differences in species distribution, composition varies

greatly, but nearly all hammocks contain gumbo-limbo

[Bursera simaruba (L.) Sarg.] and pigeon-plum (Coccoloba

diversifolia Jacq.) in the canopy and stopper (Eugenia spp.)

in the midstory and understory layers. 

Other common canopy species found in many hammocks

include poisonwood [Metopium toxiferum (L.) Krug &

Urban], willow bustic [Dipholis salicifolia (L.) A. DC.],

strangler fig (Ficus aurea Nutt.), wild-tamarind, mastic

[Mastichodendron foetidissimum (Jacq.) H.J. Lam], live

oak, and cabbage-palm [Sabal palmetto (Walt.) Lodd ex

J.A. & J.H. Schult]. Temperate species are less common in

hammocks on the Florida Keys (Schomer and Drew 1982),

while some tropical species such as black-ironwood

[Krugiodendron ferreum (Vahl) Urban], Jamaica-dogwood

[Piscidia piscipula (L.) Sarg.], and thatchpalm (Thrinax

morrisii H. Wendl.) are more common. Other trees, such as

lignum vitae (Guaiacum sanctum L.) and milkbark

(Drypetes diversifolia Krug & Urban), grow only in the

Keys. Hammocks in western Florida generally have fewer

species; and the canopy is more likely to be dominated by

one or a few species (Craighead 1971). 

Although there are several species in the canopy, most of

the woody species in a hammock community occur in the

midstory and understory layers (table 1). Hammocks contain

few herbaceous species (Snyder et al. 1990), having a clean

forest floor composed of leaflitter (Small 1916). Olmsted et

al. (1980) reported herbaceous cover, including tree

seedlings to be 1 to 5 percent, except in canopy gaps.

Epiphytes (e.g., ferns, bromeliads, and orchids) are common

around solution holes and canopy gaps where light is

prevalent (Carr 1973). Air plants are less prevalent on the

Keys because of a drier climate. 

Natural Disturbance

Frosts, droughts, fires, and tropical storms significantly

stress the vegetation of south Florida hammocks

(Richardson 1977). Most species, however, are well

adapted to these natural forces as shown by the stable

species composition during a 25-year period reported by

Alexander (1967) for a hammock near Miami. The dense

canopy of hammocks acts like a natural greenhouse,

keeping the interior warmer in winter, which limits most

frost damage to the edge (Craighead 1974). The closed 
3

Table 1—Major tree species of tropical and subtropical hammocks of Floridaa

Positionb/scientific name Common name Rangec Type

Overstory:

Annona glabra L. Pond-apple Alld Tropical

Bursera simaruba (L.) Sarg. Gumbo-limbo All Tropical

Coccoloba diversifolia Jacq. Pigeon-plum All Tropical

Dipholis salicifolia (L.) A. DC. Bustic All Tropical

Ficus aurea Nutt. Strangler fig All Tropical

Ficus citrifolia Mill. Shortleaf fig All Tropical

Lysiloma latisiliquum (L.) Benth. Wild-tamarind All Tropical

Manilkara bahamensis (Baker) Lam & Meeuse Wild-dilly LG,K Tropical

Mastichodendron foetidissimum (Jacq.) H.J. Lam Mastic All Tropical

Metopium toxiferum (L.) Krug & Urban Poisonwood MR,EG,K Tropical

Morus rubra L. Mulberry MR,EG Temperate

Persea borbonia (L.) Spreng. Redbay All Temperate

Quercus virginiana Mill. Live oak All Temperate

Roystonea elata (Bartr. ) F. Harper Royalpalm EG,GC Tropical

Sabal palmetto (Walt.) Lodd ex J.A. & J.H. Schult Cabbage-palm All Temperate

Sapindus saponaria L. Soapberry EG,K,GC Tropical

Simarouba glauca DC. Paradise-tree All Tropical

Swietenia mahagoni Jacq. Mahogany EG,K Tropical

Midstory:

Amyris elemifera L. Torchwood MR,K Tropical

Ardisia escallonioides Schiede & Deppe ex Schlecht.& Cham. Marlberry All Tropical

Byrsonima lucida DC. Locust-berry EG,K Tropical

Canella winterana (L.) Gaertn. Wild-cinnamon K,GC Tropical

Cephalanthus occidentalis L. Buttonbush All Temperate

Chrysobalanus icaco L. Cocoplum All Tropical

Chrysophyllum oliviforme L. Satinleaf All Tropical

Citharexylum fruticosum L. Fiddlewood MR,EG,K Tropical

Cordia sebestena L. Geiger-tree LG,K Tropical

Drypetes diversifolia Krug & Urban Milkbark K Tropical

Eugenia confusa DC. Red stopper MR,K Tropical

Exothea paniculata (Juss.) Radlk. Inkwood All Tropical

Guaiacum sanctum L. Lignumvitae K Tropical

Hippomane mancinella L. Manchineel LG,K Tropical

Krugiodendron ferreum (Vahl) Urban Black-ironwood MR,EG,K Tropical

Nectandra coriacea (Sw.) Griseb. Lancewood All Tropical

Persea borbonia var. pubescens (Pursh) Little Swampbay All Temperate

Piscidia piscipula (L.) Sarg. Jamaica-dogwood LG,K,GC Tropical

Spondias purpurea L. Hog plum Introduced

Rapanea punctata (Lam.) Lundell Myrsine All Tropical

Schoepfia schreberi J.G. Gmel. Whitewood All Tropical

Tetrazygia bicolor (Mill.) Cogn. Tetrazygia EG Tropical

Understory:

Bumelia celastrina H.B.K. Saffron-plum MR,K,GC Tropical

Drypetes lateriflora (Sw.) Krug & Urban Guiana-plum All Tropical

Eugenia spp. Stoppers All Tropical

Guapira discolor (Spreng.) Little Blolly All Tropical

Guettarda elliptica Sw. Velvetseed MR,EG,K Tropical

Gymnanthes lucida Sw. Crabwood MR,EG,K Tropical

Hypelate trifoliata Sw. White-ironwood EG,K Tropical

Prunus myrtifolia (L.) Urban West Indian cherry EG,UK Tropical

Psychotria spp. Wild coffee All Tropical

Reynosia septentrionalis Urban Darling-plum K Tropical

Schaefferia frutescens Jacq. Florida-boxwood K Tropical

Trema micranthum (L.) Blume Florida trema All Tropical

Zanthoxylum fagara (L.) Sarg. Wild-lime All Tropical

a

 Based on a compilation of species lists in Alexander (1958, 1967); Austin et al. (1977); Bureau of Land & Water Management (1976);

Craighead (1971); Davis (1943); Duever et al. (1982); Gifford (1911); Harper (1927); Harshberger (1914); Olmsted et al. (1980, 1981, 1983);

Schomer and Drew (1982); Simpson (1920); and Weiner (1979).

b

 Based on information from Long and Lakela (1976), Scurlock (1987), and Stevenson (1992).

c

 Based on Little (1979).

d

 All = all of south Florida and Keys, EG = Everglades, LG = lower glades, MR = Miami rock ridge, K = Keys, UK = upper Keys,

and GC = gulf coast. 
4

canopy, greenhouse effect also mediates moisture losses,

reducing the impact of dry periods. In addition, many

species (e.g., gumbo-limbo) drop their leaves during dry

periods and refoliate when the rainy season begins (Bureau

of Land & Water Management 1976). Natural fires start

from lightning strikes associated with thunderstorms.

Because most thunderstorms occur during the summer (wet

season) many of the hammocks are protected by

surrounding water, or the organic matter is too moist to

carry fires (Craighead 1971). If the peat is dry enough to

burn, the soil can be consumed down to bare rock,

eliminating the hammock (Schomer and Drew 1982).

High winds from tropical storms frequently strike

hammocks, but only very intense storms cause much

damage. The closed canopy deflects winds (Duever et al.

1986), and the high density of stems provides a sort of

mutual buffering (Bureau of Land & Water Management

1976) that, along with the extensive root system (Small

1922), allows most individuals to resist storm damage. A

hurricane with winds exceeding 125 miles per hour (200

kilometers per hour) occurs about every 25 years (Gentry

1974). Winds of this magnitude blow many large trees over

and prune all but the largest branches from many others

(Craighead and Gilbert 1962). This occurrence opens the

canopy, admitting sunlight, which stimulates growth of

trees and shrubs. Damage near the coast is much worse

from farther inland because of the storm surge. The

severest damage, however, is often confined to small areas

(Richardson 1977). 

Old-Growth Attributes 

Size and Composition

Old-growth hammocks, like hammocks in general, are

mostly small patches of broad-leaved forest dominated by

tropical species and surrounded by other vegetation

(Snyder et al. 1990). Hammock size ranges from 0.25 to

100 ac (0.1 to 40 ha) (Craighead 1974), with most being

less than 25 ac (10 ha) (Olmsted et al. 1983). A minimum

size of 0.6 ac (0.25 ha) is probably required for old-growth

development. Species composition of old-growth stands is

similar to that for hammocks in general. 

Tree Size and Basal Area

Although species such as mastic and mahogany can grow

much larger, to be classified as old-growth hammock, the

community must have some trees at least 16 inches (40 cm)

in diameter (table 2). The largest trees in old-growth

hammocks are at least 100 years old with a few individuals

150 years old. Old-growth hammocks on the Miami rock

ridge have a well-developed, closed canopy of hardwoods

20 to 33 feet (6 to 10 m) in height, with some large trees 50

to 56 feet (15 to 17 m) in height rising above the general

canopy and an understory of tropical trees and shrubs 3 to

16 feet (1 to 5 m) in height (Olmsted et al. 1980, 1983).

Maximum heights are less for old growth west and south

of Homestead because of lower annual rainfall (Alexander

1958). Basal area in old-growth stands averages about 260

feet2

 per ac (60 m2 per ha), with a minimum of at least 130

feet2

 per ac (30 m2 per ha) required. 

Microenvironment

The edge of many old-growth hammocks is a dense,

jungle-like growth of mostly small stems forming a barrier

to the interior (Phillips 1940, Gantz 1971). The interior of

old-growth hammocks, however, is composed mostly of

old trees with a dense, leafy canopy (Simpson 1920, Carr

1973) that filters out as much as 85 percent of ambient

sunlight (Schomer and Drew 1982), creating twilight-like

conditions even at midday (Harshberger 1914, Simpson

1920). Because of extreme shade, the herbaceous

understory is extremely sparse and composed of few

species (Olmsted et al. 1980). The forest floor is clean with

an open, almost park-like appearance (Sand 1971, Bureau

of Land & Water Management 1976). Most herbaceous

growth and epiphytes grow in the occasional canopy gaps.

Much of the bird and insect life exists high in the canopy

where sunlight is available (Simpson 1920). The solution

holes provide a specialized habitat occupied by a lush

growth of ferns.

Soil and Forest Floor

A major distinguishing attribute of old-growth hammocks

is the accumulation of an organic soil layer that is at least

4.7 inches (12 cm) thick (Olmsted et al. 1980) and can

reach depths greater than 12 inches (30 cm) (Small 1909,

Simpson 1920, Craighead 1971). This rich, dark, organic

layer develops from leaves and detritus of the hardwoods

(Gifford 1911), which have an average annual litterfall of

5,370 pounds per acre (6100 kilograms per hectare) (Ross

et al. 1992). This accumulation of organic matter conceals

much of the underlying rock. The pitted, irregular nature of

the substratum, however, is revealed at tip-up mounds,

where trees blown over by tropical storms have torn the

organic layer from the rock. Because many of the tropical

species have dense, decay-resistant woods, fallen timber

generously litters the forest floor of old-growth stands

(Simpson 1920). Many of the trees can sprout from the

base or can send up a branch from their fallen trunk to

form a new main stem. Examples of both of these

adaptations to tropical storm damage can usually be found

in old-growth stands. 
5

Table 2 (English units)—Standardized table of old-growth attributes for tropical and subtropical hammocks of

Florida

Quantifiable Value Number

attribute Range Mean of stands Sitea References

Stand density (no./acre)

Trees 1 in d.b.h. 2,090–2,390 2,240 2 EG Olmsted et al. 1980

Trees 1 in d.b.h.

and 2 ft height 3,370–6,000 4,685 2 EG Olmsted et al. 1980

Trees 2 ft height 65,540–85,250 75,400 2 EG Olmsted et al. 1980

Trees ›4 in d.b.h. 6,075 1 MR Alexander 1967

Stand basal area (ft2

/acre)

Trees ›1 in d.b.h. 190–400 300 2 EG Olmsted et al. 1980

Trees ›4 in d.b.h. 250 1 MR Alexander 1967

Age of large trees (yrs)

All species 100–200 150 UNb EG Tyrell 1992

All species 200 4 EG Craighead 1971

Swietenia mahagoni Jacq. 225 UN EG Wade et al. 1980

S. mahagoni 200 UN EG Craighead and Gilbert 1962

Maximum d.b.h. (in)

All trees 48–72 60 UN EG Craighead 1971

All trees 28–36 32 5 EG Gantz 1971

Olmsted et al. 1980

Bursera simaruba (L.) Sarg. 40 UN Long and Lakela 1976

B. simaruba 36 UN UK Bureau of Land & 

 Water Mgmt. 1976

Ficus aurea Nutt. 60 UN Small 1929

Mastichodendron foetidissimum

(Jacq). H.J. Lam 60 UN Small 1929

Metopium toxiferum (L.) Krug

& Urban 19 1 UK Author's data

S. mahagoni 60 1 EG Robertson 1962

S. mahagoni 15–17 16 UN LG Olmsted et al. 1981

a

 EG = Everglades, MR = Miami rock ridge, UK = upper Keys, LG = lower glades.

b

 UN = Unknown.
6

Table 2 (metric units)—Standardized table of old-growth attributes for tropical and subtropical hammocks of

Florida

Quantifiable Value Number

attribute Range Mean of stands Sitea References

Stand density (no./ha)

Trees 3 cm d.b.h. 5160–5895 5530 2 EG Olmsted et al. 1980

Trees 3 cm d.b.h.

and .6 m height 8325–14820 11570 2 EG Olmsted et al. 1980

Trees .6 m height 161,835–210,500 186,165 2 EG Olmsted et al. 1980

Trees ›6 cm d.b.h. 15000 1 MR Alexander 1967

Stand basal area (m2

/ha)

Trees ›3 cm d.b.h. 44–91 68 2 EG Olmsted et al. 1980

Trees ›6 cm d.b.h. 57 1 MR Alexander 1967

Age of large trees (yrs)

All species 100–200 150 UNb EG Tyrell 1992

All species 200 4 EG Craighead 1971

Swietenia mahagoni Jacq. 225 UN EG Wade et al. 1980

S. mahagoni 200 UN EG Craighead and Gilbert 1962

Maximum d.b.h. (cm)

All trees 122–183 152 UN EG Craighead 1971

All trees 72–91 82 5 EG Gantz 1971

Olmsted et al. 1980

Bursera simaruba (L.) Sarg. 100 UN Long and Lakela 1976

B. simaruba 91 UN UK Bureau of Land & Water

Mgmt. 1976

Ficus aurea Nutt. 152 UN Small 1929

Mastichodendron foetidissimum

(Jacq). H.J. Lam 152 UN Small 1929

Metopium toxiferum (L.) Krug

& Urban 48 1 UK Author's data

S. mahagoni 150 1 EG Robertson 1962

S. mahagoni 37–42 40 UN LG Olmsted et al. 1981

a

 EG = Everglades, MR = Miami rock ridge, UK = upper Keys, LG = lower Glades.

b

 UN = Unknown.
7

Indicator Species

Live oak, wild-tamarind, and mahogany do not reproduce

in the shade of old-growth hammocks but rather persist as

large individuals only. Large individuals in the upper

canopy and a lack of small individuals of these species in

the shady interior of the hammock indicate old-growth

conditions. Another striking feature of old-growth stands is

naked stems of vines hanging from the upper crowns 39 to

49 feet (12 to 15 m) above the forest floor (Simpson 1920).

Old growth also has fewer epiphytes than other hammocks

because of the very dense shade. Tree snails (Liguus spp.)

were once native to all hammocks where a closed canopy

maintained the moist, shady microclimate required to

promote the growth of the fungi and algae upon which they

fed. Although not restricted to old growth, tree snails

should be present in such stands. 

Past History

There are few stands of tropical hardwoods left in Florida

undisturbed by humans. The large mastic, mahogany, and

other species were selectively harvested for shipbuilding in

the 1800's. Because of its toxic effect on humans,

poisonwood has been selectively removed from many

forests. Wood carvers and collectors have scavenged the

downed logs from most areas. Many areas were also

cleared for agriculture sometime during the last 300 years.

Hammock vegetation will quickly reinvade abandoned

areas if fire has not destroyed the organic soil substratum.

Many of the trees grow rapidly and can reach heights of 39

feet (12 m) in 25 years. It takes much longer, however, for

old-growth characteristics to develop (150 to 200 years).

An example of a stand that meets the minimum

qualifications for old growth is Chastain hammock on

North Key Largo. Jeanne Parks1

 has observed other stands

in the area that also qualify as old-growth hammock

vegetation. The best remaining example of old-growth

hardwood hammock is on Lignumvitae Key State

Botanical Site. Other old-growth stands such as Royal

Palm and Mahogany hammocks in Everglades National

Park and Castellow and Matheson hammocks in Miami,

were severely damaged by Hurricane Andrew and it will

take several years for them to recover (Jewell 1993).

Management Recommendations

Tropical hammocks of south Florida are a unique and

important community that humans have severely depleted,

primarily by urban development, making management of

the remaining areas especially critical. After first

protecting the area from future development, the key to

maintaining this community is fire control. Fires need to be

excluded during the winter months when natural fires

rarely occur and hammock soils are dry enough to be

totally combusted. Fragmentation of hammocks by power

lines, roads, etc., should be avoided also because these

artificial openings increase the severity of hurricane

damage (Craighead and Gilbert 1962, Craighead 1974).

Old-growth hammocks also need to be established across

the entire former range of tropical hammocks. This will

provide habitat for species that inhabit only certain areas

and will increase the probability that some old-growth

stands will survive major hurricanes.

Literature Cited

Alexander, T.R. 1958. High hammock vegetation of the southern Florida

mainland. Q. J. Florida Acad. of Sci. 21:293-298.

Alexander, T.R. 1967. A tropical hammock on the Miami (Florida)

limestone--a twenty-five-year study. Ecology 48:863-867.

Austin, D.F., K. Coleman-Marois, and D.R. Richardson. 1977. Vegetation

of southeastern Florida. Florida Sci. 40(4):331-361.

Bureau of Land and Water Management. 1976. The conservation and

management of tropical hardwood hammocks in the Florida keys.

Tech. Assist. Rep. prepared in coop. with Monroe Co. (Florida) Plann.

and Zoning Dep. 24 p.

Carr, A. 1973. The Everglades. Time-Life Books, New York. 184 p.

Craighead, F.C., Sr. 1971. The trees of south Florida, Vol. 1. The natural

environments and their succession. Univ. of Miami Press, Coral

Gables, FL. 212 p.

Craighead, F.C., Sr. 1974. Hammocks of south Florida. P. 53-60 in

Environment of south Florida: Present and past, Gleason, P.J., (comp.

and ed.). Miami Geol. Soc., Miami.

Craighead, F.C., Sr., and V.C. Gilbert. 1962. The effects of Hurricane

Donna on the vegetation of southern Florida. Q. J. Florida Acad. of Sci.

25(1):1-28.

Davis, J.J. 1943. The natural features of southern Florida. Florida Geol.

Surv. Bull. 25. 311 p. 

Duever, L.C., J.F. Meeder, and M.J. Duever. 1982. Ecological portion

Florida peninsula natural region theme study. Natl. Audubon Soc.

Ecosystem Res. Unit. Naples, FL. 

Duever, N.J., et al. 1986. The Big Cypress National Preserve. Res. Rep.

No. 8, Natl. Audubon Soc., New York. 455 p.

Eyre, F.H. 1980. Forest cover types of the United States and Canada. Soc.

Am. For., Washington, DC. 148 p. 1

 Personal communication. 1993. Jeanne Parks, Biologist, Key Largo

Hammocks State Botanical Site, P.O. Box 487, Key Largo, FL 33037.
8

Fenneman, N.M. 1938. Physiography of Eastern United States. McGrawHill Book Co., New York. 714 p.

Gantz, C.O. 1971. A naturalist is southern Florida. Univ. of Miami, Coral

Gables, FL. 171 p.

Gentry, R.C. 1974. Hurricanes in south Florida. P. 73-81 in Environment

of south Florida: Present and past, Gleason, P.J., (ed.). Miami Geol.

Soc., Miami. 

Gifford, J.G. 1911. The everglades and southern Florida. Everglade Land

Sales, Miami. 185 p.

Harper, R.M. 1927. Natural resources of southern Florida. P. 27-206 in

Florida geologic survey 18th annual rep. The State Geol. Surv.,

Tallahassee, FL.

Harshberger, J.W. 1914. The vegetation of south Florida. Trans. of

Wagner Free Inst. of Sci., Philadelphia. 3:51-189.

Jewell, S.D. 1993. Exploring wild south Florida. Pineapple Press Inc.,

Sarasota, FL. 224 p.

Little, E.L., Jr. 1979. Checklist of United States trees (native and

naturalized). U.S. Dep. Agric. Handb. 541. 375 p.

Long, R.W., and O. Lakela. 1979. A flora of tropical Florida. Banyan

Books, Miami. 962 p.

Olmsted, I.C., L.L. Loope, and C.E. Hilsenbeck. 1980. Tropical hardwood

hammocks of the interior of Everglades National Park and Big Cypress

National Preserve. Everglades Natl. Park South Fla. Res. Cent. Rep.

No. T-604. 58 p.

Olmsted, I.C., L.L. Loope, and R.P. Russell. 1981. Vegetation of the

southern coastal region of Everglades National Park between Flamingo

and Joe Bay. Everglades Natl. Park South Fla. Res. Cent. Rep. No. T620. 18 p.

Olmsted, I.C., W.B. Robertson, J. Johnson, and O.L. Bass, Jr. 1983. The

vegetation of Long Pine Key, Everglades National Park. Everglades

Natl. Park South Fla. Res. Cent. Rep. No. SFRC-83/05. 64 p.

Phillips, W.S. 1940. A tropical hammock on the Miami (Florida)

limestone. Ecology 21(2):166-175.

Richardson, D.R. 1977. Vegetation of the Atlantic coastal ridge of Palm

Beach County, FL. Florida Sci. 40(4):281-330.

Robertson, W.B., Jr. 1962. Fire and vegetation in the Everglades. Proc. of

Tall Timbers fire ecology conf. 1:67-80.

Ross, M.S., J.J. O'Brien, and L.J. Flynn. 1992. Ecological site

classification of Florida Keys terrestrial habitats. Biotropica 24(4):488-

502.

Sand, G.X. 1971. The everglades today; endangered wilderness. Four

Winds Press, New York. 191 p.

Schomer, N.S., and R.D. Drew. 1982. An ecological characterization of

the Lower Everglades, Florida Bay and the Florida Keys. U.S. Fish and

Wildl. Serv., Washington, DC. FWS/OBS-82/58.1. 246 p.

Scurlock, J.P. 1987. Native trees and shrubs of the Florida Keys. Laurel

Press Inc., Bethel Park, PA. 220 p.

Simpson, C.T. 1920. In lower Florida wilds. G.P. Putnam's Sons, New

York. 393 p.

Small, J.K. 1909. Exploration in the Everglades. J. N.Y. Bot. Gard. 10:48-

55.

Small, J.K. 1916. A cruise to the Cape Sable region of Florida. J. N.Y.

Bot. Gard. 17:189-202.

Small, J.K. 1922. The botanical fountain of youth. J. N.Y. Bot. Gard.

23:117-155.

Small, J.K. 1929. From Eden to Sahara, Florida's tragedy. Sci. Press,

Lancaster, PA. 

Snyder, J.R., A. Herndon, and W.B. Robertson, Jr. 1990. South Florida

rockland. P. 230-277 in Ecosystems of Florida, Myers, R.L., and J.J.

Ewel (eds.). Central Fla. Press, Orlando, FL.

Stevenson, G.B. 1992. Trees of Everglades National Park and the Florida

Keys. Fla. Natl. Parks and Monuments Assoc., Inc., Homestead, FL. 31

p.

Tyrrell, L.E. 1992. Characteristics, distribution, and management of oldgrowth forests on units of the U.S. National Park Service: Results of a

questionnaire. Natl. Areas J. 12(4):198-205. 

Wade, D., J. Ewel, and R. Hofstetter. 1980. Fire in south Florida

ecosystems. U.S. Dep. Agric. For. Serv. Gen. Tech. Rep. SE-17. 125 p.

Weiner, A.H. 1979. The hardwood hammocks of the Florida Keys: An

ecological study. Natl. Audubon Soc. and Fla. Keys Land Trust.

Woodall, S.L. 1980. Tropical hardwoods. P. 76 in Forest cover types of

the United States and Canada, Eyre, F.H. (ed.). Soc. Am. For.,

Washington, DC.
Outcalt, Kenneth W. 1997. An old-growth definition for tropical and subtropical forests

in Florida. Gen. Tech. Rep. SRS-13. Asheville, NC: U.S. Department of Agriculture,

Forest Service, Southern Research Station. 8 p.

Tropical and subtropical hardwoods form characteristic hammock communities on

organic soils overlying the higher areas of limestone bedrock in south Florida, including

the Keys, where freezing temperatures occur infrequently. The highly diverse woody

vegetation in this community, predominantly of West Indian origin, attains its greatest

stature in the Miami area where rainfall is most plentiful. Old-growth stands have a

dense, closed canopy with some trees at least 16 inches in diameter and over 100 years

old. The dense canopy produces a shady twilight-like interior with a relatively open

forest floor. Fairly good examples of old growth with minimal past disturbances remain

on Lignumvitae Key and North Key Largo.

Keywords: Everglades, Florida, hammock, old growth, subtropical, tropical.
The Forest Service, U.S. Department of

Agriculture, is dedicated to the principle of

multiple use management of the Nation’s

forest resources for sustained yields of wood, water,

forage, wildlife, and recreation. Through forestry research,

cooperation with the States and private forest owners, and

management of the National Forests and National

Grasslands, it strives—as directed by Congress—to

provide increasingly greater service to a growing Nation.

The United States Department of Agriculture (USDA)

prohibits discrimination in its programs on the basis of

race, color, national origin, sex, religion, age, disability,

political beliefs, and marital or familial status. (Not all

prohibited bases apply to all programs). Persons with

disabilities who require alternative means for

communication of program information (braille, large

print, audiotape, etc.) should contact USDA’s TARGET

Center at 202-720-2600 (voice and TDD). To file a

complaint, write the Secretary of Agriculture, U.S.

Department of Agriculture, Washington, DC 20250, or call

1-800-245-6340 (voice) or 202-720-1127 (TDD). USDA is

an equal employment opportunity employer.