patrickbdevaney/mia9 · Datasets at Hugging Face

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2.4.2 Subcanopy
The subcanopy of pine rocklands consists of a diverse mix of temperate and tropical hardwoods
and palms. Almost 100 native plant species may be present in the subcanopy of Miami-Dade’s
pine rocklands (Bradley, unpublished data). Palms in this layer, all fairly common, include saw
palmetto, cabbage palm, and silver palm, with saw palmetto being the most common and
typically a dominant species in all pine rockland areas. Where pine rocklands historically
experienced seasonal flooding, or had a shallow depth to the water table, cabbage palm becomes
a more dominant species.
Common hardwoods in pine rocklands presently include live oak, poisonwood, southern sumac,
white indigo berry, myrsine, West Indian-lilac, snowberry, nettletree, rough velvetseed, and
willow bustic (Bradley, unpublished data). The ratio of temperate species to tropical species
declines from north to south, with many temperate species becoming absent towards the southern
end of the Miami Rock Ridge, and many tropical species becoming absent to the north. The
subcanopy in the north may resemble a central Florida sandhill more than a pine rockland further
south on the ridge. Historical composition and relative abundance of understory hardwoods may
have differed from current coverage.
In addition to the above hardwoods there are many small shrubs or sub-woody species that can
be conspicuous components of pine rocklands. These include lacy bracken fern, dwarf live oak,
pineland croton, pineland snowberry, partridge pea, and wild sage.
Subcanopy height and density varies temporally and spatially depending on time since fire,
freezes, and distance to rockland hammock communities. Fires, discussed in more detail in
Section 2.6.1 below, historically occur naturally every three (3) to seven (7) years and kill or topkill hardwoods. Freezes and cold weather kill or top-kill more sensitive tropical hardwoods such
as poisonwood and West Indian-lilac (Olmsted et al. 1993). Diversity and stem density of
hardwoods is usually higher in close proximity to rockland hammocks, which serve as a source
for seed rain into the pine rocklands.
No historical data are known that quantified the original density of palms and hardwoods in pine
rockland prior to non-indigenous settlement. Photos from the early 1900s show areas with a very
low palm/shrub layer (less than two feet), but it is difficult to know how representative these
photos are of pine rocklands as a whole (Appendix B). Pine rocklands probably had a subcanopy
layer mostly less than two (2) feet tall. Overall cover of palms and shrubs was probably less thas
25%, with a great degree of patchiness resulting in some very open areas and some very dense
areas.
2.4.3 Herb Layer
Over 225 species of herbs may be found in the pine rocklands of Miami-Dade County (Bradley,
unpublished data). The herb layer consists of forbs, grasses, ferns, and sedges. This herb layer is
much more diverse and has a greater cover where the subcanopy layer is sparse. This herb layer,
much like the subcanopy, consists of temperate and tropical species, but also has a component of
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 8
endemic species. At present, the most common herbs in Miami-Dade County pine rocklands, in
descending order, are pine fern, low rattlebox, Florida five-petalled leafflower, rhizomatous
bluestem, coastal bedstraw, three-seeded mercury, crimson bluestem, pitted stripeseed, Florida
whitetop, and wire bluestem (Bradley, unpublished data). The composition and relative
abundance of herbs in MDC pine rocklands may have differed historically from present
populations.
Composition of the herb layer varies greatly with geographic location, soils, and hydrology. Like
the subcanopy, more temperate species are to the north and tropical species to the south. The
herb layer in sandy areas of the northern Biscayne pinelands may resemble central Florida
sandhill ecosystems. Low elevation areas that flooded seasonally consist of plant species that are
common in marl prairies, such as rhizomatous bluestem, muhlygrass, sawgrass, and starrush
whitetop.
The diversity and density of the herb layer is reduced in areas of heavy hardwood density, such
as near rockland hammocks. Hardwoods limit the herb layer by limiting sunlight penetration to
the ground and by producing a layer of leaf litter that can smother small herbs and limit their
germination.
2.5 Association with Other Habitat Types
Prior to non-indigenous settlement of Miami-Dade County, pine rockland habitat was the
dominant plant community on the Miami Rock Ridge. Pine rocklands merged into other habitats,
and under proper circumstances succeeded to or from these other habitats. Ecotones between
pine rockland and other habitats were historically important habitat for many plant and animal
species.
Rockland hammocks historically occurred across the range of pine rocklands in Miami-Dade
County. Rockland hammocks are closed canopy hardwood forests usually dominated by tropical
tree species and the temperate live oak. Rockland hammocks covered small areas of a few acres
up to several hundred acres. They occurred in areas that were protected from the fires that burned
pine rocklands, typically on the edges of wetlands or in association with abundant solution holes
in the oolitic limestone. Pine rockland can succeed into rockland hammock in the absence of fire,
and rockland hammocks can succeed into pine rockland with frequent fires. Many plant species
grow primarily at the ecotone between pine rockland and rockland hammock, including several
that are now rare or imperiled. The ecotone was also very important for wildlife, which used both
ecosystems. The rockland hammock ecosystem is discussed as an independent chapter in this
management plan.
Alexander (1967) reported results of a 25-year study on pine rockland to rockland hammock
succession. He reports:
“…a complete change from pineland fire-climax to a well-established climatic climax of
West Indian tropical flora with Lysiloma bahamensis acting as the invader tree can occur
in 25 years in southern Florida.”
This statement that pine rocklands can succeed to rockland hammocks within two (2) to three (3)
decades of fire suppression has been mistakenly inferred by many readers. While pine rocklands
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 9
are fire climax communities, that is, pinelands thrive in an ecosystem subjected to a natural
frequency of fires, Alexander’s statement may not be applicable to all pine rocklands in MiamiDade County. Alexander’s results, while accurate for his study, cannot be extrapolated to most
pine rockland fragments since his study site was right between two hammocks. Most pine
rockland sites in the County occur far away from hammocks.
Alexander’s study area, established by Phillips (1940) 25 years previously, was situated between
Castellow and Ross Hammocks, which were only separated by about 500 feet. This 500 foot gap
was filled with a narrow strip of pine rockland. Succession between the Phillips and Alexander
studies was undoubtedly rapid due to heavy seed rain from the adjacent hammocks. Hardwood
stem densities, (e.g. false tamarind) may have been high at the study site even before fire
suppression. Stem densities are typically higher adjacent to rocklands because of heavy seed
rain, but frequent fires keep overall biomass low.
Long-term fire suppression in other pine rockland sites has resulted in conditions similar to
Alexander’s at only a few sites – all adjacent to rockland hammocks. The Camp Owaissa Bauer
Addition EEL site serves as an example. Even in this situation, the succeeded flora consists of a
low diversity of trees, shrubs, and herbs and does not approach the biological diversity of mature
rockland hammocks. This can be observed in the vicinity of Alexander’s study. The area is
dominated by wild tamarind and several other hardwoods, but vegetation structure and
composition is clearly distinct form the interiors of the adjacent hammocks.
More typically, pine rocklands that have been fire suppressed and are not close to rockland

2.4.2 Subcanopy

The subcanopy of pine rocklands consists of a diverse mix of temperate and tropical hardwoods

and palms. Almost 100 native plant species may be present in the subcanopy of Miami-Dade’s

pine rocklands (Bradley, unpublished data). Palms in this layer, all fairly common, include saw

palmetto, cabbage palm, and silver palm, with saw palmetto being the most common and

typically a dominant species in all pine rockland areas. Where pine rocklands historically

experienced seasonal flooding, or had a shallow depth to the water table, cabbage palm becomes

a more dominant species.

Common hardwoods in pine rocklands presently include live oak, poisonwood, southern sumac,

white indigo berry, myrsine, West Indian-lilac, snowberry, nettletree, rough velvetseed, and

willow bustic (Bradley, unpublished data). The ratio of temperate species to tropical species

declines from north to south, with many temperate species becoming absent towards the southern

end of the Miami Rock Ridge, and many tropical species becoming absent to the north. The

subcanopy in the north may resemble a central Florida sandhill more than a pine rockland further

south on the ridge. Historical composition and relative abundance of understory hardwoods may

have differed from current coverage.

In addition to the above hardwoods there are many small shrubs or sub-woody species that can

be conspicuous components of pine rocklands. These include lacy bracken fern, dwarf live oak,

pineland croton, pineland snowberry, partridge pea, and wild sage.

Subcanopy height and density varies temporally and spatially depending on time since fire,

freezes, and distance to rockland hammock communities. Fires, discussed in more detail in

Section 2.6.1 below, historically occur naturally every three (3) to seven (7) years and kill or topkill hardwoods. Freezes and cold weather kill or top-kill more sensitive tropical hardwoods such

as poisonwood and West Indian-lilac (Olmsted et al. 1993). Diversity and stem density of

hardwoods is usually higher in close proximity to rockland hammocks, which serve as a source

for seed rain into the pine rocklands.

No historical data are known that quantified the original density of palms and hardwoods in pine

rockland prior to non-indigenous settlement. Photos from the early 1900s show areas with a very

low palm/shrub layer (less than two feet), but it is difficult to know how representative these

photos are of pine rocklands as a whole (Appendix B). Pine rocklands probably had a subcanopy

layer mostly less than two (2) feet tall. Overall cover of palms and shrubs was probably less thas

25%, with a great degree of patchiness resulting in some very open areas and some very dense

areas.

2.4.3 Herb Layer

Over 225 species of herbs may be found in the pine rocklands of Miami-Dade County (Bradley,

unpublished data). The herb layer consists of forbs, grasses, ferns, and sedges. This herb layer is

much more diverse and has a greater cover where the subcanopy layer is sparse. This herb layer,

much like the subcanopy, consists of temperate and tropical species, but also has a component of

EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________

Page 8

endemic species. At present, the most common herbs in Miami-Dade County pine rocklands, in

descending order, are pine fern, low rattlebox, Florida five-petalled leafflower, rhizomatous

bluestem, coastal bedstraw, three-seeded mercury, crimson bluestem, pitted stripeseed, Florida

whitetop, and wire bluestem (Bradley, unpublished data). The composition and relative

abundance of herbs in MDC pine rocklands may have differed historically from present

populations.

Composition of the herb layer varies greatly with geographic location, soils, and hydrology. Like

the subcanopy, more temperate species are to the north and tropical species to the south. The

herb layer in sandy areas of the northern Biscayne pinelands may resemble central Florida

sandhill ecosystems. Low elevation areas that flooded seasonally consist of plant species that are

common in marl prairies, such as rhizomatous bluestem, muhlygrass, sawgrass, and starrush

whitetop.

The diversity and density of the herb layer is reduced in areas of heavy hardwood density, such

as near rockland hammocks. Hardwoods limit the herb layer by limiting sunlight penetration to

the ground and by producing a layer of leaf litter that can smother small herbs and limit their

germination.

2.5 Association with Other Habitat Types

Prior to non-indigenous settlement of Miami-Dade County, pine rockland habitat was the

dominant plant community on the Miami Rock Ridge. Pine rocklands merged into other habitats,

and under proper circumstances succeeded to or from these other habitats. Ecotones between

pine rockland and other habitats were historically important habitat for many plant and animal

species.

Rockland hammocks historically occurred across the range of pine rocklands in Miami-Dade

County. Rockland hammocks are closed canopy hardwood forests usually dominated by tropical

tree species and the temperate live oak. Rockland hammocks covered small areas of a few acres

up to several hundred acres. They occurred in areas that were protected from the fires that burned

pine rocklands, typically on the edges of wetlands or in association with abundant solution holes

in the oolitic limestone. Pine rockland can succeed into rockland hammock in the absence of fire,

and rockland hammocks can succeed into pine rockland with frequent fires. Many plant species

grow primarily at the ecotone between pine rockland and rockland hammock, including several

that are now rare or imperiled. The ecotone was also very important for wildlife, which used both

ecosystems. The rockland hammock ecosystem is discussed as an independent chapter in this

management plan.

Alexander (1967) reported results of a 25-year study on pine rockland to rockland hammock

succession. He reports:

“…a complete change from pineland fire-climax to a well-established climatic climax of

West Indian tropical flora with Lysiloma bahamensis acting as the invader tree can occur

in 25 years in southern Florida.”

This statement that pine rocklands can succeed to rockland hammocks within two (2) to three (3)

decades of fire suppression has been mistakenly inferred by many readers. While pine rocklands

EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________

Page 9

are fire climax communities, that is, pinelands thrive in an ecosystem subjected to a natural

frequency of fires, Alexander’s statement may not be applicable to all pine rocklands in MiamiDade County. Alexander’s results, while accurate for his study, cannot be extrapolated to most

pine rockland fragments since his study site was right between two hammocks. Most pine

rockland sites in the County occur far away from hammocks.

Alexander’s study area, established by Phillips (1940) 25 years previously, was situated between

Castellow and Ross Hammocks, which were only separated by about 500 feet. This 500 foot gap

was filled with a narrow strip of pine rockland. Succession between the Phillips and Alexander

studies was undoubtedly rapid due to heavy seed rain from the adjacent hammocks. Hardwood

stem densities, (e.g. false tamarind) may have been high at the study site even before fire

suppression. Stem densities are typically higher adjacent to rocklands because of heavy seed

rain, but frequent fires keep overall biomass low.

Long-term fire suppression in other pine rockland sites has resulted in conditions similar to

Alexander’s at only a few sites – all adjacent to rockland hammocks. The Camp Owaissa Bauer

Addition EEL site serves as an example. Even in this situation, the succeeded flora consists of a

low diversity of trees, shrubs, and herbs and does not approach the biological diversity of mature

rockland hammocks. This can be observed in the vicinity of Alexander’s study. The area is

dominated by wild tamarind and several other hardwoods, but vegetation structure and

composition is clearly distinct form the interiors of the adjacent hammocks.

More typically, pine rocklands that have been fire suppressed and are not close to rockland