patrickbdevaney/mia9 · Datasets at Hugging Face

text stringlengths 0 6.44k
hardwoods at low stem densities. Other sites, such as Navy Wells #23, are probably very
different than they were historically. This site now has a tall understory of hardwoods with a
very high stem density.
3.4.3 Herb Layer
The herb layer naturally has the highest diversity of plant species and a diverse array of rare
plant species. Like the subcanopy layer, the herb layer varies greatly between forest fragments.
Some sites that burned frequently and have sparse subcanopy layers have diverse herb layers.
Other sites with dense subcanopies that result in low light penetration and thick duff
accumulations have lost almost all herbaceous species. The overall herb layer in pine rockland
fragments has been degraded, with a loss in density and diversity.
3.4.4 Edges
Historically, edges in the pine rockland ecosystem were limited to ecotones with other habitat
types, especially rockland hammocks and marl prairies (see Sections 2.5 above and 3.5 below).
Because of forest fragmentation, all pine rockland fragments now have edges with artificial
communities, including lawns, agricultural fields, roads, and other vacant land. Edges create a
unique ecotone that can have impacts to the interior of natural sites (See Part I). Edges of pine
rockland fragments vary greatly in vegetation structure and composition, depending upon fire
history, soil disturbance, and management history. These edges typically have dense growths of
exotic and ruderal plant species. Abundant exotic plants include Brazilian pepper and Burma
reed. Initial establishment of these exotic plants on edges allows their population sizes to build in
disturbed soils, and then intact pine rocklands in the interior of the sites are subsequently invaded
due to a heavy seed rain.
3.5 Association with Other Habitat Types
As discussed in Section 2.5, pine rockland was historically associated with other habitat types,
especially rockland hammock and marl prairie. Today, most preserves have only a single habitat
type and have no natural ecotones with other habitats. Exceptions on EEL sites include Silver
Palm Groves, which has a small rockland hammock, and Nixon Smiley Pineland Addition,
which has several small marl prairies. The loss of ecotone habitat has resulted in the loss of many
populations of plant species restricted to the habitat, and has probably reduced the value of pine
rockland for some wildlife species.
3.6 Successional Processes Under Current Conditions
Because of forest fragmentation, human intervention, and a mosaic of urban lands between pine
rockland fragments, successional processes now differ than those discussed in Section 2.6. These
changes are discussed below.
3.6.1 Fire
Since pine rocklands are fire climax communities, natural fire frequency is of great importance.
However, fire periodicity, behavior, and intensity have all been changed on pine rockland
fragments. Under historical conditions, pine rockland fragments burned every three (3) to seven
(7) years, often in large landscape-scale, wind-driven fires. These fires were usually in the spring
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 17
or summer. Following fragmentation, fire periodicity has lengthened considerably at most sites.
Fire has been completely eliminated at some sites. This change can be attributed to two causes:
intentional fire suppression by people and the elimination of large scale landscape-level fires
because of the destruction of natural areas.
In addition to periodicity, fire behavior has changed. Natural fires were usually wind-driven head
fires that were ignited by lightning. Fires now start for a variety of reasons, including lightning,
arson, accident, and by prescription. Many fires, especially prescribed fires, are backing fires
burning into the wind. These are slow moving fires and can damage feeder roots of many plants.
They are typically used because they are easier to control.
Fire intensity has changed with the reduction in fire periodicity. Heavier fuel buildups between
fires result in hotter temperatures and higher flames. Intense fires can have long-lasting impacts
when they occur. Fires that are too intense can result in massive mortality of pines, saw
palmettos, understory hardwoods, and herbs. Following the fires, sites can be invaded more
readily by exotic pest plant species, especially natal grass, and ruderal species. Long term
vegetation recovery following intense fires has not been studied.
3.6.2 Tropical Cyclones
There has been much recent discussion about global warming and hurricane activity. Some argue
that global warming is resulting in stronger, more intense tropical cyclones (Webster et al. 2005).
Some, however, argue against this (Hoyos et al. 2006). Regardless of this debate, the widespread
changes in the overall landscape of Miami-Dade County and the changes to pine rockland
communities result in different effects of tropical cyclones on the pine rockland ecosystem.
Under natural conditions (see Section 2.6.2) hurricanes can cause mortality of some pine trees,
but mortality rates are fairly low in large pine rockland areas like Long Pine Key in ENP (Platt et
al. 2000). Outside of the national park, Hurricane Andrew in 1992 resulted in the mortality of
almost 100% of the pine canopy of most forest fragments. While hurricane winds killed many
trees, the main source of mortality was a widespread outbreak of a variety of beetles and weevils
in the weakened trees after the storm, including Ips species (I. calligraphis, I. avulsus, and I.
grandicollis), Hylobius pales, and Pachylobius picivoris (DERM 1995). This massive outbreak
did not occur in ENP. It has been hypothesized that the damage to urban fragments was due to
higher stress levels on pine trees due to decreased water levels, pollutants, fragmentation, and
altered fire regime (DERM 1995, Doren 1993).
Logging of pine trees in the 1930s and 1940s resulted in a mainly even-aged stand of pine trees
in most forest fragments. Most pine rockland sites before Hurricane Andrew had mature pines;
few sites had a varied stand age consisting of mature, sapling, and seedling trees. Once Hurricane
Andrew’s winds killed trees and subsequent insect outbreaks killed remaining adults, no young
pines were present in the subcanopy to replace the dead adults.
3.6.3 Human Controlled Processes
In some pine rockland fragments, hardwood removal has been done to either replace fire or
prepare a site for prescribed fire. For example, hardwoods in the pine rockland at Camp Owaissa
Bauer, a preserve managed by the Miami-Dade County Parks Department, were removed by
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 18
hand to prepare the site for prescribed fire. Timber thinning and mechanical hardwood removal
have not been attempted in Miami-Dade’s pine rocklands.
3.7 Rare Organisms
Despite the very small area of remaining
pine rockland, only a few species have been
documented as lost from the habitat.
However, many species are considered to
be in precarious conditions and could easily
be lost in the near future.
3.7.1 Plants
Pine rocklands are habitat to a large number
of rare organisms, including species that are
considered by one or more agencies and
organizations as Endangered, Threatened,
or Critically Imperiled. These plant species are now rare because of extensive habitat loss due to
development, fire suppression, exotic plant invasions, and poaching. The natural range of some
of these plant species does not extend south as far as ENP, and therefore, they only exist in pine

hardwoods at low stem densities. Other sites, such as Navy Wells #23, are probably very

different than they were historically. This site now has a tall understory of hardwoods with a

very high stem density.

3.4.3 Herb Layer

The herb layer naturally has the highest diversity of plant species and a diverse array of rare

plant species. Like the subcanopy layer, the herb layer varies greatly between forest fragments.

Some sites that burned frequently and have sparse subcanopy layers have diverse herb layers.

Other sites with dense subcanopies that result in low light penetration and thick duff

accumulations have lost almost all herbaceous species. The overall herb layer in pine rockland

fragments has been degraded, with a loss in density and diversity.

3.4.4 Edges

Historically, edges in the pine rockland ecosystem were limited to ecotones with other habitat

types, especially rockland hammocks and marl prairies (see Sections 2.5 above and 3.5 below).

Because of forest fragmentation, all pine rockland fragments now have edges with artificial

communities, including lawns, agricultural fields, roads, and other vacant land. Edges create a

unique ecotone that can have impacts to the interior of natural sites (See Part I). Edges of pine

rockland fragments vary greatly in vegetation structure and composition, depending upon fire

history, soil disturbance, and management history. These edges typically have dense growths of

exotic and ruderal plant species. Abundant exotic plants include Brazilian pepper and Burma

reed. Initial establishment of these exotic plants on edges allows their population sizes to build in

disturbed soils, and then intact pine rocklands in the interior of the sites are subsequently invaded

due to a heavy seed rain.

3.5 Association with Other Habitat Types

As discussed in Section 2.5, pine rockland was historically associated with other habitat types,

especially rockland hammock and marl prairie. Today, most preserves have only a single habitat

type and have no natural ecotones with other habitats. Exceptions on EEL sites include Silver

Palm Groves, which has a small rockland hammock, and Nixon Smiley Pineland Addition,

which has several small marl prairies. The loss of ecotone habitat has resulted in the loss of many

populations of plant species restricted to the habitat, and has probably reduced the value of pine

rockland for some wildlife species.

3.6 Successional Processes Under Current Conditions

Because of forest fragmentation, human intervention, and a mosaic of urban lands between pine

rockland fragments, successional processes now differ than those discussed in Section 2.6. These

changes are discussed below.

3.6.1 Fire

Since pine rocklands are fire climax communities, natural fire frequency is of great importance.

However, fire periodicity, behavior, and intensity have all been changed on pine rockland

fragments. Under historical conditions, pine rockland fragments burned every three (3) to seven

(7) years, often in large landscape-scale, wind-driven fires. These fires were usually in the spring

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

Page 17

or summer. Following fragmentation, fire periodicity has lengthened considerably at most sites.

Fire has been completely eliminated at some sites. This change can be attributed to two causes:

intentional fire suppression by people and the elimination of large scale landscape-level fires

because of the destruction of natural areas.

In addition to periodicity, fire behavior has changed. Natural fires were usually wind-driven head

fires that were ignited by lightning. Fires now start for a variety of reasons, including lightning,

arson, accident, and by prescription. Many fires, especially prescribed fires, are backing fires

burning into the wind. These are slow moving fires and can damage feeder roots of many plants.

They are typically used because they are easier to control.

Fire intensity has changed with the reduction in fire periodicity. Heavier fuel buildups between

fires result in hotter temperatures and higher flames. Intense fires can have long-lasting impacts

when they occur. Fires that are too intense can result in massive mortality of pines, saw

palmettos, understory hardwoods, and herbs. Following the fires, sites can be invaded more

readily by exotic pest plant species, especially natal grass, and ruderal species. Long term

vegetation recovery following intense fires has not been studied.

3.6.2 Tropical Cyclones

There has been much recent discussion about global warming and hurricane activity. Some argue

that global warming is resulting in stronger, more intense tropical cyclones (Webster et al. 2005).

Some, however, argue against this (Hoyos et al. 2006). Regardless of this debate, the widespread

changes in the overall landscape of Miami-Dade County and the changes to pine rockland

communities result in different effects of tropical cyclones on the pine rockland ecosystem.

Under natural conditions (see Section 2.6.2) hurricanes can cause mortality of some pine trees,

but mortality rates are fairly low in large pine rockland areas like Long Pine Key in ENP (Platt et

al. 2000). Outside of the national park, Hurricane Andrew in 1992 resulted in the mortality of

almost 100% of the pine canopy of most forest fragments. While hurricane winds killed many

trees, the main source of mortality was a widespread outbreak of a variety of beetles and weevils

in the weakened trees after the storm, including Ips species (I. calligraphis, I. avulsus, and I.

grandicollis), Hylobius pales, and Pachylobius picivoris (DERM 1995). This massive outbreak

did not occur in ENP. It has been hypothesized that the damage to urban fragments was due to

higher stress levels on pine trees due to decreased water levels, pollutants, fragmentation, and

altered fire regime (DERM 1995, Doren 1993).

Logging of pine trees in the 1930s and 1940s resulted in a mainly even-aged stand of pine trees

in most forest fragments. Most pine rockland sites before Hurricane Andrew had mature pines;

few sites had a varied stand age consisting of mature, sapling, and seedling trees. Once Hurricane

Andrew’s winds killed trees and subsequent insect outbreaks killed remaining adults, no young

pines were present in the subcanopy to replace the dead adults.

3.6.3 Human Controlled Processes

In some pine rockland fragments, hardwood removal has been done to either replace fire or

prepare a site for prescribed fire. For example, hardwoods in the pine rockland at Camp Owaissa

Bauer, a preserve managed by the Miami-Dade County Parks Department, were removed by

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

Page 18

hand to prepare the site for prescribed fire. Timber thinning and mechanical hardwood removal

have not been attempted in Miami-Dade’s pine rocklands.

3.7 Rare Organisms

Despite the very small area of remaining

pine rockland, only a few species have been

documented as lost from the habitat.

However, many species are considered to

be in precarious conditions and could easily

be lost in the near future.

3.7.1 Plants

Pine rocklands are habitat to a large number

of rare organisms, including species that are

considered by one or more agencies and

organizations as Endangered, Threatened,

or Critically Imperiled. These plant species are now rare because of extensive habitat loss due to

development, fire suppression, exotic plant invasions, and poaching. The natural range of some

of these plant species does not extend south as far as ENP, and therefore, they only exist in pine