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3.1 Current Distribution of Pine Rocklands
The distribution of the pine rockland ecosystem has declined dramatically following nonindigenous settlement. At present conditions, almost 84% of the historic Miami Rock Ridge
(approximately 126,500 acres), is now covered by agriculture, suburban lands, or urban lands,
with only small isolated areas of natural vegetation still existing. The remaining portion of the
ridge (approximately 24,500 acres) is located within ENP (Figure 2). A survey conducted from
2004 to 2005 of all remaining forest fragments in Miami-Dade County outside of ENP found that
only 1.8% of the historical extent of pine rocklands remained (Bradley, unpublished data). Only
2,273 acres of the historical estimate acreage of pine rocklands were found to remain. The
geographic range of pine rocklands has been reduced as well – the northern 12 miles of the
Miami Rock Ridge have been completely developed.
In 2005 there were 126 pine rockland fragments in Miami-Dade County outside of ENP
(Bradley, unpublished data). These fragments ranged from 0.25 acres to 800 acres, with a mean
size of 15.6 acres and a median size of 4.3 acres. Figure 2 shows the current versus historical
pine rockland habitat distribution in Miami-Dade County.
3.2 Physiography
Today’s level of human population and urban development in Miami-Dade County was made
possible by a significant effort to drain the landscape. This drainage and dewatering process
brought about other changes that are briefly discussed in the following sections.
3.2.1 Soils
Pine rockland soils are generally unchanged from historical conditions. Because the dominant
substrate of pine rocklands is oolitic limestone, there is little that can be done to it. Pockets of
soil, either quartz sand or loam, cannot erode because they are in depressions in the limestone.
The largest change to pine rockland soils is the accumulation of duff and usually organic soil on
fire suppressed sites. Under historical conditions, periodic fires limited the growth of hardwood
species that produced leaf litter, and also burned any that did accumulate. On many sites this
organic layer is now several inches thick and completely covers the limestone substrate.
Soils may have also changed in pine rocklands that previously flooded for short periods during
the summer rainy season. Dry conditions tend to reduce organic accumulations, principally
because of the lack of protective soil moisture and increased combustion in fires.
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 13
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 14
3.2.2 Hydrology
The historical hydrology of Miami-Dade County has been dramatically and permanently altered.
The water table throughout the county has dropped due to wide-scale drainage projects (see Part
I of this management plan). The water table has decreased throughout the entire range of pine
rocklands. For many forest fragments at high elevations, this is probably not of ecological
significance. Some pine rocklands, however, were close to the water table and probably flooded
periodically (see section 2.2.3). With the lowered water table these sites never flood today and
many plant species’ roots probably no longer reach ground water.
3.2.3 Sea Level Rise
Sea level rise may become a major environmental concern in South Florida if projected trends
continue. The South Florida Regional Planning Council is anticipating a five (5) foot rise in sea
level over the next 200 years. Sea level rise has already been implicated in the reduction of pine
rockland habitat in the lower Florida Keys (Ross et al. 1994), and the complete loss of pine
rocklands on Key Largo (Alexander 1953).
Sea level rise in Miami-Dade County will initially impact only the few coastal pine rocklands,
especially the Deering South Addition, an EEL site on Biscayne Bay. Loss of the pine rockland
ecosystem will be initiated not by inundation, but by saltwater intrusion to the water table, killing
pine rockland plant species. A more detailed Geographic Information Systems (GIS) analysis is
needed, but many pine rocklands may not be impacted directly because of their high elevation
and inland locations.
3.3 Climate
It has been suggested that the climate of Miami-Dade County has changed with the drainage of
wetlands (Marshall and Pielke 2004). Marshall and Pielke have hypothesized that prior to
drainage, a persistent moisture flux from heat-retaining wetlands prevented freezing
temperatures. Post-drainage freezes may have become more common.
In contrast to the findings of Marshall and Pielke (2004), large cities, such as greater-Miami, are
known to act as heat islands because of the heat retention by manmade structures. Urban heat
islands can be as much as two (2) to ten (10) degrees warmer than surrounding areas. Global
warming is also a factor, which may raise temperatures in Miami-Dade County.
Changes in climate may have many effects, although they are hard to predict. Possible impacts
may be changes in flowering and fruiting phenology of plants, fewer (or more) freezes changing
hardwood subcanopy structure and composition, changes in soil moisture and thereby seed
germination, changes in plant respiration rates, and susceptibility to biological invasions by
exotic organisms.
3.4 Vegetation Structure and Composition
Although the same three vegetation layers are still conceptually present in existing fragments of
pine rocklands, in many cases they depart significantly from the original structure and species
EEL Program, Management Plan, Part II – Pine Rockland (DRAFT) _____________________________________________________________________________________________________________________
Page 15
richness. The following paragraphs describe some of the most relevant changes and use the
description made in the previous section for comparison purposes.
3.4.1 Canopy
The historical canopy of pine rocklands, consisting of South Florida slash pine, was significantly
altered following non-indigenous settlement. The first major impact to the pine canopy was
logging. Large scale logging took place in Miami-Dade County from the very early 1900s to the
1950s (Craighead, 1971, Wade et al. 1980, USFWS 2000). Although some small areas of Long
Pine Key in ENP were never logged, it is likely that all or nearly all areas of pine rockland
outside of the national park were logged. Craighead (1971) reports a discussion with a mill
owner in 1952 who stated that during World War II every pine that could be made into a 2x4 was
cut down.
Following the end of logging activities, the pine canopy recovered in most pine rockland
fragments by 1992, resulting in an even-aged stand of mature pines. In August 1992, Hurricane
Andrew hit South Florida, and in the two years following almost the entire canopy of pine in
Miami-Dade County outside of ENP was lost. 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).
In the mid 1990s, efforts were made to reestablish pine
trees on sites where they were lost. Pine seedlings were
planted on 22 preserves, including 12 EEL sites (Table
1). Many of these trees are now 6 to 15 feet tall. A
negative result of the reintroduction of pines has been
the establishment of extreme densities of trees in some
places due to overplanting. Mortality in many plantings
was much lower than anticipated. In addition, few sites
where pines have been planted have burned. Fires

3.1 Current Distribution of Pine Rocklands

The distribution of the pine rockland ecosystem has declined dramatically following nonindigenous settlement. At present conditions, almost 84% of the historic Miami Rock Ridge

(approximately 126,500 acres), is now covered by agriculture, suburban lands, or urban lands,

with only small isolated areas of natural vegetation still existing. The remaining portion of the

ridge (approximately 24,500 acres) is located within ENP (Figure 2). A survey conducted from

2004 to 2005 of all remaining forest fragments in Miami-Dade County outside of ENP found that

only 1.8% of the historical extent of pine rocklands remained (Bradley, unpublished data). Only

2,273 acres of the historical estimate acreage of pine rocklands were found to remain. The

geographic range of pine rocklands has been reduced as well – the northern 12 miles of the

Miami Rock Ridge have been completely developed.

In 2005 there were 126 pine rockland fragments in Miami-Dade County outside of ENP

(Bradley, unpublished data). These fragments ranged from 0.25 acres to 800 acres, with a mean

size of 15.6 acres and a median size of 4.3 acres. Figure 2 shows the current versus historical

pine rockland habitat distribution in Miami-Dade County.

3.2 Physiography

Today’s level of human population and urban development in Miami-Dade County was made

possible by a significant effort to drain the landscape. This drainage and dewatering process

brought about other changes that are briefly discussed in the following sections.

3.2.1 Soils

Pine rockland soils are generally unchanged from historical conditions. Because the dominant

substrate of pine rocklands is oolitic limestone, there is little that can be done to it. Pockets of

soil, either quartz sand or loam, cannot erode because they are in depressions in the limestone.

The largest change to pine rockland soils is the accumulation of duff and usually organic soil on

fire suppressed sites. Under historical conditions, periodic fires limited the growth of hardwood

species that produced leaf litter, and also burned any that did accumulate. On many sites this

organic layer is now several inches thick and completely covers the limestone substrate.

Soils may have also changed in pine rocklands that previously flooded for short periods during

the summer rainy season. Dry conditions tend to reduce organic accumulations, principally

because of the lack of protective soil moisture and increased combustion in fires.

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

Page 13

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

Page 14

3.2.2 Hydrology

The historical hydrology of Miami-Dade County has been dramatically and permanently altered.

The water table throughout the county has dropped due to wide-scale drainage projects (see Part

I of this management plan). The water table has decreased throughout the entire range of pine

rocklands. For many forest fragments at high elevations, this is probably not of ecological

significance. Some pine rocklands, however, were close to the water table and probably flooded

periodically (see section 2.2.3). With the lowered water table these sites never flood today and

many plant species’ roots probably no longer reach ground water.

3.2.3 Sea Level Rise

Sea level rise may become a major environmental concern in South Florida if projected trends

continue. The South Florida Regional Planning Council is anticipating a five (5) foot rise in sea

level over the next 200 years. Sea level rise has already been implicated in the reduction of pine

rockland habitat in the lower Florida Keys (Ross et al. 1994), and the complete loss of pine

rocklands on Key Largo (Alexander 1953).

Sea level rise in Miami-Dade County will initially impact only the few coastal pine rocklands,

especially the Deering South Addition, an EEL site on Biscayne Bay. Loss of the pine rockland

ecosystem will be initiated not by inundation, but by saltwater intrusion to the water table, killing

pine rockland plant species. A more detailed Geographic Information Systems (GIS) analysis is

needed, but many pine rocklands may not be impacted directly because of their high elevation

and inland locations.

3.3 Climate

It has been suggested that the climate of Miami-Dade County has changed with the drainage of

wetlands (Marshall and Pielke 2004). Marshall and Pielke have hypothesized that prior to

drainage, a persistent moisture flux from heat-retaining wetlands prevented freezing

temperatures. Post-drainage freezes may have become more common.

In contrast to the findings of Marshall and Pielke (2004), large cities, such as greater-Miami, are

known to act as heat islands because of the heat retention by manmade structures. Urban heat

islands can be as much as two (2) to ten (10) degrees warmer than surrounding areas. Global

warming is also a factor, which may raise temperatures in Miami-Dade County.

Changes in climate may have many effects, although they are hard to predict. Possible impacts

may be changes in flowering and fruiting phenology of plants, fewer (or more) freezes changing

hardwood subcanopy structure and composition, changes in soil moisture and thereby seed

germination, changes in plant respiration rates, and susceptibility to biological invasions by

exotic organisms.

3.4 Vegetation Structure and Composition

Although the same three vegetation layers are still conceptually present in existing fragments of

pine rocklands, in many cases they depart significantly from the original structure and species

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

Page 15

richness. The following paragraphs describe some of the most relevant changes and use the

description made in the previous section for comparison purposes.

3.4.1 Canopy

The historical canopy of pine rocklands, consisting of South Florida slash pine, was significantly

altered following non-indigenous settlement. The first major impact to the pine canopy was

logging. Large scale logging took place in Miami-Dade County from the very early 1900s to the

1950s (Craighead, 1971, Wade et al. 1980, USFWS 2000). Although some small areas of Long

Pine Key in ENP were never logged, it is likely that all or nearly all areas of pine rockland

outside of the national park were logged. Craighead (1971) reports a discussion with a mill

owner in 1952 who stated that during World War II every pine that could be made into a 2x4 was

cut down.

Following the end of logging activities, the pine canopy recovered in most pine rockland

fragments by 1992, resulting in an even-aged stand of mature pines. In August 1992, Hurricane

Andrew hit South Florida, and in the two years following almost the entire canopy of pine in

Miami-Dade County outside of ENP was lost. 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).

In the mid 1990s, efforts were made to reestablish pine

trees on sites where they were lost. Pine seedlings were

planted on 22 preserves, including 12 EEL sites (Table

1). Many of these trees are now 6 to 15 feet tall. A

negative result of the reintroduction of pines has been

the establishment of extreme densities of trees in some

places due to overplanting. Mortality in many plantings

was much lower than anticipated. In addition, few sites

where pines have been planted have burned. Fires