2011 SOUTHEASTERN NATURALIST 10(4):741–750
Restoration of Plant Communities in Former Pine Tree
Anthony M. Rossi1,*, Ryan C. Meyer1, Keith Stokes2, and Daniel C. Moon1
Abstract - As human populations encroach on more remote areas, tree plantations are
frequently converted into suburban developments or conservation lands. The purpose of
the current study was to compare the effects of restoration treatments on the abundance
and biodiversity of two former pine plantations in northeast Florida. Restoration methods,
which varied greatly in both environmental impact and effort from minimal (non-manipulated
control plots) to thinned (removal of 90–97% of Slash Pines and exotic plant species)
to cleared (mechanical removal of all vegetation to the substrate surface), were compared
using replicated 100-m2 plots. Although sites exhibited variation in plant densities and
relative guild abundance, restoration treatment produced a significant increase in plant
abundance and relative composition of plant guilds. Plant abundance was 2–3 times higher
in cleared plots compared to thinned and control plots, respectively; not surprisingly
this was because cleared plots had large numbers of small herbaceous seedlings as well as
a shift in their plant communities to graminoid species, which are typically less shade tolerant
than other plant guilds. Moreover, the relative abundance of vines was substantially
lower in cleared plots compared to control and thinned plots, which retained all or some of
their tree and shrub cover, thereby providing support structure for climbing plants. While
plant diversity (Shannon index) exhibited a significant time-by-treatment interaction because
cleared plots initially had only 65–80% of the plant diversity compared to control
and thinned plots, cleared plots reached or exceeded them in biodiversity by the last two
sampling dates, although cleared plots at one site showed a large decline on the final sampling
date. In general, both study sites reflected high levels of graminoids in cleared plots,
while thinned plots showed more even increases across plant guilds. Lastly, pine tree diameter
(i.e., plant growth rate) was greater and canopy cover was lower in thinned plots
compared to controls, although the differences were only significant for one site. Results
from this study indicate that thinning former pine plantations with selective removal of
exotics will provide maximal plant biodiversity and tree growth rather than utilizing more
cost- and labor-intensive clearing of sites.
From 2000 to 2006, the population of Florida increased an estimated 13.2%
from 15.9 million to over 18 million people (US Census Bureau 2006). Growing
human populations result in increased encroachment into natural ecosystems; to
ameliorate lost natural habitat, tree plantations are often converted into conservation
lands. Pinus elliottii Engelm. (Slash Pine) plantations are a good choice for
restoration in northeast Florida because they are ubiquitous and semi-natural. The
benefits of green space include reducing the “heat island” effect in which cities or
metropolitan areas have significantly higher temperatures than surrounding rural
1 University of North Florida, Department of Biology, 1 UNF Drive, Jacksonville, FL
32224. 2 University of South Florida, Department of Integrative Biology, 4202 East
Fowler Avenue, Tampa, fl33620. *Corresponding author- firstname.lastname@example.org.
742 Southeastern Naturalist Vol. 10, No. 4
or non-developed land, offering inexpensive storm water control, and lowering
atmospheric CO2 (Beckett et al. 1997, Chang et al. 2006, Cunningham and Saigo
1999, San-Salazar and Rausell-Koster 2007). Urban forests also encourage physical
activity and provide increased quality of life for citizens who utilize those
areas (Chiesura 2003). Because local governments or non-profit organizations
are frequently given the task of managing public lands, developing inexpensive
guidelines for tree-farm restoration in north Florida may facilitate rejuvenation
of native habitat more quickly in these urbanizing areas. Florida tree farms offer
relative ease in restoration because the farmed tree species (generally Slash Pine
or P. palustris P. Mill [Longleaf Pine]) are native, and herbaceous seed banks
may still be intact, depending on prior land-use practices, including agriculture
and silviculture, which may have included altered fire regimes, use of pesticides,
herbicides, etc. (Andreu et al. 2009, Hedman et al. 2000).
Terrestrial habitat restoration generally involves re-establishing a portion of
the native plant community characteristic of the area prior to human disturbance
(Miller and Hobbs 2007). The goals of restoration projects may be multifaceted;
for instance, restoration projects may be utilized to increase ecosystem function
and provide native vegetation for endemic animal communities. Plants are easy
to manipulate relative to motile organisms, which may re-colonize quickly by
natural dispersal. Increasing the plant diversity of an area is likely to result in
a greater diversity of both primary consumers (i.e., herbivores) and secondary
consumers (Michel et al. 2007, Moro and Gadal 2006). Thus, plant diversity will
directly or indirectly influence all other trophic levels in an ecosystem (Chen et
al. 2006, Panzer and Schwartz 1998, Provencher et al. 2003).
Typically, the historic cycle of fires can be reinstated as a restoration tool in
the southeastern US; however, fire is not always a realistic tool due to climate,
forest conditions, and proximity to homes or commercial property. Mechanical
clearing (e.g., row thinning) may provide an alternative restoration technique that
offers some of the benefits of fire, such as opening the overstory canopy. In addition,
thinning is a disturbance that reduces dominance by one or a few species and
releases resources, reduces competition, and opens spaces which may promote
the establishment of non-dominant or rare species (Levine and Paine 1974). In
both natural and restored ecosystems, new patches are periodically created by
disturbances, which are subsequently colonized by plants, both native and exotic,
via dispersal mechanisms, seed banks, etc. (Wiens 1976). The purpose of this
study was to compare the effects of restoration techniques (control, thinning,
and clearing) on subsequent plant abundance and biodiversity in two former pine
plantations in north Florida.
The current study utilized two partially restored pine plantation sites in Jacksonville,
Duval County, FL, 30°19'56"N, 81°39'20"W. Both sites were purchased
by the City of Jacksonville (COJ) and designated for preservation in perpetuity
for local residents as part of the Preservation Project Jacksonville (PPJ) initiated
2011 A.M. Rossi, R.C. Meyer, D.C. Moon, and K. Stokes 743
in 1999. Both study sites are former pine plantations, heavily planted with Slash
Pine and both sites lacked robust herbaceous growth due to high tree densities
and leaf-litter accumulation. Betz/Tiger Point (aka: Tiger Point) is located northeast
of the city center and is surrounded by salt marsh vegetation which drains
into the Trout River and eventually the Atlantic Ocean. This site is part of the
Pumpkin Hill Buffer State Park and the greater Timucuan Ecological and Historic
Preserve. Although the ages of the remnants stands of Slash Pine at the two
sites are unknown, tree dbh was approximately 30–50 cm. At Tiger Point, Slash
Pine stands were very dense and averaged 40–60 trees per 100 m2. Sites also
had a thick undergrowth of Serenoa repens (W. Bartram) Small (Saw Palmetto)
and Ilex glabra (L.) A. Gray (Gallberry). Herbaceous growth included Galactia
elliottii Nutt. (Elliott’s Milk Pea), the bunch grass Dicanthelium spp., and Andropogon
virginicus var. glaucus (Chalky Bluestem Broomsedge), and the vine
guild included several species of Smilax (greenbrier) and Gelsemium sempervirens
(L.) (Aiton f.) (Yellow Jessamine). This site is on a small point oriented
north into Edwards Creek, is surrounded for many kilometers to the southeast,
south, and southwest by former tree farms and pinelands, and is surrounded to the
west, north, and east by the waterway. This sandhill community, which includes
large numbers of Slash Pines, Quercus laevis Walt. (Turkey Oak), Quercus falcata
Michx. (Southern Red Oak), and shrubs such as Morella cerifera (L.) Small
(Wax Myrtle) and Lyonia ferruginea (Walt.) Nutt. (Rusty Lyonia), tends to be
very sunny and dry, with few public visitors.
The second site, McGirt’s Creek, is located closer to the city center in the
southwest portion of Jacksonville. The McGirt’s Creek site is part of the St. Johns
River watershed and drains initially into the Ortega River and eventually to the
Atlantic Ocean. This site has less of an herbaceous layer, slightly more leaf litter,
and about 18–20 trees per 100 m2. This site is surrounded to the northeast,
east, and southeast by a former tree farm and wetlands, while surrounded to the
south, west, and north by suburban development and buffered by a relatively
contiguous urban forest. This site also has seasonal standing water present and
two drainage ditches approximately 2 m deep, that run 20 m along the entrance
road. Some study plots were within 20 m of these ditches. Canopy vegetation at
McGirt’s Creek is similar to Tiger Point, with Slash Pine dominating, but also
includes Quercus nigra L. (Water Oak) and Prunus umbellata Elliot (Hog Plum).
However, it lacks Saw Palmetto and Gallberry. Prominent species included Yellow
Jessamine and Gaylussacia frondosa var. tomentosa (L.) A.Gray ex Torr. var.
tomentosa (Huckleberry), and some plots contain large stands of Lachnanthes
caroliana (Lam.) Dandy (Carolina Redroot), an obligate wetland species.
It was expected that rapidly growing plants with highly dispersive seeds such
as graminoids and forbs (annuals), which are characteristic of early successional
stages, would colonize quickly in cleared and thinned plots compared to control
plots. Eventually, slower growing species with larger and less dispersive seeds,
including trees, shrubs, and woody vines, were expected to establish after the first
744 Southeastern Naturalist Vol. 10, No. 4
Materials and Methods
Within each study area, large contiguous areas of existing Slash Pine stands
were chosen so that the study plots were situated along one side of an existing logging
road at each site. Square (10 m × 10 m) study plots were established parallel to
the logging road approximately 5 m from the edge of the road. Plots were randomly
assigned to one of three groups: thinned, cleared, or control. Fifteen (n = 15) study
plots were established at the McGirt’s Creek site (n = 5 per treatment) and nine
study plots (n = 9) at the Betz / Tiger Point site (n = 3 per treatment). Plots were
100 m2, which has been shown to be an effective size for study when using multiple
plots to gather a representative sample unit (Peet et al. 1998). In thinned plots, two or
three randomly selected living Slash Pine trees were left to achieve 20% canopy cover
determined by densiometer (1–2 trees per plot); all the other Slash Pines were cut
as close to the soil surface as possible using chain saws, and all non-native species
were also removed mechanically. Cleared plots were razed to bare soil and raked,
with shrub and tree roots left in the ground; no herbicides were applied, and debris
from thinning and clearing was left several meters from each plot. Control plots received
no treatment and were used as comparison for the treatment groups.
Corners of the plots were marked using wooden stakes and two permanent,
parallel transects randomly selected to occur at 2.5, 5.0, or 7.5 m were established
in each plot; no two transects overlapped. To determine how thinning and
clearing treatments affect herbaceous plant diversity, a 1-m-wide belt transect
was used to assess plant diversity twice per year; surveys were conducted in the
growing season and during the dormant season from 2006 to 2008. Along each
transect, all plants were counted and identified to species when possible. During
the dormant season, herbaceous plants were not counted if they lacked photosynthesizing
tissues or green leaves. Tree characteristics, including canopy cover
and diameter at breast height (dbh, cm), were also measured. Canopy readings
were taken at a height of approximately 1.5 m in the center point of each plot facing
each cardinal direction. Tree diameter was assessed by dbh (cm) during 2006
and again in 2008. Only thinned and control plots were assessed in this manner
because cleared plots had no canopy cover during the period of the study.
Plant species richness (s) and diversity were assessed using a two-way ANOVA
with treatment nested within site (SPSS ver. 11.0). Shannon diversity index values
(H') were also calculated for each site. Shannon index, which provides a measure
of diversity based on the proportional abundance of each species present in
the sample, was calculated as H' = -Σ I = 1 (pi )× (lnpi ), where pi = proportion of
the total species the ith species occupies (= ni / N ). H' is a good index for diversity
because it is sensitive to rare or uncommon species and therefore may be more
useful in conservation or restoration projects. The change in relative abundance
in guilds from 2006 to 2008 was assessed using a two-way ANOVA with treatment
and survey date as fixed effects. A t-test was used to assess changes in tree
diameter (dbh) between thinned and control plots only from 2006 to 2008. Lastly,
changes in tree canopy were examined from November 2006 to November 2008,
and ANOVA was used to test for significant differences among treatment groups.
Data were checked using an F-test to ensure that the met the homogeneity of
2011 A.M. Rossi, R.C. Meyer, D.C. Moon, and K. Stokes 745
variance assumptions of ANOVA prior to analysis, and Tukey’s post-hoc tests
were used to compare treatment means when appropriate.
At both sites, mean number of individual plants per transect was higher in
cleared plots than in either thinned or control plots in 2008 (McGirt’s: F2,48 =
3.20, P = 0.045; Tiger Point: F2,24 = 3.38, P = 0.057; Fig. 1). This increase was
largely represented by small seedling individuals. Shannon diversity index values
were not significantly affected by treatment at Tiger Point (F2,48 = 2.02, P = 0.189;
Fig. 2), but differed significantly at McGirts’ Creek (F2,48 = 8.16, P = 0.001), as
cleared plots had lower diversity than thinned or control plots in all surveys except
winter 2007 (Fig. 3). At McGirt’s Creek, the decrease in diversity in control
and thinned plots in winter 2007 resulted in a significant effect of survey (F3,48 =
9.34, P < 0.001) as well as a marginal interaction between treatment and survey
(F6,48 = 2.07, P = 0.081). Neither survey date nor the treatment × survey interaction
was significant at Tiger Point (P > 0.2; Fig 2). Graminoids and vines were
the most abundant functional groups at both sites, accounting for more than 50%
of all plants in all surveys at this site, but treatments did not result in significant
changes in the relative abundances of functional groups (P > 0.2 in all cases).
Trees were dominated by Slash Pine and Diospyros virginiana L. (Persimmon)
at Tiger Point while Water Oak and Acer rubrum L. (Red Maple) dominated at
Figure 1. Mean species abundance from 2006–2008. Error bars indicate ±1 SEM.
746 Southeastern Naturalist Vol. 10, No. 4
McGirts Creek. Slash Pine diameter (dbh) changed significantly during this study
(Fig. 4). At McGirt’s Creek, dbh increased by approximately the same amount
in control plots and thinned plots (P > 0.2). At Tiger Point, however, dbh of trees in
thinned plots increased significantly more than did dbh of trees in control plots (t =
2.578, df = 7, P = 0.033). Trees in thinned plots increased in diameter by more than
4 cm, while those in control plots increased by only 2 cm (Fig. 4).
Plant community composition and plant abundance were significantly altered
by clearing and thinning treatments, which is consistent with other studies
(Dodson et al. 2007, Laughlin et al. 2006, Levin and Paine 1974). This increase
was largely caused by a greater density of seedlings (especially graminoids) in
cleared plots, and is likely a result of higher levels of light and resources available
in cleared plots. Thus, removing the dominant vegetation probably facilitated
germination of seeds, thereby encouraging seedling recruitment and stimulated
re-sprouting from underground vegetative sources. On the other hand, thinned
and control plots tended to have a significantly greater abundance of vines such as
greenbrier and Galactia (milkpea). This result is consistent with the presence of
support plants for vines such as trees and shrubs in control and thinned plots compared
to cleared plots from which these support plants were removed. Although
Figure 2. Tiger Point Shannon diversity index. Error bars indicate ±1 SEM.
2011 A.M. Rossi, R.C. Meyer, D.C. Moon, and K. Stokes 747
the two study sites showed generally similar trends, the impact of restoration
treatment varied substantially between sites; cleared plots at Tiger Point rapidly
increased in plant diversity and were similar to thinned and control plots within
six months, while cleared plots at McGirt’s Creek remained substantially lower
in plant diversity than those treatments on three of four survey dates. The difference
in response between the two sites was possibly related to the differences
in the ages and density of tree stands at the two sites. As previously mentioned,
Tiger Point was planted with Slash Pines much more recently (based upon tree
density and tree dbh) than McGirt’s Creek; as a result, removal of trees from
the latter site returned it to a much earlier successional stage compared to Tiger
Point. Thus, the response was much less dramatic at Tiger Point. Changes in the
plant community will have direct effects on local primary consumers including
birds, rodents, and insects (Waltz and Covington 2004). For instance, in cleared
and thinned plots, the increase is annual plants should favor some animals such
as songbirds that specialize on seeds of early successional annual plants (Triquet
et al. 1990). Conversely, species such as Meleagris gallopavo L. (Wild Turkey)
or Coturnix coturnix (L.) (Common Quail) that require larger fruits are expected
to benefit from thinned plots with high levels of fruit-producing shrubs.
Interestingly, herbaceous plant species richness was not affected by clearing
plots, although plant abundance (primarily in the form of seedlings) increased
Figure 3. McGirt’s Creek Shannon diversity index. Error bars indicate ±1 SEM.
748 Southeastern Naturalist Vol. 10, No. 4
in cleared plots at both sites compared to thinned and control plots. This result
suggests an intact seed bank and/or a source for recruitment of appropriate native
species nearby. Additionally, only a handful of non-native species were recorded
at either of our study sites, suggesting that these treatments may be effective
in preventing colonization by exotics in restoration of former pine plantations
in northeast Florida. Natural resource management techniques suggest that replanting
is not necessary at these sites, thereby lowering the cost of restoration.
Thinned plots generally displayed common species between control and cleared
plots. Thinned plots frequently experienced the benefits of clearing vegetation
(increased abundance of pioneer plants), while maintaining relatively high abundances
of later successional plant groups as well.
Trees responded with robust growth when the habitat was opened; Slash Pines
in the thinned treatment grew significantly faster than those in control plots, as
expected (Baldwin et al. 2000). Surprisingly, the relative abundance of tree species
at Tiger Point shifted from Slash Pine to Persimmon in a relatively short
time after thinning. At McGirt’s Creek, cleared plots showed highest abundance
for Water Oak, another non-intuitive trend which suggests that an additional
restoration step may be necessary. For instance, if hardwood reduction is a primary
management goal, then initial restoration treatments may require follow-up
monitoring or action such as herbicide, fire, or mechanical removal.
Figure 4. Mean change in tree diameter (dbh, cm) at two study sites. Error bars indicate
2011 A.M. Rossi, R.C. Meyer, D.C. Moon, and K. Stokes 749
Other species revealed high levels of reproductive potential and may be considered
for use in post-planting. Abundance of species such as Solidago spp.
(goldenrod) exhibited large increases in the short term. Ferns were another important
pioneer and most likely emerged from underground sources following
treatment application. One species that was ubiquitous at both sites was Dichanthelium
dichotomum (L.) (Panicgrass), which also proved a fast colonizer, along
with Chalky Blue Broomsedge at Tiger Point and the mesic Carolina Redroot at
McGirt’s Creek. At both sites, shrubs in high abundance included the ever-present
Gallberry along with Hypericum spp. (St. John’s wort) at Tiger Point and Vaccinium
spp. (blueberries) at McGirt’s Creek. The combined abundance of vines and
graminoids represented more than 50% of all individuals on several sampling dates
at Tiger Point, and their importance across treatment regimes should not be underestimated.
Species richness within plots is generally correlated with the local species
pool (Dickson and Foster 2008). It has therefore been suggested that the most
common pioneer species may be suitable for use in regional restoration of plant
communities (Lane and Texler 2009), thereby facilitating species selection.
Prior to establishing a restoration plan, former land practices (e.g., agriculture,
sylviculture, etc.) of the area should be considered because cropland likely has less
potential for successful restoration than pine plantations (Hedman et al. 2000).
Results from the current study suggest that thinning of former pine plantations in
northeast Florida may provide an important restoration and management tool near
urban areas. This is because thinning allows goals of restoration projects to be realized
(e.g., increased biodiversity of plants and animals endemic to an area) without
the risk associated with prescribed fires, which may be problematic near populated
areas. Thus, restoration of these former plantations should provide multiple benefi
ts to urban areas, including ecosystem functions such as water purification and
absorption of water runoff as well as increased recreational activities.
We would like to thank the University of North Florida (UNF), which provided support
for this research through a Graduate Scholar’s Grant to R.C. Meyer, as well as the
UNF Coastal Biology Program for financial support. This project was also funded by a
grant from the City of Jacksonville and the Florida Fish and Wildlife Conservation Commission
to A.M. Rossi and D.C. Moon. We also thank two anonymous reviewers for their
insightful comments that improved the manuscript.
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