Restoration of Longleaf Pine Ecosystems
Longleaf Pine Seedling Survival and the Role of Fire on a Flatwoods
Site
Cohen, Susan1, John Kush2, and Kim Ludovici 1
1USDA Forest Service, Southern Research Station, 3041 Cornwallis Rd.
Research Triangle Park, NC 27709 and 2 School of Forestry and Wildlife
Sciences, 108 M. White Smith Hall, Auburn University, AL 36849
Abstract
Natural regeneration of longleaf pine (Pinus palustris Mill.) is one
of the most important tools natural resource managers have at their
disposal to regenerate existing longleaf pine stands. National Forests
are going to longer rotations and contemplating uneven-aged management
for longleaf pine. Several studies on excessively drained sandhill sites
have indicated there is a tendency for longleaf to regenerate primarily
in gaps. The more poorly drained flatwoods sites have been largely ignored
in regeneration and gap studies yet they are generally productive and
contain high numbers of rare species. A study on the eastern Coastal
Plain of North Carolina in the Croatan National Forest was established
to examine the regeneration issue and the impacts of fire. These sites,
on Onslow soils, contain second-growth longleaf forests and have been
winter burned once every two to four years for the last 20 years. The
frequent prescribed burning regime has produced an intact understory
groundcover with high species diversity and strong competition for the
sparse resources. Nine 0.28-hectare plots were established around gaps
in 2001. The plots averaged 102.6 tress/hectare with a range from 56.6
to 198.8 tress/ha. Overstory basal area ranged from 4.6 to 10.4 square
meters/ha with an average of 7.02 square meters/ha. Grass-stage seedlings/ha
ranged from 100 to 7,657 with an average of 2,533 seedlings/ha. Seedlings
out of the grass-stage but having a height < 1.37 m averaged 303
seedlings/hectare with a range of 28.6 to 1,357 seedlings/ha. The study
sites were prescribed burned this past winter. The impacts of fire on
seedling survival will be related to a number of environmental conditions
that have been measured. Proper management of longleaf pine forests
will enable public land managers to meet the multiple-use demands placed
on that ecosystem, while preserving a rare community type.
Introduction
Longleaf pine stands once dominated more than 60 million acres in the
Southeastern US, and are characterized by an uneven-aged, open park-like
stand structure. Historic activities such as naval stores production,
species conversion and fire suppression, caused longleaf pine stands
to become critically endangered communities of the southeastern USA.
Aside from being the dominant tree species, longleaf pine is also considered
a keystone species of this community type. Reestablishing and regenerating
longleaf pine seedlings is a major priority for conserving and restoring
longleaf pine forests throughout the region. Very little is known about
longleaf pine regeneration on flatwoods sites. With National Forests
going to longer rotations and contemplating uneven-aged management for
longleaf pine, proper management of longleaf pine forests is needed
by the National Forest Systems to meet the multiple-use demands placed
on that ecosystem, while preserving a rare community type.
The Croatan National Forest, located on the North Carolina coast, contains
64,300 hectares between Morehead City and New Bern.
There is only an estimated estimate 5,062 hectares of longleaf pine
remaining (Outcalt and Sheffield, 1996) on the Croatan National Forest.
Today, one of the primary goals of forest management on the Croatan
is restoration and management of longleaf pine communities. The major
tools in this effort are proper use of fire and utilization of natural
regeneration.
Our ability to restore and manage fire-dependent ecosystems will depend
on improving our understanding of multiple regeneration processes. While
nursery production and plantation management have improved artificial
longleaf pine seedling establishment, our understanding of natural regeneration
processes has not. This study involves the collection of baseline information
on stand and site characteristics. This information will be regressed
against seedling and adult tree location to test site-specific impacts
such as temperature, moisture, light and competition.
Study sites
Study sites are located on the Croatan National Forest, Carteret County,
NC. All plots are on the Onslow soil series, a moderately to somewhat
poorly drained, loamy sand (fine-loamy, siliceous, thermic Spodic Paleudults).
This soil is highly acidic, and generally nutrient poor (Goodwin 1977).
Annual precipitation in the region averages 1210 mm but extended droughts
occur during the growing season. Mean annual temperature is 17oC with
the coldest temperatures in January (0.5oC) and the warmest in July
(32.9oC).
The study sites have a typical longleaf flatwoods/savanna vegetative
structure, with a mature, uneven-aged overstory dominated by longleaf
pine (scattered loblolly and pond pines are present), no midstory exists,
and a mix of low-growing woody and herbaceous vegetation dominates the
understory. Average stand age ranges from 70 to 100 years. For the past
20 years, these sites have been winter burned every 2-4 years. All sites
have been burned within the last year. The sites contain similar dominant
understory plants including: Gaylussacia spp., Vaccinium spp., Ilex
spp., Persea borbonia, Magnolia virginiana, Aristida stricta, Andropogon
spp., Pteridium aquilinum, Eupotorium spp.
Objectives and Hypotheses
The proposed study addresses conditions of regeneration within gaps
in natural longleaf pine stands, and intends to fill a void in regeneration
information on moderate to poorly drained soils of the eastern North
Carolina Coastal Plain. This study provides critical information for
the Croatan National Forest to use in its management and restoration
of longleaf communities. We plan to develop a monitoring program to examine relationships among longleaf
pine seed crop, seedling/sapling mortality, and subsequent growth to
edaphic conditions, stand conditions, and prescribed fire.
The significance of longleaf pine cone crops
Natural regeneration is the most important tool natural resource managers
have at their disposal to ecologically and economically regenerate existing
longleaf pine stands. However, adequate cone crops for natural regeneration
typically occur every 5-7 years, and often longer (Wahlenberg, 1946;
Maki 1952) on the Atlantic Coast.
One of the major concerns in longleaf pine management is seed production.
Compared to the other southern pines, longleaf is a sporadic seed producer.
Wahlenberg (1946) noted that good seed crops might occur every 5 to
7 years. Maki (1952) reported heavy seed crops might occur over much
of the longleaf range once in 8 to 10 years.
For successful regeneration, the minimum size of a cone crop is considered
to be 1,853cones/hectare or roughly 30 cones per tree (Boyer and White
1989). In the past 30 years, 5 of the 8 cone crops considered adequate
for natural regeneration have occurred since 1990 (Boyer 1998). The
1996-longleaf seed crop was one of those “much-anticipated”
region-wide seed crops. Whether the interest is natural or artificial
regeneration, it is important to know when to expect a bountiful seed
crop. With only been 5 crops (50 cones/tree) considered adequate for
regeneration, following what happens to the regeneration is critical
to the management of longleaf pine.
Methods
A. Nine 0.28-hectare plots have been established at several locations
on the Croatan National Forest.
B. Monitoring seedling crops: One-half of each plot was randomly selected
and all seedlings with a DBH less than 1 cm were stem mapped from plot
center. Seedling mortality has been followed through one growing season
and one dormant season burn.
C. The longleaf pine overstory has been stem mapped and data recorded
includes diameter at breast height (1.37 m; DBH), crown class, and crown
and total height.
D. Longleaf pine flower and cone counts were made in 2000 and 2001
on a subset of trees on each plot.
E. Eleven 0.25 m2 litter traps have been set up on each plot and litter
is being collected monthly. This will provide an estimate of productivity
and fuel loads.
F. Soil temperature, soil moisture, and light will be measured/collected
along transects monthly.
G. Soil cores have been taken every 10 cm to a depth of 30 cm, roots
were sieved, and a subsample of soil was collected for C/N and organic
matter content.
H. Root biomass is being determined by depth and separated into woody
and non-woody components.
I. Vegetation surveys have been conducted and percent cover of understory
plants mapped.
First-Year Findings
Plots have a typical flatwoods/savanna type structure: the overstory
is dominated by longleaf pine with a few scattered loblolly and pond
pines; there is no midstory, and a diverse understory.
The dominant herbaceous species is Aristida stricta
on all plots. Other important herb/forb/grass species include: Polygala
lutea, Pteridium aquilinum, Osmunda
cinnamomea, Dichanthelium spp.,
Eupatorium spp., Xyris
caroliniana and ambigua, Solidago
odora, Aster spp., Rhexia
spp., Aletris farinosa, Lysimachia
quadrifolia, Hypericum spp.,
Drosera brevifolia and capillaris,
Sarracenia purpurea and flava,
Arundinaria gigantea, Sabatia
spp., Platanthera spp., Calopogon
spp., Cleistes bifaria, and Andropogon
spp.
The dominant woody species are Vaccinium tenellum,
Gaylussacia frondosa, Ilex
glabra, Gaylussacia dumosa, Vaccinium
crassifolium, Liquidambar styraciflua,
Aronia arbutifolia, Acer
rubrum, Myrica cerifera,
Cyrilla racemiflora, Clethera alnifolia,
and Lyonia spp.
Longleaf Pine Overstory
The plots averaged 102.6 tress/hectare with a range from 56.6 to 198.8
tress/hectare. However, they averaged only 77.0 trees/hectare that were
large enough to be cone-bearing trees.
The average DBH was 27.0 cm with a range from 5.5 to 55.4 cm. Average
height was 17.0 m with a range of 5.5 to 27.4 m. Basal area ranged from
4.6 to 10.4 square meters/hectare with an average of 7.02 square meters/hectare.
Description of gaps within plots
- Gaps were mostly elliptical in nature and gap size averaged 0.09 hectares with a range of 0.01 to .16 hectares.
- 56% of the gaps were oriented in a north-south direction.
- The 2000 cone count found 26.5 cones/tree but the 2001 count had less
than 2 cones/tree.
- Grass-stage seedlings/hectare ranged from 100 seedlings/hectare
to 7,657 with an average of 2,533 seedlings/hectare .
- Seedlings out of the grass-stage but having a height < 1.37
m averaged 303 seedlings/hectare with a range of 28.6 to 1,357 seedlings/hectare
The remainder of the data is currently being processed and will be made
available upon completion.
LITERATURE CITED
Boyer, W.D. 1973. Air temperature, heat sums, and pollen shedding phenology
of longleaf pine. Ecology 54(2):420-426.
Boyer, W. D. 1998. Long-term changes in flowering and one production
by longleaf pine. In: Proceedings of the Ninth Biennial Southern Silvicultural
Research Conference, T.A. Waldrop (ed.), USDA Forest Service, Southern
Research Station, General Technical Report-20, pages 92-98.
Boyer, W.D., and J.B. White. 1990. Natural regeneration of longleaf
pine. In: Proceedings of the symposium on the management of longleaf
pine, R.M. Farrar, Jr. (ed.), USDA Forest Service, Gen. Tech. Rep. SO-75,
pages 94-113.
Gemmer, E.W., T.E. Maki, and R.A. Chapman. 1940. Ecological aspects
of longleaf pine regeneration in south Mississippi. Ecological Monographs
21:75-86.
Goodwin, R.A. 1977. Soil survey of Carteret County, North Carolina.
USDA Soil Service Conservation.
Maki, T.E. 1952. Local longleaf seed years. Journal of Forestry. 50(4):321-322.
Outcalt, K.W., and R.M. Sheffield. 1996. The longleaf pine forest:
trends and current conditions. USDA Forest Service Resource Bulletin
SRS-9. 23 p.
Wahlenberg, W.G. 1946. Longleaf pine: Its use, ecology, regeneration,
protection, growth, and management. Charles Lathrop Pack Forestry Foundation
with the USDA Forest Service, 429 p.
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