The
key to supporting a variety and abundance of species is to
provide a diversity of structure and vegetation (Allen et
al. 1996, Sharitz et al. 1982). In particular, an open, park-like
structure with a rich, herbaceous understory similar to historical,
fire-maintained pine communities can provide for a broad
suite of plants and wildlife. Even the most intensely managed
plantations often have high diversity in the early years
when the canopy is still open, but this diversity decreases
rapidly as the canopy closes and the stand enters the dark
stem exclusion stage (Baker and Hunter 2002). Management
strategies to increase biodiversity should minimize this
stage, maintaining a more open canopy and productive understory
throughout the rotation.
One approach to a more open structure is planting at a wider
spacing, but planting dense with subsequent thinnings may
be a more desirable approach for maintaining wood quality
(Van
Lear et al. 2004). Thinning early and often is widely recognized
as an important component of an overall strategy to increase
biodiversity (Hunter 1990, Marion et al. 1986). Thinning
has been found to benefit numerous species, including deer
(Halls
1973), quail (Dougherty 2004), small mammals (Mengak and
Guynn 2003), turkeys (Mississippi State University Extension
Service
2004), and birds (Turner et al. 2002). Thinning is recommended
as early as 15 years (Van Lear et al. 2004) or even earlier
in the absence of a pre-commercial thinning (Hurst and Warren
1980). Thinning should be repeated as frequently as every
5-10 years to maintain an open stand structure, and it should
be
heavier (e.g. 60-80 ft2/acre of residual basal area) than
is generally done for timber production (Halls 1973, Schultz
1997,
Van Lear et al. 2004).
A potential problem with heavy thinning to maintain an open
canopy is that it not only promotes herbaceous understory
growth but also hardwood growth. These hardwoods can form
a dense
midstory that shades out the herbaceous understory (Blair
and Feduccia 1977, Dickson and Wigley 2001, Hunter 1990,
Schultz
1997). Thus, without hardwood control, the biodiversity benefits
of thinning may be negated. In earlier times, the hardwoods
in natural pine stands were controlled by frequent low-intensity
fires (Noss 1988, Van Lear et al. 2004). Managers can achieve
similar results by using prescribed
burning
in conjunction with thinning. 
Once the crop trees are large enough to survive
the fire, prescribed burning at approximately 5-year intervals
can help maintain favorable conditions for biodiversity (Halls
1973, Mississippi State Extension Service 2004, Schultz 1997,
Marion et al. 1986). Many of the plants and animals associated
with southern pine communities are adapted to or even dependent
on fire, and wildlife mortality from fire is generally very
low (Landers 1987, Means and Campbell 1981, Moorman 2002).
Regular burning improves habitat for many species, including
deer (Dickson 1982), quail (Dougherty 2004), turkey (Mississippi
State University Extension Service 2004), and amphibians
and reptiles (Means and Campbell 1981). However, prescribed
burning should not be overdone or the effects on biodiversity
may become negative (Dickson 1982, Melchiors 1991). Also,
to help provide for a broad suite of species in the short
and long term, areas should not be burned evenly, but patches
of unburned areas should be left to provide for nesting and
cover (Landers 1987, Moorman 2002).
Although a dense hardwood midstory is undesirable
because it inhibits the herbaceous understory, some hardwoods
are
beneficial for biodiversity. Mature hardwoods such as oaks
provide hard mast that is important for many wildlife species
(Dickson 1982, Dickson and Wigley 2001). Maintaining a
desirable component of mast-producing hardwoods will improve
wildlife
habitat (Johnson et al. 1975, Melchiors 1991, Tappe et
al. 1993). This includes not only individual hardwoods, but
also
areas of hardwoods. An interspersion of hardwood and pine
forest types provides good wildlife habitat (Shultz 1997),
and hardwood areas should be maintained in sensitive areas
such as bottomlands, drainages, and along streams (Dickson
1982, Halls 1973, Johnson et al. 1975).
Site preparation techniques at the beginning
of the rotation should also be considered when managing for
biodiversity.
Intensive site preparation can accelerate canopy closure
and reduce the availability of fruit and forage for wildlife
(Hunter 1990). Thus, while intensive site preparation
can benefit some game species like deer, less intensive site
preparation is generally better for a diversity of wildlife
(Marion and Harris 1982, Marion et al. 1986). Locascio
et al. (1990) found that moderate intensity site preparation
produced the greatest understory biomass, and moderate
intensity
treatments may be the most cost effective, especially
for
non-industrial landowners.
Another way to support increased biodiversity
in pine plantations is by retaining key structural features
such
as snags,
coarse woody debris, and mature live trees. These elements
add additional
structural complexity that benefits a wide range of
wildlife (Allen et al. 1996, Baker and Hunter 2002, Dickson
and
Wigley 2001, Marion et al. 1986, Sharitz et al. 1992).
Maintaining
riparian buffers can provide for some of these elements
(Dickson and Wigley 2001, Thill 1990). Riparian buffers
further contribute
to biodiversity by providing for aquatic species, water
quality, and habitat connectivity (Baker and Hunter
2002, Dickson
and Wigley 2001).
All of the management practices described above will
be most effective if done in conjunction with longer
rotations.
Short
rotation management limits pine plantations to early
successional structures and does not provide for species
needing older
seral stages (Johnson et al. 1975). Because of the
dominance of short rotations, older seral stages are
becoming rare
in the region (Allen et al. 1996). Longer rotations
can provide for long-term wildlife forage as well as
key
habitat elements
such as hardwood mast, snags, and cavities (Melchiors
1991).
Summary:
Certain stand-level management practices can increase the
potential contribution of intensively managed loblolly
pine plantations to biodiversity in the South. Thinning
and prescribed burning should be done early and often
to maintain an open structure and rich, herbaceous understory
similar to the historically prevalent longleaf pine stands.
Site preparation should be less intensive, and key structure
elements such as hardwood mast and dead wood should be
maintained. These practices will be most effective over
longer rotations. Several additional considerations should
be made when managing for biodiversity. Site specific
factors
will impact results, such as land use history—old
field sites are unlikely to support biodiversity regardless
of management practices (Baker and Hunter 2002, Hedman
et al. 2000, Marion and Harris 1982, Marion et al. 1986).
Economic trade-offs should also be considered. Management
strategies that balance biodiversity with economic objectives
are more likely to be adopted on private ownerships.
Such strategies can be developed as management templates
to
guide landowners in achieving multiple objectives (see
RTI Fact Sheet 38).
A complete literature review of practices to support increased
biodiversity in intensively managed loblolly pine plantations
is available in Technical
Report C of RTI Working Paper #5.
References:
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