Providing adequate habitat for thicketdependent species in the Northeast will require a variety of a

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3. NATURAL DISTURBANCES AS A GUIDE FOR MANAGEMENT
Early-successional habitats in the northeastern
United States should historical prevalence guide
contemporary management? John A.
Litvaitis Department of Natural
Resources University of New Hampshire Durham, NH
03824
If we accept that the decline of thicket habitats
warrants intervention, what should be done?
Efforts to maintain such habitats via timber
harvests have been confronted by public
opposition. However, there seems to be
increasing support for timber harvesting methods
that mimic natural disturbance regimes.
Advocates indicate that this approach should
include scattered harvests of small groups of
trees, resulting in small patches of
early-successional habitat. Would such an
approach be effective in providing habitat for
thicket-dependent species? ? Although
natural disturbances may provide a useful guide
in relatively intact landscapes, they may not
provide an appropriate template for managing
forests in human-dominated landscapes.
?Contemporary landscapes include a variety of
land uses and dense road networks that alter
demographic and ecological processes. A recent
study of New England cottontails revealed that
intense predation by generalist carnivores caused
small patches of habitat ( 2 ha) to function as
demographic sinks (Fig. 4). Long-term
survival of cottontails in modified landscapes
will require large patches of habitat that are
demographically connected.
1. INTRODUCTION
In the northeastern United States, populations of
many species affiliated with native shrublands
and regenerating forests (collectively referred
to as thickets) are declining rapidly (Fig 1).
Much of this decline can be explained by the
maturation of second-growth forests that have
dominated the region since agricultural lands
were abandoned in the late 1800s and early 1900s.
However, urban expansion and the limited
influence of natural disturbances on the age
distribution of these maturing forests have
resulted in an apparent shortfall of thicket
habitats.
Figure 4. Maintaining small patches of thicket
habitat in human-dominated landscapes is not an
effective management strategy for New England
cottontails.
Patch size
2.5 ha 5.0 ha
Winter mortality 69 35
4. ALTERNATIVE APPROACHES
Providing adequate habitat for thicket-dependent
species in the Northeast will require a variety
of approaches. Historic land uses (that have
determined current forest age) and present-day
land uses (that affect landscape fragmentation)
may be the most important considerations
(Fig. 5). In relatively intact landscapes,
efforts to maintain sufficient amounts of
thicket habitats could rely on a sliding
scale where managers consider forest age. In
the mid- successional stands that
currently dominate the Northeast, this
would mean providing a greater abundance of
thicket habitats in managed stands to
partially offset deficits in unmanaged
stands. As regional forests mature and natural
disturbances have a larger influence on
forest structure, active management of
thicket habitats would be reduced.
?Is the decline in thicket habitats a real issue
for concern or simply an artifact of
historic land use? ? If there is a shortage,
what is the best approach for managing these
habitats?
2. CURRENT VS. HISTORIC ABUNDANCE OF THICKET
HABITATS
Efforts to reconstruct pre-Columbian (baseline)
conditions suggest that the abundance of young
forests and shrublands was greatest along coastal
areas as a result of local features (sandy
soils), frequent disturbances (fires), and
occasional catastrophic events (hurricanes)
(Fig. 2). In contrast, inland forests were
characterized by small openings caused by
disturbances that killed one or a small group of
trees (windthrow) and beaver impoundments.
?The present-day abundance of
disturbance-generated habitats may be above
baseline conditions in some regions (e.g.,
industrial forestlands of northern New England)
and below baseline levels in other areas
(e.g., southern New England and mid Atlantic)
(Fig. 3). Native shrublands (e.g., scrub
oak and pitch pine barrens) have been
disproportionately degraded or eliminated
throughout the Northeast.
Figure 5. Strategy for maintaining adequate
amounts of thicket in diverse landscapes.
In substantially modified landscapes, an effort
should be made to cluster thicket habitats and
rely on existing land uses that maintain these
habitats (Fig. 6). Such an approach would avoid
additional fragmentation of remaining forests and
increase the viability of local populations
associated with thicket habitats. Restoration
of native shrublands should be a priority
throughout the region.
Figure 6. Clustered arrangement of existing
powerline corridor (yellow) and abandoned gravel
mine (orange) could be maintained as part of a
network of thicket habitats in a human-dominated
landscape.
? Regardless of the specific manipulations used,
efforts to sustain populations of species
dependent on shrublands and
early-successional forests in the Northeast will
require creativity and public support.
ACKNOWLEDGEMENTS
Trani et al. 2001
The ideas presented here are the result of
several research efforts that were supported by
McIntire-Stennis Cooperative Forestry Research
Funds, the U.S. Fish and Wildlife Service, and a
recent grant from the National Commission on
Science for Sustainable Forestry.
Figure 2. Pre-Columbian abundance of
early-successional forests.
Figure 3. Percentage of timberland
in seedling-sapling stands (source USDA
Inventory and Analysis)