The following information about forests and forest edges may
prove helpful in determining the inherent value or priority
ranking of a preservation nomination woodlot.
An edge to area ratio is an expression of the average number of
feet in the edge, to every acre in the forest stand (i.e. 4,241
linear feet ¸ 23.6 acres = an edge to area ratio of 180).
| Stand |
Edge |
Area |
Edge to Area Ratio |
|
(in feet) |
(in acres) |
(the lower the # the better) |
| 1 |
4,241¹ |
23.6 ac. |
180 |
| 2 |
2,191¹ |
6.3 ac. |
348 |
| 3 |
5,964¹ |
46.6 ac. |
128 |
For some animal species, the more edge the better. For bird
species, nesting at the edge can be wasteful because of parasitism
and predation. Many birds and mammals enjoy working the edge for
forage, eggs, nestlings and young.
How far into a forest stand pests and predators penetrate is still
being investigated. If the distance is 300-feet as some citations
reference, then a stand must be over six acres if any portion is
to be safe from such losses. Smaller tracts will have more edge
per unit area, and the edge zones may be excellent foraging areas
and useful in many ways other than nesting. The topic of edges
and their effects are very complicated and in some cases
controversial.
Forest edges next to fields are good for some wildlife, but bad
for others. Similarly, edges can have drying winds that reduce
the quality of forest growth, alien plant intrusion, and other
conditions. Again, the phenomena of the forest edge is very
complex.
Forest structure in much of Maryland is highly fragmented and
linear, hence any larger circular stands with maximized area,
versus edge, may be inherently more valuable for preservation
through ecological time.
Other spatial and community principles and guidelines to consider
when evaluating priority retention areas or reforestation design
for Forest Conservation Act compliance include:
Spatial Principals and Guidelines :
Large areas of natural communities sustain more species than
small areas - Preserve as many large natural communities as
possible in single tracts for each ecosystem, or increase the size
of existing patches to the minimum size needed to sustain viable
wildlife populations.
Many small patches of natural communities in an area will help
sustain regional diversity - Where there is no opportunity to
preserve, increase, or create large natural community patches,
increase the number of small community patches.
The shape of a natural community patch is as important as the
size - Modify or design the shape of natural community patches
to create more interior habitat. If space is limited, a circular
area will maximize interior habitat.
Fragmentation of habitats, communities, and ecosystems
reduces diversity- Avoid fragmentation of large patches of
natural vegetation. Even a roadway, through a forest can be a
barrier to movement of small organisms, eliminate interior habitat,
and introduce unwanted species.
Isolated patches of natural communities sustain fewer species
than closely associated patches - Minimize the isolation of
patches. Corridors and an increased number of patches can prevent
isolation.
Species diversity in patches of natural communities connected by
corridors is greater than that of disconnected patches -
Maintain or develop many corridors of similar vegetation to
connect isolated patches of the same or similar community types.
Opportunities exist along roadways, rivers and streams, ravines,
fencerows, hedgerows, railroad rights-of way. Wider corridors
provide more wildlife benefits and protect water quality better
than narrower ones. Breaks in the corridor should be avoided.
A heterogeneous mosaic of natural community types sustains more
species and is more likely to support less common species than a
single homogeneous community - On large parcels, mosaics of
natural communities should be restored as the diversity of the
landscape allows. Smaller parcels should be evaluated within a
regional context with the goal of developing such mosaics on the
landscape.
Ecotones between natural communities support a variety of
species from communities and species specific to the
ecotone - Ecotones (transition zones between communities)
should be allowed to naturally develop between adjacent
communities. Increasing the interspersion of community types on
a given parcel can increase the amount of area in ecotones, but
this should not be done at the expense of reducing interior
habitat.
Community Principles and Guidelines :
Full restoration of native plant communities sustains diverse
wildlife populations - The more fully restored natural
community has a higher diversity. This means introducing as
many components of the natural community as possible.
An increase in structural diversity of vegetation increases
species diversity - Restoring tree, shrub, and herbaceous
layers that are reduced or lacking can enhance the vegetational
structure of a community. Dead logs and litter should also be
left.
A high diversity of plant species assures a year-round food
supply for the greatest diversity of wildlife Introduce as
many species known to be part of the natural community as
possible. Also retain dead, standing, and fallen trees, as they
provide important nesting sites for many cavity nesting species
and a source of food for other species.
Species survival depends on maintaining minimum population
levels - Different species will have different minimum
population requirements. The minimum population in a particular
parcel will depend upon factors listed above, such as how
connected patches are.
Low intensity and management sustains more species and costs
less than high intensity management - The maintenance
costs and environmental impacts associated with landscape
management can often be reduced by reducing management intensity. Converting areas to native vegetation adapted to site conditions can reduce management intensity. Natural forest, grassland, and wetland communities are low intensity landscapes.
