Dear HCN:
Michael Cain’s question
about forest “edges’ is a good one (HCN, 3/4/96). Too much edge can
be a very bad thing. When edges are created by large-scale forest
fragmentation – for instance, as a result of extensive clear-cuts –
then the remaining forest stands can effectively become islands
isolated from the rest of the forest, and under such circumstances
one would expect a net loss of species diversity. An increase in
forest edges can also be harmful when it is the result of
residential subdivision at the urban/wildland interface. Under
these circumstances, pets – especially cats – have a devastating
impact on bird populations, and especially on species that nest on
or close to the forest floor. This has been a pronounced problem in
Eastern states where suburbia has spread at a gallop, but the West
is by no means immune. The 20-acre ranchette is one of the greatest
threats ever known to the integrity of Western
lands.
When I write “We need to create more small
forest “edges’ in order to promote species diversity,” I am
advocating the kinds of small-scale forest disturbances necessary
to produce a landscape that would mimic a relatively natural
balance between openings and heavy cover. These openings would be
by no means large enough to create fragmented forest islands. Nor
would they entail permanent introduction to the ecosystem of exotic
predators like dogs and cats.
While it is
important to be zone-specific, if not site-specific, when making
recommendations for habitat management, it is generally helpful to
think in terms of habitat mosaics that feature a balance of forage
and cover areas, and disturbed and undisturbed sites. We get this
kind of balance when the ecosystem contains a mixture of early,
middle and late seral (successional) communities. The important
thing to remember is that these communities are not static. The
kinds of small openings and edge effects normal in pine and
transition-zone forests express this kind of dynamism: They appear
as a result of windfall or fire (or where fire has been excluded,
we can cause them to occur through light timber removal) and, as
years pass, their configuration slowly changes as they are
reabsorbed into the
forest.
Bill
deBuys
Santa Fe, New
Mexico
This article appeared in the print edition of the magazine with the headline The edge explained.
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