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The edge explained

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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


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