[PCA] Disturbance and invasion
Steve Erickson
wean at whidbey.net
Sun Sep 9 22:33:54 CDT 2012
I's somewhat disturbed by the apparent assumption by some
posters here that all invasions are traceable to anthropogenic
disturbance. There are ecosystems where disturbance is a key
factor in their creation and persistence, whether very frequent
(e.g., salt march - daily tidal), less frequent (e.g. prairie -
annual fire; forest - blow down). These disturbances create and
maintain the structure, function, and composition of these
systems, with no additional anthropogenic disturbance necessary
for invasion by introduced species. Examples in my part of the
planet (western Washington state) include:
Spartina spp - low salt marsh.
Epilobium hirsutum - high salt marsh, freshwater wetlands, pond fringe.
Cytisus scoparius - prairie.
Hedera helix; Ilex aquifolium - forest understory.
In all of the above examples these invasive species change
fundamental processes and attributes of the invaded systems
through mechanisms including direct exclusion of the native
species, structural change, and changing the systems' nutrient
levels and pathways.
And there really is no obvious commercial use that would cause
them to be hunted to extinction or even kept in check.
Ultimately, this is a philosophical question. I guess I'm a Leopoldian:
"A thing is right when it tends to preserve the integrity,
stability, and beauty of the biotic community. It is wrong when
it tends otherwise."
I take "stability" in the cyclic sense, not as in "static" or
"unchanging." And when a system is or will be fundamentally
changed by an invader, I come down on the side of the existing
system and its integrity.
-Steve
------------------------------------------
Whidbey Environmental Action Network
Preservation Education Restoration
Box 53, Langley, WA 98260
(360) 579-4202
wean at whidbey.net
www.whidbeyenvironment.org
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