I would like to second Elizabeth's challenge to the notion that extinction and
extirpation are sufficiently suitable metrics for species endangerment. From a
Southern California perspective, the areas of the region downwind of the most
heavily automobile trafficked Los Angeles County are receiving increasing
depositions of nitrogen, which is giving "weedy" non-native species a
considerable edge (bibliography below). The landscape is being at least
transformed, and somewhere down the road, habitat change must inevitably
follow--with all the attendant ecosystem effects.
Speaking from an environmental planning perspective, and if we are to break
from the typological, population-community view of conservation and move to an
ecosystem management approach that seeks to manage the processes and functions
which underwrite species and communities, one of the first things we need to
do, it seems to me, is to break from our almost exclusive reliance on the
Endangered Species Act (and its quite incidental specification of "critical
habitat"). Species extinction is a legitimate ecological concern, but
extinctions are too far down the timestream to be actually useful to
conservation action.
Cheers,
-
Ashwani
Vasishth [EMAIL PROTECTED] (818) 677-6137
Assistant Professor
Department of Urban Studies and Planning, ST 206
California State University, Northridge
http://www-rcf.usc.edu/~vasishth
* * *
Allen, E. B. & P.E. Padgett & A. Bytnerowicz & R. Minnich. 1998. "Nitrogen
Deposition Effects On Coastal Sage Vegetation of Southern California,"
Proceedings of the International Symposium on Air Pollution and Climate Change
Effects on Forest Ecosystems, Riverside, CA February 5-9, 1996. USDA Forest
Service, Pacific Southwest Research Station, PSW-GTR-166, 131-140.
http://www.fs.fed.us/psw/publications/gtrs.shtml (select GTR-166).
Cione, N.K., Padgett, P.E. & Allen, E.B. 2002. "Restoration of A Native
Shrubland Impacted By Exotic Grasses, Frequent Fire, and Nitrogen Deposition In
Southern California," Restoration Ecology, v10(2002): 376-384.
Edgerton-Warburton, L.M. & Allen, E.B. 2000. "Shifts In Arbuscular Mycorrhizal
Communities Along An Anthropogenic Nitrogen Deposition Gradient," Ecological
Applications, v10 (2000): 484-496.
Fenn, M.E. & J.S. Baron & E.B. Allen & H.M. Rueth & K.R. Nydick & L. Geiser &
W.D. Bowman & J.O. Sickman & T. Meixner & D.W. Johnson. 2003. "Ecological
Effects of Nitrogen Deposition In the Western United States," Bioscience,
v53 (2003): 404-420.
Huston, Michael A. 2004. "Management Strategies for Plant Invasions:
Manipulating Productivity, Disturbance, and Competition," Diversity and
Distributions, v10 (2004): 167-178.
Meixner, T. & E.B. Allen & K. Tonnessen & M. Fenn & M. Poth. 2002.
"Atmospheric Nitrogen Deposition: Implications for Managers of Western U.S.
Parks," Park Science, v21 (2002): 30-33.
Padgett, P. E. & E.B. Allen. 1999. "Differential Responses To Nitrogen
Fertilization In Native Shrubs and Exotic Annuals Common To Mediterranean
Coastal Sage Scrub of California," Plant Ecology, v144 (1999):93-101.
Wood, Yvonne A. & Thomas Meixner & Peter J. Shouse & Edith B. Allen. 2006.
"Landscape and Watershed Processes: Altered Ecohydrologic Response Drives
Native Shrub Loss under Conditions of Elevated Nitrogen Deposition," Journal of
Environmental Quality, v35 (2006):76-92.
At 03:22 PM -0400 4/4/06, Elizabeth Leger wrote:
>I don't understand how the metric for measuring impacts of invasive
>species became "extinction" or even "local extirpation" of native
>species.
>
>If I measure 90-99% cover of exotic species in a system (totally the
>norm in California's central valley grasslands), I'm not supposed to be
>upset about the impacts of invasive species impacts because there
>haven't been any local extinctions? That makes no sense.
>
>Beth
