OOS 45-9 - Floristic composition, beta diversity and nestedness of reference sites for restoration of xeric riparian areas

Thursday, August 6, 2009: 4:20 PM
Acoma/Zuni, Albuquerque Convention Center
Vanessa B. Beauchamp, Biological Sciences, Towson University, Towson, MD and Patrick B. Shafroth, Ft. Collins Science Center, US Geological Survey, Ft. Collins, CO
Background/Question/Methods Riparian restoration projects occasionally involve areas so altered by dams, diversions or levees that they are incapable of supporting historic phreatophytic plant communities.  This study examines potential target restoration communities for Tamarix-dominated riparian areas in the southwestern United States that are now too dry or saline to support native Populus-Sailx forests. In some instances, reference xeric riparian communities may exist at some distance from the area to be restored, making it difficult to determine which species are most appropriate for the site. We surveyed naturally abandoned riparian floodplain shrubland, grassland and savanna communities as potential reference sites for these xeric riparian habitats. Our objectives were to 1) determine if floristic composition varied with soil texture and salinity; 2) examine the extent of distance decay in this community type; and 3) determine the degree of nestedness in the plant community in relationship to soil variables. Study sites encompassed xeric riparian floodplains on five rivers in three watersheds in New Mexico, USA. Results/Conclusions Hierarchical cluster analysis identified six groups based on soil chemistry and texture, and MRPP analysis showed significant but weak differences in plant community composition between soil groups (T = -4.89, A = 0.076, P < 0.001). Sorenson similarity coefficients indicated that there was no significant relationship between plot similarity and distance between plots. Plant communities were more similar within the same site regardless of soil type, than on the same soil type between sites or watersheds.  Analysis of nestedness showed that saline tolerant species are “generalists” and are found on most other soil types, while “specialist” species are restricted to less saline locations. Taken together, these results indicate that local influences are very important in determining xeric riparian community composition. Dominant, saline tolerant species are often the same across a wide geographic areas and range of conditions, while the identity of subordinate species is largely site dependent. This phenomenon causes all sites to have the same low degree of similarity, regardless of the distance between them. In planning restoration projects in xeric riparian areas, a candidate species pool should be developed from the nearest possible reference areas, and soil salinity and texture are good predictors of which of these species will be most suited to the area being restored.
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