Acknowledgements UNM Hydrogeoecology Group NSF Grant DEB Middle Rio Grande Conservancy District Bosque del Apache National Wildlife Refuge City of Albuquerque Open Space Division New Mexico State Land Office Rio Grande Nature Center Belen Consolidated Schools Contacts Jennifer F. Schuetz Manuel C. Molles, Jr Karyth L. Becenti Research/CRB/home/index.html Flood versus nonflood riparian forests of the Middle Rio Grande, New Mexico: How do they differ? Jennifer F. Schuetz, Manuel C. Molles, Jr., and Karyth L. Becenti Department of Biology, University of New Mexico, Albuquerque, NM Abstract Over the past fifty years, volume and timing of the Rio Grande’s flow, including the annual flood pulse, have been altered due to damming and diversion of the river. As a result, the riparian forest, or bosque, is largely isolated from the river, and the native cottonwood forest is aging, not regenerating, and being invaded by exotics. Restoration of native bosque may require the use of managed floods; however, there is limited scientific data to assess this management activity. To provide information about ecological implications of overbank flooding, we are investigating how 4 flood and 4 nonflood sites within a 160 km stretch of the Middle Rio Grande differ ecologically. Significant differences between flood and nonflood sites were found for cottonwood leaf biomass, wood falling from the canopy, ground-dwelling arthropod abundance and community composition, soil moisture to a depth of 1 meter, and depth to groundwater. Differences suggested by means and standard errors were found for native, non-cottonwood leaf biomass, coarse woody debris, cottonwood leaf mass lost immediately following the May 2001 flood, net nitrogen mineralization, and forest floor litter storage. Final conclusions regarding variables that consistently distinguish flood from nonflood sites await complete analyses of datasets. Introduction River restoration is an increasing priority worldwide. Much research has been conducted with the goal of restoring U.S. rivers such as the Kissimmee (Dahm et al. 1995), Colorado (Schmidt et al. 1998) and Rio Grande (Molles et al. 1998). In addition, restoration strategies for European rivers such as the Danube (Buijse et al. 2002; Tockner et al. 1998) and Rhine (Buijse et al. 2002) have been investigated. Even restoring streams in Nigeria has become important (Udoidiong 1999). The Rio Grande’s riparian forest has not experienced a major flood since 1941 and 1942, and the river’s flow is about half of what it was 60 years ago (Crawford et. al. 1993). The riparian forest is mostly isolated from the river, exotics such as salt cedar and Russian Olive are invading the native cottonwood habitat, and the forest is getting older while very few young stands are being created. Reinstating a spring flood in the Middle Rio Grande has been shown to promote nitrogen cycling and aid in transferring water and nutrients to riparian vegetation (Lieurance et al. 1994). Another study in the Middle Rio Grande found less litterfall at a flood site, increased leaf decomposition during period of inundation, and no difference in standing stock of forest floor litter between flood and nonflood sites (Molles et al. 1998). Ellis et al. (1999) observed that coarse woody debris and standing stock of forest floor litter were lower at a natural flood site compared to an experimental flood site and a nonflood site. Resulting leaf and wood decomposition rates increased with flooding. Restoration of the native bosque along the hydrologically altered and highly controlled Rio Grande would require instituting managed late spring/early summer floods in years with good water availability. Literature Cited Buijse, A.D., H. Coops, M. Staras, L.H. Jans, G.J. Van Gees, R.E. Grifts, B.W. Ibelings, W. Oosterberg and F.C.J.M. Roozen Restoration strategies for river floodplains along large lowland rivers in Europe. Freshwater Biology 47: Crawford, C.S., A.S. Culley, R. Leutheuser, M.S. Sifuentes, L.H. White, and J.P. Wilber Middle Rio Grande Ecosystem: Bosque Biological Management Plan. U.S. Fish and Wildlife Service, District 2, Albuquerque, New Mexico, 291 pp. Dahm, C.N., K.W. Cummins, H.M. Valett, and R.L. Coleman An ecosystem view of the restoration of the Kissimmee River. Restoration Ecology 3: Ellis, L. M., C. S. Crawford, and M. C. Molles, Jr Influence of experimental flooding on litter dynamics in a Rio Grande riparian forest, New Mexico. Restoration Ecology 7(2): Lieurance, F. S., H. M. Valett, C. S. Crawford, and M. C. Molles, Jr Experimental flooding of a riparian forest: restoration of ecosystem functioning. In: Proceedings of the Second International Conference on Ground Water Ecology, J. A. Stanford and H. M. Valett (eds.), pp , American Water Resources Association, Herndon, Virginia. Molles, M. C., Jr., C. S. Crawford, L. M. Ellis, H. M. Valett, and C. N. Dahm Managed flooding for riparian ecosystem restoration. BioScience 48: Schmidt, J.C., R.H. Webb, R.A. Valdez, G.R. Marzolf and L.E. Stevens Science and values in river restoration in the Grand Canyon. Bioscience 48(9): Tockner, K., F. Schiemer and J.V. Ward Conservation by restoration: the management concept for a river-floodplain system on the Danube River in Austria. Aquatic Conservation: Marine and Freshwater Ecosystems 8: Udoidiong, O.M Restoration of stream ecosystem integrity in Akwa Ibom State, Nigeria. Journal of Environmental Science 11(1): Beeping a well Litterfall tub Sampling for net nitrogen mineralization Sampling for coarse woody debris