Floods and fire along the Rio Grande: The role of disturbance in the riparian forest

Flow regulation has largely eliminated flooding along the Rio Grande in central New Mexico and has substantially changed the riparian ecosystem. This study investigates managed flooding as a means of restoring ecosystem function and structure. A site previously isolated from flooding was experimentally flooded for one month during late springs of 1993, 1994, and 1995. A reference site remained unflooded. These sites were compared to two sites located within the riverside levee, one of which flooded naturally while the second remained largely unflooded.;Experimental flooding did not change the biomass of woody debris or forest floor litter, but both were significantly lower at the natural flood site compared to the experimental site and the two unflooded sites. Leaf and wood decomposition rates increased with flooding. The increased wood decay rate after experimental flooding suggests that a decade of annual flooding may help restore accumulations of organic debris to pre-regulation levels. Flooding may have increased litter production.;Surface-active arthropod communities remain poorly described for riparian ecosystems of the and Southwest, and effects of river regulation and habitat alteration on these potentially important invertebrates are largely unknown. Flooding did not affect total taxonomic richness, nor richness of spiders, beetles, or ants, but it slightly increased the richness of carabid beetles. Flooding altered the overall species composition, with beetles most responsive. Abundance of spiders and exotic isopods decreased after flooding, while native crickets and carabid beetles increased. Changes in species composition and abundance after experimental flooding were consistent with arthropod community structure observed at the naturally flooded site.;In the absence of flooding, fire has become an important disturbance in the riparian forest of the Middle Rio Grande. Short-term monitoring after a fire in 1996 suggests that the cottonwood forest has the capacity to recover from moderate fires. Although few cottonwoods retained viable tissue in the canopy, at least 40% of individuals were sprouting two years after the fire, and survivorship may have been as high as 80%. Survivorship of saltcedar was approximately 55%. Restoring the natural flow regime may lessen the impact of fires on riparian forests by decreasing fuel loads.