Influence of experimental flooding on litter dynamics in a Rio Grande riparian forest, New Mexico

Flow regulation, which has largely eliminated flooding along the Rio Grande in central New Mexico, has substantially changed the riparian ecosystem. W e investigated managed flooding as a means of restoring ecosystem function. After collecting baseline data during 1991 and 1992 in two riparian forest sites that had not flooded for about 50 years, we flooded an experimental site for 27-32 days during late spring of 1993, 1994, and 1995, leaving the reference site unflooded. During the final year of the study we compared t hese sites to two additional sites located within the riverside levee, one of which has been flooding naturally while the second remained largely unfl ooded. Three years of experimental flooding did not change the total biomas s of either woody debris or forest-floor litter at the experimental flood s ite. Both woody debris and forest-floor litter, however, were significantly lower at the natural flood site than at the experimental flood site and tw o unflooded sites. Leaf and wood decomposition rates increased with floodin g. The decay rate for cottonwood logs at the unflooded site (0.010 per year ) predicted a half-life of 69.3 years, while the decay rate of 0.065 per ye ar after 3 years of experimental flooding predicted a half-life of 10.6 yea rs. This suggests that a decade of annual flooding may be used to restore t he organic debris to pre-regulation levels. Flooding may also have caused a n increase in litter production. These results suggest that experimental fl ooding has initiated a process of restoring ecosystem function within the r iparian forest.