Ground arthropods as potential indicators of flooding regime in the riparian forest of the middle Rio Grande, New Mexico

In 2001 and 2002, we pit trapped arthropods at eight riparian forest sites along the middle Rio Grande, four characterized by flooding in some years (flood sites) and four others where periodic flooding no longer occurs (nonflood sites). All flood sites flooded in 2001 but not in 2002, while nonflood sites never flooded. Arthropod counts and hierarchical cluster analyses of the sites indicated (1) significantly greater abundance of carabid beetles and the isopod Porcellio laevis in 2001 than in 2002; (2) significantly greater carabid beetle abundance at flood sites during each year of the study, with the relative abundance of one carabid species, Calathus opaculus, significantly higher at nonflood sites in 2002; (3) marginally significantly higher (2001) or significantly higher (2002) carabid species richness at flood sites; (4) no obvious response of the other taxa examined (isopods, tenebrionid beetles, and the cricket Gryllus alogus) to flooding regime, although differences in isopod abundance between flood and nonflood sites approached significance in 2001; (5) successful classification of all nonflood sites and three flood sites using the Bray-Curtis Similarity Index and carabid abundance. Overall, our results suggest that carabid beetles are fairly sensitive indicators of hydrologic connectivity between the Rio Grande and its riparian forest, while the other taxa examined are not. With the number of ongoing or planned restoration efforts increasing along the middle Rio Grande, carabids may represent an important tool for monitoring the response of riparian areas to managed flooding.