Surface-active beetles as indicators of habitat change in riparian restoration along the Sacramento River, California, USA

The main goal of riparian restoration along the Sacramento River in northern California is to create habitat for declining wildlife populations and to restore ecosystem function. Since European settlement, 95% of the original 500,000 acres of riparian forest in this region has been lost. This study used surface-active beetle assemblages to measure the success of this ongoing restoration effort. We used pitfall traps to conduct monthly sampling of surface-active beetles for one year within young restoration sites (1-3 years old), old restoration sites (6-11 years old) and remnant riparian forest sites (>25 years old). Over 24,000 individuals in 31 families representing 188 morphospecies were collected. The three most common beetle families were Carabidae, Staphylinidae and Tenebrionidae. Several morphospecies were significantly associated with each forest age, some apparently restricted to either remnant riparian forests or young restoration sites. These morphospecies may be used as indicator taxa for that forest age group. Cluster Analysis and Non-Metric Multidimensional Scaling were used to determine whether beetle assemblages are tending along the desired trajectory, toward that of remnant forest. These analyses indicate that as restoration sites age, beetle assemblages increasingly resemble those found in remnant riparian forests, thus providing one measure of success of the restoration. Terrestrial arthropods provide a sensitive and valuable measure of habitat change while generating baseline data on poorly studied taxa in this region.