A terrestrial arthropod index of biological integrity for shrub-steppe landscapes

We studied arthropods in shrub-steppe at the Idaho National Engineering and Environmental Laboratory to identify scientifically sound indicators of ecological condition and to develop a terrestrial index of biological integrity (T-IBI), an analogue of the multimetric indexes used to manage water resources. We sampled terrestrial arthropods with pitfall traps in late spring at nine sites selected to reflect little or no human disturbance and diverse histories of human activity (livestock grazing, chemical contamination, physical disturbance, restoration). Our evaluation of 56 assemblage attributes - measured as taxa richness or the relative abundance of key taxonomic, trophic, or ecological groups - sought measures that varied systematically with human influence. From 21 attributes that did vary significantly with disturbance, we selected 8 for a T-IBI. This Idaho T-IBI correlated significantly with human influence across the nine sites. We compared this index with an independently developed T-IBI, also comprising eight metrics, from three years' study at the Hanford Nuclear Reservation in Washington State. Six metrics were identical in both indexes. Combining our Idaho and Hanford results, we propose a nine-metric T-IBI for shrub-steppe lands. Concordance of metrics and the index in two widely separated shrub-steppe environments suggests that T-IBI offers an effective means of measuring biological condition. Parallels in this terrestrial system with the extensive aquatic work applying the same principles further suggest that this T-IBI could be effective in guiding conservation and restoration decisions in shrub-steppe landscapes.Karr and Kimberling "A terrestrial arthropod index of biological integrity for shrub-steppe landscapes." Northwest Science. 2003; 77(3): 202-21