Assessing biotic integrity in Iberian rivers: Development of a multimetric plant index

Aquatic and riparian plant species were examined in order to propose a multimetric plant index to assess the biotic integrity in Iberian rivers. An additional analysis with two other plant indices was performed to evaluate the present approach. A floristic survey was undertaken during May and early June 2000 in southern Iberian rivers. After the identification of two vegetation types, a partial canonical correspondence analysis of the floristic data with anthropogenic variables permited the recognition of the least perturbed sites, using the environmental characteristics as co-variables to account for natural site variability. From the 22 candidate-metrics, 8 were selected for inclusion on the final multimetric index: 3 representing composition measures (number of riparian and aquatic species, and number of annual species), 3 reflecting direct human-disturbances (abundance of Arundo donax, number of exotic, ruderal species), 1 trophic measure (number of nitrophyllous species) and 1 related with the riparian integrity (relative riparian width). Quality outputs were correlated with a global disturbance measure in order to evaluate the index performance and compared with the results of other plant indices. The Iberian multimetric plant index (IMPI) displayed a promising ability to relate riparian vegetation features to the current range of global disturbance. The IMPI will need to be further validated, with an enlarged set of metrics and a wider geographical area with clearly unimpaired reference sites in each vegetation type.