A Floristic Quality Assessment system for the coastal prairie of Louisiana

Evaluation systems to assess the biotic integrity of plant communities exist for some ecosystems, but not the increasingly rare coastal prairies of Louisiana. A list of plant species occurring in Louisiana's coastal prairie was created and coefficients of conservatism (C) were assigned for each species. A Floristic Quality Index (FQI), which is calculated using the C values provided by a panel of experts, can be used to evaluate prairie remnants and restorations. We assigned C values from 0-10 based on their estimated degree of association with prairies of various levels of natural quality and their tolerance of disturbance. Those species given a rank of 0-3 are deemed to be colonizing species found in a variety of habitats and are adapted to fairly severe disturbance. Species with C values of 4-6 are those that are often common in fairly high quality coastal prairie, occur in other community types and are moderately tolerant of disturbance. Species with rankings of 7-8 are associated with high quality natural prairie habitat and slight disturbance. Those species ranking 9-10 are those restricted to very high-quality habitat and have a high fidelity to coastal prairie.

Unlike FQI systems devised for other areas, we also weight the coefficients assigned to nonnative species found in coastal prairie. We believe that the presence of exotic species in a native plant community lowers the conservation value of that community. Consequently, we assigned C values from -1 to -3 to nonnative species based on the perceived threat of their invasive potential and ability to exclude native species. Including the C values of exotic species allows the calculation of an adjusted floral quality index that provides an additional dimension to floristic quality analysis. This index will be of value to restorationists, managers and others involved in assessing the integrity of natural areas and developing management strategies based on these criteria.