Habitat Quality Assessment:
Index of Biotic Integrity
A key feature of the IBI approach is that the value calculated for each metric at
each study site is assigned a numeric "score." These scores are based on
comparing the value of the metric at the study site to the value calculated for one
or more reference sites having little or no influence from human disturbance.
For example, a low score of 1 might be assigned if the value of a metric deviates
strongly from the reference site value, an intermediate score of 3 might be assigned
if the value deviates only slightly from reference, and a high score of 5 might be
assigned if the value is comparable to the reference value. The numeric scores of 1,
3, or 5 for the individual metrics are then combined to produce the IBI, and the
study site can be rated as having "poor," "good," or
"excellent" biotic integrity in comparison to reference site IBI values.
Reference sites thus provide a standard for comparison in the IBI approach, and
the ranges of values calculated for individual metrics reflect the variation present
both in natural communities and those under stress. The highest IBI values indicate
that the community found at a given study site has excellent integrity, comparable
to the best situations without human disturbance. The lowest IBI values indicate the
poorest biotic integrity, reflecting the greatest deviation from undisturbed reference
conditions.