Introduction:

About 113 hectares within the Lomas de Barbudal Biological Reserve (RBLB) would be flooded if the Río Piedras irrigation reservoir were established in northwestern Costa Rica. Given this inevitable impact, Costa Rican legislation requires evaluating the loss of diversity in the site and compensating for it following the principle of ecological equivalence.

Objetive:

Our goal was to assess the loss of diversity at that site and evaluate the condition of an adjacent private property as a potential site to compensate for those losses.

Methodology:

The diversity, composition, and conservation priority of vascular plants, vertebrate fauna, and understory arthropods were assessed at the RBLB flood site and on an adjacent private property identified as a potential offset site. The equivalence in diversity between both sites was evaluated by assigning scores to the different indicators at the compensation site concerning those observed in RBLB. The sum of these scores represents the diversity condition of the compensation site and can be used as a criterion to support compensatory actions.

Results:

All surrogate groups recorded a high number of species, although the information provided by herbaceous plants, non-flying mammals, and reptiles was limited. In contrast, the other groups indicate a greater diversity in the potential flood site, attributed to subtle environmental differences and the better conservation at this site. Consequently, it was assessed to replace the affected area with a larger offset site area to compensate for the estimated losses in diversity.

Conclusion:

Our analysis shows that surrogate groups can be used in short-term environmental studies. However, the groups to be used must be carefully selected, considering the objectives and scope of the project. Quantifying the diversity condition of the compensation site concerning that found in a reference site seems to be a valid, repeatable, and evaluable procedure that allows establishing criteria on which to base compensatory measures.