Ecological indicators of passive restoration in South Brazil's Atlantic Forest areas with former Pinus taeda L. plantations

The use of suitable ecological indicators for assessing and monitoring passive restoration is essential to understand the dynamics of natural regeneration and the restoration course. However, most developed restoration protocols in Brazil are specifically intended for monitoring active restoration. Only a few studies are addressing ecological indicators for passive restoration. In this context, we tested indicators defined by a monitoring protocol (SMA Resolution 32/2014) formulated for active restoration, along with other indicators of richness, diversity, and functional aspects of natural regeneration. The evaluations took place in sites under passive restoration in different age classes (between three and twelve years old) and in a secondary riparian forest (reference ecosystem) inside the Mixed Ombrophilous Forest (Araucaria Forest) in South Brazil. Those sites had previously been covered and degraded by Pinus taeda L. plantations. We compared the evaluated sites with the intermediate and final reference values proposed by the protocol to define the suitability of the tested indicators and the forest restoration process. Results showed that the canopy cover, density, and richness of regenerants are suitable to evaluate areas under passive restoration with a history of degradation by forestry. However, it is necessary to adapt the protocol's reference values. We further suggest the inclusion of other indicators related to the ecosystem's structure and functionality as the herbaceous cover, dispersion syndrome, life form, and the ecological group of species, as well the definition of indicator species for the different restoration levels. Despite the low similarity in composition, structure, and functional aspects with the reference ecosystem, the passive restoration showed potential to perpetuate the successional course in the studied areas.