An approach to illustrate the naturalness of the Brazilian Araucaria forest

Abstract

The concept of “naturalness” can be associated with conservation status, resilience, and biodiversity. Its most common definition relates to the degree to which a resource is similar to its original state. Hence, we developed a naturalness assessment method for the Brazilian Araucaria forest. We used data collected within 145 systematically distributed plots over an area of ∼56 000 km2. We selected five indicators to compose a unified naturalness index: (i) evidence of human activities inside the forest stand; (ii) abundance of naturalness-indicator species; (iii) standard deviation of diameter at breast height (Sdbh); (iv) species diversity of the understory–natural regeneration layer; and (v) forest stand landscape metrics. We then calculated the Euclidean distance between the vector generated from the indicators of an ordinary forest stand and the vector generated from a theoretical reference forest (TRF) with maximum naturalness. The reduced Sdbh reflected the stands’ diminished structural diversity as result of historical logging and other ongoing human activities. Most stands presented average naturalness compared with the TRF. Besides the lack of data on undisturbed forests to thoroughly evaluate the naturalness index, evidence suggested that it summarized relevant forest attributes to the extent that protected areas presented greater naturalness than nonprotected areas.