Rediscovery of Elaphoglossum serpens (Dryopteridaceae) in Toro Negro State Forest (Puerto Rico) and the Impacts of Landscape Modification and Hurricanes on Population Decline

Elaphoglossum serpens is a narrowly endemic fern with a restricted distribution in the cloud forests of Toro Negro State Forest, Puerto Rico. To assess its population status, we conducted a two-year field study across 38.56 hectares (156,849 m2) of cloud forest in Toro Negro and adjacent private lands. We rediscovered a small population of Elaphoglossum serpens at its type locality, Cerro Jayuya, where it was previously thought to be extirpated, and documented another population at Cerro Punta for the first time since it was last collected there in 1984. While E. serpens was once considered to be common, during our recent assessment we found a total of only seven remaining individuals in two subpopulations which are approximately two kilometers apart, highlighting a sharp population decline likely driven by landscape modification, habitat fragmentation, and hurricane impacts. Additionally, we documented the presence of two other threatened Puerto Rican endemic species in the same habitat: the tree Ilex cookii Britton & P.Wilson (Aquifoliaceae), with 147 individuals, and the tree-fern Alsophila dryopteroides (Maxon) R.M. Tryon (Cyatheaceae), with 190 individuals. These findings underscore the urgent need for conservation measures to protect E. serpens and its fragile cloud forest habitat.