Monitoring of wild and transplanted individuals of the endangered species Polystichum neolobatum Nakai in the Tanzawa and Doshi Mountains, Japan

Abstract

We describe the results of a revisit survey assessing population size, leaf size, and habitat and the fate of three transplanted individuals of the endangered pteridophyte Polysticum neolobatum Nakai in the Tanzawa Mountains, Japan. We further report the same attributes, excluding transplant fate, from a nearby population in the Doshi Mountains that had not been previously visited but shared similar habitat attributes. At Tanzawa, the number of P. neolobatum declined from 21 in 2004 to only 5 immature individuals in 2020. The number of leaves per individual was typically six or fewer, leaf size was < 40 cm and there was evidence of herbivory on many individuals, likely due to grazing by sika deer. The habitat was mostly rock or weathered rock with slopes of 50° or greater. Of the three individuals previously transplanted, two were found surviving. Both were immature, even five years after transplanting, and leaf size was < 30 cm on both. At Doshi, we recorded 16 individuals in 2020, 12 of which were mature. Leaf apices were missing from eight individuals, again likely a product of sika deer grazing. All mature individuals had a maximum of five leaves and a leaf size > 40 cm. Leaves were significantly larger at Doshi relative to Tanzawa. Our results highlight how vulnerable the population of P. neolobatum at Tanzawa is to extirpation and suggest that the site may not be suitable for transplanted individuals. Individuals at Doshi were in better condition, but the population contains < 20 individuals and is experiencing damage from sika deer. We suggest that the next steps for the conservation of P. neolobatum include genetic analysis of wild individuals to guide spore collection and the establishment of ex situ populations.