The use of trees as shelters by salamanders: implications for forest management and amphibian conservation

In forest ecosystems amphibians often represent the greater portion of biomass of vertebrates. Salamanders in particular are invertebrates’ predators and, being ectotherm, they are capable to efficiently convert the major part of ingested biomass, making it available for the upper trophic levels. As a consequence, they play a key role in the nutrient and carbon cycles. Both completely terrestrial and semi-aquatic amphibians need suitable terrestrial shelters. Trees are a natural source of refuges for amphibians, that may found many shelters in the buttresses or in the ground holes formed by roots. The spectacled salamander Salamandrina perspicillata is an Italian endemism, with mainly terrestrial habits, for which we aim at investigating the selection of trees as shelters, based on tree features, using occupancy probability as a proxy of tree suitability. This research is developed within the project Life ManFor C.BD, and is aimed at finding a synthetic and quickly measurable index of tree suitability, capable to link forest management and biodiversity conservation. We investigated one hectare of beech forest in the “Montedimezzo-Pennataro” test site. For 385 trees we recorded stem diameter (DBH, starting from 10 cm), number of buttresses (BUT) and number of cavities that are created between stumps and soil in the vicinity of the buttresses loops (HOL) in order to detect if there was a relationship between such variables and the use of trees by salamanders. We conducted six surveys in the study site from October to November (2013), recording salamanders’ presence/pseudo-absence for each tree. Based on our results, occupancy models that allowed salamanders’ detection probability to vary among surveys have the best empirical support, in particular the model including all of the three site covariates (DBH, BUT and HOL). Naïve and estimated proportion of tree occupied are 0.44 and 0.71, respectively. Our research has focused over a relatively small area, investigating single tree features, in order to provide a good proxy of tree suitability by means of occupancy level. Ground level holes and buttresses seems to be essential in providing shelter sites for Salamandrina perspicillata. Since these features are correlated with DBH, a forest management option aiming at conjugating forest harvesting and salamander communities conservation may focus on the retention of those trees, having a larger DBH along with a large number of buttresses and cavities at the ground level.