Investigating the effect of resin collection and detecting fungal infection in resin-tapped and non-tapped pine trees, using minimally invasive and non-invasive diagnostics

Abstract

In pine stands systematic harvesting of forest products, such as resin extraction, are known to affect trees’ vitality and consequently their response to fungal diseases. The latter constitutes a serious threat for standing vigorous trees, thus early warning signals and short diagnosis time of fungal pathogens, are crucial for designing effective forest management practices. In this study, we explored the effects of the resin extraction process, which was one of the most prominent economic traditional activities throughout the Mediterranean region, on the pines’ growth, and we detected fungal presence in resin-tapped and non-tapped pine trees. For this, we obtained data from 333 resin-tapped and 163 non-tapped Pinus brutia trees, in 20 forest stands, on the island of Lesvos, Greece, by combining in-situ minimally invasive (tree coring) and non-invasive diagnostics (infrared thermography), with the trees’ phenotypic traits and indices. In each stand (30 × 30 m), tree cores were extracted from 34% of the total trees, while the fungal presence was confirmed (a) by the discoloration and decay patterns in the tree cores, (b) by external indicators of decay, such as fruiting bodies, and (c) by the sudden change in boring resistance during the tree cores’ extraction. To evaluate the effect of resin tapping on pines' growth, we developed hierarchical multiple linear regression models controlling parameters related to pines’ phenotypic traits, while for estimating the fungal presence, we used a set of logistic regression models. The results indicated that the number of tapping scars on the pines’ trunk surface, resulting from the resin extraction process, explained the decrease of (a) the average annual growth of the pines by 9.2%, (b) the annual growth after the resin extraction process by 11.7%, while the explanatory power increased to 19% in trees that were tapped early in their life. Fungal presence was successfully classified (a) in 91.5% of the resin-tapped trees, and (b) in 94.9% of the resin-tapped and non-tapped trees when combining trees’ phenotypic traits and indices with non-invasive diagnostics. These findings may contribute in monitoring forest stand dynamics in order to prevent or mitigate their degradation, and also towards effective management plans concerning resin extraction.