Individual tree characteristics and plasticity to climate conditions modulate resistance to bark beetle attack in Pinus uncinata.

Abstract

Forest infestation and mortality caused by bark beetles is increasing with climate change. Tree resistance to bark beetle attack may depend on resources allocation to growth or defence, which controls the shift from endemic to epidemic beetle populations. The aim of this study is to evaluate tree individual characteristics and climatic factors influencing tree resistance to bark beetle infestation in Pinus uncinata populations located in the central catalan Pyrenees. Specifically, we used standard dendroecological methods to (i) analyse tree resistance in living and dead trees in relation to growth and resin ducts formation as indicators of tree vigour and defence investment, respectively; (ii) evaluate how these processes are modulated by competition for resources; and (iii) determine the influence of climate, including temperature and drought stress, on tree resistance to bark beetles. The results indicate that trees that form larger resin ducts accumulate a greater total area of ducts leading to higher resistance to bark beetle infestation, likely due to their ability to have a higher resin flow. Competition for resources seem to modulate tree growth but it is not significantly related to resin duct characteristics. Importantly, our findings suggest that trees that survive bark beetle infestations may have greater plasticity under environmental variations: reducing growth and increasing production and total area of resin ducts under high temperatures and moderate drought conditions. Therefore, in the studied locations, investment in defence rather than in growth seem the primary determinant of the resistance of P. uncinata to bark beetles under increasing drought.