Ecogeographical determinants of investment in chemical defences in pines

Key message

Pine tree species exhibit significant levels of phenotypic variation in the investment in defences, which can be correlated with life-history traits, geographical affiliations and climate.

Abstract

Understanding the ecological and environmental correlates of tree defences has value for understanding forest susceptibility to pests and pathogens in a time of global change. In the present work, we assessed how life-history attributes and biogeography are related to chemical defences of pine trees in Palaearctic and Nearctic forests. We studied adult trees of ten pine species in forests of Portugal and Eastern North America. We measured total phenols (using gallic acid as a standard) and condensed tannins (as catechin hydrate equivalents) in the phloem of pine branches. Pine trees in forests of Eastern North America presented higher levels of total phenolic content in their phloem tissues than pine trees in forests in Portugal. Higher values of precipitation were correlated with higher phenolic content and higher temperatures were associated with higher levels of condensed tannins. A few life-history traits—the maximum height reached by each pine species, the age at which they start reproducing, and the size of seeds—were positively related with defences. The present work points to interactions between life-history attributes, climate, and geographic location as predictors of defensive investment in pines. The results are useful for understanding differences within and among pine forests in susceptibility to pests and pathogens.