Less suitable climatic conditions and pests increase tree defoliation in Spanish Iberian Peninsula forests

Abstract

Forest vulnerability to climate change is expected to differ between species and across species ranges. Therefore, it is important to develop tools that can standardize the variability in regional climate patterns and extreme events for populations and species. Extreme climate events, such as droughts and heat waves, have the potential to severely impact populations that are already close to the limits of their physiological tolerance. These factors can be further exacerbated in tree populations when coupled with detrimental biotic interactions, such as pathogen and insect infestations. We analysed a monitoring network dataset of tree defoliation from 2005 to 2013 including 560 plots situated in the Iberian Peninsula. We utilized a climatic suitability index obtained from Ecological Niche Models (ENMs), to investigate whether changes in the climatic suitability for seven forest species and the presence of biotic agents correlated with tree defoliation. Our results emphasized that higher levels of tree defoliation were significantly associated with lower climatic suitability. Likewise, these levels increased significantly with high pest intensity. Interestingly, climatic suitability interacted with pests to explain defoliation patterns. Pinus sylvestris and Quercus pyrenaica were particularly susceptible to defoliation in areas with lower climatic suitability and with increasing pest intensity. This suggest that pests play an important role in understanding species performance under less climatic suitable conditions, at least in the forests of the Spanish Iberian Peninsula. Our fundings can serve as a valuable tool for identifying forest populations and species especially susceptible to the impacts of changing climatic conditions on a regional scale. This contribution aids in the incorporation of innovative conceptual tools and processes into the decision-making and management of forest ecosystems in the current context of climate change.