Climate-driven increase in mistletoe infestation in Iberian pine forests

Abstract

Mistletoe is a common hemiparasitic plant in forest in Spain. However, more studies on mistletoe infestations are needed to determine the spatial and temporal patterns and to develop control and monitoring programmes for forest health. For this purpose, we used harmonised data from three existing forest damage networks in Spain, including ICP-Forest, from which only national data was taken, including climatic variables to model the distribution and to predict the degree of mistletoe infection using geostatistical techniques. Having selected the variables, the spatial models were evaluated using the area under the curve statistic to predict the distribution area (AUC=0.99) and one-out cross-validation to predict the degree of infection in areas with mistletoe presence. Overall, 87 % of the pine forest area is free of mistletoe. Within the affected distribution area, the Alpine region (23 %) has the highest percentage of area affected, followed by the Mediterranean region (14 %), with no records available in the Atlantic region. Regarding mistletoe abundance, the variation throughout the study period according to damage-degree class reveals a decrease of 18.2 % in “slight” class, a decrease of 2 % in “moderate” class, an increase of 15 % in “moderate-high” class and an increase of 5.2 % in “severe” class. Our results indicate that the incidence and severity of mistletoe infection are highly spatially concentrated and strongly related to climatic conditions, especially temperature and precipitation in previous years. Prediction maps showing the spatial patterns of mistletoe distribution can be useful for damage prevention and risk control.