Ecology, floristic-vegetational features and future perspectives of spruce forests affected by Ips typographus: insights from the Southern Alps

In recent years, many spruce ( Picea abies ) forests have been severely affected by bark beetle ( Ips typographus ) outbreaks in the Southern Alps, but their ecological impacts remain poorly studied. This research analyzed the distribution, ecological, and floristic-vegetational characteristics of forests recently affected by the bark beetle in the upper basin of the Oglio River (Northern Italy) and developed a MaxEnt model to predict severe insect attacks in the coming decades. The results showed that the spruce forests affected by the bark beetle are located exclusively in the sub-mountain and mountain belts (below 1,600 m a.s.l.) and that 85% of them are found in areas with high annual solar radiation (> 3,500 MJ m ⁻ ²). The predictive model for areas susceptible to severe bark beetle attacks proved highly accurate (AUC = 0.91) and was primarily defined by the mean temperature of the dry winter quarter (contribution: 80.1%), with values between − 2.5 and 2.5°C being particularly suitable for the pest. According to the model, more than 58% of the current spruce forests in the study area will exhibit high susceptibility (probability > 0.7) to severe bark beetle attacks by 2080. The floristic-vegetational and ecological analysis of plant communities of 11 bark beetle-affected areas indicated that more thermophilic and significantly different forest communities (in both floristic and physiognomic terms) are expected to develop compared to those of pre-disturbance. Furthermore, the high coverage/density of spruce snags appears to accelerate plant succession, enabling the establishment of mature forest communities in a shorter time frame.