Global change and forest disturbances in the Mediterranean basin: factors affecting pine processionary moth populations in two different bioclimatic strata in Northern Algeria

The pine processionary moth (PPM), Thaumetopoea pityocampa (Denis and Schiffer-müller), is one of the most important defoliators of pine and cedar forests on the Mediterranean margin. Repeated attacks by this pest are generating considerable natural and economic damage in the area. In order to study the population dynamic patterns of its range, a winter nest abundance survey was conducted in two different areas of cedar forest in the two National Parks of Chréa and Belezma during the three-year period 2020-2022 in northern Algeria. The altitudinal distribution of the insect was developed at three different sites in each area. The effects of temperature and precipitation on the infestation index were developed over the four-year period 2019-2022. Under a global climate change scenario, we discussed how perturbations in meteorological factors can affect PPM density in different bioclimatic layers. Data analysis revealed a permanent increase in PPM population density in Chréa forest and a gradual decrease in its size in Belezma forest. Important winter nest count values were recorded at higher elevations in the two areas mentioned above. Seasonal variation analyses show a strong correlation between perturbations in climatic parameters and winter nest abundance in both semi-arid and sub-humid strata.