Distribution and vegetation of Pinus mugo subsp. mugo dieback patches in Maiella massif (Central Italy)

Forest dieback in the last decade has been reported all over the world and not only causes a significant loss of forest yield but also affects successional trajectories. Here, we investigate the plant communities associated with Pinus mugo subsp. mugo dieback patches in Maiella massif. Dieback patches were examined by using satellite images to describe the occurrences and distribution. According to dieback patch size, we identified three ontogenetic stages: small, medium and large. To assess the effect of P. mugo on coexisting species, patch was divided into four belts according to P. mugo healthy status: OUT, FRONT, DEAD and IN zone. Within the four belt zones for each of the three ontogenetic stages, a vegetation analysis was conducted. Overall, 35 dieback patches were recorded and all are characterized by a circular shape and a size ranging from a few meters to 76.1 m. The linear correlation between the width of the inner regeneration belt and the total diameter of the patch suggests that the dieback area expands centrifugally due to the death of standing P. mugo. The increased resources, in terms of light availability caused by dieback, contribute to higher plants diversity in DEAD belts with the highest cover of hemicryptophytes. Contrariwise, in the OUT belts, not affected by dieback, plant diversity was the lowest with the highest cover of phanerophytes and a good contingent of nemoral species. Dieback affects forest structure and leads to sudden vegetation shifts that play an important role in maintaining biodiversity by allowing alternation between forest and grassland ecosystems.