Effects of landslides on the mountain vegetation of Flores Island, Azores

Question What are the consequences of frequently occurring landslides on vegetation dynamics, floristic and structural diversity? Location 39 degrees 27'N; 31 degrees 13'W - Morro Alto, Flores Island, Azores, Portugal. Methods Six comparable landslides were selected. Plots were placed at the top, slope and toe of landslides. Data on floristic composition and biovolume, demography and size structure of the dominant tree species (Juniperus brevifolia) were collected. Hierarchical agglomerative clustering and Principal Component Analysis were used in order to identify succession stages and compare succession pathways and vegetation recovery in different parts of the landslides. Results Four stages of primary succession on substrates formed by landslides were identified: pioneer (Festuca-Sphagnum grassland), assembly (Juniperus-Festuca-Sphagnum open scrub), building (Juniperus-Sphagnum scrub) and mature (Juniperus-Sphagnum woodland). Concerning J. brevifolia populations, the succession pathways are independent of location on the landslide. However, at the floristic level, there are some differences, mainly in the pioneer stage at the toes of landslides. Better abiotic conditions, resulting in a higher succession rate, are probably responsible for a faster vegetation recovery on landslide toes. Conclusion Landslides trigger succession processes that enable a massive regeneration of the dominant tree species and existence of species not present in mature forests. They are also responsible for the simultaneous occurrence of vegetation of different structures. Overall, landslides increase the floristic and structural diversity of the vegetation, consequently increasing landscape heterogeneity.