Stand structure and dynamics in a mixed and multilayered forest in the Upper Susa Valley, Piedmont, Italy

Size, age, and spatial structures were studied in a mixed, multilayered forest located in the Upper Susa Valley in Piedmont, Italy, using complete stem mapping, dendrochronology, and spatial analysis on a 1-ha permanent plot. All trees with a diameter >4 cm at 50 cm height (991) and stumps (322) were mapped, measured, and cored. The 639 cross-dated samples were used to reconstruct the disturbance history, and dendroecological results were then compared with information on forest and land use from documentary archives. The stand has undergone substantial shifts in forest structure and species composition over the last 200 years, from an open structure with larch (Larix decidua Mill.), Swiss mountain pine (Pinus uncinata L.), Norway spruce (Picea abies (L.) Karst.), and scattered regeneration to a dense multilayered structure with silver fir (Abies alba Mill.) and Norway spruce with dense regeneration. Shifts in dominance and structure were found to be consistent with land-use changes rather than with disturbance history. These results confirm the importance of multiple sources of independent data to characterize the disturbances that have affected the origin and development of stands heavily impacted by humans. Knowledge of stand history and understanding of potential ecological transformations are essential for the correct application of close-to-nature silvicultural practices.