Deadwood anisotropic facilitation on seedling establishment after a stand-replacing wildfire in Aosta Valley (NW Italy)

The capacity of a forest ecosystem to recover following major disturbances depends on the regeneration characteristics of the species and the environment at the time of establishment, resulting from several interacting biotic and abiotic factors. At climatically stressed sites major drivers of recruitment are the presence of a seed source and the availability of ‘safe sites’ for germination, particularly in the harsh conditions resulting after a stand-replacing wildfire. Post-fire rehabilitation and restoration treatments can produce a deep ecological impact on recruitment processes, acting on biotic legacies and altering the variety and abundance of microsites. Two common post-fire management strategies, salvage logging and the absence of any post-fire intervention, were contrasted in a burned area located in Aosta Valley (North-Western Italy) to identify main environmental variables affecting seedlings and to quantify the effect of shelter elements on tree recruitment. Our hypothesis is that post-fire burned wood management may greatly affect microhabitat suitability for seedling survival in a dry mountain Pinus sylvestris forest. Regeneration density five years after the fire was still low, even though tree species recruitment started immediately following the disturbance. Differences in species composition were found among the investigated treatments. Regeneration density and diversity were positively associated with deadwood. An exception was represented by Populus tremula, regenerating mostly vegetatively, whose behaviour differed from the other tree species. Ground cover conditions contributed to patterns of seedling occurrence. The strong spatial association of seedlings with deadwood suggests that deadwood produces microsites that enhance establishment of regeneration. The relationship between nurse deadwood elements and regeneration was found to be highly anisotropic, as a consequence of the higher protection from radiation and reduced soil moisture loss in the shady sides of the shelter element. In this context post-fire management, particularly when removing burned wood, should be implemented with an understanding of its potential to affect the capacity of the ecosystem to restore, influencing both directly and indirectly recruitment.