Recent forest storm events benefit pollinators regardless of windthrow characteristics

Abstract

Understanding the effects of increasingly frequent and intense natural disturbances on biodiversity is central in forest ecology research. Large-scale windthrows create novel open habitats, which can be beneficial or harmful to biodiversity, depending on the studied taxonomic group and on the post-disturbance type of management. While previous research has largely focused on the differences between unsalvaged, salvaged, and intact forests, the effects of different environmental conditions within disturbed forests remain largely unexplored, especially for pollinating insects. Three years after a major storm event that hit spruce forests in the southeastern Alps (“Vaia” storm), we sampled wild bees, hoverflies, butterflies, and tachinids in 6 intact forest sites and in 35 salvaged wind-affected sites varying in local and landscape characteristics. Windthrows hosted higher species richness of bees, hoverflies, and butterflies, while the diversity of flower-visiting tachinids did not differ between disturbed and intact forests. The diversity of the pollinator taxa sampled in windthrows was not correlated with the local diversity of forbs, but it was positively correlated among taxa. However, none of the different pollinator guilds responded to the local and landscape characteristics diversifying storm-affected areas. Our results suggest that, in the short term, transient pollinator species may exploit the resources in forest gaps created by recent large-scale storm events in an opportunistic way and without consistent relationships with the environment.