Windthrow disturbance impacts soil biogeochemistry and bacterial communities in a temperate forest

Forests across the world are subject to disturbance via wind, wildfire, and pest and disease outbreaks. Yet we still have an incomplete understanding of how these stressors impact forest biota—particularly the soil microbes, which govern forest carbon and nutrient cycling.

Here, we investigated the impact of a severe windstorm on soil bacterial communities in Kielder Forest, a temperate coniferous forest in the north of England. Within ten individual sites, defined by common stand composition and topography, we established 50 m² plots in undisturbed stands, and in nearby stands that were moderately and/or severely disturbed by windthrow. Soils were sampled within each of the 22 study plots, and analysed for changes in carbon and nitrogen content, pH, root biomass, and bacterial community structure. We separately sequenced bacteria from bulk soils, rhizosphere soils, and root tissues to assess whether disturbance impacts varied based on the proximity of microbiota to tree roots.

Less than a year after the storm, we found that the most severely disturbed stands had lower canopy cover, lower soil carbon content, higher soil pH, and a smaller fine root biomass than the undisturbed stands. Disturbance also impacted bacterial community beta-diversity, but the effects were subtle and did not vary among assemblages in bulk vs. rhizosphere soils.

Impacts of aboveground disturbance on soil biogeochemistry can be significant, but soil bacterial communities are relatively well-buffered against these changes. However, altered patterns of root growth and carbon cycling may have longer-term implications for forest recovery after windthrow disturbances.