Wind is one of the most important natural disturbances influencing forest structure, ecosystem services, and successional processes worldwide. Wind storms (i.e., blowdowns) typically result in overstory tree mortality that is intermediate in severity between small canopy gaps and large, stand-replacing events. Like other intermediate-severity disturbances, blowdowns may be more pervasive than previously recognized, and blowdown frequency may increase with anthropogenic climate change and land use. This study quantifies intermediate-severity blowdown effects on (1) live and dead legacy structure; (2) aboveground carbon storage; (3) tree regeneration and associated stand dynamics at inventory plots in four mature, mixed hardwood-conifer forest sites in the northeastern United States. We compare wind-affected forests and adjacent reference conditions (i.e., undisturbed portions of the same stands) from zero to eight years post-blowdown using parametric (ANOVA) and nonparametric (NMS ordination) analyses.
Results/Conclusions
Following recent blowdown events, overstory tree survival was variable but substantial, with live basal area ranging from 19% to 59% of reference areas. On average, initial downed coarse woody detritus biomass was 20% of standing live tree biomass in reference areas but 3.11 times higher in blowdown areas, illustrating a substantial carbon transfer from live to dead pools. Despite these dramatic changes, structural complexity remained high in blowdown areas, as indicated by the size and species distributions of overstory trees, abundance of sound and rotten downed wood, spatial patterns of light availability, and variability of tree of non-tree understory vegetation. In addition, tree species composition was similar between blowdown and reference conditions at each site, with generally shade-tolerant species dominating across multiple canopy strata (shade-intolerant density ≤10% in all cases). Rather than recruiting a new cohort of shade-intolerant trees, these blowdown events released shade-tolerant regeneration that was present prior to disturbance. Our findings suggest that intermediate-severity wind disturbance can contribute to structural complexity without hindering stand development towards late-successional species composition. This study provides a baseline for multi-cohort silvicultural systems designed to restore heterogeneity and resilience associated with natural disturbance dynamics.