Structural complexity and developmental stage after an intermediate-scale wind disturbance in an upland Quercus stand

by

Lauren Cox, Justin Hart, Callie Schweitzer, Dan Dey

University of Alabama; University of Alabama; US Forest Service, Southern Research Station; US Forest Service, Northern Research Station

Abstract – Stand structural complexity is an increasingly popular silvicultural objective, as complex structures are hypothesized to be more resistant and resilient to perturbations. On 20 April 2011, an EF1 tornado tracked 5 km through the Sipsey Wilderness in north Alabama, leaving a patchwork mosaic of disturbed areas. In summer 2014, we established a 100 x 200 m rectangular plot perpendicular to the swath of the storm within an affected Quercus alba stand. Within this plot, we recorded the location, species, diameter at breast height (dbh), and crown/decay class of all stems. Using the percent of basal area removed by the storm, we divided the plot into three disturbance severity classes, including a minimally disturbed control. To determine the structural complexity of the stand, we used multiple spatial and non-spatial indices including the Gini coefficient, nearest neighbor analysis, diameter differentiation index, and the structural complexity index. We compared values for each index among the disturbance severity classes. Using the same disturbance severity classes, we assigned each portion of the plot a developmental stage based on stem size classes present. Preliminary results indicate that the 2011 tornado removed 22% of basal area within the plot. Stem mortality was clustered near the swath of the tornado. Our results provide a comprehensive understanding of the structural attributes in upland Quercus stands after an intermediate scale wind event and may be used to inform silvicultural systems intended to enhance structural complexity.