Effects of an intermediate-scale wind disturbance on mixed pinus-hardwood stands

Abstract

All forest ecosystems are subject to natural disturbances that influence development and succession. Forest disturbances are typically classified based on severity and spatial extent with events ranging from small, single-tree gaps to large, stand replacing disturbances. Intermediate-scale disturbances occur along the gradient between the two endpoints. On 20 April 2011 in Lawrence County, AL, an EF1 tornado tracked 5 km, leaving a patchwork mosaic of disturbed areas that included multiple mixed Pinus-hardwood stands. The objectives of this thesis were to describe the effects of intermediate-scale wind disturbance on forest composition, structure, succession, and development, and to compare and contrast the effects of silvicultural entries to those of natural disturbance. The storm disproportionately removed large Pinus stems, and effectively accelerated succession and promoted hardwood dominance. The ISD created understory light levels in the disturbed neighborhoods that were significantly higher than pre-disturbance conditions after five growing seasons. Similar to the naturally disturbed stands, the intermediate treatments also accelerated succession by preferentially removing Pinus canopy stems and promoting Quercus dominance. This study addresses the gap in our understanding of the effects of intermediate-scale wind disturbance on composition, structure, succession, development, biodiversity, and sub-canopy light regimes in mixed Pinus-hardwood systems. This study will serve as a reference point for natural disturbance-based management in this forest type.