Influence of intermediate-scale wind disturbance on development and succession in quercus stands on the Cumberland Plateau
Natural disturbances play important roles in shaping the structure and composition of all forest ecosystems and can be used to guide silvicultural practices. Disturbance intensity is measured along a gradient ranging from highly localized, gap-scale events to stand-replacing events. High wind storms such as downbursts, derechos, and low intensity tornadoes typically fall in the center of this gradient and result in intermediate-scale disturbances, removing 30-60% of basal area. Despite their frequency and widespread occurrence, little is known about how intermediate-scale disturbances drive stand development. On 20 April 2011, the Sipsey Wilderness Area in Alabama was affected by an EF1 tornado with accompanying straight-line winds. Stands were sampled in a stratified subjective sampling design to evaluate the effects of intermediate-scale wind disturbance on the development of Quercus stands in regard to structure and recruitment. My specific objectives were to: 1) quantify damage severity in basal area reduction and percent canopy loss of this particular disturbance along a gradient of wind disturbance, 2) detect structural acceleration or retrogression of stand development caused by an intermediate-scale wind disturbance, and 3) elucidate compositional acceleration or retrogression for an intermediate-scale wind disturbance. I established 109 0.04 ha plots across a gradient of disturbance, classified as control (undamaged), light, and moderate to inventory the effect of wind damage on development and succession. Basal area was reduced from 25.5 m2 ha-1 to 24.0 m2 ha-1 and 15.5 m2 ha-1 (p < 0.001) for light and moderate damage, respectively. The percent of live and damaged trees for control, light, and moderate was 0.3%, 3.0%, and 10.7%, respectively. PAR was significantly increased within the moderately damaged areas (p < 0.001). Logistical regression showed an increasing probability of mortality during wind disturbance with increasing diameter. Based on my findings, this intermediate-scale disturbance increased intra-stand heterogeneity and accelerated succession, favoring shade-tolerant taxa established in the understory.