Abstract:
Strategies to enhance ecosystem resilience are increasingly needed in forest management plans. Natural and managed disturbances that alter ecosystem resilience to other perturbations are called compound disturbances. This dissertation first synthesized the literature on compound disturbances in forest ecosystems. I used a systematic review to catalogue case studies of compound forest disturbances and identify trends in the types, timing, environmental settings, and ecological consequences of each disturbance combination. The review emphasized that the detection of positive, negative, and neutral disturbance impacts on ecosystem resilience were often contingent on which response variables were used to monitor forest recovery. To illustrate and investigate this and other key concepts described in the review, I then examined a combination of wind disturbance, salvage logging, and prescribed fire in the Alabama Fall Line Hills. A range of woody plant, ground flora, and ground surface material metrics were collected before and after prescribed fire in Pinus palustris Mill. woodlands differentially impacted by an EF3 tornado and salvage logging. In support of the review, salvage logging and prescribed fire had different effects on post-wind disturbance recovery depending on which response variables were assessed. Pinus palustris saplings exhibited the greatest densities in salvage-logged sites and were more resistant to prescribed fire than most other sapling species. This indicated that recovery toward P. palustris canopy dominance was not negatively affected by salvage logging and was enhanced by prescribed fire. Ground flora diversity and community dissimilarity, however, were reduced in salvage-logged sites before and after prescribed fire. Nonetheless, prescribed fire did impose some consistent selective pressures on understory plants with common life-history strategies. Overall, this dissertation supported the use of prescribed fire to promote P. palustris woodland recovery. Leaving some wind-disturbed zones unlogged was also recommended to support ground flora resilience. Moving forward, a diversity of response variables should be measured to achieve comprehensive assessments of disturbance effects on ecosystem resilience.
