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The Relative Influence of Diseases and Other Small-Scale Disturbances on Fuel Loading in the Black Hills

Disturbances that kill trees in forests often co-occur in time and/or space. This process results in changes in the fuel loading for wildfire. Determining specific causes of changing fuel loads can be complex. Path analysis was used to estimate the relative importance and the strength of interaction of each of nine small-scale disturbances affecting forest stands in the Black Hills. Different disturbances were partitioned according to their indirect and direct effects on fuel loads. Fire and wind had the greatest indirect effects; stem rots had the smallest. Root rots had the largest direct effects. Root rots, strong wind, stem rots, suppression, human disturbances, and tree cutting all caused fuel loads to increase. Treeless meadows, stem cankers, fire, ice/snow damage, failed regeneration, and shallow soil were associated with decreasing fuel loads. Grazing, lightning, bark beetles, and competition had null impacts. Disease control has two aims: reducing fire hazard and enhancing restoration. Understanding the biology and ecology of the agents that create dead wood is as fundamental to restoration ecology as it is to forest pathology. Management and control both begin by first determining the cause.