Threshold dynamics, multifractality and universal fluctuations in the SOC forest-fire: facets of an auto-ignition model

We consider the age of trees in the SOC forest-fire (FF) model of Drossel and Schwabl [Phys. Rev. Lett. 69 (1991) 1629] and use this parameter to replace the stochastic ignition by lightning with a deterministic threshold for auto-ignition. We demonstrate that the statistical properties of the system remain essentially unchanged by the elimination of the stochastic lightning process. We proceed to examine other aspects of the system and find evidence for multifractality in the distribution of trees, and dissipation fluctuation spectra of a universal form recently found in a great variety of systems.