A history of megafires and extreme droughts in California
Many shrubland communities around the world are fire-prone and adapted to a regime of periodic high intensity crown fires. In communities such as California chaparral fire is a natural ecosystem process and disturbances in this system come about mainly through disruptions in the fire regime. Anthropogenically induced changes in fire frequency include fire management practices that exclude fire and landuse practices that increase fire frequency. Theoretically each of these disturbances have thresholds above which the recovery of the vegetation after fire is threatened. Two such risks are ‘senescence risk’ and ‘immaturity risk’ (sensu Zedler 1995). These risks are evaluated by examining past fire history on different landscapes and the pattern of recovery under different fire regimes.
The balance of evidence points to senescence risk being of minimal concern for resilience of both plant and animal communities in these shrubland landscape. This is based on the limited extent of shrubland landscapes where fire suppression has successfully excluded fire and on the recognition that chaparral plant communities are extremely resilient to very long fire return intervals Immaturity risk, however, is a major threat to both native plants and animals due to disruptions in plant reproduction and animal recolonization. Future management of these landscapes must anticipate expected global changes in anthropogenic ignitions and develop approaches to prevent excessive fire loads on these landscapes