Co-occurrence of multiple life history strategies in fire-prone landscapes

Shrubs in fire prone environments rely on two separate mechanisms for persistence in the face of fires lethal to plant shoots: 1. the ability to resprout from below ground tissues that have survived the fire; 2. seed germination, or release of serotiny, triggered by the heat or smoke a fire produces. These two mechanism lead to three life history strategies capable of persistence in the face of recurrent fire, obligate seeders (2), obligate resprouters (1), and facultative seeders (1 and 2). All three of these strategies co-occur in California chaparral and other Mediterranean-type shrublands. We simulated a spatially explicit landscape containing all three strategies and compared the relative fitness of each at varying mean fire return interval and coefficient of variation (CV) in fire return interval. Contrasts among life history strategies in optimal fire return interval are driven by differences in the timing of reproduction. Obligate seeders and facultative seeders recruit immediately after a fire event, while obligate resprouters recruit during the inter-fire period, thus more frequent fires favor seeder strategies, while longer inter-fire periods increase the fitness of obligate resprouting species. However, at return intervals shorter than the minimum age of reproduction obligate seeders are excluded from the landscape. Increasing values of CV in fire interval delayed exclusion of any strategy, however, at very high CV facultative seeders and resprouters were favored over obligate seeders. These results provide a foundation to understand the mechanisms of coexistence among these three life history types in fire-prone landscapes.