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Genetic structure of seedling cohorts following repeated wildfires in the fire-sensitive shrub Persoonia mollisssp.nectens

Ayre, D.J., Ottewell, K.M., Krauss, S.L. and Whelan, R.J. (2009) Genetic structure of seedling cohorts following repeated wildfires in the fire-sensitive shrub Persoonia mollisssp.nectens. Journal of Ecology, 97 (4). pp. 752-760.

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Increased ?re frequency is seen as a key threat to plant populations in Mediterranean-typeecosystems across the globe. Short inter-?re periods may exhaust soil-stored and ?re-stimulated seed banks of ?re-sensitive species, reducing actual and effective population sizes and eroding genetic diversity. 2. Here we used microsatellite genotyping to investigate the genetic impacts of repeated wild?res and, in particular, the contribution of above-ground genetic processes (seed and pollen dispersal) to the genetic structuring and composition of post-?re recruits in an isolated population of the ?re-sensitive shrub Persoonia mollis ssp. nectens. 3. We tested the hypothesis that limited pollen and seed dispersal, in combination with the potentially patchy effects of ?re at a ?ne scale within populations, would generate a highly struc- tured population, a decline in genetic diversity after each ?re and genetic heterogeneity between successive cohorts. 4. Wild?res killed all 25 adult plants in 1997 and, in 2001, killed all of the 476 seedlings remaining from the 1997 seedling cohort. Although there was no possibility of replenishment of the seed bank in the interval between ?res, a second cohort of 381 seedlings emerged after the 2001 ?re. 5. We found no evidence that successive ?res produced either a decline in genetic diversity, as measured by allelic richness or expected heterozygosity, or the genetic differentiation of adult and successive seedling cohorts (Pairwise FST = ?0.0125 to 0.0009). The seedling cohorts displayed less genetic structuring than anticipated. Spatial genetic structure was low, ranging from Sp = 0.02 in the 1997 seedlings to Sp = 0.06 in the 2001 seedlings, and using parentage analysis, we found that seedlings clustered under dead adults rarely re?ected simple seed shadows. 6. Synthesis. Overall, we found that a numerically large seed bank with a bet-hedging strategy of staged seed germination, in combination with genetic mixing achieved by both pollen and seed dispersal, provides a powerful buffer against the negative impacts of frequent fire in P. mollis ssp. nectens.

Item Type: Journal Article
Publisher: Blackwell Publishing
Copyright: © 2009 The Authors.
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