Pignut hickory (Carya glabra) recruitment failure on a Georgia barrier island

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Keen, Eric
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maritime forest , herbivory , pignut hickory , St. Catherine's Island
Demographic disruption in pignut hickory (Carya glabra) populations, a major canopy species, was observed for 10 years on St. Catherine’s Island, GA., and recruitment failure was identified as the central mechanism of local extinction. From 1996 to 2006 there was no recruitment by hickory seedlings into the sapling size class. Tree cores of the youngest adult trees indicate that there has been no recruitment at the study site for over 65 years. Tree cores in 4 other pignut hickory populations indicate similar patterns across the island. Field evidence of browse and a strong statistical relation (p<0.0001) between seedling density distributions and microsite protection from herbivory suggest that this trend in recruitment failure is related to the increasing abundance of deer and pigs on the island. Using a size class population projection model, we estimate that, if such recruitment failure and mortality rates continue, these hickory populations will be extirpated from the maritime forest within 200 years. The decline of this major canopy species will have extensive ecological implications. This study points to the high susceptibility of many hardwood tree species to the current biotic and abiotic conditions that are met within maritime forests on islands with a continuing history of land use.