No evidence of a long-lived seedbank in common buckthorn, Rhamnus cathartica L., within Minnesota deciduous forests

Abstract

The persistence of invasive plant species in soil seedbanks can pose a significant obstacle to effectively managing invasive plant populations. Rhamnus cathartica (common buckthorn, hereafter ‘buckthorn’) is a wide-spread invader of forest understories in North America that can quickly re-establish following removal, in part due to germination of buckthorn seedbanks. Although empirical evidence seems slight, influential organizations communicate that buckthorn seedbanks endure for at least six years. In order to assess the accuracy of such messaging, we characterize the duration of buckthorn in soil seedbanks by monitoring germination of both planted and naturally-occurring seeds. Across the 13,232 buckthorn seeds planted, germination occurred almost entirely in the first two years after planting (96.6% and 3.3% in the first and second year after planting, respectively). Our observations of naturally-occurring seedbanks displayed similar patterns, with 97.9% and 1.9% of all newly emerged seedlings found in the first and second years following removal of mature buckthorn stands, respectively. These findings indicate that re-occupation by buckthorn following removal results more from incomplete removal, an initial flush of germinants, and dispersal from outside the site than from long-lived seedbanks. Therefore, if buckthorn is removed comprehensively during two years of intensive initial management then subsequent buckthorn re-invasion is likely to be sporadic and to require less intensive, targeted follow-up management.