Browsing by Author "Roth, Alexander M."

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    No evidence of a long-lived seedbank in common buckthorn, Rhamnus cathartica L., within Minnesota deciduous forests
    (Biological Invasions, 2023-06) Schuster, Michael J.; Wragg, Peter D.; Roth, Alexander M.; Reich, Peter B.
    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.
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    Revegetation to slow buckthorn reinvasion: strengths and limits of evaluating management techniques retrospectively
    (Restoration Ecology, 2021-01) Wragg, Peter D.; Schuster, Michael J.; Roth, Alexander M.; Bockenstedt, Paul; Frelich, Lee E.; Reich, Peter B.
    Understanding the long‐term success of ecosystem restoration following invasive plant removal is challenging. Long‐term experiments are costly and slow to yield results, while management decisions must often be made immediately. Alternatively, retrospective studies can leverage contrasting historical management strategies to provide insight into long‐term vegetation responses. We used a retrospective approach to evaluate how management techniques and site characteristics affected re‐establishment of an invasive shrub, Rhamnus cathartica (common buckthorn), in midwestern North America. Following removal, buckthorn re‐establishes rapidly from resprouts and seeds, so follow‐up control is required but often lacking. We hypothesized that revegetating using native herbaceous seed after removing buckthorn increases herbaceous cover that competitively suppresses buckthorn regeneration, to a degree. We surveyed 46 management units at 24 sites. Revegetated units had higher herbaceous cover, lower buckthorn cover, and half the ratio of buckthorn:herbaceous cover compared with unseeded units. These effects, although considerable on average, were detected against a background of high variance. Seeding increased herbaceous cover and reduced buckthorn relative abundance more strongly on less acidic, more clayey soils and where follow‐up herbicide was not applied. Additional variability in revegetation impacts may have arisen from buckthorn resprouts having a head‐start on planted seeds. Only one site had both seeded and unseeded management units. This lack of blocking—a common challenge in retrospective studies—reduced statistical power. This investigation illustrates how retrospective studies can offer relatively inexpensive first assessments of long‐term effects of management techniques; for more rigorous inference, researchers can partner with managers to conduct long‐term experiments.
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    Using plants to control buckthorn (Rhamnus cathartica): Improved biotic resistance of forests through revegetation
    (Ecological Engineering, 2022) Schuster, Michael J.; Wragg, Peter D.; Roth, Alexander M.; Bockenstedt, Paul; Frelich, Lee E.; Reich, Peter B.
    Woody invaders of temperate forest understories reduce native diversity worldwide. Common buckthorn Rhamnus cathartica, is among the most widespread of such invaders in North America. Invaded communities often have seedbanks largely comprised of the dominant invader - with few native species remaining - and therefore lack the capacity to build biotic resistance against re-invasion following invader removal. Consequently, invaders, including buckthorn, often quickly re-establish in the absence of continued management. We investigated the capacity of native plant revegetation to inhibit buckthorn re-establishment from seedbanks in the understories of three forests of Minnesota, USA. Specifically, we established experimental plots subjected to seeding of 35 native species, planting of Pennsylvania sedge (Carex pensylvanica) plugs, or bare-root plantings of either mixed shrubs (Sambucus canadensis, Sambucus racemosa, Corylus americana, and Cornus racemosa) or mixed trees (Abies balsamea and Acer saccharum). We then measured buckthorn germinant establishment, growth, and survival for the following four growing seasons. We observed consistent impacts of revegetation on ground-level light availability and associated buckthorn performance. Compared to unplanted understory controls beneath the mature tree canopy, shrub plantings were the most impactful. Shrubs reduced light availability to buckthorn seedlings by 67% relative to unplanted controls (to <2% total light by the third year) and led to 51% lower year-over-year survival of buckthorn by the end of the experiment. Revegetation also suppressed buckthorn seedling growth. After four years, shrub plantings resulted in buckthorn that were 53% shorter and had 38% fewer leaves than buckthorn grown in unplanted controls. Considering the combined impacts on survival and growth, planted shrubs, trees, and sedges reduced buckthorn invasion by 89%, 81%, and 66%, respectively; and seeding alone reduced invasion by 51%. Our findings indicate that revegetating forests, particularly with shrubs and trees, can greatly reduce invasion by buckthorn and potentially other species. Greater adoption of revegetation by land managers may therefore increase native biodiversity, reduce herbicide applications, and improve the overall health and value of forests.