Browsing by Author "Schuster, Michael J."

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Fine-root biomass from Cloquet and Auclair IDENT sites
(2022-03-14) Schuster, Michael J.; Williams, Laura J; Stefanski, Artur; Bermudez, Raimundo; Messier, Christian; Belluau, Michaël; Paquette, Alain; Gravel, Dominique; Reich, Peter B; schuster@umn.edu; Schuster, Michael J
Mean fine-root biomass data gathered from the IDENT experiments in Cloquet, MN and Auclair, Quebec.
Fosamine ammonium impacts on the targeted invasive shrub Rhamnus cathartica and non-target herbs
(Invasive Plant Science and Management, 2020-06) Schuster, Michael J.; Bockenstedt, Paul; Wragg, Peter D.; Reich, Peter B.
Fosamine ammonium (Krenite®) is a foliar herbicide that primarily targets woody plant species; however, formal evaluations of its efficacy and potential for non-target impacts are scarce in the literature. The few tests of fosamine ammonium that exist focus primarily on its use in open environments, and the value of fosamine ammonium in controlling invasive understory shrubs is unclear. Here, we test the impact of fosamine ammonium on invasive common buckthorn (Rhamnus cathartica L.) and co-occurring herbaceous plants across six forest sites in Minnesota, USA. Rhamnus cathartica treated with fosamine ammonium had a 95% mortality rate, indicating high efficacy of fosamine ammonium for use against R. cathartica. Non-target impacts varied between forbs and graminoids such that forb cover was reduced by up to 85%, depending on site, whereas graminoid cover was sparse and impacts of fosamine ammonium on graminoids were unclear. These results indicate that while fosamine ammonium can provide effective control of R. cathartica and other understory shrubs, there is potential for significant non-target impacts following its use. We therefore suggest that land managers carefully consider the timing, rate, and application method of fosamine ammonium to achieve desired target and non-target impacts.
Increased light availability due to forestry mowing of invasive European buckthorn promotes its regeneration
(Restoration Ecology, 2020-03) Anfang, Carl; Schuster, Michael J.; Wragg, Peter D.; Reich, Peter B.
The invasive shrub Rhamnus cathartica L. (common buckthorn) dominates the understory of many temperate forests of eastern North America. Common buckthorn outcompetes native understory species for light, forming monospecific stands that suppress plant and animal diversity. Removing common buckthorn is a common management priority within its invasive range. In recent years, forestry mowing has become popular in removing common buckthorn. This control method removes a midstory of common buckthorn, increasing light availability to the lower understory (which could favor buckthorn regeneration) and creating a layer of mulch on the forest floor (which could suppress buckthorn regeneration). Here we investigate whether and how increased light availability and increased ground cover (mulch) resulting from forestry mowing affects buckthorn regeneration from the seed bank. We evaluated buckthorn germination, survival, and early growth in response to a factorial combination of shading treatments and buckthorn mulch depth treatments in an oak forest in Minnesota, U.S.A. Increased light availability increased buckthorn seedling survival and growth, whereas increased mulch depth did not significantly affect the number of buckthorn establishing from seed over one growing season and winter. Thus, removing buckthorn by forestry mowing (or any other method) is likely to facilitate buckthorn reestablishment by increasing light availability at the ground.
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.
Phenological niche overlap between invasive buckthorn (Rhamnus cathartica) and native woody species
(Forest Ecology and Management, 2021) Schuster, Michael J.; Wragg, Peter D.; Reich, Peter B.
Common buckthorn (Rhamnus cathartica L.) is a prolific invader of forest understories throughout eastern North America. Its ability to invade is partially attributable to its relatively high shade tolerance and ability to capture light both early and late in the growing season because of its phenological differences from native species. Competitors that mitigate this phenological advantage by casting shade early and late in the growing season may therefore increase biotic resistance against invasion. However, controlled comparisons between buckthorn and other woody understory species are scarce and to what extent buckthorn’s phenology is truly exceptional is incompletely known. Here, we compare the spring and autumn phenologies of five shade tolerant, native woody species (Sambucus canadensis, Sambucus racemosa, Corylus americana, Cornus racemosa, and Acer saccharum) to those of buckthorn in two common garden experiments. Spring phenology of buckthorn was often comparable to the five native species considered. All native species broke bud no later than 7 days after buckthorn, with S. racemosa reaching spring phenophases consistently earlier than buckthorn. In contrast to spring, buckthorn fall phenology was distinct in comparison to some natives but not all. Native species started to senesce up to 20 days earlier than buckthorn, but both Sambucus species senesced slowly and held their leaves equally long as buckthorn. These findings illustrate that buckthorn does not possess unique phenology amongst understory species. Forest communities rich in deciduous shrubs or trees that are phenologically similar to buckthorn (particularly S. racemosa) likely limit buckthorn's critical spring and fall carbon gains and exert greater biotic resistance to invasion by buckthorn.
Phenology matters: Extended spring and autumn canopy cover increases biotic resistance of forests to invasion by common buckthorn (Rhamnus cathartica)
(Forest Ecology and Management, 2020) Schuster, Michael J.; Wragg, Peter D.; Williams, Laura J.; Butler, Ethan E.; Stefanski, Artur; Reich, Peter B.
Forest light availability strongly regulates understory community composition, and low availability may confer resistance to invasion by exotic species, yet common buckthorn (Rhamnus cathartica L.) invades North American temperate forests with a broad range of light habitats. It is unclear to what extent buckthorn’s success is due to high mid-season shade tolerance versus shade avoidance permitted by early leaf out and late senescence. We used buckthorn seedlings planted into a forest diversity experiment in Cloquet, Minnesota, USA and a combined buckthorn physiology-canopy light model to test (1) how buckthorn germination, growth, and survival depend on canopy shading and (2) how canopy species richness and phenology affect light availability and buckthorn performance. Based on the mean of May, August, and October light measurements, we found that canopies that permitted ≤3% transmission of incoming light had almost complete mortality of buckthorn and that growth of surviving buckthorn was strongly tied to light availability, but not canopy richness. Compared to deciduous canopies or deciduous-evergreen mixtures, evergreen canopies restricted light availability the most and led to the smallest and least likely to survive buckthorn. Our canopy models further indicated a tight linkage between buckthorn performance and spring and autumn light availability, but not summer light availability. We conclude that spring and autumn light availability are key regulators of buckthorn performance and that buckthorn relies on shade avoidance via an extended phenology to succeed in temperate forests. Consequently, we suggest species with extended spring or autumn canopy cover offer the greatest resistance to invasion, and communities which are often leafless during such periods are most vulnerable to invasion by buckthorn and similar invasive shrubs.
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.
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.

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Browsing by Author "Schuster, Michael J."