More info for the terms: basal area
, fire management
, nonnative species
, prescribed fire
, species richness
Impacts: Many North American studies have shown that glossy buckthorn dominance can negatively affect native species richness, simplify vegetation structure, disrupt food webs, and delay succession . However, in native Scots pine (Pinus sylvestris) forests of northeastern Germany, there was a significant (P<0.001) positive relationship between the occurrence of glossy buckthorn and species richness. Forests with glossy buckthorn had significantly more threatened vascular species (P<0.05), threatened bryophyte species (P<0.001), and total woody species (P<0.001), as well as nonnative species (P<0.01) .
In its nonnative US and Canadian range, glossy buckthorn is often referred to as a "problem" species. In 2004, the eastern region of the Forest Service ranked glossy buckthorn as "highly invasive" due to its potential or known invasion of natural habitats and "replacement" of native species . In Vermont, a 1998 report characterized glossy buckthorn as "highly invasive" and noted it was displacing native plants on local and widespread scales . In a survey of The Nature Conservancy staff, glossy buckthorn was identified as a "serious threat" to multiple sites or large geographical areas . In the Leitrum Albion Road wetlands in Canada's Ottawa-Carleton area, glossy buckthorn has been referred to as a "menace" . Glossy buckthorn made the top 10 list of priority nonnative invasive plants in southern Canada considered to have a "major impact" on native vegetation .
While most studies have focused on glossy buckthorn's impact on native vegetation, there are other potential impacts on agricultural crops, birds, insects, succession, and fire ecology. Glossy buckthorn is an alternate host for the fungus that causes oat rust disease  and for alfalfa mosaic virus (Marani and Giunchedi 1976 as cited in ). A study conducted by Milwaukee's Zoological Society found that common buckthorn and glossy buckthorn supported fewer arthropods than did 11 species of native trees and shrubs . In an abandoned horse paddock in New England where glossy buckthorn dominated to the near exclusion of any understory species, the loss of the herbaceous understory led to changes in moisture, temperature, humidity, and light on the site, altering grasshopper, mouse, vole, and snake habitats. Dense glossy buckthorn stands also decreased the recruitment of native shrubs and the diversity of bird foods . One researcher suggested that "timely high-quality native food (was) replaced by easily accessible junk food"; glossy buckthorn was referred to as junk food because of its laxative effect, which may be a net energy loss (MacDougall, Land Manager for Essex County Greenbelt in Massachusetts, as cited in ).
Allelopathic potential probably does not play a part in glossy buckthorn's negative impacts. In laboratory experiments, glossy buckthorn root and leaf extracts did not inhibit germination and stimulated seedling growth of the test species. Researchers cautioned, however, that field conditions could produce results different from the laboratory setting .
Long growth periods and densely packed glossy buckthorn stems are often suggested as partly responsible for glossy buckthorn's replacement or exclusion of native species. Glossy buckthorn may have a competitive advantage, since it leafs out earlier and retains leaves longer than most associated native species . Glossy buckthorn is described as "having a serious impact on the ecology of our Midwestern forests". Dense glossy buckthorn thickets shade native tree species, decreasing tree seedling establishment, and early leaf production by glossy buckthorn restricts the light available to native spring ephemerals (McDougall, USDA/FS forester for the Northeastern Area State and Private Forestry, personal communication cited in ). However, not all research has shown a negative relationship between glossy buckthorn and native vegetation. When the composition of 58 wetlands in southeastern Ontario was studied, researchers found no evidence that nonnative wetlands species, including glossy buckthorn, excluded native species. Native species richness and nonnative species richness were positively correlated, and nonnative species were no more likely than native species to be dominant. This study, however, involved only a single year of study and did not evaluate change over time .
In some wetland habitats, glossy buckthorn threatens the persistence of rare or threatened species. In Ottawa, glossy buckthorn occurs in low-nutrient wetlands such as fens and shores where many rare and endangered species are concentrated . Since the arrival and spread of glossy buckthorn in the Gavin bog of Illinois, abundance of endangered highbush blueberries (Vaccinium corymbosum) and sensitive-listed bog birches (Betula pumila) has decreased .
Several studies have shown that glossy buckthorn can negatively affect native herbaceous cover, total species richness, and overstory recruitment. In eastern white pine stands on southeastern New Hampshire old fields, high glossy buckthorn basal area was associated with low woody seedling density (P<0.001), low herbaceous cover (P=0.048), and low groundlevel species richness (P=0.01). Generally, the variability in these factors was low with high glossy buckthorn basal area, and high with low glossy buckthorn basal area. Species on sites where glossy buckthorn dominated the midstory started growth early in the spring and/or had clonal growth habits [25,26,27]. Total herbaceous layer cover, total species richness, and woody plant seedling richness were significantly lower on plots invaded by glossy buckthorn than on uninvaded plots in a riparian savanna near Salmon Creek in the Allegheny National Forest (P<0.002). Nonwoody species richness was not significantly different between invaded and uninvaded plots, but the dominant on invaded plots was bearded shorthusk (Brachyelytrum erectum) and on uninvaded plots was wrinkleleaf goldenrod (Solidago rugosa) . In eastern white pine forests in Lebanon, New Hampshire, sugar maple, red maple, and white ash (Fraxinus americana) saplings had lower growth under a glossy buckthorn subcanopy than in areas where the subcanopy was cleared. Over a 9-year period, stem growth of the native tree saplings was significantly lower and, over a 5-year period, radial growth was significantly lower under the subcanopy than in cleared areas (P<0.05). Average sapling mortality under glossy buckthorn was 10.4% and in the open was 5.0%. Fewer than 10% of native saplings were expected to penetrate the subcanopy . During a 2-year field experiment in eastern white and red pine stands in southern New Hampshire, first-year native tree seedling density was significantly lower on plots with glossy buckthorn than on plots where the glossy buckthorn canopy was removed (P=0.048) or on uncut plots (P=0.042). Presence of glossy buckthorn did not significantly affect herbaceous cover or groundlayer species richness, but researchers noted that short experiment duration, low sample size, and/or the very low cover of herbaceous vegetation in the study area may have affected results. Native tree seedling suppression may have resulted from competition for light, space, nutrients, and/or moisture [24,26].
Control: Studies have shown variable success in the control of glossy buckthorn. "Vigorous" sprouting following top-kill makes control difficult and prolongs management. Integration of multiple methods may be most effective. Efforts to eradicate glossy buckthorn from Wisconsin in the 1950s were unsuccessful . In the Gavin bog of Illinois, glossy buckthorn dominates in the tamarack forest zone and tall shrub zone. Researchers predicted that eliminating glossy buckthorn and replacing it with native species was unlikely under any management involving fire, cutting, and herbicide treatments .
It is likely that successful management of glossy buckthorn will involve prioritization, site-specific strategy development, and a long-term commitment . Control efforts targeting glossy buckthorn seedlings are likely to succeed . Studies in a mined peat bog in Delafield, Wisconsin, showed that glossy buckthorn growth rates were highest in late spring or early summer. Control efforts may be more effective during this time . Many potential control methods are discussed in a review by Converse .
While control of glossy buckthorn is seen as a priority in southern Canada , successful control may eliminate an important food source and developmental habitat for Henry's elfin near the northern limit of its range in Ottawa-Carleton, Ontario .
Water level manipulation: In some wetland systems, glossy buckthorn dominance has coincided with low water levels. Restoration of flooding or high water tables may provide some control. In the Leitrim Albion Road wetlands in Ottawa-Carleton, aerial photos and other management records showed that increased glossy buckthorn growth coincided with draining and ditching operations . Several researchers suggest that flooding or high water tables may eliminate glossy buckthorn in areas where water tables were artificially lowered [15,39,82].
Prevention: Probably the most effective and economical management of glossy buckthorn would involve preventing its establishment. Prevention methods would likely include minimizing disturbances, restricting the sale and use of glossy buckthorn, and public education. In 11 early-seral sites in southeastern New Hampshire, glossy buckthorn was positively correlated with the abundance of agricultural fields and other disturbed lands (RÂ²=0.176, P=0.057) . In the late 1980s in eastern Massachusetts, glossy buckthorn transplants were used to vegetate artificially created wetlands . Restrictions on the use and sale of glossy buckthorn as well as increased education about its impacts would likely promote prevention.
Physical and/or mechanical: Even when done repeatedly, pulling, mowing, and/or cutting glossy buckthorn rarely provides substantial control, but some researchers note that associated native plants may benefit. In Lincoln, Massachusetts, pulling young glossy buckthorn plants from a very small area appeared to benefit sundews (Drosera spp.) and pitcher plants (Sarracenia spp.) . However, 1 year after glossy buckthorn shrubs were pulled from a site in northern Massachusetts, differences before and after were not discernible (MacDougall, Land Manager for Essex County Greenbelt in Massachusetts, as cited in ). Glossy buckthorn was generally unaffected by 3 consecutive years of June or July mowing in a sedge meadow with high shrub density in the Kettle Moraine region of southeastern Wisconsin. Glossy buckthorn density before mowing was 6.1 to 12.3 stems/mÂ² and after was 5 to 6 stems/mÂ². Before mowing, the frequency of glossy buckthorn was 66% to 86% and after was 73% to 77% . Researchers suggested that mowing increased the density of glossy buckthorn roots and may have increased glossy buckthorn's resistance to other control methods .
Glossy buckthorn stems that were cut twice in a single growing season for 2 to 3 successive years were less dense and shorter than stems on an untreated control site in a Wisconsin calcareous fen. Herbaceous ground cover was greater on sites cut twice than on sites cut once (Lovely 1983, personal communication as cited in ). While cutting did not remove glossy buckthorn from a dense thicket in Ottawa, it did increased overall native species cover. In the first growing season after cutting, overall native species cover was significantly greater on cut than on uncut plots (P=0.008). Following cutting, glossy buckthorn sprouting was "vigorous". The average number of sprouts ranged from 20 to 38/mÂ², and their average height ranged from 6 to 13 inches (16-34 cm). Native species cover increases were likely due to the short-term removal of heavy shade .
Fire: See Fire Management Considerations.
Biological: No biological controls for glossy buckthorn have been released to date (2008), but testing is occurring, and releases may be made by 2010 .
Chemical: The effectiveness of herbicides to control glossy buckthorn may increase if used in conjunction with other control methods. In Massachusetts, herbicide treatment of cut stumps provided control for 2 to 3 years. Treated stumps produced sprouts after that time . Herbicides considered useful in glossy buckthorn control are discussed by Solecki .
Integrated management: Most studies reporting some level of success in the control of glossy buckthorn involved more than one control method and repeated treatments. Heidorn  indicated that repeated cutting or girdling of glossy buckthorn followed by herbicide treatments was often effective. Since glossy buckthorn's leaf retention made it easy to identify and associated vegetation was dormant, fall treatments minimized nontarget effects . In mixed-conifer and hardwood swamps in the Cedarburg bog in Wisconsin, just 3 of 150 glossy buckthorn plants survived after cutting and stump herbicide treatments. Sprouts from the 3 survivors were small and deformed at the end of the first posttreatment growing season . When sites were plowed and seeded with little bluestem (Schizachyrium scoparium) in Lincoln, Massachusetts, glossy buckthorn abundance decreased .
Some studies suggest that the use of fire with cutting or revegetation may control glossy buckthorn. Prescribed fire and mowing were used to control glossy buckthorn in the Wolf Road Prairie in Illinois. No treatment comparisons were provided, and the effort was ongoing . Northeastern Illinois oak woodlands at Cap Sauers Holding were managed starting in 1989 with spring and/or fall prescribed fire and cutting and removal of nonnative woody vegetation. Unmanaged woodlands on the McClaughry Springs Forest Preserve also in Illinois were used as a comparison to evaluate the effectiveness of burning and cutting treatments. Fires occurred 1 to 4 times in 7 years; frequency of cutting was not provided. Glossy buckthorn density in managed woodlands decreased significantly between 1988 and 1995 (P=0.0001), but cover of glossy buckthorn increased, although not significantly, from 2.6% in 1988 to 3.3% in 1995. Researchers suggested that fall fires may have been less successful than spring fires. In unmanaged woodlands, the density of glossy buckthorn increased from 1,090 stems/ha in 1992 to 5,590 stems/ha in 1995 . On sites where stems are cleared and stumps are herbicide treated, fire and postfire seeding may limit glossy buckthorn reestablishment. In oak woodlands in University of Wisconsin's arboretum, 4 follow-up treatments were compared on sites cleared of glossy buckthorn :
Number of glossy buckthorn seedlings 1 year after follow-up treatments on cleared plots [79
] Treatment Low-severity, November prescribed fire and postfire seeding* November prescribed fire only Seeding only No additional treatments Glossy buckthorn density (seedlings/144-mÂ² plot) 6 99 143 191 *7 grass and 18 forb woodland species.