The Ecological Impacts of Common Buckthorn
what every nature lover should know
Common buckthorn is a deciduous shrub native to Europe and western Asia that has become a pervasive invasive in the Minnesota area. It was widely planted as an ornamental and hedge but now forms dense thickets across the eastern US and Canada. These thickets establish quickly (buckthorn leafs out earlier and retains leaves later than natives) and tolerate a wide range of light and soil conditions. Importantly, buckthorn has few native predators or diseases in North America– deer and insects largely avoid it – so it spreads unchecked. Below we summarize its documented impacts in Minnesota on native flora, fauna, soils, and ecosystem functions, drawing on recent scientific studies and agency reports.
Impacts of Common Buckthorn: Effects on Native Florae
In invaded forests buckthorn typically forms dense, thorny understory thickets. These thickets dramatically reduce light and space for native plants, outcompeting and replacing many understory species. For example, buckthorn’s long growing season and vigorous growth cause a significant decline in native shrub and herb abundance and diversity.
Impacts of common buckthorn: studies report that buckthorn invasions “decreases the abundance and diversity of native forest understory species and suppresses regeneration of native tree seedlings. Its early leaf-out also preempts spring resources: buckthorn “break[s] bud earlier in the year and hold[s] onto leaves later” than most native species, effectively lengthening its competitive advantage.
• Impacts of common buckthorn: In practice, heavily invaded stands often become almost monocultures of buckthorn, with very few other plants surviving under the thick canopy.
• Impacts of common buckthorn: allelopathy and Shad. Buckthorn is thought to release chemicals (allelopathy) and cast deep shade that inhibit native seedlings. Its canopy can create a nearly continuous leaf cover even in winter.
• Impacts of common buckthorn: loss of Plant Diversity. Field surveys and experiments consistently find that invaded plots have far lower species richness of native wildflowers, ferns, and small shrubs than nearby uninvaded woods.
• Impacts of common buckthorn: altered Community Composition. By displacing native forbs and trees, buckthorn homogenizes forest undergrowth. For example, in oak–hickory forests, buckthorn invasion corresponded to a near‐complete loss of low‐growing wildflowers and grasses.
The cumulative effect is that buckthorn reduces the diversity, complexity, and resilience of native plant communities. In summary, native forests with buckthorn show much sparser and less diverse understories compared to uninvaded forests.
Impacts of Common Buckthorn: Effects on Wildlife and Invertebrates
Buckthorn thickets provide poor habitat and food for many native animals. Its dense, spiny growth deters generalist wildlife, and its foliage and berries are low-quality food. Studies and agency reports note that buckthorn stands offer little to insect pollinators or insectivorous birds (“a glen full of buckthorn… [is] the equivalent of a barren desert” for butterflies and bees).
Buckthorn flowers are inconspicuous and fruits (small black berries) are mostly carbohydrates. Mice, squirrels and birds do eat the seeds, but buckthorn berries are not nutritious: they are low in protein and have a strong laxative effect on birds.
Indeed, cedar waxwings and robins that feed on buckthorn often suffer from digestive upset. In many cases buckthorn is consumed only because native food is scarce, and its seeds are then widely spread in feces, promoting further invasion.
One direct measure of fauna impact comes from insect surveys. A field study in Iowa found drastically fewer ground-dwelling insects under buckthorn: invaded plots had significantly lower abundance, species richness, and diversity of ground beetles and other insects than nearby uninvaded plots.
Ground beetle diversity and carabid abundance were especially suppressed in buckthorn stands. In general, buckthorn thickets tend to harbor many fewer beetles, ants, and spiders than native forest understory, likely because leaf litter is sparser and food webs are truncated.
In summary, buckthorn invasion degrades wildlife habitat: it replaces diverse native plant and insect communities with a monoculture that few native animals utilize. Key impacts of Common Buckthorn include reduced insect abundance and diversity (ground beetles and ants drop sharply), low-value food for birds (nutrient-poor, laxative berries), and generally less foraging and nesting resources for forest fauna. This diminishes overall ecosystem health and biodiversity.
Impacts of Common Buckthorn: Soil Chemistry and Ecosystem Processes
Buckthorn alters soils and nutrient cycles in invaded areas. Numerous studies document that soil under buckthorn accumulates higher organic matter and nutrients than adjacent native soils. For example, Heneghan et al. (2004) measured soil C and N in Illinois woods and found that beneath dense buckthorn stands soil organic carbon and total nitrogen were roughly 78–79% higher than in nearby open (native).
This nutrient enrichment comes from buckthorn’s nitrogen‐rich litter: buckthorn leaves have as much as five times the nitrogen of typical tree leaves and decompose much faster. The rapid decay of buckthorn leaf litter releases nutrients quickly into the soil, a “boom-bust” cycle of available nitrogen. In practice, invaded soils often show elevated nitrate and ammonium levels as well as higher pH and moisture.
Several key consequences have been observed:
- Higher Soil Nutrients: Studies report dramatically greater soil N and C under buckthorn. One report found “twice the amount of nitrogen in soils under buckthorn than in open areas”. Similarly, Minnesota researchers found higher soil respiration under buckthorn (indicating active microbes and carbon turnover). By contrast, open forests in Minnesota had lower nutrients and slower decomposition. Higher soil nutrients under buckthorn favor fast-growing weeds and can hinder re-establishment of native plants adapted to lower-nutrient conditions.
• Less Leaf Litter & Organic Matter: because buckthorn leaves decompose rapidly, invaded sites often have very little litter cover. Heneghan et al. reported six-fold less accumulated leaf litter under buckthorn versus open forests. Combined with the activity of invasive earthworms, leaf litter and soil humus are often much reduced. In fact, studies note that buckthorn’s combined effect with earthworms yields “a reduction in leaf litter [and] reduction in soil organic matter”. The loss of the litter layer affects water infiltration and seedbeds for native seedlings.
• Earthworms and Microbes: Buckthorn appears to facilitate invasive earthworms. Sites with buckthorn invasions generally have higher earthworm biomassnyis.info. Buckthorn leaves (high N and Ca) are particularly palatable to worms, creating a feedback: worms remove even more organic material, further lowering litter and mixing soils. Native trees tend to die out in this altered soil, while buckthorn’s shallow roots and earthworm-modified soil hold more moisture.
• Altered Nutrient Cycling: The rapid nutrient turnover under buckthorn creates pulses of nitrogen availability. For example, delayed leaf drop by buckthorn (falling as late as November) means that a flush of decomposing high-N leaves enters streams in late fall. This can destabilize nutrient dynamics and even aquatic food webs.
Impacts of Common Buckthorn: Effects on Ecosystem Services & Water Quality
By altering vegetation and soils, buckthorn also undermines key ecosystem services. Notably, its suppression of native understory and shallow root system lead to increased erosion and degraded water quality. Dense buckthorn shade eliminates groundcover plants that normally protect soil. When rains fall, bare areas under buckthorn shed water quickly: “rain will quickly wash over exposed, bare soil (like that under buckthorn bushes) and into nearby bodies of water,” carrying sediment and pollutants. As a result, runoff and stream erosion increase in buckthorn-infested areas. Field reports confirm that forests overrun by buckthorn generate more erosion and sediment loading to streams than healthy forests with intact understories.
In riparian zones, the impact is acute. Buckthorn is tolerant of wet soils and often colonizes streambanks. Photo examples show buckthorn thickets lining creeks. These thickets can destabilize banks, since their roots do not bind soil as deeply as native trees. Without native shrubs and grasses, seasonal flooding easily scours bare ground and transports soil downstreams. Moreover, when buckthorn-dominated leaves finally drop into water (up to months later than natives), their rapid decomposition delivers a “late yet exaggerated pulse” of nutrients (especially nitrogen) to aquatic systems. This unusual timing and intensity of nutrient input can disrupt stream ecology.
Finally, buckthorn infestations can impair wildlife-related services. For example, by reducing pollinator habitat (few flowers in fall-winter) and bird nesting sites, it undermines pollination and seed-dispersal services provided by the original native flora. The overall picture is one of degraded ecosystem health: forests infested by buckthorn are less effective at filtering water and supporting diverse wildlife, which lowers the integrity of entire landscapes
Genetic Research and Control Efforts
Population genetics: recent genetic studies have examined buckthorn’s diversity and invasion history. A 2020 survey using microsatellites found that North American R. cathartica populations maintain moderate genetic diversity.
Introduced populations had levels of diversity similar (or only slightly lower) than their Eurasian counterparts. This suggests multiple introductions and admixture rather than a single clonal source. In fact, researchers found “many different genotypes” in the introduced range.
There was no strong genetic bottleneck or clear differentiation between European vs. North American populations. In practical terms, this means buckthorn in North America retains substantial adaptive potential, likely inherited from diverse horticultural stock.
Seedless or thornless varieties: to our knowledge, no seedless or sterile lines of R. cathartica have been developed for invasive control. Most horticultural breeding has aimed at ornamental traits.
Some related buckthorns show such efforts: for example, nurseries market a Frangula (glossy buckthorn) cultivar (‘Fine Line’) that is both thornless and “non-invasive”brighterblooms.com. Similarly, native Carolina buckthorn (Frangula caroliniana) selections have been promoted as thornless.
But these are either related species or specially bred clones, not wild R. cathartica. No published reports describe successful breeding of seedless common buckthorn. This remains a theoretical idea rather than an applied solution.
Genetic engineering concepts: the idea of genetic biocontrol (releasing genetically engineered organisms to suppress invasives) is being explored broadly for pests and weeds, but it is still largely experimental. Approaches include releasing sterile individuals, gene-drive constructs, or sex-biasing genesfrontiersin.org. For invasive plants like buckthorn, one could imagine a gene-editing strategy to introduce sterility or vulnerability. However, no gene-drive or transgenic buckthorn has been developed or field-tested. Regulatory hurdles and ecological uncertainties are major barriers. Current research is focused on classical biocontrol: for instance, Minnesota scientists are investigating native rust fungi and insects that attack buckthorn leaves or seeds (see MITPPC projects).
Conclusion
In summary, genetic control of buckthorn is still in the conceptual stage. Genetic surveys (like the 2020 study above) inform how the species spreads but are not control tools per se. The only “genetic” management in practice is the use of sterile cultivars in horticulture (to avoid further invasion) or planting competitive natives.
Institutions active in buckthorn research include universities (Minnesota, Wisconsin, Chicago area) and agencies (USDA Forest Service, state DNRs). Breakthroughs have come in understanding buckthorn ecology (e.g. seed longevity and seedling dynamics) rather than biotech. Future prospects might include biocontrol fungi or insects, or novel RNAi/gene silencing methods, but as of 2024 none are implemented.
Parameter | Buckthorn effect (vs. native forest) |
Native understory diversity | ↓ sharply reduced (native herbs/shrubs decline dramatically) |
Ground-dwelling insect abundance/diversity | ↓ greatly lower (species richness drops) |
Soil organic carbon | ↑ ~78% higher under buckthorn |
Soil total nitrogen | ↑ ~79% higher under buckthorn |
Leaf litter accumulation | ↓ ~6× less litter under buckthorn |
Earthworm biomass | ↑ elevated in buckthorn stands |
Streambank erosion/runoff | ↑ increased (bare soil and runoff) |
Sources
Research projects | Minnesota Invasive Terrestrial Plants and Pests Center https://mitppc.umn.edu/research/research-projects
Biocontrol of glossy buckthorn and reed canarygrass with rust fungus | Minnesota Invasive Terrestrial Plants and Pests Center
https://mitppc.umn.edu/research/research-projects/biocontrol-glossy-buckthorn-and-reed-canarygrass-rust-fungus
U of M researchers uproot decades of buckthorn management practices | University of Minnesota
https://twin-cities.umn.edu/news-events/u-m-researchers-uproot-decades-buckthorn-management-practices
U of M researchers uproot decades of buckthorn management practices | University of Minnesota
https://twin-cities.umn.edu/news-events/u-m-researchers-uproot-decades-buckthorn-management-practices
European Buckthorn (Rhamnus cathartica) – Cowling Arboretum – Carleton College
https://www.carleton.edu/arboretum/about/species/flora/shrub-guide/european-buckthorn
Buckthorn: How can a shrub be so harmful? | Friends of the Mississippi River
https://fmr.org/updates/conservation/buckthorn-how-can-shrub-be-so-harmful
Invasive buckthorn can cause increased erosion and nutrient runoff into nearby waters – St. Croix 360
https://www.stcroix360.com/2019/01/invasive-buckthorn-can-cause-increased-erosion-and-nutrient-runoff-into-nearby-waters/
Rhamnus cathartica (Rosales: Rhamnaceae) Invasion Reduces Ground-Dwelling Insect Abundance and Diversity in Northeast Iowa Forests – PubMed
https://pubmed.ncbi.nlm.nih.gov/26313971/
https://nyis.info/wp-content/uploads/2024/06/Buckthorn_Heneghan.pdf
Invasive Buckthorn and Soil Composition – Natural Lands
https://wp.stolaf.edu/naturallands/2024/02/27/invasive-buckthorn-and-soil-composition/
Genetic comparison of introduced and native populations of common buckthorn (Rhamnus cathartica), a woody shrub introduced into North America from Europe | Invasive Plant Science and Management | Cambridge Core
https://www.cambridge.org/core/journals/invasive-plant-science-and-management/article/genetic-comparison-of-introduced-and-native-populations-of-common-buckthorn-rhamnus-cathartica-a-woody-shrub-introduced-into-north-america-from-europe/771CE9EA7B4752E16A57C34F716F4978
Fine Line Buckthorns for Sale | BrighterBlooms.com
https://www.brighterblooms.com/products/fine-line-buckthorn?variant=13669591875645&srsltid=AfmBOopNX5Pek_zu0bDppuDfgx76ylVm6kJ8TBLHxTOrn2bJYcBTyA6_
Frontiers | Genetic Biocontrol for Invasive Species
https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2020.00452/full
