1

This publication is part of a series of that provides an overview of the 

presence of invasive plant species monitored on an extensive systematic 

network of plots measured by the Forest Inventory and Analysis (FIA) 

program of the USDA Forest Service, Northern Research Station (NRS). 

Each research note features one of the invasive plants monitored 

on forested plots by NRS FIA in the 24 states of the Midwestern and 

Northeastern United States.

United States Department of Agriculture

An Assessment of Common Buckthorn in Northern U.S. Forests Research Note NRS-250

Forest Service

Northern Research Station

Figure 2.—Common buckthorn 

in flower. Photo by Robert Vidéki, 

Doronicum Kft., from Bugwood.org

Figure 3.—Fruit of common buckthorn. Photo by Jan 

Samanek, Phytosanitary Administration, from Bugwood.org

Background and Characteristics

Common buckthorn (Rhamnus cathartica; also known as European 

buckthorn) is a woody shrub that is native to Eurasia and was 

introduced to North America as an ornamental from Europe in the 1800s 

(Kurtz 2013). It is a problematic invader as it can grow across a range of 

light levels. In addition, plants leaf out early and the leaves remain on 

the plants until late in the season. In a Wisconsin study, Delanoy and 

Archibold (2007) found that up to 35 percent of the annual carbon is 

gained by this invader prior to leaf emergence of native species and 

leaf retention is 58 days longer than comparable native shrubs. These 

characteristics give common buckthorn a photosynthetic advantage.

Common buckthorn is also problematic in agricultural areas as it is an 

alternate host for oat crown rust (Puccinia coronata) and the primary 

overwintering host for the soybean aphid (Aphis glycines).

Accurate identification is important as there are native shrubs (e.g., 

Carolina buckthorn [Rhamnus caroliniana] and alder buckthorn 

[Rhamnus alnifolia]) that resemble common buckthorn.

Description

Growth: to 25 feet tall; foliage is shiny, mostly alternate, with smooth 

upper and lower surface and fine teeth; veins curve toward tips; thorns 

at tips of twigs (Fig. 1).

Reproduction: small greenish-yellow flowers (Fig. 2) yield abundant 

round black fruit (Fig. 3) that can remain on the tree until spring and 

remain viable for several years.

Habitat: open woodlands, urban areas.

Growth conditions: full sun to shade with vigor reduced in deep shade; 

seedling survival is affected by hot summers, cold winters, thick litter 

layers, and acidic, dry, and water-logged soils; presence declines south 

of 42° N latitude.

Control: various chemical and mechanical methods; repeated 

monitoring is necessary due to seedbanks and resprouting (Kurtz 2013).

Growth Conditions and Range

Common buckthorn is currently found in 34 states and eight Canadian 

provinces.

Figure 1.—Common buckthorn foliage and thorn. 

Photo by Chris Evans, University of Illinois, from Bugwood.org.
2

FIA crews visited 4,981 forested Phase 2 (P2) invasive 

plots across the NRS region for the 2016 inventory. These 

P2 invasive plots are a subset of the standard P2 plots 

where 40 invasive plant species1 (IPS) (39 species and one 

undifferentiated genus [nonnative bush honeysuckle]2) 

are monitored. Various attributes are collected including 

the occurrence and coverage of IPS as well as the standard 

forest variables measured on P2 plots (e.g., tree diameter, 

height). Overall, 52.0 percent of forested plots have one or 

more of the monitored invasives present.

Common buckthorn is found throughout most of the NRS 

region. This noxious shrub occurs on 321 plots (6.4 percent) 

across 19 of the 24 NRS states (Fig. 4). Field crews did not 

observe this invasive shrub in Delaware, Kansas, Maryland, 

New Jersey, or West Virginia. Detection maps (NRCS 2018) 

show common buckthorn in all 24 states of the NRS, but it 

is important to remember that this inventory samples only 

forest land.3 New York has the greatest percentage of plots 

with common buckthorn (19.9 percent). This invasive shrub 

is also prevalent in Minnesota (18.0 percent of plots), Rhode 

Island (15.4 percent), and Wisconsin (14.9 percent).

For the 2016 inventory, common buckthorn is the ninth 

most commonly observed invasive species after multiflora 

rose (30.5 percent), nonnative bush honeysuckles 

(19.4 percent), garlic mustard (11.2 percent), Japanese 

honeysuckle (8.0 percent), autumn olive (7.5 percent), 

Japanese stiltgrass (7.3 percent), Japanese barberry 

(7.1 percent), and black locust (6.5 percent). Additional 

information about the invasives monitored and county-level 

occurrence maps for the NRS region from 2005 through 

2010 can be found in Kurtz (2013).

Common Buckthorn Presence on Phase 2 Invasive Plots, 2016

1 Autumn olive (Elaeagnus umbellata), black locust (Robinia pseudoacacia), Bohemian knotweed (Polygonum xbohemicum), bull 

thistle (Cirsium vulgare), Canada thistle (Cirsium arvense), Chinaberry (Melia azedarach), common barberry (Berberis vulgaris), 

common buckthorn (Rhamnus cathartica), common reed (Phragmites australis), creeping jenny (Lysimachia nummularia), 

dames rocket (Hesperis matronalis), English ivy (Hedera helix), European cranberrybush (Viburnum opulus), European privet 

(Ligustrum vulgare), European swallow-wort (Cynanchum rossicum), garlic mustard (Alliaria petiolata), giant knotweed (Polygonum 

sachalinense), glossy buckthorn (Frangula alnus), Japanese barberry (Berberis thunbergii), Japanese honeysuckle (Lonicera japonica), 

Japanese knotweed (Polygonum cuspidatum), Japanese meadowsweet (Spiraea japonica), leafy spurge (Euphorbia esula), Louise’s 

swallow-wort (Cynanchum louiseae), multiflora rose (Rosa multiflora), Japanese stiltgrass (Microstegium vimineum), nonnative bush 

honeysuckle (Lonicera spp.), Norway maple (Acer platanoides), Oriental bittersweet (Celastrus orbiculatus), princesstree (Paulownia 

tomentosa), punktree (Melaleuca quinquenervia), purple loosestrife (Lythrum salicaria), reed canarygrass (Phalaris arundinacea), 

Russian olive (Elaeagnus angustifolia), saltcedar (Tamarix ramosissima), Siberian elm (Ulmus pumila), silktree (Albizia julibrissin), 

spotted knapweed (Centaurea stoebe ssp. micranthos), tallow tree (Triadica sebifera), tree of heaven (Ailanthus altissima).

2 The 39 IPS and one undifferentiated genus (nonnative bush honeysuckle) are hereafter referred to as “invasive species”, “invasive 

plants”, “invasives”, or “IPS”.

3 FIA defines forest land as land that is at least 10 percent stocked with trees of any size or land formerly having had such tree 

cover and not currently developed for nonforest use. Generally, the minimum area for classification as a forest is 1 acre in size and 

at least 120 feet in width. There are more specific criteria for defining forest land near streams, rights-of-way, and shelterbelt strips 

(USDA Forest Service 2015).

Common buckthorn infestation. 

Photo by Steven Katovich, USDA Forest 

Service, from Bugwood.org.

Figure 4.—Percentage of Phase 2 invasive plots with common buckthorn, 2016. 

Percentages are rounded to the nearest whole number.
3

The percentage cover of common buckthorn 

is shown in two figures, one that illustrates 

cover by state (Fig. 5) and a second that 

focuses on plot-level data (Fig. 6). It is 

important to use caution when looking at 

Figure 5 because in some states the overall 

averages are driven by a small number of 

plots. For the states with a low number of 

observances, Figure 6 is more informative 

since individual plot values can be assessed. 

Illinois is the state with the highest average 

percent cover of common buckthorn on 

plots, 21.6 percent. For the 2016 survey, 12 

of the 144 plots (8.3 percent) in this state 

had common buckthorn present. These 

maps, along with Figure 4, reveal important 

information related to the presence and 

abundance of this species in the NRS region. 

Over time these maps will allow us to 

assess changes in abundance and spread 

throughout this region.

Common Buckthorn Cover on Phase 2 Invasive Plots, 2016

Figure 6.—Average percent cover4 of common buckthorn on Phase 2 invasive plots, 2016. Approximate plot locations 

depicted. Percentages are rounded to the nearest tenth of a whole number.

Figure 5.—Average percent cover4 of common buckthorn on Phase 2 invasive 

plots, 2016. Percentages are rounded to the nearest tenth of a whole number.

4 Average percentage cover is calculated for plots based on subplot data for the portion of the plot that is forested. 

Each FIA plot consists of four circular 1/24-acre subplots located at the corners and center of an equilateral triangle that 

is 208 feet on a side.

•
4

The data analysis in this section was limited to the nine 

NRS states with common buckthorn present on greater 

than 5 percent of plots, resulting in the analysis of 1,817 

plots. Of the 1,817 plots, this noxious shrub is present 

on 278. The nine states in this analysis are Illinois, Iowa, 

Massachusetts, Minnesota, New York, North Dakota, 

Rhode Island, Vermont, and Wisconsin.

Data collected on sample plots suggest that common 

buckthorn is more common on plots near roads (Fig. 

7; t-test; p<0.05). Several studies have highlighted 

the effect of roads on invasive distribution (Kurtz and 

Hansen 2013, Lundgren et al. 2004, Predick and Turner 

2008). Roads act as conduits for seed dispersal 

and alter light and nutrient availability, as well 

as drainage. Vehicles traveling on roads carry 

propagules of many exotics which become 

dispersed along them. Wildlife, using these roads 

as corridors, also spread IPS along them.

Tree cover differs for plots with and without 

common buckthorn. The 2016 data suggest that 

there are fewer seedlings and saplings per acre 

on plots with common buckthorn (Fig. 8A and 

8B; t-test; p<0.05). Since the study is relatively 

new, with complete implementation across all of 

the NRS region in 2007, it is difficult to assess whether 

the invasive plants are influencing tree regeneration 

and growth or if the invasive plants are establishing 

where there is reduced tree cover and less competition. 

Continued investigation is important because these 

plants can outcompete native species and without 

adequate understory regeneration to replace the aging 

overstory, the future of the forest remains in question.

Further analysis of the tree data suggests that there 

is not a significant difference in the number of trees 

5 inches diameter at breast height (d.b.h.) or greater 

on plots with or without common buckthorn (Fig. 

9; p>0.05). However, there is a significant difference 

in the percentage of the plot that is forested for 

plots with and without common buckthorn (Fig. 10; 

p<0.05). It will be important to continue monitoring 

how fragmentation affects the presence of common 

buckthorn.

Monitoring IPS offers insight on the status, trends, 

distribution, and population size, and helps to detect 

new populations. These preliminary investigations 

are important as they suggest there is a difference 

between plots with and without common buckthorn 

and future studies will help determine the effects of 

these species. IPS can affect property and timber value, 

biodiversity, habitat quality, and sustainability. The 

trends reported in this research note are important 

and need to be watched in the future to help elucidate 

important factors related to the presence of these 

invasives as well as to evaluate the impacts of these 

species on ecosystems.

Characteristics of Plots with Common Buckthorn

Figure 7.—Average distance to the nearest road for 

plots with or without common buckthorn, 2016.5

5 The error bars in Figures 7 through 10 show a 68% confidence interval for the 

observed mean. Significantly different values are noted with letters (t-test; p<0.05).

Figure 8.—Number of seedlings (A) and saplings (B) per acre for 

plots with or without common buckthorn, 2016.5

Figure 9.—Trees per acre ≥5 inches d.b.h. for plots 

with or without common buckthorn, 2016.5

Figure 10.—Percentage of the plot that is forested 

for plots with or without common buckthorn, 2016.5

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Citation for this Publication

Kurtz, Cassandra M.; Hansen, Mark H. 2018. An assessment 

of common buckthorn in northern U.S. forests. Res. Note 

NRS-250. Newtown Square, PA: U.S. Department of Agriculture, 

Forest Service, Northern Research Station. 5 p. https://doi.

org/10.2737/NRS-RN-250.

FIA Program Information

Bechtold, W.A.; Patterson, P.L., eds. 2005. The enhanced Forest 

Inventory and Analysis Program: national sampling design 

and estimation procedures. Gen. Tech. Rep. SRS-80. Asheville, 

NC: U.S. Department of Agriculture, Forest Service, Southern 

Research Station. 85 p. https://doi.org/10.2737/SRS-GTR-80.

Smith, W.B. 2002. Forest inventory and analysis: a national 

inventory and monitoring program. Environmental 

Pollution. 116: 233-242. https://doi.org/10.1016/S0269-

7491(01)00255-X.

References

Czarapata, E.J. 2005. Invasive plants of the upper Midwest: 

an illustrated guide to their identification and control.

Madison, WI: University of Wisconsin Press. 215 p.

Delanoy, L.; Archibold, O.W. 2007. Efficacy of control 

measures for European buckthorn (Rhamnus cathartica) in 

Saskatchewan. Environmental Management. 40(4): 709-718. 

https://doi.org/10.1007/s00267-006-0409-1.

Kaufman, S.R.; Kaufman, W. 2007. Invasive plants: a guide 

to identification and the impacts and control of common 

North American species. Mechanicsburg, PA: Stackpole 

Books. 458 p.

Kurtz, C.M. 2013. An assessment of invasive plant species 

monitored by the Northern Research Station Forest 

Inventory and Analysis Program, 2005 through 2010. Gen. 

Tech. Rep. NRS-109. Newtown Square, PA: U.S. Department of 

Agriculture, Forest Service, Northern Research Station. 70 p. 

https://doi.org/10.2737/NRS-GTR-109.

Kurtz, C.M.; Hansen, M.H. 2013. An assessment of multiflora 

rose in northern U.S. forests. Res. Note NRS-182. Newtown 

Square, PA: U.S. Department of Agriculture, Forest Service, 

Northern Research Station. 5 p. https://doi.org/10.2737/NRSRN-182.

Lundgren, M.R.; Small, C.J.; Dreyer, G.D. 2004. Influence 

of land use and site characteristics on invasive plant 

abundance in the Quinebaug Highlands of southern New 

England. Northeastern Naturalist. 11(3): 313-332. https://doi.

org/10.1656/1092-6194(2004)011%5b0313:IOLUAS%5d2.0.

CO;2

Natural Resources Conservation Service [NRCS]. 2018. The 

PLANTS database. Greensboro, NC: U.S Department of 

Agriculture, Natural Resources Conservation Service, Plant 

Data Team. Available at https://plants.usda.gov (accessed 

March 22, 2018).

Predick, K.I.; Turner, M.G. 2008. Landscape configuration and 

flood frequency influence invasive shrubs in floodplain 

forests of the Wisconsin River (USA). Journal of Ecology. 96: 

91-102. https://doi.org/10.1111/j.1365-2745.2007.01329.x.

USDA Forest Service. 2015. Forest Inventory and analysis 

national core field guide, vol. 1: field data collection 

procedures for phase 2 plots, ver. 7.0. Washington, DC: U.S. 

Department of Agriculture, Forest Service. https://www.fia.

fs.fed.us/library/field-guides-methods-proc/docs/2015/CoreFIA-FG-7.pdf (accessed April 23, 2018).

USDA Forest Service. 2016. Forest inventory and analysis 

national core field guide, vol. 1: field data collection 

procedures for phase 2 plots, ver. 7.1. Washington, DC: U.S. 

Department of Agriculture, Forest Service. www.fia.fs.fed.us/

library/field-guides-methods-proc/ (accessed March 22, 2018).

Additional Invasive Plant Information

Invasive and Exotic Plants: 

http://www.invasive.org/species/weeds.cfm

Invasive Plant Atlas of New England: 

http://www.eddmaps.org/ipane/

Invasive Plant Atlas of the United States: 

http://www.invasiveplantatlas.org/index.html

Midwest Invasive Plant Network: http://mipn.org/

Contact

Analyst: Cassandra Kurtz, (651) 649-5149; cmkurtz@fs.fed.us

Page 1 and 5 header by Cassandra Kurtz, USDA Forest Service.

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