"Buckthorn Project" Web Page

Welcome to the web page for the NSF-RUI Project, Dynamics of European buckthorn (Rhamnus cathartica) invasion in the Northeastern United States, at Colgate University.  The goals of this project are listed below:

General goals

  1. Help to train the next generation of scientists by providing undergraduate students hands-on experience in data collection, management, and analysis, and
  2. Enhance the quality of teaching and research at Colgate University.

Specific goals

  1. Provide much needed data regarding the natural history of an invasive, exotic shrub that is problematic in much of the northern United States,
  2. Better understand why invasive species do well in some environments, but not well in others,
  3. Better understand the role of animals in facilitating and inhibiting the spread of invasive plants, and
  4. Determine the role of landscape fragmentation in facilitating or inhibiting the spread of invasive species generally, and European buckthorn in particular.

 

Project Summary

Despite the large amount of attention given to exotic species, the principles that dictate invasion success remain elusive.  In particular, our understanding of the role of biotic interactions in resisting invasion (i.e., biotic resistance) is weak (Levine et al. 2004).  Invasion is undeniably context-dependent, and evidence exists that both climate (Swincer 1986) and other organisms (D’Antonio 1993, Lambrinos 2002) can influence the extent to which exotics invade and affect communities.  Nevertheless, there exists disagreement regarding the strength of the biotic influence on invasion success. 

Our work sought to better understand the factors affecting the success of European buckthorn ([buckthorn] Rhamnus cathartica) in ecosystems of central New York.  These ecosystems shared the same macro-climate and similar soils.  Thus, variation in invasion success might be strongly attributed to the biotic communities.  By better understanding the role of biotic resistance in these habitats, we hoped to learn something about the general mechanisms by which communities resist invasion by exotic plants.

 This research topic was also of applied interest, as European buckthorn is an extensive invader that has been linked to low reproductive rates in birds (Schmidt and Whelan 1999), liver disease in mammals (Lichtensteiger et al. 1997), and changes in nutrient cycling (Heneghan et al. 2004).  A similar congeneric species, Rhamnus frangula, competitively displaces other plants (Frappier et al. 2003), and we suspect that the same is true for R. cathartica in some instances.  Thus, land managers of the northeastern and midwestern United States have implemented various control measures (Boudreau and Willson 1992).  A better understanding of the factors preventing extensive invasion in certain habitats might aid managers.

Project Activities and Findings

We studied demography and spatial distribution of buckthorn populations at three common habitats in central New York: sugar maple forests, old fields, and conifer plantations.  Buckthorn populations at sugar-maple forests were sparse, limited to seedlings, and strongly clumped near openings in the canopy. Scale of spatial clumping suggested the influence of canopy gaps.  Populations at old fields were dense, strongly biased toward seedlings, and clumped near the relatively few large buckthorn individuals.  Populations at plantations were very large and not strongly clumped.  Thus, buckthorn seems to have most extensively invaded plantations of these three habitats.

On the basis of these results, we formulated the following hypotheses.  Low numbers of seedlings at maple forests suggested low dispersal, low seed survival, or low germination.  The lack of older plants in maple forests suggested low seedling survival.  The small number of older plants compared to seedlings at old fields also suggested low seedling survival in that habitat.  Finally, invasion of plantations by buckthorn seemed virtually unlimited.

We designed a series of manipulative experiments to test the hypotheses presented above.  Our efforts were focused on early stages of the invasion process, including dispersal, seed survival, germination, and seedling survival.  We found that maple forests had the lowest dispersal, highest seed predation, and lowest seedling survival of all habitats.  Old fields had lower seedling survival than plantations.  Plantations were the most generally suitable of all habitats for buckthorn, though dispersal was lower than in old fields.  These experimental results support our observational study and point toward the critical need to better understand plantations as a habitat heavily invaded by exotics.

To better understand the potential role of seed predators in resisting invasion by exotics, we conducted another study including several exotic and native species.  We used cafeteria-type trials to evaluate preferences of rodent seed predators for 5 bird-dispersed shrubs.  We found that the two exotic taxa offered, buckthorn and bush honeysuckle (Lonicera morrowi), were consumed less intensively than the native species offered.  The time that it took rodents to attack our experimental seeds was greatest in old fields, suggesting weak risk of seed predation in that habitat, and shortest in maple forests, suggesting intensive seed predation in that habitat.

The last part of the study focused at a broad spatial scale, considering the distribution of buckthorn within the greater central New York landscape.  We used GIS and digital aerial photographs to categorize the landscape.  Our 400-km2 landscape consisted largely of deciduous forest, mixed deciduous-coniferous forest, conifer plantations, and old fields.  Thus, our intensively-studied plots were representative of major elements in the fragmented central New York landscape.  Buckthorn was frequently found at old field and plantation habitats and infrequently found at maple forests, supporting our stand-level observations.  By evaluating habitat composition at varying spatial scales we determined that although buckthorn is found in early successional and disturbed habitats, these habitats are typically imbedded within a forested landscape.

Summary

Our results support a strong influence of land-use history and fragmentation on distribution of this exotic plant.  Animals, including birds (dispersal agents) and rodents (seed predators), apparently play a role in limiting invasion in maple forests – the climax community for our study region.  Light availability at the ground was also an important factor in determining success of buckthorn in these habitats.  As eastern forests are fragmented, light availability and chances of invasion by buckthorn increase.

We encourage land managers to maintain the integrity of closed-canopy stands as a mechanism to resist invasion by this, and other, species.  We also suggest that management intervention may be necessary to prevent the extensive invasion of conifer plantations in the Northeast (Frappier et al. 2003).

References

 Boudreau D and Willson G (1992) Buckthorn research and control at Pipestone National Monument (Minnesota). Restoration and Management Notes 10: 94–95

D’Antonio CM (1993) Mechanisms controlling invasion of coastal plant communities by the alien succulent Carpobrotus edulis. Ecology 74: 83–95

Frappier B, Eckert RT and Lee TD (2003) Potential impacts of the invasive exotic shrub Rhamnus frangula L. (glossy buckthorn) on forests of southern New Hampshire. Northeastern Naturalist 10: 277–296

Heneghan L, Rauschenberg C, Fatemi F and Workman M (2004) European buckthorn (Rhamnus cathartica) and its effects on some ecosystem properties in an urban woodland. Ecological Restoration 22: 275–280

Lambrinos JG (2002) The variable success of Cortaderia species in a complex landscape. Ecology 83: 518–529

Levine JM, Adler PB and Yelenik SG (2004) A meta-analysis of biotic resistance to exotic plant invasions. Ecology Letters 7: 975–989

Lichtensteiger CA, Johnson NA and Beasley VR (1997) Rhamnus cathartica (buckthorn) hepatocellular toxicity in mice. Toxicologic Pathology 25: 449–452

Schmidt KA and Whelan CJ (1999) Effects of exotic Lonicera and Rhamnus on songbird nest predation. Conservation Biology 13: 1502–1506

Swincer DE (1986) Physical characteristics of sites in relation to invasions. In: Groves RH and Burdon JJ (eds) Ecology of Biological Invasions, pp 67–76. Cambridge University Press, Cambridge

Project Personnel

Principal investigators

 

    Dr. Deanna H. McCay - Department of Geography, Colgate University

    Dr. Timothy S. McCay - Department of Biology, Colgate University

Students

    Matthew Behum '02

    Anthony Caragiulo '03

    Jessica Czajka '08

    Matthew Dugas '03

    Matthew Feldman '06

    Sarah Fryc '05

    Katie George '05

    Amitabha Gupta '04

    Jennifer Hild '03

    David Hosford '05

    Elizabeth Juers '08

    Toby Mandel '03

    Casey Pierce '05

    David Rozolsky '06

    Heather Schwartz '04

    Amirah Shahid '05

    Brendan Smith '02

    Daniel Starobin '03

    Abigail Webb '04

 

Products

 

Four manuscripts, corresponding to the four major research efforts described above, are currently in draft form, and one of these is in review at Biological Invasions.  As papers become available they will be posted as PDFs at this website. 

 

Presentations (1 student author)

 

McCay, D.H., and T.S. McCay.  2002.  Population structure and spatial patterns of the non-native shrub Rhamnus cathartica in forested and old-field environments in the northeastern United States.  (Illustrated Paper)  98th Annual Meeting of the Association of American Geographers, Los Angeles, California, March.

Caragiulo, A.V.1, J.A. Hild1, T.L. Mandel1, T.S. McCay, and D.H. McCay.  2002.  Size, distribution, and density of European buckthorn (Rhamnus cathartica) in common northeastern landscapes.  (Poster)  25th Annual Applied Geography Conference, Binghamton, New York, October.

 McCay, D.H., and T.S. McCay.  2003.  Spatial patterns of the non-native shrub Rhamnus cathartica in environments in the northeastern United States.  (Oral Presentation) 99th Annual Meeting of the Association of American Geographers, New Orleans, Louisiana, March.

 Caragiulo, A.V.1, and T.S. McCay.  2003.  Predation on seeds of exotic and native plants by rodents in northeastern habitats.  (Poster)  National Conference on Undergraduate Research 2003 Conference, Salt Lake City, Utah.

Mandel, T.L.1, J.A. Hild1, A.V. Caragiulo1, T.S. McCay, and D.H. McCay.  2003.  Spatial patterns of European buckthorn (Rhamnus cathartica) in common northeastern landscapes.  (Poster)  National Conference on Undergraduate Research 2003 Conference, Salt Lake City, Utah.

 McCay, T.S., D.H. McCay, A.V. Caragiulo1, and T.L. Mandel1.  2004.  Ecology of invasion by European buckthorn (Rhamnus cathartica) in three common ecosystems of the Northeast.  (Oral Presentation)  Northeastern Natural History Conference, Albany, New York, May.

 McCay, T.S.  2005.  Invasion by European buckthorn in a fragmented northeastern landscape.  Environmental Studies Seminar Series, Alfred University, November.