ISSN 1188-603X

No. 345 March 24, 2005 Victoria, B.C.
Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2


From: Paul M. Catling, Biodiversity, National Program on Environmental Health, Agriculture and Agri-food Canada, Wm. Saunders Bldg., Central Experimental Farm, Ottawa, Ontario, Canada K1A 0C6 []

Many questions on new high priority invasive plants have followed presentations at the 2004 Canadian Botanical Association's second symposium on invasive alien plants in Canada. In the following notes some details are provided on five new high priority invasive species (preceded by priority rank): (1) European Common Reed (Phragmites australis subsp. australis), (4) Diffuse Knapweed (Centaurea diffusa), (14) European Lake Sedge (Carex acutiformis), (15) Sea Buckthorn (Hippophae rhamnoides), and (16) Autumn Olive (Elaeagnus umbellata).

When it comes to questions about which are the most serious invasive plants of natural habitats in Canada, the situation can change relatively quickly. Five of the top ranking candidates for "worst" nationally (listed above and discussed below) are not on the standard lists because their recognition, establishment and spread have been very recent. Each of the species discussed below received a high priority ranking (A = severe threat to native species and communities) in a recent (2005) evaluation based on NatureServe's invasive plant assessment protocol (Morse et al. 2004).

In the 1993 publication on invasive plants in Canada (White et al. 1993), none of these five were mentioned. The 1993 list was based on a current survey of Canadian botanists and is a reliable source still widely employed and little more than a decade old. The high priority of these five species today and their complete absence in a comprehensive survey only a decade old suggests that: (1) an introduced plant can spread, achieve substantial range and major impact over a short time; (2) the problem of invasive alien plants in Canada is growing; and (3) information on invasive alien plants requires continuous updating.

European Common Reed (Phragmites australis [Cav.] Trin. ex Steud. subsp. australis)

In many of the eastern US coastal National Fish and Wildlife Refuges, the invasion of European Common Reed has displaced native biodiversity by altering the structure and function of relatively diverse Spartina marshes (Marks et al., 1993). It was not until 1997 that it appeared on the Canadian Botanical Conservation Network lists (Canadian Botanical Conservation Network 1997). Suddenly the native plant appeared to have become aggressive. At the time it was not realized that there were two races of Phragmites australis, one a native of fens, bogs and river shores, the other an alien capable of growing in a wide range of habitats. Possible "invasive biotypes" were alluded to in 2001 (Small & Catling 2001) and the status and identification of native and introduced races was clarified for Canada in 2003 (Catling et al. 2003). Further information for Canada is provided by Robichaud & Catling (2003) and Catling (2004). In 2004 the native North American race was described as a distinct subspecies, Phragmites australis subsp. americana Saltonstall, P. M. Peterson & Soreng (Saltonstall et al. 2004) and distinguished from the introduced (alien invasive) lineage, Phragmites australis subsp. australis. At present the invasive alien subspecies is spreading rapidly in eastern Canada and is having major impacts. For example, it is displacing native vegetation in rich saltmarshes in the St. Lawrence estuary (pers. obs.), has become the most significant threat to native vegetation in the St. Lawrence River area (Lavoie et al. 2003), is replacing native wetland vegetation in Long Point Biosphere Reserve on the Lake Erie shore of Ontario (Wilcox et al. 2003), and is threatening the habitat of the endangered Eastern Prairie Fringed Orchid (Platanthera leucophaea) and other rare native prairie plants in the Lake St. Clair marshes (pers. obs.). Using the NatureServe ranking system it is priority number 1 in Canada - truly remarkable for a plant that was not on the list in 1993! Additional information on the biology of the plant is available from Mal & Narine (2004).

Sea Buckthorn (Hippophae rhamnoides L.)

This plant has recently attracted interest worldwide for its economic value as a nutritious food, a medicine, a soil enhancer, a pollution reducer, a source of firewood, and as a landscape management tool (e.g. Small & Catling 2002). It has been widely planted on the Canadian prairies to improve soil through nitrogen-fixing capability, to prevent erosion in dry and especially saline areas and for use as a shelterbelt. More recently it has attracted attention in Canada as an alternative crop, the leaves and berries being processed into a range of health foods and herbal products. Oil from the plant is also used for medicinal and cosmetic purposes (Li 1999, Li & Beveridge 2003).

Despite its many virtues, sea buckthorn can be a serious problem. It was apparantly first listed as an invasive in Canada in 1997 (Catling 1997). Now it is regarded by many in Alberta as a potentially very serious problem. One respondent from Calgary writes "it is escaping into the natural environment, not only in Britain but also here on the prairies, and, as a result, is destroying biodiversity vegetation .... ultimately there will be no native fruiting plants to provide winter food for grouse or other wildlife Therefore, as the native plants are displaced, there is no food for birds that depend upon insects .... This is leading to the decline of many bird species .... Here on the prairies, most of the sea buckthorn has escaped to the low lying, moist riparian areas, the richest of all in biodiversity. Where it is now established, it has turned these areas into a monoculture. From a local wildlife point of view, such colonies are now biological deserts .... because it readily spreads by rhizomes, a single seed is able to colonize an area of acres within a few years. Such areas soon become impenetrable thickets. They are so dense that little light reaches the ground, therefore all herbaceous plants disappear. The soil beneath them is now unprotected. During periods of flooding this results in the loss of topsoil, and the silting of waterways, choking insect and fish habitat .... In Calgary we now have dozens of established colonies. Volunteers have been engaged in removing some of them, but most take several years to completely control, because if one section of rhizome is overlooked it readily rejuvenates the colony." Although evidently a major and rapidly increasing problem, it does not appear on the list of the Alberta Invasive Plants Council (2005), but the Alberta Native Plant Council (2000) does list it as invasive with the comment that it "has established extensive monocultural stands on gravel and sandbars along streams." In Alberta it is already established over a relatively extensive area including Calgary, Edmonton and Hinton. According to an invasive plant newsletter in British Columbia "the potential risk to BC natural ecosystems has been brought to the attention of BC Ministry of Environment, Lands and Parks and BC Ministry of Agriculture and Fisheries." Using the NatureServe ranking system it was 15th. For some general biological information on this species, see Pearson & Rogers (1962).

Diffuse Knapweed (Centaurea diffusa Lam.)

Diffuse Knapweed has proven capable of overwhelming all native vegetation in parts of central British Columbia where it occurs in a wide range of habitat types including various dry grasslands, scrub and Ponderosa Pine transition. The plant produces chemicals that inhibit the growth of native plants (Callaway & Aschehoug 2000, Hierro & Callaway. 2003). A single plant is said to produce 18,000 seeds that can remain dormant for years (Watson & Renney, 1974: Carpenter & Murray, 1998). Its establishment results in the decline of native forage species including those used by both livestock and native deer and elk (Pidwirny 2005). It is one of 21 noxious weeds listed for all regions of British Columbia under the BC Weed Control Act. It has degraded a number of very restricted Canadian ecosystems that are imperiled. The omission of Diffuse Knapweed from lists of major invasives of natural habitats may be attributable to its limited area of abundance in Canada and/or the fact that it has been highlighted as a pest of rangelands which are sometimes viewed as agricultural rather than natural. Although not in the 1993 survey, it was included in the results of the 1996 survey as "an additional species of concern that mat warrant major problem status" )Haber 1966). Using the NatureServe ranking system it was 4th. For more information see Watson & Renney (1974), Carpenter & Murray (1998), Sheley et al. (1998), and LeJeune & Seastedt (2001).

European Lake Sedge (Carex acutiformis Ehrh.)

Presently restricted to a limited area, this sedge is extremely dominant and can exist in a variety of habitats. At a site near Ottawa it is present in permanent water to 50 cm deep and on dry slopes. It can spread rapidly by tough rhizomes and it competes very effectively for nutrients. The dense leaf cover and persisting dead leaves smother native vegetation. It is not easily distinguished from native species and could spread undetected. Although currently restricted, its remakarble potential for damage to native ecosystems resulted in a relatively high rank of 14th on the NatureServe ranking system. For more information see Catling & Kostiuk (2003).

Autumn Olive (Elaeagnus umbellata Thunb.)

This alien plant fruits abundantly, grows rapidly and is widely disseminated by birds. It resprouts after cutting and with its nitrogen-fixing capabilities, it can adversely affect the nitrogen cycle of native communities that may depend on infertile soils, especially savanna, dry prairie and sand barren. It was introduced as a "wildlife enhancement shrub." Although extensively planted in the 1960s and 1970s it was unknown as a wild plant in Canada until 1987. Although not in the 1993 survey, it was included in the 1996 survey as a species of local importance. Its rapid spread in southern Ontario and threat to native biodiversity was documented in 1997 (Catling et al. 1997). The same year it appeared on the Canadian Botanical Conservation Network lists (Canadian Botanical Conservation Network 1997) and made the top 11 in Thompson's (1997) list for Canada. This is remarkable since the plant is so recently established. Using the NatureServe ranking system it was 16th. For more information see Sather & Echardt (1987), Szafoni (1990), Catling et al. (1997) and Fire Effects Information System (2005)

Changes in priority and a longer priority list

Not only are some invasive alien plants new and already at the top of the priority list, others that were regarded as "minor" in 1993 have assumed greater significance. For example Pinus sylvestris was ranked in the top 10. Agropyron pectiniforme, Cynanchum rossicum, Cytisus scoparius, Glyceria maxima and Acer platanoides are all in the top 20.

A number of plants ranked between 20 and 30 are also very serious invasives that have increased in importance. A good example of this is the white mulberry (Morus alba). It is anticipated that without very concerted and successful intervention, the native red mulberry (Morus rubra) will be replaced by the more common invading alien, white mulberry, as a result of hybridization and competition (Husband and Burgess 2001, Ambrose et al. 2003, Canadian Wildlife Service 2004). When white mulberry was listed as a minor invasive in 1993, red mulberry was only threatened, but in 1999 the status of red mulberry was changed to the endangered category and the next category after that is "extirpated" (= gone). Clearly the damage as a result of white mulberry has become much more serious and it is ranked as number 28. This suggests that there are at least 28 major invasive alien plants in Canada as opposed to 14 in 1993.

Need for information

A major part of the strategy to deal with invading plants is early detection of new invaders. From the above examples, it is clear that the situation is ever changing. This requires an extensive and coordinated effort of environmental monitoring as well as frequent updating of information. Of course there has to be information to update. Much more information on occurrence and impact is required. One does not have to be a professional botanist to help to remedy this situation.

A very useful guide to monitoring is available on the web (Haber 1997). It is important to make the results of monitoring available periodically either electronically or through publication. Information on how the general public can help to prevent and diminish invasive species problems is available at .


Ms. Laurie Hamilton of the Alberta Native Plant Council and Mr. Gus Yaki of Calgary helped to gather information on Hippophae rhamnoides.


Alberta Invasive Plants Council. 2005.
Alberta invasives in 2004.
Alberta Native Plant Council. 2000.
A rogue's gallery of invasive non-native plants.
Ambrose, J., and Red Mulberry Recovery Team. 2003.
National Recovery Strategy for Red Mulberry (Morus rubra L.). RENEW. 25 p.
Callaway, R.M. & E. T. Aschehoug. 2000.
Invasive plants versus their new and old neighbours: a mechanism for exotic invasion. Science 290(5941): 521-523.
Canadian Botanical Conservation Network 1997.
Canadian Wildlife Service. 2004.
Species at risk: red mulberry.
Carpenter, A.T. & T.A. Murray. 1998.
The Nature Conservancy (TNC) Element Stewardship Abstract for Centaurea diffusa. 1998-1999 TNC Weed Report, Centaurea diffusa, Diffuse knapweed. Invasive Species Team, TNC, CA.
Catling, P. M. 1997.
The problem of invading alien trees and shrubs: some observations in Ontario and a Canadian checklist. Canadian Field-Naturalist 111: 338-342.
Catling, P. M. & B. Kostiuk. 2003.
Carex acutiformis dominance of a cryptic invasive sedge at Ottawa. Botanical Electronic News 315: 1-6.
Catling, P. M., G. Mitrow, L. Black, & S. Carbyn. 2004.
Status of the alien race of Common Reed in the Canadian Maritime Provinces. Botanical Electronic News 324: 1-3.
Catling, P.M., M.J. Oldham, D.A. Sutherland, V.R. Brownell, & B.M.H. Larson. 1996.
The recent spread of Autumn-olive (Elaeagnus umbellata) into southern Ontario, and its current status. Canadian Field-Naturalist 111(3): 376-380 bibl
Catling, P.M., Schueler, F.W., Robichaud, L., & B. Blossey. 2003.
More on Phragmites - native and introduced races. Bull. Can. Bot. Assoc. 36(1): 4-7.
Fire effects information System. 2005.
Elaeagnus umbellata.
Haber, E. 1996.
Invasive plants of Canada: 1996 national survey results. Biodiversity Convention Office.
Haber, E. 1997.
Guide to monitoring exotic and invasive plants. Ecological Monitoiring and Assessment Network.
Hierro,J. L.& R. M. Callaway. 2003.
Allelopathy and exotic plant invasion. Plant and Soil 256(1): 29-39.
Husband, B. C. & K. S. Burgess. 2001.
Evaluating hybridization as a cause of species endangerement: a role for systematics in plant conservation. Pp. 82-95 in Phipps, J.B. & P.M. Catling [eds.] Bioconservation and Systematics (Proceedings of the Canadian Botanical Association Conference Symposium). Canadian Botanical Association.
LeJeune, K. D. & T. R. Seastedt. 2001.
Centaurea species: the forb that won the west. Conservation Biology 15(6): 1568-1574.
Li, T.S.C. 1999.
Sea buckthorn: New crop opportunity. Pp. 335-337 in: Janick, J. [ed.], Perspectives on new crops and new uses. ASHS Press, Alexandria, VA.
Li, T.S.C. & T.H.J. Bereridge. 2003.
Sea buckthorn (Hippophae rhamnoides L.): production and utilization. National Research Council of Canada, Ottawa. 137 p.
Mal, T. K. & L. Narine. 2004.
The Biology of Canadian Weeds. 129. Phragmites australis (Cav.) Trin. ex Steud. Canadian Journal of Plant Science 84: 365-396.
Marks M., B. Lapin & J. Randall. 1993.
Element Stewardship Abstract for Phragmites australis. The Nature Conservancy.
Morse, L. E., J. M. Randall, N. Benton, R. Hiebert, & S. Lu. 2004.
An invasive species assessment protocol evaluating non-native plants for their impact on biodiversity. Version 1. NatureServe, Arlington, Virginia.
Pidwirny, M. J. 2005.
Land use and environmental change in the Thompson-Okanagan.
Robichaud, F. W. & P.M. Catling. 2003.
Potential value of first glume length in differentiating native and alien races of Common Reed, Phragmites australis. Botanical Electronic News 310: 1-3.
Saltonstall, K., P. M. Peterson & R. J. Soreng. 2004.
Recognition of Phragmites australis (Poaceae: Arundinoideae) in North America: evidence from morphological and genetic analysis. Sida 21(2): 683-692.
Sather, N. & N. Eckardt. 1987.
Element Stewardship Abstract for Elaeagnus umbellata, Autumn-olive. The Nature Conservancy. Arlington, Virginia.
Sheley, R.L., J.S. Jacobs, & M.F. Carpinelli. 1998.
Distribution, biology, and management of diffuse knapweed (Centaurea diffusa) and spotted knapweed (Centaurea maculosa). Weed Technology 12(2): 353- 362.
Small, E. & P.M. Catling. 2001.
Poorly known economic plants of Canada - 29. Common reed, Phragmites australis (Cav.) Trin. ex Steud. Bull. Can. Bot. Assoc. 34: 21-26.
Small, E. & P.M. Catling. 2002.
Blossoming treasures of biodiversity: 5. Sea Buckthorn (Hippophae rhamnoides) - a ancient crop with modern virtues. Biodiversity 3(2): 25-27.
Szafoni, R. E. 1990.
Vegetation management guideline: autumn olive, Elaeagnus umbellata Thunb. Natural Areas Journal 11(2): 121-123; 1991.
Watson, A.K. & A.J. Renney. 1974.
The biology of Canadian weeds. 6. Centaurea diffusa and C. maculosa. Canadian Journal of Plant Science 54: 687- 701.
White D.J., E. Haber, & C. Keddy. 1993.
Invasive plants of natural habitats in Canada: an integrated review of wetland and upland species and legislation governing their control. Canadian Wildlife Service, Ottawa, Canada. 121 p.
Wilcox, K. L., S. A. Petrie, L. A. Maynard & S. W. Meyer. 2003.
Historical distribution and abundance of Phragmites australis at Long Point, Lake Erie, Ontario. Journal of Great Lakes Research 29(4): 664-680.


From: Marcel Rejmanek and Kristina P. Van Katwyk, Section of Evolution and Ecology, University of California, Davis, CA 95616

Available at

The ever-growing number of publications on secondary succession on abandoned agricultural land is overwhelming. The only published bibliography on old-field succession (Haug & Van Dyne 1968) covered 120, mostly American, references. Our bibliography covers 1511 references to old-field succession and related topics from the around the world until ca. 1991. At that time we also published a brief analysis of major research trends in this area (Rejmanek 1990). Our original intention was to publish this bibliography in Excerpta Botanica, Sectio B (Gustav Fisher Verlag). However, this series, dedicated exclusively to bibliographies in plant ecology, ceased in 1995. Many new contributions have been published in the meantime. Fortunately, most of the recent references are now readily available from existing databases. Examples of particularly valuable recent publications are Schmiedeknecht 1995 (Dissertationes Botanicae 245: 1-175), Bazzaz 1996 (Plants in Changing Environments. - Cambridge University Press), Chapman & Chapman 1999 (Conservation Biology 13: 1301- 1311), Siemann et al. 1999 (Ecography 22: 406-414), Foster & Tilman 2000 (Plant Ecology 146: 1-10), Van der Putten et al. 2000 (Oecologia 124: 91-99), Meiners et al. 2002 (Ecography 25: 215-223), Hedlund et al. 2003 (Oikos 103: 4568), Bartha et al. 2003 (Appl. Veg. Sci. 6: 205-212), Falinska 2003 (Phytocoenosis 15: 1-104), Myster 2004 (Bot. Rev. 70: 381402), and Knops et all. 2005 (Ecology Letters, in press).

As can be seen from some of these references, abandoned fields are used more and more for testing of very basic ecological hypotheses. We could even say that contemporary ecological theory is inseparable from abandoned fields. Old fields are often seen as a sort of Drosophila of terrestrial ecology. At the same time, however, research on post-agricultural succession brings extremely valuable information for land management and conservation, especially in the tropics. While the majority of old-field studies have been conducted in the United States, the monographic study on old-field succession in Central Bohemia (Osbornova et al. 1990) is a multidisciplinary project that remains thus far unparalleled. The virtual absence of old-field ecological studies in Australia remains puzzling even in 2005.

References in this bibliography are classified into one or more of the 46 categories.


Haug, P.T. & G.M Van Dyne. 1968.
Secondary succession in abandoned fields: an annotated bibliography. Oak Ridge National Laboratory, Oak Ridge, Tennessee, ORNLTN-2104, 69 p.
Osbornova, J., M. Kovarova, M., J. Leps, & K. Prach [eds.] 1990.
Succession in Abandoned Fields. Studies in Central Bohemia, Czechoslovakia. Kulver Academic Publishers, Dordrecht, 168 p.
Rejmanek, M. 1990.
Foreword: old and new fields of old-field ecology. pp. iv-xiii, in: Osbornova, J. et al. [eds.] Succession in Abandoned Fields: Studies in Central Bohemia, Czechoslovakia. Kulver Academic Publishers, Dordrecht.


Coombs, E.M., J.K. Clark, G.L. Piper & A.F. Cofrancesco, Jr. [eds.] 2004.
Biological control of invasive plants in the United States. Oregon State University Press, Corvallis, OR. viii+467 p. ISBN 0-87071-029-X [soft cover] Price: US$ 45.00
Available from:
At bookstores or fax your order 1-800-426-3797 [fax]. Distributed in Canada by the UBC Press, 1-877-864-8477 [voice]. Secure online ordering:

This is an essential reference to the biological control of invasive introduced plants in the United States. It represents a collaboration of 63 authors representing 10 universities, five federal agencies, four private organizations and four overseas agencies. The authors included in the book only those species that are approved by USDA-APHIS-PPQ. In spite of this restriction, there are 94 agents covered in this book.

The first part of the book (The theory and practice of biological control) deals with problems associated with introductions of biocontrol agents: theory, testing, permits, monitoring etc. Each chapter is an in-depth introduction to the treated topic.

The second part of the book deals with the target plants and their biocontrol agents. Since the success of biocontrol depends on the understanding of bioagent's ecology, this section gives a detailed description of each agent.

The following invasive plants are treated in this section:

The last section deals with ongoing biological control projects on plants not included in Section II.

[For the 1993 historical record of the biological control programs in British Columbia see Roy Cranston's contributions in BEN # 51 and 52]

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