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Invasive alien species from a nature conservation point of view in Germany

Frank Klingenstein and Thuweba Diwani

F. Klingenstein, German Federal Agency for Nature Conservation, Konstantinstr. 110, 53179 Bonn, Germany; e-mail:; T. Diwani, Institute for Plant Nutrition, University of Bonn, Karlrobert-Kreiten-Str. 13, 53115 Bonn, Germany; e-mail:


Invasive alien species are considered to be the second most important reason for biodiversity loss on a global scale. This has increasingly been re.ected in national and international environmental policy during the past few years. Nevertheless, in central Europe the risks caused by invasive alien species are considered to be lower than in other regions. Only a few alien species have a negative impact on native biodiversity and require conservation activities. This paper discusses the criteria concerning risks and impacts as well as options for action for these cases in Germany. The impact of invasive alien species on other aspects of society (e.g. economic, human health) are considered to be the individual responsibility of the affected groups. However, because problems caused by invasive alien species frequently concern several stakeholders at the same time, strategies and regulation mechanisms should be developed and used cooperatively. Five current and intended projects of the Federal Agency for Nature Conservation are presented: two online tools, FloraWeb and NeoFlora; an early warning system; an information network with regional nature conservation agencies; and the national strategy on invasive alien species.

Evaluating the problem of invasive alien species

The problem of invasive alien species in central Europe is best understood and assessed by considering first the international and historic context of the movement of organisms.

International context of alien species

The spread of organisms into new areas is a natural process and a basic feature of biological systems. Humans themselves are important vectors of living organisms, starting with their origin as hunters and gatherers, and increasingly with settled lifestyle and agriculture since the Neolithic time. Anthropogenic spread can be intended (e.g. collection and exchange of useful animals and plants) or unintended (transportation of diseases and weeds etc.).

Box 1: From the new world

Christopher Colombo on 18 October 1492 after his landing on Guanahani/San Salvador:

"It torments me very much that I do not know all these herbs, shrubs and plants which may be very valuable for use as dyes, medicine or spices.

I will take home samples of most of them."

The fifteenth century saw the beginning of one of the greatest times of change in this human-assisted movement. On the one hand, plants and animals were no longer exported only as products or goods but were exchanged alive as whole plants, seeds or viable parts. Some examples are crops (especially from the new world; see quotation from Columbus), the beginning of garden culture (“tulip mania” in Holland 1593-1637) or scientific collections in the newly built botanical gardens. On the other hand, the speed and amount of exchange increased exponentially with the discovery of new regions by the Europeans and the improvement of transport conditions (see part A in box 2). This is the reason why the European discovery of America in 1492 is seen as a time change between the organisms introduced to Europe before (“archaeobiota”) and afterwards (“neobiota”).

This increasing biological exchange has had several effects. The introduced plants not only increased the existing native plant diversity (which might be considered as a positive effect) but also affected the established ecosystem, sometimes nearly unnoticeably and sometimes changing the entire system to such an extent as to lead to its total destruction. An especially noticeable example is the extinction of species, often highly specialized and/or endemic (i.e. occurring in only a limited area) as illustrated in part B of box 2. As a consequence of the expansion of usually widespread neobiota at the expense of rare native species, the number of species is decreasing on a global scale. Thus, alien species are considered the second most important cause for the extinction of species globally (Vitousek et al., 1997; Sandlund, Schei and Viken, 1999) and even the most important cause of extinction of animal species since 1600 (Groombridge, 1992).

Box 2: Biological globalization: the example of Hawaii

Part A: Introduction dynamics of animal and plant species

Natural settlement since existence of the islands 30 - 10 million years ago:

1 new species in 50 000 years

By the Polynesians since their settlement 1 400 years ago: 45 species

1 new species in 30 years

Since the discovery by Cook in 1778: 4 000 species

1 species in 2 weeks

Part B: Extinction and introduction balance for plant species

Original diversity

1 200 species


of this extinct

-97 species


Alien neophytes

+1 000 species


Current diversity

2 103 species


Part C: The biomass of the introduced species already exceeds those of the native ones.

Source for A: figures of Loope & Müller-Dombois, in Kowarik, 2003, p. 26. Source for B and C: Davis and Heywood, 1995.

Alien species in Germany

For Germany and central Europe in general, however, the situation is different, as shown by Kowarik (2003). Many alien species such as ribwort (Plantago lanceolata) or daisy (Bellis perennis) as archaeophytes or disc mayweed (Matricaria discoidea) as neophytes are among the 50 most common species of the German flora (refer Extinction as a result of alien species is not known and their effects on ecosystems are not as extensive as in other regions of the world. As only 5 percent of the endangered plant species in Germany are threatened by alien species (Korneck et al., 1998), they present a minor threat factor.

Remarkably, this situation is not because there are less alien species in Germany than in other regions of the world. Based on the national taxonomic reference list, 226 of the 3 384 indigenous taxa are archaeophytes and 383 are established neophytes. Another 624 neophytes are at least locally established, are currently becoming established or occur sporadically. There are in total, therefore, almost 1 000 species of neophytes (see figure 1). Further to that, 1 123 animals are known to have been introduced into Germany after 1492; of these, at least 262 are established (Geiter, Homma and Kinzelbach, 2002).

Several reasons have been offered for the less negative effects of alien species in central Europe. The most important is exclusion of tropical species because most of them cannot survive or reproduce in the European climate. Then, with the adoption of European land-use practices (e.g. permanent artificial meadows and pastures, perennial cultivation) in other regions of the world, many European species could establish in new regions outside Europe because they found suitable conditions to which they were already adapted. The main reason might be the long history of land use in central Europe, with the introduction and exchange of species throughout the past 7 000 years. The ecosystems have had more time to adapt to the new species. In contrast, other regions of the world were confronted with alien species only some 500 years ago.

Fig. 1: Numbers of species in the German vascular flora.

Source: national checklist for vascular plants, and unpublished data of Lippe & Kowarik.

Moreover, the historical land-use practices in Europe increased the number of species significantly, although those numbers have come under threat from modern intensification of land use. Many species and habitats are now preserved through nature conservation measures. One-quarter of all 226 archaeophytes are on Germany’s “red list” of endangered vascular plants, making up over 8 percent of their total (Korneck et al., 1998). This shows that “foreignness” has a strongly normative impact, changing the criteria for conservation choices, for example.

What does “invasive” mean for nature conservation?

Some alien species have clearly negative effects on the natural balance: they endanger biological diversity on one or more levels (ecosystems, species or genes). In contrast to scientifically applied definitions (e.g. Kowarik, 2003), but in accordance with nature conservation definitions (e.g. Convention on Biological Diversity and its guiding principles on invasive alien species), these species are seen as invasive species and therefore demand measures. Such a “strict” definition with clear limitation to ecological damage is of special importance for nature protection. It separates the damage relevant to nature from economic, health or other damage, which are considered the sphere of activity for the affected actors. It should also clarify that measures applied to alleviate these other forms of damage (such as pesticide application on cultivated land to protect crop plants from invasive weeds) cannot be declared to be conservation measures.

Although ecological effects can occur at all levels of biological diversity and can be caused by different processes (refer table 65 in Kowarik, 2003), four criteria for negative effects/invasiveness can be derived on a qualitative level (while threshold levels for ecological danger or damage for nature are still missing):

Immediate threats: predation and parasitism

Most directly invasive animal species can damage native species through an increased predation pressure that can be species-specific (selective feeding of certain plants or animals), but also indifferent (e.g. consumption of other amphibian species by the American bullfrog, Rana catesbeiana). Other immediate dangers come from increasing parasitism (e.g. by parasites which are used for pest control) and from the spread of illnesses within native species (e.g. death of elm trees, Ulmus spp., through the spread of a disease vector, the elm split pin beetle).

Direct threats: competition for habitats and resources

Damage relevant to conservation arises also by competition between alien species and native species for habitats and resources. Invasive alien species can displace single native species by taking over their ecological niches, such as the alien rugosa rose (Rosa rugosa) replacing the native Scotch rose (R. spinossissima) in the dunes of north Germany or raccoon dog (Nyctereutes procyonoides) versus fox (Vulpes vulpes). They can also upset whole biological communities, such as displacement of nearly all native species by stands of the Japanese knotweed (Fallopia japonica).

Indirect threats: change of ecological conditions

Changes of local site conditions, such as food chains, are more complex, but can also endanger native species indirectly. As an example, dry pastures that are falling into fallow favour the spreading of the false acacia (Robinia pseudoacacia); its nitrogen-enrichment properties, in turn, favour nitrogen-dependent species (eutrophication), which then displace the original species. Alien douglas fir (Pseudotsuga menziesii), in contrast to most native trees, is able to grow on rocks and shadow the original vegetation.

Genetic threats: hybridization and introgression

The least noticeable changes occur on the genetic level through crossing and gene exchange of native with exotic species. Examples are: genes of cultured garden forms of the native European columbine (Aquilegia vulgaris); genes of cultivated apples or pears outcrossing into the wild species; the native white headed duck (Oxyura leucocephala) endangered by hybridization with the North American ruddy duck (O. jamaicensis). Hybridization leads to the substitution of local genes with alien genes and through this to the decrease of native genes and genetic diversity. This can lead to the loss of specialized adaptation mechanisms and characteristics of local populations. The same mechanism causes the potential danger of genetically modified organisms (e.g. hybridization of genetically modified rape with related native species). Also current landscaping practices endanger the genetic diversity of local species because cheap seeds and plants of native species are imported from foreign origins for planting.

Conditions and measures

Alien species are the subject of numerous international agreements as well as European and national legislation reaching far beyond nature conservation (from the convention on ballast water up to the federal law on hunting). Besides the regulatory framework of nature conservation in Germany, the International Plant Protection Convention and its national application through the federal plant protection laws is of special importance.

Nature conservation in Germany

The most significant regulation in the field of nature protection is the Convention on Biological Diversity whose Article 8(h) and decision VI/23 (refer also footnote on page 7) place obligations on member countries and provide guidance in the management of invasive alien species (as discussed in detail in previous chapters). The guiding principles suggest comprehensive national strategies on the basis of a three-stage hierarchical approach (prevention, early detection, measures).

The biodiversity convention is transferred into national law by the German Federal Nature Conservation Act and the Federal Ordinance on the Conservation of Species. In addition, the law of the European Community is legally binding for Germany, most notably Council Regulation (EC) No 338/97 on the protection of species of wild fauna and flora by regulating trade therein, the habitats directive (Council directive 92/43/EC) and the birds directive (Council directive 79/409/EC).

In this framework different options for action arise for nature protection: acceptance, control, monitoring, public awareness and legal regulations. These are illustrated in figure 2.

Fig. 2: Options for action for former and future introductions of alien species.

Preventive measures such as building awareness and regulations can prevent future introductions. Acceptance, monitoring and control measure are applicable for all alien species. Monitoring has a central role as the basis for a decision on acceptance or control and in evaluating the success of measures.


Established species (i.e. species building viable offspring without human influence) should be accepted as new components of our fauna and flora, provided they do not cause ecological damage by having invasive characteristics.


For invasive species, case-speci.c decisions on control or eradication measures should be taken on the basis of the local conditions or situation. These measures could aim to control the species, for example by preventing propagation, preventing establishment in new sites or fixing the population size at a certain level; alternatively, they could aim to eradicate it. Kowarik (2003: figure 73) suggests case-related assessments for control measures taking into account the site conditions, possible conflicts with other conservation targets, prospects of success, consideration of costs and benefits and so on.


Monitoring is of special importance, for example to obtain information about the damage of an alien species or about the efficiency of measures. Although the federal nature conservation law includes an obligation to environmental observation, a monitoring concept for alien species is still missing. Concepts should be based on existing data and instruments (e.g. ongoing floristic mapping activities to determine the spread of alien species) and development of new mechanisms such as expert consultation and early warning systems.

Public awareness

In relation to preventive measures, informing the general public and building awareness is of special importance (as with NeoFlora, the Internet project discussed below). Information should not be reduced to the dangers of invasive species and suitable control measures, but has to focus on unintentional introduction of alien species. Besides the varying media interest in the subject there is still a lack of awareness in the private sector (e.g. holiday travel) as well as in the commercial sector (ballast water, wood packaging etc.).

Legal regulations

Legal regulations are applicable primarily to intended introductions. In contrast to plant protection, nature conservation in Germany has a limited regulatory framework and tradition to deal with alien species. Although the introduction of alien species into the landscape has to be authorized according to the Federal Nature Conservation Act (excluding their use in agriculture or forestry), there are no agreed guidelines for regional authorities or accepted procedures, for example for risk assessments.

In addition to regulation of introductions, the federal species conservation ordinance and European Community law can prohibit the ownership or sale of organisms. However, at the moment, this is applicable only to a few vertebrate species.

Plant protection

The IPPC and its transfer into national law offers an internationally agreed system, including financial and human capacity, for the implementation at national level (see chapters 6 and 13). The IPPC system has been established a long time and practical experience gained in multiple fields, for example risk assessment. Therefore, nature conservation may profit from plant protection. Cooperation between both areas is discussed on various levels (e.g. the memorandum of cooperation between the CBD and the IPPC). Regardless of the good contact between the relevant national authorities in Germany, there are still some items that have to be clarified and agreed. These are outlined below with examples for different categories of organisms.

Pest for agriculture, but not invasive

Galinsoga species are alien weeds on fields and rural land. Because these habitats are not natural, the Galinsoga species do not, by definition, endanger nature or imply ecological threats. On the other hand, they cause agricultural (economic) damage for which they are controlled or eradicated on fields by herbicides. Such control measures can not be declared as conservation measures, because these species and habitats are of no concern for conservation.

Pest for land-use practices and threat to human health, potentially invasive

The common ragweed (Ambrosia artemisiifolia) is an alien plant with an allergenic impact on humans. It occurs mainly in man-made habitats. As an agricultural weed and on rural sites it is a threat to human health. Until now, no ecological threat is known. However, it is not unlikely that the plant will spread to naturally disturbed habitats such as river plains, possibly affecting nature. In this instance, conservation activities seem advisable, but only because of the public concern.

Pest for land use, and invasive

Wild black cherry (Prunus serotina) and creeping Oregon grape (Mahonia aquifolium) have been introduced to Germany as pioneer trees for reforestation or as ornamental shrubs. They can build dense vegetation layers in alluvial forest or on dry dune pine forest preventing the regeneration of native or forest trees. They therefore have a negative impact on native plants, vegetation and ecosystems as well as forestry.

A further example is the giant hogweed (Heracleum mantegazzianum), an alien plant in natural habitats (forest) and man-made habitats (meadows). It is therefore a threat to nature and agriculture; and because of its phytotoxic character, also to human health.

In these instances, the concerns of forestry, agriculture, human health and conservation are in accord and measures could be taken jointly.

Not a pest for land use, but invasive

Plants that threaten biodiversity but are of no concern for agriculture or forestry seem to be the most common group. From the point of view of nature conservation, the main questions are: Is the plant protection system willing and able to deal with numerous “new” pest plants? Do transparent, reliable criteria and procedures exist to assess for which species the plant protection system and IPPC framework would be applicable? Would, for example, the control of the invasive campylopus moss (Campylopus introflexus), which threatens extremely rare but economically worthless plant communities on rock and sand, be applicable for phytosanitary measures?

Useful plants for agriculture or forestry, but invasive

Douglas fir (Pseudotsuga menziesii) was introduced to Europe as an ornamental. It has become a common forestry tree in some regions of Germany. In the highlands it produces a huge number of seedlings germinating relatively far from the older plants and growing into dense layers preventing regeneration of native trees such as beech (Fagus sylvatica). Therefore Douglas fir is regarded as invasive, possibly changing broadleaf forests to coniferous forests with consequences for animals, soil chemistry, groundwater conditions etc.

It is questionable if this conflict between conservation and land use can be solved within the plant protection system and IPPC framework.

Nature conservation activities in Germany

The Federal Agency for Nature Conservation (Bundesamt für Naturschutz, BfN) is the scientific authority supporting and advising the Federal Ministry of Environment in political activities (e.g. the strategy of the Council of Europe against invasive alien species and the International Convention for the Control and Management of Ships’ Ballast Water and Sediments). At present it is conducting several projects relating to invasive alien species.

Information databases and information exchange

The provision and exchange of information is a key issue in the management of invasive alien species. Moreover, information systems help raise public awareness.


The FloraWeb information system ( offers over 50 details on taxonomy, biology, ecology, habitat, distribution, threat, protection and use, as well as photos and distribution maps for all of the approximately 3 500 native and alien plant species growing wild in Germany. The data are taken from approved standard literature, and raised in the scope of research projects of the BfN, as well as by successive survey projects such as the floristic mapping of Germany and CITES database (


The NeoFlora Web site ( contains general information about alien species and data sheets for 30 invasive plant species whose biology, distribution, introduction history, impacts on nature and land use are outlined as well as possible control measures. For each species, experiences about control measures can be exchanged in discussion fora moderated by experts. A master file is available for download as a model to integrate further data sheets of plant and animal species which can be transferred to the Internet automatically.

Early warning and monitoring system

Further activities should enhance these information systems to function as an interactive early warning and monitoring system for invasive alien plant species, possibly connected with the intended revision of the national “red lists” and their expert system. This would allow direct contact with regional experts (professional and volunteers in botany or conservation) so that the up-to-date data on occurrence, spread and impact of new alien species would be available and appropriate countermeasures could be taken directly (figure 3).

Contact and exchange with local conservation authorities

Permission for introductions and control measures are the responsibility of regional and local authorities; the federal level has to provide them with information on species, legislation etc. Moreover local authorities have to be enabled to exchange views and experiences among each other. To this end, an e-mail distribution list of all responsible persons and authorities has been compiled. The existing and planned Web tools (see above) offer the possibility to build up a communication platform by maintaining discussion fora for varying relevant issues.

Fig. 3: Spread of giant hogweed (Heracleum mantegazzianum) in Germany from 1950 over 1980 to 2003.

(Data from the floristic mapping activities in Germany; see

Development of a national strategy on invasive alien species

In accord with the CBD’s guiding principles, Germany is preparing a national strategy on invasive alien species. This is financed by the BfN and compiled by the University of Göttingen (see chapter 18). The legal conditions and technical measures to prevent introductions are assessed; stakeholders are identified and their role is analysed; and suggestions for more consistent regulations, cooperation and potential roles of stakeholders are worked out.


Invasive alien species require case-by-case consideration, taking into account the local situation as a basis for possible measures. The federal level can contribute to this by offering information and a platform for information exchange. Moreover, legal and organizational concepts need to be developed and discussed with other relevant stakeholders. For the plant kingdom, the activities, experiences and concepts of plant protection seem to offer a promising approach for nature conservation also. Nevertheless, it still has to be worked out in detail how both systems can cooperate or be integrated, which rights and obligations the two areas have and which rules could help achieve the common target to prevent the introduction of new invasive alien species threatening biodiversity and/or agriculture, forestry, other human uses as well as human health.


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Geiter, O., Homma, S. & Kinzelbach, R. 2002. Bestandsaufnahme und Bewertung von Neozoen in Deutschland. Texte des Umweltbundesamtes 25/2002. Berlin, Germany, Umweltbundesamt (Federal Environmental Agency). 174 +36 +31 +52 pp.

Groombridge, B., ed. 1992. Global biodiversity: status of the earth’s living resources. Compiled by the World Conservation Monitoring Centre. London, UK, Chapman & Hall. 594 pp.

Korneck, D., Schnittler, M., Klingenstein, F., Ludwig, G., Takla, M., Bohn, U. & May, R. 1998. Warum verarmt unsere Flora? Auswertung der Roten Liste der Farn- und Blütenpflanzen Deutschlands. Schriftenreihe für Vegetationskunde, 29: 299-444.

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Vitousek, P.M., D’Antonio, C.M., Loope, L.L., Rejmanek, M. & Westbrooks, R. 1997. Introduced species: a signi.cant component of human-caused global change. New Zealand Journal of Ecology, 21(1): 1-16.

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