The invasive water primrose Ludwigia grandiflora (Michaux) Greuter & Burdet (Spermatophyta: Onagraceae) in Germany: First record and ecological risk assessment

Abstract

A population of Ludwigia grandiflora, an aquatic weed from South America, has been recorded in the North West of Germany near Leer, Lower Saxony in an old branch of the River Leda, a tributary of the River Ems. This species is new to the German flora. After an initial observation of only a few individuals in 2004, a dense growth of L. grandiflora has been observed from 2009 onwards. An ecological risk assessment, mainly based on knowledge about invasion histories in neighbouring countries, showed that this species is a threat to German biodiversity; thus, it is considered to be invasive and has been assigned to the German Black List. In accordance with nature conservation efforts, management policies are being developed by the appropriate authority to eliminate the population.

Full text

Aquatic Invasions (2011) Volume 6, Issue 1: 83–89
doi: 10.3391/ai.2011.6.1.10
© 2011 The Author(s). Journal compilation © 2011 REABIC
Open Access
83
Short Communication
The invasive water primrose Ludwigia grandiflora (Michaux) Greuter & Burdet
(Spermatophyta: Onagraceae) in Germany: First record and ecological risk
assessment
Stefan Nehring1* and Detlef Kolthoff2
1Federal Agency for Nature Conservation, Konstantinstraße 110, 53179 Bonn, Germany
2Agency for Nature Conservation, Bergmannstraße 37, 26789 Leer, Germany
E-mail: Stefan.Nehring@bfn.de (SN), Detlef.Kolthoff@lkleer.de (DK)
*Corresponding author
Received: 29 September 2010 / Accepted: 12 December 2010 / Published online: 16 December 2010
Abstract
A population of Ludwigia grandiflora, an aquatic weed from South America, has been recorded in the North West of Germany near
Leer, Lower Saxony in an old branch of the River Leda, a tributary of the River Ems. This species is new to the German flora. After
an initial observation of only a few individuals in 2004, a dense growth of L. grandiflora has been observed from 2009 onwards. An
ecological risk assessment, mainly based on knowledge about invasion histories in neighbouring countries, showed that this species
is a threat to German biodiversity; thus, it is considered to be invasive and has been assigned to the German Black List. In
accordance with nature conservation efforts, management policies are being developed by the appropriate authority to eliminate the
population.
Key words: Ludwigia grandiflora, Spermatophyta, alien species, freshwater, Germany, risk assessment, Black List
Introduction
The water primrose Ludwigia grandiflora
(Michaux) Greuter & Burdet, native to South
America, was intentionally released in 1830 in
southern France but remained restricted to the
area from the Camargue to Aquitaine during a
long period until the middle of the twentieth
century (Dandelot 2004). However, the spread of
L. grandiflora has been substantial during the
past four decades in France, where the species is
now already present in half of the country
(Dandelot 2004), and in other European
countries (records of free-living individuals in
Belgium (Bauchau et al. 1984), Ireland (F. Lucy,
personal communication), Italy (EPPO 2004),
The Netherlands (Kleuver and Holverda 1995),
Spain (EPPO 2004a), Switzerland (Vauthy et al.
2003), and the United Kingdom (Palmer 2008)).
Dandelot et al. (2005) suggested that during the
20th century, the increased use of L. grandiflora
as an ornamental aquatic plant has accelerated its
expansion in Europe. Brunel (2009) predicted
that L. grandiflora would soon occur elsewhere
in the wild if countries do not take action to
prevent its entry and spread.
First record in Germany
Here in this record, we are the first to document
the presence of Ludwigia grandiflora in German
waters (Figure 1). On 4 August 2009, a visit to
an old branch of the River Leda (53°11.01'N and
7°38.77'E), a tributary of the River Ems located
in the North West of Germany near Leer, Lower
Saxony, revealed a dense growth of water
primrose, a new alien species to the German
flora.
This stagnant old branch is isolated from the
River Leda by a dike and filled with surface and
ground water. The branch is 510 m long and on
average 30 m wide, with a maximum depth of
about 1.0 m.
On 19 August 2010 and 11 September 2010,
the site was surveyed to estimate the extent of
the invasion. These surveys revealed a very
dense population of L. grandiflora. The
population’s density was not quantified, but
several stands of different sizes were found

S. Nehring and D. Kolthoff
84
Figure 1. The invasive water primrose Ludwigia grandiflora in an old branch of the River Leda, Germany, 11 September 2010.
A) Colonization in the central part. B) Dense stand at the southern end; insert: bright yellow flower with five petals, approx. 5 cm
in diameter. C) Scattered young plants. Perspectives of photos are marked in Figure 2 (photographs by Stefan Nehring).
(Figure 2). At the southern end of the old branch,
a dense mat covered a surface area of about 40
m². The center of the invasion was situated in the
central part of the branch; L. grandiflora
occurred in two distinct areas more or less across
the whole branch. The smaller area was about 15
m in length, and the larger area was about 90 m
in length. In both areas, the greatest
concentrations of plants were in the middle of
the branch, at which the water depth is only 0.3
m due to silting tendencies. In summer, these
zones partially dry up. Between both areas,
several single plants could be observed as
emergent or floating forms. In summary,
L. grandiflora was found to cover a surface area
of roughly 1100 m² in total, which was
equivalent to 7.2 % of the whole water surface
area. On 19 August 2010, control surveys of
several other stagnant water bodies nearby did
not yield any additional detection of water
primrose.
The old branch has been used for fishing for
many decades and several anglers noted that they
had first observed L. grandiflora in 2004. The
mechanism that introduced L. grandiflora into
this water remains unknown, but the pathway
may have been human activity. The starting
point of the invasion was at the southern end of
the old branch, where the only paved country
lane in that area ends. Thus, it is very likely that
the occurrence there could be attributed either to
a person who illegally disposed of aquatic
material from a garden pond or to an angler who
stocked fish or used fish as bait taken from a
pond in which L. grandiflora was occurring. It is
well-known that small plant fragments of water

Ludwigia grandiflora in Germany
85
Figure 2. Spatial distribution of dense
stands of the invasive water primrose
Ludwigia grandiflora in an old branch
of the River Leda, Germany, 11
September 2010. Arrows indicate
perspectives of photos in figure 1.
Digital orthophoto  Surveying
administrations of federal states and
Federal Agency for Cartography and
Geodesy (http://www.bkg.bund.de).
primrose are sufficient for establishing a new
population (Dandelot 2004).
There is some taxonomic confusion in the
Ludwigia complex (Dandelot et al. 2005).
Several older European records refer to
L. uruguayensis (Camb.) Hara (e.g., Bauchau et
al. 1984; Kleuver and Holverda 1995), which is,
according to Nesom and Kartesz (2000), a
synonym of L. grandiflora. There is one native
Ludwigia species in Germany, L. palustris (L.)
Elliott, which is known as marsh-purslane; it is
very rare and very different in appearance
(Lakmann and Cordes 1996).
Ecological impacts and risk assessments
The discovery of a dense, well-established
population of Ludwigia grandiflora in German
waters is of significant concern. Invasions of
L. grandiflora have been associated with
negative effects on biodiversity and water
quality in Belgium, France and Switzerland.
Under appropriate conditions it can double in
mass in 15-20 days (Dandelot 2004). The growth
form shades out other plants and L. grandiflora
stands are typically monospecific (Dandelot

S. Nehring and D. Kolthoff
86
2004; SKEW 2009). In addition to shading,
decaying mats of Ludwigia bring about
deoxygenation of the water with potential
damage to fish stocks and to other fauna
(Lambert et al. 2010; Stiers et al. 2009). Large
plant biomass also results in an increase in
sedimentation with diverse effects on native
biocoenosis (Dandelot 2004). L. grandiflora
possesses an allelopathic activity that influences
the water quality throughout the year and
reduces the germination and survival rates of
other plant species (Dandelot et al. 2008). Whole
lake systems in France have been taken over by
Ludwigia, with a resulting loss of water for
waterfowl (Danelot 2004). This species has also
been associated with several human activity
nuisances in water bodies (Dandelot 2004).
Ecological risk assessments of L. grandiflora
have been performed in several European
countries and by the EPPO to allow the
prioritization of management measures (Table
1). However, the ecological impacts of this
species in Germany have not yet been
characterized and evaluated. In 2008, a newly
developed and tested risk assessment tool for
invasive alien species, the “German-Austrian
Black List Information System” (GABLIS), was
implemented by competent authorities in both
countries (Essl et al. 2008; Nehring et al. 2010).
It has been developed as a trans-national and
taxonomically universal risk assessment system.
This assessment is criteria based, i.e. a set of
specific criteria is used to assess the alien
species’ impact. Data used for assessment may
result from scientific reports and peer-reviewed
publications as well as from expert judgement,
and they may refer either to a reference area or
to climatically and ecologically similar areas. In
accordance with the GABLIS guidelines,
L. grandiflora is considered a threat to German
biodiversity and has been assigned to the
German Black List of invasive species (Table 2).
In GABLIS, the Black List is further separated
into three specific sub-lists (warn, action and
management lists), according to the current
distribution of the alien species and emergency
measures available. Because up until now
L. grandiflora occurs only in one locality and
since eradication measures are feasible, it
appears on the German Black List – action list
(BfN 2010). Here, immediate, intense and
sustained eradication measures make sense to
eliminate all free-living individuals in order to
avoid further spreading and to prevent loss of
biodiversity. This management approach is in
agreement with Article 40 paragraph 3 of the
new Federal Nature Conservation Act
(BNatSchG 2009, entered into force 1 March
2010), which prescribes that the competent
Federal and Länder authorities should
immediately implement suitable measures aimed
at eliminating, or preventing the spread of, newly
appearing plants and animals of invasive alien
species.
Management measures
Each invasive alien species and each site has its
own management plan based on individual
characteristics. Thiébaut (2007) summarized
various solutions that could be adapted to
individual sites of L. grandiflora colonization.
At the beginning of Ludwigia colonization,
manual removal is usually practicable. When the
plant has become well-established, mechani-
zation is necessary. Although chemical treatment
can replace or enhance manual removal
operations, it has been used only as a last resort,
where water use and environmental considera-
tions made it possible and if it is permit by the
applicable regulation. In the case of the present
invasion, management policies are being
developed by the appropriate authority to
eliminate the population. It is essential to remove
all plant material because L. grandiflora can re-
grow from small root and stem fragments and to
install a careful transport and disposal system to
prevent further spreading. After treatment,
monitoring for the early recognition of re-
emergence is essential.
The prevention of the (re)introduction of
invasive species is a key management issue. In
Europe, L. grandiflora has a high potential of
invasiveness (Brunel et al. 2010; EPPO 2004),
but it is still being sold as an ornamental plant
for garden ponds in most countries (Brunel
2009). However, for several years, the commer-
cialization of water primrose has been prohibited
in France (MEDD 2007), Portugal (MDA 1999)
and Switzerland (SBR 2008). In the Netherlands,
a new code of conduct regarding alien plants was
signed (EPPO 2010), in which the signatories
reached an agreement to stop selling six invasive
species including L. grandiflora by 1 January
2011. Regulation appears to be the most
appropriate option for preventing the detrimental
effects of invasive alien species in the long run.
Thus, the invasive L. grandiflora should be
banned from sale, especially in high-risk
countries such as Germany.

Ludwigia grandiflora in Germany
87
Table 1. Results of ecological risk assessment of Ludwigia grandiflora in Western European countries and by the European and
Mediterranean Plant Protection Organization (EPPO).
Country Protocol Result Reference
Belgium ISEIA vers. 2.6 High risk (black list A2) Branquart et al. 2010
Germany GABLIS Invasive (black list – action list) this study
Great Britain GB NNS risk assessment High risk NNSS 2010
Switzerland Weber and Gut High risk / invasive (black list) Weber and Gut 2004; SKEW 2010
Europe EPPO pest risk analysis Invasive (list of (potential) invasive alien
plants) EPPO (Brunel et al. 2010)
Table 2. Ecological risk assessment of Ludwigia grandiflora inclusive Black List classification for Germany (Assessment
protocol: “German-Austrian Black List Information System” (GABLIS); for further information, see Essl et al. (2008), Nehring
et al. (2010)).
a) General Information
Systematics and nomenclature Ludwigia grandiflora (Michaux) Greuter and Burdet
Spermatophyta, Onagraceae
Water primrose (EN), Großblütiges Heusenkraut (DE)
Important synonyms Jussiaea grandiflora, Ludwigia uruguayensis
Habitat Freshwater
Status established
Native region South America
Introduction deliberate
Import vectors Horticulture
First introduction unknown
In 1823, the first European import into France (Dandelot 2004); about 1888 cultivated in the Botanical Garden of Marburg,
Germany (Goebel 1889), however, no figures regarding date of first import are available.
First record 2004 (this study)
b) The Main Criteria - Risks To Biodiversity
1 Inter-specific competition yes
Strong inter-specific competition with native plants (Belgium, Stiers et al. 2009; France, Dandelot 2004; Switzerland, SKEW
2009); possesses an allelopathic activity that reduces the seedling survival of other plant species (France, Dandelot et al.
2008).
2 Predation and Herbivory not assessed
3 Hybridization unknown
Hybridization with other (native) Ludwigia species in the wild should not be excluded (Neson & Kartesz 2000) because in
laboratory conditions, hybridization between L. grandiflora and L. peploides is possible (Dandelot 2004).
4 Transfer of pathogens or organisms no
Currently, no endangerment of native species is known.
5 Negative effects on ecosystems yes
Monospecific stands can cover the whole surface of larger water bodies, altering the whole ecosystem by reducing light
transmission, water flow and oxygen content, as well as by increasing sedimentation (Belgium, Stiers et al. 2009; France,
Dandelot 2004, Lambert et al. 2010).
c) Additional Criteria
1 Current distribution small-scale
Only one free-living population in an old branch of the River Leda is known (this study).
2 Emergency measures available
Mechanical measures, chemical control, prevention of intentional release, public relations. Successful control measures e.g.
in France (Thiébaut 2007), Switzerland (SKEW 2009) and United Kingdom (NNSS 2010).

S. Nehring and D. Kolthoff
88
Table 2 (continued).
d) Biological-Ecological Criteria
1 Occurrence in natural, semi-natural or other high nature
value habitats
yes
The species is found in marshes and in shallow sites of inland waters, especially in still or slow-flowing waters (Dandelot
2004, this study).
2 Reproductive capacity high
In Europe, reproduction is mainly vegetative, and the plant can re-grow from small root and stem fragments (Dandelot 2004);
sexual reproduction is thermal limited (Ruaux et al. 2009).
3 Spread capacity high
Mainly by passive dispersal of plant fragments and seeds (Dandelot 2004, Ruaux et al. 2009).
4 Current spread history expansive
In the recent past strong expansion in Europe (Belgium, France, Italy, The Netherlands, Spain, Switzerland, United Kingdom)
(e.g. Dandelot 2004, Denys et al. 2004, Kleuver and Holverda 1995).
5 Monopolization of resources yes
Under favourable site conditions, biomass could double in 15-20 days (Dandelot 2004, Sheppard et al. 2006).
6 Facilitation by climate change yes
Increasing temperatures will favour stock development and spreading (Hussner 2009).
e) Additional Information
1 Negative economic effects yes
Fishing, boating, tourism, water management (Dandelot 2004).
2 Positive economic effects no
3 Negative effects on human health no
4 Knowledge gaps and research needs yes
The genus Ludwigia needs a taxonomic revision.
f) Assessment Result a)
Black List – action list
a) Classification methodology
Step 1: Scaling results in section b)
At least one “yes” in b1-b5 -> Black List
Step 2: Classification result of Step 1 and scaling results in section c)
“Black List” in Step 1 and “small scale” in c1 and “available” in c2 -> Black List – action list
The European and Mediterranean Plant
Protection Organization (EPPO) has actually
finalized a pest risk analysis on this species
(Brunel et al. 2010) that could help regulating
international trade and importation of this
species in the future.
Acknowledgements
The authors thank Ute Albrecht and Bettina Dibbern for
technical support. The digital orthophoto in Figure 2 was
kindly provided by the Federal Agency for Cartography and
Geodesy. We are grateful to Alain Dutartre and two
anonymous reviewers for constructive comments on the
manuscript.
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