Impact of invasive exotic knotweeds (Fallopia spp) on
invertebrate assemblages
Esther Gerber, Christine Krebs, Craig Murrell, Urs Schaffner (all CABI Switzerland Centre, Switzerland) and
Marco Moretti (WSL Swiss Federal Research Institute, Switzerland)
PROJECT OBJECTIVES
SUMMARY
INVASIVE EXOTIC KNOTWEEDS
The aim of the study was to quantify the
invertebrate assemblages in habitats invaded by
exotic knotweeds in central Europe and to
determine whether abundance, biomass and
species richness differed between invaded areas
and two types of native riparian vegetation.
(Fallopia (Reynoutria) japonica (Syn.: Polygonum
cuspidatum), F. (R.) sachalinensis as well as their
hybrid F. (R.) x bohemica
Fallopia
japonica
Exotic knotweeds negatively affect invertebrate
productivity and diversity.
Results were largely independent of sampling
method but varied among the feeding guilds
investigated.
In general, negative impact of exotic knotweeds
was strong compared to open vegetation, and less
strong compared to shrub vegetation
Fallopia
sachalinensis
BACKGROUND
CONCLUSIONS
There is a growing body of evidence that invasive
plant species can affect ecosystem structure and
processes and thereby cause considerable damage
to managed and natural ecosystems. While the
consequences of invasions by exotic plants on
native vegetation are relatively well documented,
their impact on native fauna has received much less
attention. Yet, studies addressing multiple trophic
guilds, e.g. plant species, herbivores, predators and
detritivores, are likely to shed important insight into
how and when invasive weeds alter ecosystem
processes.
Reduction in invertebrate abundance and biomass
can have important consequences for trophic
linkages within an ecosystem, including vertebrate
predators (Maerz et al. 2005, Biodiversity and
Conservation).
Control of invasive exotic knotweeds should
become an integrated part of nature conservation
schemes.
Exotic knotweeds are rhizomatous perennial
plants native to eastern Asia. These species are
among the “100 of the World's Worst Invaders”
and are causing significant damage to native
vegetation particularly in riparian habitats.
Control efforts should focus particularly on
preventing the invasion of open or semi-open
habitat areas.
RESULTS: INVERTEBRATES CAPTURED IN
COMBI TRAPS
PITFALL TRAPS
ALL INVERTEBRATES
b
30
125
ab
b
100
15
NGS, natural
grassland sites
75
50
NBS, natural
bush sites
2.5
1.0
0
NGS
Fallopia
NBS
NGS
NBS
Fallopia
b
a
300
b
200
100
0
NBL
S
a
400
0.0
NGS
No. individuals (2005)
500
0.5
Fallopia
NGS
NBL
S
80
No. morphospecies (2005)
a
60
a
b
40
20
0
Fallopia
NGS
NBL
S
Fallopia
Biomass, number of individuals and morphospecies richness lowest in Fallopia.
Number of individuals and morphospecies
richness lowest in Fallopia.
METHODS
ab
1.5
25
0
Biomass (2004)
a
2.0
(mean +SE)
45
No. individuals (2005)
a
No. morphospecies
ab
150
(mean + SE)
a
No. individuals
175
No. morphospecies (2005)
(mean + SE)
HERBIVORES
Freiburg im Br.
0.05
b
6
b
4
No. morphospecies (2005)
a
ab
2
b
1
2
0.00
0
NGS
NBS
Fallopia
NGS
NBS
0
Fallopia
NGS
NBS
Fallopia
PREDATORS
0.100
12
60
Biomass (2004)
No. of individuals (2005)
50
0.075
a
0.050
b
b
40
a
30
b
b
20
0.025
0.000
NGS
Germany
NBS
Fallopia
10
No. morphospecies (2005)
a
b
8
b
6
4
2
10
Sulzburg
Heitersheim
Belfort
8
a
No. morphospecies
(mean +SE)
Biomass (g)
(mean + SE)
0.10
No. of individuals (2005)
10
No. morphospecies
(mean +SE)
France
3
12
Biomass (2004)
0.15
Number of individuals
(mean +SE)
0.20
Biomass (g)
(mean + SE)
In 2004 and 2005, invertebrates were sampled at locations along river
courses with knotweed infestations. Pitfall traps and combi traps (to catch
flying insects) were established in vegetation invaded by exotic knotweed,
as well as in vegetation which can potentially be invaded by exotic
knotweeds: open vegetation (NGS, natural grassland sites), and bushdominated vegetation (NBS, natural bush sites). Invertebrates were
sampled between 12 - 28 July in 2004 and between 11 - 26 May and 15
July - 4 August in 2005. Invertebrates were sorted, counted, dried to a
constant weight at 40oC to asses biomass for each order/family (2004
samples) and separated at morphospecies level (2005 samples).
Herbivores (Orthoptera, Lepidoptera, Homoptera, Curculionidae,
Scarabidae, Chrysomelidae), a predartory group (Araneida) and a
detrivorous group (Isopoda) were analyzed seperately. Data was analysed
for each trap type using ANOVA with vegetation type, site and season
(spring, summer; for 2005 data only) as factors. When a significant effect
of vegetation type was found, differences among the groups were tested
using Tukey 's honestly significant difference test.
No. individuals
(mean +SE)
60
No. morphospecies
(mean + SE)
No. morphospecies
(mean + SE)
75
Biomass (g)
ALL INVERTEBRATES
0
0
NGS
NBS
NGS
Fallopia
NBS
Fallopia
Andelnans
Sévenance
Reinach
Delémont
DETRIVORS
1.5
ab
1.0
a
0.5
b
Circles: sites established in 2004; Stars: sites established in 2005.
No. morphospecies
(mean +SE)
Location of field sites investigated.
7
Biomass (2004)
Bolle di
Magadino
Biomass (g)
(mean + SE)
Genève
5
4
250
No. morphospecies (2005)
6
a
b
b
3
2
Number of individuals
(mean +SE)
Switzerland
1
0.0
NGS
NBS
Fallopia
0
NGS
NBS
Fallopia
No. of individuals (2005)
200
150
100
50
NGS
PARTNERS: FOEN (Federal office for the Environment,
CH), Loterie romande, Communauté de l’agglomeration
belfortaine, Conseil général du Territoire de Belfort,
Eigenbetrieb
Stadtentwässerung
und
Förderverein
Bachpatenschaften, Freiburg im Breisgau
Effect of exotic knotweeds varied among feeding guilds investigated.
Lowest values recorded in the majority of cases in Fallopia.
NBS
Fallopia