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Flora and lepidoptera fauna adversely affected by invasive
Lupinus polyphyllus along road verges
Anu Valtonen*, Juha Jantunen, Kimmo Saarinen
South-Karelia Allergy and Environment Institute, La
¨a
¨ka
¨ritie 15, FIN-55330 Tiuruniemi, Finland
ARTICLE INFO
Article history:
Received 23 March 2006
Received in revised form
14 June 2006
Accepted 30 June 2006
Available online 17 August 2006
Keywords:
Alternative habitat
Butterfly
Diurnal moth
Non-native species
Plant species
ABSTRACT
An increasing number of invasive species are changing ecosystems around the world. Road
verges have commonly become the first footholds of non-native species in the new envi-
ronments. Regularly mown road verges also offer habitats for meadow flora and fauna,
which in Europe have suffered from the radical decline of semi-natural biotopes due to
the agricultural modernization. We studied impacts of an invasive plant Lupinus polyphyllus
on the plant and Lepidoptera species composition along road verges. The plant species
composition was studied on 15 sites (with 1 m
2
quadrats) and butterflies and diurnal moths
along 15 transects (with weekly censuses) in SE Finland, each site and transect representing
equally lupine invaded verge and an adjacent non-lupine verge. The species richness and
diversity of flora and the cover and species richness of low growing (<20 cm) species, in par-
ticular, was lower in lupine verges compared to non-lupine verges. Also, the abundance of
butterflies was lower in lupine verges. As the lupine cover approached 100%, fewer butter-
flies were observed in lupine transects compared to the adjacent non-lupine transects and
a higher proportion of individuals were flying. Our results suggest that the changes in plant
species assemblages and lower plant species richness in lupine invaded areas had ‘‘bottom-
up’’ effects on higher trophic levels. Further studies on the control of lupine are urgently
needed, but meanwhile we suggest regular mowing before the lupines have shed their
seeds, together with the removal of the cuttings, to be the best management option.
2006 Elsevier Ltd. All rights reserved.
1. Introduction
Species introductions have become more common due to the
increased transport, trade, travel and tourism, which provide
vectors and pathways permitting living organisms to cross
biogeographical barriers that would usually block their way
(Vitousek et al., 1996). Some of the non-native species become
invasive and have negative effects on native species, the econ-
omy and public health (Mack et al., 2000). From the ecological
perspective the invasive species can influence all ecosystem
levels from individuals and populations to communities and
ecosystem processes. Within biogeographical regions, the
replacement of local biota with non-indigenous, human intro-
duced species results in the homogenization of ecosystems
(McKinney and Lockwood, 1999). Road verges, in particular,
have often formed footholds for invasive plant species (Trom-
bulak and Frissell, 2000), and in some parts of the world the
majority of road verge flora comprises introduced species
(Wester and Juvik, 1983). Periodic disturbances common on
road verges may eliminate or reduce the cover of competitors
and/or increase resource levels and therefore facilitate inva-
sions (Davis et al., 2000).
Despite the harsh climate, considerable numbers of alien
plant species have spread and become established in the
0006-3207/$ - see front matter 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2006.06.015
*Corresponding author: Tel.: + 358 5 432 8629; fax: + 358 5 432 8625.
E-mail addresses: valtonen@cc.joensuu.fi,all.env@inst.inet.fi (A. Valtonen), all.env@inst.inet.fi,jjantune@nic.fi (J. Jantunen),
all.env@inst.inet.fi,ksaarin@hotmail.com (K. Saarinen).
BIOLOGICAL CONSERVATION 133 (2006) 389–396
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/biocon
Nordic countries (Jonsell, 2004). Plant species have arrived
both intentionally and unintentionally along with traditional
agricultural practices and by escaping from gardens into the
wild. Some garden introductions, such as the lupine (Lupinus
polyphyllus), are so competitive that they are considered a
threat to other plant species. The lupine originates in western
North America (Jalas, 1965). It had already been introduced in
central Europe when the species was described in 1827. Over
the last few decades the lupine has been recorded as an inva-
sive species in Britain and in central Europe, where it has both
increased in frequency and advanced its altitudinal limits
(Rich and Woodruff, 1996; Kowarik, 2003; Becker et al., 2005).
In Finland, the species had escaped into the wild in four
southern and western provinces by 1965 (Jalas, 1965). Two
decades later the species had spread almost 400 km north-
wards (Lahti et al., 1995). Nowadays, the lupine is spreading
rapidly along road verges and other disturbed habitats, but
there is a clear indication that the species can spread also
to semi-natural grasslands and natural environments such
as groves of trees (The Finnish Environment Institute, 2005).
Meadow species have found important refuges in regularly
mown verges (Jantunen et al., 2006) but lupine represents a
potential threat for generally low growing plants adapted to
nutrient-poor conditions. Construction work required on road
verges every 20–30 years (Mahosenaho and Pirinen, 1999)
disturbs vegetation and provides suitable areas for invasive
species. Lupines fix nitrogen and their litter fertilizes the
nutrient poor soil (Davis, 1991) which can alter competitive
interactions by enabling colonization by, and the rapid growth
of, tall species that shade and hinder low growing species and
thus reduce plant species richness (Hobbs and Huenneke,
1992; Maron and Connors, 1996; Gosling, 2005). The height
of lupine varies between 50 and 120 cm (Mossberg and Sten-
berg, 2005) and thus a dense lupine canopy can block the light
effectively from other species. Based on other Lupinus species
it is also possible that the lupine alkaloids hinder the germi-
nation of other plant species (Muzquiz et al., 2004). The plant
species on road verges, in turn, provide resources for a wide
variety of insects (Free et al., 1975; Munguira and Thomas,
1992; Eversham and Telfer, 1994; Saarinen et al., 2005). Thus,
changes in the plant communities are likely to have effects
on higher trophic levels (Knops et al., 1999). Globally, invasive
plant species pose a threat to the existence of some rare
butterfly and other insect species (Braby and Douglas, 2004;
Samways and Taylor, 2004), but may also offer resources for
native species in the form of host-plants or nectar (Graves
and Shapiro, 2003).
The objective of this study was to determine the potential
threat of lupine on plant and diurnal Lepidoptera communi-
ties on road verges. We compared the plant and Lepidoptera
species richness, cover, abundance, diversity and assem-
blages between road verges already invaded by lupine and
adjacent non-invaded verges. Plant, butterfly and diurnal
moth species were divided into ecological groups to test
whether meadow species and low growing plant species are
particularly vulnerable to lupine invasion. Furthermore, we
compared the vegetation characteristics important to the
Lepidoptera (i.e. vegetation height providing shelter for diur-
nal moths and nectar availability, mainly used by butterflies)
between the two groups. Finally, we studied the impact of the
lupine on butterfly and diurnal moth individuals by compar-
ing their behavior in lupine and non-lupine verges.
2. Materials and methods
2.1. Vegetation study
We studied effects of lupine on flora on 15 road verge sites in
SE Finland (Fig. 1). In each site, half of the area represented lu-
pine invaded verges, while the rest represented a non-lupine
verge with either no lupines or only sporadic stands. The two
parts were located adjacently on the same side of the road
and it was assumed that the lupine stands were random col-
onizations. On each site we established ten 1 m ·1 m quad-
rats, five on the lupine verge and five on the non-lupine
verge. The quadrats were placed symmetrically in the two
parts. The distance from quadrats to the pavement edge ran-
ged between 1 and 3 m, depending on the verge width, and
the distance between quadrats ranged between 3 and 20 m,
depending on the length of the study area. We surveyed the
plant species composition between 18 and 27 July 2005, before
the verges were mown. We estimated the abundance of plant
species in each quadrat with projection cover (percentage
scale 0–100%) and measured the average vegetation height.
In data analyses, we used average number and coverage of
species of the five quadrats in each site. Additionally, we
determined the total plant species richness in the five quad-
rats. Five species groups were analysed separately: positive
indicators of semi-natural grasslands (‘‘meadow species’’)
and negative indicators of semi-natural grasslands (‘‘weed
species’’) (mainly following Pyka
¨la
¨, 2001), low growing species
(average height <20 cm), medium height species (20–50 cm)
and tall species (>50 cm).
2.2. Lepidoptera study
We studied butterflies (Hesperioidea, Papilionoidea) and other
day-active Lepidoptera (Zygaenoidea, Lasiocampoidea, Bomb-
ycoidea, Geometroidea, Noctuoidea) on 15 road verge tran-
sects, ten of which coincided with the vegetation study sites
(Fig. 1). This was due to different criteria: the transects had to
be in sunshine at midday in order to conduct the Lepidoptera
Fig. 1 – Location of vegetation study sites and Lepidoptera
transects in SE Finland.
390 BIOLOGICAL CONSERVATION 133 (2006) 389–396
counts, whereas the vegetation study sites could not be located
on road verges mown before 27 July 2005. Transects varied be-
tween 100 and 560 m in length (average 265 m). In each tran-
sect, the first half represented lupine invaded verge (average
cover of L. polyphyllus 86%) and the second half represented
non-invaded verge (average cover 4%). In 2005, we censused
14 transects weekly between late May (week 22) and late Au-
gust (week 35); one transect was censused during weeks 23–
35. At each site we walked through the transects and counted
all individuals within a 5 m ·5 msquare in front of the recorder
(Pollard and Yates, 1993). We also recorded the behavior (flying,
nectaring, basking, hiding) of each individual at first sight. All
behavior related to lupine was recorded separately.
We minimised the differences in censusing time, temper-
ature, wind speed and sunshine between the two parts of
each transect by counting the parts sequentially in varying or-
der. Starting times ranged between 9:50 and 16:15; all cen-
suses were carried out in good weather conditions, the
temperatures being P14 C, the median wind speed on the
Beaufort scale being 3 (gentle breeze), and the median sun-
shine percentage (estimated as 0%, 25%, 50%, 75% and 100%)
being 100%. Due to the adjacent location of the respective lu-
pine and non-lupine verges, the verge and road width, time
since the last soil disturbance, mowing regime, and surround-
ing environment were similar in the transect pairs. Vegeta-
tion height and nectar abundance on the study transects
were estimated once a month in June, July and August. Vege-
tation height was measured from the middle of the transect
and the average of three months was used in the statistical
analyses. Correspondingly, nectar abundance was estimated
once a month on an ordinal scale (1 = low, only few sporadic
nectar plant stands; 2 = moderate, sporadic stands through-
out the transect and 3 = high, nectar flowers abundant
throughout the transect) and the median of the three months
was used in the analyses. In addition, the nectar species rich-
ness was calculated as total number of plant species in flower
(except graminoids) recorded in three monthly evaluations.
In the data analyses, we compared the species richness
(total number of species observed) and abundance (sum of
individuals of all censuses) of butterflies and diurnal moths
separately between the lupine and non-lupine transects.
Summing up the weekly censuses captured the range of sea-
sonal activity in the Lepidoptera. Additionally, we divided the
butterflies into species typical of meadows (‘‘meadow spe-
cies’’), forest edges and clearings (‘‘forest edge species’’), and
fields, farmyards and wasteland (‘‘field margin species’’),
according to the classification by Pitka
¨nen et al. (2001). One
unclassified species Cupido argiades was included in the field
group of butterflies. Correspondingly, we separated the diur-
nal moths into meadow species and other species according
to Kuussaari et al. (2003). Four unclassified species Siona line-
ata,Thetidia smaragdaria,Cerapteryx graminis and Eriopygodes
imbecilla were included in the meadow group based on the pri-
mary habitats and host plants of their larvae.
2.3. Data analyses
We compared the paired samples of plant, Lepidoptera, vege-
tation height and nectar variables of the lupine verge and
non-lupine verge of each site with a non-parametric Sign test.
The Shannon’s diversity index of plant, butterfly and diurnal
moth communities calculated by Pc-Ord 4.0 (McCune and
Mefford, 1999) were accordingly compared. We calculated a
sequential Bonferroni correction for all test sets to lower the
risk of significant differences by chance, and used an error
rate of 0.10, as suggested by Chandler (1995). We also calcu-
lated a ratio of species richness and abundance of Lepidop-
tera in lupine vs. non-lupine verges and used it when
comparing how similar the adjacent lupine and non-lupine
verges were. The association between the ratio and the aver-
age cover of lupine in lupine verges was tested with Spearman
rank correlation. Sign tests and Spearman correlations were
performed by the program SPSS 12.0 for Windows.
Changes in composition of the plant species between the
lupine and non-lupine parts were compared by non-metric
multidimensional scaling (NMS), using Sørensen (Bray Curtis)
distance measure and the slow, through autopilot settings of
Pc-Ord 4.0 (McCune and Mefford, 1999). We further tested the
differences in the species assemblages of plants, butterflies
and diurnal moths in the lupine and non-lupine verges with
a non-parametric multi-response permutation procedure
(MRPP) using a Euclidean distance measure (Zimmerman
et al., 1985). Plant or Lepidoptera species preferring either lu-
pine or non-lupine verges were determined with an indicator
species analysis using the Monte Carlo test of significance
with 1000 runs (Dufrene and Legendre, 1997). Both MRPP
and indicator species analysis were performed using Pc-Ord
4.0 (McCune and Mefford, 1999).
3. Results
3.1. Effect of lupine on plant species
The vegetation was 39 cm taller, on average, and lupine cover
markedly higher, in lupine verges, while the cover of other
plant species was higher in non-lupine verges (Table 1). In lu-
pine verges the cover of L. polyphyllus ranged between 56%
and 78%, while only some lupines appeared in non-lupine
quadrats (cover range between 0 and 7%). A total of 139 plant
species were recorded in 15 sites (Supplementary data A).
Along with lupine, the plant species included 32 meadow spe-
cies, 23 weed species and 17 herbaceous forest species, the
rest being tree species (10) and various species of open envi-
ronments (56). The total species richness, the number of spe-
cies per quadrat (m
2
) and the species diversity were higher in
non-lupine verges (Tab le 1).
The cover of meadow species, weed species, low growing
and medium height species was significantly lower in lupine
compared to non-lupine verges, but no significant differences
emerged in tall growing species (Table 1). Furthermore, the
species richness of low growing species was significantly
lower in lupine verges, whereas the difference in meadow
species, weed species, medium height and tall growing spe-
cies was not significant.
Non-metric multidimensional scaling identified a two-
dimensional solution for the vegetation data (final
stress = 18.96; instability = 0.00001). The lupine verges were
tightly clustered, whereas the non-lupine verges were scat-
tered over the ordination space (Fig. 2). MRPP indicated a sig-
nificant difference between the lupine and non-lupine verges
BIOLOGICAL CONSERVATION 133 (2006) 389–396 391
(T=19.6, p< 0.0005). According to the indicator species
analysis, one species was indicative of lupine verges (L. poly-
phyllus,p= 0.001), while five species were indicative of the
non-lupine verges (Trifolium pratense,p= 0.001; Trifolium re-
pens,p= 0.003; Leontodon autumnalis,p= 0.009; Fragaria vesca,
p= 0.012; Vicia sepium,p= 0.030).
3.2. Effect of lupine on lepidoptera
We recorded a total of 93 Lepidoptera species and 2344 indi-
viduals along the transects: 45 (48%) species and 1512 (65%)
individuals of butterflies and 48 (52%) species and 832 (35%)
individuals of diurnal moths (Supplementary data B). The
majority of diurnal moths were geometrid moths (21 spe-
cies/472 individuals) and noctuid moths (16/324).
We found no differences in the species richness or diver-
sity of Lepidoptera between the lupine and non-lupine verges
(Tab le 2 ). However, the abundance of all individuals and but-
terfly individuals was significantly higher in non-lupine
verges compared to lupine verges. There was a mid-summer
peak of abundance both in butterflies and diurnal moths. In
non-lupine verges, the abundance of butterflies was higher
throughout the summer, whereas diurnal mothswere slightly
less abundant during the peak flight period (weeks 25–27) and
more abundant during the latter half of the study period.
There was a tendency towards higher nectar abundance in
non-lupine verges. No differences were found in diurnal moth
numbers between lupine and non-lupine verges, yet the veg-
etation was significantly higher in lupine verges.
The cover of L. polyphyllus on lupine verges was inversely
associated with the ratio of butterfly individuals in lupine
vs. non-lupine verges (Spearman rank correlation;
r
S
=0.520, p= 0.046), i.e. the higher the cover of lupine the
lower the amount of butterfly individuals found on the lupine
verges compared to the adjacent non-lupine verges. No asso-
ciation was found between the lupine cover and ratios in but-
terfly species richness (r
S
=0.190, p= 0.499) or abundance
(r
S
=0.038, p= 0.893) and species richness (r
S
=0.267,
p= 0.337) of diurnal moths.
According to the primary habitat groups of butterflies, 61%
of all recorded individuals represented meadow species, 30%
were forest edge species, and 9% belonged to field margin
species. Correspondingly, 85% of all diurnal moth individuals
belonged to species typical to meadows. Species richness in
meadow butterflies and the abundance of both meadow but-
terflies and diurnal moths were higher in the non-lupine
verges compared to the lupine verges, but the differences
were not significant after the Bonferroni correction (Table 2).
There was little difference in the proportions of the three
primary habitat groups of butterflies between the lupine
(62% meadow/27% forest edge/11% field) and non-lupine
(59%/32%/9%) verges. Correspondingly, the proportions of
meadow diurnal moths were almost the same in the lupine
(83%) and non-lupine verges (86%). The MRPP analysis indi-
cated a non-significant difference in species assemblages be-
tween the two groups for both butterflies (T= 0.358, p= 0.508)
and diurnal moths (T=0.514, p= 0.241). The only species
with a significant indicator value was the burnet moth Zyga-
ena viciae (p= 0.024), which was observed only in the non-
lupine transects.
Butterfly behavior was similar in lupine and non-lupine
verges and included flying (62% of individuals in lupine
verges/65% of individuals in non-lupine verges), nectaring
Fig. 2 – NMS ordination of the vegetation data showing
sample scores of the two axes. The lupine and non-lupine
verges of each study site are connected with a line. The
species scores of Lupinus polyphyllus and 19 other species
positively or negatively affected by lupine are overlayed. The
names of species are abbreviated to the first four letters (see
full names in Supplementary data A).
Table 1 – Differences in vegetation between the lupine
and non-lupine verges; mean, standard deviation (SD)
and significance of Sign test are reported
Lupine Non-lupine Sign test
Mean SD Mean SD p
Vegetation height (cm) 77.9 16.3 38.7 14.2 <0.0005
*
Total species richness 26.9 6.1 34.7 11.0 0.006
*
Species/m
2
11.7 2.6 15.4 3.9 0.001
*
Shannon’s diversity index 1.5 0.2 2.6 0.4 <0.0005
*
Cover of lupine (%) 69.1 7.7 1.4 1.9 <0.0005
*
Cover of other species (%) 38.1 9.2 97.3 11.2 <0.0005
*
Meadow species
Total species richness 4.7 2.5 5.8 3.2 0.180
Cover 2.1 1.9 12.7 12.1 0.001
*
Weed species
Total species richness 5.2 3.2 6.0 3.4 0.549
Cover 7.7 7.3 19.2 19.1 0.002
*
Low growing species
Total species richness 7.1 2.7 12.1 5.0 <0.0005
*
Cover 12.6 5.2 35.6 13.5 <0.0005
*
Medium height species
Total species richness 10.4 3.1 11.7 4.2 0.180
Cover 10.6 3.9 32.6 15.7 <0.0005
*
Tall species
Total species richness 7.6 3.2 8.7 3.3 0.423
Cover 14.4 7.7 26.9 20.7 0.118
* Difference is significant after Bonferroni correction.
392 BIOLOGICAL CONSERVATION 133 (2006) 389–396
(21%/20%), and basking (17%/15%). No egg laying was ob-
served. The higher the cover of lupine in lupine verges the lar-
ger the proportion of individuals flying (Spearman rank
correlation, r
S
= 0.518, p= 0.048) and the smaller the propor-
tion of nectaring individuals (r
S
=0.690, p= 0.004) (Fig. 3).
In only one case (which was a lupine verge) the proportion
of individuals nectaring was higher than the proportion of
individuals in flight. In the non-lupine verges the proportion
of individuals in flight ranged between 47% and 84% and the
proportion of individuals nectaring ranged between 0% and
37%. Eight butterfly individuals of the species Gonepteryx
rhamni,Callophrys rubi,Nymphalis io,Polyommatus icarus and
Aporia crataegi were observed visiting the flowers of lupine
once or more. Butterfly visits to lupine flowers represented
6% of all flower visits on lupine verges (n= 129) recorded dur-
ing the study and individuals basking on lupine represented
5% of all basking butterfly individuals on lupine verges
(n= 103) during the study.
Diurnal moth behavior included hiding in the vegetation
(83% of individuals in lupine verges/86% of individuals in
Table 2 – Differences in Lepidoptera numbers and vegetation characteristics important to Lepidoptera; the total, average
(with standard deviation SD), or frequency is given and the significance of Sign test is reported
Lupine Non-lupine Sign test p
Species richness (total) 75 76 0.581
Butterfly species richness (total) 35 42 0.424
Diurnal moth species richness (total) 40 34 0.607
Abundance (total) 1009 1335 0.007
*
Butterfly abundance (total) 613 899 0.007
*
Diurnal moth abundance (total) 396 436 0.057
Shannon’s diversity index
Butterflies (average ± SD) 1.9 ± 0.5 2.0 ± 0.5 1.000
Diurnal moths (average ± SD) 1.6 ± 0.5 1.7 ± 0.3 0.607
Meadow species richness
Butterflies (total) 14 17 0.035
Diurnal moths (total) 19 14 0.774
Meadow species abundance
Butterflies (total) 383 532 0.013
Diurnal moths (total) 347 389 0.035
Vegetation height, cm (average ± SD) 55.0 ± 17.5 36.0 ± 15.2 <0.0005
*
Nectar abundance (1/2/3) (frequency) 6/8/1 2/9/4 0.016
Species richness of nectar plants (total) 73 79 0.118
* Difference is significant after Bonferroni correction.
Fig. 3 – The percentage of individuals flying or nectaring corresponding to the lupine cover of the lupine transects.
BIOLOGICAL CONSERVATION 133 (2006) 389–396 393
non-lupine verges), flying (13%/10%), nectaring (2%/2%), and
basking (2%/2%). One individual of Euclidia glyphica was ob-
served visiting the flowers of lupine, which represented 14%
of all flower visits (n= 7) of diurnal moths on lupine verges.
4. Discussions and conclusions
4.1. Lupine decreases the plant species richness
The invasion of lupine decreased the available area and cover
of other plant species, which also lowered the plant species
richness and diversity. In lupine verges, the total species rich-
ness was almost eight species less than in the non-invaded
verges, on average. Although the invasion of nitrogen-fixing
plants may increase the originally low species richness on
barren soils by encouraging further invasive species to settle
(Vitousek and Walker, 1989), we found no such effect. The
cover of other non-indigenous species was very low, including
only Artemisia campestris and Melilotus albus (present on one
non-lupine site).
The higher vegetation on lupine verges suggests that the
lupine has filled the unused space above the original verge
vegetation and the low growing species have been outcom-
peted due to the shading. Since low growing species de-
creased in both species richness and cover and medium
height species only in cover, whereas tall species were not sig-
nificantly affected, shading rather than other characteristics
was the most likely cause of the decline. Yet, the majority
of the meadow species (56%) recorded in the sites were low
growing, a typical adaptation to regular mowing or grazing
(Grime, 2001). Weed species included a smaller proportion of
low growing species (27%), but in both groups the cover was
smaller in lupine verges. Three of the five indicator species
of non-lupine verges were low growing (F. vesca, L. autumnalis
and T. repens), the other two being of medium height. In addi-
tion, according to the indicator species analysis and the NMS
ordination, low and medium height nitrogen fixing plants
(T. pratense,T. repens,T. hybridum and V. sepium) were particu-
larly decreased by the lupine.
By contrast, tall growing species such as Phleum pratense,
Angelica sylvestris and Alopecurus pratensis, located close to lu-
pine verges in the NMS ordination, can compete more effi-
ciently with lupine for light. Half of the weed species (50%)
were tall growing and many of the recorded weed species
are likely to benefit from the nitrogen enhancement by lupine
(Ellenberg et al., 1991). Lupinus species are commonly used in
land reclamation processes, but the problem has been their
vigorous growth and the effects of nitrogen transferred to
other fast growing species, which often become dominant
(Bradshaw, 2000).
4.2. Lupine decreases the lepidoptera abundance
Lupine did not provide food resources for Lepidoptera. By con-
trast, it decreased the cover and species richness of potential
host plants for larvae and nectar plants for adults. The de-
creased quantity and quality of resources both adversely af-
fect the butterflies (Summerville and Crist, 2001). We
recorded, on average, 22 Lepidoptera individuals (19 butterfly
individuals) less in lupine transects compared to the adjacent
non-lupine transects. As this pattern remained throughout
the summer, individuals in flight during different times of
the summer and different phases of the lupine growth, from
vegetative growth in early summer to flowering in mid sum-
mer and withering in late summer, were all adversely
affected.
In congruence with Knops et al. (1999), our results reveal
how the loss of biodiversity in basal species (plants) in grass-
land ecosystems can impact the insect communities. For but-
terflies invasions of non-native species have been found to be
alternatively insignificant (Fleishman et al., 2005), positive if
the species have been able to switch their hosts or use the
invasive species as nectar sources (Graves and Shapiro,
2003), or negative if females oviposit on introduced plants
but the larvae are unable to complete development on the
new host plants (Schlaepfer et al., 2005). We found no evi-
dence of Lepidoptera using lupine as a host plant. Instead,
as the cover of lupine approached 100%, fewer individuals ap-
peared to be interested in the vegetation and were merely fly-
ing. On the other hand, no egg laying was observed on any
plant species growing on road verges, probably due to the
short observation period of each individual.
The butterflies actively used the nectar resources on road
verges. Nectar is an important resource for butterflies by
increasing both longevity and fecundity (Murphy et al.,
1983). In lupine invaded verges the butterflies found nectar
from plants growing in the gaps within the lupine stands,
explaining why the nectaring decreased as the cover of lupine
approached 100%. The discrepancy between the high cover of
lupine and the few visitors to lupine flowers on lupine verges
suggests that the lupine is a poor nectar plant or does not
serve nectar, and the few butterfly and moth visits to its flow-
ers were abortive attempts at obtaining nectar.
Nectar has a marked influence on the microdistribution of
butterflies in their habitats (Loertscher et al., 1995), but no
such effect on diurnal moths was found. Many of these spe-
cies do not visit flowers as adults, yet the only Lepidoptera
indicator of non-lupine sites, the burnet moth Z. viciae, visits
flowers actively. The recorded diurnal moths form a contin-
uum of species flying solely during the day to species, which
fly mostly as a result of being disturbed and are more active at
night. Therefore tall lupine stands provided hiding places for
the less active diurnal moths during the day. The lupine can-
opy grows tall in the early summer and provides more hiding
places compared to the adjacent lower vegetation. The rapid
withering of lupine explains the decline of diurnal moths on
lupine verges in the late summer.
4.3. How to control the spread of lupine?
Although the lupine may have positive effects on a limited
range of species, e.g. bumblebees and other insects collecting
lupine pollen, its uncontrolled spread possess a real threat to
meadow plant and Lepidoptera species living on road verge
environments. These species were common on semi-natural
grasslands until the modernization of agriculture during the
20th century.As only fragments of semi-natural grasslands still
remain, many of their species are more often found on alterna-
tive habitats, in particular road verges under regular manage-
ment (Jonsell, 2004; Jantunen et al., 2006). Several studies
394 BIOLOGICAL CONSERVATION 133 (2006) 389–396
have addressed the possibility of improving the management
of road verges to increase their suitability for the species of
semi-natural grasslands (Persson, 1995; Schaffers, 2000), but
to our knowledge studies concerning the management of road
verges invaded by non-indigenous plant species are lacking.
To constrain the impact of non-indigenous species, eradi-
cation, or if this is not possible, maintenance control of spe-
cies at acceptable levels, should be organised (Mack et al.,
2000). In New Zealand several plant pathogens which could
serve as biological control agents for the invasive L. polyphyllus
have been identified (Harvey et al., 1996). Mechanical and
manual removal techniques coupled with the removal of litter
and duff have been successful in the control of another inva-
sive species, Lupinus arboreus, but even when the population
of the invasive species has been successfully controlled the
fertilised soil may lead to changes in the plant species assem-
blages (Pickart et al., 1998a,b; Maron and Jefferies, 2001).
In unproductive environments, such as on road verges, an
increase in disturbance and reduction in productivity are
likely to be the best management plan for the control of inva-
sive species (Huston, 2004). We thus suggest that for as long
as studies on the control of L. polyphyllus are lacking, the con-
trol should be based on two mowings in mid and late summer
to prevent the re-flowering, with removal of the cuttings, on a
regular basis. In our study sites the lupine was often missing
in the proximity of the road under more frequent mowing
than the rest of the verge. This indicates that the species is
not well adapted to mowing, losing a large part of its biomass
during mowing and eventually withering away. Regular mow-
ing also prevents other tall species, including many weeds,
possibly invading in the wake of lupine. Unfortunately, the
intensive mowing is harmful to butterflies (Erhardt, 1985),
but these will benefit in the long run via more diverse vegeta-
tion. Eradicating the lupine by mowing may take several
years, but this is not a problem on road verges, which are
mown in any case to ensure traffic safety. In addition, manual
eradication on or close to sites where rare or endangered spe-
cies occur may be needed. The removal of cuttings, on the
other hand, can prevent the fertilising effect of lupine on
the soil. Finally, as the lupine has imposing flowers, it is pos-
sible that some people deliberately spread lupine seeds for
decorational purposes along road verges. Thus, greater public
awareness of the effects of lupine and other invasive species
is needed.
Acknowledgements
This study was financially supported by the Finnish Road
Administration, Finland’s Ministry of the Environment, Maj
and Tor Nessling Foundation and The Finnish Cultural Foun-
dation’s South Karelia Regional Fund. We also thank Leigh
Plester for the English revision and Heikki Roininen, Sanna
Saarnio, Mikko Kuussaari, Juha Po
¨yry and the anonymous ref-
erees for providing valuable comments and suggestions.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at doi:10.1016/j.biocon.2006.06.015.
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