original research article
PERIODICUM BIOLOGORUM	 UDC 57:61
VOL. 119, No 4, 239–249, 2017	 CODEN PDBIAD
DOI: 10.18054/pb.v119i4.4917	 ISSN 0031-5362
Distribution of alien species along sand dune plant
communities zonation
Abstract
Background and purpose: For a fairly long period, Velika plaža in
Ulcinj, Montenegro has been considered to be one of the best-preserved sites
with psammophilous vegetation along the Adriatic coast. In recent years,
however, this area has been significantly transformed as a result of various
human disturbances (e.g., a non-sustainable approach to touristic development,
illegal dumping, sand exploitation etc.), and has become prone to alien
plant invasions. We made a transect survey to assess the presence of alien
species in the psammophilous communities.
Materials and methods: In order to make a survey of the present state
of plant life on Velika plaža, its floristic composition and zonation of plant
communities, 20 transects were set perpendicular to the coast, regularly
every 500 m. Quadrats (2 x 2 m) were laid contiguously in the form of a
belt transect starting from the area with the first colonizing plants towards
the end of the sand dune system with forest vegetation. This resulted in a
matrix of 1124 plots and 196 species (15 alien and 181 native), on which
multivariate analysis was performed.
Results: Nine plant communities were detected, arranged in zonation
from sea to inland. All of them were characterised by the presence of alien
species. The least affected was the plant community dominated by Cladium
mariscus, while the most affected ones were dominated by Scirpoides holoschoenus
and Tripidium ravennae. Psammophilous vegetation is less
affected by alien species than wetland communities. Foredunes are dominated
by Xanthium orientale ssp. italicum, while Oenothera species are
predominant on stable dunes.
Conclusions: Sand dunes are a highly invaded ecosystem, with changed
plant communities, so conservation measures should be considered.
INTRODUCTION
Sand dunes are dynamic ecosystems located at the border between the
sea and the mainland (1). Such specific and highly dynamic environments,
governed by three interacting factors: waves, tides and sand particle
size, are inhabited by a biota with a high degree of specialization
(2, 3). Although psammophilous vegetation is known to be highly resistant
to natural disturbances, it has been shown to be very sensitive to
human–mediated disturbances, such as recreational seashore activities,
beach cleaning, nourishment and restoration, pollution, exploitation for
fisheries, biological invasions, coastal development and engineering,
mining and climate change (4-9).
DANIJELA STEŠEVIĆ1
MILICA LUKOVIĆ2
DANKA CAKOVIĆ3
NEMANJA RUŽIĆ4
NADA BUBANJA5
URBAN ŠILC6,7
1 
University of Montenegro, Faculty of Natural
Sciences and Mathematics, Biology department,
Džordža Vašingtona bb, 81 000 Podgorica,
Montenegro (danijela.stesevic@ac.me)
2
University of Kragujevac, Faculty of Hotel
Management and Tourism, Department of Natural
Science, Vojvodjanska bb, 36210 Vrnjačka Banja,
Serbia (mpetrovic.azs@gmail.com)
3 
University of Montenegro, Faculty of Natural
Sciences and Mathematics, Biology department,
Džordža Vašingtona bb, 81 000 Podgorica,
Montenegro (danka.petrovic@t-com.me)
4 
University of Montenegro, Faculty of Natural
Sciences and Mathematics, Biology department,
Džordža Vašingtona bb, 81 000 Podgorica,
Montenegro (nemanja.sharpe@gmail.com)
5
Natural History Museum of Montenegro, Trg vojvode
Bećir-bega Osmanagića 16, 81 000 Podgorica,
Montenegro (nadabubanja@t-com.me)
6 
ZRC SAZU (Research Centre of the Slovenian
Academy of Sciences and Arts), Institute of Biology,
Novi trg 2, 1000 Ljubljana,
Slovenia (urban@zrc-sazu.si)
7
BC Naklo, Strahinj 99, 4202 Naklo, Slovenia
Correspondence:
Urban Šilc
E-mail: urban@zrc-sazu.si
Key words: Psammophyte; retrodunal depressions;
vegetation; invasive species; Velika plaža; Montenegro
Received January 22, 2017.
Revised November 28, 2017.
Accepted December 28, 2017.
Danijela Stešević et al.	 Alien species in sand dune plant communities
240	 Period biol, Vol 119, No 4, 2017.
In relation to Velika plaža, illegal dumping, nonplanned
sand exploitation, urbanization and non-sustainable
tourist development are recognized as serious threats
to sand dune ecosystems (33). Because research of alien
species has not been systematically done in the area, invasive
alien species have not been listed as a threat.
We wanted to answer the following questions:
– Which alien plant species occur on the sand dunes
of Velika plaža?
– Which plant communities/habitats are more frequently
invaded?
METHODS
Study area
The study was performed on coastal sand dunes on
Velika plaža in Ulcinj (Montenegro). With a length of 12
km, this sandy beach is considered to be the longest on
the eastern Adriatic coast. Together with its hinterland, it
covers an area of 1,270 ha. According to the KöppenGeiger
system, the climate is classified as Csa type - Mediterranean
climate with hot summers (34). Psammophilous
vegetation forms two distinct belts: the one closer to
the sea is represented by four xerohalophilous plant communities,
and the second belt, which is not directly influenced
by seawater, comprises xeropsammophilous communities
of Mediterranean pastures and dry meadows (for
details see Šilc, et al. (35)). The site is very valuable from
a nature conservation point of view because the following
NATURA 2000 habitats are present: 1210 Annual vegetation
of drift lines, 1410 Mediterranean salt meadows
(Juncetalia maritimi), 2110 Embryonic shifting dunes,
2120 Shifting dunes along the shoreline with Ammophila
arenaria (white dunes), 2190 Humid dune slacks, 2220
Dunes with Euphorbia terracina, 2240 Brachypodietalia
dune grasslands with annuals, 2270* Wooded dunes with
Pinus pinea and/or Pinus pinaster, 3170* Mediterranean
temporary ponds, and 92A0 Salix alba and Populus alba
galleries (36). Under national legislation, the site was already
legally protected as a natural object in 1968 (37), in
2007 as a natural monument (38), while the installation
of fences in 2014 provided an additional conservation
measure (39). Montenegro is currently in progress of inventorying
Natura 2000 sites, but no management plans
have so far been adopted.
Vegetation sampling
To analyse the floristic composition, particularly the
presence of alien species and the zonation of plant communities,
20 transects were set perpendicular to the coast,
exactly 500 m distant from each other. Contiguous quadrats
(2 x 2 m) were laid out next to each other to form a
belt transect (40) starting from the area, with the first
colonizing plants, towards the end of the sand dune sysInvasive
alien species cause various problems for the
invaded natural ecosystems. Together with habitat fragmentation,
they are considered a major threat to native
biodiversity (10). They change native plant communities
and have a strong ecological impact on resident species,
although the impact is heterogeneous and not unidirectional
(11). The broadly accepted connection between invasive
species and native diversity decline has recently been
debated. The native species richness of dune vegetation, as
well as shrublands and abandoned fields, shows a significant
decline, in contrast to an insignificant decline for forest
habitats (12). In addition to a reduction of local plant
diversity, invasive species increase plant production of the
invaded community. Some invaders, such as Carpobrotus
edulis, affect the community composition, diversity and
succession via modification of the soil properties. It has
been shown that the effect of C. edulis on pH and nitrogen
compounds persists over time even after Carpobrotus removal
(13, 14). This suggests a possible allelopathic effect
of its litter (14). Clonal growth has recently been indicated
as an attribute that could contribute to the invasiveness of
plants (15, 16). In addition to alterations in native species
abundance (17), and a reduction of fitness and growth of
resident plant species (18), alien species can sometimes even
outcompete native species (19). The impact can further be
observed on mesofauna and ground beetle communities
(20), with a significant decrease in animal species fitness
and abundance, as well as on microbial activity (18). The
susceptibility of a plant community to invasion depends
on the characteristics of the community and the life history
traits of the potential invasive species (21).
Sand dunes are extreme ecosystems, with very strong
gradients, which are responsible for the zonation of vegetation
types. This fact, and constant disturbances (natural
and anthropogenic), make sand dunes a good object
for the study of alien invasion and a rich body of literature
has recently become available (22-28). Sand dunes are one
of the most invaded habitats (29) but different habitats
along a steep gradient are invaded differently (30).
Although the coastal dunes on Velika plaža in Ulcinj
are frequently cited as one of the best preserved psammophilous
ecosystems in the eastern Adriatic (31, 32),
various anthropogenic disturbances have started significantly
to transform the natural potential vegetation. According
to spatio-temporal analysis of the major habitat
types in the area, the anthropogenic impact has been increasing
since 1950. In the 1950s, neither the pine forests
now typical of the western part of the beach nor the asphalt
road that connects Montenegro and Albania were present,
while there were only a few houses in Štoj village. In the
1970s, construction of the road started, the pine forest was
planted, and Štoj settlement started to develop. In 2015,
the situation was significantly different, while urbanization
expanded. According to official statistics, Velika plaža in
Ulcinj is one of the most popular tourist destinations in
Montenegro, and interest is constantly growing.
Alien species in sand dune plant communities	 Danijela Stešević et al.
Period biol, Vol 119, No 4, 2017.	 241
tem, with forest vegetation. We also analysed plant communities
of interdunal depressions and humid slacks,
which are often overlooked in similar studies. For the
longest transects, which had large homogeneous areas of
singular plant communities, the quadrats were placed 20
m apart from each other along the transect (and not contiguously).
In each quadrat, the cover of plant species was
visually estimated on the Braun-Blanquet scale (41). Since
transects were performed in the late spring and early summer
of 2015, when Erigeron canadensis L., E. sumatrensis
Retz. and Oenothera species are just starting to germinate,
it was not possible to identify this species. Identification
was therefore left at the genus level. For the area, the following
Oenothera taxa were reported: O. × fallax Renner,
O. glazioviana Micheli, O. biennis L., and O. suaveolens
Pers. ((42-44) and own field observations).
Data analysis
All gathered plots were entered into the TURBOVEG
database (45). The result was a matrix of 1124 plots (876
with species present) and 196 species on which multivariate
analyses were performed. Classification (Ward
method and Euclidean distance) was made in PC-ORD
(46), using Braun-Blanquet cover values after changing
them into percentages and square-root transformation.
Clusters were identified by their diagnostic species using
the JUICE program (47). Diagnostic species were determined
using the phi-coefficient as a fidelity measure (48).
The size of all groups was standardized to equal size and
Fisher’s exact test (p<0.1) was applied.
The cumulative species pool was calculated as the total
number of species, native and alien, in a particular plant
Figure 1. Location of the studied Velika plaža (Montenegro).
Danijela Stešević et al.	 Alien species in sand dune plant communities
242	 Period biol, Vol 119, No 4, 2017.
community. The level of invasion was set as the proportion
of alien species in the community compared to its
cumulative species pool (24, 49).
We consider a plot ‘invaded’ if it contains at least one
alien species. The effect of the factor community on the
frequency of invasion (defined as the number of plots invaded
in each community) was evaluated through a chisquare
test by contingency table (50).
Since sand dunes are very extreme habitats, plant species
cover is a better indicator of environmental conditions,
so we analysed changes of cover of alien species
between plant communities in the coastal zonation (23).
For each plot, we calculated total alien and native species
cover (transformed from the Braun-Blanquet scale) in
JUICE (47). To test differences of alien cover between
plant communities, we used one-way analysis of variance
(ANOVA). The Bonferroni post-hoc test was used when
differences were statistically significant.
All univariate statistics were performed using the statistical
package SPSS (51).
Nomenclature
The nomenclature of species follows the Euro+Med list
(52), while the nomenclature of the genus Oenothera follows
Rostański (53), and for Cuscuta and Carpobrotus
species the Plant List was used (54). The invasive status of
alien species in Montenegro was determined according to
Stešević & Petrović (42, 43). In this paper, we used only
neophytes as alien species, defined as species with arrival/
first occurrence after the year 1500 (55).
RESULTS
The classification of vegetation plots revealed nine
plant communities, which we could further classify into
six dune habitats according to the Habitats Directive
Table 1. Frequency of alien plant species (neophytes) in sand dune plant communities on Velika plaža (Montenegro). Different grey colours indicate
three classes of alien taxa frequency in the plots: light grey (0-24%), dark grey (25-49%), black (50-100%). Sign + indicates the presence
of alien species outside the surveyed transects.
Annual
vegetation of
a drift line
Embryonic
shifting
dunes
Shifting
dunes along
the shoreline
with
Ammophila
arenaria
Fixed coastal
dunes with
herbaceous
vegetation
Humid dune
slack
Mediterranean
salt
meadows
(Juncetalia
maritimae)
1210 2110 2120 2130* 2190 1410
Cakilo-
Xanthietum
strumarii
Cynodon
dactylon
community
Euphorbio
paraliae-
Agropyretum
junceiformis
Medicagini
marinae-
Ammophiletum
australis
Onobrychis
caput-galli
community
Schoeno-
Erianthetum
ravennae
Holoschoenetum
romani
Cladietum
marisci
Juncetum
maritimo-
acuti
Road
verges
Amorpha fruticosa 1 1 12 20 36 53
Bidens frondosus 3 30 12
Capsicum annuum 1
Carpobrotus edulis 1
Conyza spp. (C. canadensis,
C.albida)
25 2 20 23 7
Cuscuta caestiana 3
Erigeron annuus 1
Euphorbia maculata 8 17 4
Oenothera spp. (O. fallax,
O. glazoviana, O. biennis,
O. suaveolens)
1 29 35 59 66 79 27 14
Paspalum paspalodes 2 3
Paspalum dilatatum 2 3
Xanthium orientale ssp.
italicum
72 65 24 41 3 5 67 10
Amaranthus chlorostachys +
Amaranthus retroflexus +
Aster squamatus + +
Cenchrus spinifex + +
Datura inoxia +
Physalis angulata +
Robinia pseudacacia + +
Sporobolus indicus + +
Tagetes minuta +
Alien species in sand dune plant communities	 Danijela Stešević et al.
Period biol, Vol 119, No 4, 2017.	 243
(Table 1). We use phytocoenological syntaxa for the description
of plant communities but translation into habitat
types enables comparison on a European scale.
These habitat types represent typical sand dune zonation
of plant communities from sea to mainland. These
are: aphytic beach; annual vegetation Cakilo-Xanthietum
strumarii; its degraded community with Cynodon dactylon;
embryonic sand dunes with Euphorbio paraliae-Agropyretum
junceiformis; mobile dunes with Medicagini marinae-Ammophiletum
australis; fixed dunes dominated by
Onobrychis caput-galli community; mosaic of wetland
associations Schoeno-Erianthetum ravennae, Holoschoenetum
romani, Cladietum marisci; and salt meadows dominated
by Juncus species (Juncetum maritimo-acuti).
Altogether, we found 15 alien species in the surveyed
vegetation plots, representing 7.65 % of all observed plant
Table 2. Total species number and number of alien taxa in the different communities surveyed.
Figure 2. Invasion frequency (number of invaded and not invaded plots) for each surveyed community (c2
=53.688, df=8, p<0.001).
Habitat Plant community
Nr.ofreleves
Speciespool
Alienspecies
Levelofinvasion
(%aliens)
Averagenumberof
speciesperplot
Averageproportion
ofalienspecies
perplot
Averagecoverof
alienspeciesper
plot
Annual vegetation of a drift line 1210
Cakilo-Xanthietum strumarii (Beg. 1941)
Pignatti 1958
371 62 4 0.06 3.42 0.77 1.97 ± 2.41
Cynodon dactylon community 52 64 4 0.06 9.52 1.27 3.73 ± 3.61
Embryonic shifting dunes 2110
Euphorbio paraliae-Agropyretum junceiformis
Tüxen in Br.Bl. & Tüxen 1952 corr. Darimont,
Duvigneaud & Lambdon 1962
192 67 5 0.07 8.90 0.63 2.15 ± 3.93
Shifting dunes along the shoreline
with Ammophila arenaria
2120
Medicagini marinae-Ammophiletum australis
Br.-Bl. 1921 corr. F.Prieto & T.E. Díaz 1991
17 24 3 0.13 7.53 1.12 5.66 ± 5.39
Fixed coastal dunes with
herbaceous vegetation
2130* Onobrychis caput-galli community 86 75 5 0.07 15.52 0.91 5.07 ± 5.20
Humid dune slack 2190 Schoeno-Erianthetum ravennae Pignatti 1953 66 128 6 0.05 19.03 1.29 4.71 ± 4.60
Holoschoenetum romani Tchou 1948 30 73 8 0.11 10.37 1.57 3.85 ± 1.66
Cladietum marisci Allorge 1921 11 33 1 0.03 9.09 0.36 2.73 ± 4.90
Mediterranean salt meadows
(Juncetalia maritimae)
1410 Juncetum maritimo-acuti Horvatić 1934 51 92 5 0.05 16.43 0.92 7.32 ± 10.37
Danijela Stešević et al.	 Alien species in sand dune plant communities
244	 Period biol, Vol 119, No 4, 2017.
species, while a further 10 species were observed in the
study area outside recorded plots, mostly along roads
(Table 1). Roads and pathways are an integral component
of the beach system, particularly the touristic part. At
least one alien species was found in each plant community,
but communities differed in alien species presence,
which ranged from only one species (Cladietum marisci)
to a maximum of eight species (Holoshoenetum romani).
Both extremes were observed in wetland communities
(Table 1).
In the area under examination, Amorpha fruticosa,
Oenothera spp. and Xanthium orientale ssp. italicum were
shown to have an invasion frequency that exceeded 50%
per plant community (Table 1). Amorpha fruticosa had
such a high frequency in only one plant community
(Juncetum maritimo-acuti), while Xanthium and Oenothera
spp. were highly frequent in 3 different plant communities
each.
The level of invasion was highest in mobile dunes with
Medicagini marinae-Ammophiletum australis, and in the
Holoschoenetum romani wetland community (Table 2).
There was also the highest number of alien species in the
latter. The highest cover of neophytes was found in Juncus
dominated stands (Juncetum maritimo-acuti), particularly
because of the invading deciduous shrub Amorpha
fruticosa. The lowest level of invasion (0.03%) was reported
for Cladietum marisci, with only one alien species.
Analysis of differential invasion showed a pattern of
different occurrence of alien species in sand dune habitats.
Almost half of embryonic sand dunes and Juncus dominated
communities were invaded by at least one alien species
(Fig. 2). Two-thirds of dune depressions with Cladium
mariscus were invaded by neophytes but only Amorpha
fruticosa was present (Table 1).
DISCUSSION
Our analysis revealed that alien plant species occur in
plant communities to different extents along the zonation
on sand dunes and have different impacts on species com-
position.
Low number of aliens
The number of alien species reported in most studies
of sand dunes is modest, although it can vary from 8 to
26 (even 50) (23-26, 56). It depends also on the methodology
used; some studies mention only species found in
vegetation plots (23, 57), while others also report the results
of floristic surveys (25, 28). Nevertheless, the number
is low, and differences are present mostly in the cover
Figure 3. Cover of alien plant species in different plant communities (ANOVA: F = 15.11, P < 0.001, df = 8). Letters represent statistically
significant differences according to the Bonferoni post-hoc test at p<0.05. 1 Cakilo-Xanthietum strumarii, 2 Cynodon dactylon community,
3 Euphorbio paraliae-Agropyretum junceiformis, 4 Medicagini marinae-Ammophiletum australis, 5 Onobrychis caput-galli community,
6 Schoeno-Erianthetum ravennae, 7 Holoschoenetum romani, 8 Cladietum marisci, 9 Juncetum maritimo-acuti.
Alien species in sand dune plant communities	 Danijela Stešević et al.
Period biol, Vol 119, No 4, 2017.	 245
and frequency of species. Some alien species (e.g., Agave,
Acacia, Carpobrotus edulis), stand out with high cover on
sand dunes and can alter the structure and physiognomy
of plant communities (58, 59). In our study area, Amorpha
fruticosa may be such a transformer species in wetland
communities. Amorpha is one of the worst alien species in
Europe (60). It occurs mainly in wetlands and is considered
to be a transformer species (61, 62). It is known to
change the species composition and succession of invaded
communities (63). Although Amorpha is not reported
from neighbouring sand dune regions as an invasive species
(23), it is common on embankments of riparian forests
in Albania (64). We can predict its spread in sand
dune humid slacks and wetlands, since it is already a serious
problem in other habitats in the Balkans (65-68).
Another problem is that invading species with different
life forms compared to the majority of the native species
present cause structural changes in these communities (69).
Amorpha fruticosa is a shrub species invading a herbaceous
community, and this can lead to successional changes.
Similar changes of saltmarshes due to invasion of the shrub
Baccharis halimifolia have been reported from Spain (70).
Affected plant communities
Sand dune habitats differ in their level of invasion, and
similar habitats are also differently invaded in different
climates (29, 49). It is characteristic of sand dunes that
general climatic factors are less important for species composition
than local micro-environmental factors (71, 72).
Coastal dunes are characterized by zonation of habitats,
in which environmental factors change (73). There
may be several reasons for differently invaded habitats on
sand dunes. Coastal dunes are susceptible to plant invasions
due to the low number of species, the existence of
micro-sites open to their establishment and a low level of
competition (74). It should be mentioned that both human
disturbance and environmental stress affect alien
invasions in coastal dune communities (57).
The environmental gradient along sea-inland is very
harsh, with wind, waves, tides, salinity, sand grain size,
and dune morphology all having an impact (75). As human
disturbance, direct physical disturbance of the site
(trampling, beach cleaning etc.) can be considered, but
strong propagule pressure is thought to be among the
most important reasons for alien invasions of plant communities
(23). However, there is no general rule about the
different rate of susceptibility of sand dune habitats to
invasion, at least not in Europe, although it is known that
there are strong community differences in the factors governing
invasibility (76).
Nevertheless, it has been shown that in Atlantic dunes
(NE Europe), shrub and woody communities are more
invaded (26, 28). Shrubs are also the predominant aliens
in these dunes; Rosa rugosa in particular is known as an
invader of dunes in northern Europe (77, 78), such as
(e.g., Hippophae rhamnoides) in Ireland (20). It must be
stressed, though, that native shrubs that do not belong to
these environments are also invading northern dunes (79).
A different pattern is observed in the Mediterranean,
where herbaceous sand dune plant communities are most
invaded. In some cases, mobile dunes of the Ammophiletea
class (28, 57), or transitional dunes of the Crucianelletalia
maritimae order (23), are reported to be the most invaded
communities. There are contradictory reports of climax
vegetation being very invaded (28), or macchia at the end
of sand dune zonation, with the least number of aliens
species (57). On Velika plaža, shrub vegetation was never
present at the distant end of the sand dunes from the sea,
and zonation ends with wetland or riparian vegetation
(80). A similar situation is found in the neighbouring
beach of Velipoje in Albania (81). Further south in Albania,
shrub communities are present in sand dune zonation
but with few alien species (64).
Also within the wider coastal zonation outside strict
psammophilous vegetation, different levels of invasion
can be observed. Sand dunes have an intermediate position
in terms of the number of alien taxa present, since
saltmarshes and cliffs have few alien species (25) and
woody communities are usually more invaded (26, 28).
Humid slacks behind sand dunes also have a high number
of neophytes (Table 2) and they are invaded by ruderal
species or species from other vegetation types (25, 73).
Invasive species can form monospecific communities that
represent a serious conservation problem. In our case,
Oenothera spp. can dominate in shifting and fixed dunes
and Amorpha fruticosa in wetlands.
Humid dune slacks are important parts of a dune system,
decreasing the aeolian withdrawal rate of sand due
to increasing humidity and vegetation cover (82) and their
floristic and structural composition should be preserved.
Successful invasive species have different characteristics
and traits (83). They can thrive in the same habitat as
in their native range, but they can also be from other
habitats (e.g., ruderals, weeds). Species not originally from
sand dunes are more successful in stabilized habitats and
slacks, where they find adequate conditions for their successful
establishment and reproduction (73). Oenothera
spp. are originally ornamental species that prefer open
habitats with light, sandy or gravelly, frequently disturbed
soils (84), with a ruderal strategy (25). This is congruent
with our findings, in which Oenothera spp. occur on more
shifting dunes and more fixed dunes with anthropogeneous
impact.
It is possible that some stochastic invasion effects, such
as initial population size, residence time and number of
introduction attempts (85), are responsible for the invasion
of sand dunes and this may also be the reason for
different patterns of invaded communities along the sand
dune zonation in various regions.
We already know that new species are constantly invading
sand dune communities and that changes in veg-
Danijela Stešević et al.	 Alien species in sand dune plant communities
246	 Period biol, Vol 119, No 4, 2017.
etation composition occur over time (24). Neophytes first
arrived in the Cakile maritima community but a few decades
later, mobile and fixed dunes are most invaded (24).
As the number of archeophytes may be a good predictor
of neophyte invasion risk (29), it is foreseen that sand
dune communities rich in archaeophytes will suffer further
invasion. The presence of neophytes also facilitates
the establishment of other neophytes and alien species
(17). Neophytes are useful (and often deliberately used)
for the stabilisation of dunes (86) and, as already mentioned,
such habitats are again more ready for new invasions
(87).
Conservation
Invasion of alien species has been recognized as a major
problem for conservation management, and its control
should be integrated into habitat restoration (77). In addition
to ecological effects, invasive species also bring huge
economic costs. A conservative estimate of costs of biological
invasions is at least 12.7 billion euro annually (88).
There is an extensive literature to date on control of
invasive alien species, including mechanical, chemical
and biological methods, but for dynamic habitats such as
sand dunes, uprooting and subsoil burial have been suggested
as a good combination of methods (89). A study
by Kollmann, et al. (77) showed that mechanical control
of Rosa rugosa by uprooting and burial of plants could not
fully prevent re-sprouting of root fragments. Burial needs
to be combined with hand pulling over several years, as
suggested by Pickart, et al. (89) for Lupinus arboreus,
However, the negative aspect of the burial method is that
it destroys the original dune structure (77), as well as that
it might lead to an increase of mineralization (90).
Studies of ecological success and vegetation response
after removal of the invasive Carpobrotus hybrid complex
concluded that removal reduced Carpobrotus density to a
great extent (91, 92). However, successful control will require
repeated hand-pulling treatments. Treated plots had
a significant increase in species richness, especially annual
plants, compared to invaded plots, but both had the
same native plant cover and diversity. A similar species
composition was found between plots subject to removal
and non-invaded plots, indicating that revegetation is not
necessary. Long-term monitoring is necessary to determine
whether these observed patterns of community response
are transient or stable through succession.
A recent study by Novoa, et al. (59) suggests that the
presence of C. edulis litter, which causes changes in soil
properties and microbial communities on coastal dune
ecosystems, promotes the success of ruderal opportunistic
species and constrains the establishment of native dune
species (e.g., Malcolmia littorea). To restore dune ecosystems
invaded by C. edulis successfully, it is therefore crucial
to (i) remove not only living parts of the invasive
species, but also litter, (ii) overseed the restored area with
appropriate native dune species, and (iii) follow up to remove
opportunistic ruderal species that are likely to constrain
the establishment of the sown species, and colonization
by other typical dune species.
Although the dunes are recognized as endangered ecosystems
in Montenegro, control of invasive species to date
has not been integrated into management or restoration
plans. Only trampling exclusion zones have so far been
installed on Velika plaža (39). At least for shifting and
fixed dunes on Velika plaža, removal of the most common
alien Oenothera should be performed. Another important
action would be education of beach managers to prevent
the planting of alien ornamental plants. Carpobrotus edulis
has already been planted but has not yet spread.
Suggestions for the improvement and protection of the
landscape (93) are also applicable for Velika plaža and
could be achieved by eradication of non-native flora, exclusion
of parts of the beach from intensive use (building,
dumping, high number of visitors), and the development
of sustainable forms of tourism.
Acknowledgements
We thank Filip Küzmič for comments on the final
version and Iztok Sajko for producing the map. Martin
Cregeen kindly checked our English. The research was
partly financed by ARRS through research program (P1-
0236), Rufford Grant 14048-1 and bilateral project (BI-
ME/16-17-018).
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