Applied Vegetation Science 10: 25-33, 2007
© IAVS; Opulus Press Uppsala.
- MANAGEMENT OF THREE ENDANGERED PLANT SPECIES IN DYNAMIC BALTIC SEASHORE MEADOWS -
25
Management of three endangered plant species
in dynamic Baltic seashore meadows
Rautiainen, P.*; Björnström, T.; Niemelä, M.; Arvola, P.; Degerman, A.; Erävuori, L.;
Siikamäki, P.; Markkola, A.; Tuomi, J. & Hyvärinen, M.
Department of Biology, University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland; E-mails taina.bjornstrom@oulu.fi;
marika.niemela@mtt.fi; pia.arvola@metsa.fi; [email protected].fi; lauri.eravuori@poyry.fi; pirkko.siikamaki@oulu.fi;
annamari.markkola@oulu.fi; juha.tuomi@oulu.fi; marko.hyvarinen@oulu.fi;
*Corresponding author; Fax +358 85531061; E-mail: pirjo.rautiainen@oulu.fi
Abstract
Question: Arctophila fulva var. pendulina, Primula nutans
var. jokelae and Puccinellia phryganodes are threatened early
successional species growing in the seashore meadows of the
northern Baltic Sea. Patches formed by these species are destined to be replaced by other species during primary succession
and in order to persist in the area they have to continuously
colonize new areas. We studied whether the displacement of
the species could be slowed down and their sexual and/or
vegetative reproduction enhanced by management targeted to
surrounding vegetation.
Location: Bothnian Bay, Baltic Sea, W Finland.
Methods: Vegetation surrounding patches of all study species
was mown in four successional growing seasons. Moreover, the
impact of additional soil turning on creating new favourable
growing sites was tested for A. fulva.
Results: Deterioration of suitable habitats of A. fulva and P.
nutans was markedly slowed down by management and the
vegetative and/or sexual reproduction of these species was
enhanced. In the case of P. phryganodes, however, no positive
response to management was obtained.
Conclusions: In order to improve the long-term persistence
of these three species successional vegetation changes should
be slowed down and their dispersal and colonization success
improved by continuous management of the populations. We
further suggest that the colonization of new areas should be
aided by transplantations to the non-vegetated islets, which
have recently risen from the sea and cannot be reached by
means of dispersal.
Keywords: Arctophila fulva var. pendulina; Landscape dynamics; Management; Primary succession; Primula nutans
var. jokelae; Puccinellia phryganodes.
Nomenclature: Hämet-Ahti et al. (1998).
Introduction
The rate of habitat change in relation to the rate of
species dynamics can be especially important for plants
that are dependent on a given type of habitat. If extinctions primarily occur as a consequence of habitat change,
for example, during primary succession, the species have
to disperse and successfully colonize new favourable
growing sites (Snäll et al. 2003; Jäkäläniemi et al. 2006).
To enhance the long-term persistence of early successional species one can (1) first of all apply management
practices which slow down the succession process in
locations where the species have viable populations;
(2) preserve the regime of natural disturbances creating
new colonization sites; (3) improve dispersal to the new
growing sites and improve colonization success. These
approaches may be especially useful in conservation of
the seashore plant communities.
Seashores are usually characterized by distinct vegetation zones (Tyler 1969; Vartiainen 1980; Bertness
1991). Early successional species tolerate waterlogged
soil and disturbance in lower parts of the shore, whereas
in the upper shores zones are increasingly shaped by
interspecific competition (Bertness 1991; Amsberry et al.
2000). Hence, plants on the upper shore are considered
to be better competitors (sensu Grime 1979) than species
on the lower shore and where their niches overlap the
higher shore species eventually displace lower shore ones
(Bertness 1991; but see Bockelmann & Neuhaus 1999).
In the Bothnian Bay (northernmost Baltic Sea) relatively
rapid isostatic land uplift (6.9 mm.a–1, Johansson et al.
2001) together with flat topography continuously creates
virgin land to be colonized, but still, populations of some
early successional species have become threatened in
recent decades (Ryttäri & Kettunen 1997).
The population decline of the early colonizers may
partially be a consequence of abandonment of traditional
agricultural practises such as cattle grazing and hay making that used to enlarge the area of low-growth meadows,
26
RAUTIAINEN, P.
slowed down succession and maintained higher species richness (Ryttäri & Kettunen 1997; Pykälä 2000; Jutila 2001).
In addition, eutrophication of the shores by scattered loading
from arable fields may have contributed to this development
(Ryttäri & Kettunen 1997; Hänninen & Leppäkoski 2004;
Laamanen et al. 2005). Consequently, seashore meadows
of the Baltic Sea are nowadays classified as endangered
habitats (EU Habitat Directive 92/43/EEC).
The management of seashore meadows should result in
the reduction of the space occupied by dominant species.
Enhancing sexual reproduction or vegetative spread of the
early successional species would secure the potential to
colonize new suitable areas when such opportunities arise.
In the present study, we tested for the impact of selected
management methods on the local populations of three
threatened early successional seashore plants: Arctophila
fulva var. pendulina, Primula nutans var. jokelae and Puccinellia phryganodes.
Populations of the three species are naturally rare
climatic relicts, for which the early successional environment of the Bothnian Bay has offered a suitable refugium
(Eurola 1999). The number and extensions of populations
has declined during the last decades (Ryttäri & Kettunen
1997; Siira & Merilä 1985; Siira 1994). The species have
different growth forms and predominant modes of reproduction
and they inhabit different zones of the seashore (Table 1). We
hypothesized that the removal of surrounding taller vegetation
would slow down succession, and hence prevent or alleviate
the habitat deterioration. It would also reduce interspecific
competition for light and thus enhance vegetative and sexual
reproduction and create safe sites for the establishment of new
individuals. To find out the rate of response we monitored the
changes in populations for four years. Moreover, we tested the
impact of additional soil turning on creating new favourable
growing sites for A. fulva.
Material and Methods
Study species
Arctophila fulva var. pendulina and Puccinellia phryganodes are perennial, clonal grasses. Shoots of A. fulva are
tall and they grow as scattered dense, monospecific patches
ET AL.
along rivers and seashores influenced by freshwater. A. fulva
flowers regularly in June-July, but no seedlings have been
recorded in the study area (Rautiainen et al. 2004); hence,
dispersal seems to be based on rhizomatous growth and
fragmentation of clones. However, it was recently shown
that there is a considerably high genotypic diversity within
the study population suggesting that sexual reproduction has
taken place in the past (Kreivi et al. 2005). Most of the A.
fulva patches in the study area are located in the open area
in shallow water where disturbance caused by ice scouring
creates additional open space for colonization.
P. phryganodes is a small stoloniferous, prostrate grass,
which propagates by producing easily detaching axillary
shoots dispersed by water. Flowers are formed, but as a rule
viable seeds are absent (Sørensen 1953; Bowden 1961).
The species grows on an open, often saline zone from the
shoreline to the low salt marsh meadow where other vegetation is sparse or absent. The species may even dominate
salt marsh vegetation, especially if the meadow is grazed
by waterfowl (Siira & Haapala 1969). Primula nutans var.
jokelae is a perennial rosette-forming hemicryptophyte that
reproduces by seed and also forms runners originating from
the axils of the lower leaves (Mäkinen & Mäkinen 1964). Its
flowers are insect-pollinated and seeds dispersed by water
currents (Ulvinen 1997). The species grows typically on
sandy and clay-rich low-growth seashore meadows, but not
in the very waterfront. The meadows are often inundated
for short periods in spring due to the flooding of rivers
and irregular wind-driven elevations of the sea water level
(Mäkinen & Mäkinen 1964).
Study sites and the design of experiments
The experiment with A. fulva was carried out in the
estuary of Temmesjoki River at the Liminka Bay (Fig. 1) in
2000-2003. The main components of vegetation in the area
in sequence from the sea towards the land are Schoenoplectus lacustris and S. tabernaemontanii, Eleocharis palustris
and A. fulva. The shoreline is dominated by Carex species
and further inland dense stands of Phalaris arundinacea
and Phragmites australis prevail. The soil in the area is
constituted by mud and clay.
A. fulva patches (10 to 435 m2 in area; n = 14) growing in closed vegetation were randomly selected for the
Table 1. Characteristics and the conservation status of the studied species.
Reproduction
Growth form
Habitat
Occurrence in relation to the succession stage
Conservation status in Finland
Study years
A. fulva var. pendulina
P. phryganodes
P. nutans var. jokelae
Vegetative (and sexual?)
Tall, rhizomatous
Hydrolitoral
Early
Critically endangered
2000-2003
Vegetative
Small, stoloniferous
Geolitoral
Early
Endangered
2000-2003
Sexual and vegetative
Small, rosette-forming
Upper geolitoral
Early-intermediate
Endangered
1999-2002, 2001-2004
- MANAGEMENT OF THREE ENDANGERED PLANT SPECIES IN DYNAMIC BALTIC SEASHORE MEADOWS experiment. Two patches were rejected from the analysis
as they were buried by a thick mat of plant debris in 2001.
Three permanent 1.5 m × 1.5 m experimental quadrats were
established beside every patch and randomly allocated to
one of the three treatments: (1) control, (2) mowing and (3)
mowing and additional turning of the soil with a shovel at
a depth of 10-20 cm. The turning was done in the first two
years to imitate the impact of ice scouring. The mowing
(down to the height of ca. 10 cm) of the treatment quadrats
together with a 20-cm wide marginal zone around them
was repeated annually in the mid/late July. Most of the A.
fulva shoots were also cut along with the other vegetation,
but occasionally some of them were left intact if noticed.
Cut vegetation was removed from the quadrats. Every year,
prior to the treatments, the number of A. fulva shoots was
counted and cover (%-scale) of all species was estimated
visually.
The mowing experiment with P. phryganodes was
carried out in the cape of Tauvo (Fig. 1) in 2000-2003.
The sparse and low vegetation of the study area is mainly
dominated by Agrostis stolonifera and Juncus gerardii. P.
phryganodes grows as small patches ca. 100-450 m inland
from the mean water line. The nutrient-poor soil consists
mainly of sand (Siira 1984). Randomly chosen patches
(mean area 1.1 dm2, n = 12) were subjected to mowing
treatment and another twelve served as controls. A quadrat
of 1 m × 1 m was established around each patch. The cover
of P. phryganodes and other species was estimated visually
every year before mowing. In the first year mowing was
done in late September and in the following years at the end
of July. Vegetation was cut down to the height of 5-10 cm
from the quadrats and a half meter wide marginal around
27
them and subsequently removed. As a low-stature species
P. phryganodes was mainly left intact.
Two separate management experiments were carried out
with P. nutans. First, a mowing experiment was conducted
in 1999-2002 in five sites (Fig. 1), where vegetation consists mainly of Phragmites australis, Carex nigra, Juncus
gerardii and Calamagrostis stricta. Ten 40 cm × 40 cm
quadrats were established in each population and a half of
them were randomly allocated as controls and other half
to the mowing treatment. Vegetation was annually mown
down to the height of ca. 10 cm from the area within a 2-m
radius around the centre of the quadrat at the end of July
– in the beginning of August. Rosettes of P. nutans were
left intact because they are so low-growth but flower stalks
were usually cut. However, the seeds were already ripe during the mowing. Mowed plant material was removed from
the area. Number of sterile P. nutans rosettes and flowering
individuals were censused each year. The rosettes included
also seedlings in the first three years, but in the last year the
seedlings were counted separately. The cover of vegetation
was estimated at the %-scale in 2000 and 2002.
Second, a shrub removal experiment was carried out in
one site in 2001-2004 (Fig. 1). The study area is located in
the upper part of the seashore meadow where Salix phylicifolia and Alnus incana overshadow lower vegetation. The
experimental design was similar to the one in the mowing
experiment. Ten control and ten treatment quadrats were
established. Shrubs were cut in August every year. Data
were collected in a similar manner as in mowing experiment with the exception that seedlings and rosettes were
counted separately every year and the cover of vegetation
was estimated every year.
Statistical analyses
Fig. 1. Study areas of Arctophila fulva (cross), Primula nutans
¢ = mowing experiment and ® = shrub removal) and Pucinnellia phryganodes (p).
Influence of the management on all three species was
analysed using R statistical software (Ihaka & Gentleman
1996). In the analysis, the number of A. fulva and P. phryganodes shoots and P. nutans rosettes, seedlings and flowering
individuals were used as response variables as was also the
cover of P. phryganodes. When the number of individuals
in a year concerned (shoots, rosettes, flowering shoots or
seedlings) was used as a response variable, a generalized
linear model with a log-link was built for the data analysis
as customary with variables following a negative binomial
distribution (Crawley 2004). The impact of treatment was
evaluated by the change in the model deviance (subsequently referred to as ΔDev) that follows a χ2 distribution
(see e.g. McCullagh & Nelder 1989). Orthogonal contrasts
with the z-statistic were applied in the analysis of the general
effect of the treatment on number of A. fulva shoots (2,–1,–1;
control vs. mean impact of treatments) and the potential difference between the two different management treatments
(0, –1, 1; mowing vs. mowing and soil turning).
28
RAUTIAINEN, P.
In the experiment with A. fulva the number of shoots
was explained by a model fitted sequentially starting from
the intercept and adding the main effects of the PATCH
(as a block factor) and the TREATMENT. A similar modelling approach was carried out in the experiments with
P. nutans where the number of sterile rosettes, flowering
shoots and seedlings (in the mowing experiment only
in the last year) were used as response variables. In the
mowing experiment with P. nutans, POPULATION (as a
block factor) and TREATMENT were added sequentially
and their significance was evaluated as above. The shrub
removal experiment was carried out in one population as
paired quadrats, and hence, the variable QUADRAT was
added into model prior to the TREATMENT. The impact
of the treatment on the number of P. phryganodes shoots
was analysed in a similar manner with the exception that
the design did not involve a blocking factor. The change
in the cover of P. phryganodes following treatment was
analysed by one-way ANOVA following an arcsine-root
transformation of the cover estimates.
Results
The number of A. fulva shoots declined in the control
quadrats from the median (Md) of 4 to 0 in the last two
years, whereas in both treatments the number of shoots
increased (Fig. 2). Management affected the number of
shoots positively already in the first year after the start of the
experimenter the start of the experiment (ΔDev = 6.04, df =
2, p = 0.049) and this trend was further enhanced during the
subsequent years (e.g. in 2002-0003 ΔDev = 25.97, df = 2,
p < 0.001). The contrast analysis revealed that the control
quadrats and the treated ones differed during all study years
(years 2001-2003, z-range: 2.90-4.90, p-range: 9.73*10–7
– 0.0038). More A. fulva shoots were constantly found in the
treated quadrats than in the controls, and, moreover, from
the two different treatments the combined cutting and soil
turning scored higher median number of shoots in all years
than mere cutting (range of Md: 4-8 vs. 0-3.5, respectively).
This difference was confirmed to be statistically significant
in the last study year (z = 2.29, p < 0.05) by analysis of the
contrast within the TREATMENT factor. One should keep in
mind that the distributions in shoot numbers were extremely
skewed and there were, for example, some treated plots in
which the shoot number exceeded 100. The impact of the
PATCH variable was statistically significant in all years
(data not shown) and, hence, the use of patches as a block
factor was well grounded in the modelling.
In the beginning of the experiment with A. fulva, sedges
(mainly Carex aquatilis) were dominant species in all quadrats with an estimated average cover of 75 % in control,
57 % in mowed and 82 % in mowed and turned ones. The
overall cover of sedges increased slightly during the experi-
ET AL.
ment in the control treatment, whereas soil turning reduced
markedly the cover of sedges (down to 14%) in the next
year but it soon recovered reaching almost 50 % in the last
year. Mowing treatment had only a minor impact on the
cover of sedges. There was no significant difference in the
cover of Poaceae species between the two manipulation
treatments. Other species competing with A. fulva covered
usually only negligible areas in quadrats and, hence, they
were pooled into one group. Their cover decreased in both
the control and the mowing treatment but increased when
mowing was combined with the soil turning.
The response of P. phryganodes to mowing was in stark
contrast to that of A. fulva. The cover and the number of
shoots of P. phryganodes declined in both the mowed and
the control quadrats during the experiment and there was no
statistically significant difference between the control and
the mowing treatments. The total cover of vascular plants
was relatively low in the beginning of the experiment: ca.
24 % in both control and mowing quadrats. In the control
quadrats it remained approximately the same during the
first three years but increased about 10% in the last year.
In the mowed quadrats the total cover decreased one year
after mowing but started to increase in the second year,
reaching almost the same level as in the control ones (ca.
30 %) in the last year. In both the control and the mowed
quadrats the increase of total plant cover was mainly due
to the expansion of Juncus gerardii.
In general, mowing increased markedly the number
of P. nutans individuals in all demographic stages. In the
first year after the start of the experiment the control and
the mowed quadrats did not differ from each others, but in
two years the number sterile rosettes (Md: 27 vs. 22) and
flowering individuals (Md: 3 vs. 1) in the mowed quadrats
exceeded those in the control ones. This trend was statistically significant already in 2001 as indicated by the changes
in model deviance when the TREATMENT factor was fitted
(ΔDev = 7.06, df = 1, p = 0.008 and ΔDev = 27.09, df =
1, p < 0.001, respectively) and continued as such in 2002
(ΔDev= 14.61, df = 1, p < 0.001 and ΔDev = 11.20, df = 1,
Fig. 2. Number of A. fulva shoots in the experimental quadrats
in the last study year (2003). The lower boundary of the box
indicates the 25th percentile, a line within the box the median,
and the upper boundary the 75th percentile. Error bars above
and below the box indicate the 90th and 10th percentiles and
the dots outliers.
- MANAGEMENT OF THREE ENDANGERED PLANT SPECIES IN DYNAMIC BALTIC SEASHORE MEADOWS p = 0.001, respectively, Fig. 3). Seedlings were separated
from the sterile rosettes only in the last study year and then
the number of seedlings was significantly higher in the
mowed quadrats than in the control ones (TREATMENT,
ΔDev = 11.32, df = 1, p = 0.001) even though in terms of
Md the difference was a minor one (1 vs. 0, Fig. 3).
The number of rosettes was dependent on the study
location in all study years as indicated by the statistically
significant changes in the model deviance when the LOCATION was fitted (data not shown), whereas the locationdependency of the number of flowers in quadrats varied
between years. Moreover, the location had a significant
main effect on the number of seedlings in year 2002 (data
not shown).
The cover of vegetation in the mowing experiment was
assessed in 2000 and 2002. The total cover of vegetation
increased considerably in both the treated and the control
quadrats, but the species proportions were different. In
both treatments sedges increased in cover, but the increase
was higher in the control quadrats (from 2% to 25% and
in mowing from 2% to 18%). Also the cover of P. nutans
increased in both the treated and the control quadrats: the
increase in absolute terms was considerably higher in the
mowed quadrats (from 8% to 38% and in control from 2%
to 21%) but in relative terms in the control quadrats (tenfold
vs. fivefold). The amount of litter was much higher in the
control quadrats than in the mowed ones at the end of the
experiment (60% and 27%, respectively).
In the shrub removal experiment the total number of
P. nutans individuals was higher in the treatment quadrats
compared to the control ones already in a year after the start
of the experiment. This was mostly due to the increased
number of sterile rosettes in the mowed quadrats when
compared to the control ones in year 2002 (Md: 45 vs. 33,
TREATMENT, ΔDev = 5.48, df = 1, p = 0.02) and following study years (ΔDev = 9.88, df = 1, ΔDev = 6.69, df =
1, p = 0.01; 2003 and 2004, respectively, Fig. 4). Also the
number of seedlings was higher in the treatment quadrats
every year after the shrub removal, but the difference could
not be tested due to too many zero-values. In fact, there was
no need for testing as in the last year of the experiment there
were no seedlings in any of the control quadrats, whereas
the Md for treated quadrats was 5.5 (Fig. 4). Removing
shrubs also increased the flowering of P. nutans in the last
two years (Md: treatment vs. control, 2.5 vs. 0 and 6 vs. 0,
respectively Fig. 4) and these differences were statistically
significant (ΔDev = 44.73, df = 1, p < 0.001 and ΔDev =
106.26, df = 1, p < 0.001, respectively).
In the beginning of the shrub removal experiment the cover
of shrub layer was approximately 60 % in both the control
and the treatment quadrats. The field layer consisted mainly
of Lathyrus palustris, Carex nigra and Vicia cracca and its
cover remained approximately the same in treatment quadrats
but increased in the control ones (from 19 % to 58 %).
29
Fig. 3. Number of flowering individuals, sterile rosettes and
seedlings of P. nutans in (a) the last study year (2002) of the
mowing experiment.
Fig. 4. Number of flowering individuals, sterile rosettes and
seedlings of P. nutans in the last study year (2004) of the shrub
removal experiment.
30
RAUTIAINEN, P.
Discussion
Impact of treatments on the target species
A. fulva benefited from both cutting the surrounding
vegetation and turning the soil. The number of shoots
increased in both treatments, while it decreased almost to
zero in the untreated quadrats during the experiment. Turning the soil together with mowing was more effective than
mere mowing. The management was effective especially
against tall, tussock forming sedges (e.g. Carex aquatilis),
which form dense stands impenetrable by the other species.
Mowing restrained their growth only slightly, because the
sedges regenerated rapidly from the basal meristems left
intact by mowing: a common phenomenon for tiller-forming
species (e.g. Stammel et al. 2003). Soil turning, however,
reduced the cover of sedges effectively. It imitated the effect
of ice scouring by breaking the tussocks and the roots of
sedges. It also cut the roots and the rhizomes of A. fulva,
but the species was able to grow rapidly new shoots from
the small rhizome fragments. This is probably an adaptation
to its unpredictable environment, where ice scouring both
destroys vegetation and creates open areas and floating
plant debris may bury vegetation. The advantage of such
adaptation was clearly seen in the 1960s, when the mouth of
Temmesjoki river was dredged (Siira 1994): A. fulva rapidly
spread to areas where soil was disturbed. However, despite
the increase in the number of shoots in both the mowing
and the turning treatments, A. fulva was not able to form
as dense stands as it usually does in open space.
In contrast to A. fulva, P. phryganodes showed no
positive response to the mowing. Despite the fact that the
mowing reduced the cover of competing vegetation at the
start of the experiment while most of the creeping shoots of
P. phryganodes were left intact, the cover and the number
of shoots of P. phryganodes decreased during the experiment. Interspecific competition for light and space may not
be the main reason for the decline of P. phryganodes along
succession in Tauvo, as the total cover of vegetation was
fairly low in the study area already in the beginning of the
experiment. Relatively dry summers during the study years
may have enhanced the replacement of P. phryganodes by
later successional species. Nutrient poor, dry and rather
coarsely textured sandy soil of the area may not provide
optimal conditions for the shallow rooted species. Srivastava
& Jefferies (1996) studied the habitat requirements of P.
phryganodes by transplant experiments and concluded that
high salinity, low soil moisture and low nitrogen content
were associated with the decreased growth and survival of
transplanted tillers of P. phryganodes (see also McLaren
& Jefferies 2004). The largest and densest P. phryganodes
population in the Bothnian Bay area is found on the Isomatala islet characterized by fine textured and nutrient-rich
soil (Siira & Merilä 1985). At this site the species dominates
ET AL.
the lowest salt marsh vegetation at least partly owing to the
intensive grazing by Anser anser (greylag goose) (Niemelä
et al. unpubl., see also Hik et al. 1992).
Management resulted in an increase of both vegetative
and sexual reproduction of P. nutans. Its response to the
mowing and the shrub removal was parallel: the number
of sterile rosettes, seedlings and flowering individuals
increased. The effect of shrub removal was first noticed as
an enhancement of vegetative reproduction and later as an
increase of sexual reproduction. As a low-stature species
P. nutans is a poor competitor for light. In the improved
light conditions P. nutans was able to increase the number
of flowering individuals. Results are similar to those from
the management experiment by Brys et al. (2004) with
Primula veris: only a limited number of P. veris individuals
were able to flower and shed seeds without management.
According to Valverde & Silvertown (1995) the number of
seeds per plant and the percentage of seedling establishment
were positively correlated with the light conditions in the
woodland herb, Primula vulgaris.
Up to 550 seeds can be found in one inflorescence of P.
nutans (Degerman pers. obs.) and, hence, it is not surprising
that the number of seedlings increased markedly after the
increase in the number of flowering plants. The increase
of seedlings may also be due to the enhanced germination
of seeds in better light conditions. Also the seedling stage
is susceptible for the light. The poor survival of seedlings
in tall and dense swards may be a consequence of the low
light level (Bullock 2000). In addition, the amount of litter
was clearly higher in the control quadrats at the end of the
experiment. Litter may affect seed germination and seedling
establishment by shading, changing the surface temperature
and the humidity of soil or by allelopathy (Crawley 1997;
Baskin & Baskin 1998; Jutila 2003; Becerra et al. 2004).
Moreover, the removal of vegetation and litter may create
proper microsites for the seed germination and the seedling
establishment (Brys et al. 2004; Ehrlén et al. 2004; Hoffmann & Isselstein 2004).
Conclusions and implications for management
Our results indicated that management as used in the
present study was able to slow down the deterioration of
suitable habitats for two of the studied species, A. fulva
and P. nutans, and enhance their vegetative and/or sexual
reproduction. P. phryganodes may be more dependent on
the narrow competition-free habitat newly emerging from
the sea. Thus, the removal of taller plant species is not effective enough to enable its persistence above the lowest
shore. The potential to colonize new habitats was improved
especially in P. nutans, which is capable of long-distance
dispersal by seeds. Dispersal abilities were not investigated
in the present study, but one can assume that the two veg-
- MANAGEMENT OF THREE ENDANGERED PLANT SPECIES IN DYNAMIC BALTIC SEASHORE MEADOWS etatively reproducing graminoids are relatively ineffective
in their long-distance dispersal.
Any of the population management methods used is
hardly able to completely alleviate the impact of seashore
meadow succession on populations of the focal species but
rather delay the replacement of the populations by later successional species. The land uplift in the Bothnian Bay has
been continuously creating new land for early successional
species to colonize (Cramer & Hytteborn 1987). However,
during the previous two decades the long-term mean of the
sea level has been ca. 5 cm higher than predicted on the
basis of the historical linear trend (Johansson et al. 2004),
potentially indicating a long-term trend of rising sea level
that is counteracting the land uplift. If this is the case one can
speculate that the reduction in competition-free space available for early colonists can make these populations more
susceptible for local the extinction. Moreover, eutrophication of the Baltic Sea (Laamanen et al. 2005) may improve
conditions for some invasive species, such as Phragmites
australis, thus further decreasing the area suitable for early
successional species.
In addition to the methods used in our experiment other
means of management could be employed.
Large-scale mowing in the seashore meadows and
subsequent litter removal would enhance the conditions
for early successional species but especially A. fulva and
P. phryganodes may also need soil turning to aid the establishment of vegetative propagules. However, soil turning is
very laborious, as no heavy machinery can be used due to
the soft soil, and therefore, the targeted soil turning could
be feasible only when small populations are in the immediate risk of extinction. Mowing should be carefully planned
in order to avoid accumulation of plant debris on A. fulva
stands. Debris floats and rafts more easily in areas where
there is no tall vegetation to block it. Even though the species is well adapted to the disturbances of the waterfront,
the recovery of patches from the suffocation by debris is
often protracted.
Moreover, grazing and concomitant trampling by cattle
could provide an effective management tool for preserving
and creating suitable habitats (Pykälä 2000; Jutila 2001).
Transplantations of the species to non-vegetated habitats,
which have recently risen from the sea and are beyond the
reach of extant individuals, might help to lower the risk of
regional extinction (see e.g. Oostermeijer 2003).
Some recent studies have considered the rate of landscape change together with the amount of habitat as a
critical factor for the population persistence (Keymer et
al. 2000; Matlack 2005). This kind of shift in paradigm
may in fact be very important in understanding why often,
in spite of rigorous management efforts, many threatened
plant populations disappear. If landscape changes too fast
in relation to the scale of colonization-extinction process
the population may be lost even though there seems to be
31
enough habitat available for its persistence. Keymer et al.
(2000) point out that management methods that simultaneously destroy and restore habitat can have a dramatic
negative effect on populations. Hence, management that is
targeted to increase the habitat persistence and slow down
the landscape change, such as used with A. fulva, may turn
out to be more successful in preservation of threatened
populations than management of a plant community as a
whole.
Acknowledgements. The study was financially supported by
the Academy of Finland (project #47973), Maj and Tor Nessling
Foundation, Wihuri Foundation, University of Oulu, Societas pro
Fauna et Flora Fennica, Finnish Foundation for Nature Conservation and Kone Foundation. We are grateful to two anonymous
referees for their constructive comments on the manuscript. We
also thank all our field assistants and Eero Vierikko who cut the
shrubs in the P. nutans experiment.
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Received 15 August 2005;
Accepted 20 January 2006;
Co-ordinating Editor: J. Pfadenhauer.