Article - Polish Journal of Ecology

POLISH JOURNAL OF ECOLOGY
(Pol. J. Ecol.)
59 4 677–686 2011
Regular research paper
Kinga KOSTRAKIEWICZ
Department of Plant Ecology, Institute of Botany, Jagiellonian University,
Lubicz str. 46, 31–512 Kraków, Poland, e-mail: kinga.kostrakiewicz@uj.edu.pl
THE EFFECT OF GAPS SIZE ON COLONIZATION PROCESS
IN MOLINIETUM CAERULEAE MEADOWS
WITH DIFFERENT HABITAT CONDITIONS
ABSTRACT: The disturbances defined as
an external factor causing biomass removal are a
key component of all ecosystems. In phytocenoses
with a continuous vegetation cover and a large
proportion of perennial plants the fine-scale disturbances
create gaps, which are the temporary
competitor-free microsites suitable for plant recruitment.
The investigations of natural colonization
of different size gaps in Molinietum caeruleae
meadows were carried out in patches dominated
by small species creating delicate, erect or procumbent
stems (MC), prevailed by large-tussock
grasses (GR), and overgrown by willows (SA).
Each patch was represented by ten plots, divided
into four square subplots of 0.16 m 2 , 0.09 m 2 ,
0.04 m 2 and 0.01 m 2 . In each of them the aboveground
parts of plants were clipped and removed
with the litter. The seedlings recruitment was observed
in 2007–2009.
The highest species richness in gaps was observed
in the MC patch and might be caused by
week competition for light from neighbouring
plants with delicate, procumbent stems and narrow
leaves. The smaller rate of recruitment in SA
and GR patches could be caused by overshading
willows as well as by the competition from large
and dense tussocks of Deschampsia caespitosa and
Molinia caerulea. At all patches species richness
declined with the decreasing gap size. The developed
seedling pool represented both species occurring
in the surrounding canopy and such which
were not found there. However, their contribution
varied between particular patches. Regardless gap
size, the MC seedling pool was dominated by species
which did not occur in the established vegetation,
whereas in GR gaps both groups were represented
by similar numbers of taxa and the SA gaps
become dominated by species present in the surrounding
canopy. Irrespective of patch character,
in each subplot the medium-seeded species were
represented most abundantly. The recruitment of
genets of large-seeded species decreased, while
the abundance of individuals of small-seeded taxa
increased with the increasing gap size.
In the light of the performed study, one might
suggest that extent-controlled disturbances can
be used as an effective way of the conservation of
Molinietum caeruleae patches dominated by small
meadow species being outcompeted by large-tussock
grasses and over-shaded by willows.
KEY WORDS: Molinietum caeruleae, gap
area, plant cover, seed mass, seedlings, species recruitment
1. INTRODUCTION
A key component of all ecosystems are
disturbances defined as an external factor
causing biomass removal (Grime 2001). The
detailed characteristics of agents and features
of disturbances have been reviewed by S ousa
(1984). In phytocenoses with continuous

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Kinga Kostrakiewicz
vegetation cover and a large proportion of
perennial plants the fine-scale disturbances
assure origination of gaps, which are temporary
competitor-free microsites suitable for
re-colonization (Harper 1977). Gaps are
important for seedling recruitment in many
communities, including temperate grassland,
sub-alpine grassland, alpine tundra, savannah,
dessert, temperate forest, tropical forest
(reviewed by Bullock 2000). The openings
provide an opportunity for the regeneration
of species already present in the community,
as well as for the invasion of species from the
outside. Theoretical studies of Geritz et al.
(1999) suggested that gaps provide an arena
for the seed size game. The small-seeded species
depend on disturbance at microsites and
may exhibit relatively greater recruitment
success in places where competition decreases,
whereas larger-seeded species are more
successful in surrounding neighborhood.
Until recently the studies of natural colonization
of gaps were have been very scarce.
The majority of investigations concentrated
on colonization of openings which occurred
in the result of disturbances with different
severity in old fields (L avorel et al. 1998),
grasslands (McIntyre and L avorel 2001),
as well as forests (Dalling and Hubbell
2002, Dzwonko and Gawroński 2002).
Little attention was given to the colonization
of openings originated in the result of disturbances
with various dimensions. Such observations
were carried out in semi-natural pastures
(Eriksson and Eriksson 1997) and
forests (Degen et al. 2005). The studies of
the role of opening size on recruitment process
are still strongly desired. Such observations,
conducted in threatened communities
are important not only because of academic
interest, but also for successful nature conservation,
providing basis for restoration projects
and policies.
Nowadays the Molinietum caeruleae
meadows belong to the most endangered
communities in Europe; they are affected by
the agricultural practices, such as intensification
of management, forest plantation or land
abandonment (Fuller 1987, Green 1990,
Prah 1993, Joyce and Wade 1998, Muller
2000, Diemer et al. 2001). Therefore, the
present study was undertaken to investigate
the colonization of gaps of different size in
Molinietum caeruleae patches with various
habitat conditions. The specific aims of the
study were: (1) to assess the effect of gap size
on species recruitment; (2) to investigate the
influence of opening area on the appearance
of taxa present and absent in established vegetation;
(3) to study the impact of gap dimensions
on colonization by small-, medium- and
large-seeded species.
Table 1. Habitat characteristics of the patches dominated by small meadow species (MC), prevailed by
large-tussock grasses (GR) and overgrown by willows (SA).
Patch abbreviations MC GR SA
Patch area (m 2 ) 1400 1450 1300
Number of species in patch 56 49 46
Main dominant plant species
in the vegetation cover
(species with cover > 20%)
Subdominant species in the vegetation
cover
(species with cover 5–20%)
Lathyrus pratensis,
Lotus corniculatus,
Briza media,
Lysimachia vulgaris,
Betonica officinalis,
Leucanthemum
vulgare, Gentiana
pneumonanthe,
Stellaria graminea
Molinia caerulea,
Deschampsia
caespitosa,
Serratula tinctoria,
Galium boreale,
Polygonum bistorta,
Salix repens ssp.
rosmarinifolia, S.
cinerea, S. aurita,
Phragmites australis,
Galium boreale,
G. verum,
Serratula tinctoria,
Chamanerion
angustifolium
Maximal vegetation height (cm) 157 210 247
Mean vegetation height (cm) 120 170 180
Mean vegetation cover (%) 100 99 98
Mean cryptogam cover (%) 0 1 2

The colonization of gaps in Molinietum caeruleae meadows
679
2. STUDY AREA
The studies were carried out in Kostrze
district localised on the western edge of
Kraków, south of the Vistula River (southern
Poland). The research area is at ca 210 m a.s.l,
on a low flood terrace of the river, 3.0–6.0 m
high. The greatest territory is occupied by
Molinietum caeruleae patches, which are relicts
of vast meadows once stretching from Czernichów
(west of Krakow) to Niepołomice
Primeval Forest situated 20 km east from
Krakow (Z arzycki 1958). The changes in
water regime and abandonment of traditional
land use for at least a dozen years promoted
the development of Phragmites swamps and
willow brushwood leading to the fragmentation
of meadows (Dubiel 1991, 1996).
The investigations were conducted at
area with three adjacent, abandoned Molinietum
caeruleae patches with different species
composition (Fig.1). The patch labeled
MC (50°01’50.4’’N, 19°52’03.2’’E) measured
ca 1400 m 2 and was dominated by species
creating delicate, erect or procumbent stems,
small-tussock grass and short rosette-forb
species. The site named SA (50°01’50.9’’N,
19°52’02.9’’E), covered an area of ca 1450 m 2
and was prevailed by willows and surrounded
by groups of densely grown trees and bushes.
The patch labelled GR (50°01’52.5’’N,
19°52’03.0’’E) measured ca 1300 m 2 and was
dominated by large-tussock grasses forming
high stems. The detailed descriptions of habitat
conditions in above mentioned patches
are presented in Table 1.
3. MATERIAL AND METHODS
In March 2007, 10 permanent 0.5 × 1.2
m plots were randomly established in all the
patches. They were set at a distance of at least
2 m from the border of the patch to avoid edge
effect. Plots were divided into four squareshaped
adjacent subplots measuring 0.16 m 2
(subplot I), 0.09 m 2 (subplot II), 0.04 m 2 (subplot
III), and 0.01 m 2 (subplot IV). In each
of them the litter and above-ground part of
the biomass were clipped and removed. Such
treatment is considered as an optimal for
seedling establishment on the basis of result
of my preliminary studies (Kostrakiewicz
2007–2008 unpubl.) and similar experiments
Kostrze
0
MC
Kraków
200 m.
Vistula
Study area
G R
Bodzów
The study patches
MC- dominated by small meadow species
GR- prevailed by large tussock grasses
SA- overgrown by willows
- the experimental plot
Kostrze
Vistula
Pychowice
KRAKÓW
Vistula
The area of experimental subplots
I - 0.16 m 2
II - 0.09 m 2
III - 0.04 m 2
IV - 0.01 m 2
(Kotorová and Lepš 1999). The design of
experiment is shown on Fig. 1. The generative
offspring establishment was monitored once a
week in May, June, July, as well as August, and
once every two weeks in April, September and
October, in the years 2007, 2008 and 2009.
The seedlings and saplings were removed and
determined according to Csapodý (1968)
and Muller (1978) with support of comparative
collection. The genets of rare and
protected plants were replanted and marked
with plastic rings and sticks. The nomenclature
of taxa follows Mirek et al. (2002). The
recruitment of species in permanent subplots
was characterized by mean cumulative
numbers of all taxa found in the three years
period. Each species which appeared in seedling
pool was attributed into ‘occurred’ or ‘not
occurred’ category in established vegetation.
S A
I II III IV
Fig. 1. The locality of the study area and experimental
design.

680
Kinga Kostrakiewicz
A list containing all taxa with presence/absence
data is given in APPENDIX I. Then,
the mean cumulative numbers of taxa found
and not found in the plant cover were calculated
for all particular subplots. Information
about seed weight of species growing in the
experimental plots was obtained from Seed
Information Database (Liu et al. 2008). Following
the paper of Kahmen and Poshold
(2008), seed mass was considered with three
categories: small ( 2.0 mg). A complete list of
species that appeared in the study plots with
their seed masses, is given in APPENDIX II.
Subsequently, the mean cumulative numbers
of seedlings of small-, medium- and largeseeded
species, which appeared in particular
subplots, were calculated.
The statistical analysis, done on untransformed
data, was based on nonparametric
Kruskal-Wallis test, which was applied to
examine whether there were significant differences
in mean number of taxa which appeared
in subplots with different size within
each patch. The chi-square statistics were used
to check whether there were significant differences
between subplots with different size,
within each patch, in average abundance of:
• species present and absent in established
vegetation
• seedlings of large-, medium- and smallseeded
species
4. RESULTS
4.1. The effect of size of gaps
on species recruitment
The greatest species abundance was
found in MC patch, while much lower levels
of recruitment were observed in GR and SA
sites. At all the patches the numbers of taxa
appearing in seedling pool declined significantly
with decreasing gap size. In MC patch
from 45.8 species in the largest gaps to 36.7
species in the smallest openings were recorded
(H = 23.99, P

The colonization of gaps in Molinietum caeruleae meadows
681
in plant cover, were found. In site GR from
11.8 to 14.7 taxa present in established vegetation
and from 14.1 to 19.1 taxa not observed
in plant canopy were recorded. In SA
locality from 11.1 to 13.9 species observed in
standing vegetation and from 4.9 to 7.4 new
colonizers were noted. The applied statistical
analysis confirmed that in openings with
different size created within the particular
patch, the recruitment of species present and
absent in established vegetation were quite
similar (Fig. 3).
4.3. The impact of gap dimensions
on colonization by small-, mediumand
large-seeded species
Irrespective of vegetation character, in the
seedling pool of each subplot the mediumseeded
species were represented most abundantly.
Additionally it was found, that with
augmentation of opening size the number
of seedlings of large-seeded species significantly
declined, while the abundance of individuals
of small-seeded taxa increased (Fig. 4).
The mean species number
The mean species number
50
40
30
20
10
0
50
40
30
20
10
0
I
I
II
II
MC
GR
III
III
χ 2 =0.035
IV
χ 2 =0.027
IV
The mean seedling number
The mean seedling number
120
100
80
60
40
20
120
100
80
60
40
20
N=3542
χ 2 =17.25**
N=2459
χ 2 =12.95*
The mean species number
50
40
30
20
10
0
SA
χ 2 =0.167
I II III IV
The mean seedling number
120
100
80
60
40
20
N=1360
χ 2 = 14.28**
- species absent in plant cover
- species present in plant cover
Fig. 3. The mean cumulative numbers of species
occurred in seedling pool present and absent in
plant cover in particular subplots in MC, GR and
SA patches in the years 2007–2009. There are not
significant differences among particular subplots
within each patch (χ test, df = 3).
MC – patch dominated by small meadow species,
GR – patch prevailed by large-tussocks grasses,
SA – patch overgrown by willows.
- small-seeded species
- medium-seeded species
- large-seeded species
Fig. 4. The mean cumulative numbers of seedlings
of small-, medium- and large-seeded species in
particular subplots in MC, GR and SA patches in
the years 2007–2009. Asterisks mean differences
statistically significant between subplots within
each patch (χ test, df = 6).
*P ≤ 0.05, **P < 0.01
MC – patch dominated by small meadow species,
GR – patch prevailed by large-tussocks grasses,
SA – patch overgrown by willows.

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Kinga Kostrakiewicz
In MC patch, in the largest openings, 48.4
seedlings of medium-seeded species, 35.0 genets
of small-seeded taxa and 19.0 individuals of
large-seeded species were noted. In the smallest
gaps 41.6 seedlings of intermediate-seeded
taxa, 24.1 individuals of large-seeded species
and 11.8 of small-seeded taxa were found (χ
test = 17.25, P

The colonization of gaps in Molinietum caeruleae meadows
683
ristic model developed by Eriksson and Jakobsson
(1998), based on a presumed tradeoff
between seed size and seed number, and on
a negative relationship between seed size and
recruitment of seedlings. Authors highlighted
that plants either produce few, large seeds, each
with a high probability of successful establishment,
or they create many small seeds, with a
low possibility of recruitment. Therefore, species
with medium-sized seeds have the greatest
colonization ability and are should be most
abundant in plant cover of grasslands. Additionally
it should be stressed that observations
performed during present investigation bringing
evidence that the germination success of
small-seeded species augments, while that of
large-seeded species diminishes as the gap size
increases, do support previous investigations
carried out in grasslands (Burke and Grime
1996), and forests (Foster and Janson 1985,
van Ulft 2004 and cited literature). Above
mentioned authors claimed that in greater gaps
increases the risk of desiccation, which is a far
more important seed mortality agent for large
than for smaller seeded species. In minor openings,
seedlings from larger seeds have higher
survival rates because they are better provisioned
to competition from established plants.
Concluding, it should be pointed out, that
disturbances in vegetation canopy may be an
effective way for conservation management
of Molinietum caeruleae meadows. Although
it seams that the best results gives creation of
openings in patches prevailed by small-statured
species, also the gaps made in sites overgrown
by large-tussock grasses or willows
contribute well to recruitment process and
augmentation of species diversity. Additionally
it should be stressed, that different area
of gaps, promoting the recruitment of species
with distinct seed mass, is very important
source of heterogeneity in taxa composition.
ACKNOWLEDGMENTS: I would like to
thank Prof. dr hab. Anna Hillbricht-Ilkowska and
two anonymous referees and for constructive suggestions
and many helpful comments on an earlier
version of the manuscript.
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Received after revision April 2011

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APPENDIX I. The list of species appearing in gaps in patches dominated by small meadow species
(MC), prevailed by large-tussocks grasses (GR) and overgrown by willows (SA).
(P- species occurred in plant cover, A- species absent in plant cover).
Species MC GR SA Species MC GR SA
Achillea millefolium L. A P Lathyrus pratensis L. P
Angelica sylvestris L. A P P Leucanthemum vulgare Lam. P A P
Betonica officinalis L. (Trevis.) P A Lotus corniculatus L. P A A
Betula pendula Roth. P Lychnis flos-cucculi L. P A A
Caltha palustris L. A Lysimachia vulgaris L. P P P
Campanula patula L. A Lythrum salicaria L. A A
Cardamine pratensis L. P A A Molinia caerulea (L.) Moench P
Centaurea jacea L. P A Myosotis palustris (L.) L. Em. Rchb. P A
Cerastium holosteoides Fr. A Ononis spinosa L. A
Cirsium arvense (L.) Scop. A P A Parnassia palustris L. P A A
Crepis paludosa (L.) Moench. A P P Plantago lanceolata L. A A P
Cruciata glabra (L.) Erhend. P A A Polygonum bistorta L. P P A
Daucus carota L. A P P Populus tremula L. P
Deschampsia caespitosa (L.) P.Beauv P P Potentilla erecta (L.) Raeusch. A P P
Dianthus superbus L. A P P Prunella vugaris L. A P A
Epilobium hirsutum L. A Ranunculus acris L. A P P
Filipendula ulmaria (L.) Maxim. A P A Ranunculus repens L. A P P
Filipendula vulgaris Moench. A A P Rumex acetosa L. A A P
Galium boreale L. P P P Sanguisorba officinalis L. P P P
Galium uliginosum L. A A A Selinum carvifolia (L.) L. P P P
Galium verum L. A A P Serratula tinctoria L. P P P
Gentiana pneumonanthe L. P A P Stellaria graminea L. P P P
Geranium pratense L. A A P Succisa pratensis Moench. P A P
Geum rivale L. A A Trifolium pratense L. A A A
Heracleum sphondylium L. A Trollius europaeus L. A
Holcus lanatus L. P Valeriana officinalis L. A
Inula salicina L. A P Vicia cracca L. A A
Iris sibirica L. P P A Viola palustris L. A

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APPENDIX II. The seeds mass (in grams) of species found in seedling pool in patches dominated by
small meadow species (MC), prevailed by large-tussocks grasses (GR) and overgrown by willows (SA)
(Liu et al. 2008).
Large-seeded species
species
Seed
mass
Medium-seeded species Seed
mass
Small-seeded species Seed
mass
Iris sibirica L. 15.8 Ranunculus acris L. 1.5 Inula salicina L. 0.45
Vicia cracca L. 14.7 Trifolium pratense L. 1.5 Leucanthemum vulgare Lam. 0.41
Lathyrus pratensis L. 12.0 Selinum carvifolia (L.) L. 1.49 Potentilla erecta (L.) Raeusch. 0.4
Betonica officinalis L. (Trevis.) 11.4 Cruciata glabra (L.) Erhend. 1.43 Galium uliginosum L. 0.35
Geranium pratense L. 9.0 Succisa pratensis Moench. 1.3 Myosotis palustris L. 0.35
Heracleum sphondylium L. 7.5 Cirsium arvense (L.) Scop. 1.3 Holcus lanatus 0.3
Ononis spinosa L. 5.14 Plantago lanceolata L. 1.3 Betula pendula Roth. 0.29
Polygonum bistorta L. 4.81 Caltha palustris L. 1.1 Stellaria graminea L. 0.27
Angelica sylvestris L. 2.74 Centaurea jacea L. 1.06 Deschampsia caespitosa (L.) 0.24
P.Beauv
Ranunculus repens L. 2.5 Valeriana officinalis L. 1.1 Achillea millefolium L. 0.2
Serratula tinctoria L. 2.38 Geum rivale L. 1.01 Lychnis flos-cucculi L. 0.19
Sanguisorba officinalis L. 2.1 Prunella vugaris L. 1.0 Cerastium holosteoides Fr. 0.18
Trollius europaeus L. 1.0 Lysimachia vulgaris L. 0.14
Daucus carota L. 1.0 Populus tremula L. 0.11
Lotus corniculatus L. 1.0 Dianthus superbus L. 0.1
Viola palustris L. 0.81 Epilobium hirsutum L. 0.1
Filipendula vulgaris 0.81 Gentiana pneumonanthe L. 0.05
Filipendula ulmaria (L.) 0.8 Parnassia palustris L. 0.03
Maxim.
Rumex acetosa L. 0.8 Campanula patula L. 0.02
Molinia caerulea (L.) 0.7
Moench
Lythrum salicaria L. 0.68
Galium boreale L. 0.64
Cardamine pratensis L. 0.6
Galium verum L. 0.58
Crepis paludosa (L.)
Moench.
0.57