Declining Diversity in Abandoned Grasslands of the
Carpathian Mountains: Do Dominant Species Matter?
Anna Mária Csergő1,3*, László Demeter2, Roy Turkington3
1 Department of Horticulture, Sapientia University, Târgu-Mureş, Romania, 2 Department of Environmental Engineering, Sapientia University, Miercurea-Ciuc,
Romania, 3 Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
Abstract
Traditional haymaking has created exceptionally high levels of plant species diversity in semi-natural grasslands of
the Carpathian Mountains (Romania), the maintenance of which is jeopardized by recent abandonment and
subsequent vegetation succession. We tested the hypothesis that the different life history strategies of dominant
grasses cause different patterns of diversity loss after abandonment of traditional haymaking in two types of meadow.
Although diversity loss rate was not significantly different, the mechanism of loss depended on the life history of
dominant species. In meadows co-dominated by competitive stress-tolerant ruderals, diversity loss occurred following
the suppression of dominant grasses by tall forbs, whereas in meadows dominated by a stress-tolerant competitor,
diversity loss resulted from increased abundance and biomass of the dominant grass. We conclude that
management for species conservation in abandoned grasslands should manipulate the functional turnover in
communities where the dominant species is a weaker competitor, and abundance and biomass of dominant species
in communities where the dominant species is the stronger competitor.
Citation: Csergő AM, Demeter L, Turkington R (2013) Declining Diversity in Abandoned Grasslands of the Carpathian Mountains: Do Dominant Species
Matter? PLoS ONE 8(8): e73533. doi:10.1371/journal.pone.0073533
Editor: James F. Cahill, University of Alberta, Canada
Received April 11, 2013; Accepted July 22, 2013; Published August 27, 2013
Copyright: © 2013 Csergo et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The project was funded by DG Environment through the European Forum on Nature Conservation and Pastoralism and Barbara Knowles Fund,
in collaboration with the Pogány-havas Association. The funders had no role in study design, data collection and analysis, decision to publish, or
preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: csergo.anna.maria@gmail.com
Introduction
species may have higher impact on ecosystem functions than
the community diversity itself (“mass ratio” versus “species
diversity” hypotheses [8,11]). In spite of our growing knowledge
of these processes, the effects of dominant species on diversity
loss from these extremely diverse, now abandoned meadows,
has received little study [12].
In empirical studies it is difficult to separate the effects of
dominant species on diversity from that of external conditions,
because dominance itself is a reflection of the environment and
disturbance events [13,14]. Consequently, when subjected to
similar disturbance regimes such as mowing, the diversity of
two mature plant communities should diverge depending on the
identity and abundance of the dominant species [12] and
abiotic conditions [15] (but see 16,17 for the importance of
regional species pools and land use history).
It is widely acknowledged that mowing increases levels of
plant species diversity [5] by altering the balance of
competition-colonization processes [13,14,18], niche overlap
[19] and abiotic conditions [20]. Nevertheless, very little
research has focused on the differences in species diversity
induced in mowed grasslands by functionally different dominant
species [21]. Conversely, cessation of mowing reverses the
Traditional landscapes are currently becoming a focus of
biodiversity
conservation
efforts
[1].
Among
them,
anthropogenic temperate grasslands attain global plant species
maxima at scales ≤50 m2 [2]. Such high levels of diversity
evolved during extended periods of traditional small-scale
farming practices, but have been lost over the last century in
most of Europe because of major socio-economic changes and
unsustainable land use policies and practices. In the
Carpathian Mountains of Eastern Europe, abandonment of
traditional land use is rather recent, and abandoned grasslands
are only now reverting to forests after a long period of arrested
succession [3,4]. Much research effort is being focused on
understanding the reasons for the high vascular plant diversity
in traditionally managed meadows and the major species loss
following abandonment [5]. Studies in various habitat types
have shown that the identity of dominant species is critical to
species diversity [6], compositional stability [7] and ecosystem
functions [8]. The identity of dominant species may affect
species establishment [6], species loss [9] and compensation
for loss [10]. Moreover, the relative dominance of a single
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Diversity Loss in Abandoned Hay Meadows
processes that cause high diversity and leads to species
decline [22]. Usually, it is the gradually decreasing evenness of
species in communities that increases the extinction risk [23].
Nonetheless, if the dominant species of two mature
communities belong to different functional groups, unequal
shifts in dominance and species loss rate can be expected.
Here we report the results of a study carried out in two types
of hay meadow in the Carpathian Mountains. One is codominated by either Festuca rubra or F. nigrescens with
Agrostis capillaris (Fescue meadows) and the other is
dominated by Brachypodium pinnatum (Tor Grass meadows).
These species are functionally different because Festuca spp.
and A. capillaris develop small tussocks and thin stolons,
whereas Brachypodium pinnatum develops only extravaginal
tillers and strong belowground stolons [24]. According to
Grime’s [13,24] classification of established life history
strategies, Festuca spp. and A. capillaris are competitive
stress-tolerant ruderals (CSR), whereas Brachypodium
pinnatum is a stress-tolerant competitor (CS). Therefore we
tested the following hypotheses: 1. Species diversity will
decline in abandoned meadows regardless of meadow type,
because the species-rich state had been previously created
and maintained by mowing. 2. The abundance of dominant
grasses will increase less (or will decrease) in Fescue- than
Tor Grass meadows following abandonment because Festuca
spp. and Agrostis capillaris are weaker competitors than
Brachypodium pinnatum. 3. Because Festuca spp. and
Agrostis capillaris are weaker competitors, diversity loss
following abandonment will be significantly slower in Fescuethan Tor Grass meadows. As a secondary objective, we tested
whether abiotic conditions will lead to a higher variability of
diversity patterns that would be generated by abandonment
and meadow type alone.
The life history strategy of dominant species was an
important driver of species depletion in the studied abandoned
hay meadows. This confirms the deterministic nature of
species loss and carries implications for managers of traditional
agricultural landscapes.
Figure 1. Map of the research area in the Carpathian
Mountains (46°41’ N, 25°94’ E). The left panel indicates the
geographic position of the five sampling sites within the
Carpathian Mountains in Romania, Eastern Europe. The right
panel shows the approximate area sampled at each site.
Legend: 1 – Somlyó/ Șumuleu (SOM), 2 – Csomortán/ Șoimeni
(CSOM), 3 – Kolos/Kolos (KOL), 4 – Pogányhavas/Muntele
Păgân (POG), 5 – Jávárdi/Iavardi (JÁV).
doi: 10.1371/journal.pone.0073533.g001
Site description
The study was conducted in the Ciucului Mountains of the
Southeastern Carpathians (46°41’ N, 25°94’ E), in the historic
province of Transylvania in Romania, at altitudes between
749–1328 m (Figure 1). The climate is boreal-mountainous and
average total annual precipitation ranges between 580–1200
mm. Hay meadows are a dominant landscape feature, and
there is high variation of land use and topoclimatic conditions in
the area. Meadows are traditionally mown by hand using a
scythe. Sheep may temporarily graze the meadows at least
once a year (mostly in autumn). The steep foothills were
probably terraced in the Middle Ages as in other areas of
Romania [25], and the process continued in the 18th century.
Terraces were ploughed until the second half of the 20th
century, when they were abandoned for hay making. Since the
breakdown of socialist land use policies in the late 1980s, large
grassland areas including terrace slopes have been
abandoned, and large parts of the landscape currently
experience secondary succession [3]. The time since
abandonment in the studied plots was between one and five
years based on interviews with land-owners and on tree ring
counts.
Methods
Ethics statement
Our study was carried out entirely on private lands. We
sampled the vegetation on several different farms, where
landowners of these traditionally managed grasslands were at
ease with giving permission to work. On a few occasions we
did encounter red listed species, but there is no formal
mechanism in Romania for getting permission to study such
species outside protected areas. However, our study was
purely observational and nondestructive, so when we did
encounter rare species they were merely recorded along with
all other species in plots. In addition, in all sites at some time
during the growing season the farmers used to mow these
grasslands (along with the rare species), which is a part of the
long-term management practices that have occurred in these
areas.
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Dominant species
Festuca spp. and A. capillaris are much weaker competitors
than B. pinnatum, because B. pinnatum has a competitive
index (calculated from differences in height, growth form and
yearly accumulation of litter) of 7-7.5, while the other three
species each have a competitive index of 3.5 [24,26]. Festuca
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Diversity Loss in Abandoned Hay Meadows
spp. and A. capillaris have wider ecological tolerance than B.
pinnatum, but B. pinnatum is more successful than Festuca
spp. in drier conditions [27]. Both Fescue- and Tor Grass
meadows are widespread in hill and mountain areas of the
Carpathian Basin, and develop mature equilibrial structure
maintained by traditional management. In the Carpathian
Mountains, Tor Grass meadows are less common at high
elevations than on foothills and naturally occur at forestgrassland ecotones and following clear-cutting of forest. These
Tor Grass meadows are gradually replaced by Fescue
meadows under mowing. When managed, both meadow types
have high levels of diversity and consequently are protected in
Europe [28]. The nomenclature of species follows [29].
missing mown Tor Grass meadows in one locality (JÁV) and
because two sites had either only Fescue (POG) or Tor Grass
(CSOM) meadows, and consequently in this first exercise we
followed a complete randomized design in which sites were
used as replicates instead of blocks. Land use and dominant
species were used as fixed effects, and replicates were
introduced as random effects to control for variability among
sites. Residuals were checked for normality (KolmogorovSmirnov test) and homoscedasticity (Bartlett test). Subsequent
pairwise comparisons were performed using Bonferronicorrected t-tests. The model was compared with an Analysis of
Covariance (ANCOVA) to factor out existing differences due to
abiotic site conditions. In addition to elevation, one of the
following topoclimatic parameters: slope, potential direct
incident solar radiation (PDIR) or heat load (HL) was chosen
based on the strongest linear relationship with the dependent
variables. Because HL was highly correlated with PDIR
(Pearson’s ρ=0.820, p<0.001), this variable was abandoned in
subsequent analyses. The relationships between species
richness and species evenness were analyzed for both
meadow types using Pearson correlations.
To evaluate whether abandonment differentially affected
abundance of the two dominant species, a one-way ANOVA
was conducted on each meadow type separately, following a
randomized complete block design. First, percentage cover of
dominant species was standardized by total vegetation cover
within a plot. The relative cover resulted was used as a
dependent variable, land use as fixed effect, and four (Fescue)
and three (Tor Grass) sites were used as blocks. Residuals
were checked for normality and homoscedasticity and
transformation of the percentage cover values was not
required. For Fescue meadows, the abundance of the
codominant A. capillaris was added to the abundance of
Festuca spp. to compute the final cover values of dominant
species. Subsequent pairwise comparisons were performed
using Bonferroni-corrected t-tests. To factor out confounding
effects of the environment, the abiotic parameters were
included as covariates in additional ANCOVAs, similarly to the
first test.
To investigate how abundance of the two species impacted
diversity relative to abiotic factors, partial regressions were
produced separately for each meadow type (partial statement,
multiple linear regression models, SAS; NFescue=67, NTor
Grass=52). The partial regressions were built using residuals of
diversity estimates and of dominant species relative cover.
Residuals of diversity estimates were saved from a full multiple
linear regression model where the relative cover was omitted
and explanatory variables were elevation, PDIR and slope.
Residuals of dominant relative cover were saved from a
second full model where the dominant relative cover was
regressed on the remaining regressors.
Sampling procedure
Because abandonment was not studied experimentally, we
conducted interviews with land-owners and a posteriori
statistical analyses to detect site-specific reasons for
abandonment. Generally, abandonment at the studied sites
appeared to be driven by random factors which perhaps related
to farmer’s individual choices rather than to distance from the
villages, hay quality or site ecological conditions (unpublished
results).
Five sites were chosen to account for the high topographic
variability of the study area: two lower elevation (749-818 m)
sites, (Somlyó/Șumuleu (SOM), Csomortán/Șoimeni (CSOM)),
and three at higher (942-1328 m) elevations, Kolos/Kolos
(KOL), Jávárdi/Iavardi (JÁV) and Pogányhavas/Muntele Păgân
(POG) (Figure 1). We wished to sample combinations of two
types of land use (mown and abandoned) and two dominant
species (Fescue meadows and Tor Grass meadows), but
because all four combinations did not occur at every site, four
sites were chosen to represent each dominant grass: SOM,
KOL, JÁV and POG for Fescue meadows, and SOM, KOL,
JÁV, CSOM for Tor Grass meadows. Each site had both mown
and abandoned meadows, except JÁV where all Tor Grass
meadows were abandoned. Low elevation Tor Grass meadows
were situated exclusively on terraced foothills, where terraces
were mown and terrace slopes were previously mown, now
abandoned. To account for environmental heterogeneity within
each meadow type, the available combinations were
subsampled with 4 to 13, randomly placed 1 m2 subplots,
totaling 128 subplots. The percentage cover of each vascular
plant species and of total vegetation was estimated visually in
each subplot. Geographic coordinates, elevation, slope angle
and aspect were extracted from GPS records and topographic
maps (Vegetation data are provided in Table S1).
Data analysis
Species diversity was measured as species richness
(number of species / 1m2 subplot) and species evenness (Evar
[30]). Potential direct incident solar radiation (PDIR) and heat
load (HL) were computed from slope angle, aspect and
geographical coordinates, following [31]. A two-way Analysis of
Variance (ANOVA) was used to obtain mean differences in
diversity estimates between the four combinations of land use
and dominant species (i.e., meadow types) (procglm in SAS
9.2 [32]). The dataset was slightly unbalanced because of
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Results
Effect of abandonment and meadow type on diversity
There was a significantly lower species richness in
abandoned than mown meadows (29.6±1.9 vs. 36.6±1.9
species, p=0.023) and a marginally significant higher species
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Diversity Loss in Abandoned Hay Meadows
The relative cover of dominant grasses averaged over
mowed and abandoned meadows was similar in the two
meadow types (mean ±1SE=41.6%±2.4 in Fescue-, and 39.5%
±3.0 in Tor Grass meadows).
richness in Fescue- than Tor Grass meadows (35.4±1.8 vs.
30.8±1.9 species [means ±1SE], p=0.109) (ANOVA,
F[14,113,0.05]=9.53, pmodel<0.001). Elevation had a significant effect
on species richness, with 36.2±0.7 species in high elevation-,
and 28.0±1.3 species in low-elevation meadows (means ±1SE;
p=0.051, F[16,111,0.05]=8.73, p<0.001. There was a marginal
interaction of PDIR with replicates (sites), with low elevation
abandoned Tor Grass meadows (terrace slopes) having higher
PDIR and lower richness (19.6±1.2) than their mowed Tor
Grass counterparts on terraces (33.0±2.1) (means ±1SE;
p=0.102, ANCOVA). Slope on its own had no significant effect
on species richness (p<0.392) (ANCOVA, F[15,112,0.05]=9.19,
pmodel<0.001). Due to a significant variation of species richness
across sites (p<0.001) (Figure 2A,B), no significant land use ×
meadow type interaction was detected in either the ANOVA or
ANCOVA model (p>0.270). Despite this non-significant result,
species richness in abandoned versus mowed meadows was
lower with an average of only 4.6 species/m2 (12.0%) in
Fescue meadows, compared to 8.9 species/m2 (26.9%) in Tor
Grass meadows (ANCOVA-corrected means).
Only meadow type had a significant effect on species
evenness (pmeadow type=0.021, pland use=0.445), with slightly higher
values in Fescue- than Tor Grass meadows (0.27±0.007 vs.
0.24±0.008) (means ±1SE) (ANOVA, F[14,113,0.05]=2.36, pmodel
=0.007). There was no significant interaction of abiotic
variables with either (i) site (p>0.270, ANCOVA) or (ii) species
evenness (p>0.121) (ANCOVA, F[16,111,0.05]>2.18, pmodel<0.05).
Due to a significant variation of evenness across sites
(p<0.048) (Figure 2C,D), no land use × meadow type
interaction was detected in either the ANOVA or ANCOVA
model (p>0.467) (The SAS code and detailed results for this
section are provided in Material S1).
The relationship of species richness to species evenness
was positive and significant only in Tor Grass meadows
(Pearson’s r=0.190, p=0.123 in Fescue-, and r=0.569, p<0.01
in Tor Grass meadows).
Effect of dominant species cover on diversity
After accounting for the effect of environmental parameters
(elevation, slope, PDIR), the relative cover of Festuca spp. with
A. capillaris had a weak positive effect, and B. pinnatum
relative cover had a stronger negative effect on species
richness (Figure 3A,B). In Fescue meadows, dominant grass
relative cover had no effect on species evenness (Figure 3C),
whereas in Tor Grass meadows the relationship was negative
and significant (Figure 3D).
Discussion
The mountain hay meadows in the Carpathian Mountains are
a highly diverse anthropogenic grassland ecosystem that is
threatened by cessation of traditional management. Averaging
40.5 plant species/m2 at local (site) level and reaching 50
species/m2 (likely even more following additional surveys in
spring), these hay meadows are among the most diverse seminatural grasslands in Europe, which average 40.4 species/m2
and have up to 79 species/m2 [2 and references therein]. Longterm moderate disturbance (mowing and seasonal light
grazing) has caused convergent and high levels of diversity in
both Fescue and Tor Grass meadows. The cause of species
depletion following abandonment is strongly dependent on the
life history strategy of the dominant species, which confirms the
deterministic nature of species loss [9]. In meadows codominated by the CSR strategists and weaker competitors,
Festuca spp. and A. capillaris, diversity loss occurs because
the dominant grasses are suppressed by forbs such as
Laserpitium latifolium and Trollius europaeus. In meadows
dominated by the CS strategist and stronger competitor B.
pinnatum, diversity loss results from increased abundance and
biomass of dominant species.
Effect of abandonment on dominant species cover
The summed relative cover of Festuca spp. with A. capillaris,
and of B. pinnatum was not significantly different in abandoned
versus mown plots (36.8%±4.9 vs. 47.6%±4.5, p=0.207 and
49.9%±7.2 vs. 33.6%±6.9[means ±1SE], p=0.245 respectively)
(ANOVA, FFescue[7, 59, 0.05]=3.08, pmodel=0.008; FTor Grass[5, 46,
0.05]=4.51, pmodel=0.002). The differences were dampened by
land use × site interactions in both meadows (pFescue=0.100, pTor
Grass=0.053) (Figure 2E,F). In Fescue meadows there was a
combined interaction of elevation and slope with sites
(p<0.087), high-elevation meadows having steeper slopes and
lower dominant grass cover than lower elevation meadows
(means ±1SE = 38.9±2.6 vs. 55.5±4.6). No significant
interaction of either abiotic parameter with site existed in Tor
Grass meadows (p>0.321). Neither elevation, PDIR or slope on
their own had an effect on the relative cover of the dominant
grass in either land use model (p>0.335) (ANCOVA FFescue[8, 58,
0.05]<3.91, pmodel<0.05; FTor Grass[6, 45, 0.05]<2.67, pmodel<0.05) (The
SAS code and detailed results for this section are provided in
Material S2).
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Effect of abandonment on diversity
Our results support hypothesis 1 i.e, species diversity
declined in abandoned meadows regardless of meadow type.
Following only one to five years of abandonment, grassland
diversity declined by 12 and 27% in Fescue- and Tor Grass
meadows respectively, which is a worrying loss. Similar
depletion rates were reported from other previously mown and
abandoned grasslands (e.g. 21-57% loss in 10-20 years [33]).
Although we expected that species loss would be driven by
decreasing evenness as in most abandoned meadows [23], the
significant driver of evenness patterns was the meadow type,
and not abandonment. With a similar overall abundance of
dominant grasses in the two meadows, a lower evenness in
Tor Grass meadows may be explained by the fewer and less
abundant species, which is an intrinsic feature of this plant
community. The slight decrease of evenness following
abandonment was caused by increasing abundance of B.
pinnatum in Tor Grass meadows and increased cover of a few
tall forb species in both meadows (e.g. Laserpitium latifolium,
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Diversity Loss in Abandoned Hay Meadows
Figure 2. Mean (± 1SE) species diversity and dominant grass relative cover in combinations of meadow types and land
use regimes. Diversity is measured as species richness (top panels) and species evenness (middle panels). Significant differences
(ANOVA, post-hoc Bonferroni-corrected pairwise t tests; p<0.05) between mown and abandoned meadows are marked with an
asterisk. Low elevation sites are shown in black. Abbreviations: SOM – Somlyó/ Șumuleu, CSOM – Csomortán/ Șoimeni, KOL –
Kolos/Kolos, POG – Pogányhavas/Muntele Păgân, JÁV – Jávárdi/Iavardi.
doi: 10.1371/journal.pone.0073533.g002
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Diversity Loss in Abandoned Hay Meadows
Figure 3. The relationship of dominant grass cover to species diversity. Partial regressions of the dominant grass relative
cover and species richness (top panels) and species evenness (bottom panels) in two meadow types, after accounting for the effect
of abiotic variables.
doi: 10.1371/journal.pone.0073533.g003
Effect of abandonment on dominant species cover
Trollius europaeus, Salvia pratensis, Chrysanthemum
corymbosum, Betonica officinalis), a pattern often reported in
early stages of abandonment [34]. Species depletion from
abandoned meadows is to be expected because mowing
prevented the expression of competitive dominants and
maintained the grasslands in a relatively stable species-rich
state. With abandonment there is a reversion towards a
species-poorer mixed temperate forest, a cycle often seen in
periodically perturbed ecosystems [35]. Bushes of Salix
triandra and saplings of Populus tremula and Picea abies were
common in our abandoned meadows, and young poplar stands
can dominate the meadows very quickly (pers. obs.).
Nonetheless, over a short abandonment period a general
decrease of diversity is not necessarily accompanied by a
declining number of species having a high conservation value.
In Fescue grasslands for example, a similar number of redlisted species were found under both management regimes,
and some of the species were unique to abandoned meadows
(unpublished results).
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Our results support hypothesis 2 i.e, the abundance of
dominant grasses increase less or even decrease in meadows
dominated by weaker competitors, because the weak
competitors Festuca spp. and A. capillaris had lower cover,
whereas the stronger competitor B. pinnatum had higher cover
in abandoned compared to mowed meadows.
When mown, all studied species lose significant above- and
belowground biomass [36,37]. However, Festuca spp. and A.
capillaris are more resistant to defoliation [38], can develop
compensatory growth responses to clipping [39] and
disturbance can enhance their recruitment [40], making them
good mowing indicators [41]. However, despite a high clonal
mobility, F. rubra is sensitive to shading and the identity of its
neighbors [42] and is disadvantaged when overgrown by a
herbaceous canopy. Therefore, in abandoned meadows where
light becomes limiting, Festuca spp. is vulnerable to
displacement.
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Diversity Loss in Abandoned Hay Meadows
pinnatum are critical to species loss from Tor Grass meadows
following abandonment. Such fundamental differences among
dominant species may be important to conservation managers,
having the potential to predict the resistance or resilience of
local communities to diversity loss following abandonment
[45,48].
In contrast, B. pinnatum is larger than Festuca spp. and A.
capillaris and consequently is more vulnerable to nitrogen and
carbohydrate loss when mown. This is critical for regeneration
of species with underground rhizomes and stolons after
mowing because taller species are affected more than shorter
species [21,39]. Indeed, Pons et al. [43] and Bobbink and
Willems [44] showed that leaf nitrogen is concentrated in the
upper part of a B. pinnatum canopy and nitrogen loss is the
main cause of the species’ decline when mown. Following
cessation of mowing, B. pinnatum increased cover probably as
a response to release from mowing suppression, and due to its
ability to regenerate from belowground structures [36].
However, there were no overall significant quantitative changes
in abundance of either of the dominant grasses, presumably
because of the short time since abandonment.
Effect of environment on diversity
Abiotic conditions added high variability to the expected
diversity patterns. Species richness, evenness and dominant
species relative cover were all affected by significant
interactions with sites. Elevation had positive effect on species
richness with, for example, more endemic species added to the
regional pool. The Eastern Carpathian Mountains is a region of
high endemism [49] and most of these endemic species occur
in high elevation grasslands. Likewise, climate-driven
geographic distributions augmented diversity of other high
elevation grasslands such as those in the Appalachian
Mountains [50]. In addition, in high elevation Fescue meadows
on steeper slopes, dominant grasses had lower cover and all
other species higher cover than at low elevations. The effect of
slope angle is probably confounding with the distribution of
management regimes. Low elevation, less steep meadows are
close to human settlements and have probably been subjected
to a more intensive mowing regime, which is known to increase
Festuca spp. abundance and decrease diversity [41].
Therefore, moderate management regimes of high elevation
meadows are better alternatives of land use practices in terms
of plant diversity [51].
High solar radiation in abandoned Tor Grass meadows on
terrace slopes was related to decreased levels of diversity. This
effect often occurs under low moisture conditions on steep
slopes associated with high solar radiation [52]. In abandoned
meadows subjected to drought conditions, subordinate species
have first to pass through abiotic filters, and then compete with
dominant species for nutrients or space [53], which strongly
reduced diversity in our system. However, terrace slopes
allowed rare stress tolerators with low competitive ability (e.g.
Aster amellus, Linum hirsutum) to persist within the abandoned
grasslands. Consequently, despite producing lower local
diversity, particular topographic conditions may increase the
landscape-level species pool of hay meadows and are valuable
for conservation [54].
Effect of dominant species on diversity
Hypothesis 3 is rejected because diversity loss following
abandonment was not significantly lower in meadows
dominated by the weaker competitors Festuca spp. and A.
capillaris. Although the decline of species richness and
evenness in Fescue meadows was, on average, less than in
Tor Grass meadows following abandonment, differences were
not significant because of high landscape-level variability of
diversity patterns in both meadow types.
However, opposite effects of abandonment on dominant
grass abundance triggered different mechanisms of species
loss. In mowed Fescue meadows, reduced competition and
lower niche overlap increased species richness while at the
same time enhanced vegetative propagation and seedling
recruitment of dominant species [19,40,42]. Following
abandonment, increasing competition for light reversed the
relative importance of these mechanisms and caused both
species richness and dominant species cover to decline.
Evenness did not decrease substantially because dominant
grasses were overtopped by a few stronger competitive forbs
(e.g. Trollius europaeus). Such a rapid turnover of functional
groups is specific to species-rich communities with even
dominance distributions [45] and in our system seems to be
dependent upon management regime (i.e., mowing or
abandonment). Consequently, in Fescue meadows the effect of
dominant grasses on species loss following abandonment
appears to be very weak. Not surprisingly, species richness is
independent of species evenness.
In contrast, abandoned Tor Grass meadows lost more
species than Fescue meadows at all sites. The difference may
partly be attributed to higher B. pinnatum cover, which concurs
with current evidence on compositional instability of abandoned
Tor Grass meadows [36]. The causes of the negative impact of
B. pinnatum on diversity may include its high competitive
superiority and ability to slow down species turnover [46,47].
However, the abundance of B. pinnatum generally increased
very little with abandonment, and other factors such as copious
litter accumulation (pers. obs.) might have had a stronger
negative impact on diversity [46]. As expected, the lower
species richness of Tor Grass meadows was related to
reduced community evenness, similarly to other dominant
species [23]. Consequently, abundance and biomass of B.
PLOS ONE | www.plosone.org
Conclusions
In abandoned hay meadows of the Carpathian Mountains,
the life history strategy of the dominant species is an important
driver of species loss. This result is critical for conservation and
for land managers of traditional agricultural landscapes. In
communities dominated by weak competitive grasses,
maintaining high plant diversity is not achieved by manipulating
dominant grass cover, but rather, by preventing species-poor
assemblages of tall forbs from becoming dominant on the long
run. In contrast, in communities dominated by competitive
grasses, manipulation of dominant species’ abundance and
biomass are both crucial to the maintenance of high diversity.
Despite a significant loss of plant diversity, short-term
7
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Diversity Loss in Abandoned Hay Meadows
(DOCX)
abandonment episodes may not be entirely detrimental to the
grassland ecosystems and benefits to rare plant preservation
or invertebrate communities (as in [55]) should be more closely
examined. In addition, high landscape-level heterogeneity may
produce site-specific diversity patterns in both types of
grasslands, which highlights the complexity of factors that
modulate coexistence processes at a regional scale and the
need to adjust the management practices accordingly.
Table S1. Vegetation data in 1 m2 subplots sampled in two
different types of meadow under mowing and
abandonment in the Carpathian Mountains.
(XLS)
Acknowledgements
We thank Valérie Lemay, Abdul-Azim Zumrawi and Tony
Kozak for help with research methodology and data analysis,
and Bill Harrower, Zsolt Molnár and Eszter Ruprecht for
discussions. Field assistants were Alpár Kelemen and
Gabriella Péter. We are grateful to the two reviewers whose
comments have considerably helped us improve this
manuscript.
Supporting Information
Material S1. SAS code and table of results for the ANOVA
and ANCOVA models testing for the effect of
abandonment and meadow type on diversity in the
Carpathian Mountains.
(DOCX)
Author Contributions
Material S2. SAS code and table of results for the ANOVA
and ANCOVA models testing for the effect of
abandonment on dominant species cover in two types of
meadow in the Carpathian Mountains.
Conceived and designed the experiments: AMC LD. Performed
the experiments: AMC LD. Analyzed the data: AMC RT.
Contributed reagents/materials/analysis tools: RT. Wrote the
manuscript: AMC RT.
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