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SHORT COMMUNICATION
Reintroduction of a Rare Plant (Gladiolus
imbricatus) Population to a River Floodplain—How
Important is Meadow Management?
Ülle Jõgar1,2 and Mari Moora1
Abstract
In seminatural grasslands, the success of reintroduction of
locally extinct rare plant species may depend on the ambient management regime. We aimed to study to what
extent the success of the restoration of a rare species
(Gladiolus imbricatus) depends on management conditions. A management experiment with traditional cutting
by scythe and hay removal, mowing (machine cutting and
hay removal), mulching (machine cutting without hay
removal), spring burning, and unmanaged control, combined with reintroduction of seeds of Gladiolus, was conducted in an Estonian flooded meadow in which the
species had become extinct. Seeds were reintroduced in
2003 in all management treatments and populations monitored until 2006. Mulching, mowing, and traditional man-
Introduction
The main factors influencing the restoration of seminatural grassland are site conditions and availability of suitable
plant propagules. In fragmented landscapes, rare plant
species are often characterized by limited dispersal,
recruitment, and persistence (Poschlod & Bonn 1998;
Eriksson & Ehrlen 2001), and their arrival probability is
low (Zobel et al. 2006). In addition, grassland species may
differ in their sensitivity to management conditions, especially in the early establishment stage, which may influence the success of restoration (Austerheim & Eriksson
2003; Moora et al. 2003; Lindborg 2006).
In Estonia, only 12,500 ha of flooded meadows existed in
the early 1990s compared to 83,000 ha in 1939 (Leibak &
Lutsar 1996). As in the rest of Europe, increased attention
has been paid to the conservation of seminatural grasslands
in Estonia (Kukk & Kull 1997). However, the status of populations of rare plant species has rarely been addressed.
1
Institute of Ecology and Earth Sciences, Department of Botany, University of
Tartu, Tartu 51005, Estonia
2
Address correspondence to U. Jõgar, email [email protected]
Ó 2008 Society for Ecological Restoration International
doi: 10.1111/j.1526-100X.2008.00435.x
382
agement resulted in the greatest establishment, whereas
the subsequent mortality was not influenced greatly by
management regime. The population started to increase
in mulching treatment in the third season due to vegetative growth. The results indicate that the establishment
of G. imbricatus is primarily seed limited under current
conditions, whereas favorable management significantly
enhances establishment in a river floodplain meadow.
Successful restoration depends on seed addition and
proper grassland management—mowing to a height of
approximately 15 cm and mulching.
Key words: dispersal limitation, establishment and survival of seedlings, grassland management, rare species,
restoration, sowing.
Gladiolus imbricatus is a spectacular species that was
formerly present in managed flooded meadows, but
became locally extinct in most places. In the current study,
we attempted to estimate the effect of different grassland
management regimes on the reintroduction of the locally
extinct population of G. imbricatus to a river floodplain
meadow. In order to determine the optimal grassland
management to enhance recolonization of this endangered species, a field experiment was established in a formerly irregularly managed flooded meadow in Estonia.
Methods
Gladiolus imbricatus L. ([Iridaceae] Moora et al. 2007 for
details) is a declining species in Europe (Schnittler & Günther 1999) and red listed in Estonia (Lilleleht 1998). The
seeds are relatively large (1.8 mg) and one plant produces
200–400 seeds, which germinate well after winter. The
seeds lack efficient dispersal syndromes and the species is
not represented in the seed bank (Wagner et al. 2003).
The experimental research (cf Fig. 1 for design) was
performed on a floodplain meadow (96 ha) in Soomaa
National Park (58°269280 N; 25°59500 E), Estonia. The
meadow was annually mown and hay removed until the
Restoration Ecology Vol. 16, No. 3, pp. 382–385
SEPTEMBER 2008
Reintroduction of G. imbricatus
Figure 1. Experimental design at Soomaa flooded meadow. Three homogeneous sampling areas (sites 1–3) were selected at meadow in 2000.
Within each area, five 10 x 20–m plots were assigned randomly one of five experimental treatments: traditional—cutting hay with a scythe (to
a height of approximately 5 cm) and removal of the hay; mulching—machine cutting (to a height of approximately 15 cm) without removal of the
hay; mowing—cutting with a machine with removal of hay; burning in April; and unmanaged control. The cutting took place in early August. Four
study squares of 2 x 2 m were established in each experimental plot. In September 2003 study squares received 50 Gladiolus imbricatus seeds.
Seedlings were counted in October 2003, May, June, and August 2004, June 2005, and July 2006 (Fig. 2).
late 1980s and irregularly mown between 1990 and 2000.
Management experiment was started in 2000 and sowing
of Gladiolus was carried out in September 2003.
General linear models (GLM) mixed model analysis
with Tukey Honestly Significant Differences (HSD) post
hoc multiple comparison test with p 0.05 (StatSoft
2001) was applied to study the effect of management on
seedling establishment and survival over three seasons
(cf Table 1).
Results
Establishment
There were significant differences between experimental
treatments (Table 1; Fig. 2a). The highest establishment
rate was recorded in the mowing and mulching, and the
lowest rates were recorded in burning and unmanaged
treatments. Establishment was significantly different with
time: fewer seedlings were recorded in May and in August
Table 1. Results of mixed model GLMs.
Establishment
Survival and Growth
Source of Variation
df
F
p Value
df
F
p Value
Treatment
Site (treatment)
Error
Time
Time 3 treatment
Time 3 site (treatment)
Error
4
10
45
2
8
20
90
10.41
1.45
<0.0001
0.189
4.85
2.87
0.004
0.03
10.73
3.45
1.55
<0.0001
0.002
0.08
4
5
30
2
8
10
60
3.73
4.77
2.25
0.03
0.0002
0.03
Effect of grassland management regime (treatment), sampling site (site), time and their interaction on the Gladiolus imbricatus establishment over first season (3
months) and survival and growth over three seasons. Repeated model design where time (month or year) was used as a repeated measures factor was applied. A sampling site with three levels in case of establishment data in 2004 and with two levels in case survival data (due to the destruction by spring flood in 2005 of one sampling
area) was included in to the model as a random factor. Treatment was nested within the site.
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Restoration Ecology
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Reintroduction of G. imbricatus
between the first and third season (p < 0.05). Interaction
between time and treatment was significant due to the
mulching treatment by which population size was significantly (p < 0.05) smaller after the first season but increased
during the third season (Fig. 2b).
Figure 2. Establishment of experimentally sown Gladiolus imbricatus
seedlings in first season (a), and survival and growth over 3 years (b).
Mulching—machine cutting and hay left in the field; mowing—machine
cutting and hay removed; traditional—cutting with scythe and hay
removed; unmanaged—no biomass removal; burning—burning in
April (burning was skipped in 2003 and 2005, when the spring flood
already began in March and lasted until mid-May).
compared to the June. Recordings in May and August were
not statistically different (p > 0.05), whereas seedling abundance in June was the greatest. Interaction between time
and treatment was significant. In the three cutting treatments, seedling abundance increased during the first half of
the growing season but remained unchanged in the unmanaged and burning treatments during the season (Fig. 1).
Survival and Growth
There were significant differences in survival and growth of
the experimental populations over three seasons (Table 1;
Fig. 2b). The population in the mowing treatment was significantly larger (p < 0.05) than the populations in unmanaged and burning treatment. There was a gradual decrease
of population sizes over time, differences were significant
384
Discussion
The reintroduction of Gladiolus imbricatus in the flooded
meadow community was successful—the seedlings established and survived over the three seasons in all management treatments. There were, however, clear differences
in the success of the reestablishment of target species
between management regimes.
Seedling establishment was most successful in the
mulching treatment. Litter has often been shown to have
a negative impact on seedling recruitment (Overbeck et al.
2003). However, the relationship between germination
success and litter presence/absence in a wet meadow might
be species specific (Kotorova & Leps 1999; Eckstein &
Donath 2005; Hölzel 2005). Species with large seeds tend to
react more positively to litter presence than species with
small seeds (Donath et al. 2006). Gladiolus imbricatus has
relatively large seeds and, like other large-seeded meadow
species, it benefited from mulching.
The relatively poor establishment of Gladiolus in the
scythe mowing treatment was somewhat surprising, as this
has been a traditional management regime for this type of
meadow. The cutting height—on average 15 cm by tractor
and 5 cm by scythe—might explain this result because
lower cut evidently results in higher evaporation, which
may lead to increased water stress for seedlings (Eckstein
2005). Hölzel and Otte (2004) showed that most floodplain meadow species need simultaneously light and high
moisture for germination and establishment.
Although different management regimes resulted in
clear differences in establishment of Gladiolus during the
first season, the survival of target plants over the 3 years
was less affected by management regimes. Earlier findings
on other wet meadows species also indicate differences in
safe site requirements for seedling establishment and survival of immature plants (Hitchmough 2003). Observations
of G. imbricatus in a coastal meadow (Moora et al. 2007)
showed, however, that mowing favors germination and
early establishment stages in the natural population as
well. We recorded an increase in the target plant population during the third year with the mulching treatment, due
possibly to daughter corm production by the sown plants.
In favorable conditions, daughter corm production starts in
the second season (Moora & Jõgar, unpublished data).
The results of this experiment indicate that seed limitation,
rather than microsite limitation, regulates the reestablishment of the local population of Gladiolus. In particular, we
argue that the arrival probability of G. imbricatus is very low
and the proper meadow management needs to ensure that
a few available diaspores have the highest possible rate of
establishment.
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Reintroduction of G. imbricatus
Implications for Practice
d Traditional management is not always better than
modern techniques therefore modern available techniques may be efficient restoration tools.
d Conservation and restoration activities in grasslands
should consider the low arrival probability of rare
species—sowing of formerly present rare species
should be considered as a restoration tool.
d In restoration and maintenance of rare species populations in flooded meadow communities cutting is
a key factor when recruitment from seeds is considered. An additional biomass removal may enhance
some species regeneration but large-seeded species
like Gladiolus imbricatus may favor mulching.
d Burning is not an efficient management tool in a wet
meadow compared with cutting.
Acknowledgments
The Estonian Science Foundation (5809) and Tartu University (TBGBO0553) financed the work. We are thankful
to the Soomaa National Park for their kind assistance in
the field, and to M. Zobel and R. Szava-Kovats, who commented on the first draft of the manuscript.
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