Phytocoenologia 35 (23) 171175 BerlinStuttgart, August 26, 2005
Vegetation and ecology of ephemeral wetlands 
an introduction
by Ulrich Deil, Freiburg i.Br. (Germany)
with 1 figure
Vegetation ecologists prefer to study plants in extreme environments, because
selective forces are strong and adaptations are more obvious than
under mesic conditions. Concerning the environmental factor "water",
most scientists cluster either to the "permanent wet group" or to the "dry
fraction". There is however a third, small party of colleagues dealing with
sites, which switch every year from the littoral to the terrestrial phase.
These habitats offer an extreme environment, too. Favourable edaphic conditions
exist only for a very short time of the growing season (during the
limosal ecophase) and year-to-year variability is high. It is a plant life between
inundation and desiccation, shifting periodically from flooding to
water shortage.
The aim of this thematic volume is to enhance the knowledge about the
fascinating ecosystem "ephemeral wetlands" and to compile studies from
all over the world (see Fig. 1), covering a broad spectrum of topics like
habitat typology, vegetation classification, seasonal and year-to-year dynamics,
ecophysiology of resurrection plants, seed banks, experimental approaches
for habitat restoration and conservation aspects.
The volume starts with a series of regional monographs, dedicated to
vegetation analysis and classification according to floristic similarity. Seasonal
wetlands are mostly linked to subhumid or semiarid conditions and
therefore are widespread in mediterranean climates. In the Neoarctis for
example, vernal pools and their flora have been considered as quite unique
to the State of California already in early papers. This claim is confirmed
by the contribution of Barbour and co-workers: Based upon a recently
sampled set of some hundred releve´s, they classify vernal pool vegetation
as a class of its own, restricted to the californian phytogeographical sector,
the Downingio bicornutae-Lastenietea fremontii. Pool depth and
inundation period are important differentiating environmental factors. The
plant cover of long submerged sites, floristically well characterised, is
grouped in the new order Lastenietalia glaberrimae.
The vegetation with small and short living wetland species in the Southwestern
corner of the Australian continent with annual rainfall of 500 to
1000 mm was studied by Pignatti & Pignatti. In 1994 they described the
class Centrolepidi-Hydrocotyletea alatae, endemic to SW Australia.
DOI: 10.1127/0340-269X/2005/0035-0171 0340-269X/05/0035-0171 $ 1.25
" 2005 Gebrüder Borntraeger, D-14129 Berlin  D-70176 Stuttgart
172 U. Deil
Fig. 1. Location of studies on ephemeral wetland vegetation included in the present
volume.
Based upon new data for the deserts of Western Australia, they now compare
the floristic composition of the periodic winter wet habitats under
subhumid conditions with those of episodic lakes and erratic flooded claypans
in an arid climate. The questions of convergent evolution, niche equivalence
and paleogeographic patterns between the Australis and the Western
Palearctis are discussed by comparing the genus and family spectra of
ephemeral wetlands in SW Australia with those in Central Italy.
A centre of diversity in ephemeral wetland vegetation and flora is the
western part of the Iberian Peninsula. This area is submitted to an atlantic
subtype of the mediterranean climate. Four Isoetes species (I. durieui,
I. histrix, I. setaceum, I. velatum) occur sympatrically there and Molina
studies the distribution patterns, ecological requirements and floristic combinations
of these Quillwort swards. Macroscale pattern varying with altitude
and slope aspect as well as microscale pattern depending on soil properties
are analysed by Rudner in the Serra de Monchique (Portugal) and
on the Campo de Gibraltar (Spain). Soil water potential, soil texture, soil
depth, air capacity, gravel import rate and the duration of seeping water are
some of the edaphic and hydrologic factors explaining the floristic patterns.
The relationships between land use and seasonal pond communities, as well
as their spatial and temporal distribution in relation to the flooding period,
have been investigated by Espi´rito Santo & Arse´nio in the Guadiana
Valley in Southern Portugal. Soil mobilisation by agricultural activities is a
human impact threatening these habitats.
Like in the mediterranean bioclimate, the oceanic parts of the temperate
climatic zone of Europe are richer in plant species and phytocoenoses than
the subcontinental regions. Poland constitutes the eastern periphery of the
173Vegetation and ecology of ephemeral wetlands  an introduction
distribution range of some taxa and syntaxa of the Isoeto-Nanojuncetea.
Popiela presents a synthesis of this class for the Polish territory and
raises the interesting question, whether the ecological and sociological amplitude
is reduced at the margins of the distribution range. Based upon the
observation, that secondary, man-made habitats become more and more
important to Eastern Europe, she formulates the hypothesis of an anthropogenic
expansion of these species.
At the Eastern fringes of the Eurasian continent, ephemeral wetland vegetation
on nutrient-poor soils is characterised by Eriocaulon species. Shimoda
gives a synthesis of the Eriocaulon hondoensis communities in
Japan. Numerous ponds have been constructed and managed for rice field
irrigation over hundreds of years. Their emerging shores offer a suitable
habitat for short living plants and amphibious perennials. Current changes
in rural societies and land management affect the pond environment, and
the ephemeral wetland specialists are becoming more and more outcompeted
by weedy annuals.
Until now, ephemeral wetlands have been poorly studied in tropical regions.
Müller & Deil present a synopsis of the plant communities of
seasonal ponds and semipermanent freshwater lakes in tropical West Africa.
Water depth, duration of flooding, and the trophic level of the soil and the
water body are the most important differentiating ecological factors. The
new class Rhamphicarpo fistulosae-Hygrophiletea senegalensis
combines the vegetation of amphibious environments with short-term inundation
at meso- and eutrophic sites. The communities of the Eriocaulo
pumili-Ophioglossion gomezianum colonise seasonal ponded rock
pools and depressions over lateritic crusts with oligotrophic conditions.
The latter communities belong to the class Drosero-Xyridetea. They
have close floristic and ecological relationships to ephemeral flush vegetation
on tropical inselbergs. Porembski & Watve outline the environmental
conditions and the flora of this habitat in tropical Africa and present initial
data for India.
Variations in time and vegetation dynamics are prominent characters of
temporary wet habitats. Two contributions are dedicated to these aspects,
both based upon permanent plot studies. Rudner investigated the seasonal
fluctuations and the year-to-year variations in two regions of the Iberian
Peninsula. He documents floristic composition, species diversity and soil
water content in the autumnal, spring and summer ecophases and analyses
the species turnover from Isoeto-Nanojuncetea to Helianthemetea
communities. The interannual fluctuations of the apparent vegetation equal
or surpass the intraannual species turnover, indicating the strong influence
of the temporal rainfall patterns on the germination of the annual satellite
species.
Vegetation dynamics on exposed bottoms of nursery fish ponds and
storage ponds in Southern Bohemia (Czech Republic) are analysed by
Sˇumberova´ and co-workers. The study attempts to explain the relationship
of vegetation cover and floristic spectrum on the one hand and abiotic
factors and management of the ponds on the other hand. According to the
174 U. Deil
type of summer drying and vegetation phase, spring and summer ponds
can be distinguished. Annual species with extremely short life cycles like
Coleanthus subtilis are restricted to nursery fish ponds, drained shortly
between April and June. In the storage ponds, dried mostly in summer
and early autumn, thermophilic annuals such as Lindernia dubia are to be
found.
Seasonal rock pools on granitic outcrops are carbon-limited ecosystems
in the aquatic phase and water-limited ecosystems in the terrestrial phase,
characterised further by an extreme nutrient shortage. One functional plant
type highly adapted to these stressful conditions are aquatic resurrection
plants. Heilmeier and his team study Chamaegigas intrepidus, the "fearless
giant dwarf". This poikilohydric cormophyte species is endemic in ephemeral
rock pools of the Namib desert. The dehydration tolerance mechanisms
of C. intrepidus are compared with the less dessication-tolerant
species Limosella grandiflora. Niche-partitioning and gene-flow between
subpopulations are further topics of this paper.
The importance of a large and persistent seed bank for the long term
survival of ephemeral wetland vegetation in highly disturbed habitats is
demonstrated by Bissels and co-authors. Seed bank analyses and inundation
experiments with soil samples from arable fields in the Upper Rhine
Valley in Germany are carried out, and apparent vegetation and underground
floristics are compared in primary vs. secondary habitats. Arable
fields are characterised by the predominance of mudflat species of the
classes Isoeto-Nanojuncetea and Bidentetea, and the additional occurrence
of weed species. Seed densities were exceptional high (a maximum
of 707,072 seeds m2
for Juncus bufonius).
Two contributions record results of restoration projects and management
experiments, carried out in different climatic zones. Rhazi and co-workers
study the consequences of shrub clearing at Roque-Haute, a former basalt
quarry in Southern France. Since the abandonment of the traditional grazing
regime, the pond floor was colonised by trees and by Typha angustifolia.
Removal of the high growing perennials initiates the re-establishment
of annual ephemeral wetland species from the seed bank and increases the
vitality of Isoetes setacea. The positive effects of litter removal and ribbon
cutting for the establishment of Isoeto-Littorelletea species in oligotrophic
heathland ponds in Northwestern Germany are proved by Urban
in long-term observations. Colonisation processes on bare soil were studied
for up to nine years.
In the final review article Deil tries to work out some common characters
of ephemeral wetland vegetation on the one hand, and to outline the variability
in flora, life forms and ecology in seasonal wet habitats on the other hand.
Beyond the aim to review the available literature and to summarise the present
state of knowledge, such a global perspective of ephemeral wetlands offers
the opportunity of asking for co-evolved adaptations of keystone species
and for niche-equivalent taxa in different floristic kingdoms.
The IAVS-Congress 2003 in Naples (Italy) was dedicated to the topic
"water and vegetation". In one section of this meeting, a series of lectures
175Vegetation and ecology of ephemeral wetlands  an introduction
related to ephemeral wetland vegetation were presented and most of these
contributions are included in this issue of PHYTOCOENOLOGIA. Some
other colleagues, studying temporarily ponded or flooded habitats, were
invited to participate, and to my great pleasure, they accepted. Last but not
least, I am very grateful to all authors for respecting the strict time schedule
in the publication process.
Freiburg, February 2005
Address of the author:
Ulrich Deil, Institute of Biology, Department of Geobotany, University of Freiburg,
Schänzlestrasse 1, D-79104 Freiburg i.Br., Germany. E-mail: ulrich.deil@biologie.uni-
freiburg.de