Mediterranean Temporary Pools Research Articles

Ecological niche differentiation among six annual Lythrum species in Mediterranean temporary pools.

The ecological niche defines the favourable range of a species in a multidimensional space of ecological factors that determine the presence and function of individuals. This fundamental concept in ecology is widely used to understand plant species coexistence and segregation. In this study, we test for ecological differentiation among six annual Lythrum species that are characteristic of temporary pools in the South of France, where they either coexist or occur separately. We first analysed the co-occurrence of species at two different geographical scales: cluster analyses of species presence in 10km grid cells and coexistence in 0.25 m2 quadrats within populations of each species. Second, for three to nine populations of each species, we quantified a range of biotic and abiotic parameters using point contacts and soil measurements in five 0.25 m2 quadrats per population. We performed PCA on all variables and analysed each variable separately to compare the ecological niche features of the six species. A phenological index was assessed for the plant community of each site. We detected highly localized niche differentiation in terms of soil pH (all species) and for a range of variables among pairs of species. The six species also showed marked differences in the flowering period relative to the mean and variability of flowering time in their local community. These fine-scaled niche differences are associated with phylogenetic distances among species and may contribute to species' coexistence. These results are integrated in a conservation management plan for the habitat of the rarest species in this group.

A history of discoveries and disappearances of the rare annual plant Lythrum thesioides M.Bieb.: new insights into its ecology and biology

ABSTRACT Mediterranean temporary pools are threatened ecosystems that host a unique plant community, mostly composed of annual species with large and long-lived seed banks. The longevity of their seed bank, the scarcity of their habitat, the small size of their populations and the low frequency of above-ground vegetation result in a low probability of detection of these species. The discovery of new populations of such rare species are thus important for our understanding of the ecology of the temporary pool ecosystem. Lythrum thesioides M.Bieb., 1808 is a very rare annual species of temporary pools and river banks which was thought to be extinct in the South of France until 1998. Here, we review the distribution of the species and report the recent discovery of a population during a targeted search combining historical data on wetland occurrence on a particular geological substrate. We present new information on its autecology, pollen morphology and the karyotype. Only three populations are currently known worldwide for Lythrum thesioides, and only one of these has favorable management conditions. Thus, we outline new conservation perspectives in the context of a targeted search project and the conservation management of one population.

Moisture and soil parameters drive plant community assembly in Mediterranean temporary pools

For the Mediterranean plant diversity hotspot, temporary pools combine a highly variable, rainfall-dependent habitat with high and endangered plant diversity within small surfaces. They show alternating phases of drought and flooding, corresponding to the characteristic summer drought and winter rain of Mediterranean climate. This alternation is coupled with a moisture gradient that behaves as a selective filter on vascular plants. The main aim of our study was to show how plant functional traits respond to this moisture gradient, to build a greater understanding of the underlying functional mechanisms, and to formulate assembly rules. Our data showed that the frequency of plants with smaller seeds, later onset of flowering and hydrophytes increased with increasing water levels. These relations were uncovered by controlling for site effects using a mixed model approach. We discuss how our data can provide a basis to understand the limiting factors for plants with high conservation value, and what management strategies can be adopted in the context of environmental change.

Ecological features affect patterns of plant communities in Mediterranean temporary rock pools

In this paper, the results of a study on the ecology, floristic composition and spatial assemblages of temporary limestone rock pool plant communities of a central Mediterranean area (S Sicily, the Maltese Islands and Lampedusa) are presented. A total of 76 temporary pools were studied, distributed between the infra-mediterranean and thermo-mediterranean bioclimatic belt. For each temporary rock pools, the floristic composition and cover of the species were determined using standard relevé methods. Moreover, for 50 of these pools, pH, conductivity, soil depth, water-level, altitude and floristic richness and diversity index were assessed. The plant communities were analysed using unweighted pair group method using arithmetic averages and Euclidean distance classification and ordination methods such as canonical correspondence analysis (CCA). A total of four plant communities with specific floristic composition were established, each one with a different dominant species: Callitriche truncata; Elatine gussonei; Tillaea vaillantii and Lythrum hyssopifolia. According to the CCA, the spatial patterns of plant communities follow an ecological gradient related to water level and depth/size of the rock pools: these are the main ecological features affecting the distribution of the plant communities of rock pools. In addition, floristic richness and diversity index showed a slight increase in trend from temporary pools submerged for long periods towards pools submerged for short periods.

Late Quaternary history of a Mediterranean temporary pool from western Morocco, based on sedimentological and palynological evidence

Using sedimentological and pollen analysis, a reconstruction is presented here for the origin and history of a temporary pool from the quartzitic-sandstone Benslimane Plateau (W. Morocco). The pool is one of many that originated from the dismantling of a past hydrographical network, dated to the end of the Lower Pleistocene. Infilling of the pool began only recently between 5000 and 4000cal. BP, and probably was in response to Neolithic-induced degradation of the regional vegetation cover. The almost continuous pollen occurrence of Isoetes velata-type, Myriophyllum alterniflorum and Ranunculus-type throughout the palynological sequence indicates that the organisation of local plant communities in concentric belts (a central aquatic community, an intermediate amphibious one, and a peripheral terrestrial one) has remained unchanged since the Mid-Holocene. The stability of the vegetation structure and composition over more than 4000years confirms the adaptation of the hydrophytic communities to human-induced disturbances (mainly grazing).The long-term pool longevity is attributed to an equilibrium between wind erosion and sedimentation. The sediment accumulation balance that was null or negative during most of the Pleistocene became positive under the influence of Neolithic activities, which may also be linked to unfavourable climatic conditions. These results have important implications for the long-term conservation of biodiversity, as these rare habitats are rapidly declining. Since temporary pools also protect the quartzitic-sandstone plateau from erosion, their disappearance could trigger the reorganisation of the hydrological network and the resumption of soil erosion.

Effects of hydrology on recruitment of Pilularia minuta Durieu (Marsileaceae), an endangered plant of Mediterranean temporary pools

Hydrological requirements for germination and development of P. minuta were assessed through a 5-year field survey in Garâa Sejenane, Tunisia, and an experiment under controlled conditions. The spatial distribution of P. minuta was recorded in the field annually, while the experiment tested the effects of water levels and flooding dates on germination (the emergence of new individuals) and development. Water level was found to be the major factor affecting the germination and the development of P. minuta with flooding date as a secondary limiting factor. For germination to occur, the sediment must be completely waterlogged. Water depths of 5–10cm are optimal for plant development. In addition, the plant needs a minimal flooding period of seven weeks to develop. Late-spring precipitation appears to be more critical than earlier rains.

Mediterranean temporary ponds in Puglia (South Italy): a “joyau floristique” to protect

Mediterranean temporary ponds are priority habitats within the Natura 2000 network of the European Union (code 3170). They are isolated habitats, located in various Mediterranean countries, of high conservation value, with unique flora, successional stages and ecological characteristics. The vascular flora of Mediterranean temporary pools was studied to determine the diversity and ecology of these habitats: 47 sites and 63 rare species characteristic of the Isoëto-Nanojuncetea phytosociological class were found. The results suggest that the vascular flora of temporary pools is very rare in Puglia, although rare ferns are better represented than previously reported. These habitats are difficult to detect, so it is necessary to prevent the loss and destruction of these “jewels” by adopting suitable management measures.

Plant diversity and conservation value of continental temporary pools

Temporary pools are unusual habitats because they share features of aquatic and terrestrial ecosystems. They are habitats of community interests according to the Natura 2000 network (Natura code: 3130 and 3170), and can be found in several climatic regions where they harbours various wetland habitats. Whereas Mediterranean temporary pools are well studied, only a few papers deal with their continental counterparts, probably because they are mainly found on arable fields often displaying decades-lasting dormancy. This study aims at filling this gap in our knowledge by evaluating plant species composition, habitat types and diversity of temporary pools in a region of continental climate. We analysed data from 185 phytosociological relevés (79 historical and 106 contemporary data) from different types of waterlogged arable fields, including rice paddy fields, from the Pannonian Ecoregion. We found significant differentiations of rice paddy fields from ‘other’ waterlogged arable fields according to ordination, classification and regression analyses. Diversity partitioning of species abundance data showed that these habitats have a very high alpha (species number, Simpson and Shannon) and beta diversity, which means that all the sites have high importance in habitat conservation. We found many vascular plants listed in IUCN and national red lists among the indicator and characteristic species of continental temporary pools. Our results demonstrate the conservation importance of continental temporary pools in relation to habitat and biodiversity management and conservation planning.

Diversity and ecological characteristics of vascular flora in Mediterranean temporary pools

Vascular flora of Mediterranean temporary pools has been studied with the aims to define its diversity and to individuate the ecological characteristics of the different plant groups associated with this relevant and endangered habitat type. Overall, 246 species were found of which 108 were terrestrial, 57 generalist of aquatic or wet habitats and 81 typical of temporary water and strongly linked to temporary pools. The results suggest that: (i) vascular flora associated with Sardinian Mediterranean temporary pools is rich and diversified; (ii) rare ferns are better represented than previously reported; (iii) plant species are generally heliophilous and acidophilous, specialized temporary pool species mainly differing from the unspecialized ones in relationship to their soil moisture requirements; (iv) these habitats are particularly important for maintaining regional freshwater biodiversity.

Vegetation of Mediterranean temporary pools: a fading jewel?

Although Mediterranean temporary pools are of great value for conservation, they are in rapid decline under the impact of various forms of anthropogenic pressure. Their disappearance from the landscape may result in a weakening of the biological connections between pools due to increasing isolation and the impoverishment of their communities. In Western Morocco (province of Benslimane), temporary pools have undergone severe regression over the past decades. The quantification of these losses and the impact on the richness of plant communities remain, however, unstudied. Since this is of vital importance for the conservation of the biodiversity of these habitats, a study has been undertaken associating (1) an assessment of the pool losses (both in density and surface area) between 1955 and 2001 using remote sensing, (2) surveys of vegetation and water depth (in 2006) in 48 pools, and (3) an assessment of the density and surface area of pools occurring within a 3 km radius around each of the sampled pools. The results show a loss of 23% in number and 61% in surface area of pools in the province over a period of 47 years. This decline, promoted by their small size and shallowness, is probably related to socio-economic changes (intensification of agricultural practices and population growth). The richness in characteristic and rare species of the pools was related to both local (water depth) and regional features (land use, pool density and total water surface area in the surrounding landscape). The significant impact of the current density of pools and their total surface area on the conservation value of the studied pools suggests a weakening of the metacommunity dynamics between pools. Given the rapid socio-economic changes in the province and the current rate of pool disappearance (0.5% per year) we predict a continuing reduction in pool density with a high risk of the widespread loss of their unique flora in the long term.

Post-disturbance dynamics of plant communities in a Mediterranean temporary pool (Western Morocco): Effects of disturbance size

Mediterranean temporary pools are frequently visited habitats where domestic livestock and wild herbivores generate numerous physical soil disturbances. Using two sizes of experimental plots (large, 1.20 m × 1.20 m; small, 0.3 m × 0.3 m), the effects of soil disturbances on vegetation dynamics and the vertical distribution of seeds were studied in one Moroccan temporary pool. Results show a very rapid regeneration of temporary wetland vegetation in disturbed plots. The speed of regeneration depends on the size of disturbance and hydrology. There was an almost complete return of vegetation to the reference state in the small disturbed plots by the end of the 1st year. This fast restoration was mainly due to seed banks, which play a key role in the resilience of pools to the different sizes of disturbances frequently generated by herbivores, but also to lateral colonization by perennials.

Impact of grazing on the species richness of plant communities in Mediterranean temporary pools (western Morocco)

The impact of grazing on the vegetation of Moroccan temporary pools has been studied at 2 scales: regional (inter-pools) and local (intra-pools). Half of the 16 forest pools studied is located in a reserve and ungrazed. The other half, located within public forest, is grazed. Vegetation relevés coupled to water-depths measurements were carried out in each pool. The results showed a significant effect of grazing on both scales of analysis. This effect was found in the species composition of the vegetation, which differed between the 2 types of pools, and in the lower species richness and abundance of plant species in the grazed pools. These differences are interpreted as resulting from the selection by herbivores and the differential tolerance of species to disturbance. These impacts are likely to expose certain species to local extinction by reducing their populations.

Modern pollen–vegetation relationships within a small Mediterranean temporary pool (western Morocco)

Morocco is rich in temporary pools which harbour numerous rare plant species. Long-term conservation of such threatened plant communities should be based on the understanding of their past dynamics. Despite conditions unfavourable to pollen preservation, surface sediments of acidic temporary pools are shown to contain pollen assemblages likely to allow vegetation reconstruction. Knowledge of the modern relationships between pollen and vegetation is, however, necessary for interpreting fossil data in terms of past vegetation. Surface pollen assemblages and floristic surveys of a temporary pool in Benslimane forest, western Morocco, are compared in order to evaluate the pollen record of the local hydrophytic vegetation. Floristic surveys were carried out for 12 years (1996–2008) along two crossing permanent transects. A set of 21 surface-sediment samples, taken along the same transects in 2007, were analysed for pollen. The spatial relationships between vegetation and pollen assemblages are explored by means of multivariate analyses, statistical tests and linear regressions. The calculation of representation indices moreover allows proposing quantitative ways for pollen-based plant-abundance reconstruction. Results reveal that the vegetation structure along the hydrological gradient is well recorded in the pollen assemblages, with: (1) a marginal zone characterised by terrestrial taxa and rare amphibious taxa ( Elatine, Pilularia), (2) an intermediate zone of amphibious taxa ( Alisma-type, Illecebrum/Paronychia, Isoetes velata-type), and (3) a central zone of aquatics ( Myriophyllum alterniflorum, Ranunculus-type). The best correlation between the pollen record and total pool vegetation was found in the centre of the pool, which supports the reliability of the study of a single core from the centre of the pool for the reconstruction of the past dynamics of the local hydrophytic vegetation. Both the qualitative ‘community’ approach (representation indices and indicator pollen taxa) and the quantitative ‘taxa’ approach (correction factors) suggest that reconstructions of past populations can be achieved from a few taxa, namely Isoetes velata-type, Myriophyllum alterniflorum and Ranunculus-type. For these taxa, regression parameters (slope and y-intercept) have been calculated between pollen percentages and plant percentages in present vegetation, and between pollen influxes and plant abundances, respectively. These parameters can be extended to interpret fossil data from other temporary pools within the same region to reconstruct their relative and absolute past plant abundances.

Recent discovery of the small pillwort ( Pilularia minuta Durieu, Marsileaceae) in Tunisia: Hope for an endangered emblematic species of Mediterranean temporary pools?

This article presents a synthesis of all localities where Pilularia minuta, an endangered Pteridophyte endemic of acidic Mediterranean temporary pools, was observed since its discovery in 1835. It aims at analysing the implications of its recent discovery in Tunisia, based on the comparison between new and previously published floristic surveys. The obtained data confirm the heliophilous pioneer character of P. minuta and reveal a disturbance-favoured behaviour in Tunisia. The small pillwort, which occurs in 16 locations around the Mediterranean basin, could be characterised by a good dispersion. However, it experienced the extinction of a quarter of its known populations over the last century. This decline seems to have affected only small populations (Maritime-Alps, France; Lazio, Italy) and highly disturbed areas (Algeria), while large ones (Sardinia, Italy; Corsica and Hérault, France; Andalusia, Spain; western Morocco), presumably more stable, survived. In a context of metapopulation, these large populations could be considered as ‘source populations’, and should be taken more especially in account in conservation strategies. Further investigations are needed for improving the conservation of the rare plants of Mediterranean temporary pools as well as contributing to a better knowledge of the mechanisms controlling their distribution and their present-day status. To cite this article: A. Daoud-Bouattour et al., C. R. Biologies 332 (2009).

Vegetation recolonisation of a Mediterranean temporary pool in Morocco following small-scale experimental disturbance

Disturbances are key factors in the dynamics and species richness of plant communities. They create regeneration niches allowing the growth of new individuals in patches submitted to lower intensity of competition. In Mediterranean temporary pools, the intense summer drought constitutes for communities a large-scale disturbance whose intensity varies along the topographical and hydrological gradient between the centre and the edges. In this context, the importance of small-scale disturbance, such as those created by trampling and rooting herbivores in temporary pools, is poorly known. The recolonisation of small bare patches of a woodland temporary pool in western Morocco was studied experimentally in the field. The experiment was carried out using nine small control plots and nine experimental plots (sterilisation of the soil) distributed along the topographical gradient (centre, intermediate and edge zones). The area covered by plant species, and the water levels, were recorded for the plots over two successive hydrological cycles (2006/2007 and 2007/2008). The effects of natural history traits (size of seeds, presence or absence of dispersal mechanisms and annual/perennial) on the success of recolonisation of individual species were analysed. The results show that the experimental plots were rapidly recolonised. The community composition apparently was affected by the very dry conditions during the first year of the experiment, when annual species were largely absent and the clonal perennial species (Bolboschoenus maritimus and Eleocharis palustris) were dominant in the centre and intermediate zones, whilst not a single species colonised the edge zone. In the second year, less dry hydrological conditions allowed annual plants to appear in all three zones. After 2 years, the species composition of the vegetation in the experimental plots was similar to that of the unsterilised (control) plots. The abundance of plants in the centre zone was identical for experimental and control plots; in the intermediate and edge zones, the species’ abundance was lower in the experimental plots than in the control plots, suggesting an incomplete return to the reference condition (control state). Differences in abundance of species were uncorrelated with the size of seeds or to the annual/perennial nature of the plants, but were particularly dependent on the hydrological conditions, which favoured lateral colonisation by perennials (runners, rhizomes). These results show that recovery from the minor disturbances can be rapid in Mediterranean temporary pools.

Ten-year dynamics of vegetation in a Mediterranean temporary pool in western Morocco

The aim of this work was to test the hypotheses that the species composition of the vegetation of one pool in Morocco change continuously along with rainfall fluctuations, that among the vegetation can be recognized Pool species and Opportunistic species with distinct dynamics in time. We expected the Pool species to show lower inter-annual variation than the Opportunistic species. This hypothesis was tested in a 10-year study of the species composition of the vegetation along two permanent transects. The results showed high cumulative species richness (95 species) with large differences between years and a predominance of annual species (77). The proportion of Pool species during these 10 years was low (39%) when compared to opportunists (61%). In dry years the Opportunistic species were dominant and declined during wet years. The number of Pool species was correlated with the amount of rainfall. A large number of these species revealed a preference for wet years. No negative interaction between annuals/perennials and pools/non-pools species was found, suggesting that competition was not a major process during the survey. The intensity of the drought and flood stress, related to climate fluctuations, seems to be the main factors controlling the species composition of the vegetation of this unstable habitat. However, beyond the inter-annual fluctuation of the species composition of the vegetation a directional change was noticed. This directional change could result from a recovery process of the vegetation during the first years of the study after a severe flood which extirpated most of the Opportunistic species of the pool. In the last years this directional change of the species composition of the vegetation is less clear and random recruitment of the Opportunistic species from the surrounding forested habitats could contribute to explain inter-annual changes. The data collected over these 10 years led to the speculation of hypotheses on the consequences of climate change. The expected reduction of humid years and of rainfall regionally may lead to important changes in the species composition of the vegetation of the temporary pools in Morocco.

Competition in microcosm between a clonal plant species (Bolboschoenus maritimus) and a rare quillwort (Isoetes setacea) from Mediterranean temporary pools of southern France

Bolboschoenus maritimus, a clonal species, is locally invasive in Mediterranean temporary pools where it threatens endangered rare plant species such as Isoetes setacea. The combination of management modifications (grazing) and of the progressive accumulation of fine sediments in the pools contributed to the establishment of competitive perennial plants such as B. maritimus. The competitive advantage of B. maritimus on I. setacea has been studied in controlled conditions. The goal of this experiment was to assess the role of environmental conditions in the output of the competition between Bolboschoenus and Isoetes, notably hydrology and soil richness. For this purpose, Isoetes was cultivated alone (three individuals/pot) and with Bolboschoenus (three individuals of both species). The experiment was run with five replicates on six types of sediment (gradient of richness in sand/silt/clay) combined with three hydrological treatments (flooded, wet. and dry). The competitive advantage of Bolboschoenus was measured as the ratio of the production of Isoetes in mixture versus monoculture. The results showed that Isoetes was always outcompeted by Bolboschoenus. However, the competitive advantage of Bolboschoenus on Isoetes, was more related to hydrology than to soil richness. The competitive advantage of Bolboschoenus was very high in wet and flooded conditions and very low in dry conditions. This situation may lead to the extinction, medium-term, of the populations of I. setacea. The introduction of ovine grazing or of cut back practices in temporary pools could reduce the B. maritimus biomass and help toward the conservation of I. setacea populations.

Experimental study of the effect of hydrology and mechanical soil disturbance on plant communities in Mediterranean temporary pools in Western Morocco

Physical soil disturbance and the hydrology of temporary pools affect the biomass, species composition and richness of plant communities. Disturbance liberates sites for the random recruitment of new individuals. The addition of seeds modifies the structure of the communities. In order to verify these hypotheses concerning the vegetation of temporary pools, an experiment was carried out using 72 soil samples collected from a pool in Western Morocco and placed in containers. Three types of laboratory treatments were applied, each combined with control treatments: soil disturbance (control/disturbed), hydrology (flooded, saturated and dry) and seed addition (sowing/no sowing). The total biomass, the annual and perennial species richness were calculated for each sample to test the effects of disturbance, hydrology and seed addition on the biomass and species richness of the various plant communities. The results show that disturbance reduces the total biomass, especially of perennials, but without significantly increasing the richness of annuals. Seed addition does not affect the total biomass and reduces total richness only in saturated soil, where biomass production is high. The most extreme stress conditions (drought and flooding) limit the abundance of species and therefore competition.

Experimental management of Mediterranean temporary pools for conservation of the rare quillwort Isoetes setacea

Mediterranean temporary pools represent unique species-rich habitats with many rare and endangered species. The Roque-Haute Natural Reserve is one of the few sites in France with Isoetes setacea Lam., a very rare Mediterranean quillwort, considered as a keystone species determining a priority habitat for the European Union. Land uses changes have favoured the invasion of the pools by several shrub and tree species (e.g., Ulmus minor, Fraxinus angustifolia subsp. oxycarpa). Clearing shrubs in an experimental area of one pool resulted in the increase of I. setacea as compared to control, combining a higher cover in previously occupied quadrats and more quadrats occupied. Litter accumulation had a negative effect on the population of Isoetes but this effect was detectable only in the cleared area. Light attenuation was shown experimentally to be detrimental to the vegetative and regenerative production of I. setacea. Clearing of the shrubs and removal of the litter led to an increase in the I. setacea populations and therefore appears to be an effective technique for restoring these plant communities invaded by shrubs. Long-term shrub control should be ensured by reintroducing sheep grazing in order to enhance the sustainable conservation of this oligotrophic habitat.

The LIFE Project “Conservation of Mediterranean temporary pools”

The LIFE Project “Conservation of Mediterranean temporary pools”