Mediterranean Steppe Research Articles

Soil Requirements of Four Salt Tolerant Species in Two Saline Habitats

In this paper we investigated the response to some edaphic factors of the guiding species in two habitats of interest for the European Union (Habitats Directive 92/43/EEC). For the priority habitat 1510 (Mediterranean salt steppes, Limonietalia), we chose Limonium cossonianum. For habitat 1420 (Mediterranean and thermo-Atlantic halophilous scrubs, Sarcocornietea fruticosi), we chose Arthrocnemum macrostachyum, Sarcocornia fruticosa, and Sarcocornia perennis subsp. alpini. We studied four coastal wetlands in the bay of Almería (southeast of Spain), where we set up a grid of sampling plots. In each of these plots we related the presence of these species with a series of edaphic variables measured at specific times of the year for two years. Habitat 1510 is made up of moderately halophilous species that grow on soils that are saturated only in very wet weather conditions and cannot tolerate flooding for long periods of time. By contrast, the species of habitat 1420 are genuinely halophilous and the soils they grow on are often saturated and subject to frequent and prolonged flooding. The differences between these species are mainly rooted in different levels of tolerance to flooding-drying cycles (anoxia). Our results could be used as a criterion for the restoration of the habitats mentioned in the Habitats Directive, such as degraded salt marshes, and abandoned salt works, among others.

Can ecological engineering restore Mediterranean rangeland after intensive cultivation? A large-scale experiment in southern France

Ecological restoration has been identified as one of the possible ways to replace biodiversity loss. While ecological engineering methods can successfully restore some ecosystem attributes, restoration is generally incomplete, mainly due to lack of target species propagule dispersal, unsuitable abiotic conditions and negative biotic interactions, especially after intensive cultivation. How best to restore reference ecosystems is therefore a vital research objective, not only on a small experimental scale but also on a large scale. This study aimed to determine which ecological engineering techniques are the most suitable for large-scale restoration of a low-productive species-rich ecosystem after intensive cultivation. Experiments were carried out at La Crau in southern France, within a 357ha land rehabilitation project whose aim was to recreate a herbaceous sheep-grazed habitat. We investigated: (i) covering species seeding, (ii) topsoil removal, (iii) hay transfer, and (iv) soil transfer as methods to restore a steppe plant community in this rehabilitated area, using the last remaining French Mediterranean steppe as a reference ecosystem. Species-richness, diversity and composition of vascular plant communities were monitored over three years. The rehabilitation made it possible to recover a large area dominated by grasses but with vegetation different from that of the steppe. Hay transfer was successful in transferring some target species, but the number of target species did not significantly increase by the end of the third year. Covering species seeding seemed to provide a suitable area for target species colonization, but probable competition with grasses needs to be monitored. The greatest similarity in richness, diversity, and composition with the reference ecosystem was obtained with topsoil removal and soil transfer, which made it possible to recover the species-richness and, to some extent, the composition of the steppe. Our findings show that current ecological restoration and ecological engineering techniques can lead to at least partial restoration of some ecosystem attributes. However, they also underline the importance of in situ conservation of natural habitats rather than restoring them after their destruction.

Biological soil crust influence on germination and rooting of two key species in a Stipa tenacissima steppe

Background and aims In Mediterranean steppes, Stipa tenacissima tussocks facilitate the establishment of vascular plants. We hypothesized that this effect may partially reflect the indirect interaction between Stipa tenacissima, biological soil crusts (BSC), and seeds. Methods We explored the relationship between BSC composition and soil surface conditions (surface roughness and hydrophobicity by using the water drop penetration time test), and seed germination and seedling rooting in aS. tenacissima steppe in southeastern Spain. We explored the causal factors of seed germination at two spatial scales and used SADIE index to represents the soil surface heterogeneity. Results Microsites strongly differed in BSC compositionand soilsurface conditions. Germination of two key species, Pistacia lentiscus and Brachypodium retusum, was not affected by BSC type. In contrast, rooting was lower on soil from open areas covered by BSC than on soil from open areas dominated by bare soil and soil collected under the tussocks. The effect was similar in both species. Lichens were probably responsible for the decrease in rooting. Conclusions Our results suggest that lichen cover and the cover of bare soil and mosses may hamper and facilitate rooting, respectively. By affecting seedling rooting, BSC may contribute to the facilitative effect of Stipa tenacissima.

Topsoil removal improves various restoration treatments of a Mediterranean steppe (La Crau, southeast France)

AbstractQuestionCan topsoil removal improve restoration efficiency of several ecological engineering techniques (nurse species seeding, hay transfer and soil transfer) for restoring a Mediterranean steppe, species‐rich plant community?LocationLa Crau area, southeast France (Provence).MethodsAfter the rehabilitation of a 357‐ha herbaceous, sheep‐grazed rangeland suitable for threatened steppe birds in a formerly abandoned industrial orchard in the last French Mediterranean steppe (La Crau area), four experimental treatments were applied, with or without topsoil removal. Topsoil was removed on a 5000‐m² area and the four treatments (control, nurse species seeding, hay transfer and soil transfer) were applied within this area where topsoil was removed and within the area where topsoil was not removed. Three years later, soil chemistry, soil seed bank, vegetation cover and height, plant species richness, composition and diversity were compared.ResultsRemoving topsoil partly restored soil conditions and significantly reduced the non‐target seed bank. Moreover, species richness and similarity to the reference steppe was significantly increased with topsoil removal. Topsoil removal, combined with soil transfer and hay transfer, created a community that most closely resembled the reference during the study period.ConclusionIn order to restore plant community composition, topsoil removal is a relevant method to increase the efficiency of other ecological restoration techniques, especially those that strengthen dispersal processes.

Restoring degraded arid Mediterranean areas with exotic tree species: Influence of an age sequence of Acacia salicina on soil and vegetation dynamics

Acacia salicina Lindl. is an Australian leguminous tree widely planted outside its original distribution as a multi-purpose species, and successfully establishes on degraded areas. The objective of this study was to determine how an age sequence of 3, 5, 9 and 13-year-old A. salicina plantations affected soil properties and flora diversity of an arid Mediterranean steppe. Soil samples were taken from the upper 10cm of soil under tree canopies and in the associated open spaces. The results showed that tree establishment and development enhanced soil contents of total C, total N, available P and exchangeable K+, Ca2+, Mg2+ and Na+. These trends increased significantly with increasing plantation age. At the same time A. salicina facilitated the colonization and development of understory vegetation. Indeed, the number of plant species, the total plant cover, the perennial species density, the plant biomass and the diversity all attained higher values under tree canopies and increased with increasing plantation age. The soil dynamic under 13-year-old A. salicina plantations reflected two phases in the restoration sequence, characterized by nominal changes during tree establishment (0–5 years) and showing marked and rapid changes associated with the start of canopy closure (5–13 years). A. salicina establishment could be an effective and applicable measure to restore soil and vegetation and control desertification in the Mediterranean arid steppes.

First-year results of a multi-treatment steppe restoration experiment in La Crau (Provence, France)

Background and aims – Intense agriculture phases on old plant communities, such as Mediterranean steppes, can lead to low resilience. Two main obstacles to the spontaneous recolonization of these plant communities are often the low dispersal of target species and the high dispersal and establishment potential of unwanted species. The aim of the study is to find the most efficient restoration treatments to restore these plant communities. Methods – After the rehabilitation of an herbaceous sheep-grazed community on a formerly intensively cultivated orchard in the last French Mediterranean steppe (La Crau, Provence, France), four experimental restoration treatments were applied to restore the steppe plant community: (i) topsoil removal to lower ruderal species seed banks and soil trophic levels, (ii) nurse species seeding to rapidly occupy niches, and then to provide safe sites for target species once sheep grazing is reintroduced, (iii) hay transfer to provide local species seeds, and (iv) soil transfer to provide local species propagules with associated microorganisms. One year later, plant species richness, composition and diversity are compared. Results – Although the communities developing on areas seeded with nurse species and where topsoil was removed differed most widely from the reference ecosystem, i.e. steppe, these restoration treatments succeeded in achieving their goal by significantly lowering the abundance of unwanted dominant species. While hay transfer did not have a significantly higher species richness than that of the rehabilitated area, it showed promising results, as some germinations of target species were observed. One year only after the treatment was applied, soil transfer provided a community richness and composition very close to that of the reference ecosystem, but not with the same vegetation structure. Conclusion – In order to restore plant community composition, the more the treatment strengthens community dispersal, the more efficient it is. The gain in efficiency is closely linked with the cost of the treatment.

The Mediterranean salt steppes (order Limonietalia Br.-Bl. & O. Bolòs 1958) in Tuscany (Central Italy)

We conducted a phytosociological study of the halophile, chamaephytic, and hemicryptophytic communities found on coastal sand dunes and salt marshes in Tuscany, which mainly consist of Limonium spp. We describe the presence in Tuscany of communities referred to as Mediterranean salt steppes (Limonietalia), although we emphasize that they cover only small areas. We describe a new association, Limbardo crithmoidis-Limonietum etrusci, and a new alliance endemic to Tuscany, Limonion etrusci.

Determinants and dynamics of banded vegetation pattern migration in arid climates

Dense vegetation bands aligned to contour levels and alternating at regular intervals with relatively barren interbands have been reported at the margins of all tropical deserts. Since their discovery in the 1950s, it has been supposed that these vegetation bands migrate upslope, forming a space–time cyclic pattern. Evidence to date has been relatively sparse and indirect, and observations have remained conflicting. Unequivocal photographic evidence of upslope migration (a few decimeters per year) is provided here for three independent dryland areas exhibiting periodic banded pattern: (1) the U.S. northeastern Chihuahuan Desert, (2) the Somalian Haud, and (3) the Mediterranean steppes of eastern Morocco. Migration speeds, averaged through time and space using Fourier cross‐spectral analysis, are shown to be directly proportional to pattern scale (wavelength). A sequence of aerial photographs of the Chihuahuan Desert showed that migration was not continuous, but intermittent in response to fluctuating weather regimes. The rates at which bands expanded upslope and contracted downslope were better predicted by the change in annual rainfall than by its average level. However, the migration of banded patterns cannot be considered as systematic because in our observations of three other banded systems located in the Somalian Haud, central Australia, and western New South Wales, migration was undetectable at the available image resolution. In each of the six sites under study, the modal value of band orientation axes was verified to be approximately orthogonal to the steepest slope. Our results underscore the importance of taking both the spatial structure and the past climate sequence into account for understanding vegetation dynamics in arid to semiarid ecosystems. In addition, we show how Fourier spectral analysis applied to historical series of optical images can serve to quantify landscape dynamics at a decadal time scale.

Is Evolution of Blind Mole Rats Determined by Climate Oscillations?

The concept of climate variability facilitating adaptive radiation supported by the “Court Jester” hypothesis is disputed by the “Red Queen” one, but the prevalence of one or the other might be scale-dependent. We report on a detailed, comprehensive phylo-geographic study on the ∼4 kb mtDNA sequence in underground blind mole rats of the family Spalacidae (or subfamily Spalacinae) from the East Mediterranean steppes. Our study aimed at testing the presence of periodicities in branching patterns on a constructed phylogenetic tree and at searching for congruence between branching events, tectonic history and paleoclimates. In contrast to the strong support for the majority of the branching events on the tree, the absence of support in a few instances indicates that network-like evolution could exist in spalacids. In our tree, robust support was given, in concordance with paleontological data, for the separation of spalacids from muroid rodents during the first half of the Miocene when open, grass-dominated habitats were established. Marine barriers formed between Anatolia and the Balkans could have facilitated the separation of the lineage “Spalax” from the lineage “Nannospalax” and of the clade “leucodon” from the clade “xanthodon”. The separation of the clade “ehrenbergi” occurred during the late stages of the tectonically induced uplift of the Anatolian high plateaus and mountains, whereas the separation of the clade “vasvarii” took place when the rapidly uplifting Taurus mountain range prevented the Mediterranean rainfalls from reaching the Central Anatolian Plateau. The separation of Spalax antiquus and S. graecus occurred when the southeastern Carpathians were uplifted. Despite the role played by tectonic events, branching events that show periodicity corresponding to 400-kyr and 100-kyr eccentricity bands illuminate the important role of orbital fluctuations on adaptive radiation in spalacids. At the given scale, our results supports the “Court Jester” hypothesis over the “Red Queen” one.

Taxonomic and functional diversity of farmland bird communities across Europe: effects of biogeography and agricultural intensification

In eight European study sites (in Spain, Ireland, Netherlands, Germany, Poland, Estonia and Sweden), abundance of breeding farmland bird territories was obtained from 500 × 500 m survey plots (30 per area, N = 240) using the mapping method. Two analyses were performed: (I) a Canonical Correspondence Analysis of species abundance in relation to geographical location and variables measuring agricultural intensification at field and farm level to identify significant intensification variables and to estimate the fractions of total variance in bird abundance explained by geography and agricultural intensification; (II) several taxonomic and functional community indices were built and analysed using GLM in relation to the intensification variables found significant in the CCA. The geographical location of study sites alone explains nearly one fifth (19.5%) of total variation in species abundance. The fraction of variance explained by agricultural intensification alone is much smaller (4.3%), although significant. The intersection explains nearly two fifths (37.8%) of variance in species abundance. Community indices are negatively affected by correlates of intensification like farm size and yield, whereas correlates of habitat availability and quality have positive effects on taxonomic and functional diversity of assemblages. Most of the purely geographical variation in farmland bird assemblage composition is associated to Mediterranean steppe species, reflecting the bio-geographical singularity of that assemblage and reinforcing the need to preserve this community. Taxonomic and functional diversity of farmland bird communities are negatively affected by agricultural intensification and positively affected by increasing farmland habitat availability and quality.

Remote sensing data predict indicators of soil functioning in semi-arid steppes, central Spain

A substantial part of current research efforts on desertification are devoted to establish monitoring systems to evaluate the status of natural resources and the onset of desertification processes. Methodologies based on ground-collected soil and plant indicators are being increasingly used for this aim because they are affordable yet do not compromise accuracy. Despite their inherent value, these methods have limitations regarding the extent of the area that can be monitored using them. Such limitations can be overcome combining field-based approaches with remote sensing data, which allow the establishment of monitoring programs over large areas. In this article we tested the relationship between a field methodology based on indicators of ecosystem functioning, the landscape function analysis (LFA), and a vegetation index (NDVI) obtained from satellite images of the ASTER sensor using data gathered in Stipa tenacissima steppes from central Spain. LFA uses soil surface indicators to assess the condition of a given ecosystem by producing three numerical indices (stability, infiltration and nutrient cycling) reflecting the status of basic soil functions. We found a significant positive linear relationship between the NDVI, the three LFA indices and some key structural attributes of vegetation related to the cover of perennial plants. Our results indicate that NDVI can be used as a surrogate of ecosystem functioning in semi-arid Mediterranean steppes, and thus can be a helpful index to monitor the functional status of large areas in these ecosystems, and the possible onset of desertification processes.

Hay Transfer Promotes Establishment of Mediterranean Steppe Vegetation on Soil Disturbed by Pipeline Construction

The Coussouls de Crau Nature Reserve is a xeric steppe providing a habitat for remarkable animals. Over the past centuries, this steppe has been partly destroyed and fragmented and has been reduced to 9,500 ha out of the 55,000 ha existing before the 16th century. Although this ecosystem is protected, 23 ha of natural habitat were nonetheless destroyed in 2006 during the construction of an underground pipeline. To mitigate potential future damage, an original experiment in restoration ecology was adapted and tested: the technique of hay transfer. The objective of this experiment was to find ways of accelerating steppe vegetation colonization on the soil over the buried pipelines by the reintroduction of steppe species. A factorial experiment was set up to test the effects of habitat characteristics, grazing, and hay transfer. The results obtained for 3 years after the experimentation setup are conclusive in favor of using hay transfer for the restoration of Mediterranean steppe ecosystem. Hay transfer has significantly increased the species richness on restored areas and has allowed the reintroduction of some typical steppe species. Among these species, we found a wide variety of annual grasses which play a key role in the recovery of steppe vegetation and provide food for sheep flocks. Sheep herding must be maintained during the ecological restoration of the herbaceous steppe community, because grazing significantly increases species richness on restored areas without changing species assemblies.

Histoire plio-pléistocène des écosystèmes végétaux de Méditerranée sud-occidentale : apport de l’analyse pollinique de deux sondages en mer d’Alboran

The pollen analysis of sediments of two boreholes located in the northeastern Morocco (Nador 1) and in the southeastern Spain (Andalucia G1) has allowed shedding a new light on the vegetation and climate of the North African littoral plains, the Rif Massif and the Betic Range during the Pliocene. The vegetation around the Alboran Sea was open and xeric during the Zanclean, dominated by herbs including subdesertic elements as Calligonum, Lygeum, Nitraria and Neurada. This type of vegetation indicates a dry and hot climate. The southwestern Mediterranean steppes have therefore a climatic character; they existed before the presence and the heavy pressure of Man on the environment. From the Piacenzian, the development, at Andalucia as well as at Nador, of Artemisia and the appearance of some altitude trees such as Cedrus and Cathaya indicate a vegetation change linked to a climatic change. Modifications in the vegetation observed during the same period in northwestern Mediterranean seem to indicate that the vegetation changes observed at Andalucia and Nador are controlled by the appearance of the first arctic glacial-interglacial cycles. The cedar tree appears at Nador only at the end of the Piacenzian, at time of the first cooling, while it has been found punctually in Messinian and early Pliocene sediments of Habibas in Algeria and in Messinian sediments of the Bou Regreg section at Salé in Morocco. The regular presence of Cedar at Bou Regreg during the Messinian, allows supposing that it was present in the Middle Atlas Mountains and that its development was favoured by colder conditions.

Temporal dynamics of herbivory and water availability interactively modulate the outcome of a grass–shrub interaction in a semi‐arid ecosystem

The study of plant–plant interactions along grazing and abiotic stress gradients is a major research topic in plant ecology, but the joint effects of both stressors on the outcome of plant–plant interactions remains poorly understood. We used two different factorial experiments conducted in a semi‐arid Mediterranean steppe to assess: 1) the role of the perennial grass Stipa tenacissima, a low‐palatability species, providing protection from rabbit herbivory to the shrub Retama sphaerocarpa (experiment 1), and 2) the effects of environmental amelioration provided by Stipa on the recovery of Retama after rabbit damage under two contrasted levels of water availability (experiment 2). In the experiment 1, water stress worked as an indirect modulator of herbivore protection by Stipa. This species protected Retama seedlings from rabbit herbivory during the wetter conditions of spring and winter, but this effect dissapeared when rabbit pressure on Retama increased during summer drought due to the decrease in alternative food resources. In the experiment 2, Stipa exerted a negative effect on the survival of Retama seedlings during the three years of the experiment, regardless of inter‐annual differences in rainfall or the watering level applied. This negative effect was mainly due to excessive shading. However, Stipa increased Retama recovery after initial rabbit impact, overriding in part this negative shade effect. Conversely, Stipa impact on the Fv/Fm of Retama seedlings depended on the intra‐annual water dynamics and its experimental manipulation, overall contradicting predictions from the stress–gradient hypothesis. The complex interactions found between herbivory, microclimatic amelioration from Stipa, and water availability as drivers of Retama performance illustrate the importance of considering the temporal dynamics of both biotic and abiotic stressors to fully understand the outcome of plant–plant interactions.

Disturbance of the biological soil crusts and performance of Stipa tenacissima in a semi-arid Mediterranean steppe

Biological soil crusts (BSC) play a major role in water and nutrient fluxes in semi-arid and arid areas, affecting the establishment of vascular plants and contributing to the spatial arrangement of vegetated and open areas. However, little is known regarding their effects on the performance of extant vegetation. By using experimental manipulations (surface soil cutting and herbiciding), we evaluated the effect of the physical structure and the biotic component of smooth biological soil crusts on soil moisture dynamics, and on the nutrient and water status, growth rate, and reproductive effort of Stipa tenacissima tussocks in a semi-arid steppe. Soil moisture content was weakly reduced after cutting the soil surface and was not affected by herbicide application. Cutting and herbiciding the biological soil crust had no effect on most morpho-functional and reproductive traits measured in S. tenacissima tussocks. The integrated water use efficiency of this species, as measured by 13C natural enrichment, decreased when the biotic community of biological soil crusts was killed with herbicide. In the S. tenacissima steppe studied, killing the BSC and breaking the continuity of the structural crust had a weak effect on the short-term performance of this species, but our results suggest that BSC exert a control on slope hydrology beyond that provided by physical soil crusts.

The age and history of the French Mediterranean steppe revisited by soil wood charcoal analysis

In the Mediterranean basin, steppe vegetation is considered to be the result either of land clearing in the Neolithic or the result of harsh environmental conditions (shallow soils and/or Mediterranean drought). For the first time, a study was carried out in the French Mediterranean steppe area of the Crau in Southeastern France using soil wood charcoal analysis, a technique in which charcoals found in the soil are identified and dated. According to some authors, an original mixed oak and beech forest may have covered the plain and have been cleared in the Neolithic, or, in the view of other authors, the steppe vegetation may have existed in its present form since the Lateglacial period. A total of 14 soil samples and 23 C14 datings were performed. Our results show that no species of ancient forests dominated by Quercus pubescens and Fagus sylvatica or Q. ilex were present at the end of the Neolithic or during the Bronze Age. Only earlier successional species such as Pinus pinea/halepensis, Phillyrea angustifolia and Prunus sp. were burnt during these periods. The other charcoal identified from the Roman Empire, Middle Ages and Modern periods seem to be better correlated with pastoral settlements than natural secondary succession processes. These results obtained at a local scale confirm those already available from the western Mediterranean, which have shown that human impacts were the determining factors of the evolution of the Mediterranean vegetation during the Neolithic and Bronze age.

The phylogeographical history of the Iberian steppe plant Ferula loscosii (Apiaceae): a test of the abundant‐centre hypothesis

The geology and climate of the western Mediterranean area were strongly modified during the Late Tertiary and the Quaternary. These geological and climatic events are thought to have induced changes in the population histories of plants in the Iberian Peninsula. However, fine-scale genetic spatial architecture across western Mediterranean steppe plant refugia has rarely been investigated. A population genetic analysis of amplified fragment length polymorphism variation was conducted on present-day, relict populations of Ferula loscosii (Apiaceae). This species exhibits high individual/population numbers in the middle Ebro river valley and, according to the hypothesis of an abundant-centre distribution, these northern populations might represent a long-standing/ancestral distribution centre. However, our results suggest that the decimated southern and central Iberian populations are more variable and structured than the northeastern ones, representing the likely vestiges of an ancestral distribution centre of the species. Phylogeographical analysis suggests that F. loscosii likely originated in southern Spain and then migrated towards the central and northeastern ranges, further supporting a Late Miocene southern-bound Mediterranean migratory way for its oriental steppe ancestors. In addition, different glacial-induced conditions affected the southern and northern steppe Iberian refugia during the Quaternary. The contrasting genetic homogeneity of the Ebro valley range populations compared to the southern Iberian ones possibly reflects more severe bottlenecks and subsequent genetic drift experienced by populations of the northern Iberia refugium during the Pleistocene, followed by successful postglacial expansion from only a few founder plants.

Stipa tenacissima Does not Affect the Foliar δ13C and δ15N of Introduced Shrub Seedlings in a Mediterranean Semi‐arid Steppe

AbstractRecent studies have shown that the tussock grass Stipa tenacissima L. facilitates the establishment of late‐successional shrubs, in what constitutes the first documented case of facilitation of woody plants by grasses. With the aim of increasing our knowledge of this interaction, in the present study we investigated the effects of S. tenacissima on the foliar δ13C, δ15N, nitrogen concentration, and carbon : nitrogen ratio of introduced seedlings of Pistacia lentiscus L., Quercus coccifera L., and Medicago arborea L. in a semi‐arid Mediterranean steppe. Six months after planting, the values of δ13C ranged between −26.9‰ and −29.6‰, whereas those of δ15N ranged between −1.9‰ and 2.7‰. The foliar C : N ratio ranged between 10.7 and 53.5, and the nitrogen concentration ranged between 1.0% and 4.4%. We found no significant effect of the microsite provided by S. tenacissima on these variables in any of the species evaluated. The values of δ13C were negatively correlated with predawn water potentials in M. arborea and were positively correlated with relative growth rate in Q. coccifera. The values of δ15N were positively correlated with the biomass allocation to roots in the latter species. The present results suggest that the modification of environmental conditions in the are surrounding S. tenacissima was not strong enough to modify the foliar isotopic and nitrogen concentration of shrubs during the early stages after planting.(Managing editor: Ya‐Qin Han)

Seed vs. microsite limitation for seedling emergence in the perennial grass Stipa tenacissima L. (Poaceae)

This paper examines the relative influence of seed and microsite availability in the seedling emergence of Stipa tenacissima, a perennial grass inhabiting semi-arid Mediterranean steppes. A correlative approximation was used to establish 21 (10 × 10 m) plots along a climatic gradient in the Northern limit of the geographic distribution in East Spain. Seed production, seed removal by ants, ant nest density, and the relative cover of S. tenacissima, other perennial plants and bare ground, as explanatory variables, were measured in each plot. Multiple linear regression with forward stepwise selection procedure was used to analyze the relationships between seedling emergence and the explanatory variables. There was large variation between and within plots of all the studied variables, but cover of perennial plants was the only explanatory variable included in the regression model when all the plots were used for the analysis. We suggest that this result was the consequence that high annual precipitation on the Northernmost plots had on the cover of perennial plants and it is consistent with the experimental evidence that shadowing by perennial plants negatively affects germination and performance of the S. tenacissima seedlings. Once the Northernmost plots were removed from the model of regression then seed production, seed removal by ants and ant nest density significantly affected seedling emergence. We concluded that microsite quality, defined in relation to the shadowing capacity of perennial species, was more influential than seed and microsite availability at the Northern limit of the geographic distribution of S. tenacissima.

Are Ecosystem Composition, Structure, and Functional Status Related to Restoration Success? A Test from Semiarid Mediterranean Steppes

Abstract Theoretical models emphasize the importance of considering the composition, structure, and functioning of an ecosystem when restoring it. However, there is a lack of empirical studies evaluating how these ecosystem attributes are linked, if any, to the success of restoration actions. We conducted experimental plantings of the native late‐successional shrub Pistacia lentiscus in 10 semiarid steppes located in southeast Spain and related seedling survival rates to measures of ecosystem structure and composition and to surrogates of ecosystem functioning. Seedling survival widely differed among the studied steppes and 17 months after planting ranged from 0 to 89%. Mortality occurred mostly during the first summer in the field, coinciding with a strong drought lasting 3 months. Survival was lower in the steppes located at the highest altitudes and with the highest values of total plant cover, species richness, shrub cover, and functionality. Seedling survival was mainly controlled by abiotic conditions and showed a negative relationship with some of the surrogates of ecosystem functioning evaluated. Our results suggest, but cannot confirm, that the functional status of the ecosystem may not limit the early stages of establishment of P. lentiscus in semiarid steppes and that abiotic conditions play an overriding role in this process. If true, its introduction in these areas would not necessarily need a previous phase of recovery of ecosystem functions like nutrient cycling and infiltration.