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MS-M was supported by the Spanish Ministry of Science and Innovation (FPU predoctoral grant and the project PROPIFEN PGC2018-101773-B-I00). MM acknowledges a grant from the Swiss National Science Foundation (project n.175101) and funding from the Canada Research Chairs Program. PS was funded by the project "Ecologia Funcional de los Bosques Andaluces y Predicciones Sobre Sus Cambios Futuros" (ForChange) (UCO-27943) by Junta de Andalucia (Spain), the project "Funcionalidad y servicios ecosistemicos de los bosques andaluces y normarroquies: relaciones con la diversidad vegetal y edafica ante el cambio climatico" by "Ayudas a la I CD del Plan Andaluz de Investigacion, Desarrollo e Innovacion (PAIDI) 2020," Junta de Andalucia (Spain) and European FEDER funds. JQ and RN-C were funded by the project ESPECTRAMED (CGL2018-86161-R) from Spanish Research Agency, Ministry of Science and Innovation. RN-C was funded by the projects ISOPINE (UCO-1265298) and SilvAdpat Network RED2018-102719., We acknowledge the E-OBS dataset from the EU-FP6 project UERRA (http://www.uerra.eu) and the Copernicus Climate Change Service, and the data providers in the ECA&D project (https://www.ecad.eu). We thank Robert Scheller, Brian Miranda, Rafael Villar, and Núria Aquilué for useful insights on project conceptualization during the initial steps of this work. We also thank two reviewers for the comments and suggestions made to earlier versions of this manuscript., The use of spatially interactive forest landscape models has increased in recent years. These models are valuable tools to assess our knowledge about the functioning and provisioning of ecosystems as well as essential allies when predicting future changes. However, developing the necessary inputs and preparing them for research studies require substantial initial investments in terms of time. Although model initialization and calibration often take the largest amount of modelers' efforts, such processes are rarely reported thoroughly in application studies. Our study documents the process of calibrating and setting up an ecophysiologically based forest landscape model (LANDIS-II with PnET-Succession) in a biogeographical region where such a model has never been applied to date (southwestern Mediterranean mountains in Europe). We describe the methodological process necessary to produce the required spatial inputs expressing initial vegetation and site conditions. We test model behaviour on single-cell simulations and calibrate species parameters using local biomass estimations and literature information. Finally, we test how different initialization data-with and without shrub communities-influence the simulation of forest dynamics by applying the calibrated model at landscape level. Combination of plot-level data with vegetation maps allowed us to generate a detailed map of initial tree and shrub communities. Single-cell simulations revealed that the model was able to reproduce realistic biomass estimates and competitive effects for different forest types included in the landscape, as well as plausible monthly growth patterns of species growing in Mediterranean mountains. Our results highlight the importance of considering shrub communities in forest landscape models, as they influence the temporal dynamics of tree species. Besides, our results show that, in the absence of natural disturbances, harvesting or climate change, landscape-level simulations projected a general increase of biomass of several species over the next decades but with distinct spatio-temporal patterns due to competitive effects and landscape heterogeneity. Providing a step-by-step workflow to initialize and calibrate a forest landscape model, our study encourages new users to use such tools in forestry and climate change applications. Thus, we advocate for documenting initialization processes in a transparent and reproducible manner in forest landscape modelling., Spanish Government PROPIFEN PGC2018-101773-B-I00, Swiss National Science Foundation (SNSF) European Commission 175101, Canada Research Chairs, Junta de Andalucia European Commission UCO-27943, project "Funcionalidad y servicios ecosistemicos de los bosques andaluces y normarroquies: relaciones con la diversidad vegetal y edafica ante el cambio climatico" by "Ayudas a la I CD del Plan Andaluz de Investigacion, Desarrollo e Innovacion (PAIDI) 2020, European Commission, project ESPECTRAMED from Spanish Research Agency, Ministry of Science and Innovation CGL2018-86161-R, project ISOPINE UCO-1265298, Project SilvAdpat Network RED2018-102719, Spanish Ministry of Science and Innovation (FPU predoctoral grant)

Multiple ecosystem functions need to be considered simultaneously to manage and protect the several ecosystem services that are essential to people and their environments. Despite this, cost effective, tangible, relatively simple and globally relevant methodologies to monitor in situ soil multifunctionality, that is, the provision of multiple ecosystem functions by soils, have not been tested at the global scale. We combined correlation analysis and structural equation modelling to explore whether we could find easily measured, field-based indicators of soil multifunctionality (measured using functions linked to the cycling and storage of soil carbon, nitrogen and phosphorus). To do this, we gathered soil data from 120 dryland ecosystems from five continents. Two soil surface attributes measured in situ (litter incorporation and surface aggregate stability) were the most strongly associated with soil multifunctionality, even after accounting for geographic location and other drivers such as climate, woody cover, soil pH and soil electric conductivity. The positive relationships between surface stability and litter incorporation on soil multifunctionality were greater beneath the canopy of perennial vegetation than in adjacent, open areas devoid of vascular plants. The positive associations between surface aggregate stability and soil functions increased with increasing mean annual temperature. Synthesis and applications. Our findings demonstrate that a reduced suite of easily measured in situ soil surface attributes can be used as potential indicators of soil multifunctionality in drylands world-wide. These attributes, which relate to plant litter (origin, incorporation, cover), and surface stability, are relatively cheap and easy to assess with minimal training, allowing operators to sample many sites across widely varying climatic areas and soil types. The correlations of these variables are comparable to the influence of climate or soil, and would allow cost-effective monitoring of soil multifunctionality under changing land-use and environmental conditions. This would provide important information for evaluating the ecological impacts of land degradation, desertification and climate change in drylands world-wide. Fil: Eldridge, David J.. University of New South Wales; Australia Fil: Delgado Baquerizo, Manuel. Universidad Rey Juan Carlos; España Fil: Quero, José L.. Universidad de Córdoba; España Fil: Ochoa, Victoria. Universidad Rey Juan Carlos; España. Universidad de Alicante; España Fil: Gozalo, Beatriz. Universidad Rey Juan Carlos; España. Universidad de Alicante; España Fil: García Palacios, Pablo. Universidad Rey Juan Carlos; España Fil: Escolar, Cristina. Universidad Rey Juan Carlos; España Fil: García Gómez, Miguel. Universidad Politécnica de Madrid; España Fil: Prina, Aníbal. Universidad Nacional de La Pampa; Argentina Fil: Bowker, Mathew A.. Northern Arizona University; Estados Unidos Fil: Bran, Donaldo Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina Fil: Castro, Ignacio. Universidad Experimental Simón Rodríguez; Venezuela Fil: Cea, Alex. Universidad de La Serena; Chile Fil: Derak, Mchich. No especifíca; Fil: Espinosa, Carlos I.. Universidad Técnica Particular de Loja; Ecuador Fil: Florentino, Adriana. Universidad Central de Venezuela; Venezuela Fil: Gaitán, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Suelos; Argentina. Universidad Nacional de Luján. Departamento de Tecnología; Argentina Fil: Gatica, Mario Gabriel. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Departamento de Biología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina Fil: Gómez González, Susana. Universidad de Cádiz; España Fil: Ghiloufi, Wahida. Université de Sfax; Túnez Fil: Gutierrez, Julio R.. Universidad de La Serena; Chile Fil: Guzman, Elizabeth. Universidad Técnica Particular de Loja; Ecuador Fil: Hernández, Rosa M.. Universidad Experimental Simón Rodríguez; Venezuela Fil: Hughes, Frederic M.. Universidade Estadual de Feira de Santana; Brasil Fil: Muiño, Walter. Universidad Nacional de La Pampa; Argentina Fil: Monerris, Jorge. No especifíca; Fil: Ospina, Abelardo. Universidad Central de Venezuela; Venezuela Fil: Ramírez, David A.. International Potato Centre; Perú Fil: Ribas Fernandez, Yanina Antonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina Fil: Romão, Roberto L.. Universidade Estadual de Feira de Santana; Brasil Fil: Torres Díaz, Cristian. Universidad del Bio Bio; Chile Fil: Koen, Terrance B.. No especifíca; Fil: Maestre, Fernando T.. Universidad Rey Juan Carlos; España. Universidad de Alicante; España

14 páginas.-- 5 figuras.-- 2 tablas.-- 83 referencias.-- Electronic supplementary material The online version of this article https://doi.org/10.1007/s00468-017-1646-z) contains supplementary material, which is available to authorized users, Key message This study reinforces the existence of the leaf economics spectrum in Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as main drivers of variability in structural and nutrient traits of leaves. Abstract Leaf structural and nutrient traits are key attributes of plant ecological strategies, as these traits are related to resource-use strategies and plant growth. However, leaf structure and nutrient composition can vary among different habitats, leaf habits or phylogenetic groups. In this study, we measured 13 leaf traits (one structural—leaf mass per area, LMA—and 12 nutrient traits) in 98 Mediterranean woody species growing over a wide range of environmental conditions, with the final aim of discerning the main causes of leaf trait variability. The variance decomposition results show that phylogeny, leaf habit and habitat type affected in several ways the structural and nutrient traits studied. Leaf nutrient concentrations are strongly positively correlated amongst themselves, and negatively correlated with LMA, in accordance with the “leaf economics spectrum”. We found that leaf habit and phylogeny were important causes of variation in LMA and in a broad number of leaf nutrients (i.e., C, N, Mg, S, K), while other micronutrients seemed to be more dependent on the environment (i.e., Cu and Mn). In summary, our study reinforces the existence of the leaf economics spectrum in a broad pool of Mediterranean woody species, and demonstrates the strong influence of phylogeny, leaf habit and environmental context as the main drivers of variability in some leaf structural and nutrient traits., This study was funded by the Spanish MEC coordinated project DIVERBOS (CGL2011-30285-C02-01 and C02-02), the Andalusian ANASINQUE project (PGC2010-RNM-5782), the Life+Biodehesa Project (11/BIO/ES/000726), ECO-MEDIT (CGL2014-53236-R), RESTECO (CGL2014-52858-R) and European FEDER funds.

Over the last decades, there has been a growing interest in evaluating the predicted potential impacts of future climatic conditions on ecosystem functioning. Ecological indicators developed to assess ecosystem functioning strongly rely on soil and vegetation variables. In the current investigation, we evaluated the structural and functional status of a southern Mediterranean Stipa tenacissima steppe along an increasing aridity gradient. We estimated also the predicted effects of aridity on their functioning. The wide variation of LFA indices, vegetation structural attributes and soil properties among the different study sites revealed structural and functional heterogeneity in S . tenacissima steppes with the increasing aridity. Correlations obtained between LFA indices and most patch attributes showed the importance of vegetation structural attributes on the functioning of S . tenacissima steppes. On the other hand, correlations found between LFA indices and most measured soil variables verified the significance of LFA indices in monitoring soil functioning in southern Mediterranean S . tenacissima steppes. The strong negative relationships observed between aridity and stability, nutrient cycling indices demonstrated that increasing aridity can reinforce erosive processes and deteriorate nutrient cycling (i.e. aridity decreased soil carbon, nitrogen and enzymatic activities). Similarly, aridity was negatively related to vegetation structural attributes including patch cover and landscape organization index. This finding suggests that any increase in aridity can promote the loss of perennial vegetation cover. The current investigation highlighted that predicted increasing aridity will dramatically affect the functioning of southern Mediterranean S . tenacissima steppes, especially in the more arid areas.

Soil bacteria and fungi play key roles in the functioning of terrestrial ecosystems, yet our understanding of their responses to climate change lags significantly behind that of other organisms. This gap in our understanding is particularly true for drylands, which occupy ∼41% of Earth´s surface, because no global, systematic assessments of the joint diversity of soil bacteria and fungi have been conducted in these environments to date. Here we present results from a study conducted across 80 dryland sites from all continents, except Antarctica, to assess how changes in aridity affect the composition, abundance, and diversity of soil bacteria and fungi. The diversity and abundance of soil bacteria and fungi was reduced as aridity increased. These results were largely driven by the negative impacts of aridity on soil organic carbon content, which positively affected the abundance and diversity of both bacteria and fungi. Aridity promoted shifts in the composition of soil bacteria, with increases in the relative abundance of Chloroflexi and α-Proteobacteria and decreases in Acidobacteria and Verrucomicrobia. Contrary to what has been reported by previous continental and global-scale studies, soil pH was not a major driver of bacterial diversity, and fungal communities were dominated by Ascomycota. Our results fill a critical gap in our understanding of soil microbial communities in terrestrial ecosystems. They suggest that changes in aridity, such as those predicted by climate-change models, may reduce microbial abundance and diversity, a response that will likely impact the provision of key ecosystem services by global drylands.

International audience; Despite their importance, how plant communities and soil microorganisms interact to determine the capacity of ecosystems to provide multiple functions simultaneously (multifunctionality) under climate change is poorly known. We conducted a common garden experiment using grassland species to evaluate how plant functional structure and soil microbial (bacteria and protists) diversity and abundance regulate soil multifunctionality responses to joint changes in plant species richness (one, three and six species) and simulated climate change (3 degrees C warming and 35% rainfall reduction). The effects of species richness and climate on soil multifunctionality were indirectly driven via changes in plant functional structure and their relationships with the abundance and diversity of soil bacteria and protists. More specifically, warming selected for the larger and most productive plant species, increasing the average size within communities and leading to reductions in functional plant diversity. These changes increased the total abundance of bacteria that, in turn, increased that of protists, ultimately promoting soil multifunctionality. Our work suggests that cascading effects between plant functional traits and the abundance of multitrophic soil organisms largely regulate the response of soil multifunctionality to simulated climate change, and ultimately provides novel experimental insights into the mechanisms underlying the effects of biodiversity and climate change on ecosystem functioning.

Aims Climate and human impacts are changing the nitrogen (N) inputs and losses in terrestrial ecosystems. However, it is largely unknown how these two major drivers of global change will simultaneously influence the N cycle in drylands, the largest terrestrial biome on the planet. We conducted a global observational study to evaluate how aridity and human impacts, together with biotic and abiotic factors, affect key soil variables of the N cycle. Location Two hundred and twenty-four dryland sites from all continents except Antarctica widely differing in their environmental conditions and human influence. Methods Using a standardized field survey, we measured aridity, human impacts (i.e. proxies of land uses and air pollution), key biophysical variables (i.e. soil pH and texture and total plant cover) and six important variables related to N cycling in soils: total N, organic N, ammonium, nitrate, dissolved organic:inorganic N and N mineralization rates. We used structural equation modelling to assess the direct and indirect effects of aridity, human impacts and key biophysical variables on the N cycle. Results Human impacts increased the concentration of total N, while aridity reduced it. The effects of aridity and human impacts on the N cycle were spatially disconnected, which may favour scarcity of N in the most arid areas and promote its accumulation in the least arid areas. Main conclusions We found that increasing aridity and anthropogenic pressure are spatially disconnected in drylands. This implies that while places with low aridity and high human impact accumulate N, most arid sites with the lowest human impacts lose N. Our analyses also provide evidence that both increasing aridity and human impacts may enhance the relative dominance of inorganic N in dryland soils, having a negative impact on key functions and services provided by these ecosystems.

Aim The global spread of woody plants into grasslands is predicted to increase over the coming century. While there is general agreement regarding the anthropogenic causes of this phenomenon, its ecological consequences are less certain. We analysed how woody vegetation of differing cover affects plant diversity (richness and evenness) and the surrogates of multiple ecosystem processes (multifunctionality) in global drylands, and how these change with aridity. Location Two hundred and twenty-four dryland sites from all continents except Antarctica, widely differing in their environmental conditions (from arid to drysubhumid sites) and relative woody cover (from 0 to 100%). Methods Using a standardized field survey, we measured the cover, richness and evenness of perennial vegetation. At each site, we measured 14 soil variables related to fertility and the build-up of nutrient pools. These variables are critical for maintaining ecosystem functioning in drylands. Results Species richness and ecosystem multifunctionality were strongly related to woody vegetation, with both variables peaking at a relative woody cover (RWC) of 41–60%. This relationship shifted with aridity. We observed linear positive effects of RWC in dry-subhumid sites. These positive trends shifted to humpshaped RWC–diversity and multifunctionality relationships under semi-arid environments. Finally, hump-shaped (richness, evenness) or linear negative (multifunctionality) effects of RWC were found under the most arid conditions. Main conclusions Plant diversity and multifunctionality peaked at intermediate levels of woody cover, although this relationship became increasingly positive in wetter environments. This comprehensive study accounts for multiple ecosystem attributes across a range of levels of woody cover and environmental conditions. Our results help us to reconcile contrasting views of woody encroachment found in the current literature and can be used to improve predictions of the likely effects of encroachment on biodiversity and ecosystem services.

Dryland ecosystems account for ca. 27% of global soil organic carbon (C) reserves, yet it is largely unknown how cli- mate change will impact C cycling and storage in these areas. In drylands, soil C concentrates at the surface, making it particularly sensitive to the activity of organisms inhabiting the soil uppermost levels, such as communities domi- nated by lichens, mosses, bacteria and fungi (biocrusts). We conducted a full factorial warming and rainfall exclusion experiment at two semiarid sites in Spain to show how an average increase of air temperature of 2-3 °C promoted a drastic reduction in biocrust cover (ca. 44% in 4 years). Warming significantly increased soil CO2 efflux, and reduced soil net CO2 uptake, in biocrust-dominated microsites. Losses of biocrust cover with warming through time were par- alleled by increases in recalcitrant C sources, such as aromatic compounds, and in the abundance of fungi relative to bacteria. The dramatic reduction in biocrust cover with warming will lessen the capacity of drylands to sequester atmospheric CO2. This decrease may act synergistically with other warming-induced effects, such as the increase in soil CO2 efflux and the changes in microbial communities to alter C cycling in drylands, and to reduce soil C stocks in the mid to long term.

One of the most important changes taking place in drylands worldwide is the increase of the cover and dominance of shrubs in areas formerly devoid of them (shrub encroachment). A large body of research has evaluated the causes and consequences of shrub encroachment for both ecosystem structure and functioning. However, there are virtually no studies evaluating how shrub encroachment affects the ability of ecosystems to maintain multiple functions and services simultaneously (multifunctionality). We aimed to do so by gathering data from ten ecosystem functions linked to the maintenance of primary production and nutrient cycling and storage (organic C, activity of β-glucosidase, pentoses, hexoses, total N, total available N, amino acids, proteins, available inorganic P and phosphatase activity), and summarizing them in a multifunctionality index (M). We assessed how climate, species richness, anthropic factors (distance to the nearest town, sandy and asphalted road, and human population in the nearest town at several historical periods) and encroachment by sprouting shrubs impacted both the functions in isolation and M along a regional (ca. 350 km) gradient in Mediterranean grasslands and shrublands dominated by a non-sprouting shrub. Values of M were higher in those grasslands and shrublands containing sprouting shrubs (43% and 62%, respectively). A similar response was found when analyzing the different functions in isolation, as encroachment by sprouting shrubs increased functions by 2%–80% compared to unencroached areas. Encroachment was the main driver of changes in M along the regional gradient evaluated, followed by anthropic factors and species richness. Climate had little effects on M in comparison to the other factors studied. Similar responses were observed when evaluating the functions in isolation. Overall, our results showed that M was higher at sites with higher sprouting shrub cover, longer distance to roads and higher perennial plant species richness. Our study is the first documenting that ecosystem multifunctionality in shrublands is enhanced by encroaching shrubs differing in size and leaf attributes. Our findings reinforce the idea that encroachment effects on ecosystem functioning cannot be generalized, and that are largely dependent on the traits of the encroaching shrub relative to those of the species being replaced.

International audience; 1. Habitat filtering (HF, trait convergence) and niche differentiation (ND, trait divergence) are known to impact upon plant community structure. Both processes integrate individual responses to the abiotic environment and biotic interactions. Thus, it is difficult to clearly identify the underlying abiotic and biotic factors that ultimately impact community structure by looking at community-level patterns of trait divergence or convergence alone. 2. We used a functional trait-based and multiscale approach to assess how biotic interactions and aridity determine the functional structure of semi-arid shrublands sampled along a large aridity gradient in Spain. At the regional scale, we investigated functional differences among species (axes of specialization) to identify important traits for community assembly. At the community scale, we evaluated the relative impact of HF and ND on community structure using a null model approach. Finally, at the plant neighbourhood scale, we evaluated the impact of biotic interactions on community structure by investigating the spatial patterns of trait aggregation. 3. The shrub species surveyed can be separated along four axes of specialization based on their above-ground architecture and leaf morphology. Our community scale analysis suggested that the functional structure of semi-arid communities was clearly non-random, HF and ND acting independently on different traits to determine community structure along the aridity gradient. At the plant neighbourhood scale, the spatial distribution of species was also clearly not random, suggesting that competition and facilitation impacted on the observed changes in the functional diversity of shrubland communities along the aridity gradient. 4. Synthesis: Our results demonstrated that HF and ND acted simultaneously on independent traits to jointly determine community structure. Most importantly, our multiscale approach suggested that competition and facilitation interplayed with aridity to determine this structure. Competition appeared to be constant along the aridity gradient and explained the high functional diversity observed in semi-arid shrublands. Facilitation affected subordinate and rare species and, thus, may act to enhance the biodiversity of these ecosystems. Finally, the framework employed in our study allows moving forward from the examination of patterns to the development of mechanistic traitbased approaches to study plant community assembly.

12 páginas.-- 5 figuras.-- 1 tabla.-- 75 referencias-- The online version of this article (doi:10.1007/s11258-016-0677-7) contains supplementary material, which is available to authorized users., Increasing temperature and drought intensity is inducing the phenomenon of the so-called “hotter drought”, which is expected to increase in frequency over the coming decades across many areas of the globe, and is expected to have major implications for forest systems. Consequences of hotter drought could be especially relevant for closely related species overlapping their distributions, since differences in response can translate into range shifts. We assessed the effect of future climatic conditions on the performance of five ecologically distinct pine species common in Europe: Pinus halepensis, P. pinaster, P. nigra, P. sylvestris and P. uncinata. We hypothesised that Mediterranean species inhabiting dry, low-elevation sites will be less affected by the expected warming and drought increase than species inhabiting cold-wet sites. We performed a controlled conditions experiment simulating current and projected temperature and precipitation, and analysed seedling responses in terms of survival, growth, biomass allocation, maximum photochemical efficiency (Fv/Fm) and plant water potential (Ψ). Either an increase in temperature or a reduction in water input alone reduced seedling performance, but the highest impact occurred when these two factors acted in combination. Warming and water limitation reduced Ψ, whereas warming alone reduced biomass allocation to roots and Fv/Fm. However, species responded differentially to warmer and drier conditions, with lowland Mediterranean pines (P. halepensis and P. pinaster) showing higher survival and performance than mountain species. Interspecific differences in response to warmer, drier conditions could contribute to changes in the relative dominance of these pine species in Mediterranean regions where they co-occur and a hotter, drier climate is anticipated., This work was supported by the project ECOLPIN (AGL2011-24296) to P.V-S. and by EU Marie Curie (FP7-2011-IEF- 300825) and Juan de la Cierva (FPDI-2013-15867) Fellowships to L.M.

Global Ecosystem Analysis The relationship between species richness and the functional properties of their ecosystems has often been studied at small scales in experimental plots. Maestre et al. (p. 214 ; see the Perspective by Midgley ) performed field measurements at 224 dryland sites from six continents and assessed 14 ecosystem functions related to carbon, nitrogen, and phosphorus cycling. Positive relationships were observed between perennial plant species richness and ecosystem functionality. The relative importance of biodiversity was found to be as large as, or larger than, many key abiotic variables. Thus, preservation of plant biodiversity is important to buffer negative effects of climate change and desertification in drylands, which collectively cover 41% of Earth's land surface and support over 38% of the human population.

Mediterranean forest plantations are currently under an intense debate related to their ecological function, sustainability and future performance. In several Mediterranean countries, efforts are directed to convert pine plantations into mixed and more diverse forests. This research aims to evaluate the effect of the spatial configuration of pine plantations on regeneration and plant diversity in order to facilitate plantation management towards more diversified stands. Spatial characteristics of plantations (proximity to different vegetation types, fragmentation and internal patch structure) were related to abundance of seedlings of an ecologically important broadleaved species, Holm Oak (Quercus ilex L.), and the Shannon diversity index of the community. Q. ilex seedling abundance and plant diversity in pine plantation patches are favoured by the proximity to oak patches located uphill. Fragmentation affected only plant diversity, with smaller patches having more diversity. The internal structure of the pine patch influenced both regeneration of Q. ilex and diversity. Pine patches with lower pine tree density were characterized by higher diversity and less Q. ilex regeneration confirming that internal structure affects species differently. From a management perspective, the process of conversion of Mediterranean pine plantations to mixed oak–pine forests could be facilitated by (1) having the seed source uphill from the plantation, (2) increasing the fragmentation of plantations and (3) promoting the internal heterogeneity of plantations to create a diverse range of light environments matching the different requirements of species. Zusammenfassung Die okologische Funktion, die Nachhaltigkeit und die Zukunft der Plantagenwirtschaft im Mittelmeerraum werden gegenwartig heftig diskutiert. In verschiedenen Landern des Mittelmeerraumes sollen Kiefernplantagen in arten- und strukturreichere Mischbestande umgebaut werden. Ziel dieser Forschungsarbeit ist es, den Einfluss der raumlichen Beschaffenheit von Kiefernplantagen auf Verjungung und Pflanzendiversitat einzuschatzen, damit der Umbau zu vielfaltigeren Bestanden erleichtert werden kann. Die raumlichen Eigenschaften der Bestande (Nahe zu anderen Vegetationstypen, Fragmentierung und Struktur) korrelieren mit der Haufigkeit von okologisch wichtigen Eichensamlingen, Steineiche (Quercus ilex), und dem Shannon Diversitatsindex der Gemeinschaft. Die Haufigkeit von Q. ilex-Samlingen und die Pflanzenvielfalt der Kiefernflachen werden durch

Drought stress is known to limit plant performance in Mediterranean-type ecosystems. We have investigated the dynamics of the hydraulics, gas exchange and morphology of six co-existing Mediterranean woody species growing under natural field conditions during a drought that continued during the entire summer. Based on the observed minimum leaf water potentials, our results suggest that the six co-existing species cover a range of plant hydraulic strategies, from isohydric to anisohydric. These differences are remarkable since the selected individuals grow within several meters of each other, sharing the same environment. Surprisingly, whatever the leaf water potentials were at the end of the dry period, stomatal conductance, photosynthesis and transpiration rates were relatively similar and low across species. This result contradicts the classic view that anisohydric species are able to maintain gas exchange for longer periods of time during drought stress. None of the plants showed the expected structural acclimation response to the increasing drought (reduction of leaf-to-sapwood area ratio), thereby rejecting the functional equilibrium hypothesis for our study system. Instead, three of the six species increased photosynthetic area at the branch level. The observed dissimilar patterns of gas exchange, hydraulics and morphology across species seem to be equally successful given that photosynthesis at the leaf level was maintained at similar rates over the whole dry period.

Here, we investigate small-scale spatial variation of environmental factors potentially influencing woody-plant establishment for 3 years (2004, 2005 and 2006) along a heterogeneous landscape. Environmental variables of over 2883 potential microsites were sampled in different landscape units with a spatially explicit design, and seeds of four tree species were sown at the different microsites. We used spatial-analysis techniques to quantify spatial heterogeneity of the environment surrounding the seeds, and to relate seedling and sapling survival to the spatial structure of environmental factors studied. Most environmental variables showed aggregated spatial patterns among landscape units. However, survival showed random spatial patterns in most of the cases, although it may depend on year-to-year variation of precipitation. Thus, spatial patterns of survival were random under both wet and dry conditions, while aggregated patterns emerged under intermediate conditions. Aggregated survival, if detected, was better explained by the environmental variables studied as plant age increased. In addition, the spatial consistency found across demographic stages, represents hotspots of recruitment, for which direct identification would be critical for restoration activities. Our results showed a balance between stochasticity at early stages and environmental determinism at later stages, showing, behind the idiosyncratic character of plant recruitment, stronger general rules at sapling stages.

Intransitive competition networks, those in which there is no single best competitor, may ensure species coexistence. However, their frequency and importance in maintaining diversity in realworld ecosystems remain unclear. We used two large data sets from drylands and agricultural grasslands to assess: (1) the generality of intransitive competition, (2) intransitivity–richness relationships and (3) effects of two major drivers of biodiversity loss (aridity and land-use intensification) on intransitivity and species richness. Intransitive competition occurred in > 65% of sites and was associated with higher species richness. Intransitivity increased with aridity, partly buffering its negative effects on diversity, but was decreased by intensive land use, enhancing its negative effects on diversity. These contrasting responses likely arise because intransitivity is promoted by temporal heterogeneity, which is enhanced by aridity but may decline with land-use intensity. We show that intransitivity is widespread in nature and increases diversity, but it can be lost with environmental homogenisation.

We used a functional trait-based approach to assess the impacts of aridity and shrub encroachment on the functional structure of Mediterranean dryland communities (functional diversity and community-weighted mean trait values [CWM]), and to evaluate how these functional attributes ultimately affect multifunctionality (i.e., the provision of several ecosystem functions simultaneously).Shrub encroachment (the increase in the abundance/cover of shrubs) is a major land cover change that is taking place in grasslands worldwide. Studies conducted on drylands have reported positive or negative impacts of shrub encroachment depending on the functions and the traits of the sprouting or non-sprouting shrub species considered.Functional diversity and CWM were equally important as drivers of multifunctionality responses to both aridity and shrub encroachment. Size traits (e.g., vegetative height or lateral spread) and leaf traits (e.g., specific leaf area and leaf dry matter content) captured the effect of shrub encroachment on multifunctionality with a relative high accuracy (r2=0.63). Functional diversity also improved the resistance of multifunctionality along the aridity gradient studied.Maintaining and enhancing functional diversity in plant communities may help to buffer negative effects of ongoing global environmental change on dryland multifunctionality.

The monitoring of ecosystem processes has become an essential tool for combating desertification. Monitoring techniques are often based on indicators of ecosystem functioning. Among them, the Landscape Function Analysis (LFA) method allows the assessment of ecosystem geochemical functioning by means of an easy, precise, consistent and cheap approach. This method has never been used to assess the functioning of the Moroccan alfa steppes (Stipa tenacissima L.). In the present study, we applied the LFA method to characterize the functioning of alfa steppes in 12 sites distributed throughout Eastern Morocco. We checked for correlation between the LFA indices and variables of soil functioning. Our results showed that LFA indices can be used as surrogates of soil properties related to soil functioning such as organic C, total N, pH and salinity. Moroccan steppes showed a low level of functionality compared to similar steppes in Spain, and require conservation and ecological restoration measures. The use of the LFA method in alfa steppes can be used to increase our understanding of their functioning, and may help managers to design more efficient management plans., Le suivi des processus écologiques est devenu un outil nécessaire dans les efforts de lutte contre la désertification. Les techniques de suivi disponibles sont généralement basées sur les indicateurs du fonctionnement de l’écosystème. Parmi ces techniques, la méthode de l’analyse fonctionnelle du paysage, connue sous le nom LFA (Landscape Function Analysis), permet d’évaluer le fonctionnement géochimique de l’écosystème de manière facile, précise, consistante et peu chère. Cette méthode n’a jamais été appliquée pour caractériser le fonctionnement des steppes d’alfa (Stipa tenacissima L.) marocaines. Dans la présente étude, nous avons appliqué la méthode LFA pour caractériser le fonctionnement des steppes d’alfa dans douze sites situés à l’est du Maroc. Nous avons testé la corrélation entre les indices LFA et les variables du fonctionnement du sol. Les résultats ont montré que les indices LFA peuvent être utilisés comme équivalents des variables du fonctionnement du sol comme le C organique, le N total, le pH et la salinité. Comparées aux steppes espagnoles, les steppes marocaines ont montré des niveaux fonctionnels bas justifiant des actions adéquates de conservation et de restauration écologique. L’application de la méthode LFA pour les steppes d’alfa est susceptible d’améliorer nos connaissances sur le fonctionnement de ces écosystèmes et d’aider les gestionnaires à mieux concevoir les plans d’aménagement y afférents., Derak Mchich, Maestre Fernando T., Quero José L., Ochoa Victoria, Escolar Cristina, Soliveres Santiago, García-Palacios Pablo. Caractérisation du fonctionnement des steppes d’Alfa marocaines par la méthode de l’analyse fonctionnelle du paysage. In: Ecologia mediterranea, tome 41 n°2, 2015. pp. 61-72.

Aim: Geographical, climatic and soil factors are major drivers of plant beta diversity, but their importance for dryland plant communities is poorly known. The aim of this study was to: (1) characterize patterns of beta diversity in global drylands; (2) detect common environmental drivers of beta diversity; and (3) test for thresholds in environmental conditions driving potential shifts in plant species composition. Location: Global. Methods: Beta diversity was quantified in 224 dryland plant communities from 22 geographical regions on all continents except Antarctica using four complementary measures: the percentage of singletons (species occurring at only one site); Whittaker's beta diversity, ?(W); a directional beta diversity metric based on the correlation in species occurrences among spatially contiguous sites, ?(R2); and a multivariate abundance-based metric, ?(MV). We used linear modelling to quantify the relationships between these metrics of beta diversity and geographical, climatic and soil variables. Results: Soil fertility and variability in temperature and rainfall, and to a lesser extent latitude, were the most important environmental predictors of beta diversity. Metrics related to species identity [percentage of singletons and ?(W)] were most sensitive to soil fertility, whereas those metrics related to environmental gradients and abundance [(?(R2) and ?(MV)] were more associated with climate variability. Interactions among soil variables, climatic factors and plant cover were not important determinants of beta diversity. Sites receiving less than 178 mm of annual rainfall differed sharply in species composition from more mesic sites (> 200 mm). Main conclusions: Soil fertility and variability in temperature and rainfall are the most important environmental predictors of variation in plant beta diversity in global drylands. Our results suggest that those sites annually receiving c. 178 mm of rainfall will be especially sensitive to future climate changes. These findings may help to define appropriate conservation strategies for mitigating effects of climate change on dryland vegetation

The importance of biological soil crusts (biocrusts) for the biogeochemistry of drylands is widely recognized. However, there are significant gaps in our knowledge about how climate change will affect these organisms and the processes depending on them. We conducted a manipulative full factorial experiment in two representative dryland ecosystems from central (Aranjuez) and southeastern (Sorbas) Spain to evaluate how precipitation, temperature and biocrust cover affected the assimilation and net C balance of biocrusts. Chlorophyll fluorescence, net photosynthesis and dark respiration were measured in situ bimonthly during a year. We also conducted daily cycle measurements of net photosynthesis in winter and at the end of spring. In Sorbas, warming reduced the fixation of atmospheric C in biocrust-dominated microsites throughout the year. In Aranjuez, there was an interaction between the three factors evaluated; during winter, net photosynthesis was significantly greater in high biocrust cover plots under natural conditions and in the rainfall exclusion treatment. During the daily surveys, rainfall exclusion and warming reduced C fixation in Sorbas and in Aranjuez respectively. The effects of the treatments evaluated varied with the rainfall and non-rainfall water inputs (NRWIs) registered before the measurements. Our results suggest that changes in NRWI regimes as consequence of warming could have a greater impact on the C balance of biocrusts than changes in rainfall amounts. They also indicate that climate change may reduce the photosynthetic ability of lichens, with a consequent reduction of their dominance in biocrust communities at the mid to long term. This could reduce the ability of dryland ecosystems to fix atmospheric C.

[EN] Pine seedling survival and growth in eastern Spain have often been related to site preparation, planting date and seedling stock. However, in spite of the acknowledged importance of spatial heterogeneity in seedling performance, little is understood about how topography-related spatial patterns may modify seedling response to plantation, particularly on dry sites. We tested the hypotheses that growth and survival of Pinus halepensis seedlings are related to stock quality, plantation date and topographic conditions, as well as the spatial pattern of environmental variables using a spatially explicit design. The plantation treatment consisted of three seedling stocks, two plantation dates and two contrasted quality sites. Topographic features, such as slope, aspect, Compound Topographic Index and flow accumulation, were measured using GPS and low density LiDAR, with growth and survival monitored over a period of one and two years, respectively. The spatial pattern of the study variables was examined via spatial analysis by distance indices (SADIE). The relative importance of each topographic variable explaining the spatial pattern (local aggregation indices, v) of seedling response was examined using ordinary least squares (OLS) regressions. P. halepensis seedlings showed higher survival and growth in better sites and early plantations, but they were very similar between seedling stocks. A significantly greater proportion of seedlings survived in early date of plantation (54%) compared to medium date (36%), and in the favorable site (51%) versus the restrictive site (38%). Seedlings also grew significantly faster for those treatments during the first year. However, stock quality had few effects on survivorship and growth. All the topographic and seedling response variables exhibited an aggregated spatial pattern. Seedling survival was clearly associated with topographic patterns, particularly to those related to water availability (CTI and flow accumulation), indicating that on topographic-spatial scales, seedling response is driven by soil-water dynamics in Mediterranean ecosystems. The topographic morphology described by LiDAR was also closely linked to seedling response, thus suggesting the potential of these data to evaluate reforestation success. Accurate maps of topographic factors may indicate whether a plantation has a higher survival and growth potential and with routine reforestation planning activities such as soil preparation. (C) 2014 Elsevier B.V. All rights reserved., We are grateful to the Generalitat of Valencia for its assistance in using the experimental forests. Our thanks also to VAERSA for their help with the field work, especially to Antonio Ibanez, and Martha Gaustad for revising the English. Financial support was received from DIVERBOS (CGL2011-30285-C02-02) project. We also acknowledge the financial support from University of Cordoba-Campus de Excelencia CEIA3 and the Sustainable Forest Restoration Management Research Program.

The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. Wefind a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition1. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems. Fil: Delgado Baquerizo, Manuel. Universidad Pablo de Olavide; España. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España Fil: Maestre, Fernando T.. Universidad Pablo de Olavide; España. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España Fil: Gallardo, Antonio. Universidad Pablo de Olavide; España Fil: Bowker, Matthew A.. Northern Arizon University/school Of Forestry; Fil: Wallenstein, Matthew D.. Northern Arizona University; Estados Unidos Fil: Bran, Donaldo Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España Fil: Gatica, Mario Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina Fil: Hepper, Estela Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Prina, Anibal Oscar. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Pucheta, Eduardo Raúl. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina Fil: Huber Sannwald, Elisabeth. Instituto Potosino de Investigación Científica y Tecnológica; México Fil: Jankju, Mohammad. Ferdowsi University of Mashhad; Irán Fil: Liu, Jushan. Northeast Normal University. Institute of Grassland Science,; China Fil: Mau, Rebecca L.. Northern Arizona University; Estados Unidos Fil: Miriti, Maria. Ohio State University; Estados Unidos Fil: Monerris, Jorge. Université du Québec a Montreal; Canadá Fil: Naseri, Kamal. Ferdowsi University of Mashhad; Irán Fil: Noumi, Zouhaier. Université de Sfax; Túnez Fil: Polo, Vicente. Universidad Rey Juan Carlos. Departamento de Biología y Geología. Área de Biodiversidad y Conservación; España Fil: Ramírez Collantes, David A.. International Potato Center; Perú Fil: Romão, Roberto. Universidade Estadual de Feira de Santana. Departamento de Ciencias Biológica, Herbario; Brasil Fil: Tighe, Matthew. University of New England; Australia Fil: Torres, Duilio. Universidad Centroccidental ‘‘Lisandro Alvarado’’; Venezuela Fil: Torres Díaz, Cristian. Universidad del Bio Bio. Facultad de Ciencias. Departamento de Ciencias Básicas. Laboratorio de Genómica y Biodiversidad; Chile Fil: Ungar, Eugene D.. The Volcani Center. Agricultural Research Organization. Institute of Plant Sciences; Israel Fil: Val, James. Office of Environment and Heritage; Australia Fil: Wamiti, Wanyoike. National Museums of Kenya. Zoology Department; Kenia Fil: Wang, Deli. Northeast Normal University. Institute of Grassland Science; China Fil: Zaady, Eli. Gilat Research Center; Israel

13 pages, 5 figures, 1 table, 66 references. We thank Wageningen University for facilitating the stay of Lorena Gómez-Aparicio and José Luis Quero., The combined effects of shade and drought on plant performance and the implications for species interactions are highly debated in plant ecology. Empirical evidence for positive and negative effects of shade on the performance of plants under dry conditions supports two contrasting theoretical models about the role of shade under dry conditions: the trade-off and the facilitation hypotheses. We performed a meta-analysis of field and greenhouse studies evaluating the effects of drought at two or more irradiance levels on nine response variables describing plant physiological condition, growth, and survival. We explored differences in plant response across plant functional types, ecosystem types and methodological approaches. The data were best fit using quadratic models indicating a humped-back shape response to drought along an irradiance gradient for survival, whole plant biomass, maximum photosynthetic capacity, stomatal conductance and maximal photochemical efficiency. Drought effects were ameliorated at intermediate irradiance, becoming more severe at higher or lower light levels. This general pattern was maintained when controlling for potential variations in the strength of the drought treatment among light levels. Our quantitative meta-analysis indicates that dense shade ameliorates drought especially among drought-intolerant and shade-tolerant species. Wet tropical species showed larger negative effects of drought with increasing irradiance than semiarid and cold temperate species. Non-linear responses to irradiance were stronger under field conditions than under controlled greenhouse conditions. Non-linear responses to drought along the irradiance gradient reconciliate opposing views in plant ecology, indicating that facilitation is more likely within certain range of environmental conditions, fading under deep shade, especially for drought-tolerant species., This study was partly supported by the postdoctoral grant MCINN (Spain) to J.L.Q. (ref 2007-0572).

The great spatial and temporal heterogeneity of Mediterranean ecosystems can influence establishment success in woody species, whose natural regeneration occurs to a very small extent. In this work, the effect of the spatial pattern of environmental variables (light availability, soil moisture and herbaceous production) on seedling emergence, growth, survival and establishment success was examined by using a spatially explicit approach. Seeds of four Quercus species differing in leaf longevity (Quercus ilex, Quercus suber, Quercus faginea and Quercus pyrenaica) were sown in two plots located in a holm oak forest (southern Spain). The spatial pattern of the studied variables was examined by Spatial Analysis by Distance Indices. All environmental variables exhibited an aggregated spatial pattern. There was no clear spatial association between the environmental variables and emergence and survival. Only soil moisture during the dry season was spatially associated with the establishment success of all the species. Species also differed in survival and establishment success, with evergreens having higher percentages than deciduous. No aggregated spatial pattern for growth and morphological traits was apparent, these being more dependent on seed mass than on environmental factors. Identifying which microsites facilitate regeneration may provide useful hints with a view in focusing restoration endeavours on microenvironments with high survival percentage.

Understanding seedling performance across resource gradients is crucial for defining the regeneration niche of plant species under current environmental conditions and for predicting potential changes under a global change scenario. A 2-year field experiment was conducted to determine how seedling survival and growth of two evergreen and two deciduous Quercus species vary along gradients of light and soil properties in two Mediterranean forests with contrasting soils and climatic conditions. Half the seedlings were subjected to an irrigation treatment during the first year to quantify the effects on performance of an alteration in the summer drought intensity. Linear and non-linear models were parameterized and compared to identify major resources controlling seedling performance. We found both site-specific and general patterns of regeneration. Strong site-specificity was found in the identity of the best predictors of seedling survival: survival decreased linearly with increasing light (i.e. increasing desiccation risk) in the drier site, whereas it decreased logistically with increasing spring soil water content (i.e. increasing waterlogging risk) in the wetter site. We found strong empirical support for multiple resource limitation at the drier site, the response to light being modulated by the availability of soil resources (water and P). Evidence for regeneration niche partitioning among Quercus species was only found at the wetter site. However, at both sites Quercus species shared the same response to summer drought alleviation through water addition: increased first-year survival but not final survival (i.e. after two years). This suggests that extremely dry summers (i.e. the second summer in the experiment) can cancel out the positive effects of previous wetter summers. Therefore, an increase in the intensity and frequency of summer drought with climate change might cause a double negative impact on Quercus regeneration, due to a general reduction in survival probability and the annulment of the positive effects of (infrequent) 'wet' years. Overall, results presented in this study are a major step towards the development of a mechanistic model of Mediterranean forest dynamics that incorporates the idiosyncrasies and generalities of tree regeneration in these systems, and that allow simulation and prediction of the ecological consequences of resource level alterations due to global change.

10 pages, 3 figures, 3 tables, 55 references., Most of our knowledge regarding ontogenetic niche shifts in plants has been derived from studies involving only two or unconnected life stages. Approaches covering a broader range of different life stages are still needed to fully understand the implications of ontogenetic niche shifts for plant regeneration dynamics. We investigated ontogenetic shifts in the endangered Mediterranean tree species Acer opalus ssp. granatense (A. opalus) comparing the environmental characteristics of individuals of different ages with those of a random sample of available microsites. In addition, since herbivory could be a limiting factor, herbivory damage was quantified. Differences in environmental characteristics between locations of individual plants and randomly selected points became larger with plant age, suggesting that the regeneration niche of A. opalus shifts during ontogeny, undergoing a contraction. The presence of shrubs and adult trees, the depth of the litter layer, and herbivory were the main factors influencing these changes. A. opalus can germinate in all available microhabitats its seeds can reach, but saplings establish and grow only in a subset of microhabitats, which represent a change in tolerance to extrinsic factors. Old saplings establish under the canopy of shrubs, far away from tree cover that could block light required in the oldest stage. Therefore, temporal changes in the nature and strength of plant–plant interactions are also occurring. The ecological concept of niche shifts reveals the microsites with higher probabilities of long-term sapling survival of A. opalus: shrub cover involves an array of environmental changes crucial for the successful establishment of A. opalus saplings under stressful Mediterranean conditions, from microhabitat amelioration to herbivory protection., This study was supported by the Grant FPI-MEC to JLQ (BES-2003-1716), and by the coordinated Spanish CICYT projects HETEROMED (REN2002-04041) and DINAMED (CGL2005-05830). LGA was supported by a postdoctoral fellowship from the University of Granada and by a Fullbright postdoctoral fellowship (FU2004-1288) from the Spanish Ministerio de Educación y Ciencia (MEC). FTM was supported by Fullbright (FU2003-0398) and Ramón y Cajal research fellowships from MEC. This research is part of the REDBOME (http://www.ugr.es/~redbome/) and GLOBIMED (http://www.globimed.net) networks on forest ecology.

12 pages, 6 figures, 1 table, 78 references. We thank the Consejería de Medio Ambiente, Junta de Andalucía, and the Direction of the Sierra Nevada National Park, for permission for the field work, constant support and facilities. We are also especially grateful to Sergio de Haro for his help during the field work. Martin F. Quigley made valuable comments on an earlier version of the manuscript. David Nesbitt looked over the English version of the manuscript., Spatial heterogeneity of abiotic factors influences patterns of seedling establishment at different scales. In stress-prone ecosystems such as Mediterranean ones, heterogeneity generated by shrubs has been shown to facilitate the establishment of tree species. However, how this facilitation is affected by spatial scale remains poorly understood. We have experimentally analysed the consequences of the abiotic heterogeneity generated by pioneer shrubs on survival, growth and physiology of seedlings of three important tree species from Mediterranean mountains (Acer opalus ssp. granatense, Quercus pyrenaica and Quercus ilex). Patterns of abiotic heterogeneity and seedling performance were studied at two scales differing in grain: 1) the microhabitat scale, by using open interspaces as controls of the effect of different shrub species, and 2) the microsite scale, analysing the effects of fine-grain heterogeneity (within-microhabitat heterogeneity). Results showed that, at the microhabitat scale, seedling establishment of the three tree species significantly benefited from the modification of the abiotic environment by nurse shrubs. However, we found shrub-seedling interactions to be species-specific, due to differential modification of both aboveground (light availability) and belowground (soil compaction, water content, and fertility) abiotic factors by nurse shrub species. Heterogeneity at the within-microhabitat scale was rather high, although it did not significantly affect seedling performance of any of the tree species. The study demonstrates that the effects of the abiotic heterogeneity generated by shrubs are not consistent across the range of spatial scales considered. The regeneration niche of tree species becomes very complex at fine spatial scales, and thereby estimators of abiotic heterogeneity are valuable descriptors of spatial patterns of seedling establishment only when microsite ‘‘noise’’ is averaged out at greater scales., This study was supported by a PFPU-MECD grant to L.G.A., and projects REN2001- 4552-E and HETEROMED REN2002-04041-CO2-01/GLO from the Spanish Ministry of Science and Technology (MCYT). This collaborative research was favoured by the thematic network GLOBIMED, also supported by MCYT.

While much is known about the factors that control each component of the terrestrial nitrogen (N) cycle, it is less clear how these factors affect total N availability, the sum of organic and inorganic forms potentially available to microorganisms and plants. This is particularly true for N-poor ecosystems such as drylands, which are highly sensitive to climate change and desertification processes that can lead to the loss of soil nutrients such as N. We evaluated how different climatic, abiotic, plant and nutrient related factors correlate with N availability in semiarid Stipa tenacissima grasslands along a broad aridity gradient from Spain to Tunisia. Aridity had the strongest relationship with N availability, suggesting the importance of abiotic controls on the N cycle in drylands. Aridity appeared to modulate the effects of pH, plant cover and organic C (OC) on N availability. Our results suggest that N transformation rates, which are largely driven by variations in soil moisture, are not the direct drivers of N availability in the studied grasslands. Rather, the strong relationship between aridity and N availability could be driven by indirect effects that operate over long time scales (decades to millennia), including both biotic (e.g. plant cover) and abiotic (e.g. soil OC and pH). If these factors are in fact more important than short-term effects of precipitation on N transformation rates, then we might expect to observe a lagged decrease in N availability in response to increasing aridity. Nevertheless, our results suggest that the increase in aridity predicted with ongoing climate change will reduce N availability in the Mediterranean basin, impacting plant nutrient uptake and net primary production in semiarid grasslands throughout this region.

Jucker and Coomes claim that the relationship between plant species richness (biodiversity) and ecosystem multifunctionality (B-EMf) reported in our study changes along environmental gradients. We point out flaws in their analytical approach and then reanalyze our data to further demonstrate that the B-EMf relationship does not substantially change along environmental gradients.

Dryland vegetation is characterized by discrete plant patches that accumulate and capture soil resources under their canopies. These “fertile islands” are major drivers of dryland ecosystem structure and functioning, yet we lack an integrated understanding of the factors controlling their magnitude and variability at the global scale. EEA Bariloche Fil: Ochoa-Hueso, Raúl. Universidad Autónoma de Madrid. Department of Ecology; España Fil: Eldridge, David J. University of New South Wales. School of Biological, Earth and Environmental Sciences; Australia Fil: Delgado-Baquerizo, Manuel. University of Colorado. Cooperative Institute for Research in Environmental Sciences; Estados Unidos. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; España Fil: Soliveres, Santiago. University of Bern. Institute of Plant Sciences; Suiza Fil: Bowker, Matthew A. Northern Arizona University. School of Forestry; Estados Unidos Fil: Gross, Nicolás. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; España. Institut Nationale de la Recherche Agronomique; Francia. Université La Rochelle. Centre d’étude biologique de Chizé; Francia Fil: Le Bagousse-Pinguet, Yoann. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; España Fil: Quero, José L. Universidad de Córdoba. Escuela Técnica Superior de Ingeniería Agronómica y de Montes. Departamento de Ingeniería Forestal: España Fil: García-Gómez, Miguel. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; España Fil: Valencia, Enrique. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; España Fil: Arredondo, Tulio. Instituto Potosino de Investigación Científica y Tecnológica. División de Ciencias Ambientales; México Fil: Beinticinco, Laura. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Bran, Donaldo Eduardo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bariloche; Argentina Fil: Cea, Alex. Universidad de La Serena. Departamento de Biología; Chile Fil: Coaguila, Daniel. Instituto de Ensino Superior de Rio Verde; Brasil Fil: Dougill, Andrew J. University of Leeds. School of Earth and Environment; Gran Bretaña Fil: Espinosa, Carlos I. Universidad Técnica Particular de Loja. Departamento de Ciencias Naturales; Ecuador Fil: Gaitan, Juan Jose. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Suelos; Argentina Fil: Guuroh, Reginald T. University of Cologne. Botanical Institute. Range Ecology and Range Management Group; Alemania. CSIR-Forestry Research Institute of Ghana; Ghana Fil: Guzmán, Elizabeth. Universidad Técnica Particular de Loja. Departamento de Ciencias Naturales; Ecuador Fil: Gutiérrez, Julio R.. Universidad de La Serena. Departamento de Biología; Chile. Centro de Estudios Avanzados en Zonas Áridas (CEAZA); Chile. Instituto de Ecología y Biodiversidad; Chile Fil: Hernández, Rosa M. Universidad Experimental Simón Rodríguez. Centro de Agroecología Tropical. Laboratorio de Biogeoquímica; Venezuela Fil: Huber-Sannwald, Elisabeth. Instituto Potosino de Investigación Científica y Tecnológica. División de Ciencias Ambientales; México Fil: Jeffries, Thomas. Western Sydney University. Hawkesbury Institute for the Environment; Australia Fil: Linstädter, Anja. University of Cologne. Botanical Institute. Range Ecology and Range Management Group; Alemania Fil: Mau, Rebecca L. Northern Arizona University. Center for Ecosystem Science and Society: Estados Unidos Fil: Monerris, Jorge. Université du Québec à Montréal. Pavillon des Sciences Biologiques. Département des Sciences Biologiques; Canadá Fil: Prina, Anibal. Universidad Nacional de La Pampa. Facultad de Agronomía; Argentina Fil: Pucheta, Eduardo. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Físicas y Naturales. Departamento de Biología; Argentina Fil: Stavi, Ilan. Dead Sea and Arava Science Center, Israel Fil: Thomas, Andrew. Aberystwyth University. Department of Geography and Earth Sciences; Gran Bretaña Fil: Zaady, Eli. Agricultural Research Organization. Gilat Research Center. Natural Resources; Israel Fil: Singh, Brajesh K. Western Sydney University. Hawkesbury Institute for the Environment; Australia. Western Sydney University. Global Centre for Land-Based Innovation; Australia Fil: Maestre, Fernando T. Universidad Rey Juan Carlos. Escuela Superior de Ciencias Experimentales y Tecnología. Departamento de Biología y Geología, Física y Química Inorgánica; España