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Mediterranean forests are considered to be highly vulnerable ecosystems to climate change because they are water- and nutrient-limited. However, experimental evidence of the combined effects of increasing drought and warming on biogeochemical cycles in these ecosystems is still extremely scarce. To fill this gap, we analyzed during four consecutive years the impacts of rainfall reduction (RE; ambient vs. ~30% reduction in rainfall), soil warming (W; ambient vs. ~ 1 °C increase) and their interaction on biogeochemical cycling of C, N and P in Mediterranean forests. Rainfall exclusion translated into quick significant reductions of soil organic matter (SOM), enzymatic activity (β-glucosidase, urease and acid phosphatase activities) and nutrient availability (ammonium, nitrate and phosphorus) one year after the application of the treatments. These effects were consistent over time. Warming acted synergistically with rainfall reduction to further decrease C-related variables (SOM and β-glucosidase). SOM reduction in forest soils might be the result of delayed leaf senescence as a drought tolerant trait in the forest trees. Warming also had direct positive effects on N- and P- related variables that partially counteracted the negative effects of rainfall reduction on these variables. Overall, our results showed that the different components of climate change (drought and warming) have complex direct and interactive effects on biogeochemical cycles of Mediterranean forests that differ among soil nutrients (C, N, P). Consequently, drought and warming might cause an unbalance in natural biogeochemical cycles of Mediterranean forests, with important consequences for ecosystem functioning.

14 páginas.- 6 figuras.- 1 tabla.- referencias.- Additional supporting information may be found in the online version of the article at the publisher’s website, Although plant–plant interactions (i.e. competition and facilitation) have long been recognised as key drivers of plant community composition and dynamics, their global patterns and relationships with climate have remained unclear. Here, we assembled a global database of 10,502 pairs of empirical data from the literature to address the patterns of and climatic effects on the net outcome of plant interactions in natural communities. We found that plant interactions varied among plant performance indicators, interaction types and biomes, yet competition occurred more frequently than facilitation in plant communities worldwide. Unexpectedly, plant interactions showed weak latitudinal pattern and were weakly related to climate. Our study provides a global comprehensive overview of plant interactions, highlighting competition as a fundamental mechanism structuring plant communities worldwide. We suggest that further investigations should focus more on local factors (e.g. microclimate, soil and disturbance) than on macroclimate to identify key environmental determinants of interactions in plant communities., This work was supported by the National Natural Science Foundation of China (32071524, 31770514 and 31870711). International research travel by J.H.C.C. was partly funded by the Royal Netherlands Academy of Arts and Sciences (KNAW, CEP grant 12CDP007).

Context Land-use and climate change are leading to more frequent and intense tree damage and mortality events. Drought-induced tree mortality is occurring worldwide leading to broad-scale events, but the spatial patterns of tree damage and mortality, their underlying drivers and their variation over time is largely unknown. Objectives We investigated the spatial patterns of tree damage and mortality across Mediterranean forests of the Iberian Peninsula, the underlying effects of competition and climate, and how the spatial patterns and relationships with underlying drivers changed over time. Methods We used the Spanish Forest Inventory to analyse the autocorrelation in tree damage and mortality across forest types, hurdle-gamma models to quantify the effect of competition and climate on tree damage and mortality, and cross-correlograms to assess their spatial dependence and its change over time. Results We observed a greater magnitude and a stronger autocorrelation in tree damage than mortality, with positive aggregation up to 20 kilometres. There was a spatial dependence between tree damage and mortality with their drivers, with spatial aggregation increasing with water availability, drought intensity and competition. The spatial dependence of tree damage and mortality with the underlying drivers increased over time, particularly for drought intensity. Conclusions Our results suggest that the combined effect of intense competition and drought could favour more extensive die-off and tree mortality events, providing key information for identifying vulnerable areas and the planning of adaptation measures.

5 figuras.- 1 tabla.- This article is in Press, Journal Pre-proof, Climate change is a fundamental process affecting terrestrial ecosystems. However, there is relatively little knowledge about its impacts on soil communities, with a large degree of uncertainty regarding their resistance to predicted alterations in temperature and, particularly, precipitation. Moreover, most studies exploring the response of soil biota to predicted rainfall reduction have focused on mesic environments and soil microbes, which limit our ability to find general patterns across ecosystems and soil organisms. In this study, we analysed the impact of predicted climate change scenarios of rainfall reduction on soil food webs of Mediterranean water-limited forests using nematodes as bioindicators. We took advantage of replicated rainfall exclusion infrastructures (30% exclusion) established in Quercus forests of southern Spain in 2016 (2-year exclusion) and of southern France in 2003 (15-year exclusion) to explore the sensitivity of the soil food web to predicted reductions at short- and long-term scales. Rainfall reduction had large negative short-term effects on nematode abundance, particularly of lower trophic groups (bacterivores and fungivores). Rainfall reduction had also consistent short- and long-term impacts on community composition (decrease of fungivores, marginal increase of omnivores) and nematode-based indicators of soil food web structure (higher maturity and structure index, lower prey:predator ratio). These results can be considered indicative of a low resistance of the soil food web to rainfall reductions predicted by climate change. Overall, our findings demonstrate the sensitivity of water-limited forests to further reductions in soil water availability, which might substantially alter their soil communities and likely affect the many ecosystem processes that they control., This study was funded by the MICINN projects INTERCAPA (CGL2014-56739-R) and MICROFUN (RTI2018-094394-B-I00). P.H. was supported by a FPI-MICINN grant. L.M. was supported by the fellowship IV2 from VI-PPIT (Univ. Sevilla) and the project PID2019-108288RA-I00 (MINECO). OG acknowledges financial support provided by the Spanish Ministry of Economy and Competitiveness (MINECO) and by the European Social Fund through the Ramón y Cajal Program (RYC-2017-23666). Puéchabon is supported by the OSU OREME (UMS 3282) and the French national research infrastructure ANAEE-France (ANR-11-INBS-0001).

Plant recruitment interactions (i.e., what recruits under what) shape the composition, diversity, and structure of plant communities. Despite the huge body of knowledge on the mechanisms underlying recruitment interactions among species, we still know little about the structure of the recruitment networks emerging in ecological communities. Modeling and analyzing the community-level structure of plant recruitment interactions as a complex network can provide relevant information on ecological and evolutionary processes acting both at the species and ecosystem levels. We report a data set containing 143 plant recruitment networks in 23 countries across five continents, including temperate and tropical ecosystems. Each network identifies the species under which another species recruits. All networks report the number of recruits (i.e., individuals) per species. The data set includes >850,000 recruiting individuals involved in 118,411 paired interactions among 3318 vascular plant species across the globe. The cover of canopy species and open ground is also provided. Three sampling protocols were used: (1) The Recruitment Network (RN) protocol (106 networks) focuses on interactions among established plants (“canopy species”) and plants in their early stages of recruitment (“recruit species”). A series of plots was delimited within a locality, and all the individuals recruiting and their canopy species were identified; (2) The paired Canopy-Open (pCO) protocol (26 networks) consists in locating a potential canopy plant and identifying recruiting individuals under the canopy and in a nearby open space of the same area; (3) The Georeferenced plot (GP) protocol (11 networks) consists in using information from georeferenced individual plants in large plots to infer canopy-recruit interactions. Some networks incorporate data for both herbs and woody species, whereas others focus exclusively on woody species. The location of each study site, geographical coordinates, country, locality, responsible author, sampling dates, sampling method, and life habits of both canopy and recruit species are provided. This database will allow researchers to test ecological, biogeographical, and evolutionary hypotheses related to plant recruitment interactions. There are no copyright restrictions on the data set; please cite this data paper when using these data in publications., Fondo Europeo de Desarrollo Regional, Grant/Award Number, ICTS-2017-08-CSIC-4; SUMHAL, Grant/Award Numbers: 418RT0555, 501100011033, LIFEWATCH-2019-09-CSIC-13, MCIN/ AEI/10.13039, PGC2018-100966-B-100, PID2020-113157GB-I00, POPE 2014-2020

8 páginas.- 2 figuras.- 1 tabla.- 76 referencias.- Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.agrformet.2022.109002, Worldwide, Mediterranean-climate type forests are seriously threatened by climate change and Phytophthora cinnamomi, an extremely aggressive soilborne pathogen listed among the 100 worst invasive alien species. This study examines for first time the effects of annual and seasonal changes in temperature and rainfall under different climatic scenarios on P. cinnamomi dynamics in a Mediterranean forest naturally infested. We followed seasonally and during four years (2016-2020) P. cinnamomi abundance in the soil taking advantage of a climate change infrastructure that simulates a 30% rainfall reduction using rainout shelters and an increase in soil temperature using open top chambers. Seasonal abundance of P. cinnamomi was strongly linked to spring precipitation: the large inoculum density during this season suffered a strong decrease during the dry summer that was maintained until the next spring, despite of fall rains. Thus, inoculum density in spring may be considered the best indicator of the potential of P. cinnamomi infection in natural ecosystems. The two climatic treatments had significant effects on P. cinnamomi abundance, but only in some combinations of seasons and years. Rainfall exclusion had a negative effect on the spring abundance of P. cinnamomi mostly in wet years, causing a reduction as large as 30% in comparison with the control treatment. Meanwhile, warming effect varied from slightly negative in winter to positive in spring and early summer, causing increases as large as 31% in comparison with the control treatment. Overall, we provide novel experimental evidence suggesting that a drier climate might limit the abundance and activity of P. cinnamomi in water-limited forests, but that this negative effect might be at least partly counteracted by the positive effects of warming. These results also imply that P. cinnamomi represents an increasing threat under climate change for the conservation of forest ecosystems where water is not a limiting factor., This project received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement No 706055 and from the project CGL2014-56739-R (Ministry of Economy, Industry and Competitiveness, Government of Spain)

12 páginas.- 4 figuras.- 4 tablas.- 114 referencias.- Supplementary data to this article can be found online at https://doi.org/10.1016/j.soilbio.2022.108560., The loss of tree health is a global concern with many unknown cascading impacts on the diversity and function of forest ecosystems. Specifically, it is uncertain how the process of tree decline and mortality driven by exotic pathogens might alter the soil microbiome. Here we combined high-throughput sequencing, neighborhood models, and network analysis to explore the impacts of the decline of a Mediterranean tree species, Quercus suber, on the diversity, composition and network structure of soil fungal and bacterial communities in forests invaded by the exotic pathogen Phytophthora cinnamomi. The belowground footprint of pathogen-driven tree decline implied an increase in the taxonomic and phylogenetic diversity of both bacteria and fungi, but also a severe reduction of tree-symbiotic fungi and Proteobacteria known to have positive effects on plant growth and disease suppression. Moreover, we detected alterations of the topology of soil microbial networks in declining tree neighborhoods (lower connectivity, higher modularity), with implications for ecosystem function. Our findings reveal the large impacts that moderate levels of tree decline can have on the soil microbiome of invaded forests, and highlight the recovery of a functionally diverse and highly connected soil microbiome as a key target in the restoration of these disturbed systems., This research was supported by the Ministerio de Ciencia e Innovación (MICINN) projects INTERCAPA (CGL2014-56739-R) and MICROFUN (RTI2018-094394-B-I00). AJMP was supported by a post-doctoral fellowship funded by the Portuguese Foundation for Science and Technology (SFRH/BPD/111015/2015), JDB by a FPI-MEC grant (BES-2012-055113) and EVS by a FPU-MICINN grant (FPU16/04616).

12 páginas.- 2 figuras.- 1 tabla.- referencias.-Additional Supporting Information may be found in the online version of this article https://doi.org/10.1111/jvs.13083, Questions To gain insights into the role of species-by-species replacements in cloud forest community structuring, we asked: (1) What are the effects of the spatial distribution of standing individuals on the seed rain, soil seed bank, and sapling density and survival in this cloud forest? and (2) What is the prevalence of conspecific vs. heterospecific replacements in the regeneration of this forest? Location Santo Tomás Teipan, Oaxaca State, southern Mexico. Methods In a 1-ha cloud forest plot we assessed seed rain, seed bank, and sapling density and survival of four canopy tree species (Chiranthodendron pentadactylon, Cornus disciflora, Quercus laurina, Oreopanax xalapensis). All standing individuals of these and other tree species (dbh ≥ 2.5 cm) were mapped. We used neighbourhood models to examine the spatial patterns of the three life cycle stages relative to the spatial distribution of adults. The neighbourhood effect was assessed through the Neighbourhood Index, which integrates information on size (dbh) and distance to adults. Data analysis was based on maximum likelihood and model selection procedures. Results We found large between-species differences regarding the spatial patterns of seeds and saplings. Three species showed evidence for the Janzen-Connell effect operating at the seed (C. pentadactylon and Q. laurina) or sapling (O. xalapensis) stage. We also found support for a critical role of specific microsite factors (i.e., niche differentiation) in the regeneration of two species (C. pentadactylon and C. disciflora). Conclusions Seed and sapling distribution patterns suggest the prevalence of heterospecific replacements, and that both Janzen-Connell and niche differentiation effects contribute to this pattern. Our results largely support the notion that the prevalence of heterospecific replacements among canopy species promotes species coexistence in cloud forests, This estudy received partial support from the Mexican Science Council (CONACyT–México) through a doctoral scholarship and a post-doctoral grant to NRM-D. The Faculty of Sciences, Universidad Nacional Autónoma de México, provided additional funding.

Martinez-Munoz, M., Gomez-Aparicio, L., Perez-Ramos, I.M. 2019. Techniques to promote tree regeneration in Mediterranean savannah-like ecosystems. Ecosistemas 28(3):142-149. Doi.: 10.7818/ECOS.1798 Savannah-liked ecosystems have a serious problem of lack of natural regeneration of their dominant tree species. Although there are different techniques of assisted regeneration to alleviate this problem, further scientific studies will be necessary to analyze the efficiency level of these techniques under future climate change scenarios. In this study, we have reviewed the main factors limiting assisted regeneration of oak species in dehesa ecosystems, and we have identified the efficiency level of the main techniques commonly used to promote tree recruitment from an agro-ecological perspective. For this purpose, we have carried out a bibliographic review and conducted surveys to some researchers with relevant experience in this area. Results from this study indicate that water stress during summer, the unfavorable soil conditions over seedling establishment and the high seed predation rates and plant grazing are the most limiting factors for oak recruitment in the study ecosystems. In the second part of the study, we recommended a number of agro-ecological techniques as a function of the efficiency level reported in previous scientific studies, and we highlighted those techniques that require further investigation according to experts´ opinions (e.g. the use of nurse plants or the application of watering treatments). The information provided by this study will be used as a useful tool in management and conservation plans of dehesas with the aim of assuring their persistence and potentiating their adaptation abilities under future environmental scenarios.

8 páginas.- 4 figuras.- 2 tablas.- referencias.- Supplementary material associated with this article can be found, in the online version, at https://doi.org/10.1016/j.agrformet.2020.108295, The structure and function of Mediterranean mixed oak forests are seriously threatened by climate change and the exotic pathogen Phytophthora cinnamomi. Both factors have been individually studied in some detail, but we have a poor understanding of their interactive effects on plant performance and species coexistence. We conducted a greenhouse experiment where seedlings of three coexisting species with contrasting susceptibility to the pathogen (Quercus suber, Quercus canariensis and Olea europaea var. sylvestris) were planted in pairs under different scenarios of drought (control vs. 30% rainfall reduction), warming (control vs. 3°C increase) and pathogen presence (control vs. soil infested with P. cinnamomi). At the end of the experiment, we assessed the severity of root symptoms and plant morphological traits (shoot and root biomass, root tissue density and specific root length). Results showed that seedlings of the three species, including O. europaea and Q. canariensis (species considered as resistant and tolerant to the pathogen, respectively), showed in general significantly higher root symptoms and lower shoot and root biomass than non-inoculated seedlings, independently of the drought, warming and plant treatments. We found, however, some interactive effects of the climatic treatments and P. cinnamomi on root traits of the two Quercus species. Variations in the specific root length (SRL) and root tissue mass density (RTD) of Quercus spp. suggest a compensation of the negative effects of both stressors on seedling performance. Overall, our results suggest that the warming and drought predicted for Mediterranean forests during spring might not have a relevant impact on the infectivity ability of P. cinnamomi, supporting its great adaptability to these changing climatic conditions. Therefore, in Mediterranean forests infected by P. cinnamomi, it becomes crucial to avoid the spread and multiplication of the pathogen during spring, since its destructive ability at high inoculum levels is largely independent of environmental conditions., This work was supported by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement No 706055.

14 páginas.- 2 figuras.- 1 tabla.- referencias.- Additional supporting information may be found in the online version of this article at http://onlinelibrary.wiley.com/doi/10.1002/ecy.3430/suppinfo, Interactions among plant species and their soil biota drive plant–soil feedbacks (PSFs) that play a major role in the dynamics and diversity of plant communities. Among the different components of the soil community, pathogens are considered to be the main drivers of negative PSFs. Despite this, the number of studies that have experimentally quantified the contribution of soil pathogens to PSFs remains considerably low. Here we conducted a greenhouse experiment with oomycete-specific fungicide to quantify the contribution of soil pathogens, and particularly oomycete pathogens, to individual and pairwise PSFs in forest communities. We used as a case study Mediterranean mixed forests dominated by Quercus suber and invaded by the oomycete pathogen Phytophthora cinnamomi. The fungicide treatment was crossed with a competition treatment to explore how conspecific neighbors might modify pathogen effects. To place the results of the experiment in a wider context, we also conducted a systematic review of published papers that explicitly used fungicide to explore the role of pathogens in PSF experiments. Our experimental results showed that oomycete pathogens were the main drivers of individual PSFs in the study forests. Oomycete effects varied among tree species according to their susceptibility to P. cinnamomi, driving negative PSFs in the highly susceptible Q. suber but not in the coexistent Olea europaea. Oomycete-driven PSFs were not modified by intraspecific competition. Oomycete pathogens were also major contributors to negative pairwise PSFs assumed to promote species coexistence. Results from the systematic review supported the novelty of our experimental results, since only three studies had previously used oomycete-specific fungicide in a PSF context and none in systems invaded by exotic oomycetes. Overall, our results provide novel evidence of oomycete pathogens (including the exotic P. cinnamomi) as fundamental drivers of negative individual and pairwise PSFs with implications for species coexistence in invaded communities. Although in the short-term invasive pathogens might contribute to species coexistence by causing self-limitation in dominant species, strong inter-specific variation in self-limitation might undermine coexistence in the long-term. Because of the increasing number of exotic oomycetes worldwide, further attention should be given to oomycetes as drivers of PSFs in plant communities., This research was supported by the MICINN projects CGL2011-26877 and CGL2014-56739-R. J. Domínguez-Begines was supported by a FPI-MEC grant (BES-2012-055113), and J. M. Ávila by a FPU-MEC grant (AP2010-0229).

7 figuras.- 1 tablas.- referencias.- Data and associated code to reproduce the results are stored in Figshare (https://figshare.com/s/6ad186835f2ce6527ffa). Data is currently under embargo and it will be released upon publication. Nonetheless, data can be available under reviewer request if needed., Litter decomposition is a fundamental process for nutrient cycling and C fluxes between terrestrial ecosystems and the atmosphere. Multiple factors such as environmental conditions, litter quality, and decomposer organisms are known to influence this ecological process in direct and indirect ways. However, it remains poorly understood to what extent this entangled bank of complex interactions can be disrupted by several global change drivers such as climate change and invasive species. Here we report main findings from a litter decomposition experiment conducted in a natural mixed forest invaded by Phytophthora cinnamomi, an exotic oomycete well-known for causing tree disease and forest decline. In two Mediterranean forest types (namely woodland and closed forest), we first built a rainfall exclusion infrastructure to reduce natural precipitation by 30 %. Then, we followed the spatial variation in C and N leaf litter dynamics as well as the abundance of the exotic oomycete P. cinnamomi during 18 months under both control and rainfall exclusion conditions using a litter bag methodology with different mesh sizes to further evaluate the indirect role of mesofauna abundance and diversity in litter C and N temporal dynamics. Significant reductions in soil moisture produced by the experimental rainfall exclusion increased directly C litter loss with time, and indirectly via increases in overall mesofauna abundance and changes in the ratio between predators and decomposers. N litter dynamics were in contrast modulated mainly by initial litter quality. Surprisingly, P. cinnamomi abundance did not correlate with variation in initial litter quality as previously suggested, but we found that the exotic oomycete was negatively correlated with both decomposer and predator abundances. These results suggest it might participate indirectly in litter decomposition dynamics through the biotic soil component. Synthesis: Contrary to expected, our results show that a moderate but realistic rainfall reduction can accelerate the litter decomposition process. It also points out to litter fauna as a key component modulating the indirect impacts of global change drivers on litter decomposition., This study was funded by the MICINN projects INTERCAPA (CGL2014-56739-R) and MICROFUN (RTI2018-094394-B-I00). PH was supported by a FPI-MICINN grant. LM was supported by the fellowship IV2 from VI-PPIT (Univ. Sevilla) and the project PID2019-108288RA-I00 (MINECO). OG acknowledges financial support provided by the Spanish Ministry of Economy and Competitiveness (MINECO) and by the European Social Fund through the Ramón y Cajal Program (RYC-2017-23666)

9 páginas.- 3 figuras.- 1 tabla.- 75 referencias.- Supporting Information may be found in the online version of this article https://doi.org/10.1111/rec.13539, The natural regeneration of forests is declining in human-modified landscapes and overcoming ecological barriers to the seedling establishment is paramount to its restoration. This study focus on two common forest regeneration barriers: excessive sun exposure and low-quality soils. A degraded clearing with eroded and compacted soils within a disturbed oak forest in Mexico was chosen, and 20 experimental plots in a randomized factorial block design were set up to test seedling performance in the artificial shade and in forest topsoil that was transferred from a nearby remnant forest, as well as a combination of both. We sowed 400 acorns from two oak species (Quercus eduardii and Q. viminea) and monitored the emerging seedlings for 63 months. Our results confirm different survival and growth rates between species, ontogenetic stages, and environmental micro-conditions. The effect of artificial shade on seedling performance was positive in weathered soil but negative or neutral in transferred forest soil. Restoration interventions did not have additive benefits; seedling performance was improved by both restoration interventions applied separately though was not further enhanced when both actions were combined. Both species had different mechanisms to cope with water stress, which resulted in different photosynthetic rates under full sun. Trade-offs resulted in different life stages that were more enhanced by different restoration strategies; survival and growth were most enhanced by applying artificial shade or transferring forest topsoil, respectively. Restoration practitioners may prioritize seedling survival in harsh conditions and growth in less severe degraded sites or apply interventions sequentially over time. © 2021 Society for Ecological Restoration., This work was supported by the Secretary of Public Education (SEP) and the National Council for Science and Technology (CONACyT; grants CB-2015-01-257738 to DD and fellowshipno. 574853 to MBRR).

16 páginas.- 3 figuras.-Supporting information are accessible at h ttps://doi.org/10.17632/y8k3fddnz2.1, An increase in tree mortality rates as a consequence of biotic disturbances has been detected worldwide. Biotic disturbances in forests might cause significant impacts at ecosystem-level, with strong effects on soil biological activity and organic matter transformation. However, very few empirical studies have explored to date the consequences of biotic disturbances for soil microbial communities and C and N cycles. Here, we assessed the effects of Quercus suber dieback, caused by the exotic root pathogen Phytophthora cinnamomi, on the soil microbial community and key components of the C and N cycle. We used a spatially explicit neighborhood approach to analyze the effects of Q. suber trees with different health status and non-declining coexistent species on soil variables. The study was replicated in the two main Q. suber forest types of the region (closed forests and open woodlands) with contrasting soil texture characteristics. Pathogen-induced tree dieback did not affect microbial functional diversity or biomass, but translated into lower soil microbial respiration. Tree mortality induced changes in several variables of the C and N cycle, but the sign and magnitude of these effects varied depending on the local characteristics of soil texture. Coexistent species differed strongly from Q. suber in their effects on the C and N cycle. Overall, our results show that tree dieback due to invasive pathogens translates into complex short- and long-term effects on different components of the C and N cycles, despite no effects on microbial functional diversity and biomass., This research was supported by the Ministerio de Ciencia e Innovación (MICINN) projects CGL2010-21381 and CGL2011-26877 (RETROBOS). J.M.A. was supported by a FPU-MEC grant (AP2010-0229) and B.I. FPI-MICINN grant (BES-2009-017111).

10 páginas.- 3 figuras.- 1 tabla.- 47 referencias.- Supplementary information is available for this paper at https://doi.org/10.1038/s41467-020-17960-5, Ecologists have long argued that higher functioning in diverse communities arises from the niche differences stabilizing species coexistence and from the fitness differences driving competitive dominance. However, rigorous tests are lacking. We couple field-parameterized models of competition between 10 annual plant species with a biodiversity-functioning experiment under two contrasting environmental conditions, to study how coexistence determinants link to biodiversity effects (selection and complementarity). We find that complementarity effects positively correlate with niche differences and selection effects differences correlate with fitness differences. However, niche differences also contribute to selection effects and fitness differences to complementarity effects. Despite this complexity, communities with an excess of niche differences (where niche differences exceeded those needed for coexistence) produce more biomass and have faster decomposition rates under drought, but do not take up nutrients more rapidly. We provide empirical evidence that the mechanisms determining coexistence correlate with those maximizing ecosystem functioning., O.G. acknowledges postdoctoral financial support provided by the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No 661118-BioFUNC.

Background and aims Since its emergence in the mid‐20th century, invasion biology has matured into a productive research field addressing questions of fundamental and applied importance. Not only has the number of empirical studies increased through time, but also has the number of competing, overlapping and, in some cases, contradictory hypotheses about biological invasions. To make these contradictions and redundancies explicit, and to gain insight into the field’s current theoretical structure, we developed and applied a Delphi approach to create a consensus network of 39 existing invasion hypotheses. Results The resulting network was analysed with a link‐clustering algorithm that revealed five concept clusters (resource availability, biotic interaction, propagule, trait and Darwin’s clusters) representing complementary areas in the theory of invasion biology. The network also displays hypotheses that link two or more clusters, called connecting hypotheses , which are important in determining network structure. The network indicates hypotheses that are logically linked either positively (77 connections of support) or negatively (that is, they contradict each other; 6 connections). Significance The network visually synthesizes how invasion biology’s predominant hypotheses are conceptually related to each other, and thus, reveals an emergent structure – a conceptual map – that can serve as a navigation tool for scholars, practitioners and students, both inside and outside of the field of invasion biology, and guide the development of a more coherent foundation of theory. Additionally, the outlined approach can be more widely applied to create a conceptual map for the larger fields of ecology and biogeography., Global Ecology and Biogeography, 29 (6), ISSN:1466-822X, ISSN:1466-8238

BackgroundRecent evidence suggests that soil microbial communities can regulate plant community dynamics. In addition, the drought tolerance of plants can be enhanced by soil microbes. So far, few studies have assessed the variation in the microbiome of specific plant species along environmental gradients. Yet understanding these dynamics is essential to improve predictions of plant-soil feedbacks and the consequences of ongoing climate changes. Here we characterized the soil microbiome of two co-occurring Mediterranean oaks along a precipitation gradient, using amplicon sequencing of phylogenetic marker genes for prokaryotes and fungi. Additionally, we identified tree-specific and locally-specific microbes potentially responsible for tree community dynamics.ResultsWe show that two co-occurring, evergreen Mediterranean oak species harbor distinct microbiomes along a precipitation gradient. The soil microbial diversity increased along the precipitation gradient, for prokaryotic α and β diversity and for fungal β diversity. Quercus ilex harbored richer fungal communities than Quercus suber, and host-specific taxa more often belonged to fungi than to prokaryotes. Notably, the microbial communities at the dry end of the precipitation gradient harbored more locally-specific prokaryotic and fungal taxa than the microbial communities with a higher diversity, at the wet end of the gradient, suggesting higher specialization in drier areas.ConclusionsEven congeneric tree species, belonging to the same functional group, can harbor distinct and specific soil microbiomes. These microbiomes become more similar and consist of more specialized taxa under drier compared with wetter conditions. With this, our study offers a step towards a better understanding of the context-dependency of plant-soil feedbacks by going beyond α and β diversities and focusing on specialized taxa potentially driving community changes along environmental gradients. We hope that our study will stimulate future research assessing the importance of context-dependency of interactions between plants and soil communities in a changing world.

10 páginas.- 3 figuras.- referencias, The long-term conservation of Mediterranean mixed oak forests is seriously threatened by the massive mortality of Quercus suber caused by the exotic pathogen Phytophthora cinnamomi. This species frequently grows in mixed forests under natural conditions, but nothing is known about how its level of disease might be altered by the diversity and identity of coexisting neighbours varying in susceptibility to the exotic pathogen. Here we analysed the individual and combined effects of Q. suber and the main coexisting tree species (Quercus canariensis and Olea europaea subsp. europaea var. sylvestris) in mixed forests of southern Spain on the production of infective and survival spores of P. cinnamomi. Through in vitro experiments, it was demonstrated that mixtures of Q. suber and Q. canariensis highly stimulated the production of P. cinnamomi zoospores in comparison with both species in monocultures. Olea europaea did not stimulate zoospore production. Under controlled conditions, the initial and final densities of inoculum in soil planted with monocultures of O. europaea and Q. canariensis did not differ. However, inoculum densities significantly decreased along the experiment in Q. suber mixtures with O. europaea and Q. canariensis. Phytophthora cinnamomi was able to infect and cause root rot symptoms on all tree species, including O. europaea var. sylvestris. We concluded that mixed stands of Q. suber and Q. canariensis are able to stimulate P. cinnamomi infectivity and survival much more than monospecific stands, and consequently under favourable conditions for root disease development, the coexistence of Q. suber and Q. canariensis might exacerbate Mediterranean forests decline. This study also constitutes the first report of O. europaea var. sylvestris as host and inductor of P. cinnamomi sporulation under controlled conditions., This project has received funding from the European Research Coun-cil (ERC) under the European Union's Horizon 2020 research andinnovation program under grant agreement No. 706055. Many thanksto Dr. M.E. Sánchez (University of Córdoba) for the critical review ofthe manuscrip

7 páginas.- 3 figuras.- 37 referencias, Drought has been assumed as a predisposing factor in the decline caused by Phytophthora cinnamomi on Mediterranean Quercus forests, enhancing cork oak susceptibility to the root infection. However, P. cinnamomi outbreaks appear associated to waterlogged soils, with infections being particularly successful when soil moisture content fluctuates from flooding to water deficiency. We obtained cork oak seedlings potentially predisposed to Phytophthora disease by exposing them to a short (3 weeks) or a long (6 weeks) drought. These seedlings subjected to drought, together with well-watered seedlings, were exposed to two different soil concentrations of P. cinnamomi inoculum (chlamydospores) and submitted to high soil humidity for 4 weeks. Values of root necrosis were significantly higher in inoculated oak seedlings compared to non-inoculated control seedlings, but no significant differences were observed depending on previous drought treatments. Consequently, drought cannot be considered as a predisposing factor required for Phytophthora root disease development in cork oaks; although the adverse effects of both factors (drought and Phytophthora root infections) likely have synergistic consequences in the decline and death of affected oaks. © 2020, Koninklijke Nederlandse Planteziektenkundige Vereniging., With acknowledgement to MINECO, Spain (project CGL2014-56739-R), and LIFE program, EU (project LIFE+ 11 BIO/ES/000726) for financial support; and ME Sánchez from ETSIAM, Universidad de Córdoba (Spain), for the critical review of the manuscript.

11 páginas.-- 3 figuras.-- 2 tablas.-- 47 referencias.-- Electronic supplementary material The online version of this article ( https://doi.org/10.1007/s11104-018-3567-z) contains supplementary material, which is available to authorized users, Aims: Plant-soil feedbacks (PSFs) have been shown to be relevant drivers of forest community dynamics. However, few studies have explored variation of PSFs along environmental gradients. In a framework of climate change, there is a great need to understand how interactions between plants and soil microbes respond along climatic gradients. Therefore, we compared PSFs along a precipitation gradient in Mediterranean oak forests and included trait responses. Following the Stress Gradient Hypothesis (SGH), we expected less negative or even positive PSFs in the physically harsh dry end of our gradient and more negative PSFs in the wettest end. Methods: We grew Quercus ilex and Quercus suber acorns on soil inoculated with microbes sampled under adults of both species in six sites ranging in annual precipitation. After 4 months, we measured shoot biomass and allocation and morphological traits above and belowground. Results: We found negative PSFs for Q. ilex independent of precipitation, whereas for Q. suber PSFs ranged from positive in dry sites to negative in wet sites, in agreement with the SGH. The leaf allocation showed patterns similar to shoot biomass, but belowground allocation and morphological traits revealed responses which could not be detected aboveground. Conclusions: We provide first evidence for context-dependent PSFs along a precipitation gradient. Moreover, we show that measuring root traits can help improve our understanding of climate-dependent PSFs. Such understanding helps to predict plant soil microbe interactions, and their role as drivers of plant community dynamics under ongoing climate change., This study was supported by the Swiss National Science Foundation (SNSF) in the context of a mobility fellowship granted to G.R. (P2BEP3_162092). L.G.A. acknowledges support from the MICINN project INTERCAPA (CGL-2014-56739-R).

13 páginas.- 4 figuras.- 4 tablas.- 93 referencias, Emergent diseases are an increasing problem in forests worldwide. Exotic pathogens are now threatening forests where pathogens have not traditionally been considered to be major ecological drivers of tree demography, such as water‐limited Mediterranean forests. However, how pathogens might limit regeneration in invaded forests is largely unknown. Here we used fungicide to analyse the impact of soil‐borne oomycete pathogens on seedling establishment at community level in Mediterranean forests invaded by the exotic oomycete Phytophthora cinnamomi . Fungicide effects were modelled as a function of the tree neighbourhood composition, the seed mass of the target species, and the abiotic environment. Fungicide application had positive effects on seedling performance that varied in magnitude and spatial structure among coexisting species. Seed mass predicted fungicide effects on seedling emergence, but not on survival or growth. Positive fungicide effects were modulated by levels of abiotic resources, mainly water, increasing with soil moisture. Our results support a novel role for soil‐borne oomycete pathogens as one more axis of the regeneration niche of woody species in water‐limited forests. Given the increasing numbers of exotic oomycete pathogens worldwide, more research is needed to understand the role of this relevant microbial group as a factor shaping seedling establishment., This research was supported by the Ministerio de Economía y Competitividad (MICINN) projects CGL2011-26877 and CGL2014-56739-R. JD-B was supportedby a FPI-MEC grant (BES- 2012-055113) and JMA by a FPU-MEC grant (AP2010-0229

With ongoing biodiversity loss, it is important to understand how the mechanisms that promote coexistence relate to those that increase functioning in diverse communities. Both coexistence and biodiversity functioning research have unified their mechanisms into two classes. However, despite seeming similarities, theory suggests that coexistence and biodiversity mechanisms do not necessarily map onto each other, yet direct empirical evidence for this prediction is lacking. We coupled field-parameterized models of competition between 10 plants with a biodiversity-functioning experiment measuring biomass production, litter decomposition, and soil nutrient content under contrasting environmental conditions. We related biodiversity mechanisms (complementarity and selection effects), to coexistence mechanisms (niche and fitness differences). As predicted by theory, complementarity effects were positively correlated with niche differences and differences in selection effects were correlated with fitness differences. However, we also found that niche differences contributed to selection effects and fitness differences to complementarity effects. Despite this complexity more stably coexisting communities (i.e. those in which niche differences offset fitness differences) produced more biomass, particularly under drought. This relationship was weaker for litter decomposition rates and soil nutrient acquisition, showing that the mechanisms promoting plant coexistence may differ from those promoting high levels of functions that are less directly related to plant performance. We provide the first empirical evidence that the mechanisms promoting stable coexistence correlate with those driving high biomass production. These findings establish a link between stable coexistence and functioning, which could allow better predictions of how diversity loss induced by global change translates to changes in ecosystem function.

Aim Biodiversity loss and climate-driven ecosystem modification are leading to substantial changes in forest structure and function. However, the effects of diversity on demographic responses to the environment are poorly understood. We tested the diversity hypothesis (measured through functional diversity) and the mass ratio hypothesis (measured through functional identity) in relation to tree growth, tree mortality and sapling abundance. We sought to determine whether functional diversity underlies demographic responses to environmental variation in European forests. Location Europe (Spain, Germany, Wallonia, Finland and Sweden). Methods We used data from five European national forest inventories from boreal to Mediterranean biomes (c. 700,000 trees in 54,000 plots and 143 tree species) and the main forest types across Europe (i.e. from needle-leaved evergreen forests to broad-leaved deciduous forests). For each forest type, we applied maximum likelihood techniques to quantify the relative importance of stand structure, climate and diversity (i.e. functional diversity and functional identity) as determinants of growth, mortality and sapling abundance. We also tested whether demographic responses to environmental conditions (including stand density, evapotranspiration and temperature anomalies) varied with functional diversity. Results Our results suggest that functional diversity has a positive effect on sapling abundance and growth rates in forests across Europe, while no effect was observed on tree mortality. Functional identity has a strong effect on mortality and sapling abundance, with greater mortality rates in forests dominated by needle-leaved individuals and a greater abundance of saplings in forests dominated by broad-leaved individuals. Furthermore, we observed that functional diversity modified the effects of stand density on demographic responses in Mediterranean forests and the influence of evapotranspiration and temperature anomalies in forests widely distributed across Europe. Main conclusion Our results suggest that functional diversity may play a key role in forest dynamics through complementarity mechanisms, as well as by modulating demographic responses to environmental variation.

16 páginas.-- 2 tablas.-- 5 figuras.--104 referencias.-- Additional supporting information may be found online in the Supporting Information section at the end of the article in http://dx.doi.org/10.1111/1365-2745.13091, 1.Tree defoliation and mortality have considerably increased worldwide during the last decades due to global change drivers such as increasing drought or invasive pests and pathogens. However, the effects of this tree decline on soil food webs are poorly understood. 2.In this study we evaluated the impacts of Quercus suber decline on soil food webs of Mediterranean mixed forests invaded by the exotic oomycete pathogen Phytophthora cinnamomi, using soil nematodes as bioindicator taxa. We used a spatially‐explicit neighborhood approach to predict the characteristics of the nematode community (diversity, trophic structure, and several indices indicative of soil food web conditions) as a function of the characteristics of the tree and shrub community (species composition, size and health status). 3.Our results indicate that the process of defoliation and mortality of Q. suber caused significant alterations in the nematode trophic structure increasing the abundance of lower trophic levels (bacterivores, fungivores and herbivores) and decreasing the abundance of higher levels (predators and omnivores). Furthermore, Q. suber decline altered the functional composition of soil communities, producing a setback of the ecological succession in the soil food web to an earlier stage (decrease in the maturity index and increase in the plant‐parasitic index), simplified soil food webs (decrease in the structure index), and shifts in the predominant decomposition channel (increase in the fungivores/bacterivores ratio). 4.We also detected contrasting characteristics of the nematode community in neighborhoods dominated by coexisting woody species, which suggests potential for long‐term indirect effects on soil food webs due to the substitution of Q. suber by non‐declining species. 5.Synthesis:Our study provides novel results that show the major impacts that ongoing health deterioration of dominant tree species can have on the structure and composition of soil food webs in forest systems invaded by exotic pathogens, with cascading consequences for soil biogeochemical processes in both the short‐ and long‐term, This research was supported by the Ministerio de Economía y Competitividad (MICINN) projects CGL2011-26877and CGL2014-56739-R. JDB was supported bya FPI-MEC grant [BES-2012-055113].

11 páginas.- 4 figuras.- 2 tablas.-- 44 referencias.- Supplementary Information accompanies this paper at https://doi.org/10.1038/s41467-019-10453-0 .- Data availability Estimation of species demographic parameters and pairwise competitive coefficients for both climatic treatments are available at Dryad Digital Repository https://doi.org/10.5061/dryad.5d1s952. Average species means for the 19 functional traits included in this experiment are included in Supplementary Table 1., Functional traits are expected to modulate plant competitive dynamics. However, how traits and their plasticity in response to contrasting environments connect with the mechanisms determining species coexistence remains poorly understood. Here, we couple field experiments under two contrasting climatic conditions to a plant population model describing competitive dynamics between 10 annual plant species in order to evaluate how 19 functional traits, covering physiological, morphological and reproductive characteristics, are associated with species’ niche and fitness differences. We find a rich diversity of univariate and multidimensional associations, which highlight the primary role of traits related to water- and light-use-efficiency for modulating the determinants of competitive outcomes. Importantly, such traits and their plasticity promote species coexistence across climatic conditions by enhancing stabilizing niche differences and by generating competitive trade-offs between species. Our study represents a significant advance showing how leading dimensions of plant function connect to the mechanisms determining the maintenance of biodiversity., Funding support to conduct the experiment was provided by the Spanish Ecological Terrestrial Society (AEET, Jóvenes Investigadores grant 2014/2). I.M. P.-R. and L.M. were funded by a “Ramón & Cajal” contract (RYC-2013-13937) and an “Acción 6 UJA” fellowship (EI_RNM4_2017), respectively. O.G. acknowledges postdoctoral financial support provided by the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement (No. 661118-BioFUNC). I.M.P.-R. and L.G.-A. also thank support from the MICINN projects DECAFUN (CGL2015-70123-R) and INTERCAPA (CGL-2014-56739-R).

44 páginas.- 4 figuras.- 2 tablas.- 51 referencias.- Supplementary Information accompanies this paper at https://doi.org/10.1038/s41467-019-10453-0.- Estimation of species demographic parameters and pairwise competitive coefficients for both climatic treatments are available at Dryad Digital Repository https://doi.org/ 10.5061/dryad.5d1s952. Average species means for the 19 functional traits included in this experiment are included in Supplementary Table 1., Functional traits are expected to modulate plant competitive dynamics. However, how traits and their plasticity in response to contrasting environments connect with the mechanisms determining species coexistence remains poorly understood. Here, we couple field experiments under two contrasting climatic conditions to a plant population model describing competitive dynamics between 10 annual plant species in order to evaluate how 19 functional traits, covering physiological, morphological and reproductive characteristics, are associated with species¿ niche and fitness differences. We find a rich diversity of univariate and multidimensional associations, which highlight the primary role of traits related to water- and light-use-efficiency for modulating the determinants of competitive outcomes. Importantly, such traits and their plasticity promote species coexistence across climatic conditions by enhancing stabilizing niche differences and by generating competitive trade-offs between species. Our study represents a significant advance showing how leading dimensions of plant function connect to the mechanisms determining the maintenance of biodiversity., Funding support to conduct the experiment was provided by the Spanish Ecological Terrestrial Society (AEET, Jóvenes Investigadores grant 2014/2). I.M. P.-R. and L.M. were funded by a “Ramón & Cajal” contract (RYC-2013-13937) and an “Acción 6 UJA” fellowship (EI_RNM4_2017), respectively. O.G. acknowledges postdoctoral financial support provided by the European Union Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement (No. 661118-BioFUNC). I.M.P.-R. and L.G.-A. also thank support from the MICINN projects DECAFUN (CGL2015-70123-R) and INTERCAPA (CGL-2014-56739-R).

8 páginas.- 5 figuras.- 1 tabla.- 77 referencias.- Supplementary material related to this article can be found, in the online version, at Doi: https://doi.org/10.1016/j.envexpbot.2019.04.011, The changes in climate registered at the planetary scale threaten the persistence of current populations for many plant species, with effects particularly evident at the edges of species distributions. However, intraspecific differences in functional traits could modulate the plant responses to the expected increase in drought. Using a traitbased approach, we evaluated under controlled conditions how Quercus suber seedlings from the latitudinal edges of the distribution range of the species respond to different watering treatments in terms of vegetative growth and biomass allocation. In addition, we simulated an extreme drought by stopping watering until death to determine chemical and physiological traits under drought stress and to identify which morphological traits were more associated to drought resistance (expressed as survival time without watering). Seedlings from the northern provenance presented higher aboveground biomass allocation (i.e. shoot length and biomass allocation to shoot and leaves), while the southern ones were characterised by longer roots and higher biomass allocation to roots. Under extreme drought, seedlings from the southern provenance maintained higher photosynthetic rates than northern seedlings and were able to modulate their water-use efficiency (estimated from δ13C) depending on environmental conditions, which allowed them to survive for a longer period. Finally, drought resistance was partially explained by the plant biomass allocation pattern. Traits related to growth in height and light interception were negatively related with drought resistance, whereas traits involving investment in root biomass were positively related with resistance. These geographical differences evidence a local adaptation to drought at the southern edge of Q. suber distribution. Our results highlight the importance of the conservation of the genetic resources that peripheral populations harbour at distribution edges., This research was funded by a Large Research Grant (6007210) awarded from the British Ecological Societyand by a fellowship Plan 6-UJA (EI_RNM4_2017) to L.M. I.M.P.R and L.G.A. also thank support from the MICINN projects DECAFUN(CGL2015-70123-R) and INTERCAPA (CGL-2014-703 56739-R)

8 páginas.- 5 figuras.- 2 tablas.- 60 referencias, Climate change and exotic pests and pathogens are causing alarming forest declines worldwide. However, we still lack a comprehensive understanding of how damage caused by exotic pests and pathogens might vary under the different scenarios of water availability imposed by a changing climate, particularly in water-limited forests as those that occupy Mediterranean areas. In this paper we aimed to experimentally analyse the interactive effects of the aggressive exotic pathogen Phytophthora cinnamomi and climate change-related reductions in soil moisture on seedling performance of the Mediterranean host Quercus suber. We conducted a full-factorial greenhouse experiment where the physiology and growth of Q. suber seedlings was measured in soils with different combinations of P. cinnamomi inoculum density (0, 30, 60 and 120 colony forming units per gram of dry soil) and soil moisture (15%, 40%, 50% and 100% soil water holding capacity) simulating different invasion and climate change scenarios. We found additive effects of P. cinnamomi and drought on Q. suber performance aboveground, although these effects were not always negative. In fact, seedlings showed a compensatory physiological response to P. cinnamomi infection by increasing their net photosynthetic rates. Our results also supported important interactive effects of pathogens and soil moisture on belowground performance. Thus, the inoculum density in the soil required to cause significant root damage in experimental seedlings decreased as soil moisture increased. From a climate change perspective, these results suggest that an average drier climate might imply sub-optimal conditions for P. cinnamomi infections allowing for a slower advance of the disease in invaded areas. However, this effect will be modulated by the also predicted more frequent extreme climatic events. A higher frequency of extreme rain events that saturate the soil might be particularly beneficial for P. cinnamomi, boosting its soil density beyond any possible response capacity of susceptible hosts. © 2019, This study was funded by the MICINN project INTERCAPA ( CGL2014-56739-R ). P.H. was supported by a FPI-MICINN grant, L.M. by an “Acción 6 UJA” fellowship (EI_RNM4_2017), O.G. by a Marie Sklodowska-Curie grant agreement ( No 661118-BioFUNC ), and I.M.P.R by a “Ramón & Cajal” contract ( RYC-2013-13937 ).

19 páginas.-- 5 figuras.-- 3 tablas.-- 56 referencias.-- The online version of this article (https://doi.org/10.1007/s10533-018-0521-3) contains supplementary material, which is available to authorized users., Ecosystems worldwide must simultaneously cope with several global change drivers with potential strong effects on ecosystem functioning. These drivers might interact in unexpected ways, but our still limited understanding of these interactive effects precludes us from predicting the impact of global change on ecosystem functioning. In this study we assessed the direct effects of pathogen-induced tree mortality and predicted warming and drought on C, N and P in Mediterranean forest soils affected by the decline of their dominant tree species (i.e. Quercus suber) due to the invasive pathogen Phytophthora cinnamomi. We also explored the potential indirect effects due to species replacement after Q. suber mortality. To achieve our goal, we conducted a soil incubation experiment using soils collected under Q. suber trees with different health status (i.e. healthy, defoliated and dead trees) and from coexistent shrubs (i.e. pioneer and late successional shrubs). These soils were incubated under controlled temperatures and soil moistures, mimicking various climate change scenarios predicted for 2050 and 2100 in the Mediterranean Basin. Our results showed that P. cinnamomi-induced mortality and future warming and drought may interact to simultaneously alter biogeochemical cycles in Q. suber forest soils. Resistance of studied variables to changes in temperature and moisture tended to be lower for dead trees than for healthy and defoliated trees. Moreover, we found that soil respiration and nutrient availability might be affected indirectly by P. cinnamomi-induced mortality due to species replacement. Overall, our results support a high potential of invasive pathogen species for modifying the response of soil functioning to climatic stressors., This research was supported by the Ministerio de Ciencia e Innovación (MICINN) projects CGL2010-21381, CGL2011-26877 (RETROBOS) and CGL2014-56739-R (INTERCAPA). J.M.A. was supported by a FPU-MEC Grant (AP2010-0229).

12 páginas.-- 3 figuras.-- 1 tabla.-- 58 referencias.-- Special Feature: Intransitive competition and species coexistence.-- Data available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.5d1s9 (Matías, Godoy, Gómez-Aparicio, & Pérez-Ramos, 2018)., El artículo esta en libre acceso en la revista.-- free access article in this review, Very little is known about how variation in environmental conditions alters the strength and the structure of competitive networks and what are the consequences of this for species coexistence. We performed a competition experiment with 10 annual plant species to parameterise a population model describing species’ dynamics according to their vital rates and pairwise competitive coefficients. Seeds from all species were sown under two different climatic scenarios: (1) right before the first major storm of the growing season and (2) after an imposed fall drought of 2 months simulating an extreme climatic event of intense aridity. Species’ demography and competitive responses were used to estimate pairwise stabilising niche differences and average fitness differences. In addition, we used tools from network theory to characterise the structure of multispecies competition from the determinants of species coexistence. Specifically, we evaluated changes in competitive dominance between species pairs, and the prevalence of intransitive competitive relationships for 120 triplets between these two climatic events. The experimental extreme event significantly reduced fitness differences between species pairs. Such an equalising mechanism promotes coexistence. However, niche differences were also reduced in such a way that the number of species pairs whose niche differences overcame their fitness differences was reduced from six to two. Contrary to our expectations, the extreme event did not increase the hierarchy of competitive dominance. Instead, and depending on the technique used, the prevalence of intransitivity remained marginally similar (17% to 22%) or significantly increased from 19.4% to 29.8%. This pattern was likely a consequence of the significant changes in competitive dominance between species pairs (26 changes out of 45; 58%). Although fitness differences were equalised and intransitive competition promoted, our model predicted a lower likelihood of coexistence under the extreme event for both species pairs and triplets, mainly because competitive interactions did not promote enough niche differences to balance the observed fitness asymmetries in our competitive networks. Synthesis. We empirically proved that an extreme climate results in communities with reduced niche and fitness differences in which species are less likely to coexist despite the increasing prevalence of intransitive competition., Was funded by a Juan de la Cierva grant (FPDI-2013-15867). O.G. acknowledges postdoctoral financial support provided by the Spanish Ministry for Education and Science (Juan de la Cierva, JCI-2012-12061), and by the European Union Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 661118-BioFUNC. Funding support to conduct the experiment was provided by the Spanish Ecological Terrestrial Society (AEET, Jóvenes Investigadores grant 2014/2). L.G.-A. acknowledges support from the MICINN project INTERCAPA (CGL-2014-56739-R) and European FEDER Funds. I.M.P.-R thanks the funding provided by the Ramón & Cajal Research Programme (RYC-2013-13937) and the Spanish MINECO project DECAFUN (CGL2015-70123-R).

16 páginas.-- 5 figuras.-- 1 tablas.-- 56 referencias.-- This article belongs to the Special Issue "Ecology and Management of Invasive Species in Forest Ecosystems"., There is growing recognition of the importance of soil fauna for modulating nutrient cycling processes such as litter decomposition. However, little is known about the drivers promoting changes in soil fauna abundance on a local scale. We explored this gap of knowledge in a mixed oak forest of Southern Spain, which is under decline due to the invasion of the exotic soil-borne pathogen Phytophthora cinnamomi. Meso-invertebrate abundance found in soil litter was estimated at the suborder level. We then explored their statistical correlations with respect to light availability, tree and litter characteristics, and P. cinnamomi abundance. Oribatida and Entomobryomporpha were the most abundant groups of Acari and Collembola, respectively. According to their trophic level, predator and detritivore abundances were positively correlated while detritivores were, in turn, positively correlated with pathogen abundance and negatively influenced by light availability and tree defoliation. These overall trends differed between groups. Among detritivores, Diplopoda preferred highly decomposed litter while Oribatida and Psocoptera preferred darker environments and Poduromorpha were selected for environments with lower tree defoliation. Our results show the predominant role of light availability in influencing litter fauna abundances at local scales and suggest that the invasive soil-borne pathogen P. cinnamomi is integrated in these complex relationships., O.G. acknowledges postdoctoral financial support provided by the European Union Horizon research and innovation program under the Marie Sklodowska-Curie grant agreement No 661118-BioFUNC. O. G. also thanks research support from the Spanish Ministry of Economy and Competitiveness through the IMPLANTIN project (CGL2015-65346-R). L.G.A. acknowledges support from the MICINN project INTERCAPA (CGL-2014-56739-R).

We thank A.J. Muñoz‐Pajares, L. Rodríguez and G. Rutten for their help and logistic support during field sampling and M.E. Sánchez, M. Serrano and M.A. Romero for pathogen analyses and interest‐ ing discussions., Data will be available from the Dryad Digital Repository upon acceptance., Aim: Impacts of different global change drivers are altering the performance of plant species worldwide. However, these pressures usually differ across the species’ distri‐ bution range. To properly assess the combined effect of global change at species level, we need to evaluate its consequences across their complete distribution. We focused on recent decline in Cork oak (Quercus suber L.) populations given its high ecological and economic relevance. Location: We selected 10 different sites (and two populations per site) separated about one degree in latitude across the core distribution of Q. suber, following a transcontinental aridity gradient. Methods: To evaluate the current trends in population dynamics across the species’ distribution and the factors implied on population decline, we evaluated the effect of latitude, aridity, pathogens (Phytophthora cinnamomi), stand density and tree size on seed and crop size, demographic structure, dominance of recruitment bank, defolia‐ tion and mortality. Results: We found an increase in seed weight as latitude decreased, with a homogene‐ ous low crop size across the complete distribution. Demographic structure was deter‐ mined by latitude, precipitation and pathogen abundance. We detected a trend towards reduced sapling densities towards the southern edge of the distribution, with a demo‐ graphic structure dominated by old trees. The low sapling density at the southern edge translates into a loss of dominance with respect to other woody species, suggesting an alteration of community structure in the mid‐term future. Tree density, precipitation and pathogen abundance determined tree mortality across the species distribution, with a higher abundance of pathogens in central‐latitude populations. Main conclusions: Our results allow the early detection of declining trends and the evaluation of the main risks for species’ conservation, suggesting potential for range displacement of the species driven by the recruitment failure at the southern edge of the distribution and a likely range expansion at northern populations., This research was funded by the Large Research Grant (6007210) awarded from the British Ecological Society to L.M. L.G.A. acknowledges support from the MICINN project INTERCAPA (CGL‐2014‐56739‐R) and European FEDER Funds

8 páginas.-- 3 figuras.-- 1 tabla.-- 50 referencias.-- Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.foreco.2017.05.060, Tree species often exhibit considerable variability among individuals in seed crop size and averaged seed mass within the same year. However, very little is known about the consequences for seed consumers’ preferences of this potentially large between-individual variability. In this study we quantified seed production and seed manipulation rates by animals over three years in two coexisting oak species of southeast Mexico (Quercus germana and Q. xalapensis) with the principal aim of evaluating the influence of two relevant plant traits (individual crop size and seed mass) on the responses of two guilds of acorn consumers with contrasting foraging behaviors and dietary breadths (vertebrate versus granivorous insects). We detected interactive effects of these two plant traits on seed consumers’ preferences, with important differences between the two groups of acorn-feeding animals. In general, high densities of large-sized acorns triggered a negative density-dependent response (i.e. satiating effect) in granivorous insects and a positive response (i.e. attractive effect) in vertebrates, whereas the opposite occurred when considering the fraction of small-sized acorns. The potential consequences of producing bigger seeds will partly depend on the relative abundance of the two guilds of acorn consumers. Thus, in plant populations with overabundance of vertebrates, the higher attraction of large-sized seeds for these generalist consumers could counteract the satiating effect exercised on granivorous insects through multi-infestation. However, in forest sites with less abundance of vertebrates, the risk of seed predation (mostly by insects) could be reduced in those trees producing huge quantities of large-sized seeds. In summary, we found clear evidences that the direction and magnitude of density-dependent seed removal can differ not only between different groups of seed consumers but also among different fractions of seed size, which highlights the importance of considering this plant trait to better understand the complexity of mechanisms operating in these plant-animal interactions., This study was supported by the Ramón y Cajal Research Programme to IMPR [RYC-2013-13937] and the Consejo Nacional de Ciencia y Tecnología for the doctoral scholarship [No. 272172] awarded to Yureli García De La Cruz for studies at the Centro de Investigaciones Tropicales, Universidad Veracruzana, Mexico.

5 páginas.-- 46 referencias.-- SPECIAL FEATURE–EDITORIAL META-ANALYSIS IN PLANT ECOLOGY, The inherent complexity of nature produces a diverse and varied set of outcomes for any given ecological process. However, the advance of ecology requires making generalizations that synthesize current knowledge and guide new basic research and practical applications. Among the synthesis tools available for this specific purpose, meta-analysis is one of the most accurate and powerful methods. This Special Feature examines the use that meta-analysis has received in plant ecology over the last two decades and provides examples of synthesis applied to contemporary topics in different areas of plant ecology from populations to ecosystems. The number of meta-analyses in plant ecology has been increasing rapidly in the last two decades. However, this increase has not been accompanied by a parallel increase in quality. The opening review paper in this Special Feature provides a checklist of quality criteria specific to ecological meta-analysis that will largely contribute to improvement of the methodological and reporting standards of meta-analyses. The following five papers in the Special Feature demonstrate the advantages of application of meta-analysis compared with other techniques of research synthesis. Meta-analysis is applied here to demonstrate the consistency of ecological hypotheses across large spatial scales (e.g. Janzen-Connell hypothesis), understand sources of variation in the magnitude of ecological processes (e.g. herbivory effects on leaf life span, effects of intraspecific genetic diversity on communities and ecosystems), measure synergistic impacts of environmental change drivers (e.g. CO2, drought, land use) or assess research gaps within a certain sub-discipline of plant ecology (e.g. landscape fragmentation). Synthesis. Meta-analysis can contribute to the advance of ecological theory by synthesizing the available evidence on specific topics and informing the scope of generalizations. However, plant ecologists can only take full advantage of this capacity if we improve our knowledge on how and when to conduct a proper meta-analysis, and by avoiding the frequent misuses that have characterized the use of this statistical tool in the ecological literature thus far., Support from the Spanish Ministry of Science and Innovation (project CGL2011-26877).

12 páginas.-- 4 figuras.-- 2 tablas.-- 80 referencias.-- Información suplementaria de 16 páginas (1 figuras, 4 apéndices y 7 tablas) incluida en el Preprint de acceso abierto. o en http://dx.doi.org/10.1111/ddi.12193, Aim For tree species, adult survival and seedling and sapling recruitment dynamics are the main processes that determine forest structure and composition. Thus, studying how these two life stages may be affected by climate change in the context of other abiotic and biotic variables is critical to understand future population trends. The aim of this study was to assess the sustainability of cork oak (Quercus suber) forests at the core of its distributional range under future climatic conditions. Location Southern Spain. Methods Using forest inventory data collected at two periods 10 years apart, we performed a comprehensive analysis to evaluate the role of different abiotic and biotic factors on adult survival and recruitment patterns. Results We found that both life stages were influenced by climatic conditions, but in different ways. Adult tree survival was negatively impacted by warmer spring temperatures, while recruitment was positively affected by warmer winter temperatures. Our results also revealed the importance of soil texture as a modulator of winter precipitation effects on adult survival. With higher winter precipitation, adult survival increased in sandy soils and decreased in clayish soils. Therefore, under predicted future climate scenarios of wetter winters and warmer temperatures, the presence of cork oaks is more likely to occur in sandy soils vs. clayish soils. Biotic conditions also affected these life stages. We found a negative effect of heterospecific but not conspecific trees on both adult survival and seedling recruitment. Main conclusions Overall, the sustainability of the studied forests will be highly dependent not only on future climatic trends, but also on their interaction with other key factors – soil properties in particular – that modulate the effects of climate on demographic rates., Supported by the Ministerio de Ciencia e Innovación (MICIIN) projects INTERBOS-CGL2008-04503-C03-03 (MCI) and DIVERBOSCGL2011-30285-C02-01 (MCI) and the Junta de Andalucía project ANASINQUE-PGC2010-RNM-5782. Supported by a Formación de Personal Investigador (FPI)-MICINNgrant and P.R.B. by a Formación de PersonalUniversitario (FPU)-MEC grant.

This research was initially supported by INTERBOS3-CGL2008-04503-C03-03 and SUM2008-00004-C03-01 projects, and by FUNDIV (ENV.2010.2.1.4-1) at a later stage. PRB was supported by a FPU fellowship (AP2008-01325). The study has been supported by the TRY initiative on plant traits (http://www.trydb.org). The TRY initiative and database is hosted, developed and maintained by J. Kattge and G. Bonisch (Max-Planck-Institute for Biogeochemistry, Jena, Germany). TRY is supported by DIVERSITAS, IGBP, the Global Land Project, the UK Natural Environment Research Council (NERC) through its program QUEST (Quantifying and Understanding the Earth System), the French Fondation pour la Recherche sur la Biodiversite (FRB) and GIS "Climat Environnement et Societe" France.

12 páginas.-- 4 figuras.-- 3 tablas.-- 80 referencias.-- The online version of this article (doi:10.1007/s10342-017-1064-1) contains supplementary material, which is available to authorized users, Forests worldwide have been recently affected by severe decline and mortality, while our understanding about forest decline across spatial scale is still limited. In this work, we study how Quercus suber trees adjust their physiology, in terms of water use efficiency and secondary growth, to pathogen-induced oak decline at the whole-tree, local and landscape scales. This work was carried out in Mediterranean mixed forests where their dominant key species Q. suber is affected by a severe decline and mortality induced by the exotic soil-borne pathogen Phytophthora cinnamomi. Significant differences were not observed between defoliated and healthy trees, either in terms of water use efficiency or growth at the whole-tree scale. We found that limiting conditions, such as low soil depth and high pathogen abundance, induced trees to higher water use efficiency at local and landscape scales. Overall our findings point out that Q. suber trees subjected to soil drought and root pathogens increase water use efficiency to some extent, while this response might not be enough for the trees to overcome the physiological stress associated with the pathogen-induced dieback. We discuss the complex way by which adult Q. suber trees physiologically respond to P. cinnamomi-induced mortality, improving our understanding of the likely consequences of chronic oak decline in the future., This research was supported by the Ministerio de Ciencia e Innovación (MICINN) projects CGL2011-26877 (RETROBOS) and CGL2014-56739-R (INTERCAPA). J.M.A. was supported by a Formación de Profesorado Universitario FPU-Ministerio de Educación y Ciencia grant (AP2010-0229).

14 páginas.-- 6 figuras.-- 4 tablas.-- 53 referencias.-- Electronic supplementary material The online version of this article (doi:10.1007/s10530-017-1582-2) contains supplementary material, which is available to authorized users., Negative interactions have been suggested as a major barrier for species arriving in a new habitat. More recently, positive interactions drew attention from community assembly theory and invasion science. The invasional meltdown hypothesis (IMH) introduced the idea that positive interactions among non-native species could facilitate one another’s invasion, even increasing their impact upon the native community. Many studies have addressed IMH, but with contrasting results, reflecting various types of evidence on a multitude of scales. Here we use the hierarchy-of-hypotheses (HoH) approach to differentiate key aspects of IMH, organizing and linking empirical studies to sub-hypotheses of IMH. We also assess the level of empirical support for each sub-hypothesis based on the evidence reported in the studies. We identified 150 studies addressing IMH. The majority of studies support IMH, but the evidence comes from studies with different aims and questions. Supporting studies at the community or ecosystem level are currently rare. Evidence is scarce for marine habitats and vertebrates. Few sub-hypotheses are questioned by more than 50% of the evaluated studies, indicating that non-native species do not affect each other’s survival, growth, reproduction, abundance, density or biomass in reciprocal A ↔ B interactions. With the HoH for IMH presented here, we can monitor progress in empirical tests and evidences of IMH. For instance, more tests at the community and ecosystem level are needed, as these are necessary to address the core of this hypothesis. © 2017 The Author(s)

Aim There is increasing concern regarding sustainable management and restoration of planted forests, particularly in the Mediterranean Basin where pine species have been widely used. The aim of this study was to analyse the environmental and structural characteristics of Mediterranean planted pine forests in relation to natural pine forests. Specifically, we assessed recruitment and woody species richness along climatic, structural and perturbation gradients to aid in developing restoration guidelines. Location Continental Spain. Methods We conducted a multivariate comparison of ecological characteristics in planted and natural stands of main Iberian native pine species (Pinus halepensis, Pinus pinea, Pinus pinaster, Pinus nigra and Pinus sylvestris). We fitted species-specific statistical models of recruitment and woody species richness and analysed the response of natural and planted stands along ecological gradients. Results Planted pine forests occurred on average on poorer soils and experienced higher anthropic disturbance rates (fire frequency and anthropic mortality) than natural pine forests. Planted pine forests had lower regeneration and diversity levels than natural pine forests, and these differences were more pronounced in mountain pine stands. The largest differences in recruitment – chiefly oak seedling abundance – and species richness between planted and natural stands occurred at low-medium values of annual precipitation, stand tree density, distance to Quercus forests and fire frequency, whereas differences usually disappeared in the upper part of the gradients. Main conclusions Structural characteristics and patterns of recruitment and species richness differ in pine planted forests compared to natural pine ecosystems in the Mediterranean, especially for mountain pines. However, management options exist that would reduce differences between these forest types, where restoration towards more natural conditions is feasible. To increase recruitment and diversity, vertical and horizontal heterogeneity could be promoted by thinning in high-density and homogeneous stands, while enrichment planting would be desirable in mesic and medium-density planted forests.

Most large-scale multispecies studies of tree growth have been conducted in tropical and cool temperate forests, whereas Mediterranean water-limited ecosystems have received much less attention. This limits our understanding of how growth of coexisting tree species varies along environmental gradients in these forests, and the implications for species interactions and community assembly under current and future climatic conditions. Here, we quantify the absolute effect and relative importance of climate, tree size and competition as determinants of tree growth patterns in Iberian forests, and explore interspecific differences in the two components of competitive ability (competitive response and effect) along climatic and size gradients. Spatially explicit neighborhood models were developed to predict tree growth for the 15 most abundant Iberian tree species using permanent-plot data from the Spanish Second and Third National Forest Inventory (IFN). Our neighborhood analyses showed a climatic and size effect on tree growth, but also revealed that competition from neighbors has a comparatively much larger impact on growth in Iberian forests. Moreover, the sensitivity to competition (i.e. competitive response) of target trees varied markedly along climatic gradients causing significant rank reversals in species performance, particularly under xeric conditions. We also found compelling evidence for strong species-specific competitive effects in these forests. Altogether, these results constitute critical new information which not only furthers our understanding of important theoretical questions about the assembly of Mediterranean forests, but will also be of help in developing new guidelines for adapting forests in this climatic boundary to global change. If we consider the climatic gradients of this study as a surrogate for future climatic conditions, then we should expect absolute growth rates to decrease and sensitivity to competition to increase in most forests of the Iberian Peninsula (in all but the northern Atlantic forests), making these management considerations even more important in the future.

13 páginas, 4 figuras., 1. Traditionally, techniques of plant manipulation during restoration have focused on the reduction of competition by ‘problematic’ existing vegetation. However, the increasing recognition of facilitation as a main process regulating the composition of communities has brought a change in the practice of restoration towards a better awareness of the benefits inherent to conserving neighbouring vegetation. 2. Here, I provide the results of a meta-analysis of published studies that have manipulated interactions among plants with the objective of restoring degraded terrestrial systems. I created four different data sets corresponding to the variables most commonly used to measure plant performance (i.e. emergence, survival, growth and density), and asked whether the benefits of facilitation as a restoration tool vary depending on the study duration, the life-form of the neighbour and target species, and the ecosystem type. 3. Neighbour effects varied strongly among performance estimators. Positive effects were frequently found for emergence and survival, whereas neutral or negative interactions predominated for growth and density. 4. No clear support existed for a relationship between study duration and neighbour effect. 5. The life-form of the interacting species, particularly of neighbours, largely influenced the interaction outcome. Herbs had strong negative effects, especially on other herb species, whereas shrubs had large facilitative effects, especially on trees. 6. Semiarid and tropical systems showed in general more positive neighbour effects than wetlands and particularly mesic temperate systems, where negative interactions predominated. However, these results were largely influenced by the over-representation of herb species in wetlands and temperate habitats, survival facilitation being found in all systems when only woody species were considered. 7. Synthesis. Pre-existing vegetation can have large impacts on species establishment in degraded habitats. Inhibition predominates in herbaceous communities typical of early-successional stages, whereas facilitation prevailes in communities dominated by shrubs and trees. Even productive systems (e.g. mesic temperate habitats) appear suitable for the application of facilitation as a restoration tool of woody communities. Whereas restoring herbaceous communities seems largely reliable on removal techniques, augmenting populations of nurse shrubs and trees should be considered a promising strategy for restoring woody late-successional communities., This study was supported by a Juan de la Cierva contract to L.G.A, the coordinated Spanish MCINN project INTERBOS (CGL2008-04503-C03-01 ⁄ BOS) and the GESBOME project (RNM 1890) from the Excellence Research Group Programme of the Andalusian Government.

Question: How does habitat degradation affect recruitment limitation and its components (seed limitation versus establishment limitation) of woody plant communities in a Mediterranean landscape? Location: 1600-1900 m a.s.l. in the Sierra Nevada National Park, southern Spain. The landscape is a mosaic composed of native forest and two degraded landscape units: reforestation stands and shrubland. Methods: We evaluated fruit production, seed rain, seedling emergence and seedling survival in two consecutive years with contrasting rainfall patterns. Seed and seedling data were used to calculate values of seed and establishment limitation. Results: In general, the woody community was both severely seed- and establishment-limited. Species were less seed-limited in the landscape units with higher adult density (i.e. shrub species in shrubland, Pinus spp. in reforestation stands). In contrast, degradation did not exacerbate establishment limitation, which was severe in all landscape units. This general pattern was modulated by the biogeographical distribution, dispersal type, and life form of the species. Boreo-alpine species were more limited in establishment than species with a typical Mediterranean distribution. Zoochorous species were less seed-limited in the landscape units preferred by dispersers (i.e. native forest). Tree species were more establishmentlimited than shrub species, irrespective of the landscape unit. Seed limitation, and especially establishment limitation, varied among years, with establishment being almost nil in the very dry year. Conclusion: In the case of Mediterranean landscapes, when degradation from human impact involves a reduction in the adult abundance of the woody plant community (trees and shrubs), seed limitation increases, although establishment limitation is generally high in all landscape units, especially for boreo-alpine species. Conservation and restoration strategies should take into account our results showing that tree species were unable to recruit in an extremely dry year, because more aridity is expected under a climatic change scenario in Mediterranean ecosystems.

18 pages, 6 figures, 5 tables, 69 references. We are especially grateful to Patrick H. Martin for his collaboration throughout each phase of this project. We thank Star Child, James McCardle and the staff of the IES analytical laboratory for their help with the sampling collection and analyses. Peter Groffman, Lynn Christenson, Lisa Martel and David Lewis offered invaluable help with the microbial analyses. We thank the Dark Entry Forest Association, the Childs family and Nancy Nichols for permission to do research in their properties., Changes in the composition of a community due to the invasion by exotic plant species can lead to modification of ecosystem function that, in turn, produces feedbacks that drive further changes in community composition. The development of predictive models of this process requires an understanding of the spatial extent of the impacts of the exotic species, particularly during early stages of invasion. The main objective of this study was to characterize the neighborhood dynamics of ecosystem transformations by the invasive tree species Norway maple (Acer platanoides L.) and tree of heaven (Ailanthus altissima Mill.) in temperate forests of the northeastern United States. By using a neighborhood approach in multiple sites, we sought to determine (1) the magnitude and spatial extent of the effects of the two invasive species on soil properties and processes; (2) whether the effects of the invasive species were site dependent; and (3) the differences in the effects of invasive versus native tree species on ecosystem processes. Our results showed that Norway maple and tree of heaven alter the functioning of temperate forest ecosystems even at relatively low densities by increasing cycling rates (i.e., net N mineralization, net nitrification, Ca mineralization) and nutrient availability (i.e., pH, Ca, Mg, K, N). At the neighborhood scale, the spatial extent of the impact of the two species varied strikingly among soil properties. Moreover, the neighborhood effects of the two invasive species were site dependent, with the magnitude of the impact increasing with soil fertility. At the community level, Norway maple and to a lesser extent tree of heaven had stronger effect on soils than any of the dominant native tree species considered. We conclude that the invasion of northeastern forests by Norway maple and tree of heaven is characterized by predictable, neighborhood-specific acceleration of nutrient cycling rates and localized increases in nutrient pools. These ecosystem alterations have enormous potential for the modi. cation of competitive hierarchies in forest communities. In particular, Norway maple and tree of heaven may change relative abundances within the native community to the benefit of native species that are more competitive on nutrient rich sites., This work was supported by a Postdoctoral Fulbright Fellowship (FU2004-1288) to L. G. A. and a grant from U.S.D.A. (2003-35320-13583) to C. D. Canham and P. L. Marks. This is a contribution to the program of the Institute of Ecosystem Studies.

Question: Positive interactions are predicted to be common in communities developing under high physical stress or high herbivory pressure due to neighbour amelioration of limiting physical and consumer stresses, respectively. However, when both stress sources meet in the same community, the relative importance of the two facilitation mechanisms is poorly understood. We ask: What is the relative importance of abiotic vs. biotic mechanisms of facilitation of tree saplings by shrubs in Mediterranean mountain forests? Location: Sierra Nevada, SE Spain (1800–1850 m a.s.l.) Methods: Saplings of four tree taxa (Acer opalus ssp. granatense, Quercus ilex, Pinus nigra ssp. salzmanii and P. sylvestris var. nevadensis) were planted following a 2 × 2 factorial design: two levels of herbivory (control and ungulate exclusion) and two microhabitats (under shrubs and in open areas). Sapling survival and growth were monitored for five years. Results: Shrubs had positive effects on sapling survival both in control...