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In addition to well-known effects on species ecophysiology, phenology, and distributions, climate change is widely predicted to impact essential ecosystem services such as decomposition and nutrient cycling. While temperature and soil moisture are thought to influence litter decomposition, elucidating consistent soil process responses to observed or predicted shifts in climate have proven difficult to evidence. Here we investigated how aspect (i.e., north-south orientation), a natural model for variation in soil temperature, influenced soil physico-chemical conditions and decomposition of two standardised litter types (Green tea and Rooibos teabags) in Pole-facing (PF) and Equator-facing (EF) roadside verges spanning a 3000 km and 27° latitudinal gradient across Europe. Despite average daily temperatures being 1.5 - 3.0 °C warmer on EF than PF slopes, there were only minor region-specific differences in initial soil physico-chemical conditions and short-term variation in litter decomposition (i.e., litter mass loss was higher in EF-verges for the first month of deployment only) associated with aspect. We conclude that previously observed differences in soil environments and the decomposition process associated with slope orientation, is largely litter or environment specific, although medium-term soil-decomposition in semi-natural grassland ecosystems may also be insensitive to the magnitude of temperature variation within the range predicted by the IPCC SSP1–2.6 emissions scenario. Nonetheless, consistent average and extreme temperature differences between adjacent PF- and EF-aspects along roadside verges provides a model system to explore exactly how resilient the soil environment and the micro-organisms responsible for decomposition, are to temperature variation.

As climate becomes drier, plant disease dynamics will change. However, there is a lack of experimental data exploring how climate change scenarios will modify the abundance of aggressive pathogens threating forest ecosystems. In this study, we aimed to fill this gap by analysing the effect of a drier climate on the population dynamics of Phytophthora cinnamomi, one of the 100 worst invasive alien species on earth. The study was conducted over 5 years (2016–2020) in two Mediterranean mixed forests of Southern Spain invaded by the pathogen. The two forests varied in soil properties (texture) and species composition (closed forest of Quercus suber and Quercus canariensis vs. open woodland of Quercus suber and Olea europaea). The abundance of P. cinnamomi resistance spores in the forest soil was analysed every spring taking advantage of rainfall exclusion infrastructures that removed 30 % of the rainfall, simulating predicted climate change scenarios for the Mediterranean basin. Results showed that P. cinnamomi abundance in the forest soil was influenced by both soil texture and tree species composition, being lower in sandy soils and under Olea europaea compared to Quercus species. More importantly, we found a general negative effect of the rainfall exclusion treatment on pathogen abundance across soils and species. The longitudinal assessment of P. cinnamomi abundance in the soil also revealed that the pathogen had the capacity to survive at low density during dry years and increase its population in response to subsequent wet years. Overall, our findings suggest that the aridification of the Mediterranean climate might imply a reduction in average pathogen abundance, but that it would not be enough to preclude peaks of high pathogen abundance in response to the extreme heavy rains and floods also predicted by climate change models. © 2024 The Authors

Understanding the interactive effects of global change drivers on tree demography is fundamental for realistic predictions of future forest dynamics. Multiple studies have shown increasing drought and exotic pathogens to severely threaten forest persistence by increasing mortality and decreasing growth of adult trees. However, much less is known about their effects on regeneration, and how they might affect seedling performance in additive and non-additive (synergistic or antagonistic) ways.Here we aimed to fill this gap by experimentally exploring the effects of increasing drought and soil-borne pathogens on tree regeneration in two types of mixed oak forests (Quercus suber-Q. canariensis and Q. suber-Olea europaea) invaded by the exotic soil-borne oomycete Phytophthora cinnamomi, one of the most aggressive plant pathogens on earth. We conducted a seed sowing experiment with oomycete-specific fungicide taking advantage of rainfall exclusion infrastructures that excluded 30% of the annual rainfall, simulating predictions of climate change models for Mediterranean systems. Seedling emergence, survival and growth of the three tree species were followed during 3 years.We found that neutral or positive drought effects on regeneration dominated over negative effects in the tree community. Moreover, most positive drought effects on the dominant species (Q. suber) were not direct, but indirectly mediated by soil-borne pathogens. This was shown by the fact that positive drought effects disappeared with fungicide application.Synthesis: Overall, our results suggest that rainfall reductions predicted by climate change models for the Mediterranean region might have minor direct negative effects on early regeneration of tree species, but could play a major indirect role by limiting the negative effects of exotic pathogens on highly susceptible tree species. These findings highlight that antagonisms among global change drivers should be recognized as important forces that might s

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

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.

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.

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

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.

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.

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 realis

[EN] Results provided by a panel of experts reveal that some of the vital challenges facing Agroecology in the near future involve its contribution to Climate Action, to increasing biodiversity or to the co-creation of knowledge by researchers and farmers, as well as the application of criteria of Circular Bioeconomy to agro-food production and distribution. Other noteworthy challenges refer to the design of agroecosystems at landscape scale or the creation of agroecological local food systems enabling an upscaling of production and consumption, [ES] Los resultados de un panel de expertos reflejan que algunos importantes desafíos que tiene la Agroecología cara al futuro próximo son su contribución a la Acción por el Clima, a la mejora de la biodiversidad o a la co-creación de conocimiento entre investigadores y campesinos, así como la aplicación de criterios de Bioeconomía Circular en la producción y distribución agroalimentarias. El diseño de agroecosistemas a escala de paisaje o la creación de sistemas alimentarios locales agroecológicos que posibiliten un salto de escala de la producción y el consumo constituyen también otros retos destacables.

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.

In the current era of Big Data, existing synthesis tools such as formal meta-analyses are critical means to handle the deluge of information. However, there is a need for complementary tools that help to (a) organize evidence, (b) organize theory, and (c) closely connect evidence to theory. We present the hierarchy-of-hypotheses (HoH) approach to address these issues. In an HoH, hypotheses are conceptually and visually structured in a hierarchically nested way where the lower branches can be directly connected to empirical results. Used for organizing evidence, this tool allows researchers to conceptually connect empirical results derived through diverse approaches and to reveal under which circumstances hypotheses are applicable. Used for organizing theory, it allows researchers to uncover mechanistic components of hypotheses and previously neglected conceptual connections. In the present article, we offer guidance on how to build an HoH, provide examples from population and evolutionary biology and propose terminological clarifications.

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

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

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 wi

In the current era of Big Data, existing synthesis tools (e.g. formal meta-analysis) are useful for handling the deluge of data and information. However, there is a need for complementary tools that help to (i) structure data and information, (ii) closely connect evidence to theory and (iii) further develop theory. We present the hierarchy-of-hypotheses (HoH) approach to address these issues. In an HoH, hypotheses are conceptually and visually structured in a hierarchically nested way, where the lower branches can be directly connected to empirical results. Used as an evidence-driven, bottom-up approach, it can (i) show connections between empirical results, even when derived through diverse approaches; and (ii) indicate under which circumstances hypotheses are applicable. Used as a theory-driven, top-down method, it helps uncover mechanistic components of hypotheses. We offer guidance on how to build an HoH, provide examples from population and evolutionary biology and propose terminological clarifications.

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.

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.

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.

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.

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.

[EN]: 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., Las dehesas presentan un serio problema de falta de regeneración natural de sus especies arbóreas dominantes. Aunque existen diferentes técnicas de regeneración asistida para tratar de paliar este problema, se hacen necesarios nuevos estudios que analicen su eficiencia ante futuros escenarios de cambio climático. En este trabajo se han revisado los principales factores que limitan la regeneración asistida de especies de Quercus en ecosistemas de dehesa y se ha identificado el grado de eficiencia de las principales técnicas empleadas para promover el reclutamiento de árboles desde una perspectiva agroecológica. Para ello, se ha llevado a cabo una revisión bibliográfica y se han realizado entrevistas a investigadores relevantes en la materia de este estudio. Los resultados indican que los principales factores limitantes de la regeneración asistida son el estrés hídrico, las desfavorables condiciones del suelo, las altas tasas de depredación de semillas y la herbivoría de plántulas y brinzales. En la segunda parte del trabajo se recomiendan una serie de técnicas agroecológicas en función del grado de eficiencia reportado en estudios científicos previos, y se resaltan aquéllas destacadas por los expertos que merecen un mayor esfuerzo de investigación (p.ej. el uso de plantas nodrizas o la aplicación de riegos). La información aportada por este trabajo podrá ser usada como herramienta útil en los planes de gestión y conservación de las dehesas con el fin de asegurar su persistencia y potenciar su capacidad de adaptación ante futuros escenarios de cambio climático.

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.

Aim: Impacts of different global change drivers are altering the performance of plant species worldwide. However, these pressures usually differ across the species' distribution 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, defoliation and mortality. Results: We found an increase in seed weight as latitude decreased, with a homogeneous low crop size across the complete distribution. Demographic structure was determined by latitude, precipitation and pathogen abundance. We detected a trend towards reduced sapling densities towards the southern edge of the distribution, with a demographic 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

Droughts associated with climate change alter ecosystem functions, especially in systems characterized by low biodiversity, such as agricultural fields. Management strategies aimed at buffering climate change effects include the enhancement of intraspecific crop diversity as well as the diversity of beneficial interactions with soil biota, such as arbuscular mycorrhizal fungi (AMF). However, little is known about reciprocal relations of crop and AMF diversity under drought conditions. To explore the interactive effects of plant genotype richness and AMF richness on plant yield under ambient and drought conditions, we established fully crossed diversity gradients in experimental microcosms. We expected highest crop yield and drought tolerance at both high barley and AMF diversity. While barley richness and AMF richness altered the performance of both barley and AMF, they did not mitigate detrimental drought effects on the plant and AMF. Root biomass increased with mycorrhiza colonization rate at high AMF richness and low barley richness. AMF performance increased under higher richness of both barley and AMF. Our findings indicate that antagonistic interactions between barley and AMF may occur under drought conditions, particularly so at higher AMF richness. These results suggest that unexpected alterations of plant-soil biotic interactions could occur under climate change. © 2019, The Author(s).

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 beyo

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.

El estudio de las interacciones planta-suelo ha experimentado un enorme avance en la última década, gracias a una comunidad científica cada vez más convencida de que resulta clave conectar el subsistema aéreo y subterráneo de los ecosistemas terrestres para lograr un completo entendimiento de su funcionamiento. El estudio de las interacciones planta-suelo resulta particularmente relevante en un contexto de Cambio Global, tanto porque la respuesta de las plantas a los factores de cambio (ej. cambio climático) está condicionada indirectamente por las características edáficas, como porque el Cambio Global implica en sí mismo cambios directos de gran magnitud en el subsistema suelo (ej. introducción de organismos edáficos exóticos). En esta charla se usarán distintos ejemplos para ilustrar como la vulnerabilidad de los sistemas forestales a un incremento de la aridez está condicionada por variables físico-químicas del suelo (textura, profundidad, pH), así como por la composición y diversidad de su microbioma. Asimismo, se discutirá la creciente importancia de los patógenos edáficos exóticos como factores limitantes de la supervivencia y regeneración de especies leñosas mediterráneas. Desde una perspectiva aplicada, estos ejemplos ponen de manifiesto que la consideración de la heterogeneidad edáfica puede contribuir enormemente a realizar predicciones mucho más precisas y realistas de la vulnerabilidad de especies y ecosistemas al Cambio Global. Asimismo, el manejo de las propiedades edáficas, y en concreto de su microbioma, ha de ser considerado como una prometedora vía de investigación que puede ofrecer nuevas técnicas de adaptación de los bosques a escenarios ambientales caracterizados por mayor estrés abiótico y biótico. Finalmente, una mayor presencia en la gestión forestal del conocimiento reciente sobre interacciones planta-suelo llevará necesariamente a la revisión de técnicas tradicionales de actuación, como por ejemplo en la toma de decisiones sobre calidad de

Forested landscapes are rapidly being transformed by increasing rates of tree mortality caused by global-change factors such as exotic pathogens or extreme droughts. Disturbance of tree communities can have cascading impacts on biodiversity at all organization levels. However, how soil microorganisms respond to tree dieback and the implications for ecosystem recovery is largely unknown. Here we combined spatially-explicit neighborhood models, DNA metabarcoding, and a field experiment to explore how the decline of the Mediterranean tree Quercus suber altered the diversity, composition and network structure of belowground fungal communities in forests invaded by the exotic pathogen Phytophthora cinnamomi, and whether such changes had cascading impacts on Q. suber recruitment. We found that Q. suber dieback caused a reduction of the taxonomic diversity of soil fungal communities but increased their phylogenetic diversity, likely due to the colonization of unhealthy soils by rare taxa not present in healthy soils. Tree neighborhoods dominated by defoliated or dead oaks had soil fungal communities with higher relative abundance of saprophytic and pathogenic fungi, lower abundance of ectomycorrhizal fungi, and very distinct network structure (e.g. lower modularity) than healthy neighborhoods. Such changes had negative feedbacks on Q. suber regeneration, since seedling performance was negatively related to fungal phylogenetic diversity but positively influenced by ectomycorrhizal abundance. Our results showed that oak dieback exerted a strong influence on the diversity and structure of soil fungal networks, promoting new assemblages impoverished in mutualistic taxa. This implies that oak dieback has far-reaching multi-trophic effects that may affect regeneration and ecosystem recovery

Global change is altering the performance of plant species worldwide. However, these pressures usually differ across the species’ distribution range. To properly assess the combined effect of global change drivers at species level, we need to evaluate its consequences across their complete distribution. To evaluate the current trends in population dynamics across species’ distribution and the factors implied on population decline, we selected ten sites separated about one degree in latitude across the core distribution of Quercus suber, following a transcontinental aridity gradient, and determined the variations in key ecological indicators of population performance: reproductive investment, demographical structure, dominance of recruitment bank, defoliation and mortality. Demographic structure was determined by latitude, precipitation and Phytophthora cinnamomi abundance (a soil borne-pathogen causing death in Q. suber). We detected a trend towards reduced sapling densities at the southern distribution, with a demographic structure dominated by old trees. The low sapling density at the southern edge translates into a loss of dominance respect other woody species, suggesting an ongoing alteration of community structure. Population density, precipitation and pathogen abundance were the main causes of tree mortality across the species distribution, with a higher abundance of P. cinnamomi at central-latitude populations. Our results allow the early detection of declining trends and the evaluation of the main risks for the maintenance of important forest, and suggest an ongoing range displacement of the species driven by the recruitment collapse at the southern edge of the distribution and a high potential for range expansion at northern populations.

Soil fauna plays an essential role for nutrient cycling processes, but the drivers promoting changes in its abundance and diversity, particularly within a global change context are largely unknown. In spring 2016, we built a rainfall exclusion experiment (30% rainfall reduction) to explore soil fauna responses to simulated climate change in a mixed oak forest of southern Spain invaded by the exotic soil-borne pathogen Phytophthora cinnamomi. We identified soil fauna groups at the suborder taxonomic level and its trophic position at the beginning of the experiment and after one year in both experimental and control plots. We then analysed the effect of the rainfall reduction treatment on temporal changes in the abundance and diversity of soil measofauna. We also explored statistical correlations with fine-scale biotic and abiotic parameters by means of structural equation models. Primarily, we observed that one year of experimental rainfall reduction strongly decreased predator abundance but not detritivore abundance. Moreover, light availability, tree defoliation and the abundance of P. cinnamomi were identified as the main drivers of the changes in the abundance of particular detritivore groups. Our results demonstrate rapid responses of the abundance and composition of the litter mesofauna to climate change-related drought, with the organisms in the higher trophic levels being the more susceptible to increasing dryness. Multiple tree and litter characteristics influenced litter fauna abundance at local scale, suggesting that global change drivers as climate change and invasive exotic species are modifying these complex relationships.

Climate change and exotic pathogens are two key global change factors driving the decline of Quercus species in forests worldwide. However, very little is known about the interactive effects of these two factors on biogeochemical cycles. Here, we assessed for the first time the consequences of the simultaneous impact of climate change and soil-borne pathogens on nutrient cycling. We conducted a field experiment in a Mediterranean forest affected by Quercus suber decline, evaluating how drought (ambient vs. ~30% reduction in rainfall), warming (ambient vs. ~2.5 °C increase) and the abundance of the oomycete pathogen Phytophthora cinnamomi affected nutrient availability in soils (microbial biomass nitrogen, NH4+, NO3-, and urease, phosphatase and ß-glucosidase activities). One year after the beginning of the experiment, the drought trea ment decreased by 19% the soil phosphatase activity in spring and caused substantial reductions in microbial biomass nitrogen and NH4+ (60% and 33%, respectively) in summer. Warming also caused very rapid changes in nutrient availability, increasing NH4+ concentration in summer by 38%. Moreover, P. cinnamomi abundance was positively correlated with urease and ß-glucosidase activities. We did not find any short term interaction between the climate treatments and P. cinnamomi abundance. Our findings suggest that drought can have a very rapid negative impact on nutrient cycling in Mediterranean forests that could be partially buffered by the effects of warming and P. cinnamomi infection. Climate change and soil-borne pathogens can have counteracting effects on nutrient cycling, supporting the need for more studies that analyze their simultaneous effect on ecosystem functioning.

The structure and function of Mediterranean mixed oak forests is seriously threatened by climate change and exotic pathogens, specifically the soil-borne pathogen Phytophthora cinnamomi. These two factors have been individually studied in some detail, but nothing is known about their interactive effects on plant performance and species coexistence. To explore these interactive effects, we conducted an experiment in growth chambers where seedlings of Quercus suber, Quercus canariensis and Olea europaea were planted in pairs under different scenarios of drought (control vs. 30% rainfall reduction), warming (control vs. 3ºC increase) and pathogen presence (control vs. soil infected with P. cinnamomi). At the end of the experiment, the severity of radical symptoms was evaluated. Preliminary results showed that the different climate-change scenarios did not influence the severity of the root disease. The three tree species showed severe symptoms of disease in all climatic scenarios, including O. europaea (a species so far described as resistant to P. cinnamomi) and Q. canariensis (a species considered as tolerant to the pathogen). Our preliminary results do not support interactive effects of climate change and P. cinnamomi infection on root damage, suggesting that these two stress factors could act simultaneously limiting seedling performance in Mediterranean forests. Our results also provide novel evidence of a much higher susceptibility of dominant Mediterranean tree species to P. cinnamomi than previously thought, which can seriously threaten the long-term conservation of Mediterranean mixed forests

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

La supervivencia de los bosques mixtos mediterráneos, donde conviven en equilibrio alcornoques, quejigos y acebuches, está seriamente amenazada por la muerte masiva de alcornoques por la podredumbre radical causada por Phytophthora cinnamomi (Pc). Aunque hasta la fecha se han descrito al alcornoque, quejigo y acebuche como susceptible, tolerante y resistente a Pc, se conoce muy poco sobre el efecto interactivo que estas especies tienen sobre la epidemiología de la enfermedad radical, lo cual es fundamental para entender la dinámica evolutiva de los bosques afectados. Por ello, el objetivo de este trabajo es analizar de forma experimental el efecto interactivo que alcornoques, acebuches y quejigos tienen sobre la capacidad multiplicativa y de supervivencia de Pc. Para ello, mediante ensayos in planta combinando las tres especies dos a dos, se evaluó su capacidad para estimular la producción de zoosporas de Pc, obteniendo que el alcornoque combinado consigo mismo era capaz de producir significativamente más zoosporas que el quejigo, y el acebuche, con efecto nulo. Sin embargo, cuando se disponen alcornoque y acebuche, la producción de esporas no difiere del alcornoque solo. En cuanto a la combinación alcornoque-quejigo, la producción de zoosporas fue significativamente más elevada que para los demás tratamientos, incluidos el alcornoque y quejigo de forma independiente, lo cual supone un efecto sinérgico sobrePc y, por lo tanto, un mayor riesgo para la supervivencia de los bosques mixtos integrados por estas dos especies. Actualmente, se están realizando ensayos en invernadero para determinar el efecto que la combinación de estas especies tiene sobre la viabilidad de las clamidosporas de Pc y el progreso de la enfermedad radical.

En las últimas décadas, el incremento de la temperatura, la reducción de las precipitaciones y la invasión por especies patógenas exóticas han incrementado la tasa de mortalidad de especies forestales mediterráneas. En la Península Ibérica, la sequía junto a la invasión del patógeno exótico Phytophthora cinnamomi son la principal causa de muerte del alcornoque (Quercus suber) y de la encina (Quercus ilex). Sin embargo, poco se sabe acerca del impacto que estos factores tienen al incidir conjuntamente sobre otros componentes del ecosistema, como son las comunidades de microorganismos y los ciclos biogeoquímicos que controlan. Debido a ello, esta tesis se propone abordar por primera vez de forma experimental el efecto interactivo del cambio climático (reducción de precipitaciones e incremento de la temperatura) y de la invasión del patógeno P. cinnamomi sobre los ciclos biogeoquímicos (ciclos del carbono y del nitrógeno) relacionando tales efectos con las comunidades microbianas edáficas en bosques mixtos afectados por el decaimiento del alcornoque. Para ello, en el Parque Natural de los Alcornocales (Cádiz) se han seleccionado dos tipos de bosque de características contrastadas; el bosque de Q. suber ‐ O. europaea y el bosque de Q. suber ‐ Q. canariensis, y en cada bosque se han establecido 6 parcelas experimentales (3 de exclusión de lluvia y 3 control) y cámaras abiertas de control de la temperatura. Se hipotetiza que la reducción de las precipitaciones y el incremento de la temperatura tendrán efectos no aditivos sobre los ciclos biogeoquímicos difíciles de predecir por separado y, además, existirán efectos indirectos e interacciones mediados por el patógeno exótico. En concreto, se analizará la diversidad funcional y composición de las comunidades microbianas edáficas y procesos como la disponibilidad de nutrientes en el ecosistema (cantidad de amonio, nitrato, carbono y nitrógeno en la biomasa microbiana y en la materia orgánica disuelta, etc.), el reciclado de

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.

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

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 ecological impacts of forest plantations are a focus of intense debate, from studies that consider plantations as "biological deserts" to studies showing positive effects on plant diversity and dynamics. This lack of consensus might be influenced by the scarcity of studies that examine how the ecological characteristics of plantations vary along abiotic and biotic gradients. Here we conducted a large-scale assessment of plant regeneration and diversity in plantations of southern Spain. Tree seedling and sapling density, plant species richness, and Shannon's (H') diversity index were analyzed in 442 pine plantation plots covering a wide gradient of climatic conditions, stand density, and distance to natural forests that act as seed sources. Pronounced variation in regeneration and diversity was found in plantation understories along the gradients explored. Low- to mid-altitude plantations showed a diverse and abundant seedling bank dominated by Quercus ilex, whereas high-altitude plantations showed a virtually monospecific seeding bank of Pinus sylvestris. Regeneration was null in plantations with stand densities exceeding 1500 pines/ha. Moderate plantation densities (500-1000 pines/ha) promoted recruitment in comparison to low or null canopy cover, suggesting the existence of facilitative interactions. Quercus ilex recruitment diminished exponentially with distance to the nearest Q. ilex forest. Richness and H' index values showed a hump-shaped distribution along the altitudinal and radiation gradients and decreased monotonically along the stand density gradient. From a management perspective, different strategies will be necessary depending on where a plantation lies along the gradients explored. Active management will be required in high-density plantations with arrested succession and low diversity. Thinning could redirect plantations toward more natural densities where facilitation predominates. Passive management might be recommended for low- to moderate-de