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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

Climate change is threatening ecosystem functioning and sustainability worldwide. In silvopastoral systems, ongoing warmer and drier conditions could impact productivity and quality of pastures (in terms of protein content and digestibility), with important economic consequences. However, the extent to which climate change could alter other nutritional traits with a potential role in livestock nutrition and production, such as essential fatty acids and amino acids, is a question that remains poorly known. We designed a field manipulative experiment of increased temperature (+2–3 °C) and rainfall exclusion (−30%) aimed to evaluate the influence of forecasted climate variations on the yield and nutritional composition of pastures (i.e. proteins, lipids, fibers, amino acids, fatty acids and digestibility) in a Mediterranean silvopastoral system. To test whether scattered trees typical of these ecosystems could buffer the effects of higher aridity, experimental plots were installed under trees and in open grasslands. First, we found that plant communities under tree canopies were less productive but exhibited higher quality than those located in open grasslands, likely due to the shade and higher soil fertility provided by trees. Both climatic stressors had a significant influence on pasture productivity and nutritional composition. Thus, pastures subjected to rainfall reduction produced less biomass with higher content in nitrogen, proteins, essential amino acids and lipids, likely as a mechanism of plant tolerance to water stress. In contrast, warming increased plant productivity and enhanced the proportion of unsaturated fatty acids, likely mediated by alterations in plant community composition. Finally, our results suggest that trees might slow the impact of climate change on productivity and specific amino acids in pasture. These results could be also applied for the design of management strategies to ensure the ecologic and economic value of silvopastoral ecosyste

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.

Many plant species are being threatened by increasingly drought conditions due to current climate change at planetary scale. This global trend is leading to the scientific community to investigate the potential role of local adaptations through intraspecific differences in functional traits that may boost conservation strategies by modulating the plant responses to reduced water availability. We assessed under controlled conditions the effect of four different drought intensities on the survival time and morphological traits of Quercus suber seedlings collected from nine populations covering the complete latitudinal distribution of the species. Functional morphological traits related to biomass allocation and leaf and root display were analyzed. We then related these traits with the survival time after a terminal desiccation, used as a drought-resistance proxy and expressed as survival time without watering. Abundant watering availability allowed seedlings to survive for a longer period compared to drier conditions. Further, all morphological traits differed across watering levels, showing a very plastic response. Acorns from southern latitudes produced very large seedlings compared to those gathered from northern latitudes. However, the larger biomass implied higher evaporative water loss, inducing lower survival of southern populations under extreme drought conditions. We further found a clear trend toward maximizing those traits related with belowground growth (i.e., root surface area, root average diameter and root volume) in southern populations aimed to increase water uptake, overcoming the most limiting factor for plant growth in that area. Our results support that increased root development allow cork oak to maintain its functioning after being subjected to damage caused by reduced water availability, whereas high aerial biomass allocation is a handicap for survival under drought stress conditions. This study identifies drought-resistant populations and morp

Background and aims Forecasted climate change and overgrazing are threatening the sustainability of dehesas, human-managed ecosystems where pastures, livestock and scattered trees coexist. Pasture quality is particularly sensitive to these global-change drivers, but there are still many gaps to broaden knowledge about the interactive effects of both factors on it. In addition, scattered trees might play a relevant role in maintaining high levels of pasture quality under future scenarios of higher aridity, but its role remains largely unexplored. Methods We designed a field manipulative experiment of rainfall exclusion and increased temperature aimed to evaluate the impact of forecasted climate on pasture quality under different historical grazing intensities. To test the potential buffering effect of trees, experimental plots were installed equally in two habitat types: under trees and open grassland. Results Warming reduced the nutrient concentration of pasture, while drought increased it. Tree canopy improved soil fertility, which translated into an increase in pasture quality. Livestock exclusion and high grazing intensity caused a decrease in pasture quality, whereas moderate grazing intensity exerted positive effects on it. Finally, warming beneath tree canopy negatively affected the P concentration of pasture, specifically in the site subjected to moderate grazing intensity. Conclusion Our findings suggest that communities subjected to moderate grazing are more sensitive to climate change from a nutritional standpoint, likely because this management type provides high levels of P to the soil. In addition, we highlight the essential role of trees in agroforestry ecosystems to maintain high values of nutritional quality of pasture.

Sustainability and functioning of silvopastoral ecosystems are being threatened by the forecasted warmer and drier environments in the Mediterranean region. Scattered trees of these ecosystems could potentially mitigate the impact of climate change on herbaceous plant community but this issue has not yet tested experimentally. We carried out a field manipulative experiment of increased temperature (+2–3 °C) using Open Top Chambers and rainfall reduction (30%) through rain-exclusion shelters to evaluate how net primary productivity and digestibility respond to climate change over three consecutive years, and to test whether scattered trees could buffer the effects of higher aridity in Mediterranean dehesas. First, we observed that herbaceous communities located beneath tree canopy were less productive (351 g/m2) than in open grassland (493 g/m2) but had a higher digestibility (44% and 41%, respectively), likely promoted by tree shade and the higher soil fertility of this habitat. Second, both habitats responded similarly to climate change in terms of net primary productivity, with a 33% increase under warming and a 13% decrease under reduced rainfall. In contrast, biomass digestibility decreased under increased temperatures (−7.5%), since warming enhanced the fiber and lignin content and decreased the crude protein content of aerial biomass. This warming-induced effect on biomass digestibility only occurred in open grasslands, suggesting a buffering role of trees in mitigating the impact of climate change. Third, warming did not only affect these ecosystem processes in a direct way but also indirectly via changes in plant functional composition. Our findings suggest that climate change will alter both the quantity and quality of pasture production, with expected warmer conditions increasing net primary productivity but at the expense of reducing digestibility. This negative effect of warming on digestibility might be mitigated by scattered trees, highlighting the imp

Increasing air temperatures and decreasing rainfall can alter Mediterranean ecosystems, where summer heat and drought already limit plant regeneration. Manipulative field studies can help to understand and anticipate community responses to climate changes. In a Mediterranean oak wooded pasture, we have investigated the effects of warming (W, via open-top chambers increasing 1.4 °C mean air temperature), reduced rainfall (D, via gutters removing 33% of rainfall) and the combination of both factors (WD) on the winter-annual Geranium dissectum L. We measured reproductive phenology and output, leaf physiology during the reproductive phase, and plant relative abundance. Warming had a positive effect on plant height and little effects on leaf physiology. Rainfall reduction enhanced leaf water use efficiency. However, the most noticeable effects occurred in WD plants, which exhibited lower leaf predawn water potential and earlier flowering phenology in the first year of treatment, and a higher ratio of leaf dark respiration (R) to net CO2 assimilation (Pn) at comparable temperatures in the third year, compared to control plants. Leaf R at ambient temperature was similar across climatic treatments. The relative abundance of G. dissectum decreased by 23% over three years, but similarly across treatments. A short life cycle helps G. dissectum to escape severe late-spring heat and drought stress. Moreover, stomata closure and thermal acclimation of R can attenuate plant stress impact on reproduction. Adaptability of the short-lived annual G. dissectum could mitigate climate change impact on community composition over short periods (e.g. three years); however, a reduction in net carbon gain could eventually affect its reproductive success and persistence in the community. © 2022 The Authors

The objective of the present study was to analyse the fruit yield and the lipid and phenolic composition of the seeds from the edible halophyte Crithmum maritimum growing in different types of soil with variable physicochemical properties. Seed oil content ranged between 8.39–11.66 % and showed high nutritional value, and the phenolic composition (423−603 mg TPC 100 g−1) presented high levels of quercetin-type compounds with high pharmaceutical interest. The strong conservation of these traits, together with a high and stable fruit production, suggests that C. maritimum could be cultivated in soils with no agronomical relevance to produce seeds as an accessible and environmentally friendly source of good quality oil and phenolics for industrial purposes. © 2022 Elsevier Inc.

Crithmum maritimum L. is an edible halophyte with large potential in human nutrition field. However, it is unclear whether its nutritional value is maintained throughout the contrasting habitats where it commonly grows (cliffs, sandy and rocky beaches) and the nutritional profile of cultivated plants still remains uncertain. In this work, we provided for the first time a comparison of the nutritional profile of C. maritimum across its different type of habitats in the south of Spain and between wild plants and plant material under optimal growing conditions. The protein, amino acids, lipids, fatty acids, minerals composition and phenolic content of plants were analysed. Plants under field conditions exhibited a nutritionally balanced composition (3.8–6.2 g protein/100 g DW, 4.9–7.5 mg lipids/g WW, 3.9–5.0 g Na/100 g DW), with high phenolic content (30.2–48.0 mg/g DW) regardless of the variability of the contrasting habitats. In contrast, under optimal conditions, C. maritimum showed a greater protein and lipid content (10.2 g/100 g DW and 9.6 mg/g WW, respectively), and lower sodium accumulation (1.2 g/100 g DW), allowing a greater consumption of this halophyte without exceeding the daily intake recommendations. Conversely, phenolics were strongly decreased in these plants (6.1 mg/g DW) likely due to the absence of stress factors. © 2021 Elsevier Inc.

Mycorrhizal fungi are key components of whole-plant adaptive strategies to cope with different abiotic and biotic constraints. Although they are particularly sensitive to different global change drivers, there are still many gaps on the mechanisms underpinning shifts in mycorrhizal associations under different climatic and management scenarios. We carried out a field manipulative experiment of rainfall exclusion and increased temperature aimed to evaluate the impact of forecasted warming and drying on mycorrhizal associations of savanna plant communities subjected to different grazing history. Additionally, we compiled detailed information on the abiotic and biotic environment with the final aim of disentangling the direct and indirect effects of climate change on this widespread mycorrhizal symbiosis. Our results suggest that climate change could induce relevant changes in mycorrhizal associations, primarily promoted by warming, which decreased the abundance of mycorrhizae but induced higher activity of nutrient exchange between the host–plant and the mycosymbiont. Temperature did not only affect this symbiosis in a direct way, but also exerted relevant indirect effects via changes in soil functioning and other root-colonizing microorganisms such as dark septate endophytes. Grazing history influenced the allocation of fungal structures inside the host-root, but its effect differed as a function of the climatic treatment. Results from this study suggest that mycorrhizal fungi might become less prevalent in plant communities inhabiting savanna ecosystems under future scenarios of increasing aridity. In agreement with this finding, higher temperatures also promoted the predominance of plants with root traits that favour efficient resource acquisition by themselves without the help of a mycorrhizal partner. Our results provide new insights into the interactive effects of the two main threats facing Mediterranean savanna ecosystems, as well as potentially useful informa

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

Aims Soil abiotic factors influence plant defensive traits by shaping the costs of defence production and these bottom-up effects on plants can in turn affect insect herbivory. However, few studies have disentangled direct and indirect effects of soil abiotic factors on plant defences and insect herbivory. Methods To address this gap, we tested the influence of soil abiotic factors on seed predation via changes in plant defences for sea fennel (Crithmum maritimum), a common coastal plant in southern Spain whose seeds are consumed by specialist caterpillars (Aethes species). To this end, we estimated seed predation on plants across several sea fennel populations, as well as measured different types of putative chemical seed defences (phenolics, terpenes) and soil abiotic factors (macro- and micro-elements, physicochemical variables). Results We found a positive association between seed chemical defences (terpenes such as alpha-thujene, alpha-pinene, beta-pinene, beta-myrcene, alpha-terpinene, y-terpinene, and thymol methylether) and seed predation. In addition, a few macro- and micro-elements such as Ca, S and Sr negatively correlated with seed defences; other macro- and micro-elements or physicochemical variables had no detectable association with defences. Despite observed effects of soil abiotic factors on defences and of the latter on seed predation, there was no detectable indirect effect of soil abiotic factors on seed attack. Conclusions Our findings suggest that variation in a few key soil macro- and micro-elements in coastal environments can exert an important influence on seed chemical defences in sea fennel, with potential consequences for interactions between sea fennel and seed predators.

Soil respiration (RS) is one of the most important carbon fluxes in terrestrial ecosystems, and it is considered as a keystone in predicting ecosystem functioning. Changes in climate and land use may alter RS, triggering feedbacks between RS and other ecosystem components. Different factors might simultaneously alter RS, but the consequences of the interactive effects for ecosystems functioning remain poorly understood. Here, the impact of the expected changes in climate were analysed in a factorial field study over two consecutive years in a Mediterranean savannah ecosystem. We assessed how the interaction of changes in climate with grazing legacy and habitat structure influences RS. We simulated different climate scenarios (ambient, drier, warmer, and drier and warmer conditions) forecasted for the study area at three adjacent sites with different grazing legacies (high, medium, and low) and for the two most important habitat types (open grasslands and under tree canopy). We also considered other factors that could affect RS, such as soil organic C, microbial biomass or net primary productivity, unravelling the direct and indirect effects of the factors controlling RS over time by using structural-equation models (SEMs). Overall, RS was higher under tree canopy than in open grasslands, and high grazing intensity tended to alter RS differently through seasons. Warming scenario consistently increased RS, while drought reduced it (especially in moist seasons), with a moderate increase of RS resulting from the combination of warming and drought. Tree canopy modulated the impact of climate on RS. The SEM analyses identified soil moisture, temperature, grazing legacy and canopy as the main factors controlling RS, although they presented seasonal variations in the size and direction of their effects. Thus, the projected changes in climate can deeply alter ecosystem functioning of carbon sequestration, although their impact can be modulated by canopy cover and management

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.

Understanding why co-occurring plant species show differential phenological sensitivities to climate fluctuations, and more specifically to the joint variation in temperature and precipitation, is critical to make accurate predictions on how climate change could alter community dynamics and ecosystem functioning. However, the role that some relevant functional traits involved in resource uptake and/or stress tolerance could play on these inter-specific differences in phenological sensitivity remains largely unknown. In this study we evaluated experimentally how five co-occurring herbaceous species with contrasting functional strategies respond to current and ongoing climatic scenarios of increased temperature, decreased water availability and both abiotic changes acting interactively. To decompose the direct effect of climate change and the indirect effect of neighbors on plant performance and reproductive phenology, each of the five species was exposed to a density gradient of competitor species. Although the study species were more sensitive to changes in temperature than in water availability, the combined effect of both abiotic cues triggered very heterogeneous responses. Species with higher SLA values were particularly sensitive to climate change, delaying their reproduction and lengthening their flowering period under warmer scenarios while maintaining a high plant growth rate. In contrast, the species with the lowest SLA values exhibited less phenological variability to climate alterations, but they were more strongly affected by neighbor density compared to species with opposite trait values. These species-specific responses to climatic shifts altered the synchrony of phenological events at the community level. The most important changes appeared under the two scenarios of increased temperature, where 4 out of 5 species overlapped their flowering periods. Our findings indicate that the ongoing scenarios of increasing temperature and aridity could disrupt the

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

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.

Understanding how plant species will respond to the new environmental conditions predicted by global change models is nowadays a crucial research aim in ecology. Variation in plant reproductive phenology is an important plant feature to evaluate species’ responses to climate change as it has direct implications for community dynamics and ecosystem functioning. However, to what extent coexisting plant species are sensitive to different climate scenarios in order to maintain fitness homeostasis is a question that remains largely untested. In this study, we carried out an experiment under controlled conditions using five annual plant species co-occurring in Mediterranean grasslands of oak-Savannahs (Dehesas) that spanned a wide range of different functional strategies. Seedlings of these species were transplanted into mesocosms filled with a mixed substrate of sterile sand-loam and peat. Each mesocosms was considered as a community of 18 individuals in which its spatial design allows us to target specific individuals with varying identity and number of competitors. This design was done to decompose the direct effect of environmental conditions and the indirect effect of neighbors (including both intra and interspecific competition) on plant performance. A total of 144 communities were equally distributed into two glasshouse units subjected to different temperature ranges, using a randomized block design with four climatic treatments: a ´control` treatment (simulating current averaged meteorological conditions in Mediterranean savanna-like systems), a ´dry` treatment (with a reduction of 33% in watering, anticipating future predictions of climate change models), a ´warming` treatment (with an increase of 3-4ºC), and a ´dry+warming` treatment (to evaluate the interactive effects of both sources of abiotic stress). This study will significantly contribute to advance our understanding on how species’ responses to different climate change scenarios will modify community com

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.

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

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