Mediterranean Grasslands Research Articles

Phenotypic plasticity of water-related traits reveals boundaries to the adaptive capacity of a dominant European grass species under increased drought

The intensification of droughts due to climate change is a global concern, and many plant species face increasing water deficits. Understanding the role of phenotypic plasticity in plant adaptation to these changing conditions is crucial. This research focuses on Bromopsis erecta, a dominant perennial grass in European and Mediterranean grasslands, to predict its potential adaptation to climate change. We assessed plants from shallow and deep soils (i.e., with contrasting water reserves) of a Mediterranean rangeland in southern France, and tested the effect of six years of experimentally increased summer drought compared to the ambient conditions on plant traits, survival and abundance. In both field and common garden experiments, we measured water-related traits, including static traits under non-limiting water conditions, and dynamic traits, such as rates of trait variation during drought. Trait plasticity was determined as a reaction norm to increasing soil water stress and was tested against changes in B. erecta abundance over the past decade, including the study period. Trait plasticity was detected only for leaf dry matter content (LDMC), revealing that the resource strategy of B. erecta became more conservative over less than a decade with higher LDMC and leaf thickness according to the plant economic spectrum. No plasticity was found for osmotic potential or specific leaf area. The variability of other traits was ascribed to the possible lagging effect of previous water stress and was associated more with soil depth than with previous summer drought intensity. The abundance decline of B. erecta, which dropped from 20 % to around 5 % in shallow soils, was not associated with the plasticity of LDMC but was positively correlated with variations in leaf base membrane damage, meaning unexpectedly, that plants exposed to the most severe summer drought also had the most sensitive leaf base membranes, a possible sign of maladaptive trait plasticity in the population. This key trait response reveals boundaries to the adaptive capacity of this perennial grass to survive pluri-annual drought.

Successional stages in Mediterranean grasslands differ in the quality of ecosystem services in urban greenspaces

Urban habitats represent new opportunities to study natural processes such as ecological succession. Our work focused for the first time on the changes in ecosystem services occurring in the ecological succession from annual to perennial grasslands in Mediterranean peri-urban greenspaces. Student’s t test was used to analyse the influence of the grassland type on plant and soil features, and showed that soil under perennial grassland had a significantly higher C content and arylamidase and arylsulfatase activity than annual grasslands. In contrast, annual grasslands showed a significantly higher plant-species richness, and their soils had higher bulk density and phenoloxidase and arylamidase activity compared to perennial grasslands. Neither the labile nor recalcitrant fractions of the organic matter showed any significant difference between communities. When all the soil factors were included together, Redundancy Analysis revealed a significant gradient in soil phenoloxidase activity and organic matter distinguishing perennial from annual grasslands. We conclude that when annual grasslands give way to perennial grasslands through natural succession in Mediterranean greenspaces, certain ecosystem services such as soil carbon storage and water regulation improve, while biodiversity maintenance declines. Thus, Mediterranean urban greenspaces where natural succession occurs should be handled in such a way as to preserve both type of habitats in order to improve a wider range of ecosystem services.

Temporal trajectories of plant functional traits in mediterranean grasslands under different grazing regimes

AbstractAimsMediterranean grasslands are semi‐natural ecosystems that have been affected by land‐use intensification and abandonment during the past decades. Adaptative multi‐paddock grazing regimes, where grazing alternates with long periods of vegetation recovery, have been proposed as a more biodiversity‐friendly management compared with continuous grazing. This study aimed to compare the effect of these two different grazing regimes on a set of plant traits in mediterranean grassland vegetation over time.LocationCentral part of Sardinia (Italy) at 350 m a.s.l. in a permanent grassland system.MethodsWe applied the point quadrat method to quantify the specific contribution of each species along permanent transects in spring and winter from 2018 to 2022. We considered the following plant traits: leaf dry matter content, life forms, flowering start and length of flowering. Overall, we performed 128 surveys and measured traits for 61 species. We ran a linear mixed model to test the effect of season, grazing regimes and years on functional diversity and community‐weighted mean for single traits.ResultsAdaptative multi‐paddock regimes over time increased the leaf dry matter content. However, compared with grazing regimes, seasonality through time had the greatest effect on flowering traits and life forms.ConclusionThe relatively small variation in the plant traits suggests that the mediterranean grassland was rather stable despite wide variation in grazing regimes, probably linked to their long history of human association. Nonetheless, adaptative multi‐paddock regimes may have higher beneficial effects compared with continuous grazing, favouring more palatable species and improving soil fertility. By contrast, the high variation in the plant traits over time suggests a high vulnerability of the same grassland to climatic changes.

Grasses don’t always win: Short-term effects of fertilization on taxonomic and functional diversity of a Mediterranean annual grassland

Nitrogen pollution has increased dramatically over the last decades, becoming a major contributor to biodiversity loss and compositional changes globally. While the main effects of excessive nutrients on plant communities are well established, Mediterranean grasslands have been less studied despite their high levels of biodiversity. Moreover, evidence has shown that the impacts of nutrients may depend on additional factors, namely soil conditions and grazing, increasing the uncertainty about the effects of increasing nutrient availability in these systems. In this work, we assessed the short-term effects (1 year) of fertilization in an extensively grazed oak open woodland (called montado, or dehesa), in Spain. Plots comprised a complete randomized design with four treatments: control (not fertilized), fertilization with nitrogen at a rate of 100 kg N ha−1, fertilization with phosphorous (50 kg P ha−1) and fertilization with both N and P (100 kg ha−1 N + 50 kg ha−1 P). We assessed changes in plant species composition and functional diversity and evaluated the association between species and fertilization treatments with an indicator species analysis. Our results showed that species diversity increased with NP fertilization and that forbs in particular increased in cover and richness. SLA and seed mass also showed differences compared to the control. The Community-weighted mean and functional dispersion of groups based on growth form and N-fixing ability were not influenced by fertilization. Two species were significantly associated with fertilized plots: the spiny forb Carlina racemosa and the latex-producing forb Tolpis barbata. Our study suggests that short-term fertilization may alleviate nutrient limitations in these systems, increasing plant diversity, although longer-term studies are needed to understand the effects of a continuous increase in nutrient availability.

Competition between alien and native species in xerothermic steno-Mediterranean grasslands: Cenchrus setaceus and Hyparrhenia hirta in Sicily and southern Italy

AbstractPerennial dry grassland communities, vital for plant biodiversity conservation in the Mediterranean, often harbor rare and endangered species. However, these habitats face threats, including the invasion of alien species. Cenchrus setaceus, a highly invasive grass, is spreading in the Mediterranean region. Historical records and observations document its establishment and invasiveness across various Italian regions. This study investigates the impact of C. setaceus on native grasslands dominated by Hyparrhenia hirta. We assessed the impact of C. setaceus invasion on plant biodiversity in Sicily and southern Italy, and we identified and characterized plant species’ composition using Ellenberg indicator values. The intention to analyze species richness, diversity, and ecological indicators is also emphasized. Starting from the use of the phytosociological method, multivariate analysis and Ellenberg indicator values to assess the impact of C. setaceus on grasslands composition were considered. There are several similarities and differences in diversity, floristic composition, and ecological traits between the two grassland types. A deep comparison with central European studies and evaluation of the impact of C. setaceus on species richness and community dynamics in Mediterranean habitats were concluded. Although C. setaceus is invading native grasslands, it does not drastically reduce species richness. The ecological implications of the invasion are explored, urging ongoing monitoring and collaborative efforts for effective conservation. The importance of interdisciplinary cooperation is highlighted to address the threat of invasive species and sustain the biodiversity of Mediterranean grasslands.

Restoring stone and dominant grass species cover in a Mediterranean grassland: 20‐year effects on soil, vegetation, and arthropod communities

Long‐term studies are needed to monitor recovery following restoration, as it may take decades or even centuries, particularly in the case of Mediterranean dry grasslands, for communities to reach their former equilibrium before the degradation occurred. A multi‐component approach is also needed to evaluate restoration success and better understand the complex impacts of former restoration projects on present‐day ecological interactions and ecosystem functions. The objective of this study was to address the restoration of a Mediterranean grassland in southern France, 20 years after implementation. Particularly, we examine the long‐term impact on soil, vegetation, and arthropods of the reintroduction of a dominant grass species (Brachypodium retusum) and the restoration of the natural stone cover on a degraded former cultivated field. Soil analyses revealed that reestablishing stone cover only slightly acidified the soil, while B. retusum presence enhanced soil fertility. Brachypodium retusum also decreased the nutritional value of forage and increased plant biomass and litter. Plant composition shifted with treatments: B. retusum and stone cover favored xeromesophilous species, while B. retusum alone encouraged less palatable species. The soil seed bank composition and abundance were positively influenced by stone cover but negatively impacted by B. retusum reintroduction. Negative outcomes on some arthropods and mesofauna were measured in treatments with both B. retusum and stones, except for Acari, which were positively impacted by the presence of stones. The findings emphasize that B. retusum is an ecological engineer with complex effects on the different ecosystem components.

Urban Natural Spaces as Laboratories for Learning and Social Awareness

Mediterranean areas contain a great diversity of flora and phytocenosis, due to the different substrates and the special Mediterranean climate, and it is in the Iberian Peninsula where the greatest diversity is concentrated. The need for didactic techniques that generate awareness and good learning results is considered of great relevance in order to obtain well-trained environmental managers. We proceed to the research on different phytosociological groups. The one with the largest number of associations or plant communities is the one located in nitrified environments near urban areas; the group of communities dominated by Poa bulbosa is of great interest for sheep farming, while, for equine and bovine farming, the communities rich in grasses and legumes that are located in rural environments rich in organic matter are of interest. The latter communities are also interesting because they act as a sink for CO2. Due to the serious alterations in Mediterranean grasslands, we propose cultural, socio-educational, and socio-economic strategies to increase family income, thus avoiding the south–north migratory flow, as well as combining exploitation and conservation, and promoting sustainable development.

Multilayer diffusion networks as a tool to assess the structure and functioning of fine grain sub‐specific plant–pollinator networks

Interaction networks are a widely used tool to understand the dynamics of plant–pollinator ecological communities. However, while most mutualistic networks have been defined at the species level, ecological processes such as pollination take place at different scales, including the individual or patch levels. Yet, current approaches studying fine‐grain sub‐specific plant–pollinator networks only account for interactions among nodes belonging to a single plant species due to the conceptual and mathematical limitations of modeling simultaneously several plant species each composed of several nodes. Here, we introduce a multilayer diffusion network framework that allows modeling simple diffusion processes between nodes pertaining to the same or different layers (i.e. species). It is designed to depict from the network structure the potential conspecific and heterospecific pollen flows among plant individuals or patches. This potential pollen flow is modeled as a transport‐like system, in which pollen grain movements are represented as random‐walkers that diffuse on an ensemble of bipartite layers of conspecific plants and their shared pollinators. We exemplify this physical conceptualization using a dataset of nine fine‐grain sub‐specific plant–pollinator networks from a Mediterranean grassland of annual plants, where plant nodes represent groups of conspecifics within patches of 1 m2. The diffusion networks show pollinators effectively connecting sets of patches of the same and different plant species, forming a modular structure. Interestingly, different properties of the network structure, such as the conspecific pollen arrival probability and the number of conspecific subgraphs in which plants are embedded, are critical for the seed production of different plant species. We provide a simple but robust set of metrics to calculate potential pollen flow and scale down network ecology to functioning properties at the individual or patch level, where most ecological processes take place, hence moving forward the description and interpretation of species‐rich communities across scales.

Ungulate herbivores promote contrasting modifications of soil properties and organic carbon stabilization in a grazed grassland versus rewilded woodland environment

Large vertebrate herbivores are ecosystem engineers, provoking cascading effects on soil properties through modifications of plant communities as well as direct modulation of organic matter incorporated into soils. However, most studies have been carried out with domestic ungulates in grasslands, and the effects which predominate in grasslands may not be generalizable to other ecosystems. It is not well understood how trophic rewilding with wild ungulates may affect soil processes, especially in non-grassland systems albeit rewilding of natural areas is a process associated with larger trends of land abandonment, shrub encroachment or land use change. In this study we investigated ungulate herbivore exclusion in two geographically and pedo-climatically equivalent but ecologically distinct contexts: a Mediterranean grassland with domesticated herbivores, and a reforested area populated by a community of wild ungulates. In each context, long-term herbivore exclusion zones were used to understand the effect of herbivores on soil properties and particularly on soil organic carbon (SOC). Samples from the topsoil (0–5 cm) were taken inside and outside the exclosures distributed between the two contexts, and ecosystem-level effects and responses to grazing were investigated. We found that soil properties’ response to grazing depended on the ecological context in which the grazing occurred. SOC contents in the grassland increased by up to 37% with grazing, while grazing reduced SOC concentrations by 23% in the rewilded area. In both cases, grazing was also associated with significant alterations of soil microbial biomass, the microbial metabolic quotient (qCO2), and aggregate stability, but the effects were opposite: On one hand, domesticated herbivores in the grassland positively influenced carbon stabilization which was strongly associated with soil microbial processes and characteristics, and additionally the proportion of stable macroaggregates was increased. In contrast, wild ungulate herbivory in the forest ecosystem reduced SOC concentrations, accompanied by decreased microbial biomass and increased microbial maintenance costs, and stable macroaggregates were reduced. The results indicate the importance of ecological context in determining the effect of herbivores on soil properties and processes and suggest that the directionality of effects on SOC may change owing to the predominance of different mechanisms of SOC stabilization. Consequently, this study provides evidence that the management of ungulates in rangelands or forests can be associated with different outcomes as related to crucial soil properties such as SOC contents and aggregation.

Is Joint Management between Conservationists and Farmers Sustainable and Biodiversity-friendly? A Ten-year Study in Residual Grasslands of a Protected Area.

In recent decades, there has been a discernible reduction in temperate and Mediterranean grasslands with consequences on the decline of biodiversity and landscape heterogeneity. When this decline is due to agricultural abandonment, a renewed joint management, combining bush clearing by conservationists and grazing by farmers, should favor the maintenance of grasslands, their protected habitats and species and forage production. Rainfall irregularity explains part of the variation of these parameters. To verify these hypotheses, we conduct a comprehensive, multi-scale, multi-taxa study over a ten-year period in a Mediterranean protected area. At the regional scale, experimental plots in which this joint management was implemented are representative of residual managed grasslands of the protected area. At the mesoscale, rainfall irregularity is the main factor explaining inter-annual differences in the biomass of open landscapes, while fauna depends on management, tree cover and trophic resources. At the local scale, in a representative experimental plot, clearing had an immediate negative impact on plant richness and bird and positive on forage. Over a decade, plant biodiversity increased while forage, specialist plants and bird maintained, despite the regrowth of bush. Drought had a negative impact on richness, plant and forage abundance and phenological asynchrony on butterflies. In conclusion, joint management has positive, neutral and negative impacts to be considered before implementing this strategy. This long-term monitoring study draws important lessons for designing a sustainable management of grasslands under abandonment and irregular climate, that should be applied in temperate and Mediterranean regions that are increasingly vulnerable to these trends.

Exploring dynamics of floristic composition in Mediterranean grasslands: a case study from Sardinia, Italy

Mediterranean grasslands stand out as biodiversity hotspots due to their inclusion of diverse habitats that foster a remarkable range of biological diversity, characterized by inter-annual variability of floristic composition. This study aims to assess the inter-annual dynamics of the floristic composition in a grassland within a typical silvopastoral system in the Mediterranean basin, within the framework of rainfall variability. The study was performed on a farm representative of Mediterranean silvopastoral systems in Central-Western Sardinia (Italy). Vegetation surveys started in the spring of 2018 and concluded in the spring of 2022. They were conducted annually in the spring (S) and winter (W) seasons, using the point quadrat method along eight permanent transects. The dynamics of floristic composition were compared within and between years in terms of variability of specific percentage contribution (CSP) of each plant species. The results highlighted substantial differences in the composition of plant assemblages between the two seasons (W vs S) and between surveys within each season for all a posteriori comparisons. Anthemis arvensis, Lolium rigidum, Festuca ligustica and Medicago polymorpha were the main discriminating plant species between seasons. Considering the discriminant species between the four winter surveys, we found a positive effect of August rain on Cynodon dactylonCSP and a negative one on Trifolium subterraneumCSP. Considering the spring surveys, we found a positive effect of January rain on L. rigidum and a negative effect on Plantago lanceolata. The rain affected the inter-annual dynamics of floristic composition in the Mediterranean grasslands. Other factors, such as temperature, remain to be investigated. Moreover, a more extended data series may allow us to strengthen our results.

Plant Diversity in Archaeological Sites and Its Bioindication Values for Nature Conservation: Assessments in the UNESCO Site Etruscan Necropolis of Tarquinia (Italy)

In archaeological sites, plants can be a risk for monument conservation. However, in these sites, a refugium for plant biodiversity is often detected, such as in the UNESCO site Etruscan necropolis of “Monterozzi” in Tarquinia, which still holds a Special Protection Area for bats. In this site, we previously evaluated the positive and negative effects of vascular plants on the conservation of the hypogeal tombs. To contribute in assessing the role of archaeological sites in supporting plant diversity and interpreting its bioindication values for nature conservation, we analyse in this relevant place the floristic interest and richness and the plant communities growing on tumuli, trampled, and less disturbed areas. The results revealed the presence of several plants with high naturalistic interest, such as the community’s representative of synanthropic and natural Mediterranean grasslands, which arise both from the present and the past uses of the area. The high naturalistic values of the site are also assessed, considering its remarkable richness of species/area compared with the well-known archaeological sites of Rome. These findings further indicate that plant diversity needs to be considered in planning management activities in archaeological sites to also protect their natural values.

Viral but not bacterial community successional patterns reflect extreme turnover shortly after rewetting dry soils.

As central members of soil trophic networks, viruses have the potential to drive substantial microbial mortality and nutrient turnover. Pinpointing viral contributions to terrestrial ecosystem processes remains a challenge, as temporal dynamics are difficult to unravel in the spatially and physicochemically heterogeneous soil environment. In Mediterranean grasslands, the first rainfall after seasonal drought provides an ecosystem reset, triggering microbial activity during a tractable window for capturing short-term dynamics. Here, we simulated precipitation in microcosms from four distinct dry grassland soils and generated 144 viromes, 84 metagenomes and 84 16S ribosomal RNA gene amplicon datasets to characterize viral, prokaryotic and relic DNA dynamics over 10 days. Vastly different viral communities in each soil followed remarkably similar successional trajectories. Wet-up triggered a significant increase in viral richness, followed by extensive compositional turnover. Temporal succession in prokaryotic communities was much less pronounced, perhaps suggesting differences in the scales of activity captured by viromes (representing recently produced, ephemeral viral particles) and total DNA. Still, differences in the relative abundances of Actinobacteria (enriched in dry soils) and Proteobacteria (enriched in wetted soils) matched those of their predicted phages, indicating viral predation of dominant bacterial taxa. Rewetting also rapidly depleted relic DNA, which subsequently reaccumulated, indicating substantial new microbial mortality in the days after wet-up, particularly of the taxa putatively under phage predation. Production of abundant, diverse viral particles via microbial host cell lysis appears to be a conserved feature of the early response to soil rewetting, and results suggest the potential for 'Cull-the-Winner' dynamics, whereby viruses infect and cull but do not decimate dominant host populations.

Uncovering the dark side of agriculture: How land use intensity shapes soil microbiome and increases potential plant pathogens

Soil microbiome plays a critical role in maintaining key soil processes such as litter decomposition, nutrient cycling, and plant productivity. In this study, we aimed to investigate the variability of soil chemicals, microbial diversity, and composition in seven ecosystems i.e., Fagus sylvatica and Quercus ilex forests, a Mediterranean grassland and shrubland, a vineyard, a horticultural cultivation in open field and under greenhouse, across a gradient of land-use intensity in Southern Italy. Soil chemistry included pH, organic matter, total nitrogen, and C/N ratio, and soil microbiota was characterized by high-throughput sequencing of 16S and ITS genes. Our results showed that greenhouse soils had the highest pH, while Fagus had the lowest. Horticultural, greenhouse, and grassland soils had low levels of OM and total N, while shrubland had relatively high levels of OM, total N, and C/N ratio. Fagus soils, on the other hand, had the highest levels of OM, total N, and C/N ratio. Bacterial diversity was lowest in horticultural soils, whereas fungal diversity was highest in shrubland soils. Pseudomonadota were the predominant bacteria in Fagus, grassland, and vineyard soils, while Actinomycetota dominated in Quercus, shrubland, and greenhouse soils. However, Cyanobacteria was predominant in horticultural soils. On the other hand, the Ascomycota was predominant in all ecosystems except Quercus soils, where the Basidiomycota was dominant. Our bipartite network analysis revealed that bacteria are often the same in different ecosystems while fungi tend to be specific to a particular habitat. Moreover, in agricultural ecosystems, fungal pathogens belonging to Alternaria, Fusarium, Gibellulopsis, Stemphylium, Acremonium, and Curvularia are more abundant, especially in greenhouse. The findings of this study provide important insights into the variability of soil microbial diversity and community composition in different ecosystems, highlighting the essential role of preserving natural ecosystems while managing agricultural ones, given their higher abundance of pathogens.

Structural asymmetry in biotic interactions as a tool to understand and predict ecological persistence.

A universal feature of ecological systems is that species do not interact with others with the same sign and strength. Yet, the consequences of this asymmetry in biotic interactions for the short- and long-term persistence of individual species and entire communities remains unclear. Here, we develop a set of metrics to evaluate how asymmetric interactions among species translate to asymmetries in their individual vulnerability to extinction under changing environmental conditions. These metrics, which solve previous limitations of how to independently quantify the size from the shape of the so-called feasibility domain, provide rigorous advances to understand simultaneously why some species and communities present more opportunities to persist than others. We further demonstrate that our shape-related metrics are useful to predict short-term changes in species' relative abundances during 7 years in a Mediterranean grassland. Our approach is designed to be applied to any ecological system regardless of the number of species and type of interactions. With it, we show that is possible to obtain both mechanistic and predictive information on ecological persistence for individual species and entire communities, paving the way for a stronger integration of theoretical and empirical research.

Testing a novel pasture quality index using remote sensing tools in semiarid and Mediterranean grasslands

Estimating the nutritional value of herbage is a core aspect of livestock pasture management. Quantitative information related to significant findings is essential for assessing nutritional provision and preventing pasture degradation. Here, we developed a new Pasture Quality Index (PQI) that indicates the nutritional quality of pastures based on their nutritional value and the composition of plant functional groups of the vegetation. We applied the model on a regional scale using VENμS satellite data, collected more than 450 plant samples, and applied pasture quality parameters analysis. Pasture samples were collected from paddocks under two different grazing intensities in Israel in a semiarid and a Mediterranean grassland. Pasture quality was estimated five times over two years at mid- and peak vegetation growth stages. The PQI included: protein content, fiber content, dry matter digestibility and the proportion of unpalatable spiny thistles. A support vector machine regression model was used to train statistical models that relate ground truth PQI data to the reflectance values of the VENμS satellite. Large-scale forage quality maps at 5 m spatial resolution were created. Fine-resolution drone orthomosaics were used to enhance the satellite-based predictions accuracy, resulting in a model accuracy of R2 = 0.86. We observed that nutritional quality showed strong dependence on seasonality and the grazing regime, with higher quality observed during mid-growth compared to peak growth. Higher quality was also observed under grazing compared to ungrazed paddocks. The occurrence of unpalatable thistles in grazed paddocks significantly reduced the pasture quality at the Mediterranean grassland. To summarize, the PQI enables the integration of several quality indicators into an index that helps in detecting the effects of grazing management on rangelands. In addition, high accuracy was achieved in relating the overall PQI and high spatiotemporal resolution satellite imagery data. Our developed methodology enables site-specific, spatially explicit, frequent, and area-extensive pasture quality assessment that can aid in optimizing livestock management in various ecosystems.

Functional Groups Response to Water Deficit in Mediterranean Ecosystems.

Enhanced drought, more frequent rainfall events and increased inter-annual variability of precipitation are the main trends of climate expected for the Mediterranean. Drought is one of the most important stressors for plants and significantly impacts plant communities causing changes in plant composition and species dominance. Through an experiment under controlled conditions, we assessed the response of Mediterranean species from different functional groups (annual grass, annual forb, annual legume, and perennial shrub) to moderate and severe water deficit. Changes in plant traits (leaf dry matter), biomass and physiology (water status, photosynthesis, pigments, and carbohydrate) were evaluated. The studied species differed in their response to water deficit. Ornithopus compressus, the legume, showed the strongest response, particularly under severe conditions, decreasing leaf relative water content (RWC), pigments and carbohydrates. The grass, Agrostis pourreti and the forb, Tolpis barbata, maintained RWC, indicating a higher ability to cope with water deficit. Finally, the shrub, Cistus salviifolius, had the lowest response to stress, showing a higher ability to cope with water deficit. Despite different responses, plant biomass was negatively affected by severe water deficit in all species. These data provide background for predicting plant diversity and species composition of Mediterranean grasslands and Montado under climate change conditions.

Subsoiling for planting trees in dehesa system: long-term effects on soil organic carbon

Incorporating trees into agricultural systems, including grasslands, increases the soil organic carbon sequestration and contributes to climate change mitigation. Site preparation for tree establishment is a common practice that can involve a variety of techniques and agricultural implements such as subsoiling. This study aimed to evaluate the long-term effects of subsoiling on soil organic carbon (SOC) concentrations and stocks in a Mediterranean grassland afforested with holm oaks 22 years ago and now converted into a Dehesa agroforestry system. The study was conducted in a dehesa farm in Southwest Spain. Soil samples were taken at six depths under 10 tree canopies within and outside the original subsoiling line. Subsoiling significantly decreased SOC concentration. Mean SOC concentration in the first 20 cm was 30% lower at the subsoiling line. SOC stocks for the first 60 cm were 2660 g m−2 within the subsoiling line and 4320 g m−2 outside the line. There was a clear reduction in SOC concentration and stock with increasing depth. Root abundance and deeper rooting increased with subsoiling but did not translate into sufficient carbon accumulation in the soil, which is moderate even after 22 years. This study reveals that, in the long term, there is a trade-off in CO2 sequestration between tree planting and soil subsoiling, highlighting the need for further research into the potential benefits and detriments of subsoiling.

Ozone and Temperature May Hinder Adaptive Capacity of Mediterranean Perennial Grasses to Future Global Change Scenarios.

Climate warming is recognized as a factor that threatens plant species in Mediterranean mountains. Tropospheric ozone (O3) should also be considered as another relevant stress factor for these ecosystems since current levels chronically exceed thresholds for plant protection in these areas. The main aim of the present study was to study the sensitivity of four Mediterranean perennial grasses to O3 and temperature based on plant growth, gas exchange parameters (photosynthesis-A, stomatal conductance-gs, and water use efficiency-WUE), and foliar macro- (N, K, Ca, Mg, P, and S) and micronutrients (B, Cu, Fe, Mn, Mo, and Zn) content. The selected species were grasses inhabiting different Mediterranean habitats from mountain-top to semi-arid grasslands. Plants were exposed to four O3 treatments in Open-Top chambers, ranging from preindustrial to above ambient levels, representing predicted future levels. Chamber-less plots were considered to study the effect of temperature increase. Despite the general tolerance of the grasses to O3 and temperature in terms of biomass growth, WUE and foliar nutrient composition were the most affected parameters. The grass species studied showed some degree of similarity in their response to temperature, more related with phylogeny than to their tolerance to drought. In some species, O3 or temperature stress resulted in low A or WUE, which can potentially hinder plant tolerance to climate change. The relationship between O3 and temperature effects on foliar nutrient composition and plant responses in terms of vegetative growth, A, gs, and WUE constitute a complex web of interactions that merits further study. In conclusion, both O3 and temperature might be modifying the adaptation capacity of Mediterranean perennial grass species to the global change. Air pollution should be considered among the driving favors of biodiversity changes in Mediterranean grassland habitats.

System Dynamics Tools to Study Mediterranean Rangeland’s Sustainability

Rangelands are a key resource present all over the world and cover half of all emerged lands. They are even more important in drylands, where they cover 48% of the total area. Their intensification and the additional pressure added by climate change push these socio-ecological systems towards desertification. Over the last two decades, we have developed and applied System Dynamics (SD) models for the study of Mediterranean grasslands. In addition, we have designed procedures and analysis tools, such as global sensitivity analysis, stability analysis condition, or risk analysis, to detect the main drivers of these socio-ecological systems and provide indicators about their long-term sustainability. This paper reviews these works, their scientific background, and the most relevant conclusions, including purely technical and rangeland-related ones, as well as our experience as systemic modelers in a world driven by field specialists.