Mediterranean Grasslands Research Articles

Shrub encroachment in Mediterranean mountain grasslands: Rate and consequences on plant diversity and forage availability

AbstractQuestionShrub encroachment has been confirmed in the past decades all over the world and is currently viewed as a “global process” threatening many grass‐dominated biomes. In southern Europe has generally been related to rural depopulation, land‐use changes and grazing abandonment. Nevertheless, in several mountain ranges of the Iberian Peninsula with secular pastoralism and high shrub cover, neither stocking rate nor traditional management has substantially altered in the past decades. Within this framework, to deepen our knowledge of shrub encroachment and to adopt, if necessary, appropriate control measures, we aim to discover: (i) the overall expansion rate in the main grassland–shrub communities; (ii) the course of shrub expansion; and (iii) the consequences for grassland floristic composition, plant diversity and frequency of the main forage functional groups throughout the period of woody expansion.LocationThis study was undertaken in Moncayo Natural Park (Spain), a climate and vegetation crossroads with remarkable presence of four widespread Mediterranean shrubs:Cytisus oromediterraneus,Erinacea anthyllis,Juniperus communisandJ. sabina.MethodsTo determine the expansion rates of those shrubs, we examined four distinct and sufficiently separated grazing areas (and different shrub combinations), each with four different stages of shrub cover, over a 6‐year period. To assess changes in vegetation structure between 2008 and 2014 during the different stages of shrub encroachment, we used a pairedt‐test comparing 14 parameters related to the diversity, life‐form spectra and abundance of grazing plants. The influence of year, cover category and zone was jointly assessed using a Linear Mixed Model.ResultsFor the whole territory, we found an increase in average yearly cover of 1.3% (with high variation between the four species), although at the zone scale (areas with a particular shrub dominance) this increase was significant in only half of them. When the four shrubs occur together,Juniperusspecies show faster expansion rates than the other two species, although in only a few cases was the increase significant over the 6 years of the study. We found a significant decrease in total plant diversity and a significant increase in dominance between cover categories and years. Looking at the vegetation life‐forms, the increase in chamaephytes and phanerophytes, which include invader shrubs, caused a decrease in therophytes and hemicryptophytes. Finally, grasses and leguminous plants, which constitute the main livestock food intake, showed noticeable reductions, resulting in loss of pastoral value.ConclusionsAlthough cessation of grazing has been noted as the main cause of shrub encroachment in Mediterranean grasslands, our results, suggest that encroachment occurs despite the maintenance of stocking rate and livestock management, and leads to a decrease in plant diversity and grassland quality. Focusing on use of the territory and taking into account the prevalence of negative effects after shrub encroachment, additional measures to safeguard ecological and pastoral values in Mediterranean mountain grasslands should be considered, particularly on sites of nature conservation interest with a long grazing history.

Functional assembly of grassland plant species in native communities in Spain and recipient communities in California

Abstract A major aim in invasion ecology is to understand the role of exotic species in plant communities. Whereas most studies have explored the traits of exotic species in the context of the introduced community, functional comparisons of entire assemblages of species in their native and introduced communities have rarely been analysed. Taking advantage of the unidirectional invasion of plant species of European origin (i.e. colonizers) into California, this study aims to investigate the relative importance of plant traits, environmental factors and invasion status in biological invasions. We compared the functional structure (i.e. trait composition and diversity) along resource availability gradients in recipient and native Mediterranean grassland communities in California and Spain, respectively. Traits were related to resource use in above‐ground and below‐ground organs and reproductive strategy. We also investigated how niche differences vary along environmental gradients between coexisting colonizer and native species assemblages within communities. There were clear differences in the functional structure of Mediterranean grassland communities between regions, which were associated with the resource availability gradient. Paradoxically, the most acquisitive communities occurred in resource‐poor sites, highlighting that rapid acquisition and use of resources permit species to cope with environmental stress through stress avoidance. In Spain, colonizer species had greater specific leaf area than non‐colonizers. Yet, differences between colonizer and non‐colonizer species in Spain for other traits were mostly absent and did not change along the gradient. This might be a result of the greater native species richness as a consequence of the agricultural practices that have taken place in Europe for millennia and reflect that the entire species pool of grasslands is adapted to agricultural landscapes. In comparison, in California, colonizer species were more acquisitive in their use of resources than natives under favourable conditions, but functionally converged in resource‐limited sites. Synthesis. These results underscore that the importance of niche differences between native and colonizer species as a community assembly mechanism is strongly subjected to the influence of habitat filtering. Trait comparisons are context dependent, and a correct interpretation of filtering processes in community assembly requires a regional perspective.

Mediterranean grassland succession as an indicator of changes in ecosystem biodiversity and functionality

The abandonment of agricultural lands triggers a secondary succession of plant species which implies important changes in soil quality. Annual Mediterranean grasslands are known to be persistent on abandoned agriculture lands in the western Mediterranean. We used plant taxonomic and functional approaches to determine the role of Mediterranean grasslands as an indicator of changes in ecosystem biodiversity and functionality. We tested the hypothesis that Mediterranean grasslands are a suitable model for monitoring biodiversity and soil fertility in a secondary succession. Soil and vegetation features on 21 permanent plots were monitored in 2016 and 2020. Numerical classifications based on floristic composition showed two different plant communities independently of the sampling year: early-stage grasslands in the first post-abandonment decade and late-stage grasslands after the first post-abandonment decade. Generalized linear model and redundancy analysis also revealed differences in growth forms, functional traits and soil functionality between communities. Late-stage grasslands was characterized by enriched bryophyte coverage and an impoverishment in hemicryptophytes and plant latex segregators growing on soils with a higher hydrolase enzyme activity and TOC content compared to early-stage grassland. Our results suggest that annual Mediterranean grasslands growing on siliceous soils denoting a mature-stage succession, and floristically characterized by the symbiont plant with Ascomycota, Tuberaria guttata, and a high bryophyte cover, are worthy of recognition for conservation.

Spatial turnover of soil viral populations and genotypes overlain by cohesive responses to moisture in grasslands.

Viruses shape microbial communities, food web dynamics, and carbon and nutrient cycling in diverse ecosystems. However, little is known about the patterns and drivers of viral community composition, particularly in soil, precluding a predictive understanding of viral impacts on terrestrial habitats. To investigate soil viral community assembly processes, here we analyzed 43 soil viromes from a rainfall manipulation experiment in a Mediterranean grassland in California. We identified 5,315 viral populations (viral operational taxonomic units [vOTUs] with a representative sequence ≥10 kbp) and found that viral community composition exhibited a highly significant distance-decay relationship within the 200-m2 field site. This pattern was recapitulated by the intrapopulation microheterogeneity trends of prevalent vOTUs (detected in ≥90% of the viromes), which tended to exhibit negative correlations between spatial distance and the genomic similarity of their predominant allelic variants. Although significant spatial structuring was also observed in the bacterial and archaeal communities, the signal was dampened relative to the viromes, suggesting differences in local assembly drivers for viruses and prokaryotes and/or differences in the temporal scales captured by viromes and total DNA. Despite the overwhelming spatial signal, evidence for environmental filtering was revealed in a protein-sharing network analysis, wherein a group of related vOTUs predicted to infect actinobacteria was shown to be significantly enriched in low-moisture samples distributed throughout the field. Overall, our results indicate a highly diverse, dynamic, active, and spatially structured soil virosphere capable of rapid responses to changing environmental conditions.

Grazing intensity gradient inherited from traditional herding still explains Mediterranean grassland characteristics despite current land-use changes

Grazing is well-known to shape plant populations and plant communities and to affect several compartment characteristics of grazed ecosystems. Semi-natural grassland conservation depends on the maintenance of traditional extensive grazing systems which can exist for centuries, even millennia. However, very few studies have concomitantly investigated the effect of grazing management on plant, forage, litter and soil compartments and the implications of their potential interactions for conservation after recent changes in grazing practices.This study thus aimed to identify the concomitant effects of sheep grazing on the latter compartments of Mediterranean grasslands. We further investigated the effects of a recent change from millenia-old traditional herding to contemporary fenced free grazing. We also sought to determine how this change may impact the agronomic and ecological value of these grasslands.Surveys were carried out at 6 different study sites paired by the two different grazing practices in a French Mediterranean sub-steppic vegetation (“Crau” plain in Southeastern France).Using linear models and distance-based redundancy analysis, effects of grazing intensity, grazing practices and their interactions were tested on plant community, forage, litter and soil physicochemical properties. Our results show that, there was a significant effect of grazing intensity on the four studied compartments, with significantly higher species richness and evenness at moderate grazing intensity. Biomass was also significantly higher at moderate grazing intensity. Digestibility of forage, litter quality and soil fertility decreased significantly under less intensive grazing. Significant differences were also found in the relative size of the areas covered by each plant communities. Recent fenced free grazing led to significantly more intensively grazed zones, with more mesophilous/nitrophilous vegetation. Conversely, in zones traditionally less intensively grazed, the contemporary free grazing led to higher plant species-richness but again with more mesophilous species. Implications for conservation management are that the legacy of millennia-old traditional herding still compensates partly for the effects of changing practice to contemporary fenced free grazing on plant community composition but not on their relative sizes. This indicates an increase in grazing intensity in the remotest zone which could lead to grassland plant community homogenization.

Fertiliser application modulates the impact of interannual climate fluctuations and plant-to-plant interactions on the dynamics of annual species in a Mediterranean grassland

ABSTRACT Background Climate and land-use changes, which include the application of various types of organic and inorganic fertilisers, have been reducing the species diversity of Mediterranean grasslands and threatening its conservation. Annual plants are one of the most diverse functional groups of species in these grasslands, despite suffering competitive pressure from perennial herbaceous and woody species, and they are essential for ecosystem functioning and stability. Aims To quantify how fertilisation modulates the impact of plant-to-plant interactions and climate fluctuations on the dynamics of annuals in Mediterranean grasslands. We hypothesised that the application of sewage sludge would increase competition between functional groups, reducing the abundance of annuals in the long-term, but would buffer the negative impacts of drought on the year-to-year fluctuation of the diversity of annuals. Methods In a semi-natural species-rich Mediterranean grassland in northern Spain, we analysed the changes in the taxonomical and functional composition and diversity of annuals over 14 years in response to variations in the abundance of perennial herbaceous and woody species, climate fluctuations and fertilisation with sewage sludge. We quantified separately the patterns of year-to-year fluctuations and long-term trends. Results The frequency and diversity of annuals decreased with higher abundance of perennial herbaceous species, drought in June and cold winters. The addition of sewage sludge decreased the abundance of annuals in the long-term, seemed to promote competition between annuals and other functional groups at an interannual scale, and mitigated the negative effects of drought and cold. Conclusions Fertilisation influences differently the temporal response of annuals to climate fluctuations and plant-to-plant interactions.

Phenological patterns of herbaceous Mediterranean plant communities in spring: is there a difference between native and formerly-cultivated grasslands?

Background and aims – Plant phenology, defined as the timing of recurring life events like leaf flushing, flowering, or fruiting, is highly sensitive to environmental factors such as photoperiod, temperature, and moisture. Phenological synchrony between interacting species – such as plants and their pollinators – is of major importance to the structure and functioning of ecosystems. Plant phenology might also be affected by changes in edaphic conditions. However, whether former agricultural activities may shift phenological patterns of plant communities remains poorly understood. In this study, we evaluated the impact of past agricultural practices on herbaceous plant community phenology in the protected Mediterranean xeric grassland of La Crau (France). Material and methods – We compared (1) species composition, and (2) phenological patterns of annuals, perennials, Bromus rubens (annual), and Lobularia maritima (perennial), in formerly-cultivated plots – abandoned for 30 years – and intact native grassland plots (steppe), both subjected to itinerant sheep grazing. Key results and conclusion – Our results suggest that former agricultural activities can affect species composition of Mediterranean xeric grassland communities with differences visible after 30 years of abandonment, but only altered phenological patterns slightly. We suggest that climatic factors and sheep grazing acted as strong habitat filters constraining community assembly at the phenological level.

Impact of prescribed burning, mowing and abandonment on a Mediterranean grassland: A 5-year multi-kingdom comparison

Mediterranean grasslands are semi-natural, fire-prone, species-rich ecosystems that have been maintained for centuries through a combination of fire, grazing, and mowing. Over the past half century, however, grasslands have faced numerous threats, including the abandonment of traditional agro-pastoral practices. Our hypothesis was that mowing and prescribed burning are management practices potentially effective in counteracting the reduction of plant diversity triggered by land abandonment. However, the long-term effects of such management practices on plant communities and soil microbiota in Mediterranean grassland remain poorly studied. Here, we conducted a 5-year field experiment comparing prescribed fire, vegetation mowing, and abandonment in a fire-prone Mediterranean grassland in southern Italy in order to evaluate the capability of such management strategies to counteract the detrimental impacts of land abandonment on plant diversity and the associated increase of wildfire. We combined vegetation analysis and soil chemical characterization and several microbiota analyses, including microbial biomass and respiration, arthropod community, and high-throughput sequencing of bacterial and eukaryotic rRNA gene markers. Burning and mowing significantly increased plant species richness and diversity compared to abandonment plots, reducing the abundance of perennial tall grasses in favour of short-lived species. Standing litter followed the same trend, being 3.8-fold greater and largely composed of grass remains in the abandoned compared to burnt and mowed plots. In the soil, prescribed burning caused significant increase in pH, a reduction in organic carbon, total N, and cation exchange capacity. Diversity and taxonomic composition of bacterial and fungal microbiota was affected by burning and mowing treatments. Abandonment caused shifts of microbiota towards a fungal-dominated system, composed of late successional fungi of the Basidiomycota. Fast-growing and putative fungal pathogens were more abundant under burnt and mowed treatments. Soil arthropods were influenced by vegetation and microbiota changes, being strongly reduced in mowed plots. Our study demonstrated that grassland abandonment promotes the spread of tall grasses, reducing plant diversity and increasing the risk of wildfire, while prescribed burning and mowing are effective in counteracting such negative effects.

Transgenerational responses to climate change in Mediterranean annual species with contrasting functional strategies

Increasing temperature and aridity predicted by climate change models in the Mediterranean region will pose a significant challenge for the survival of some plant species. The mechanisms by which species modify their phenotype across generations in response to the environment have been identified as essential to cope with the new climatic conditions. However, this transgenerational transfer remains unexplored for species with contrasted resource-use strategies (fast-growing or acquisitive versus stress-tolerant or conservative species). For this purpose, transgenerational responses to warming and drought of annual plant species with different resource-use strategies were assessed by conducting three experiments. In a field experiment, climatic treatments of increased temperature and rainfall exclusion were imposed on five herbaceous species typical of Mediterranean grasslands. The descendants of the individuals sampled in the field were employed in two greenhouse experiments to: (1) analyze the transgenerational response by re-imposing warming and drought conditions, and (2) identify possible maternal effects by maintaining them at optimal conditions of air temperature and water availability and comparing with maternal performance. We measured reproductive output, plant growth and survival variables as plant performance indicators. We found contrasting transgenerational responses to warming and drought depending on the functional strategy of the species. Direct effects of the abiotic stressors on parental plants were retained or new ones appeared in their offspring, with special negative impact on one of the most acquisitive species ( Crepis capillaris ). In contrast, the most conservative species ( Bromus madritensis ) highly tolerated increased climatic stress but deleterious maternal effects were registered, given the high negative impact on the performance of the descendants of maternal plants that were subjected to climatic treatments. Our study highlights the importance of evaluating plant responses to stress across generations to better understand their potential ability to face new environmental conditions in species with different functional strategies. • Transgenerational response to climate change varies with plant functional strategy. • Acquisitive plant species are highly sensitive to warming and drought. • Maternal effects compromise the response to climate change of conservative species.

Network-based analysis reveals differences in plant assembly between the native and the invaded ranges

Associated with the introduction of alien species in a new area, interactions with other native species within the recipient community occur, reshaping the original community and resulting in a unique assemblage. Yet, the differences in community assemblage between native and invaded ranges remain unclear. Mediterranean grasslands provide an excellent scenario to study community assembly following transcontinental naturalisation of plant species. Here, we compared the community resemblance of plant communities in Mediterranean grasslands from both the native (Spain) and invaded (Chile) ranges. We used a novel approach, based on network analysis applied to co-occurrence analysis in plant communities, allowing us to study the co-existence of native and alien species in central Chile. This useful methodology is presented as a step forward in invasion ecology studies and conservation strategies. We found that community structure differed between the native and the invaded range, with alien species displaying a higher number of connections and, therefore, acting as keystones to sustain the structure within the invaded community. Alien species acting like keystones within the Chilean grassland communities might exacerbate the threat posed by biological invasions for the native biodiversity assets. Controlling the spread of the alien species identified here as keystones should help managing potential invasion in surrounding areas. Network analyses is a free, easy-to-implement and straightforward visual tool that can be widely used to reveal shifts in native communities and elucidate the role of multiple invaders into communities.

Long‐term and year‐to‐year stability and its drivers in a Mediterranean grassland

Abstract Understanding the mechanisms underlying community stability has become an urgent need to protect ecosystems from global change and resulting biodiversity loss. While community stability can be influenced by species richness, synchrony in annual fluctuations of species, species stability and functional traits, the relative contributions of these drivers to stability are still unclear. In semi‐natural grasslands, land‐use changes such as fertilization might affect stability by decreasing richness and influencing year‐to‐year fluctuations. In addition, they can promote long‐term directional trends, shifting community composition and influencing grassland maintenance. Thus, it is important to consider how species and community stability vary year‐to‐year but also in the long term. Using a 14‐year vegetation time series of a species‐rich semi‐natural Mediterranean grassland, we studied the relative importance of richness, synchrony, species stability and functional traits on community stability. To assess land‐use change effects on stability, we applied a fertilization treatment. To distinguish stability patterns produced by year‐to‐year fluctuations from those caused by long‐term trends, we compared the results obtained using a detrending approach from those without detrending. Independently of the treatment and approach applied, the most stable communities were those composed of asynchronous species with low specific leaf area. Fertilization decreased year‐to‐year and long‐term community stability by increasing community‐weighted mean of specific leaf area, decreasing species stability or also reducing richness in the case of year‐to‐year stability. Additionally, traits such as seed mass had an indirect effect on stability through synchrony. Long‐term trends appeared in control and fertilized plots (due to fertilization), decreasing community and species stability and leading to differences in the relationships found between community stability and some of its drivers. This reflects the importance of accounting for the effect of temporal trends on community and species stability using both a long‐term and a year‐to‐year approach. Synthesis. Stability is influenced by richness, synchrony and functional traits. Fertilization decreases species and community stability by promoting long‐term trends in species composition, favouring competitive species and decreasing richness. Studying stability at the community level and species level, and accounting for the effect of trends is essential to understand stability and its drivers more comprehensively.

Contrasting effects of eucalyptus, pine and oak plantations on nest predation risk in Mediterranean grasslands

Large scale afforestation (i.e., establishment of forests on farmland, grassland and other land not previously forested) is increasingly regarded as a cost-effective option to mitigate climate change by promoting carbon sequestration. However, this strategy can have negative biodiversity impacts, potentially causing the loss and fragmentation of open habitats of conservation value, as well as edge effects that can extend well beyond forest boundaries. Mitigating impacts of afforestation programs thus requires a detailed understanding of the mechanisms whereby they affect biodiversity, particularly where new plantations are established close to areas important for open habitat species. Here, we examined how afforestation with oak, pine or eucalyptus trees, commonly planted in Mediterranean Europe, may have distinct effects on nest predation risk of grassland birds in southern Portugal. We used artificial nests with quail eggs and camera traps to: (i) identify nest predators and estimate predation risk of ground-nesting birds in grasslands adjacent to oak, pine and eucalyptus plantations across a distance gradient (0 m to 300 m) from the plantation edge; and (ii) examine how predation risk was influenced by avian predator abundance, sward height and vegetation clearing for photo-monitoring (nest-site manipulation), and their interactions with plantation type. Carrion crow was by far the main egg predator identified, followed by Montagu’s harrier, raven and magpie. Overall, nest predation risk and predator abundance were higher around eucalyptus plantations, compared to either pine or oak plantations. Predation decreased with increasing sward height, but this effect was less noticeable when vegetation around nests was cleared. In pine and oak plantations, predation risk was slightly higher close to edges, and decreased with distance from the edge. Conversely, in eucalyptus plantations predation was lower close to edges, and increased with distance to edges. Distance effects around eucalyptus plantation were, however, absent in manipulated nests. Overall, results show that afforestation with different tree species has distinct impacts on predation risk of artificial nests in Mediterranean farmland. This is probably a consequence of an increasing structural complexity of the plantations, from oak to eucalyptus, driven by differences in tree growth rates and undergrowth cover. These findings suggest that farmland afforestation should favour agro-forest plantations with slow growing species (oak and pine) to mitigate negative effects on breeding grassland birds in adjacent open habitats.

Fine-Tuned Ecological Niche Models Unveil Climatic Suitability and Association with Vegetation Groups for Selected Chaetocnema Species in South Africa (Coleoptera: Chrysomelidae)

Despite beetles (Coleoptera) representing most existing animal species, the ecological and biogeographical factors shaping their distribution are still unclear in many regions. We implemented state-of-the-art ecological niche models (ENMs) and niche overlap analysis to investigate climate–occurrence patterns for five flea beetle species of the genus Chaetocnema in South Africa (C. brincki, C. danielssoni, C. darwini, C. gahani, and C. natalensis). ENMs were fitted through Maxent and Random Forests, testing various parameterizations. For each species, tuned ENMs attaining good discrimination on spatially independent test data were selected to predict suitability across the study region and individuate its main climatic drivers. Percentage coverage of climatically suitable areas by seventeen Afrotropical vegetation formations was also computed. Predicted suitable areas do not extend far away from known presence localities, except for C. brincki and C. gahani in north-eastern South Africa. Temperate grasslands and shrublands cover most of suitable areas for C. brincki and C. gahani, along with warm temperate forests, as well as for C. danielssoni, in this case being followed by tropical flooded and swamp forests. Climatic suitability for C. darwini mainly relates to the Mediterranean grasslands and scrublands of the southern coastal region, while suitable areas for C. natalensis encompass various vegetation formations, coherently with its wide distribution. The environmental niche of C. danielssoni significantly overlaps with those of the wide-ranging C. darwini and C. natalensis, suggesting that historical factors, rather than low climatic tolerance, has determined its restricted distribution in the Western Cape Province. Maxent and Random Forests were confirmed to be of great help in disentangling the environment–occurrence relationships and in predicting suitability for the target species outside their known range, but they need to be properly tuned to perform at their best.

Assessment of Drought Indexes on Different Time Scales: A Case in Semiarid Mediterranean Grasslands

Drought is a significant challenge to semiarid Mediterranean grasslands, Increasing the accuracy of monitoring allows improving the conservation and management of these vital ecosystems. Meteorological drought is commonly monitored by the Standard Precipitation Index (SPI) or the Standard Precipitation Evapotranspiration Index (SPEI). On the other hand, agriculture drought is estimated by the Vegetation Health Index (VHI). This work aims to optimise the correlation between both drought types using the best transformation of VHI and the most appropriate time scale. Two drought-vulnerable Mediterranean grasslands were selected to evaluate the performance of the drought indexes. The SPI and the SPEI were calculated using data obtained from nearby weather stations. MODIS data were used to calculate the VHI. This index was standardised, naming it as SVHI. Our results revealed that SPEI was better correlated with VHI compared to SPI. In addition, SVHI obtained better results in the critical vegetation phases than VHI. Overall, SPEI and SVHI were the best correlated indexes. The quarterly scale showed stronger relationships than the monthly scale and the most correlated time frame were Mediterranean spring and autumn. This fact suggests that SPEI and SVHI could provide a plus point for increasing the precision of vegetation monitoring during these periods.

Estimating pasture quality of Mediterranean grasslands using hyperspectral narrow bands from field spectroscopy by Random Forest and PLS regressions

Mediterranean grasslands are a cornerstone ecosystem to provide ecosystem services and sustain human societies. The sustainability and provision of ecosystem services by these systems rely on their management. One of the main attributes to perform sustainable and effective management is pasture quality, which is crucial for animal performance in rainfed extensive systems. Remote sensing of grasslands can be an effective tool to inform the management of grasslands. The forthcoming high-priority mission candidate of the European Space Agency, Copernicus Hyperspectral Imaging Mission for the Environment (CHIME) with continuous narrow bands of ≥10 nm spectral resolution could be an asset to provide accurate information on the pasture quality of high-diverse and heterogeneous grasslands. In this study, we investigated the potential of CHIME-like field spectroscopy data at 10 nm resolution to assess the quality of Mediterranean permanent grasslands. The pasture quality indicators used were: crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and enzyme digestibility of organic matter (EDOM). To do so, two machine learning methods commonly used in remote sensing were implemented: Partial Least Squares (PLS) regression and Random Forest (RF) regression. The results using all bands in the 400–2300 nm spectral range and the results obtained by Backward Feature Elimination (BFE) were also compared. Finally, using importance measures of PLS and RF and the BFE approach, the importance and stability of the bands to assess the pasture quality indicators were explored. The results showed that field spectroscopy CHIME-like data at 10 nm of spectral resolution show potential to predict CP at “good” accuracy and NDF at “moderate” accuracy level in Mediterranean permanent grasslands. PLS outperformed RF to predict CP and NDF in terms of accuracy and certainty of the predictions. The BFE approach increased the accuracy of the predictions, especially in PLS, for which a percentage decrease of ΔRMSE = -12.5% was achieved in cross-validation to predict CP. The models built by BFE approach to predict CP using PLS provided a mean R2 value of 0.82 and a range of 0.68–0.90 in bootstrapped predictions. The RMSE was low (mean RMSE = 2.23%) and the mean RPD = 2.47 with values ranging from 1.81 to 3.23. RF models to predict CP produced mean R2 value of 0.68, mean RMSE = 3.00% and mean RPD = 1.82. ADF and EDOM were predicted with poor accuracy and similarly by both, PLS and RF. The bands located in the red-edge and NIR region showed high importance and stability to assess the best-predicted variables. Bands centred at 700, 710, 1160, 1170 and 1180 are highly stable and important to predict CP. The bands from the SWIR region had lower stability. This study provides insightful results on the use of hyperspectral data and future satellite missions such as CHIME to assess the pasture quality of Mediterranean grasslands that can be crucial to inform the management and monitoring of Mediterranean permanent grasslands.

Vernal pool wetlands respond to livestock grazing, exclusion and reintroduction

AbstractIn disturbance‐adapted ecosystems, the removal of disturbance can lead to losses of diversity and sometimes irreversible changes in community composition. It is important to identify the thresholds at which these changes can occur, and to understand the reversibility of these shifts. We examined this question in a vernal pool ecosystem that evolved with low to moderate levels of grazing disturbance. In this system, it is not clear whether the negative effects of long‐term grazing exclusion are reversible through grazing reintroduction.We compared adjacent vernal pool wetlands in annual Mediterranean grasslands under three grazing management strategies: continuously grazed (100+ years), long‐term excluded (40+ years) and 2 years of reintroduced grazing. We also asked whether grazing treatments altered pool characteristics that are likely to influence plant community composition, and how these relationships changed with environmental conditions.Reintroducing grazing to vernal pools led to both increased diversity and native cover, but the effects on native cover were more immediate than on diversity. We identified several biotic and abiotic mechanisms related to this pattern, including changes to competitive dynamics that favour small statured native annuals and increases in hoofprint microdepressions that make soil moisture more available to plants.Synthesis and applications. Our results show that reintroduced grazing at moderate stocking rates can have significant effects on plant communities after just 2 years and can increase native cover more quickly than overall diversity. Our findings suggest that the negative effects of long‐term grazing exclusion in vernal pools may be reversible, but that land managers interested in restoring diversity should plan to monitor beyond the first two years of grazing reintroduction.

The spatial configuration of biotic interactions shapes coexistence-area relationships in an annual plant community

The increase of species richness with area is a universal phenomenon on Earth. However, this observation contrasts with our poor understanding of how these species-area relationships (SARs) emerge from the collective effects of area, spatial heterogeneity, and local interactions. By combining a structuralist approach with five years of empirical observations in a highly-diverse Mediterranean grassland, we show that spatial heterogeneity plays a little role in the accumulation of species richness with area in our system. Instead, as we increase the sampled area more species combinations are realized, and they coexist mainly due to direct pairwise interactions rather than by changes in single-species dominance or by indirect interactions. We also identify a small set of transient species with small population sizes that are consistently found across spatial scales. These findings empirically support the importance of the architecture of species interactions together with stochastic events for driving coexistence- and species-area relationships.

Performance of Singular Spectrum Analysis in Separating Seasonal and Fast Physiological Dynamics of Solar‐Induced Chlorophyll Fluorescence and PRI Optical Signals

AbstractHigh temporal resolution measurements of solar‐induced chlorophyll fluorescence (F) and the Photochemical Reflectance Index (PRI) encode vegetation functioning. However, these signals are modulated by time‐dependent processes. We tested the applicability of the Singular Spectrum Analysis (SSA) for disentangling fast components (physiology‐driven) and slow components (controlled by structural and biochemical properties) from PRI, far‐red F (F760), and far‐red apparent fluorescence yield (Fy∗760). The proof of concept was developed on spectral and flux time series simulated with the Soil Canopy Observation of Photochemistry and Energy fluxes (SCOPE) model. This allowed the evaluation of SSA decomposition against variables that are independent of physiology or are modified by it. Slow SSA‐decomposed components of PRI and Fy∗760 showed high correlations with the reference variables (R2 = 0.97 and 0.96, respectively). Fast SSA‐decomposed components of PRI and Fy∗760 were better related to the physiological reference variables than the original signals during periods when leaf area index (LAI) was above 1 m2 m−2. The method was also successfully applied to predict light‐use efficiency (LUE) from the fast SSA‐decomposed components of PRI (R2 = 0.70) and Fy∗760 (R2 = 0.68) when discarding data modeled with LAI < 1 m2 m−2 and short‐wave radiation Rin < 250 W m−2. The method was then tested on data acquired in a Mediterranean grassland. In this case, the fast SSA‐decomposed component of apparent LUE∗ showed a stronger correlation with the fast SSA‐decomposed component of Fy∗760 (R2 = 0.42) than with original Fy∗760 (R2 = 0.01). SSA‐based approach is a promising tool for decoupling physiological information from measurements acquired with automated proximal sensing systems.

Climate change impacts on the Alpine, Continental and Mediterranean grassland systems of Italy: A review

The ongoing climate change, which is threatening grassland agroecosystems throughout Europe, is also evident in the Italian grasslands. These systems, often located in marginal areas, are species-rich ecosystems characterized by variable, and often unreliable, grass and forage production and strongly dependent on interactions between climate, soil and agricultural management practices (e.g. land abandonment, lack of investments on innovation, stocking rates reduction, etc.), making them very sensitive and vulnerable to climate change. This review draws from the scientific literature the impacts of current and expected climatic changes on grassland and forage crop systems framed in three different bio-climatic zones of Italy, namely the Alpine, Continental and Mediterranean, and focussing on: i) grassland biodiversity and vegetation; and ii) forage production and quality. The main aims of this review are to: i) revise the existing literature in the domain, highlighting different or common trends among different Italian biogeographical regions; ii) provide information on the main climatic impacts analysed and drivers involved in the studied evolutions; and iii) point out the knowledge gaps currently pending in order to hypothesize the future scenarios of research in this sector. Even if this review has pointed out differences in approaches, adopted methodologies and purposes of conducted researches, some common trends can be highlighted, though located in three different environments. Expected warming and modification on rainfall pattern will produce deep changes in vegetation of grassland types, with reduction or the disappearance of cold tolerant species and a spread of xeric/thermophilus ones and shrubby vegetation and with a general upward shift of vegetation types in mountain areas. Moreover, a general reduction of aboveground biomass is expected, as summer droughts is considered a main driver able to force grassland productivity. Finally, warming and rainfall reduction are considered the main factors able to reduce forage quality and palatability of grasslands, as a consequence of reduction of nitrogen content in the available biomass and of the higher spread of less unpalatable species and shrubs. The hypothesis is that the information gained from this review can provide insights on the current level of knowledge on the expected impacts of climate change on Italian grassland systems, and support the development of policy strategies for adaptation at national level. Highlights - This review highlights grassland systems responses to climate change in the Alpine, Apennine and Mediterranean areas of Italy.- Future climate will determine deep changes in grassland composition, extension and productivity. - Droughts is considered the main factor affecting forage quality and palatability.- Further research is needed to understand climate change impacts on grassland vegetation in the Mediterranean.

Anthills: stressor or opportunity for plant assemblage diversity? Evidence from Mediterranean Dasypyretum grasslands

We explored the structure of plant assemblages that settles around the anthills of a guild of Hymenoptera Formicidae (Messor wasmanni Krausse 1910, Tapinoma nigerrimum Nylander 1856 and Aphaenogaster spinosa Emery 1878), observable in urban grasslands dominated by Dasypyrum villosum (Rome, Central Italy). Since it is known that ants act as a disturbing factor on plant assemblages of grasslands, our hypothesis was that vegetation structures suffer from some stressorsthat affect, in this plant association, the dominant plant structure. We compared the plant assemblages observed in the plots of the anthills with the control grassland assemblages using a diversity/dominance diagram. We recorded 63 plant taxa. The average number of plant species was found to be significantly lower in anthill plots than in control grassland plots. In anthill plots, dominant plant species (Polygonum romanum, Poa trivialis Vulpia myuros, Aira elegantissima and Vulpia ligustica) have been found to be different from control grassland plots (Convolvolus arvensis, Dasypyrum villosum, Poa trivialis and Sheradia arvensis). Anthill plant assemblages were found to be significantly different (One-way PERMANOVA) and poorer in terms of species richness, less diversified, and with a reduced species turnover than control grassland plots. Whittaker plot analysis seems to show that the plant assemblages of the control, with greater evenness, emphasize a stressed condition in anthill plant assemblages. Non-metric multidimensional scaling shows a set of species strictly linked to anthills. Our data seem to confirm the role of ants as a stressor in the plant assemblage structures of Mediterranean urban grasslands. However, our results also show that the peculiar ant nest conditions may favor plant species less represented in the Dasypyretum grasslands (i.e. Polygonum romanum) or even absent in this plant assemblage (i.e. Aira elegantissima, Cynodon dactylon and Poa annua), thus increasing the overall local plant diversity.