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1. Previous investigations of the role of pathogens as drivers of community dynamics in forests have mostly focused on interspecific interactions between canopy trees and seedlings via soil feedbacks. However, feedbacks can also occur directly between canopy trees and seedlings when spores of foliar and stem pathogens fall onto seedlings regenerating underneath the canopy. 2. We studied pathogen spillover between canopy trees and conspecific and heterospecific regeneration in the Pinus nigra-Diplodia sapinea pathosystem. We sampled 70 pine stands distributed across a temperature gradient of 9.5-13.7°C (mean annual temperature). In each stand, we linked spore load and spore survival in the canopy with pathogen biomass and disease severity in regenerating seedlings. The density of regenerating seedlings and the health status of conspecific and heterospecific seedlings were also measured. The strength of canopy-understorey interactions was correlated with both climatic and stand variables. 3. The most severe symptoms of disease in regenerating seedlings were found in the warmest stands. Structural equation models suggested that disease severity in seedlings was mediated by an increased spore spillover from the canopy. Temperature also increased the pathogen survival rate within seedlings, further contributing to disease severity. Interestingly, disease severity in the canopy did not correlate with spore load in the canopy, suggesting that adult trees were spilling pathogens onto the understorey regardless of their health status. Pathogen spillover increased in more open stands. Greater disease severity in seedlings correlated with stands with a higher density of oak seedlings. Synthesis. 4. These results suggest an understudied mechanism of the Janzen-Connell theory, according to which, canopy-understorey negative feedbacks could be driven by canopy pathogens. Our data also suggest that temperature shapes canopy-understorey interactions, which implies that under a warming climate scenario, an acceleration of conspecific negative feedbacks could be expected, with implications for forest regeneration dynamics. M.C. was supported by the AGAUR FI fellowship 2021FI_B00223 from the Secretariat for Universities and Research of the Ministry of Business and Knowledge of the Government of Catalonia and the European Social Fund. M.D.C. was supported by the Ministry of Science and Innovation of Spain via competitive grant CGL2017- 89149-C2-2-R. JO was supported by the ‘Ramón y Cajal’ fellowship RYC-2015-17459 from the Ministry of Science and Innovation of Spain. This project was partly funded by the grant PID2021- 127328OB-I00 from Ministry of Science and Innovation of Spain. We acknowledge the contribution of the anonymous reviewers for their helpful comments. more...

International audience; Long-term monitoring programs are fundamental to detect changes in ecosystem health and understand ecological processes. In the current context of increasing anthropogenic threats on marine ecosystems, understanding the dynamics and response of communities becomes essential. We used data collected over 14 years in the REBENT benthic coastal invertebrates monitoring program, at a regional scale in the North-East Atlantic, covering a total of 26 sites and 979 taxa. Four distinct habitats were studied: two biogenic habitats associated with foundation species in the intertidal and subtidal zones and two bare sedimentary habitats in the same respective tidal zones. We used community trajectory analysis (CTA), a statistical approach that allows for quantitative measures and comparisons of temporal trajectories of ecosystems. We compared observed community trajectories to trajectories simulated under a non-directional null model in order to better understand the dynamics of the communities, their potential drivers, and the role of the studied habitats in these dynamics. Despite strong differences in the community compositions between sites and habitats, the communities followed non-directional dynamics during the 14 years monitored, which suggested stability at the regional scale. However, the shape, size, and direction of the trajectories of benthic communities were more similar within than among habitats, also suggesting the influence of the nature of the habitat on community dynamics. Results showed a higher variability in community composition the first years of the monitoring in the intertidal bare habitat and confirmed the role of biogenic habitats in maintaining temporal stability. They also highlighted the need to apprehend the role of transient and rare species and the scale of observation in temporal beta diversity analyses. Finally, our study confirmed the usefulness of CTA to link observed trajectory patterns to fundamental ecological processes. more...

Drought impacts on vegetation function have been widely assessed globally but our understanding of the global patterns of drought recovery and its mechanistic underpinnings is comparatively less understood. The quantification of vegetation resilience to drought has been mostly based on the analysis of time series of remotely-sensed vegetation indices, tree-ring data or ecosystem-level fluxes. While useful, these approaches have not provided a mechanistic link between resilience patterns and post-drought effects on plant hydraulics because they lack sufficient temporal and spatial resolution. Resilience quantified from tree-level sap flow can provide these mechanistic insights on post-drought effects but its estimation using classical resilience metrics requires defining a reference sap flow, unaffected by drought. Here, we compare two different approaches to estimate tree water use resilience to soil drought for >500 drought events using global, tree-level sap flow data in the SAPFLUXNET database (Poyatos et al. 2021). For both approaches, soil droughts were defined using the same criteria based on soil relative extractable water (REW), ensuring a minimum intensity and duration (10 days) and the presence of well-defined pre- and post-drought periods with REW values sustainedly above the threshold. In the first approach, we apply classical resilience metrics obtained from the comparison of pre- and post-drought sap flow. We show that water use resilience is related to soil drought characteristics such as intensity and duration and also to atmospheric vapour pressure deficit. In the second approach, we present a model-based resilience framework in which actual sap flow during and after a drought is compared against a reference sap flow modelled using a random forest regression with hydrometeorological drivers, but excluding potential drought legacy effects. This latter approach is tested in two Mediterranean forests in SAPFLUXNET where additional data on tree water status (leaf water potentials or tree water deficit derived from automatic dendrometry) are also available. We show that the model-based resilience framework applied to sap flow data is a promising avenue to better understand the global patterns of drought recovery and the underlying hydraulic mechanisms.Poyatos, R. et al.: Global transpiration data from sap flow measurements: the SAPFLUXNET database, Earth System Science Data, 13, 2607–2649, https://doi.org/10.5194/essd-13-2607-2021, 2021. more...

Regional-level applications of dynamic vegetation models are challenging because they need to accommodate the variation in plant functional diversity, which requires moving away from broadly-defined functional types. Different approaches have been adopted in the last years to incorporate a trait-based perspective into modeling exercises. A common parametrization strategy involves using trait data to represent functional variation between individuals while discard taxonomic identity, but this strategy ignores the phylogenetic signal of trait variation and cannot be employed when predictions for specific taxa are needed, as in applications to inform forest management planning. An alternative strategy involves adapting the taxonomic resolution of model entities to that of the data source employed for large-scale initialization and estimating functional parameters from available plant trait databases while adopting alternative solutions for missing data and non-observable parameters. Here we report the advantages and limitations of this second strategy according to our experience in the development of MEDFATE (v. 2.8.1), a novel cohort-based and trait-enabled model of forest dynamics, for its application over a region in the Western Mediterranean Basin. First, 217 taxonomic entities were defined according to woody species codes of the Spanish National Forest Inventory. While forest inventory data were used to obtain some empirical parameter estimates, a large proportion of physiological, morphological, and anatomical parameters were mapped to measured plant traits, with estimates extracted from multiple databases and averaged at the required taxonomic level. Estimates for non-observable key parameters were obtained using meta-modeling and calibration exercises. Missing values were filled using imputation procedures based on trait coordination, taxonomic averages or both. The model properly simulated observed historical basal area changes, with a performance similar to an empirical model trained for the same region. While strong efforts are still required to parameterize trait-enabled models for multiple taxa, estimation procedures can be progressively refined, transferred to other regions or models and iterated following data source changes by employing automated workflows. We advocate for the adoption of trait-enabled population-structured models for regional-level projections of forest function and dynamics. more...

Centro de Investigación Forestal (CIFOR), Minimum water potential (Ψmin ) is a key variable for characterizing dehydration tolerance and hydraulic safety margins (HSMs) in plants. Ψmin is usually estimated as the absolute minimum tissue Ψ experienced by a species, but this is problematic because sample extremes are affected by sample size and the underlying probability distribution. We compare alternative approaches to estimate Ψmin and assess the corresponding uncertainties and biases; propose statistically robust estimation methods based on extreme value theory (EVT); and assess the implications of our results for the characterization of hydraulic risk. Our results show that current estimates of Ψmin and HSMs are biased, as they are strongly affected by sample size. Because sampling effort is generally higher for species living in dry environments, the differences in current Ψmin estimates between these species and those living under milder conditions are partly artefactual. When this bias is corrected using EVT methods, resulting HSMs tend to increase substantially with resistance to embolism across species. Although data availability and representativeness remain the main challenges for proper determination of Ψmin , a closer look at Ψ distributions and the use of statistically robust methods to estimate Ψmin opens new ground for characterizing plant hydraulic risks., This research was supported by the Spanish Ministry of Scienceand Innovation (MICINN) via competitive grants CGL2017-89149-C2-1-R and CGL2017-89149-C2-2-R. AV thanksMICINN for the project Inertia (PID201-111332RB-C22). JM-V benefited from an ICREA Academia award. We want to thankSanna Sevanto, Nate McDowell and co-authors for making theSUMO water potential data publicly available (https://doi.org/10.15485/1439886). more...

Mediterranean forests and fire regimes are closely intertwined. Global change is likely to alter both forest dynamics and wildfire activity, ultimately threatening the provision of ecosystem services and posing greater risks to society. In this paper we evaluate future wildfire behavior by coupling climate projections with simulation models of forest dynamics and wildfire hazard. To do so, we explore different forest management scenarios reflecting different narratives related to EU forestry (promotion of carbon stocks, reduction of water vulnerability, biomass production and business-as-usual) under the RCP 4.5 and RCP 8.5 climate pathways in the period 2020–2100. We used as a study model pure submediterranean Pinus nigra forests of central Catalonia (NE Spain). Forest dynamics were simulated from the 3rd National Forest Inventory (143 stands) using SORTIE-nd software based on climate projections under RCPs 4.5 and 8.5. The climate products were also used to estimate fuel moisture conditions (both live and dead) and wind speed. Fuel parameters and fire behavior were then simulated, selecting crown fire initiation potential and rate of spread as key indicators. The results revealed consistent trade-offs between forest dynamics, climate and wildfire. Despite the clear influence exerted by climate, forest management modulates fire behavior, resulting in different trends depending on the climatic pathway. In general, the maintenance of current practices would result in the highest rates of crown fire activity, while management for water vulnerability reduction is postulated as the best alternative to surmount the increasingly hazardous conditions envisaged in RCP 8.5. This work was funded by the Spanish Ministry of Science and Inno- vation, projects FIREPATHS (PID 2020-116556RA-I00) and UMBRA-CLIM (PID 2019-111781RB-I00), and by the ERANET FORESTERRA project INFORMED (grant number: 29183). LEM was funded with a scholarship by the MSc in European Forestry Programme at the Uni- versity of Lleida. This work was also funded by project FirEUrisk - DEVELOPING A HOLISTIC, RISK-WISE STRATEGY FOR EUROPEAN WILDFIRE MANAGEMENT, which has received funding from the Eu- ropean Union’s Horizon 2020 research and innovation programme under grant agreement No 101003890. more...

Live Fuel Moisture Content (LFMC) is one of the main factors affecting forest ignitability as it determines the availability of existing live fuel to burn. Currently, LFMC is monitored through spectral vegetation indices or inferred from meteorological drought indices. While useful, neither approach provides mechanistic insights into species-specific LFMC variation and they are limited in the ability to forecast LFMC under altered future climates. Here, we developed a semi-mechanistic model to predict daily variation in LFMC across woody species from different functional types by adjusting a soil water balance model which estimates predawn leaf water potential (Ψpd). Our overarching goal was to balance the trade-off between biological realism, which enhances model applicability, and parameterization complexity, which may limit its value within operational settings. After calibration, model predictions were validated against a dataset comprising 1659 LFMC observations across peninsular Spain, belonging to different functional types and from contrasting climates. The overall goodness of fit for our model (R2 = 0.5) was better than that obtained by an existing models based on drought indices (R2 = 0.3) or spectral vegetation indices (R2 = 0.1). We observed the best predictive performance for seeding shrubs (R2 = 0.6) followed by trees (R2 = 0.5) and resprouting shrubs (R2 = 0.4). Through its relatively simple parameterization, the approach developed here may pave the way for a new generation of process-based models that can be used for operational purposes within fire risk mitigation scenarios. This work was partly founded by the Spanish Government, grant number RTI2018-094691-B-C31 (MCIU/AEI/FEDER, EU) . R.B-R. ac-knowledges the Community of Madrid for the predoctoral contract PEJD-2019-PRE/AMB-15,644 funded by the Youth Employment Initia-tive (YEI) . M. De C. was supported by the Spanish Ministry of Science and Innovation via competitive grant CGL2017-89149-C2-2-R. UNED founding for open access publishing. more...

Drought-associated woody-plant mortality has been increasing in most regions with multi-decadal records and is projected to increase in the future, impacting terrestrial climate forcing, biodiversity and resource availability. The mechanisms underlying such mortality, however, are debated, owing to complex interactions between the drivers and the processes. In this Review, we synthesize knowledge of drought-related tree mortality under a warming and drying atmosphere with rising atmospheric CO2. Drought-associated mortality results from water and carbon depletion and declines in their fluxes relative to demand by living tissues. These pools and fluxes are interdependent and underlay plant defences against biotic agents. Death via failure to maintain a positive water balance is particularly dependent on soil-to-root conductance, capacitance, vulnerability to hydraulic failure, cuticular water losses and dehydration tolerance, all of which could be exacerbated by reduced carbon supply rates to support cellular survival or the carbon starvation process. The depletion of plant water and carbon pools is accelerated under rising vapour pressure deficit, but increasing CO2 can mitigate these impacts. Advancing knowledge and reducing predictive uncertainties requires the integration of carbon, water and defensive processes, and the use of a range of experimental and modelling approaches., Enhanced drought frequency and magnitude have impacted tree mortality, leading to multiple examples of regional-scale dieback. This Review outlines the mechanisms leading to mortality, including carbon starvation and hydraulic failure. more...

[EN] Species response to land use can be examined under a functional perspective, where habitats are described according to species´ resource dependencies. Distribution or abundance models based on resource availability rather than land use types can be more informative about the ultimate processes behind observed population or distribution trends. Habitat use may depend on resources available, as well as disturbances that affect accessibility to such resources. Increasing human presence and urban encroachment may thus alter the relationships between habitat suitability and species abundance. Using 10 years of field data, we investigated whether variability in Little Bustard (Tetrax tetrax) abundance was explained by functional habitat suitability (assessed through resource-based models) and urban encroachment. We found that spatial and temporal variations in Little Bustard abundance were explained by functional habitat suitability and avoidance of urban areas, but that the significance of each variable varied with spatial scale. Little Bustard abundance at each observation point significantly increased with local nesting but not foraging habitat suitability, and decreased with increasing proportion of urban areas. At larger spatial scales, temporal changes in Little Bustard abundance were highly significantly related to changes in foraging habitat suitability. Moreover, the positive relationship between foraging habitat suitability and Little Bustard abundance weakened as the proportion of urban areas increased, and almost disappeared when the proportion of urban areas was more than 5%. Our results underline the benefits of using resource-based models to better understand processes that relate animal abundance and habitat suitability, while simultaneously considering avoided elements of the landscape., [FR] Le comportement des espèces en fonction de l’affectation des terres peut être examiné dans une perspective fonctionnelle, selon laquelle les habitats sont décrits suivant la dépendance des espèces envers les ressources. Les modèles de répartition ou d’abondance fondés sur la disponibilité des ressources, plutôt que sur le type d’affectation des sols, peuvent être plus informatifs sur les processus ultimes qui sous-tendent les tendances observées en matière de population ou de répartition. L’utilisation de l’habitat peut dépendre des ressources disponibles et des perturbations qui affectent l’accessibilité à ces ressources. La présence humaine croissante et l’empiètement urbain accru peuvent donc modifier les relations entre l’adéquation de l’habitat et l’abondance des espèces. En utilisant 10 ans de données prises sur le terrain, nous avons cherché à savoir si la variabilité de l’abondance de l’Outarde canepetière (Tetrax tetrax) s’expliquait par l’adéquation fonctionnelle de l’habitat (évaluée par des modèles basés sur les ressources) et l’empiètement urbain. Nous avons constaté que les variations spatiales et temporelles de l’abondance de l’Outarde canepetière s’expliquaient par l’adéquation fonctionnelle de l’habitat et l’évitement des zones urbaines, mais que l’importance de chaque variable variait selon l’échelle spatiale. L’abondance de l’outarde à chaque point d’observation a augmenté significativement avec l’adéquation de l’habitat local pour la nidification mais pas pour l’alimentation, et a diminué avec la proportion croissante de zones urbaines. À des échelles spatiales plus grandes, les changements temporels de l’abondance de l’outarde étaient fortement liés aux changements de l’adéquation de l’habitat pour l’alimentation. De plus, la relation positive entre l’adéquation de l’habitat pour l’alimentation et l’abondance de l’outarde a diminué à mesure que la proportion de zones urbaines augmentait, et l’espèce était presque totalement absente lorsque la proportion de zones urbaines était supérieure à 5 %. Les présents résultats soulignent les avantages de l’utilisation de modèles fondés sur les ressources pour qu’on comprenne mieux les processus qui relient l’abondance des animaux et l’adéquation de l’habitat, tout en considérant simultanément les éléments du paysage qui sont évités., This study was developed as part of the Project "Steppeahead" (funded by FGCSIC, CSIC, and Banco Santander). Several people helped with fieldwork over the years; special thanks are due to Eladio García, Israel Hervás, and Javier Viñuela for contribution to field censuses, and Ana Benítez and Carlos Martín for field land use data 2008-2011. Fidel Sánchez-Campos helped with the initial GIS database. Fieldwork was partially supported by projects MCYT-REN2003-07851/GLO, CGL2004-02568/BOS, CGL2007-66322/BOS, and CGL2008-04282/BOS, and was partially self-funded. more...

Projecting forest dynamics as a function of alternative management strategies and climatic conditions is key to develop sound forest policy and management planning. In Spain there is a need for a full set of climate-sensitive individual-tree growth and yield models suitable for country-level simulations. In this paper we present environmentally driven models for forest stand dynamics based on distance-independent individual-tree growth and yield. The data for model calibration are based on the second, third and fourth surveys of the Spanish National Forest Inventory, including 50,359 plots and 838,620 trees, representing a broad gradient in forest types and environmental conditions. The results develop a total of 182 models for diameter increment, height increment, total height, survival and ingrowth for 27 species and species groups. The models are integrated into a full forest projection system to perform simulations of forest dynamics and resulting changes in the provision of ecosystem services, including the effects of climate, and forest management. Its potential is illustrated through an array of simulations of forest dynamics in the region of Catalonia under alternative climatic and management scenarios. The resulting models and projections provide a solid basis for the simulation of national or regional climate-sensitive forest scenarios, with the possibility of being applied to other regions, and may be used for future management and planning efforts. This research was supported by structural CTFC funding provided by the Department of Agriculture of the regional Government of Catalonia, the ‘Instituto Nacional de Investigaciones Agrarias’ (INIA), and the Spanish Ministry of Economy and Competitiveness (research project CGL2017–89149-C2–2-R), Ramon y Cajal fellowship (RyC2012–11109). This research also received funding from the European Union’s H2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 101007950 (DecisionES) more...

International audience; The extent to which water availability can be used to predict the enlargement and final dimensions of xylem conduits remains an open issue. We reconstructed the time course of tracheid enlargement in Pinus sylvestris trees in central Spain by repeated measurements of tracheid diameter on microcores sampled weekly during a 2 yr period. We analyzed the role of water availability in these dynamics empirically through time-series correlation analysis and mechanistically by building a model that simulates daily tracheid enlargement rate and duration based on Lockhart's equation and water potential as the sole input. Tracheid enlargement followed a sigmoid-like time course, which varied intra- and interannually. Our empirical analysis showed that final tracheid diameter was strongly related to water availability during tracheid enlargement. The mechanistic model was calibrated and successfully validated (R-2 = 0.92) against the observed tracheid enlargement time course. The model was also able to reproduce the seasonal variations of tracheid enlargement rate, duration and final diameter (R-2 = 0.84-0.99). Our results support the hypothesis that tracheid enlargement and final dimensions can be modeled based on the direct effect of water potential on turgor-driven cell expansion. We argue that such a mechanism is consistent with other reported patterns of tracheid dimension variation. more...

Protected areas (PAs) are essential for biodiversity conservation and the provision of ecosystem services (ES), representing 15% of the earth’s surface and targeted to increase until 17% by 2020. But previous studies showed different results on the effectiveness of PAs in preserving ES and biodiversity, which has implications for landscape conservation. (1) To know whether the spatial distribution of ES (carbon stocks and water provision), biodiversity (woody and bird richness) and conservation variables (threatened bird richness, habitats and geology) varies between PAs (with different protection status) and buffer zones; and (2) to quantify and compare the percentage of high values (hotspots) of ES, biodiversity and conservation variables inside PAs (with different protection status) and buffer zones. We analyzed 108 PAs from a Mediterranean region using linear mixed models with ES, biodiversity and conservation variables as response factors, and type of zone (PA vs buffer) and protection status as fixed factors. We found higher values of carbon stocks in PAs than in buffer zones. We also found more coverage of community-interest habitats, priority-habitats and geological-interest sites in PAs than in buffer zones. However, PAs with higher degree of protection did not provide higher levels of ecosystem services and biodiversity, or vice versa. We found more hotspots of woody richness, bird richness and threatened bird richness in buffer zones than in PAs. This study highlights the importance of landscape planning in conservation, which should include PAs within broader landscapes by considering also their buffer zones and non-PAs. It also emphasizes the importance of integrating ES and biodiversity to define effective conservation policies. more...

Fire regimes are shifting or are expected to do so under global change. Current fire suppression is not able to control all wildfires, and its capability to do so might be compromised under harsher climate conditions. Alternative fire management strategies may allow to counteract predicted fire trends, but we lack quantitative tools to evaluate their potential effectiveness at the landscape scale. Here, we sought to quantify changes in fire regimes induced after the implementation of different fire management strategies. We developed and applied a new version of the model MEDFIRE in Catalonia (Mediterranean region of ~32,000 km2 in NE Spain). We first projected burnt area from 2016 to 2100 resulting from climate change under the Representative Concentration Pathway 8.5 scenario of HadGEM-CC model and under current fire suppression levels. We then evaluated the impacts of four fire management strategies: ‘Let it burn’, fixed effort of prescribed burning with two different spatial allocations, and adaptive prescribed burning dynamically adjusting efforts according to recent past fires. Results predicted the emergence of novel climates associated with similar barometric configurations to current conditions but with higher temperatures (i.e. hot wind events). These novel climates led to an increase in burnt area, which was partially counteracted by negative fire-vegetation feedbacks. All prescribed burning scenarios decreased the amount of high-intensity fires and extreme fire events. The ‘Let it burn’ strategy, although less costly, was not able to reduce the extent of high-intensity fires. The adaptive prescribed burning scenario resulted in the most cost-efficient strategy. Our results provide quantitative evidence of fire management effectiveness, and bring to light key insights that could guide the design of fire policies fit for future novel climate conditions. We propose adaptive landscape management focused on the reduction of fire negative impacts rather than on the elimination of this disturbance from the system. more...

Key message We present a structured and curated database covering 21 years of LFMC measurements in the Catalan region, along with an associated R package to manage updates and facilitate quality processing and visualisation. The data set provides valuable information to study plant responses to drought and improve fire danger prediction. Dataset access is athttps://doi.org/10.5281/zenodo.4675335, and associated metadata are available athttps://metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/583fdbae-3200-4fa7-877c-54df0e6c5542. more...

Total fidelity value index can be used for the assignment of new releves to existing vegetation units and it can be used to refine classifications derived from unsupervised clustering. Diagnostic species is an important concept in vegetation classification. Apart from its usefulness to characterize species niche preferences, the diagnostic species concept is used in vegetation classification: (1) for the assignment of new releves to the vegetation units of an existing classification; (2) to refine vegetation classifications by reassigning releves that sustain the definition of vegetation units. The main aims were to evaluate the relative predictive performance of different statistical fidelity measures for the reassignment of releves to existing vegetation units, and in which cases reassignments improve the quality of the original classification. We took the classifications produced by three commonly used unsupervised classification methods, and all releves were reassigned to the closest vegetation unit according to the total fidelity value index (TFVI), where fidelity value had been calculated using one of eight distinct statistical measures, and according to the frequency-positive fidelity index (FPFI). Classifications obtained after releve reassignments were compared to the initial ones using the Adjusted Rand Index. The quality of all classification solutions, including the initial ones, was evaluated using thirteen different evaluator statistics. The predictive performance of IndVal was the best among all eight fidelity indices in the TFVI framework, and also outperformed FPFI. The TFVI framework based on group-equalized fidelity indices produced better results than other assignment rules in terms of the chosen evaluator statistics. Re-assignments based on IndVal, r, or FPFI produced classifications with the best quality, when combining the results of all evaluators. We conclude that TFVI based on IndVal and r has the best quality for assigning of new releves to existing vegetation units, and it also could be used to refine classifications derived from unsupervised clustering. Consequently, our results reiterate that TFVI, which is new in vegetation sciences, can be a good alternative for FPFI, as the most commonly used in the assignment of vegetation plots (releves), to predefined vegetation types in large datasets. more...

Growing evidence that individuals of many generalist animals behave as resource specialists have attracted substantial research interest for its ecological and evolutionary implications. Variation in resource preferences is considered to be critical for developing a general theory of individual specialization. However, it remains to be shown whether diverging preferences can arise among individuals sharing a similar environment, and whether these preferences are sufficiently stable over time to be ecologically relevant. We addressed these issues by means of common garden experiments in feral pigeons (Columba livia), a species known to exhibit among-individual resource specialization in the wild. Food-choice experiments on wild-caught pigeons and their captive-bred cross-fostered descendants showed that short-term variation in food preferences can easily arise within a population, and that this variation may represent a substantial fraction of the population foraging niche. However, the experiments also showed that, rather than being limited by genetic or vertical cultural inheritance, food preferences exhibited high plasticity and tended to converge in the long-term. Although our results challenge the notion that variation in food preferences is a major driver of resource specialization, early differences in preferences could pave the way to specializations when combined with neophobic responses and/or positive feedbacks that reinforce niche conservation. more...

Mediterranean forests play a key role in providing services and goods to society, and are currently threatened by global change. We assessed the future provision of ecosystem services by Mediterranean pine forests under a set of management and climate change scenarios, built by combining different regional policies and climate change assumptions. We used the process-based model SORTIE-ND to simulate forest dynamics under each scenario. We coupled the outputs of SORTIE-ND with empirical and process-based models to estimate changes in harvested timber, carbon storage, mushroom yield, water provision, soil erosion mitigation and habitat for biodiversity by 2100, and assessed the trade-offs and synergies between services. Our results suggest that future provision of ecosystem services by Mediterranean forests will be more strongly determined by management policies than by climate. However, no management policy maximized the provision of all services. The continuation of the business-as-usual management would benefit some services to the detriment of water provision, but leads to higher vulnerability to extreme drought-events or wildfires. Managing for reducing forest vulnerability will balance the provision of services while reducing the risk of damage to forest functioning. We also found multiple spatial synergies between ecosystem services provision, likely driven by differences in site productivity. This work was supported by the Spanish Government through the INMODES project (grant number: CGL2017-89999-C2-2-R), the ERA-NET FORESTERRA project INFORMED (grant number: 29183), the ERANET-SUMFORESTS project FutureBioEcon (PCIN-2017-052), and the Generalitat de Catalunya (CERCA Program). AMO, AA and MC were supported by Spanish Government through Juan de la Cierva and Ramón y Cajal fellowship programs (IJCI-2016-30349, IJCI-2016-30049 and RYC-2012-11109 respectively). SdM benefited from a Serra-Húnter Fellowship provided by the Generalitat de Catalunya. more...

Water content in living vegetation (or live fuel moisture content, LFMC), is increasingly recognized as a key factor linked to vegetation mortality and wildfire ignition and spread. Most often, empirical indices are used as surrogates for direct LFMC measurements.In this paper, we explore the functional and ecophysiological drivers of LFMC during drought at the leaf and canopy scale using the SurEau-Ecos model, and a three years dataset of leaf and canopy scale measurements on a mature Quercus ilex forest, including an extreme drought. The model is based on forest hydrology and plant hydraulics and allows to simulate temporal variations of water potential and content at a daily time step. At leaf level, it simulates the relationship between water potential and water content by separating the apoplasm and the symplasm. Symplasm water content is modeled using the pressure volume curve theory, and apoplasm water content is modelled using the xylem vulnerability to cavitation. Fuel moisture content was upscaled to the canopy level by accounting for foliage mortality estimated from drought induced cavitation.The model was parameterized either with site-measured traits or using a calibration procedure, and compared with water potential and LFMC measured at leaf level, and NDVI variation measured at canopy level and taken as a surrogate for foliage mortality.At leaf level, LFMC prediction using measured hydraulic traits could be improved by considering year-to-year osmotic adjustments. At canopy level, foliage mortality due to drought induced cavitation was a key driver of LFMC decline during the most extreme drought.A sensitivity analysis showed that parameters driving soil water balance (leaf area index, soil water capacity, and regulation of transpiration) and parameters determining pressure volume curves are key traits driving LFMC dynamics at leaf level. At the canopy level, parameters that drives hydraulic failure were the most sensitive and included, both soil water balance parameters and hydraulic traits (the leaf vulnerability to cavitation) were the main drivers of LFMC decline during extreme drought.We also showed that under normal historic weather conditions, most variation of LFMC are linked to reversible symplasm dehydration, however under future, hotter and dryer conditions, most variations are due to the decline canopy of LFMC driven by foliage mortality. more...

Fungi are responsible for many of the processes that occur in natural ecosystems and largely determine forest ecosystem dynamics, such as the ability of trees to access limiting nutrients and sequester carbon. Understanding and predicting climate change impacts on fungal dynamics over large scales is key in order to gain further insights into the effects of global change on natural ecosystem functioning and related ecosystem services. In this study, we use predictive models based on machine learning algorithms to estimate, in a spatially explicit way, the historical and future (1976–2100) evolution of mycorrhizal and saprotrophic macrofungal productivity in Mediterranean forest areas under climate change scenarios. The greatest changes in total productivity, as well as mycorrhizal fungi, are predicted to occur in subalpine and montane pine forests, where fungal productivity is estimated to decrease, and will be more pronounced under climate change scenarios with higher expected increase in temperature. In contrast to mycorrhizal species, saprotrophic fungi could benefit from pronounced changes in climate and increase their productivity in supra- and mesomediterranean regions at mid-range elevations. Moreover, we estimated that fungal productivity has also changed historically in some scattered areas where changes in climate over the years may have led to a decrease in productivity. This study contributes to raising awareness on the need for anticipating potential global change impacts on this key element of ecosystem functioning, and for deploying possible management policies oriented toward maintaining the important role of fungal productivity in both climate change mitigation and adaptation. We thank the “Agencia Estatal de Meteorología (AEMET)” and “Servei Meteorològic de Catalunya (SMC)” for providing daily weather station data. This work was supported by the Secretariat for Universities and of the Ministry of Business and Knowledge of the Government of Catalonia and the European Social Fund. This work was partially supported by the Spanish Ministry of Science, Innovation and Universities (Grant No. RTI2018–099315-A-I00) and by the National Parks Autonomous Agency (Organismo Autónomo de Parques Nacionales, OAPN) (Grant No. 2711/2021). J.A.B. and Sd-M benefitted from a Serra-Húnter Fellowship provided by the Government of Catalonia. more...

Author(s): Batllori, E; De Caceres, M; Brotons, L; Ackerly, DD; Moritz, MA; Lloret, F | Abstract: Understanding ecosystem responses to compound disturbance regimes and the influence of specific sequences of events in determining ecosystem shifts remains a challenge. We use a modelling framework for Mediterranean-type ecosystems to assess the effects of fire–drought interactions on long-term vegetation dynamics and to identify disturbance-driven changes in trait composition (tree seeder vs. tree resprouter prevalence) and ecosystem state (forest vs. non-forest). Changes in tree seeder and the tree resprouter dominance show nonlinear, threshold-type trends over gradients of increasing compound disturbance frequency. Vegetation composition thresholds mostly occur in a narrow range of the compound fire–drought disturbance space. Additionally, trait compositional switches and the likelihood of sudden changes in ecosystem state are promoted by fire-drought interactions. Distinct sequences of disturbance events cause vegetation transitions, disrupting ecosystem resilience, even under moderate recurrence of individual disturbances. An extreme drought year followed by one or two large fire events promotes shifts from resprouter- to seeder dominance. Contrastingly, a large crown fire followed by an extreme drought promotes changes from seeder to resprouter dominance. This disturbance sequence is also a mechanism strong enough to trigger sudden shifts in ecosystem state (from forest to non-forest). Synthesis. Thresholds of change in vegetation composition occur over a narrow range of the modelled gradients of compound fire-drought recurrence, and the loss of ecosystem resilience is contingent on particular sequences of disturbance events. Overall, our findings highlight that disturbance interactions define the relative location of tipping points in ecosystem state, and that effects and feedbacks of compound disturbance regimes increase the long-term likelihood of sudden ecosystem shifts and, therefore, uncertainty in predicting vegetation state. more...

While classification of vegetation can be conducted in many ways, international homogenization of procedures and typologies is desirable for human societies that are highly connected in terms of sharing biodiversity information. This Special Issue of Phytocoenologia includes 12 papers that document several of the plot-based classification approaches currently used throughout the world. The issue includes approaches from five continents, but noticeable gaps are South America, middle-eastern countries, northern Africa and southeastern Asia. We include in this editorial a brief synthesis of the papers included in the Special Issue, with respect to (1) the amount of vegetation-plot data and characteristics of the classification systems developed in different areas and (2) the concepts and procedures of classification approaches. One of the most important common attributes among the classification approaches is the need to define vegetation units at a low level of abstraction. ‘Association’ (and perhaps ‘alliance’ too) may be a classification level for which international homogenization of procedures would be most easy to achieve, perhaps establishing different consistent classification sections depending on ecological conditions. Several papers in this issue demonstrate that multiple approaches may coexist for higher levels, as long as they abstract vegetation from the same low level units by focusing on a specific set of concepts and defined from the perspective of applications. more...

Efforts to develop mechanistic tree growth models are hindered by the uncertainty of whether and when tree growth responses to environmental factors are driven by carbon assimilation or by biophysical limitations of wood formation. In this study, we used multiannual weekly wood-formation monitoring of two conifer species (Larix decidua and Picea abies) along a 900 m elevational gradient in the Swiss Alps to assess the biophysical effect of temperature and water potential on wood formation. To this end, we developed a model that simulates the effect of water potential on turgor-driven cambial division, modulated by the effect of temperature on enzymatic activity. The model reproduced the observed phenology of tracheid production, as well as intra- and interannual tracheid production dynamics of both species along the elevational gradient, although interannual model performance was lower. We found that temperature alone explains the onset of tracheid production, yet water potential appears necessary to predict the ending and the total amount of tracheids produced annually. We conclude that intra-annual cambial activity is strongly constrained by both temperature and water potential at all elevations, independently of carbon assimilation. At the interannual scale, biophysical constraints likely interact with other factors. more...

International audience; AbstractKey messageAllometric biomass equations developed for individual shrubs can be applied to estimate shrubland fuels from measurements of cover and average height by species.ContextShrubs are a major component of surface fuels in many fire-prone ecosystems. Shrub fuel loading is often estimated by “double sampling”, where data from a destructive vegetation survey is used to model vegetation-fuel relationships (development phase), and these relationships are then applied to vegetation data from a second survey (application phase). Vegetation-fuel relationships can be modeled at different levels of vegetation detail, from individual plants to stands, but the increased effort of detailed measurements may compromise large-scale applications.AimsTo facilitate fuel loading assessments in Mediterranean shrublands, we present and test a novel method to estimate stand-level shrub loading that consists in applying individual-level allometric equations to vegetation plot data collected by measuring the percent cover and mean height of each shrub species.MethodsWe used individual-level data (i.e., plant dimensions and dry weights) to develop allometric equations for total and fine (leaves and branches more...

Mediterranean forests are prone to fire and highly diverse in environmental conditions, species composition, and forest structure. While much is known about fire hazard and forest responses to fire in Mediterranean climate regions, our understanding of the spatial distribution of fuel characteristics and their dynamics remains incomplete. We hypothesized that fire hazard in heterogeneous Mediterranean regions is primarily explained by the variation in fuel loading and flammability characteristics of the understory layer across the landscape and over time. We used the Spanish National Forest Inventory data to estimate overstory and understory fuel characteristics, compare their spatial and temporal variations across Catalonia (NE Spain) over the last 25 years, and assess the role of climate conditions in explaining spatial distribution and dynamics of fuel characteristics. Our results showed that fuel characteristics strongly depend on the species composition of the overstory and understory layers. Fuel characteristics of both vegetation layers were significantly different and poorly correlated with each other. Although both strata showed significantly different rates of change in most fuel characteristics, the average changes were, in general, very small for the time window considered. Forests in the warmest and driest environments showed the highest flammability characteristics in both overstory and understory layers in contrast to mountain communities. We did not find, however, a remarkable effect of climatic conditions on the rates of change of fuel characteristics during the study period. Altogether, these findings confirm the importance of considering the spatial variation of fuel characteristics of different vegetation strata separately and provide critical information on forest vulnerability to develop appropriate fire mitigation policies in Mediterranean ecosystems., This project was funded by MINECO via DRESS (CGL2017-89149-C2-2-R), ForRes (RTI2018-098778-B-I00), UMBRACLIM (PID2019-111781RB-I00) and INMODES (CGL2017-89999-C2-1-R) projects. more...

Land-use/land-cover (LULC) change models integrate the effects of anthropogenic drivers of landscape change. Spatially explicit LULC change models help at understanding the landscape mosaic that emerges from the interplay between local-scale decisions as well as regional and national policies. These models produce valuable spatially explicit scenarios of LULC change that underpin biodiversity impact and ecosystem services assessments. Most raster-based LULC change models adopt the demand-allocation approach to simulate land transitions (i.e. the transformation of one land-cover type to another for a given spatial unit). In a demand-allocation framework the expert fixes the demand (or quantity of change) and the LULC change model uses a spatial procedure to allocate the change (i.e. to select the cells to be transformed to the target land-cover type). Here, we propose a spatial allocation procedure that builds on the assumption that land transitions occur in two phases: change occurrence and change spreading (or contagion). The allocation procedure uses a sorted queue of cells waiting to undergone change. Three parameters (rate of change occurrence, rate of change spreading and acceleration of change-contagion) control the order of cells order in the queue, and ultimately determine the emergence and extent of patches-of-change. We performed a sensitivity analysis where we show that the relation between both rates (i.e. change occurrence and change spreading) allows patches-of-change expand before other patches arise or vice versa. We provide a simple protocol to implement the allocation procedure as the core of a spatial explicit LULC change model, and we applied this protocol in the development of a new model, called MEDLUC, that intends to replicate the most relevant transitions observed in Mediterranean landscapes: urbanisation, rural abandonment and agriculture conversion. For Catalonia, a region in NE Spain, MEDLUC reproduces the empirical patches-of-change distributions from a 16-year period at two spatial resolutions (1 km2 and 1 ha). Overall, our allocation procedure performs better than a null model for urbanisation and rural abandonment at both resolutions, while it does worse when modelling agriculture conversion. more...

Fundamental to the establishment of exotic species in natural environments is that the invader finds an appropriate niche in the novel environment. However, it is currently unclear whether this is achieved by competitively displacing native species from their niches and/or by exploiting niche opportunities not monopolized by native species. Combining phylogenetic analyses with field observations and an ecological opportunity experiment, we here contrasted the competition and niche opportunity hypotheses as explanations for the success of an alien passerine, the Red-billed Leiothrix Leiothrix lutea, in a forest reserve from the Western Mediterranean basin. The invasion of Leiothrix provided a rare opportunity to assess the relative importance of each hypothesis because the avian community of the reserve has been systematically surveyed for the last 27 years, and hence species abundance data were available before and after the irruption of the invader. The invader established itself with relatively little resistance or consequences for native species, reflecting the opportunist-generalist nature of both the invader and the invaded native community. Although we cannot completely discard a role of competition, these results yield greater support to the crucial importance of niche opportunities to invade natural environments. more...

Adequately assessing the ecosystem resilience and resistance is a challenging and essential question in the current context of widespread environmental change. Here we suggest the use of a quantitative measure we call Persistence Index (PI) to assess the capacity of communities to maintain their functions and services after disturbances. First, we present the formulation of PI that is based on the diversity, abundance, and redundancy of disturbance- and taxon-specific response traits. Then, we use simulated data sets to study the effects of species richness and the number and frequency of traits on PI values. Finally, we illustrate our approach by assessing the persistence capacity of forest communities in Peninsular Spain and the Balearic Islands in response to fire, drought and windstorm events. The Persistence Index was found to be relatively independent on the number of considered traits, but variable according to the frequency of traits in the community. In the evaluation made with national forest inventory data, PI was found to vary within and among different forest types, being particularly high in stands dominated by non-native species (e.g. Eucalyptus sp.) or in mixed-stands composed by evergreen and deciduous broadleaf species. We also found PI values to increase with the number of species present in the stand, although this relationship saturated due to overlap in species response traits. The presented index is complementary to other approaches developed to study the functional structure of communities through the distribution of species in a functional space. It can be applied to a broad spectrum of communities subjected to different types of stressors, making it a useful tool to guide ecosystem management decisions in a context of changing climate and uncertain disturbance regimes. This study was funded by the Spanish Ministry of Economy and Competitiveness via the RESILFOR project (AGL2012-40039-C02-01). Additional funding came from the European Commission through the Marie Curie IRSES project NEWFORESTS and the Era-Net FORESTERRA project INFORMED. The Spanish Ministry of Economy and Competitiveness provided MSP with support through a FPI predoctoral contract (BES-2013-063019) and LC and MdC through a Ramón y Cajal fellowship (RYC-2009-04985, RYC-2012-11109). We thank three anonymous reviewers and J.R. González-Olabarría for comments and constructive criticisms on the study. more...

Vegetation classification is a basic requirement of research and conservation. Numerous classifications have been established throughout the world during the 20th century, but steps toward international classification systems and standards are currently being sought. We introduce here a new working group of the International Association of Vegetation Science, the Vegetation Classification Working Group (VCWG), which will function as a scientific panel devoted to vegetation classification at any spatial or organizational scale, particularly the underlying methodologies and standards, ultimately allowing greater understanding and crosswalks among national classification systems. The VCWG currently has 166 members from 41 countries of six continents, a website for information, established subgroups for specific activities, and initiated a Special Issue on classification for Phytocoenologia. We summarize here the background of the VCWG, current and future activities, and contact information for those interested in becoming involved. more...