Various indices have been developed to experimentally quantify resistance and recovery (two components of engineering resilience) in response to anthropogenic and natural disturbances. This diversity complicates the selection of appropriate metrics for comparing resilience across ecosystems and studies. The presence of both positive and negative disturbances further aggravates this challenge. We propose that a suitable index for quantifying resistance and recovery in experiments should satisfy four key criteria: symmetry, monotonicity, boundedness and standardization. They are inspired by methodological parallels between resilience and plant interaction quantification. Particularly, we highlight the importance of symmetry for fairly comparing the effects of disturbances with differing directional impacts. We review and compare six metrics commonly used for resilience quantification and find that none satisfies all four criteria. Specifically, the popular index of log‐transformed response ratio violates both boundedness and symmetry, making it sensitive to outliers and inappropriate for comparing increases vs. decreases induced by disturbances. By further evaluating six metrics developed for plant interaction quantification, we identify one metric (NInt A )—commonly used in that field but not in resilience research—that meets all four criteria. Synthesis and applications . We propose these four criteria as guidelines for developing and selecting appropriate metrics to quantify and compare resistance and recovery in experiments. We recommend the identified standardized index of resistance and recovery (NInt A ), as it enables fair and generalizable comparisons of the effects of both positive and negative disturbances across studies and ecosystems. Furthermore, this metric can support more robust predictions of tipping point's risks and restoration outcomes.

Fires are generally considered to promote biodiversity, although this relationship can be affected by several factors, including fire regime and ecosystem type. Given the ongoing global change, a better understanding of this connection is needed to assess the extent to which projected increases in fire frequency may affect current biodiversity trends. A major challenge lies in vegetation-fire feedback, which often mediates the changes in fire regime. To shed light on the role of fires in promoting or limiting biodiversity, we studied the compositional and functional diversity of simulated plant communities as a function of different fire frequencies. We extended an existing model to include a large number of species. The model reproduces successional dynamics and is parameterized to represent Boreal and Mediterranean plant communities. Fire events are stochastic, with frequency that depends on the community flammability, and plants have different fire responses, thus representing a vegetation-fire feedback. For both ecosystems, we found that fires generally have a positive effect on diversity. All of the biodiversity indicators analyzed, to some extent, peaked at intermediate fire frequency. Interestingly, we observe a decoupling between compositional and functional diversity. These results are related to the vegetation-fire feedback and underline its importance for biodiversity in fire-prone ecosystems. ### Competing Interest Statement The authors have declared no competing interest. Piano Nazionale di Ripresa e Resilienza PNRR, P2022NRLF2 Italian National Biodiversity Future Center, CN 00000033 European Union-NextGenerationEU

Facilitative interactions among species are key in plant communities. While experimental tests support the Stress Gradient Hypothesis (SGH) as an association between facilitation and stress, whether the shape of net effects along stress gradients can be predicted is controversial, with no available mathematical modelling approaches. We proposed a novel test, using a modification of the R* model to study how negative and positive partial effects of plant interactions in drylands combine along two common stress gradients. We modelled different interactions: competition for water and light, amelioration of soil infiltration and/or grazing protection, obtaining that intensity and importance of facilitation did not generally increase along stress gradients, being dependent on the interaction type. While along the water stress gradient net interactions became more positive, reaching a maximum and then waning again, various outcomes were observed along the grazing gradient. Shape variety was mainly driven by the various shapes of the partial positive effects. Under resource stress, additive interaction effects can be expected, whereas when including grazing, the effects were non-additive. In the context of the SGH, deconstructing the effect of positive and negative interaction in a pairwise mechanistic models of drylands does not show a unique shape along stress gradients.

Las diferentes leyes autonómicas de patrimonio cultural y el borrador de la reforma de la Ley del Patrimonio Histórico Español (Ministerio de Cultura y Deporte 2021) reflejan la evolución de los conceptos patrimoniales, ampliando las categorías a proteger. Es el caso, por ejemplo, de la arquitectura defensiva e industrial o del paisaje cultural, que no se entenderían sin su entorno y sin la huella y la articulación del territorio dejada por el ser humano a lo largo del tiempo. La complejidad de estas categorías patrimoniales, compuestas por elementos de naturaleza material e inmaterial, requiere de una comprensión de sus procesos evolutivos, así como de una gestión integral de posibles afecciones desde las primeras etapas de la evaluación ambiental de proyectos. Una propuesta que ha intentado paliar las dificultades asociadas a esta complejidad es la herramienta redactada por el Consejo Internacional de Museos y Sitios (ICOMOS) denominada Evaluación de Impacto Patrimonial, que tiene como objetivo la prevención de impactos en la salvaguarda de sitios declarados Patrimonio Mundial. En este artículo analizamos la práctica de las Evaluaciones de Impacto Patrimonial en Europa y su relación con el procedimiento de Evaluación del Impacto Ambiental de proyectos, a través de una revisión bibliográfica, con el propósito de documentar los análisis publicados al respecto y hacer una valoración crítica de su uso, evaluando sus ventajas e inconvenientes.

Across plant communities worldwide, fire regimes reflect a combination of climatic factors and plant characteristics. To shed new light on the complex relationships between plant characteristics and fire regimes, we developed a new conceptual mechanistic model that includes plant competition, stochastic fires, and fire-vegetation feedback. Considering a single standing plant functional type, we observed that highly flammable and slowly colonizing plants can persist only when they have a strong fire response, while fast colonizing and less flammable plants can display a larger range of fire responses. At the community level, the fire response of the strongest competitor determines the existence of alternative ecological states (i.e., different plant communities) under the same environmental conditions. Specifically, when the strongest competitor had a very strong fire response, such as in Mediterranean forests, only one ecological state could be achieved. Conversely, when the strongest competitor was poorly fire adapted, alternative ecological states emerged-for example, between tropical humid savannas and forests or between different types of boreal forests. These findings underline the importance of including the plant fire response when modeling fire ecosystems, for example, to predict the vegetation response to invasive species or to climate change.

Temporary activities and events may have significant environmental impacts. However, they are often outside the scope of environmental assessment (EA) processes. Environmental requirements in authorization processes of activities are rare, except for some major events in sensitive areas. This article analyzes, first, the environmental impacts of outdoor temporary activities and events through a literature review; all the analyzed activities may have significant negative impacts. Then, the authorization of temporary activities, and their inclusion in EA systems, in a sample of jurisdictions worldwide was analyzed. Applying EA processes is more an exception than a rule for temporary activities. The article discusses the factors that influence activities' impacts, the conflict between precaution and operation, and the benefits and drawbacks of the application of different EA schemes to temporary activities, concluding with some proposals to improve the consideration of environmental aspects in activities' authorization. Before the authorization of activities and events, their environmental impacts should be analyzed and taken into account. This can be achieved through regulations in management plans submitted to strategic EA, through screening processes, or through environmental impact assessment when significant impacts are expected. Integr Environ Assess Manag 2023;19:1320-1332. © 2023 SETAC.

The different regional heritage laws and the draft reform of the Spanish Historical Heritage Law (Ministry of Culture and Sport 2021) reflect the evolution of heritage concepts, expanding the categories to be protected. This is the case, for example, of defensive and industrial architecture or the cultural landscape, which would not be understood without its environment and without the footprint and articulation of the territory left by the human being over time. The complexity of these heritage categories, made up of elements of a tangible and intangible nature, requires an understanding of their evolutionary processes from the early stages of the environmental assessment of projects. A proposal that has tried to alleviate the difficulties associated with this complexity is the tool drafted by the International Council of Museums and Sites called Heritage Impact Assessment, which aims to safeguard World Heritage sites.

Background Current assessments of the effects of climate change on future wildfire risk are based on either empirical approaches or fire weather indices. No study has yet used process-based models over national scales to understand how and where will increases in climate aridity affect the likelihood of fire activity through changes in the moisture content of live (LFMC) and of dead (DFMC) fuels. Here, we used process-based models to forecast changes in LFMC and DFMC under the 21st century climatic conditions projected from moderate and high greenhouse gas emission scenarios (RCP4.5 and RCP8.5). Predictions were performed across broad productivity gradients in peninsular Spain to understand how productivity mediates the effects of climate change on fuel moisture dynamics. Results LFMC and DFMC were predicted to decline under the climatic conditions projected for the coming decades. Increases in the annual frequency of days with fuel moisture content below wildfire occurrence thresholds were predicted to extend fire season lengths by 20 days under RCP4.5 and by 50 days under RCP8.5. The effects of climate change on LFMC and DFMC varied linearly and negatively with productivity (stronger fuel moisture decreases in least productive environments). Although we observed a significant mitigation effect from rising CO 2 (via increases in water-use efficiency), it was not enough to offset LFMC declining trends induced by increased temperature and aridity. Conclusions We predicted that the warmer and more arid climatic conditions projected for the 21st century will lead to generalized declines in fuel moisture, lengthening fire seasons, and increasing wildfire danger. The use of process-based models to forecast LFMC dynamics allowed the consideration of plant species capabilities to buffer climate change impacts. Significant increases in the fire season length predicted in the most productive environments, currently with large fire return intervals, would pose an increase of fire danger in major Spanish carbon sinks. Finally, the CO 2 mitigation effect would not be enough to offset climate change-driven declines in seasonal LFMC levels.

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 forecasting LFMC under changing projected climate. 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 ( Ψ pd ). 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 1,659 LFMC observations at 37 sites across peninsular Spain, belonging to different functional types and from contrasting climates. The goodness of fit for our model ( R 2 = 0.5) was overall higher than that obtained by existing model based on drought indices ( R 2 = 0.3) or spectral vegetation indices ( R 2 = 0.3). We observed the highest predictive performance for seeding shrubs ( R 2 = 0.6), intermediate for trees ( R 2 = 0.5) and lowest for resprouting shrubs ( R 2 = 0.4). Through its relatively simple parameterization, the approach developed here may pave the way for a new generation of process-based models that are used for operational purposes within fire prevention scenarios.

Questions Flooding and drought stress are expected to increase significantly across the world and plant responses to these abiotic changes may be mediated by plant-plant interactions. Stress tolerance and recovery often require a biomass investment that may have consequences for these plant-plant interactions. Therefore, we questioned whether phenotypic plasticity in response to flooding and drought affected the balance between competition and facilitation for species with specific adaptations to drought or flooding. Location Utrecht University. Methods Stem elongation, root porosity, root:shoot ratio and biomass production were measured for six species during drought, well-drained and submerged conditions when grown alone or together with conspecifics. We quantified competition and facilitation as the 'neighbour intensity effect' directly after the 10-day treatment and again after a seven-day recovery period in well-drained conditions. Results Water stress, planting density and species identity interactively affected standardized stem elongation in a way that could lead to facilitation during submergence for species that preferably grow in wet soils. Root porosity was affected by the interaction between neighbour presence and time-step. Plant traits were only slightly affected during drought. The calculated neighbour interaction effect indicated facilitation for wetland species during submerged conditions and, after a period to recover from flooding, for species that prefer dry habitats. Conclusions Our results imply that changing plant-plant interactions in response to submergence and to a lesser extent to drought should be considered when predicting vegetation dynamics due to changing hydroclimatic regimes. Moreover, facilitation during a recovery period may enable species maladapted to flooding to persist.

The monitoring of live and dead fuels’ moisture content (LFMC and DFMC) dynamics plays a crucial role in wildfire management and prevention. In this study, we estimate LFMC and DFMC across the 21st century, considering the meteorological conditions derived from medium- and high-greenhouse gas emission scenarios (Representative Concentration Pathway scenarios 4.5 and 8.5) by selecting a representative subset of global and regional climate model combinations. A stable atmospheric CO2 concentration was also considered to assess possible CO2 mitigation effects. We applied semi-mechanistic models to infer moisture content dynamics across 36 study sites located in peninsular Spain, which corresponds to the monospecific stands of twelve tree species. Overall, our results indicate that both live and dead fuels’ moisture content dynamics will experience generalized declining trends in the coming decades. Furthermore, increases in the number of days per year when these fuels’ moisture content falls below wildfire occurrence thresholds will extend the lengths of fire seasons. Moreover, we observe a significant CO2 mitigation effect, although it is not enough to offset the declining trends in LFMC induced by climate change. Finally, the results suggest that, in ecosystems where plant biomass is abundant enough to sustain a fire, the moisture content of live fuels will be the main limiting factor for the occurrence of future large wildfires.

Fuel moisture limits the availability of fuel to wildfires in many forest areas worldwide, but the effects of climate change on moisture constraints remain largely unknown. Here we addressed how climate affects fuel moisture in pine stands from Catalonia, NE Spain, and the potential effects of increasing climate aridity on burned area in the Pyrenees, a mesic mountainous area where fire is currently rare. We first quantified variation in fuel moisture in six sites distributed across an altitudinal gradient where the long-term mean annual temperature and precipitation vary by 6–15 °C and 395–933 mm, respectively. We observed significant spatial variation in live (78–162%) and dead (10–15%) fuel moisture across sites. The pattern of variation was negatively linked (r = |0.6|–|0.9|) to increases in vapor pressure deficit (VPD) and in the Aridity Index. Using seasonal fire records over 2006–2020, we observed that summer burned area in the Mediterranean forests of Northeast Spain and Southern France was strongly dependent on VPD (r = 0.93), the major driver (and predictor) of dead fuel moisture content (DFMC) at our sites. Based on the difference between VPD thresholds associated with large wildfire seasons in the Mediterranean (3.6 kPa) and the maximum VPD observed in surrounding Pyrenean mountains (3.1 kPa), we quantified the “safety margin” for Pyrenean forests (difference between actual VPD and that associated with large wildfires) at 0.5 kPa. The effects of live fuel moisture content (LFMC) on burned area were not significant under current conditions, a situation that may change with projected increases in climate aridity. Overall, our results indicate that DFMC in currently fire-free areas in Europe, like the Pyrenees, with vast amounts of fuel in many forest stands, may reach critical dryness thresholds beyond the safety margin and experience large wildfires after only mild increases in VPD, although LFMC can modulate the response.

AbstractIncreases in drought frequency in combination with overgrazing may result in degradation of (semi‐) arid ecosystems. Facilitative interactions between plants are a key mechanism in preventing degradation, but it is poorly understood how they respond to increased stress by combined drought and herbivory. In this study, we used an ecohydrological model, to simulate the plant growth of two plant species interacting with each other under different rainfall and herbivory pressure scenarios. The functional traits of the two modeled plants were based on a prior field experiment in southeastern Spain, in which an unpalatable “nurse” species protected a palatable protégé species from herbivory. Moreover, the nurse species was more drought‐resistant; that is, it had a lower wilting point, whereas the protégé species had a higher optimal growth rate. Firstly, we investigated the coexistence of the two plant species growing under a single limiting resource, focusing on the effect of intra‐seasonal rainfall variability. We found that longer periods without rainfall within the wet season resulted in stable coexistence, whereas nearly constant rainfall led to competitive exclusion of the protégé by the nurse species. Secondly, we investigated how plant interactions varied along our studied gradients. Using the neighbor effect intensity and importance indices, we found that competitive effects increased with more constant rainfall. Moreover, higher herbivory rates resulted in increased facilitative effects of the nurse on the protégé species, but facilitative effects could only prevail over competitive effects under currently observed or higher intra‐seasonal rainfall variability. This study highlights the relevance of intra‐seasonal rainfall variability in explaining coexistence of species in dryland ecosystems and shows that increasing intra‐seasonal rainfall variability or herbivory pressure can result in more facilitative effects from a nurse species. This information is crucial to obtain a better insight into the long‐term coexistence of species, and the resulting stability of dryland ecosystems in response to future climate change.

The ‘stress-gradient hypothesis’ predicts increasing facilitative interactions with increasing environmental stress, but it remains unclear if the prevailing type of interaction (i.e. facilitative or competitive) between dominant and subordinate plant species occurring in harsh environments is dependent on the plant functional type. In addition, most plant-species removal experiments in grasslands are short-term (1–2 years), which may imprecisely reflect transient effects arising from methodological limitations. We conducted a dominant species removal experiment in a subalpine ecosystem, containing a mosaic of grass-dominated and shrub-dominated community patches, both of which are common in the subalpine zone of the Qinghai-Tibetan Plateau. We examined the direction and magnitude of the effects of three co-dominant grass and a dominant shrub species on subordinate species richness and biomass over a 6-year period. Removal of the dominant grass species alleviated their competitive pressure on subdominant grasses, which resulted in similar total and grass biomass detected in the final year of the study. By contrast, shrub removal showed no effects on its subordinate species biomass. Furthermore, neither the removal of the dominant shrubs nor the grasses altered their respective subordinate species richness. Thus, in subalpine ecosystems that experience harsh environmental conditions, our results showed that the direction of interactive effects of dominant plant species on subordinate species may be dependent on the plant functional type and are not necessarily facilitative. Furthermore, we showed that longer-term plant-removal experiment observations may be required to better determine the effects of species removal for this subalpine and other montane ecosystem(s).

Fire is an important disturbance process, having significant socio-economic consequences on the one hand, while fulfilling a vital ecological role on the other. Across fire-prone ecosystems, different fire regimes can be found, reflecting a combination of climatic factors and of different plant species characteristics. Ecosystem flammability and fuel load are the most evident and well-studied aspects of fire regime, with only recently attention being devoted to plant traits associated with fire adaptation and post-fire response. The aim of this research is to understand the role that plant traits have in driving fire regimes in different fire-prone ecosystems across the world. A mathematical, mechanistic model was developed representing vegetation dynamics, including stochastic fires and different plant fire-responses. We observe that differences in combinations of plant traits are an important factor in determining alternative ecological states. This is driven by differences in how plants determine fire occurrence and in relation to competition between plant species. Differing plant communities under the same climatic conditions can occur when the most competitive plant types do not have a strong resistance to fires, leading to different ecological and fire regime states for example in some tropical savannas and forests, or in Boreal forests. Conversely, when the dominant plant type has a very strong, post-fire response (at individual level), as e.g. in Mediterranean forests, only one ecological state is possible. This research can help improving understanding of changes in fire regime in the future to assist in fire management efforts, and underlines the importance of including plant fire-responses when modelling fire ecosystems under climate-change scenarios.

Research Highlights: Pre-programmed cell death in old Aleppo pine needles leads to low moisture contents in the forest canopy in July, the time when fire activity nears its peak in the Western Mediterranean Basin. Here, we show, for the first time, that such needle senescence may increase fire behavior and thus is a potential mechanism explaining why the bulk of the annual burned area in the region occurs in early summer. Background and Objectives: The brunt of the fire season in the Western Mediterranean Basin occurs at the beginning of July, when live fuel moisture content is near its maximum. Here, we test whether a potential explanation to this conundrum lies in Aleppo pine needle senescence, a result of pre-programmed cell death in 3-years-old needles, which typically occurs in the weeks preceding the peak in the burned area. Our objective was to simulate the effects of needle senescence on fire behavior. Materials and Methods: We simulated the effects of needle senescence on canopy moisture and structure. Fire behavior was simulated across different phenological scenarios and for two highly contrasting Aleppo pine stand structures, a forest, and a shrubland. Wildfire behavior simulations were done with BehavePlus6 across a wide range of wind speeds and of dead fine surface fuel moistures. Results: The transition from surface to passive crown fire occurred at lower wind speeds under simulated needle senescence in the forest and in the shrubland. Transitions to active crown fire only occurred in the shrubland under needle senescence. Maximum fire intensity and severity were always recorded in the needle senescence scenario. Conclusions: Aleppo pine needle senescence may enhance the probability of crown fire development at the onset of the fire season, and it could partly explain the concentration of fire activity in early July in the Western Mediterranean Basin.

En los ultimos 15 anos, 3 millones de hectareas de bosques se han convertido en matorrales o pastizales en los paises mediterraneos de la Union Europea, siendo el fuego y la sequia los principales motores de esa deforestacion. Se analiza la deforestacion inducida por los efectos conjuntos del fuego y la sequia en tres escalas jerarquicas: resistencia en individuos, resiliencia de poblaciones y transiciones a un nuevo estado. A nivel individual se analiza la resistencia estructural y fisiologica y la capacidad de rebrote. Cuando los individuos perecen, el segundo paso hacia la deforestacion es una resiliencia limitada de la poblacion, esto es, una baja capacidad para regenerarse tras el fuego. Si los individuos mueren y la poblacion no se recupera, se producira una transicion a un nuevo estado de vegetacion. Las especies con capacidad de rebrote proporcionan un papel amortiguador contra la deforestacion en bosques dominados por especies que regeneran sexualmente y carecen de banco de semillas. Aunque la diversificacion de rodales con especies rebrotadoras suele ser ventajosa para incrementar la resiliencia de la masa, existen lagunas de conocimiento sobre como la composicion de la masa afecta a la inflamabilidad, a la resistencia frente a la sequia y sobre el sindrome de agotamiento de los rebrotes. La gestion debe adaptarse para mantener los bosques mediterraneos bajo un clima cambiante, prestando ademas mayor atencion a la aparicion de nuevos riesgos de incendios en zonas antes libres de ellos, como los bosques de montana.

Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire-induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade-offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post-fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the "resprouter exhaustion syndrome," a condition where pre-fire drought stress, or short fire return intervals, seriously restrict post-fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire-free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.