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Polylepis trees occur throughout the Andean mountain region, and it is the tree genus that grows at the highest elevation worldwide. In the humid Andes where moisture is rarely limiting, Polylepis trees must adapt to extreme environmental conditions, especially rapid fluctuations in temperature, ultraviolet radiation and vapor pressure deficit (VPD). However, Polylepis ' water-use patterns remain largely unknown despite the importance of understanding their response to microclimate variation to determine their capacity to maintain resilience under future environmental change. We conducted a study in a Polylepis reticulata Kunth forest in the Ecuadorian Andes to evaluate its tree water-use dynamics and to identify the main environmental drivers of transpiration. Tree sap flow was monitored simultaneously with soil volumetric water content (VWC) and microclimate during 2 years for trees growing in forest edge and interior locations. We found that sap flow was primarily controlled by VPD and that VWC exerted a secondary role in driving sap flow dynamics. The highest values for sap flow rates were found when VPD > 0.15 kPa and VCW < 0.73 cm3 cm−3, but these threshold conditions only occurred during brief periods of time and were only found in 11% of our measurements. Moreover, these brief windows of more favorable conditions occurred more frequently in forest edge compared with forest interior locations, resulting in edge trees maintaining 46% higher sap flow compared with interior trees. Our results also suggest that P. reticulata has a low stomatal control of transpiration, as the sap flow did not decline with increasing VPD. This research provides valuable information about the potential impacts of projected future increases in VPD due to climate change on P. reticulata water-use dynamics, which include higher sap flow rates leading to greater transpirational water loss due to this species' poor stomatal control. [ABSTRACT FROM AUTHOR]

This insight article comments on: Ziegler C, Cochard, H, Stahl C, Bastien Gérard LF, Goret J, Heuret P, Levionnois S, Maillard P, Bonal D, Coste S. 2024. Residual water losses mediate the trade-off between growth and drought survival across saplings of 12 tropical rainforest tree species with contrasting hydraulic strategies. Journal of Experimental Botany 75, 4128–4147. [ABSTRACT FROM AUTHOR]

This paper describes the assumptions, equations, and procedures of the RheaG weather generator algorithm (WGA). RheaG was conceived for the generation of robust daily meteorological time series, whether in static or transient climate conditions. Here we analyze its performance in four Iberian locations—Bilbao, Barcelona, Madrid, and Sevilla—with differentiated climate characteristics. To validate the RheaG WGA, we compared observed and generated meteorological time series' statistical properties of precipitation, maximum temperature, and minimum temperature for all four locations. We also compared observed and simulated rain events spell length probabilities in all four locations. Finally, RheaG includes two weather generation procedures: one in which monthly mean values for meteorological variables are unconstrained and one in which they are constrained according to a predefined baseline climate variability. Here, we compare the two weather generation procedures included in RheaG using the observed data from Barcelona. Our results present a high agreement in the statistical properties and the rain spell length probabilities between observed and generated meteorological time series. Our results show that RheaG accurately reproduces seasonal patterns of the observed meteorological time series for all four locations, and it is even able to differentiate two climatic seasons in Bilbao that are also present in the observed data. We find a trade-off between generation procedures in which the unconstrained procedure better reproduces the variability of monthly and yearly precipitation than the constrained one, but the constrained procedure is able to keep the same climatic signal across meteorological time series. Thus, the first procedure is more accurate, but the latter is able to maintain spatial autocorrelation among generated meteorological time series. [ABSTRACT FROM AUTHOR]

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 discarding taxonomic identity. However, this strategy ignores the phylogenetic signal of trait variation and cannot be employed when predictions for specific taxa are needed, such 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, adopting diverse 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 (version 2.9.3), 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 records were used to obtain some empirical parameter estimates, a large proportion of physiological, morphological, and anatomical parameters were matched 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 addressed using imputation procedures based on trait covariation, taxonomic averages or both. The model properly simulated observed historical changes in basal area, 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, and to incorporate intra-specific trait variability, estimation procedures such as those presented here 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 and population-structured models for regional-level projections of forest function and dynamics. [ABSTRACT FROM AUTHOR]

Forest models are instrumental for understanding and projecting the impact of climate change on forests. A considerable number of forest models have been developed in the last decades. However, few systematic and comprehensive model comparisons have been performed in Europe that combine an evaluation of modelled carbon and water fluxes and forest structure. We evaluate 13 widely used, state‐of‐the‐art, stand‐scale forest models against field measurements of forest structure and eddy‐covariance data of carbon and water fluxes over multiple decades across an environmental gradient at nine typical European forest stands. We test the models' performance in three dimensions: accuracy of local predictions (agreement of modelled and observed annual data), realism of environmental responses (agreement of modelled and observed responses of daily gross primary productivity to temperature, radiation and vapour pressure deficit) and general applicability (proportion of European tree species covered). We find that multiple models are available that excel according to our three dimensions of model performance. For the accuracy of local predictions, variables related to forest structure have lower random and systematic errors than annual carbon and water flux variables. Moreover, the multi‐model ensemble mean provided overall more realistic daily productivity responses to environmental drivers across all sites than any single individual model. The general applicability of the models is high, as almost all models are currently able to cover Europe's common tree species. We show that forest models complement each other in their response to environmental drivers and that there are several cases in which individual models outperform the model ensemble. Our framework provides a first step to capturing essential differences between forest models that go beyond the most commonly used accuracy of predictions. Overall, this study provides a point of reference for future model work aimed at predicting climate impacts and supporting climate mitigation and adaptation measures in forests. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Drought limits tree water use and growth of Mediterranean trees. However, growth and water use strategies are rarely addressed simultaneously across species and drought conditions. Here, we investigate the link between stem diameter variations and sap flow in four co-existing Mediterranean trees ( Pinus halepensis Mill., Quercus pubescens Willd., Quercus ilex L. and Arbutus unedo L.), under relatively wet (2011) and dry (2012) conditions. Continuous stem diameter variations were converted to basal area increment (BAI) and de-trended to estimate tree water deficit (Δ W ), an indicator of stem hydration. P. halepensis and Q. pubescens showed the most and the least conservative sap flow density ( J S ) regulation under drought, respectively, with Q. ilex and A.unedo showing intermediate drought responses. All species, except A. unedo , showed some between-year variability in the environmental control of J S . Seasonal stem shrinkage in response to drought (i.e., increasing Δ W ) and subsequent trunk rehydration after rainfall (i.e., decreasing Δ W ) occurred in all species. Vapor pressure deficit (VPD) and soil moisture ( θ ) interacted to determine seasonal variation in Δ W . Interestingly, in the dry year, 2012, more species-specific differences were found in the responses of Δ W to θ and VPD. Across species, J S and Δ W began to decline at similar soil moisture thresholds, underpinning the tight link between J S and Δ W under varying drought conditions. Annual BAI decreased proportionally more than tree-level transpiration ( J T ) between the wet (2011) and the dry (2012) year, hence growth-based WUE (WUE BAI = BAI/ J T ) decreased for all species, albeit less acutely for P. halepensis . Overall, despite their contrasting leaf habit and wood type, the studied Mediterranean tree species show coordinated responses of transpiration, water storage dynamics and growth-based WUE which allow them to cope with seasonal and interannual drought. [ABSTRACT FROM AUTHOR]

Predicting the large-scale consequences of drought in contrasting environments requires that we understand how drought effects differ among species originating from those environments. A previous meta-analysis of published experiments suggested that the effects of drought on both stomatal and non-stomatal limitations to photosynthesis may vary consistently among species from different hydroclimates. Here, we explicitly tested this hypothesis with two short-term water stress experiments on congeneric mesic and xeric species. One experiment was run in Australia using Eucalyptus species and the second was run in Spain using Quercus species as well as two more mesic species. In each experiment, plants were grown under moist conditions in a glasshouse, then deprived of water, and gas exchange was monitored. The stomatal response was analysed with a recently developed stomatal model, whose single parameter g1 represents the slope of the relationship between stomatal conductance and photosynthesis. The non-stomatal response was partitioned into effects on mesophyll conductance (gm), the maximum Rubisco activity (Vcmax) and the maximum electron transport rate (Jmax. We found consistency among the drought responses of g1, gm, Vcmax and Jmax, suggesting that drought imposes limitations on Rubisco activity and RuBP regeneration capacity concurrently with declines in stomatal and mesophyll conductance. Within each experiment, the more xeric species showed relatively high g1 under moist conditions, low drought sensitivity of g1, gm, Vcmax and Jmax, and more negative values of the critical pre-dawn water potential at which Vcmax declines most steeply, compared with the more mesic species. These results indicate adaptive interspecific differences in drought responses that allow xeric tree species to continue transpiration and photosynthesis for longer during periods without rain. [ABSTRACT FROM AUTHOR]

Isoprene and monoterpenes are highly reactive organic compounds, emitted by most plant species, which play an important role in air chemistry and air pollution. Different leaf-scale isoprenoid emission models are available. These models are scaled to the canopy through coupling them to terrestrial biogeochemical models and thus used to generate regional emissions inventories. Although the leaf scale models have been shown to perform similarly, large unexplained differences exist in regional emissions inventories. This may be explained in part by the complete lack of inter-comparisons of emission model estimates when scaled from the leaf to the canopy. In this paper we address this problem by coupling four different isoprene emission models (Guenther et al. model, Niinemets et al. model, BIM2 and the Martin et al. model) to two terrestrial biogeochemical model platforms (MoBiLE, GOTILWA+) that describe canopy structure differently. Simulations of isoprene emissions for the Puechabon Mediterranean holm oak stand are analysed, with both canopy photosynthesis models constrained using FLUXNET measurements. The results demonstrate that even with constrained canopy level photosynthesis, large model platform dependent within canopy differences can exist in both modelled photosynthesis and emissions. This results in large differences in modelled isoprenoid emissions, due to the relatively higher sensitivity of emissions to canopy microclimate, in particular temperature. This is the first time emission results from two biogeochemical platforms have been compared, and demonstrates that different canopy descriptions can lead to larger differences in modelled emissions than that attributable to the difference between the emission models themselves. This is an important aspect that has not been acknowledged by the emission modelling community. [Copyright &y& Elsevier]

Abstract: Climate change will increase the frequency and the intensity of droughts in the Mediterranean region, likely reducing growth and increasing mortality of holm oaks (Quercus ilex), one of the most abundant species of Mediterranean forests. In water-limited systems such as those of the Mediterranean, carbon allocation patterns strongly favour belowground accumulation, especially in large subterranean structures called lignotubers. The resilience of these forests depends largely on the replenishment rate of these carbon reserves after disturbances. An experimental thinning, with two intensities (removal of 40% and 80% of basal area), was performed in 1992 in a holm oak forest at the Prades Experimental Complex of Catchments (NE Spain). In 2002, a second thinning was carried out in subplots within the former experimental 0.5 ha plots. Samples from the lignotubers of holm oak trees were analyzed for starch, and both mobile and immobile chemical components, in order to assess the resilience of holm oaks to repeated disturbances. Our results show that after 10 years, starch stocks in the lignotubers have only recovered to half their former values. Removing 40% of the basal area instead of 80% is suggested to be the better managing option for this kind of forests. [Copyright &y& Elsevier]

Plant trait variability, emerging from eco-evolutionary dynamics that range from alleles to macroecological scales, is one of the most elusive, but possibly most consequential, aspects of biodiversity. Plasticity, epigenetics, and genetic diversity are major determinants of how plants will respond to climate change, yet these processes are rarely represented in current vegetation models. Here, we provide an overview of the challenges associated with understanding the causes and consequences of plant trait variability, and review current developments to include plasticity and evolutionary mechanisms in vegetation models. We also present a roadmap of research priorities to develop a next generation of vegetation models with flexible traits. Including trait variability in vegetation models is necessary to better represent biosphere responses to global change. Dynamic vegetation models are the main tools to assess climate change effects on terrestrial vegetation. Therefore, a realistic representation of biological processes in these models is of utmost importance. Intraspecific trait variability is ubiquitous in plants and, thus, the underlying processes causing it should be represented. Yet, trait variability is only used to a limited extent in current vegetation models. Empirical and theoretical studies make clear that intraspecific trait variability underpins evolutionary and plastic plant responses to environmental changes. We review progress towards 'next-generation' models that include evolutionary and plastic processes, including those explicitly representing genetic mechanisms. Modeling paradigms where plant diversity emerges mechanistically are necessary to understand both functional trade-offs (e.g., leaf and wood economics spectra) and spatial patterns of genetic and phenotypic variability as exposed by genomic and ecological data. [ABSTRACT FROM AUTHOR]

Robinia pseudoacacia L. occupies large areas of Mediterranean riparian zones of the northeast of the Iberian Peninsula. This study investigates the influence of the invasive alien nitrogen-fixing R. pseudoacacia on leaf litter nitrogen (N) inputs and soil N availability in a mixed riparian forest in NE Spain. We measured annual leaf litter N inputs, decomposition rates, soil N processes, and soil N concentrations at three sections (near-stream, intermediate, and hillslope) across a riparian forested zone. Moreover, we explored changes in soil N availability associated with the presence of R. pseudoacacia by means of an empirical forest floor model. Leaf litter N content was higher for R. pseudoacacia than for the native non-fixing species. Although the contribution of R. pseudoacacia to annual leaf litter N inputs increased from the near-stream to the hillslope section, soil N mineralization, nitrification, and N availability were similar among sections. Simulations suggest that soil N availability was higher at the near-stream than at the hillslope section without the presence of R. pseudoacacia. However, this pattern smoothed down as R. pseudoacacia spread across the riparian forest. Overall, our results suggest that the spreading of R. pseudoacacia across the riparian zone contributed to homogenize soil N availability over time, and highlight that an integrated spatiotemporal view of the invasive process is needed to assess its impact on soil N biogeochemistry. [ABSTRACT FROM AUTHOR]

In the last decades, the global interest in the role of forests as carbon sinks has grown, and thus, studies aimed at estimating tree biomass have progressively increased. However, few surveys have focused on young coppices, although they are abundant worldwide in areas regenerating after disturbance (e.g. wildfire, clearcutting). In the Mediterranean Basin, young coppices are very frequent, and most of them are formed by evergreen and deciduous oaks ( Quercus spp.). In this survey, we have studied the biomass allocation patterns of two oaks coexisting in coppices, the evergreen Quercus ilex and the deciduous Quercus cerrioides, comparing them in the light of their different leaf habit, which may influence their physiological performance in the context of climate change. We have also obtained allometric equations for each species and its components, which we have used to calculate the carbon stock in the sampled area, as an insight into the potential of young oak coppices to sequester carbon. The results indicate a higher biomass investment of Q. ilex in the stump and a higher leafiness and allocation to roots in Q. cerrioides. In the light of these differences, the evergreen Q. ilex could be defined as a 'resource-saving' species in comparison with the more 'resource-demanding' Q. cerrioides. The allometric equations were able to predict from 78 to 99 % of the variation in biomass using diameter as predictor variable for all the tree components aside of the stump. Overall carbon stock estimation in the young coppice of our study area was 43.2 Mg ha, of which 62 % is stored belowground. These results highlight the importance of biomass allocation in the belowground compartment in Mediterranean young oak coppices as a temporal carbon sink. Moreover, they provide evidence that these forests may store a relevant amount of carbon, often ignored in forest inventories. [ABSTRACT FROM AUTHOR]

Fire is a major agent involved in landscape transformation and an indirect cause of changes in species composition. Responses to fire may vary greatly depending on life histories and functional traits of species. We have examined the taxonomic and functional responses to fire of eight taxonomic animal groups displaying a gradient of dietary and mobility patterns: Gastropoda, Heteroptera, Formicidae, Coleoptera, Araneae, Orthoptera, Reptilia and Aves. The fieldwork was conducted in a Mediterranean protected area on 3 sites (one unburnt and two burnt with different postfire management practices) with five replicates per site. We collected information from 4606 specimens from 274 animal species. Similarity in species composition and abundance between areas was measured by the Bray-Curtis index and ANOSIM, and comparisons between animal and plant responses by Mantel tests. We analyze whether groups with the highest percentage of omnivorous species, these species being more generalist in their dietary habits, show weak responses to fire (i.e. more similarity between burnt and unburnt areas), and independent responses to changes in vegetation. We also explore how mobility, i.e. dispersal ability, influences responses to fire. Our results demonstrate that differences in species composition and abundance between burnt and unburnt areas differed among groups. We found a tendency towards presenting lower differences between areas for groups with higher percentages of omnivorous species. Moreover, taxa with a higher percentage of omnivorous species had significantly more independent responses of changes in vegetation. High- (e.g. Aves) and low-mobility (e.g. Gastropoda) groups had the strongest responses to fire (higher R scores of the ANOSIM); however, we failed to find a significant general pattern with all the groups according to their mobility. Our results partially support the idea that functional traits underlie the response of organisms to environmental changes caused by fire. [ABSTRACT FROM AUTHOR]

Aim Our aim was to map the climate dependence of tree species distributions (probability of occurrence) and forest growth (net primary productivity) by comparing the congruence and incongruence between correlative and process-based modelling approaches. Location Iberian Peninsula, south-western Europe. Methods We used forest inventory data for three widespread tree species ( Quercus ilex, Pinus halepensis and Pinus sylvestris) to model climatic suitability with an ensemble of seven correlative species distribution models (using biomod). We then simulated forest net primary productivity ( NPP) as a surrogate of forest growth for forests of each species using an ecophysiological process-based model ( gotilwa+) along a gradient of climatic suitability. The spatial distribution of the growth estimates was then compared with that of the suitability estimates, and robust regression was used to classify regions in terms of model congruence. Results Quercus ilex and P. sylvestris both showed a positive relationship between forest NPP and climatic suitability. The main discrepancies were found in the north of the peninsula, where there was high potential forest growth but low climate suitability. Low forest-growth estimates in areas of high suitability only appeared for P. sylvestris in southern montane regions. Pinus halepensis always showed a negative relationship between estimated growth and climatic suitability. The analysis of other ecophysiological parameters (mean leaf life and leaf area index) suggests that this tree species has different physiological strategies that allow differential growth rates in areas of low suitability. Main conclusions We found that the relationship between estimated growth and distribution varies strongly in different areas and species. Mapping the incongruences between the predicted climatic suitability and growth allowed us to identify regions where other factors (e.g. biotic interactions) may be more significant than the physiological limits on growth. We show that new insights into species distributions can be gained from mapping the differences between correlative and process-based models. [ABSTRACT FROM AUTHOR]