Vulnerability of Spanish forests under climatic change: evaluation through models

Los bosques son ecosistemas fundamentales en la generación de servicios ecosistémicos y, por tanto, para el bienestar humano. El cambio global (incluyendo cambio climático y cambios en el uso del suelo) puede, sin embargo, alterar la dinámica y el funcionamiento de los ecosistemas, afectando al futuro suministro de servicios ecosistémicos. La vulnerabilidad frente al cambio global depende de la exposición (magnitud del cambio), la sensibilidad (susceptibilidad al cambio), y la capacidad de adaptación (habilidad para ajustarse al cambio) de las especies. En el presente trabajo presentamos diversas aproximaciones de modelización que permiten analizar los diferentes componentes de la vulnerabilidad, e incluimos ejemplos desarrollados para bosques de la península Ibérica. A pesar de estos avances, la evidencia empírica y teórica para integrar los impactos potenciales (i.e. incluyendo la exposición y la sensibilidad) y la capacidad de adaptación de las especies, es escasa. Por ello, para una adecuada evaluación sería necesario mejorar el conocimiento existente sobre la sensibilidad y capacidad de adaptación de las especies y su respuesta frente a cambios ambientales extremos (por ejemplo, mediante redes de seguimiento a largo plazo), integrando adecuadamente la información obtenida en modelos que incluyan procesos basados en diferentes niveles de organización biológica, desde procesos fisiológicos a modelos agregados de distribución de especies.Forest ecosystems contribute to human well-being providing critical ecosystem services. Global change (including climate and land-use changes), however, can alter ecosystem functioning and structure, even jeopardizing the future supply of ecosystem services. Vulnerability to global change depends on exposition (magnitude of the change), sensitivity (susceptibility to the change), and adaptive capacity (ability to adjust to the change) of the species. Here, we summarize diverse modeling approaches to analyze the different components of vulnerability, providing specific examples focused on Iberian forests. Despite of these advances, our empirical and theoretical ability to provide integrated assessments of potential impacts (i.e. including both exposition and sensitivity) of climate change and adaptive capacity is still very limited. An adequate estimation of vulnerability requires improving our knowledge about the adaptive capacity of species and their response to extreme environmental changes (e.g. through long-term monitoring networks), as well as integrating the knowledge obtained from models developed at different levels of biological organization, from physiological process-based models to aggregated species distribution models.Esta revisión ha sido financiada por el proyecto REMEDINAL-2 de la Comunidad de Madrid (S2009/AMB-1783) y el proyecto IN-2013-004 de The Leverhulme Trust

Revealing patterns of local species richness along environmental gradients with a novel network tool

How species richness relates to environmental gradients at large extents is commonly investigatedaggregating local site data to coarser grains. However, such relationships often change with the grainof analysis, potentially hiding the local signal. Here we show that a novel network technique, the"method of reflections", could unveil the relationships between species richness and climate withoutsuch drawbacks. We introduced a new index related to potential species richness, which revealedlarge scale patterns by including at the local community level information about species distributionthroughout the dataset (i.e., the network). The method effectively removed noise, identifying howfar site richness was from potential. When applying it to study woody species richness patterns inSpain, we observed that annual precipitation and mean annual temperature explained large parts ofthe variance of the newly defined species richness, highlighting that, at the local scale, communitiesin drier and warmer areas were potentially the species richest. Our method went far beyond whatgeographical upscaling of the data could unfold, and the insights obtained strongly suggested that itis a powerful instrument to detect key factors underlying species richness patterns, and that it couldhave numerous applications in ecology and other fields.Comunidad de MadridMinisterio de Economía y Competitivida

Drought impacts on tree growth of two pine species along an altitudinal gradient and their use as early-warning signals of potential shifts in tree species distributions.

Mediterranean pine forests are at risk of experiencing a decline in tree growth in response to climatewarming if rising temperatures amplify drought stress. In mountain areas, tree growth could be enhancedin temperature-limited high elevations, whilst it might decline at water-constrained low elevations.Species differential responses could, however, modulate the impact of drought on forests along altitudinalgradients. To test for evidence of species differential drought impacts along an altitudinal gradient, westudied the growth responses of two Iberian pine species (Pinus sylvestris and Pinus nigra) subjected toMediterranean conditions in Eastern Spain. We analysed the stability of growth (basal area increment)responses to climate and drought during the 1950&-2014 period by using resistance and resilience indices.Pinus sylvestris growth was enhanced by warm spring temperatures, while Pinus nigra growth wasimproved by a positive spring water balance. Pinus sylvestris growth decreased temporally at the lowerend of its altitudinal range, whereas Pinus nigra growth decreased at the upper end. Pinus sylvestris exhibitedlow growth stability at its low-elevation limit. Pinus nigra resistance also decreased along its altitudinalrange, but this effect was compensated by a high resilience. In mixed stands the results werecontrasting, with Pinus sylvestris (at the lower altitudinal range) being more vulnerable to droughtinducedgrowth decline than Pinus nigra (at the upper altitudinal range).Ministerio de Economía y Competitivida

Effects of climate, species interactions, and dispersal on decadal colonization and extinction rates of Iberian tree species

We studied the relative importance of climate, abundance of potentially competing species, and dispersal in explaining local colonization and extinction rates of tree species throughout mainland Spain. We used a Bayesian framework to parameterize a patch occupancy model to 23 species censused in 46,596 permanent plots in a 1 × 1 km grid across most Spanish forests. For most species, dispersal was the single best predictor of colonization, whereas climate and dispersal were equally important as predictors of extinction. Precipitation was positively correlated with the colonization rate of 12 out of 13 deciduous broad-leaved species, and negatively correlated with the extinction rate of nine of them. In contrast, precipitation equally decreased colonization and extinction of five out of eight of needle-leaved species (Juniperus and Pinus spp.). There was, however, marked variation among species in the magnitude of these effects, with some species exhibiting contrasting patterns for the colonization and the extinction process. Abundance of competing tree species (= summed plot basal area) was consistently correlated with decreased colonization of all needle-leaved species, and it increased the extinction rate of 6 out of 8 of these species. It had, nonetheless, weak facilitative effect on some broad-leaved species by promoting colonization (3 of 13 species) and decreasing extinction (7 of 13 species). With local colonization and extinction data, non-equilibrial and dynamic species distribution modelling can be improved by incorporating measures of biotic interactions and dispersal effects, along with traditional climate variables.Ministerio de Economía y CompetitividadComunidad de Madri

Effects of climate, species interactions, and dispersal on decadal colonization and extinction rates of Iberian tree species

We studied the relative importance of climate, abundance of potentially competing species, and dispersal in explaining local colonization and extinction rates of tree species throughout mainland Spain. We used a Bayesian framework to parameterize a patch occupancy model to 23 species censused in 46,596 permanent plots in a 1 × 1 km grid across most Spanish forests. For most species, dispersal was the single best predictor of colonization, whereas climate and dispersal were equally important as predictors of extinction. Precipitation was positively correlated with the colonization rate of 12 out of 13 deciduous broad-leaved species, and negatively correlated with the extinction rate of nine of them. In contrast, precipitation equally decreased colonization and extinction of five out of eight of needle-leaved species (Juniperus and Pinus spp.). There was, however, marked variation among species in the magnitude of these effects, with some species exhibiting contrasting patterns for the colonization and the extinction process. Abundance of competing tree species (= summed plot basal area) was consistently correlated with decreased colonization of all needle-leaved species, and it increased the extinction rate of 6 out of 8 of these species. It had, nonetheless, weak facilitative effect on some broad-leaved species by promoting colonization (3 of 13 species) and decreasing extinction (7 of 13 species). With local colonization and extinction data, non-equilibrial and dynamic species distribution modelling can be improved by incorporating measures of biotic interactions and dispersal effects, along with traditional climate variables.Ministerio de Economía y CompetitividadComunidad de Madri

Environmental heterogeneity, bird-mediated directed dispersal, and oak woodland dynamics in Mediterranean Spain

Vegetation dynamics in complex landscapes depend on interactions among\ud environmental heterogeneity, disturbance, habitat fragmentation, and seed dispersal\ud processes. We explore how these features combine to affect the regional abundances and\ud distributions of three Quercus (oak) species in central Spain: Q. faginea (deciduous tree), Q.\ud ilex (evergreen tree), and Q. coccifera (evergreen shrub). We develop and parameterize a\ud stochastic patch occupancy model (SPOM) that, unlike previous SPOMs, includes\ud environmentally driven variation in disturbance and establishment. Dispersal in the model\ud is directed toward local (nearby) suitable habitat patches, following the observed seed-caching\ud behavior of the European Jay. Model parameters were estimated using Bayesian methods and\ud survey data from 12 047 plots. Model simulations were conducted to explore the importance of\ud different dispersal modes (local directed, global directed, local random, global random). The\ud SPOM with local directed dispersal gave a much better fit to the data and reproduced observed\ud regional abundance, abundance–environment correlations, and spatial autocorrelation in\ud abundance for all three species. Model simulations suggest that jay-mediated directed dispersal\ud increases regional abundance and alters species–environment correlations. Local dispersal is\ud estimated to reduce regional abundances, amplify species–environment correlations, and\ud amplify spatial autocorrelation.\ud Parameter estimates and model simulations reveal important species-specific differences in\ud sensitivity to environmental perturbations and dispersal mode. The dominant species Q. ilex is\ud estimated to be highly fecund, but on the edge of its climatic tolerance. Therefore Q. ilex gains\ud little from directed dispersal, suffers little from local dispersal, and is relatively insensitive to\ud changes in habitat cover or disturbance rate; but Q. ilex is highly sensitive to altered drought\ud length. In contrast, the rarest species, Q. coccifera, is well adapted to the climate and soils but\ud has low fecundity; thus, it is highly sensitive to changes in dispersal, habitat cover, and\ud disturbance but insensitive to altered drought length. Finally, Q. faginea is estimated to be\ud both at the edge of its climatic tolerance and to have low fecundity, making it sensitive to all\ud perturbations. Apparently, co-occurring species can exhibit very different interactions among\ud dispersal, environmental characteristics, and physiological tolerances, calling for increased\ud attention to species-specific dynamics in determining regional vegetation responses to\ud anthropogenic perturbations

Last-century forest productivity in a managed dry-edge Scots pine population: The two sides of climate warming

Climate change in the Mediterranean, associated with warmer temperatures andmore frequent droughts, is expected to impact forest productivity and the functioning of forests ecosystems as carbon reservoirs in the region. Climate warming can positively affect forest growth by extending the growing season, whereas increasing summer drought generally reduces forest productivity and may cause growth decline, trigger dieback, hamper regenera- tion, and increase mortality. Forest management could potentially counteract such negative effects by reducing stand density and thereby competition for water. The effectiveness of such interventions, however, has so far mostly been evaluated for short time periods at the tree and stand levels, which limits our confidence regarding the efficacy of thinning interventions over longer time scales under the complex interplay between climate, stand structure, and forest management. In this study, we use a century-long historical data set to assess the effects of climate and management on forest productivity. We consider rear-edge Scots pine (Pinus syl- vestris) populations covering continental and Mediterranean conditions along an altitudinal gradient in Central Spain. We use linear mixed-effects models to disentangle the effects of alti- tude, climate, and stand volume on forest growth and ingrowth (recruitment and young trees' growth). We find that warming tends to benefit these tree populations, warmer winter temperature has a significant positive effect on both forest growth and ingrowth, and the effect is more pronounced at low elevations. However, drought conditions severely reduce growth and ingrowth, in particular when competition (stand volume) is high. We conclude that summer droughts are the main threat to Scots pine populations in the region, and that a reduction of stand volume can partially mitigate the negative impacts of more arid conditions. Mitigation and adaptation measures could therefore manage stand structure to adopt for the anticipated impacts of climate change in Mediterranean forest ecosystems.Ministerio de Economía y Competitivida

Distribution of pines in Europe agrees with seedling differences in foliage frost tolerance, not with xylem embolism vulnerability

Drought and frosts are major determinants of plant functioning and distribution. Both stresses can cause xylem embolism and foliagedamage. The objective of this study was to analyse if the distribution of six common pine species along latitudinal and altitudinalgradients in Europe is related to their interspecific differences in frost tolerance and to the physiological mechanismsunderlying species-specific frost tolerance. We also evaluate if frost tolerance depends on plant water status. We studied survivalto a range of freezing temperatures in 2-year-old plants and assessed the percentage loss of hydraulic conductivity (PLC) duexylem embolism formation and foliage damage determined by needle electrolyte leakage (EL) after a single frost cycle to −15 °Cand over a range of predawn water potential (psipd) values.Consejo Nacional de Ciencia y Tecnología (México)Ministerio de Ciencia, Innovación y UniversidadesComunidad de Madri

Evaluating the combined effects of climate and land-use change on tree species distributions

A large proportion of the world's biodiversity is reportedly threatened by habitat loss and climate change. However, there are few studies that investigate the interaction between these two threats using empirical data.Here, we investigate interactions between climate change and land use change in the future distribution of 23 dominant tree species in mainland Spain. We simulated changes up to year 2100 using a climate-dependent Stochastic Patch Occupancy Model, parameterized with colonization and extinction events recorded in 46 569 survey plots.We estimated that the distribution of 17 out of 23 tree species are expanding, and hence not at equilibrium with the climate. However, climate change will make the future occupancy of 15 species lower than expected if climate, and habitat, remained stable (baseline scenario).Climate change, when combined with 20% habitat loss, was estimated to reduce species occupancy by an average of 23% if habitat loss is spatially clumped, relative to baseline projections, and by 35% if scattered. If habitat loss occurred in areas already impacted by human activities, species occupancy would be reduced by 26%. Land-use changes leading to habitat gain (i.e. creation through e.g. reforestation), could slightly mitigate the effects of climate change; but a 20% increment in habitat would reduce climate-change-driven losses in species occupancy by only ~3%.Synthesis and applications. The distributions of the most common tree species in mainlandSpain are expanding, but climate change threatens to reduce this expansion by 18% for 15of the 23 studied species. Moreover, if the habitat of these species is simultaneously lost, theoccupancies of all of them will be reduced further, with variation depending on the spatialpattern of the lost habitats. However, we did not detect synergies between climate change andhabitat loss. The combined effect (with 20% habitat loss) was 5–13% less than what it wouldbe if the effects were additive. Importantly, reforestation could partially offset the negativeeffects of climate change, but complete mitigation would require an increase in forested landof 80%, and the prioritization of territories that are less impacted by human activities.Ministerio de Economía y CompetitividadComunidad de Madri

Identifying forest structural types along an aridity gradient in peninsular Spain: Integrating low-density LiDAR, forest inventory, and aridity index

Forest structure is a key driver of forest functional processes. The characterization of forest structure across spatiotemporal scales is essential for forest monitoring and management. LiDAR data have proven particularly useful for cost-effectively estimating forest structural attributes. This paper evaluates the ability of combined forest inventory data and low-density discrete return airborne LiDAR data to discriminate main forest structural types in the Mediterranean-temperate transition ecotone. Firstly, we used six structural variables from the Spanish National Forest Inventory (SNFI) and an aridity index in a k-medoids algorithm to define the forest structural types. These variables were calculated for 2770 SNFI plots. We identified the main species for each structural type using the SNFI. Secondly, we developed a Random Forest model to predict the spatial distribution of structural types and create wall-to-wall maps from LiDAR data. The k-medoids clustering algorithm enabled the identification of four clusters of forest structures. A total of six out of forty-one potential LiDAR metrics were utilized in our Random Forest, after evaluating their importance in the Random Forest model. Selected metrics were, in decreasing order of importance, the percentage of all returns above 2 m, mean height of the canopy profile, the difference between the 90th and 50th height percentiles, the area under the canopy curve, and the 5th and the 95th percentile of the return heights. The model yielded an overall accuracy of 64.18%. The producer's accuracy ranged between 36.11% and 88.93%. Our results confirm the potential of this approximation for the continuous monitoring of forest structures, which is key to guiding forest management in this region.Agencia Estatal de InvestigaciónUniversidad de AlcaláComunidad de MadridDepartamento de Educación del Gobierno VascoMinisterio de Ciencia e Innovació