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Abstract: The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous forest types. We reveal a bimodal distribution of forest leaf types across temperate regions of the Northern Hemisphere that cannot be explained by the environment alone, suggesting signatures of alternative forest states. Moreover, we empirically demonstrate the existence of positive feedbacks in tree growth, recruitment and mortality, with trees having 4–43% higher growth rates, 14–17% higher survival rates and 4–7 times higher recruitment rates when they are surrounded by trees of their own leaf type. Simulations show that the observed positive feedbacks are necessary and sufficient to generate alternative forest states, which also lead to dependency on history (hysteresis) during ecosystem transition from evergreen to deciduous forests and vice versa. We identify hotspots of bistable forest types in evergreen-deciduous ecotones, which are likely driven by soil-related positive feedbacks. These findings are integral to predicting the distribution of forest biomes, and aid to our understanding of biodiversity, carbon turnover, and terrestrial climate feedbacks.

Abstract The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous forest types. We reveal a bimodal distribution of forest leaf types across temperate regions of the Northern Hemisphere that cannot be explained by the environment alone, suggesting signatures of alternative forest states. Moreover, we empirically demonstrate the existence of positive feedbacks in tree growth, recruitment and mortality, with trees having 4–43% higher growth rates, 14–17% higher survival rates and 4–7 times higher recruitment rates when they are surrounded by trees of their own leaf type. Simulations show that the observed positive feedbacks are necessary and sufficient to generate alternative forest states, which also lead to dependency on history (hysteresis) during ecosystem transition from evergreen to deciduous forests and vice versa. We identify hotspots of bistable forest types in evergreen-deciduous ecotones, which are likely driven by soil-related positive feedbacks. These findings are integral to predicting the distribution of forest biomes, and aid to our understanding of biodiversity, carbon turnover, and terrestrial climate feedbacks.

IntroductionDrought-associated tree mortality has been increasing worldwide since the last decades, impacting structure and functioning of forest ecosystems, with implications for energy, carbon and water fluxes. However, the understanding of the individual vulnerability to drought-induced mortality is still limited.MethodsWe aimed to identify the factors that triggered the mortality of the widely distributed Pinus sylvestris L. in an extensive forest area in central Spain. We compared radial growth patterns in pairs of alive and recently dead individuals that co-occur in close proximity and present similar age and size, thereby isolating the effects of size and environment from the mortality process. Temporal dynamics of growth, growth synchrony, and growth sensitivity to water availability (precipitation minus potential evapotranspiration) were compared between alive and recently dead trees.Results and discussionOver the last 50 years, although we did not detect significant differences in growth between alive and dead trees, an increase in the growth synchrony and sensitivity to water availability (i.e. slope of the climatic water balance in the growth model) was observed in all trees as drought intensity increased. 20 years before mortality, dead individuals showed lower growth synchrony and growth sensitivity to water availability than alive ones, without significant differences in growth. Recorded reduction in growth synchrony and growth sensitivity to water availability in dead trees suggests a decoupling between tree growth and climate, which could increase the risk of hydraulic failure and/or carbon starvation under increasingly arid conditions. Thus, the use of reduced growth sensitivity to water availability as potential early-warning signal of tree mortality, together with reduced growth synchrony, should be further explored, particularly in pine species in seasonally dry areas.

Global tree abundance is demonstrated to correlate with latitudinal variables, with tree size and self-thinning strategies impacting current estimates of tree count.

Book Review of: Plant functional diversity: organism traits, community structure and ecosystem properties Eric Garnier, Marie-Laure Navas, and Karl Grigulis Oxford University Press, 2016, £70.00 (hardback) / £37.50 (paperback), 256 pp. ISBN: 978-0-19-875736-8 (hardback) / 978-0-19-875737-5 (paperback).

Correlations between tree species diversity and tree abundance are well established, but the direction of the relationship is unresolved. Here the authors use path models to estimate plausible causal pathways in the diversity-abundance relationship across 23 global forests regions, finding a lack of general support for a positive diversity-abundance relationship, which is prevalent in the most productive lands on Earth only

Abstract For decades, ecologists have investigated the effects of tree species diversity on tree productivity at different scales and with different approaches ranging from observational to experimental study designs. Using data from five European national forest inventories (16,773 plots), six tree species diversity experiments (584 plots), and six networks of comparative plots (169 plots), we tested whether tree species growth responses to species mixing are consistent and therefore transferrable between those different research approaches. Our results confirm the general positive effect of tree species mixing on species growth (16% on average) but we found no consistency in species‐specific responses to mixing between any of the three approaches, even after restricting comparisons to only those plots that shared similar mixtures compositions and forest types. These findings highlight the necessity to consider results from different research approaches when selecting species mixtures that should maximize positive forest biodiversity and functioning relationships.

The North Atlantic Oscillation (NAO) drives biological responses in terrestrial ecosystems through oscillatory modes of climatic variability. Here, the authors show how landscape scale productivity responses to NAO are contingent upon the Atlantic Multidecadal Oscillation in southwestern Europe.

The prediction of tree growth is key to further understand the carbon sink role of forests and the short-term forest capacity on climate change mitigation. In this work, we used large-scale data available from three consecutive forest inventories in a Euro-Mediterranean region and the Bertalanffy–Chapman–Richards equation to model up to a decade’s tree size variation in monospecific forests in the growing stages. We showed that a tree-level fitting with ordinary differential equations can be used to forecast tree diameter growth across time and space as function of environmental characteristics and initial size. This modelling approximation was applied at different aggregation levels to monospecific regions with forest inventories to predict trends in aboveground tree biomass stocks. Furthermore, we showed that this model accurately forecasts tree growth temporal dynamics as a function of size and environmental conditions. Further research to provide longer term prediction forest stock dynamics in a wide variety of forests should model regeneration and mortality processes and biotic interactions.

Woodlands represent highly significant carbon sinks globally, though could lose this function under future climatic change. Effective large-scale monitoring of these woodlands has a critical role to play in mitigating for, and adapting to, climate change. Mediterranean woodlands have low carbon densities, but represent important global carbon stocks due to their extensiveness and are particularly vulnerable because the region is predicted to become much hotter and drier over the coming century. Airborne lidar is already recognized as an excellent approach for high-fidelity carbon mapping, but few studies have used multi-temporal lidar surveys to measure carbon fluxes in forests and none have worked with Mediterranean woodlands. We use a multi-temporal (5-year interval) airborne lidar data set for a region of central Spain to estimate above-ground biomass (AGB) and carbon dynamics in typical mixed broadleaved and/or coniferous Mediterranean woodlands. Field calibration of the lidar data enabled the generation of grid-based maps of AGB for 2006 and 2011, and the resulting AGB change was estimated. There was a close agreement between the lidar-based AGB growth estimate (1.22 Mg ha−1 yr−1) and those derived from two independent sources: the Spanish National Forest Inventory, and a tree-ring based analysis (1.19 and 1.13 Mg ha−1 yr−1, respectively). We parameterised a simple simulator of forest dynamics using the lidar carbon flux measurements, and used it to explore four scenarios of fire occurrence. Under undisturbed conditions (no fire) an accelerating accumulation of biomass and carbon is evident over the next 100 years with an average carbon sequestration rate of 1.95 Mg C ha−1 yr−1. This rate reduces by almost a third when fire probability is increased to 0.01 (fire return rate of 100 years), as has been predicted under climate change. Our work shows the power of multi-temporal lidar surveying to map woodland carbon fluxes and provide parameters for carbon dynamics models. Space deployment of lidar instruments in the near future could open the way for rolling out wide-scale forest carbon stock monitoring to inform management and governance responses to future environmental change.

Los Inventarios Forestales Nacionales informan sobre el estado de los bosques y la productividad de los recursos forestales nacionales. En los inventarios forestales los bosques se muestrean generalmente a nivel nacional, formando parte de las estadísticas nacionales y estando disponibles para la comunidad científica para futuros análisis. Gran parte de nuestro conocimiento actual sobre la relación entre la diversidad biológica y el funcionamiento de los ecosistemas proviene de experimentos realizados en pastizales. La investigación en bosques ha sido sin embargo más tardía, en parte debido a las dificultades de establecer experimentos de larga duración. Sin embargo, durante las últimas décadas, el uso de los Inventarios Forestales Nacionales ha permitido estudiar los efectos de la diversidad a escalas regionales, nacionales e incluso continentales. En este trabajo revisamos cómo los Inventarios Forestales Nacionales han contribuido a avanzar en el conocimiento de los efectos de la diversidad en el funcionamiento de los bosques. Sintetizamos los resultados más relevantes de la literatura y presentamos resultados clave de Inventarios Forestales Nacionales armonizados a escala europea, como los del Proyecto Europeo FunDivEUROPE. Generalmente se observa un efecto positivo de la diversidad arbórea sobre la productividad forestal y la biomasa a lo largo de gradientes latitudinales y ambientales. Hasta el momento existen pocos estudios que integren funciones múltiples. El incremento del número de funciones medidas en los inventarios forestales permitirá disponer de un conocimiento esencial para comprender la respuesta y vulnerabilidad de los ecosistemas forestales frente al cambio climático.

Evolutionary history can explain species resemblance to a large extent. Thus, if closely related species share combinations of traits that modulate their response to environmental changes, then phylogeny could predict species sensitivity to novel stressors such as increased levels of deforestation. To test this hypothesis, we used 66,949 plots (25-m-radius) of the Spanish National Forest Inventory and modelled the relationships between local (plot-level) stem density of 61 Holarctic tree species and forest canopy cover measured at local and landscape scales (concentric circles centred on the plots with radiuses of 1.6, 3.2 and 6.4 km, respectively). Then, we used the output model equations to estimate the probability of occurrence of the species as a function of forest canopy cover (i.e. response to forest loss), and quantified the phylogenetic signal in their responses using a molecular phylogeny. Most species showed a lower probability of occurrence when forest canopy cover in the plots (local scale) was low. However, the probability of occurrence of many species increased when forest canopy cover decreased across landscape scales. We detected a strong phylogenetic signal in species response to forest loss at local and small landscape (1.6 km) scales. However, phylogenetic signal was weak and non-significant at intermediate (3.2 km) and large (6.4 km) landscape scales. Our results suggest that phylogenetic information could be used to prioritize forested areas for conservation, since evolutionary history may largely determine species response to forest loss. As such, phylogenetically diverse forests might ensure contrasted responses to deforestation, and thus less abrupt reductions in the abundances of the constituent species.

Book Review of: Plant functional diversity: organism traits, community structure and ecosystem properties Eric Garnier, Marie-Laure Navas, and Karl Grigulis Oxford University Press, 2016, £70.00 (hardback) / £37.50 (paperback), 256 pp. ISBN: 978-0-19-875736-8 (hardback) / 978-0-19-875737-5 (paperback).

Los objetivos principales de este trabajo son: a) describir algunas características importantes relativas a los rasgos funcionales en plántulas de las especies del género Quercus, b) determinar cómo varía la proporción de hoja, tallo y raíz en adultos, y c) estimar las tasas de crecimiento relativo(RGR) de estas especies para plántulas e individuos adultos. Para ello, usamos los datos de experimentos realizados en plántulas bajo condiciones controladas, del Inventario Forestal Nacional (IFN2 e IFN3) y de las ecuaciones alométricas desarrolladas por Montero et al. (2005). Las especies de Quercus se caracterizan por tener semillas grandes, y las plántulas presentan una baja RGR y área específica foliar (SLA) y una alta proporción de raíz (RMR). Uno de los factores más importantes que explican las diferencias en RGR entre las especies de Quercus (tanto en plántulas como en adultos) es la diferencia en SLA. Considerando los datos de biomasa de árboles, se observa que la proporción de hoja (LMR) y de raíz (RMR) disminuye con el tamaño, mientras que la proporción de tallo (SMR) aumenta con éste. Si consideramos un árbol medio de 20 cm de diámetro de tronco, los valores de LMR son de sólo 1-5 % y los de SMR van del 50 al 80 %. Considerando los datos del IFN, dentro de cada especie existe una gran variación en RGR. Aun así, cuando se comparan las RGR de las plántulas con los adultos se observa una relación significativa y positiva. Uno de los factores que afectó significativamente a RGR fue el tamaño del árbol, de forma que árboles de mayor tamaño crecían más lentamente.

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 me-jorar 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.

The modification of typical age-related growth by environmental changes is poorly understood, In part because there is a lack of consensus at individual tree level regarding age-dependent growth responses to climate warming as stands develop. To increase our current understanding about how multiple drivers of environmental change can modify growth responses as trees age we used tree ring data of a mountain subtropical pine species along an altitudinal gradient covering more than 2,200 m of altitude. We applied mixed-linear models to determine how absolute and relative age-dependent growth varies depending on stand development; and to quantify the relative importance of tree age and climate on individual tree growth responses. Tree age was the most important factor for tree growth in models parameterised using data from all forest developmental stages. Contrastingly, the relationship found between tree age and growth became non-significant in models parameterised using data corresponding to mature stages. These results suggest that although absolute tree growth can continuously increase along tree size when trees reach maturity age had no effect on growth. Tree growth was strongly reduced under increased annual temperature, leading to more constant age-related growth responses. Furthermore, young trees were the most sensitive to reductions in relative growth rates, but absolute growth was strongly reduced under increased temperature in old trees. Our results help to reconcile previous contrasting findings of age-related growth responses at the individual tree level, suggesting that the sign and magnitude of age-related growth responses vary with stand development. The different responses found to climate for absolute and relative growth rates suggest that young trees are particularly vulnerable under warming climate, but reduced absolute growth in old trees could alter the species' potential as a carbon sink in the future.

Tree mortality is a key process underlying forest dynamics and community assembly. Understanding how tree mortality is driven by simultaneous drivers is needed to evaluate potential effects of climate change on forest composition. Using repeat-measure information from c. 400,000 trees from the Spanish Forest Inventory, we quantified the relative importance of tree size, competition, climate and edaphic conditions on tree mortality of 11 species, and explored the combined effect of climate and competition. Tree mortality was affected by all of these multiple drivers, especially tree size and asymmetric competition, and strong interactions between climate and competition were found. All species showed L-shaped mortality patterns (i.e. showed decreasing mortality with tree size), but pines were more sensitive to asymmetric competition than broadleaved species. Among climatic variables, the negative effect of temperature on tree mortality was much larger than the effect of precipitation. Moreover, the effect of climate (mean annual temperature and annual precipitation) on tree mortality was aggravated at high competition levels for all species, but especially for broadleaved species. The significant interaction between climate and competition on tree mortality indicated that global change in Mediterranean regions, causing hotter and drier conditions and denser stands, could lead to profound effects on forest structure and composition. Therefore, to evaluate the potential effects of climatic change on tree mortality, forest structure must be considered, since two systems of similar composition but different structure could radically differ in their response to climatic conditions.

The juvenile life stage is a crucial determinant of forest dynamics and a first indicator of changes to species' ranges under climate change. However, paucity of detailed re‐measurement data of seedlings, saplings and small trees means that their demography is not well understood at large scales, and rarely represented in forest models in detail. In this study we quantify the effects of climate and density dependence on recruitment and juvenile growth and mortality rates of thirteen species measured in the Spanish Forest Inventory. Single‐census sapling count data is used to constrain demographic parameters of a simple forest juvenile dynamics model based on the perfect plasticity approximation model (PPA) within a likelihood‐free parameterisation method, Approximate Bayesian Computation. Our results highlight marked differences between species, and the important role of climate and stand structure, in controlling juvenile dynamics. Recruitment had a hump‐shaped relationship with conspecific density, and for most species conspecific competition had a stronger negative effect than heterospecific competition. Mediterranean species showed on average higher mortality and lower growth rates than temperate species, and in low density stands recruitment and mortality rates were positively correlated. Under climate change our model predicted declines in recruitment rates for almost all species. Reliable predictive models of forest dynamics should include realistic representation of critical early life‐stage processes and our approach demonstrates that existing coarse count data can be used to parameterise such models. Approximate Bayesian Computation may have wide application in many fields of ecology to unlock information about past processes from single survey observations. [ABSTRACT FROM AUTHOR]

Concern is rising on whether forest function and structure will recover from drought-related impacts, which are expected to increase under global warming. Understanding demographic mechanisms underlying resilience (i.e. capacity of a system or individual to restore its structure and function prior to a disturbance) is critical for properly assessing forest vulnerability to drought. The simultaneous estimation of resilience of the main demographic rates governing tree population dynamics (growth, recruitment and survival) allows for a comprehensive assessment of forest response capacity. We evaluate the resilience of a large Pinus pinaster forest (approx. 7500 ha) in Southern Europe to one of the driest decades of the last 70 years (i.e. 1942–52). As forest structure and management influence demographic rates, their effects were removed prior to calculating resilience values for growth, recruitment and survival. The extremely dry conditions negatively impacted tree growth and recruitment during drought and slightly decreased survival in the decade after drought. Resilience values were mostly high, despite some low values for recruitment or survival in some forest sections, which indicate a general recovery of growth and recruitment and an absence of widespread reductions in survival after drought. A joint analysis of the Demographic Resilience Index (calculated by combining growth, recruitment and survival resilience; DRI) and resilience values of each rate allows to detect demographic compensation effects. High DRI values, even in sections where resilience in recruitment or survival was low, indicate that low resilience values in a given rate were compensated by high resilience in the remaining rates. Recorded resilience could allow the long-term persistence of the studied forest, although increased frequency and intensity of droughts might exceed the critical threshold of system’s resilience. Our approach provides a step toward an exhaustive resilience assessment; however, further research should consider potential resilience thresholds arising from more complex non-linear dynamics. [ABSTRACT FROM AUTHOR]

Woodlands represent highly significant carbon sinks globally, though could lose this function under future climatic change. Effective large-scale monitoring of these woodlands has a critical role to play in mitigating for, and adapting to, climate change. Mediterranean woodlands have low carbon densities, but represent important global carbon stocks due to their extensiveness and are particularly vulnerable because the region is predicted to become much hotter and drier over the coming century. Airborne lidar is already recognized as an excellent approach for high-fidelity carbon mapping, but few studies have used multi-temporal lidar surveys to measure carbon fluxes in forests and none have worked with Mediterranean woodlands. We use a multi-temporal (five year interval) airborne lidar dataset for a region of central Spain to estimate above-ground biomass (AGB) and carbon dynamics in typical mixed broadleaved/coniferous Mediterranean woodlands. Field calibration of the lidar data enabled the generation of grid-based maps of AGB for 2006 and 2011, and the resulting AGB change were estimated. There was a close agreement between the lidar-based AGB growth estimate (1.22 Mg ha-1 year-1) and those derived from two independent sources: the Spanish National Forest Inventory, and a tree-ring based analysis (1.19 and 1.13 Mg ha-1 year-1, respectively). We parameterised a simple simulator of forest dynamics using the lidar carbon flux measurements, and used it to explore four scenarios of fire occurrence. Under undisturbed conditions (no fire occurrence) an accelerating accumulation of biomass and carbon is evident over the next 100 years with an average carbon sequestration rate of 1.95 Mg C ha-1 year-1. This rate reduces by almost a third when fire probability is increased to 0.01, as has been predicted under climate change. Our work shows the power of multi-temporal lidar surveying to map woodland carbon fluxes and provide parameters for carbon dynamics models. Space deployment of lidar instruments in the near future could open the way for rolling out wide-scale forest carbon stock monitoring to inform management and governance responses to future environmental change. [ABSTRACT FROM AUTHOR]

Land use and land cover change is a major component of global change, which directly alters habitat composition, biodiversity and ecosystem functioning. The regional analysis of land cover changes in heterogeneous landscapes can be masked by spatial variations caused by both bioclimatic and socioeconomic factors. Recognizing these influences, however, can be critical for designing conservation policies suited for each region. In this study, we examined the main processes of land cover change in Spain during c. 20 years (1987–2006), using CORINE land cover maps and five comparative spatial frameworks based on biomes (temperate and Mediterranean) and protection levels (Nationally Designated areas, European Natura Net 2000 and unprotected areas). We observed high land cover persistence ( ca. 93%) throughout Spain, but with important anthropization processes and internal changes in natural areas – which experienced a slight decrease – while, agrarian areas remained almost stable. However, there were significant differences in the occupation, intensity and direction of change depending on the biome and protection level. The Mediterranean region had lower persistence and higher anthropization processes than the temperate region, suggesting a high vulnerability to land cover changes for natural habitat and related species. Overall, we observed a lower intensity of anthropization processes in protected areas, increasing the persistence of natural and agrarian areas; key habitats for species conservation. The highest persistence of natural areas corresponds to Nationally Designated Protected (NDP) areas, while in Natura Net 2000 we found the highest agrarian areas persistence. Nevertheless, Natura Net 2000 areas – with the exception of those nominated as NDP – had the largest increase of artificial surfaces as well as the highest internal processes of change within natural areas due to disturbances. The trends reported in this study suggest the importance of effective management plans and conservation measures that ensure both habitat and species conservation, especially in the Mediterranean region. In the case of Natura Net 2000, where traditional agricultural and livestock activities had a larger importance, it would be advisable to definitively implement the pending management plans, which are feasible and compatible with local human activities. [ABSTRACT FROM AUTHOR]

• Heterospecific tree density negatively affects non-native tree success. • Species and functional diversity decrease Eucalyptus and Pinus performance. • Colonization increases with propagule availability in the surrounding landscape. • High annual temperatures and sand content decrease Eucalyptus and Pinus success. • Management favours both adult and juvenile Pinus radiata trees. Non-native trees enhance services that are fundamental for human well-being. Yet, the extensive use of non-native trees has the potential of causing environmental and socio-economic harm. Eucalyptus and Pinus are the most widely distributed and extensively planted tree genera worldwide, because their rapid growth allows profitable production of timber and pulp. Their naturalization is causing severe effects on the environment, but the relative importance of underlying factors determining their demographic performance is not well known. Thus, our aim was to evaluate the relative importance of biotic, abiotic, and anthropogenic factors driving demographic changes of Eucalyptus and Pinus at the regional scale. We compiled environmental variables and demographic data for Eucalyptus globulus , Eucalyptus camaldulensis , and Pinus radiata across 6388 permanent forestland plots surveyed in the Spanish Forest Inventory (SFI). We used the second (1986–1996), third (1997–2007), and fourth (2008–2017) SFI datasets to quantify annual changes in basal area per plot between consecutive inventories (ΔBA; m2 ha−1 year−1). We also quantified the components of ΔBA: tree ingrowth (transitions from juvenile to adult trees), growth, and mortality. We evaluated juvenile recruitment with in-situ regeneration (No. juvenile trees ha−1) within plots already occupied by the focal species in the previous inventory, and with natural colonization of plots where the focal species was absent at the beginning of the time interval. We found that the structure of the biotic community was especially important to explain demographic performance of non-native trees growing in benign environments (E. globulus and P. radiata), whereas abiotic factors were particularly important regulating basal area increments of E. camaldulensis , which occurs in harsher environments. Basal area increments decreased with species and functional richness, heterospecific density, mean annual temperature, and increased with soil capacity to retain nutrients and water. Colonization of new plots increased with propagule availability in the surrounding landscape. Tree cutting was beneficial for P. radiata. Collectively, our results suggest that non-native trees perform better in forests with high propagule pressure, low biotic resistance, favourable abiotic conditions, and human management. [ABSTRACT FROM AUTHOR]

• The AGB of top 1% trees is a better proxy than plant diversity for AGB dynamic. • Secondary forest has higher AGB gain, net change, but lower loss than intact forest. • Topography regulates the structure, composition and AGB dynamic of temperate forest. Large trees, as the versatile provider of ecosystem services, are the most susceptible to episodic disturbance regimes such as extreme climate and biotic agents across the globe, and hence, largely determine forest demographic processes. Despite the recognized fundamental ecological significance of large-diameter trees to above-ground biomass (AGB) stock, relatively little is known about their distinctive role, interplaying with abiotic and biotic drivers, in shaping forest AGB dynamics (i.e., gain and loss) at regional or larger extents. Here, we hypothesized that the AGB of few large trees drives AGB stock and dynamics (gain and loss) better than species diversity and trait composition in temperate forests along topography and soil gradients. We analyzed two repeated forest inventories data from 700 plots (including 74,300 adult trees) across 15 plots in temperate forests of northeastern China, including old-growth and disturbed forests. A steady net AGB change increase was found for 13 of the 15 plots. Despite disturbed forests were recovering from post-logging disturbance with a lower density of large-diameter trees and AGB stock than old-growth plots, disturbed forests had higher AGB gain, net AGB change and lower AGB loss than old-growth forests. The largest trees (i.e. top 1% AGB or diameter) were consistently more important for explaining AGB stock, gain and loss compared to plant diversity and trait composition. Besides, the elevation-related topographic factors were more direct determinants of forest AGB accumulation than soil nutrients, and also exerted the indirect impacts via increasing the dominance of resource-conservative trees, stand structural diversity and top 1% large trees. Overall, we highlight the key overruling effect of top 1% large trees on AGB stock and dynamics in response to local environmental factors. This study could improve our understanding of the multiple ecological mechanisms underlying the global change drivers of forest AGB stock and dynamics. [ABSTRACT FROM AUTHOR]

• We evaluated tolerance to recurrent droughts in ecologically distinct pine species. • Inter-specific differences in resilience to drought were only detected in saplings. • P. pinaster was more resilient and recruit better than P. nigra and P. sylvestris. • Inter-specific responses were consistent to biogeographical origin of each species. • This highlights the importance of including juvenile responses in predictive models. Understanding species' tolerance to recurrent extreme droughts is key to predict species' performance and forest dynamics under ongoing climate change. Inter-specific differences in juvenile responses can largely shape forest composition and structure. However, the vulnerability of tree species is typically evaluated in adult canopy dominant individuals. The question of whether inter-specific differences in drought tolerance vary between adult and young trees remains largely unexplored. We sampled canopy dominant trees and saplings of three co-occurring pine species with different drought tolerance (Pinus pinaster , P. nigra and P. sylvestris) in a relict forest in the Northern Iberian plateau. Using basal area increment in canopy dominant trees and shoot elongation in saplings, we reconstructed annual growth for the period 2000–2015 and calculated resilience and resistance indices to two consecutive extreme droughts (2005 and 2012). We used generalized least square models to analyze species-specific differences in resistance and resilience in adults and saplings, respectively after accounting for tree size and stand basal area effects. In addition, we recorded living and dead saplings to assess inter-specific dissimilarities after the drought events. Drought events strongly reduced the growth of both adults and saplings (40% on average), but they were more resilient to the 2005 than to the 2012 drought. Increased magnitude and frequency of drought events led to inter-specific differences in drought responses, which were revealed in saplings rather than adults after the 2012 drought. P. pinaster saplings were more resilient than P. nigra and P. sylvestris , consistently to the drought stress experienced by each species in the dry-edge of their natural ranges. Moreover, a greater recruitment and similar sapling mortality confirm P. pinaster as the most successful pine species from a demographic perspective. In addition, tree size reduced resilience whereas basal area in the tree neighborhood did not show any significant effect on pine tolerance to drought. In conclusion, we showed that increased the magnitude and frequency of drought events uncovers species-specific differences in drought resilience in saplings rather than adults. Our results suggest potential shifts in the dominance of P. pinaster as the expense of P. nigra and P. sylvestris under climate change in this relict forest. This highlights the need to include juveniles and demographic rates in models aiming to describe and predict species responses to climate change in dry-edge forests. [ABSTRACT FROM AUTHOR]