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Some tree species have shown to be very vulnerable to drought and heat waves in the Mediterranean Basin, causing a loss of important socio-economic and ecosystem forest services. In this regard, oaks are important but vulnerable species which are showing losses in terms of productivity and growth and rising mortality rates. Dendroecological studies using retrospective analysis of wood anatomical traits and tree rings have demonstrated their potential to assess long-term patterns of growth and vigor in several Mediterranean oak species. Moreover, the long-term reconstruction of wood anatomical traits such as transversal lumen area, allows investigating hydraulic adjustments of trees through time.In this study, we reconstructed changes in wood anatomy for a 38-year long period (1980-2017) to investigate how drought impacted the hydraulic functionality and triggered dieback in five ring-porous oak species from Italy and Spain (Quercus robur, Quercus frainetto, Quercus cerris, Quercus canariensis, Quercus pubescens). We compared non-decaying (ND) and decaying (D) coexisting trees of each species showing low and high defoliation levels, respectively. We analyzed earlywood anatomical traits (vessel area, hydraulic diameter, vessel density, theoretical hydraulic conductivity, etc.) in these species and analysed them considering a ranking of increasing drought tolerance: Q. robur, Q. frainetto, Q. cerris, Q. canariensis, and Q. pubescens.We observed differing growth patterns and xylem conduit area responses in D trees compared with ND trees. The D trees formed narrower EW vessels than ND and the Dh were lower in D trees compared with ND trees. We discuss the relationships between radial growth, changes in wood anatomy and hydraulic functioning of trees focusing on those proved more sensitive to growth decline and mortality in order to highlight the climatic triggers of dieback in ring-porous oak species as related to hydraulic failure.

Increasing drought severity can affect the healthy status of forests and determine changes in structural and ecophysiological responses to such extreme climate events. Reduced canopy cover, productivity and tree growth and recent dieback phenomena are widespread responses to drought. However, favourable climatic conditions can improve the post-drought recovery capacity of forests, but also make them vulnerable to drought damage through structural overshoot by altering the root to shoot ratio due to wet conditions. Due to the lack of integrated and retrospective field data, the patterns and responses of forests to wet-dry climate variability are still poorly understood. In this work we used remote sensing data (NDVI) to characterise the canopy conditions and combined them with field and tree-ring width data to assess the effects of the summer 2017 drought on Mediterranean tree species in southern Italy (Fraxinus ornus, Quercus pubescens, Acer monspessulanum, Pinus pinaster). By comparing radial growth and resilience indices we found that growth responses to drought depended not only on tree species but also on site conditions. Overall, the growth decline due to drought was followed by a rapid recovery, while negative legacies to drought were found at lower quality sites, which corresponded to sites with the lowest NDVI values. Indeed, trees at these sites showed high growth rates before drought, in response to wet winter-spring conditions, and then suffered more from drought stress. Our results demonstrated how structural overshoots predisposes to drought damage and induced negative legacies. Specific knowledge on the effects of drought overshoot over time is important for analysing and understanding current forest responses and dynamics.

Understanding processes controlling forest dynamics has become particularly important in the context of ongoing climate change, which is altering the ecological fitness and resilience of species worldwide. However, whether forest communities would be threatened by projected macroclimate change or unaffected due to the controlling effect of local site conditions is still a matter for debate. After all, forest canopy buffer climate extremes and promote microclimatic conditions, which matters for functional plant response, and act as refugia for understory species in a changing climate. Yet precisely how microclimatic conditions change in response to climate warming will depend on the extent to which vegetation structure and local topography shape air and soil temperature. In this study, we posited that forest microclimatic buffering is sensitive to local topographic conditions and canopy cover, and using meteorological stations equipped with data-loggers we measured this effect during 1 year across a climate gradient (considering aspect as a surrogate of local topography) in a Mediterranean beech treeline growing in contrasting aspects in southern Italy. During the growing season, the below-canopy near-ground temperatures were, on average, 2.4 and 1.0 °C cooler than open-field temperatures for south and north-west aspects, respectively. Overall, the temperature offset became more negative (that is, lower under-canopy temperatures at the treeline) as the open-field temperature increased, and more positive (that is, higher under-canopy temperatures at the treeline) as the open-field temperature decreased. The buffering effect was particularly evident for the treeline on the south-facing slope, where cooling of near-ground temperature was as high as 8.6 °C for the maximum temperature (in August the offset peaked at 10 °C) and as high as 2.5 °C for the average temperature. In addition, compared to the south-facing slope, the northern site exhibited less decoupling from free-air environment conditions and low variability in microclimate trends that closely track the free-air biophysical environment. Although such a decoupling effect cannot wholly isolate forest climatic conditions from macroclimate regional variability in the south-facing treeline, it has the potential to partly offset the regional macroclimatic warming experienced in the forest understory due to anthropogenic climate change.

Key message Juglans, Fraxinus, Quercus and Pinus species seem to better maximize the carbon–water ratio providing useful indications on species selection for forestry plantations in areas with increasing drought risk. Abstract Maximizing carbon sequestration for a given water budget is extremely important in the contest of climate change in the Mediterranean region, which is characterized by increasing temperatures and rising water stress. This issue is fundamental for plantation stands, where limited water availability during the growing season reduces CO2 assimilation and, consequently, tree growth. In this study, the main objective was to investigate the performances in terms of carbon–water balance of conifer (Pinus halepensis and Cupressus sempervirens) and hardwood (Quercus robur, Juglans regia, Fraxinus excelsior and Populus spp.) mixed plantations. To this aim, we used carbon isotope signatures to evaluate the intrinsic water-use efficiency (iWUE) and the species-specific relationship between basal area increments (BAI) and iWUE. At the species level, the highest iWUE values corresponded to the lowest carbon accumulation in terms of BAI, for water-saving species such as Cupressus. Conversely, Populus had the lowest iWUE and the highest BAI accumulation. Juglans, Fraxinus, and Pinus showed the most balanced ratio between BAI and iWUE. Overall, no clear correlation of iWUE and BAI was evident within all species, except for Populus and Cupressus. Considering projected aridification and increased temperatures that will negatively impact the growth, our data suggest that Pinus, for conifers, and Quercus, Juglans, Fraxinus for hardwood species should be preferred when choosing species for forestry plantation, as they performed better in terms of BAI and iWUE ratio.

Sperry’s packing rule predicts the optimum packing of xylem conduits in woody plants, where the frequency of xylem conduits varies approximately inversely with the square of the conduit radius. However, it is well established that such anatomical disposition does not remain fixed but is subject to a suite of adaptations induced by physiological constraints driven by both ontogenetic development and environmental characteristics. Here we challenge the hypothesis that increasing frequency of xylem conduits, concomitant with the decrease in their lumen area along the xylem pathway, would affect the spatial distribution of vessels inside tree-rings and their aggregation. To this end, we measured the vessels’ anatomical characteristics inside each tree-ring along with a complete radial series taken at different stem heights of Fagus sylvatica L. trees. Point pattern analysis indicated a significant effect of the distance from the tree base and a weak effect of cambial age on the nearest neighbour distance among xylem vessels, suggesting that vessels were closer to each other near the apex, and became progressively more distant toward the base. The spatial pattern of xylem vessels violated the assumption of complete spatial randomness, vessel spatial arrangement followed a uniform distribution at different distances from the tree base. Although there was an increase in the intensity and proximity among vessels, we demonstrated that no patterns of aggregation between vessels were found in sampled F. sylvatica trees. Rather, point pattern profiles clearly highlighted a lack of aggregation of vessels in the face of a regular spatial distribution in the annual growth rings along the stems.

The original version of this article unfortunately contained a mistake. The figures previously used are the old version and some symbols in the figure captions were displayed incorrectly. Final versions of figures with their captions are provided here.

Forest dieback phenomena occur all over the world and have been mainly attributed to extreme droughts and heatwaves. These phenomena are more pronounced in the Mediterranean basin, causing a significant impact on the structure, composition, and productivity of forests. Understanding the response of Mediterranean forests to extreme climate events is of paramount importance to assess their vulnerability to such phenomena. The present study combined both radial growth data and remotely sensed indices (i.e., Normalized Difference Vegetation Index, NDVI) to analyse the vegetation status of selected deciduous forest stands impacted by the summer 2017 heatwave. We surveyed several sites of the Southern Apennines mountains range in order to: I) investigate the growth response of forest vegetation in terms of resilience and resistance and II) characterize their ability to recover after extreme climatic events. Overall, we observe a significant reduction in radial growth after 2017 in all studied stands. Moreover, the vegetation shows clear signs of "recovery" that are strictly dependent on species-specific and site-specific conditions. In this study we will highlight how these stands responded to the heatwave occurred in the 2017 and how these events can affect the future vegetation dynamics either in terms of growth and evolution of Mediterranean ecosystems.

The role of forest biodiversity in supporting ecosystem functioning is remarked to be context-dependent, and changes in environmental conditions could alter the shape of biodiversity-ecosystem functioning (BEF) relationships. However few studies have explored the processes underlying shifts in BEF relationships along abiotic gradients, which limits our ability to predict how the BEF relationship will respond to the rapid future changes in environmental conditions caused by climate change. In this study, we sought to test (i) how a water limitation gradient shapes the functional composition and diversity of forests, (ii) how functional composition and diversity of trees relate to forest productivity, and (iii) if functional diversity is more strongly related to productivity in the Mediterranean or temperate climate. To address these points, we created a functional trait data set covering traits of most of the tree species within the Italian peninsula, using forest surveyed data sets from the National Forest Inventory. We found that functional composition varied with water limitation as tree communities tended to have more `conservative` resource strategies (e.g., low specific leaf area and high wood density) under increased water limitation. Functional diversity´s response was highly variable, however, increased water limitation has been found to enhance also functional diversity in the temperate domain. Biodiversity positively influenced forest productivity through a combination of mass ratio and niche complementary effects in Italian forests, but the relative importance of these effects is dependent on the functional trait and bioclimate considered. Niche complementary effects showed a more predominant effect on productivity in the Mediterranean compared to temperate forests. Overall, our results suggest that biodiversity plays an important role in driving forest productivity under more environmental stressed conditions by promoting beneficial interactions between species and complementarity in resources.

Increasing aridity, primarily driven by higher temperatures and lower precipitation, will threaten the stability and health status of Mediterranean forest ecosystems. Vegetation phenology has been globally acknowledged as a key tool to track the timing of seasonal plant and animal activities as well as changes in the forest ecosystems in response to climate change. In this study, we sought to address the phenological behavior of Mediterranean forest stands exhibiting evident decline symptoms. We investigated how phenological and productive indices for Quercus cerris, Quercus pubescens, and Quercus frainetto stands would be able to reflect the seasonal vegetative dynamics of forests affected by dieback, through a multi-scale and multi-temporal approach. To this, we compared nearby stands showing different vigor, i.e., dieback vs non-dieback, assessed as growths decline, elevated crown transparency, and rising tree mortality rate. For this purpose, phenological metrics of greenness (NDVI, Normalized Difference Vegetation Index) and phenological (PPI, Plant Phenology Index) spectral indices were derived from either MODIS Terra and Aqua or Sentinel 2 satellites. Our results indicated peculiar site-specific phenological patterns. We observed that dieback forest stands - characterized by a high percentage of trees showing canopy defoliation - exhibited different phenological behavior compared with non-dieback stands. Shifts in length of growing season and seasonal amplitude among dieback and non-dieback stands occurred, that probably affect seasonal productivity. Furthermore, climatic fluctuations may have also affected such phenological patterns. Aligning proxies for the phenological and productive status of forest vegetation may improve our understanding of the responses of dieback forests to the changing climate, mainly in the Mediterranean region.

Xylem is a multifunctional tissue that allows water transport, mechanical support, and storage of nutrients. These functions are provided by different cells, with different anatomy among species but also within individual trees. For the latter, it is well established that such anatomical disposition does not remain fixed but it is subject to a suite of adaptations induced by physiological constraints driven by both ontogenetic development and environmental characteristics.For these reasons, in this study, we assessed 1) the spatial distribution of xylem conduits and their aggregation inside Fagus sylvatica L. tree-rings, and 2) the systematic variation of tip-to-base conduit widening and conduit packing occurring during tree growth.In order to achieve these goals, we quantified the axial and radial xylem conduit patterns through measurement of conduit anatomical characteristics inside every tree-ring along complete radial series taken at different stem heights in eight Fagus sylvatica L. trees, sampled from two different sites in the Italian Apennines.Our results showed a significant effect of the distance from the tree base and a weak effect of cambial age on the nearest neighbour distance among xylem conduits, suggesting that conduits were closer to each other near the apex, and became progressively more distant toward the base. However, point pattern profiles clearly highlighted a lack of aggregation between conduits along the stems.In addition, the axial scaling of conduits (β) follows a power trajectory according to the theoretical prediction, while the xylem conduits packing exponent (α) was lower than the predicted Sperry’s packing rule. Furthermore, no consistent trend was found for the scaling exponent (β) during tree ontogeny, confirming that tip-to-base conduit widening is an adaptation, favored by natural selection to minimize the increase in hydraulic resistance when the individual stem grows longer and conductive path length increases.

Mediterranean mountainous forest ecosystems are key hotspots to study the impact of climate change, thus understanding the species-specific growth response is of great relevance. In this study, we take advantage of the few remnant patches of old-growth forests located in the Pollino Massif (southern Italy), to evaluate how the growth of conspecific young and old trees responded to climate. Indeed, thanks to their remote critical topographic conditions in which these patches are located, they have remained nearly untouched from human pressure over the last centuries. We compared two conifer species (Abies alba, Pinus heldreichii var. leucodermis) vs. two hardwood species (Fagus sylvatica, Quercus cerris) in four stands situated along an altitudinal gradient. Younger trees grew faster than their conspecific oldest trees during their juvenile stage, regardless of the environmental conditions and species studied, highlighting more favorable recent climatic and environmental conditions for growth compared to the past. Rising temperature had a positive effect on growth rate in high-elevation young and old P. leucodermis individuals. However, F. sylvatica, inhabiting mesic sites at lower elevation, had slow growth with the least difference in growth rates between young and old trees. Similarly, the growth rates of old tree species found at lower elevation (Q. cerris and A. alba, respectively) tended to be relatively stable since 1950, except for A. alba, increased over the last two decades. Climate sensitivity in recent decades differed between young and old trees in some of the species, with younger trees tending to be more sensitive in Pinus and Abies, and older trees being more sensitive in Fagus. Such disparity in climate sensitivity and long-term growth reactions to climate should be recognized and considered when forecasting the future dynamics of old-growth forests.

Old-growth mountain forests represent an ideal setting for studying long-term impacts of climate change. We studied the few remnants of old-growth forests located within the Pollino massif (southern Italy) to evaluate how the growth of conspecific young and old trees responded to climate change. We investigated two conifer species (Abies alba and Pinus leucodermis) and two hardwood species (Fagus sylvatica and Quercus cerris). We sampled one stand per species along an altitudinal gradient, ranging from a drought-limited low-elevation hardwood forest to a cold-limited subalpine pine forest. We used a dendrochronological approach to characterize the long-term growth dynamics of old (age > 120 years) versus young (age < 120 years) trees. Younger trees grew faster than their older conspecifics during their juvenile stage, regardless of species. Linear mixed effect models were used to quantify recent growth trends (1950–2015) and responses to climate for old and young trees. Climate sensitivity, expressed as radial growth responses to climate during the last three decades, partially differed between species because high spring temperatures enhanced conifer growth, whereas F. sylvatica growth was negatively affected by warmer spring conditions. Furthermore, tree growth was negatively impacted by summer drought in all species. Climate sensitivity differed between young and old trees, with younger trees tending to be more sensitive in P. leucodermis and A. alba, whereas older F. sylvatica trees were more sensitive. In low-elevation Q. cerris stands, limitation of growth due to drought was not related to tree age, suggesting symmetric water competition. We found evidence for a fast-growth trend in young individuals compared with that in their older conspecifics. Notably, old trees tended to have relatively stable growth rates, showing remarkable resistance to climate warming. These responses to climate change should be recognized when forecasting the future dynamics of old-growth forests for their sustainable management. © 2021 The Authors

Wildfires have large-scale and profound effects on forest ecosystems, and they force burned forest areas toward a wide range of post-fire successional trajectories from simple reduction of ecosystem functions to transitions to other stable non-forest states. Fire disturbances represent a key driver of changes in forest structure and composition due to post-fire succession processes, thus contributing to modify ecosystem resilience to subsequent disturbances. Here, we aimed to provide useful insights into wildfire severity and post-fire recovery processes at the European continental scale, contributing to improved description and interpretation of large-scale wildfire spatial patterns and their effects on forest ecosystems in the context of climate change. We analyzed fire severity and short-term post-fire vegetation recovery patterns across the European forests between 2004 and 2015 using Corine Land Cover Forest classes and bioregions, based on MODIS-derived spectral metrics of the relativized burn ratio (RBR), normalized difference vegetation index (NDVI) and relative recovery indicator (RRI). The RBR-based fire severity showed geographic differences and interannual variability in the Boreal bioregion compared to that in other biogeographic regions. The NBR-based RRI showed a slower post-fire vegetation recovery rate with respect to the NDVI, highlighting the differential sensitivities of the analyzed remote sensing-spectral metrics. Moreover, the RRI showed a significant decreasing trend during the observation period, suggesting a growing lag in post-fire vegetation recovery across European forests.

The disturbance and recovery of European Forest ecosystems are greatly affected by wildfires, requiring continued monitoring to observe vegetational structure altered over time. One of the most important parameters is “fire severity” defined as magnitude of environmental change caused by wildfires. Due to correlation between severity and post-fire recovery vegetation, fire severity is an important indicator to define operations in the burned areas. Satellite based-data is becoming a key information for near real-time mapping and monitoring burned area after wildfire disturbances. Moderate resolution Imaging Spectroradiometer (MODIS) time-series data allows for both the capture of the initial disturbance and the ability to monitor the subsequent vegetation regeneration with spectral vegetation indices. In this study, the Google Earth Engine (GEE) platform, was used to analyse post-fire spectral recovery of European forests through the Normalized Difference Vegetation Index (NDVI) and the Relative Recovery Indicator (RRI) based on the Normalized Burn Ratio (NBR). We assessed Normalized Burn Ratio time series in order to determine trends in the short term rates of spectral recovery for three forest land cover classes and European Biogeographic regions disturbed by wildfire (2004-2013), using a series of 5-year post-disturbance time window. NBR pattern of mixed forests showed a lower variability than broadleaved and coniferous forest, indicating high resilience to environmental disturbances. Results indicate different trends of forest recovery according to different spectral indices analysed for European forest ecosystems. During the analysis period (2004-2013) we found that post-fire spectral recovery rates decreased over ten years of observation in each land cover classes and Biogeographic regions. These trends could be related to on-going climate changes affecting the Mediterranean region.Keywords: Fire severity, Forest, Google Earth Engine, Modis (time series), Recovery, Spectral index, Wildfire.

In accordance with European objectives, the Basilicata region intends to promote the use of energy systems and heat generators powered by lignocellulosic biomass, so the present study aimed to investigate the availability of logging residues and most suitable areas for the construction of bioenergy production plants. The life cycle assessment (LCA) methodology was employed to conduct an environmental impact assessment of the biomass distribution and its transport, and spatial LCA was used to evaluate the impact of regional transport. One cubic meter kilometer (m3 km−1) was used as the functional unit and a small lorry was considered for the transport. The results showed that the available harvesting residues amounted to 36,000 m3 and their loading environmental impact accounted for 349 mPt m−3. The impacts of transport (4.01 mPt m−3) ranged from 3.4 to 144,400 mPt km−1 forest parcel−1, mainly affecting human health (95%) and, second, the ecosystem quality (5%). Three possible sites for bioenergy plant location were identified considering the environmental impact distribution due to feedstock transport. Findings from this research show the importance of considering the LCA of biomass acquisition in site selection and can fill the knowledge gaps in the available literature about spatial LCA.

The future trajectory of atmospheric CO2 concentration depends on the development of the terrestrial carbon sink, which in turn is influenced by forest dynamics under changing environmental conditions. An in‐depth understanding of model sensitivities and uncertainties in non‐steady‐state conditions is necessary for reliable and robust projections of forest development and under scenarios of global warming and CO2 enrichment. Here, we systematically assessed if a biogeochemical process‐based model (3D‐CMCC‐CNR), which embeds similarities with many other vegetation models, applied in simulating net primary productivity (NPP) and standing woody biomass (SWB), maintained a consistent sensitivity to its 55 input parameters through time, during forest ageing and structuring as well as under climate change scenarios. Overall, the model applied at three contrasting European forests showed low sensitivity to the majority of its parameters. Interestingly, model sensitivity to parameters varied through the course of >100 yr of simulations. In particular, the model showed a large responsiveness to the allometric parameters used for initialize forest carbon and nitrogen pools early in forest simulation (i.e., for NPP up to ~37%, 256 g C·m−2·yr−1 and for SWB up to ~90%, 65 Mg C/ha, when compared to standard simulation), with this sensitivity decreasing sharply during forest development. At medium to longer time scales, and under climate change scenarios, the model became increasingly more sensitive to additional and/or different parameters controlling biomass accumulation and autotrophic respiration (i.e., for NPP up to ~30%, 167 g C·m−2·yr−1 and for SWB up to ~24%, 64 Mg C/ha, when compared to standard simulation). Interestingly, model outputs were shown to be more sensitive to parameters and processes controlling stand development rather than to climate change (i.e., warming and changes in atmospheric CO2 concentration) itself although model sensitivities were generally higher under climate change scenarios. Our results suggest the need for sensitivity and uncertainty analyses that cover multiple temporal scales along forest developmental stages to better assess the potential of future forests to act as a global terrestrial carbon sink.

L'analisi delle citazioni è un metodo bibliometrico comunemente utilizzato per valutare l'attività scientifica svolta da ricercatori e istituzioni in uno specifico campo di ricerca. In questo lavoro sono valutate e confrontate le riviste forestali italiane peer-reviewed - Annals of Silvicultural Research, Dendronatura, Forest@, iForest, L'Italia Forestale e Montana, Sherwood - attraverso un'analisi bibliometrica basata su indicatori quantitativi. Annals of Silvicultural Research, edita online dal CREA Centro di ricerca Foreste e Legno, pubblica in inglese articoli scientifici, recensioni, relazioni di progetti internazionali e note su tutti gli aspetti connessi alla selvicoltura. iForest e Forest@ sono due riviste online peer-reviewed pubblicate dalla Società Italiana di Selvicoltura ed Ecologia Forestale, la prima in inglese, la seconda in italiano; iForest e Forest@ abbracciano un'ampia gamma di aspetti di ricerca riguardanti le scienze forestali: di particolare interesse sono gli studi che affrontano le basi biologiche ed ecologiche per la gestione sostenibile degli ecosistemi forestali. L'Italia Forestale e Montana è una rivista scientifica online pubblicata dall'Accademia Italiana di Scienze Forestali, che contiene articoli scientifici e recensioni, note tecniche, lettere, opinioni, notizie e recensioni di libri in tutti i campi delle scienze forestali, inclusa la politica e l'economia forestale. Sherwood e Dendronatura, curate rispettivamente da una casa editrice privata e dall'Associazione dei Forestali della provincia di Trento, sono due riviste tecniche dedicate principalmente a decisori, proprietari forestali, forestali professionisti e funzionari forestali e tecnici delle amministrazioni pubbliche. L'impatto bibliometrico di queste riviste forestali è stato analizzato utilizzando i database di Google Scholar e Scopus per il quinquennio 2014-2018.

A major component of climate change is an increase in temperature and precipitation variability. Over the last few decades, an increase in the frequency of extremely warm temperatures and drought severity has been observed across Europe. These warmer and drier conditions may reduce productivity and trigger compositional shifts in forest communities. However, we still lack a robust, biogeographical characterization of the negative impacts of climate extremes, such as droughts on forests. In this context, we investigated the impact of the 2017 summer drought on European forests. The normalized difference vegetation index (NDVI) was used as a proxy of forest productivity and was related to the standardized precipitation evapotranspiration index, which accounts for the temperature effects of the climate water balance. The spatial pattern of NDVI reduction in 2017 was largely driven by the extremely warm summer for parts of the central and eastern Mediterranean Basin (Italian and Balkan Peninsulas). The vulnerability to the 2017 summer drought was heterogeneously distributed over Europe, and topographic factors buffered some of the negative impacts. Mediterranean forests dominated by oak species were the most negatively impacted, whereas Pinus pinaster was the most resilient species. The impact of drought on the NDVI decreased at high elevations and mainly on east and north-east facing slopes. We illustrate how an adequate characterization of the coupling between climate conditions and forest productivity (NDVI) allows the determination of the most vulnerable areas to drought. This approach could be widely used for other extreme climate events and when considering other spatially resolved proxies of forest growth and health.

As reported in several studies, the presence of Abies alba Mill (silver fir) has been declining throughout its natural range over a large part of mountainous belt in the Mediterranean area. In such a context, regeneration establishment depends mainly on the occurrence of a suitable combination of water and light availability. Thus, before planning any forest management practice, it is essential to investigate on the optimal microclimate conditions influencing the success of natural regeneration of silver fir. To this aim, changes in growth and photosynthesis together with C, N and O isotope compositions have been investigated on silver fir naturally recruited saplings, growing in mixed stands with Fagus sylvatica on Apennine mountains (southern Italy). The apical dominance ratio (ADR, ratio between apical shoot length and length of first whorl lateral twigs) has been used as an indicator for microclimate conditions in which saplings grow. Based on the range of ADR values (i.e. from 0.10 to 1.30), saplings were distributed in four classes. As expected, increases in height, root collar diameter and radial growth correspond to enhancing ADR values, gaining the optimal conditions in class IV. This latter also displayed the best performance in terms of maximum CO2 assimilation at saturating light (A max) and water-use efficiency as assessed by carbon isotope discrimination analysis. Conversely, class I and II seem to display the highest performance in terms of CO2 respiration rate (R d) and absolute water loss saving as assessed by the application of oxygen isotopes. We conclude that, in relatively mild Mediterranean areas, forest managers should promote silvicultural treatments favouring light conditions and migration of saplings towards class IV of ADR. This class represents the optimal microclimate for regeneration establishment of silver fir.

We analyzed the Italian National Forest Inventory data set to evaluate the interdependence of forest productivity, tree species richness (used to indicate biodiversity), climate, and soil factors. We tested the hypotheses that the relationship between biodiversity and forest productivity is positive and significant for all forests in Italy and whether the relationship is the same for forests growing in the temperate and Mediterranean bioclimatic domains (regions) of Italy. We used generalized additive models to explore the univariate response curves for the data and then performed structural equation modeling (SEM) and multi-group SEM analyses to evaluate the relationship between biodiversity and productivity. We found that the SEM model for the entire dataset explained about 60% of the variation in forest productivity. In addition, the variation associated with species richness was greater than variation due to climatic factors and the variation in climate factors was greater than the variation in soil factors (all relative to their contributions to productivity). The multi-group SEM showed a more predominant effect of biodiversity and climate on productivity in Mediterranean compared to temperate forests. In both cases, we observed a moderate effect of soil (factors) on forest productivity. Our results support the hypothesis that increasing tree diversity in forests could help reduce the effects of climate warming and enhance ecosystem productivity in the Mediterranean region.

Forest decline induced by climate change is a global phenomenon that affects many tree species, mainly in drought-prone areas as the Mediterranean region. In southern Italy, several oak species have shown decline symptoms and elevated mortality since the 2000s due to drought stress. However, it remains to be answered whether decline occurred alone or whether a pathogen was also involved. To this aim, we compared two coexisting oak species in a forest located in southern Italy which are assumed to be less (Quercus cerris) and more tolerant to drought (Quercus pubescens). We sampled fifteen couples of neighboring declining (D) and non-declining (ND) trees of both species. Wood cores were taken from all trees to perform dendrochronological analyses to detect the decline onset and link it to potential climatic drivers. Carbon isotope ratios (d13C) were analyzed in wood of the two vigor classes to compare their water-use efficiency. Phytophthora presence was also assessed in soil samples from ten D-ND couples of trees per species. The oak species most affected by drought-induced decline in terms of leaf shedding and mortality was Q. cerris, i.e., the least tolerant to drought. In both species, the D trees showed a reduced growth rate compared with ND trees from 2000 onward when drought and warming intensified. Q. pubescens showed higher growth sensitivity to precipitation, temperature and drought than Q. cerris. This sensitivity to climate was magnified in D trees whose growth decreased in response to warm and dry conditions during the prior winter and the late summer. The Q. pubescens D trees were more efficient in their water use than ND trees before the growth divergence between D and ND trees amplified. In the studied area, Phytophthora quercina was isolated from 40% of the sampled trees, and tended to be more frequent amongst ND than amongst D trees. Our data suggests that droughts and warm summer conditions triggered oak decline. The high prevalence of P. quercina in the studied area warrants further study as a potential predisposing factor.

Aim: High‐elevation forest line or tree line is an ecological ecotone representing the upper elevation thermal limit for forest development. The current tree line position is the result of the past human activity interacting with climatic and topographic conditions. In this study, we investigate how climate, local topographic factors and anthropogenic disturbance currently affect tree line distribution. Location: Apennine Mountains, 900 km latitudinal gradient along the Italian Peninsula. Methods: Overall, 302 mountain peaks were studied, comprising 3,622 km of measured tree lines. The position of the Fagus sylvatica tree line in all peaks was assessed and correlated with 58 selected variables representing climate, topography and human disturbance. Results: The mean tree line elevation was 1,589 m a.s.l., with considerable variability among peaks. Contrary to our expectations, the tree line elevation was lower in the warmer southerly exposed slopes compared to north‐facing aspects, where we found the highest tree line (2,141 m a.s.l.). Correlation analysis indicates that both climatic and human density variables are associated with tree line elevation, with the climate having more influence in high elevation mountains, while human impact plays a prominent role in low elevation mountain peaks. Specifically, we found negative correlations between density of the resident population around each peak and tree line elevation at all examined dates (1861, 1921, and 2011), suggesting a pervasive negative impact of human activity on tree lines. As regards climatic variables, tree line elevation showed a stronger negative correlation with winter and spring months temperature than with mean annual temperature. Noteworthy, climatic variables had stronger effect on high elevation peaks (>1,900 m a.s.l.) compared with low elevation ones (

Questions Do vascular plant species richness and β-diversity differ between managed and structurally complex unmanaged stands? To what extent do species richness and β-diversity relate to forest structural attributes and heterogeneity?. Location Five National Parks in central and southern Italy. Methods We sampled vascular plant species composition and forest structural attributes in eight unmanaged temperate mesic forest stands dominated or co-dominated by beech, and in eight comparison stands managed as high forests with similar environmental features. We compared plant species richness, composition and β-diversity, across pairs of stands (unmanaged vs. managed) using Generalized Linear Mixed (effect) Models (GLMMs). β-diversity was quantified both at the scale of each pair of stands using plot-to-plot dissimilarity matrices (species turnover), and across the whole dataset, considering the distance in the multivariate species space of individual plots from the centroid of the plots within the same stand (compositional heterogeneity). We modelled the relationship between species diversity (richness and β-diversity) and forest structural heterogeneity and individual structural variables using GLMMs and Multiple Regression on Distance Matrices. Results Species composition differed significantly between managed and unmanaged stands, but not richness and β-diversity. We found weak evidence that plant species richness increased with increasing levels of structural heterogeneity and canopy diversification. At the scale of individual stands, species turnover was explained by different variables in distinct stands, with variables related to deadwood quantity and quality being selected most often. Conversely, we did not find support to the hypothesis that compositional heterogeneity varies as a function of forest structural characteristics at the scale of the whole dataset. Conclusions Structurally complex unmanaged stands have a distinct herb-layer species composition from that of mature stands in similar environmental conditions; nevertheless, we did not find significantly higher levels of vascular plant species richness and β-diversity in unmanaged stands. β-diversity was related to patterns of deadwood accumulation, while for species richness the evidence that it increases with increasing levels of canopy diversification was weak. These results suggest that emulating natural disturbance, and favoring deadwood accumulation and canopy diversification may benefit some, but not all facets of plant species diversity in Apennine beech forests. This article is protected by copyright. All rights reserved.

In this study, we investigated the role of climatic variability and atmospheric nitrogen deposition in driving long-term tree growth in canopy beech trees along a geographic gradient in the montane belt of the Italian peninsula, from the Alps to the southern Apennines. We sampled dominant trees at different developmental stages (from young to mature tree cohorts, with tree ages spanning from 35 to 160 years) and used stem analysis to infer historic reconstruction of tree volume and dominant height. Annual growth volume (G V ) and height (G H ) variability were related to annual variability in model simulated atmospheric nitrogen deposition and site-specific climatic variables, (i.e. mean annual temperature, total annual precipitation, mean growing period temperature, total growing period precipitation, and standard precipitation evapotranspiration index) and atmospheric CO 2 concentration, including tree cambial age among growth predictors. Generalized additive models (GAM), linear mixed-effects models (LMM), and Bayesian regression models (BRM) were independently employed to assess explanatory variables. The main results from our study were as follows: (i) tree age was the main explanatory variable for long-term growth variability; (ii) GAM, LMM, and BRM results consistently indicated climatic variables and CO 2 effects on G V and G H were weak, therefore evidence of recent climatic variability influence on beech annual growth rates was limited in the montane belt of the Italian peninsula; (iii) instead, significant positive nitrogen deposition (N dep ) effects were repeatedly observed in G V and G H ; the positive effects of N dep on canopy height growth rates, which tended to level off at N dep values greater than approximately 1.0 g m −2 y −1 , were interpreted as positive impacts on forest stand above-ground net productivity at the selected study sites.

International audience; AbstractKey messageA remote sensing-based approach was implemented to detect the effect of a late spring frost on beech forests in the Mediterranean mountain region. The analysis of spatio-temporal variability of frost effects on normalised difference vegetation index (NDVI) highlighted the distribution of the canopy damage across the forest according to geomorphic factors such as slope, aspect, and altitude.ContextIncreased intensity and frequency of extreme temperatures such as late spring frosts and heat waves represent the main drivers affecting forest ecosystem structure and composition in the Mediterranean region.AimsThe main objective of this study was to evaluate the effects of a late spring frost disturbance, which occurred during spring 2016 in southern Italy, through the assessment of the spatial pattern of the damage to the beech forest canopy associated with the peak decrease in normalised difference vegetation index (NDVI), and the analysis of the NDVI temporal recovery after this frost disturbance.MethodsThe forest areas affected by frost were detected through the NDVI differencing technique based on Landsat 8 (OLI/TIRS) imagery time series. The influence of local geomorphic factors (i.e., aspect, elevation, and slope) on forest NDVI patterns was assessed by means of a generalized additive model (GAM).ResultsA rather counterintuitive NDVI patterns emerged according to the forest exposition, with NDVI significantly higher on the north facing areas than the southerly ones. The main canopy damage occurred at about 1250 m and reached up to 1500 m asl, representing the altitudinal range affected by the frost disturbance. Finally, the full canopy recovery occurred within 3 months of the frost event.ConclusionThe analysis of seasonal Landsat 8 image time series related to local geomorphic factors, such as aspect, slope, and altitude, and plant phenology on a frost event date, contributed to highlight the NDVI spatio-temporal variation and canopy recovery of a Mediterranean mountain beech forest.

Hydraulic theory suggests that tall trees are at greater risk of drought-triggered death caused by hydraulic failure than small trees. In addition the drop in growth, observed in several tree species prior to death, is often interpreted as an early-warning signal of impending death. We test these hypotheses by comparing size, growth, and wood-anatomy patterns of living and now-dead trees in two Italian oak forests showing recent mortality episodes. The mortality probability of trees is modeled as a function of recent growth and tree size. Drift-diffusion-jump (DDJ) metrics are used to detect early-warning signals. We found that the tallest trees of the anisohydric Italian oak better survived drought contrary to what was predicted by the theory. Dead trees were characterized by a lower height and radial-growth trend than living trees in both study sites. The growth reduction of now-dead trees started about 10 years prior to their death and after two severe spring droughts during the early 2000s. This critical transition in growth was detected by DDJ metrics in the most affected site. Dead trees were also more sensitive to drought stress in this site indicating different susceptibility to water shortage between trees. Dead trees did not form earlywood vessels with smaller lumen diameter than surviving trees but tended to form wider latewood vessels with a higher percentage of vessel area. Since living and dead trees showed similar competition we did not expect that moderate thinning and a reduction in tree density would increase the short-term survival probability of trees., This research was financially supported by the project “Alarm of forest mortality in Southern Italy” (Gorgoglione Administration, Basilicata Region, Italy) and by the CGL2015-69186-C2-1-R project (Spanish Ministry of Economy).

International audience; AbstractKey messageApical dominance ratio (ADR), reported as a suitable indicator for the growth and development ofAbies alba, is concurrently determined by morphological and functional plant traits. Structural equation modeling (SEM) proved here to be an effective multivariate technique to represent the contribution of different variables in explaining ADR variability.ContextDuring the natural recruitment of understory tree saplings, the light environment and competition among individuals may change drastically as well as their growth patterns. To cope with this, saplings have a remarkable ability to accordingly modify their physiology and morphology. Therefore, understanding the ecological significance of plant structural patterns requires an integrated view of morphological, architectural, and physiological attributes of plants.AimsHere, we applied a SEM approach to understand the mechanisms influencing the ADR, recently reported as suitable indicator of the growth conditions favoring silver fir (Abies alba Mill.) natural regeneration in Mediterranean areas.MethodsA series of plant traits (e.g., root-collar diameter, leaf mass per area, and isotope composition) were combined into two main latent variables, namely Morphology and Physiology, to account for their relative contribution in explaining the ADR variability.• ResultsOur results underline the importance of variables accounting for the photosynthetic capacity and leaf economics in determining ADR; among them, leaf mass per area (LMA) emerged as an important driving variable.• ConclusionSEM proved to be an effective multivariate technique to represent the coordination of different morphological and functional variables in explaining ADR variability in silver fir.

International audience; Drought stress causes forest dieback that is often explained by two interrelated mechanisms, namely hydraulic failure and carbon starvation. However, it is still unclear which functional and structural alterations, related to these mechanisms, predispose to dieback. Here we apply a multi-proxy approach for the characterization of tree structure (radial growth, wood anatomy) and functioning (δ13C, δ18O and non-structural carbohydrates (NSCs)) in tree rings before and after drought-induced dieback. We aim to discriminate which is the main mechanism and to assess which variables can act as early-warning proxies of drought-triggered damage. The study was tailored in southern Italy in two forests (i.e., San Paolo (SP) and Oriolo (OR)) where declining and non-declining trees of a ring-porous tree species (Quercus frainetto Ten.) showing anisohydric behavior coexist. Both stands showed growth decline in response to warm and dry spring conditions, although the onset of dieback was shifted between them (2002 in SP and 2009 in OR). Declining trees displayed a sharp growth drop after this onset with reductions of 49% and 44% at SP and OR sites, respectively. Further, contrary to what we expected, declining trees showed a lower intrinsic water-use efficiency compared with non-declining trees after the dieback onset (with reductions of 9.7% and 5.6% at sites SP and OR, respectively), due to enhanced water loss through transpiration, as indicated by the lower δ18O values. This was more noticeable at the most drought-affected SP stand. Sapwood NSCs did not differ between declining and non-declining trees, indicating no carbon starvation in affected trees. Thus, the characterized structural and functional alterations partially support the hydraulic failure mechanism of dieback. Finally, we show that growth data are reliable early-warning proxies of drought-triggered dieback.

The present study investigated the utility of Moderate Resolution Imaging Spectroradiometer (MODIS)-derived sPRI (scaled photochemical reflectance index) and its relationship to photosynthetic light-use efficiency (LUE) calculated from eddy covariance tower data. The analysis was performed over two consecutive years (2003–2004) in a Mediterranean Quercus cerris L. forest site in Italy. Temperature and rainfall conditions differed markedly over the study period, with 2003 being a notable drought year and 2004 a non-drought year. MODIS ocean bands 11 (centred at 531 nm) and 12 (centred at 551 nm) were used for calculating sPRI. LUE exhibited substantial variability within 2003 and 2004, and a moderate relationship between MODIS-sPRI and LUE was observed during the wet year, and for backscattering scenes. This demonstrated the capacity of sPRI to detect xanthophyll cycle activation by vegetation during high light conditions. However, our results show that sPRI should be used with care, particularly under sev...

Partially mycoheterotrophic (mixotrophic) plants gain carbon from both photosynthesis and their mycorrhizal fungi. This is considered an ancestral state in the evolution of full mycoheterotrophy, but little is known about this nutrition, and especially about the physiological balance between photosynthesis and fungal C gain. To investigate possible compensation between photosynthesis and mycoheterotrophy in the Mediterranean mixotrophic orchid Limodorum abortivum, fungal colonization was experimentally reduced in situ by fungicide treatment. We measured photosynthetic pigments of leaves, stems, and ovaries, as well as the stable C isotope compositions (a proxy for photosynthetic C gain) of seeds and the sizes of ovaries and seeds. We demonstrate that (1) in natural conditions, photosynthetic pigments are most concentrated in ovaries; (2) pigments and photosynthetic C increase in ovaries when fungal C supply is impaired, buffering C limitations and allowing the same development of ovaries and seeds as in natural conditions; and (3) responses to light of pigment and (13)C contents in ovaries shift from null responses in natural conditions to responses typical of autotrophic plants in treated L. abortivum, demonstrating photoadaptation and enhanced use of light in the latter. L. abortivum thus preferentially feeds on fungi in natural conditions, but employs compensatory photosynthesis to buffer fungal C limitations and allow seed development.

The effects of climate change are easily recognizable in the Mediterranean region, one of the most important hotspots of plant biodiversity worldwide. Mediterranean forests are fragile ecosystems threatened by grazing, fires and intensive forest cuttings. Interacting with such disturbances, climate change is fuelling an everincreasing fragmentation process and the loss of ecosystem services.What can trees do to cope with climate change? The main strategies are to migrate, to adapt to new environmental conditions or to rely on phenotypic plasticity. However, it has been estimated that spread rates that allowed a successful escape from past glaciations are far below what would be necessary for species migration to track future climatic warming. In addition, notwithstanding large genetic variation and potentially fast adaptation, there is only anecdotal evidence that forest trees can genetically adapt to contemporary environmental change over a limited number of generations.In the near future, a deep knowledge of evolutionary processes involved in forest tree responses to climate change is required. This must rely on a sound multidisciplinary approach upon which effective strategies for the conservation of forest genetic resources should be based. Only through a joined multi-disciplinary effort, high quality data can be generated to understand the biological processes coming along with ongoing climate change and what is their relative relevance.In the present work, we outline a research project on adaptive responses of Pinus leucordermis. The project is based on the joined evaluation of genetic and ecophysiological characteristics at the individual level from the fragmented populations present in the Pollino National Park. Results on the distribution of genotypic and phenotypic variation along ecological gradients will provide local managers with effective tools for maintaining invaluable forest genetic resources.

This study aimed to assess the combined effects of long-term nitrogen (N) supply and nitrogen deposition (N dep) on carbon (C) accumulation within Sitka spruce [Picea sitchensis (Bong.) Carr.] plantations in Scotland. Six study sites established from 1970 to 1982 were periodically N-fertilized, monitored over time and commonly surveyed in 2010. Soil, aboveground biomass, and ground vegetation C stock changes were analyzed; aboveground C stocks were correlated with total additional N experienced at each site, that is, the sum of experimental N supply (N add) and site-specific accumulated N dep from 1900 to 2010. Results showed a positive N effect on aboveground tree C stock and no decline in tree growth was observed either during fertilization or after the latest N addition. The amount of C in litter was significantly higher in experimentally N-treated plots, whereas the amount of C in understory vegetation was higher in control plots. Pooling all the compartments (that is, understory vegetation, litter, soil, and tree biomass) the total ecosystem C content was estimated for each site, and at most sites a higher C stock was estimated for N-treated plots. Differences in aboveground C accumulation rates between treated and control plots were lower at sites with high levels of accumulated N dep. Our results indicate that site-specific accumulated N dep should be considered to understand tree growth responses to N fertilization.

The objectives of this study were to provide a quantitative description of the long-term effects of environmental variability on xylem functional traits, in order to better assess xylem capacity to change in response to climate change. Twenty-six sites throughout the world, primarily in Europe, were chosen where results from long-term measurements of anatomical traits were previously published. Published data on long-term xylem anatomy (conduit size and density) and ring width variability were compiled across a range of tree species, which was subsequently related to variability in temperature, precipitation and nitrogen deposition rates across the study sites using generalized additive models and Bayesian methods. We found some appreciable relationships between xylem traits (conduit area Ac and conduit density Dc) and environmental variables; whereas combined trait indices (lumen fraction: Ac × Dc and vessel composition: Ac/Dc) were found to be rather constant across a wide range of environmental conditions and to be decoupled from tree growth rates. Overall, results suggested xylem traits coordinated towards a homeostasis in xylem function, which appeared to act across a wide range of environmental conditions. Results showed also nitrogen deposition was associated with xylem traits and vessel composition: Increased nitrogen availability due to nitrogen deposition might facilitate construction of a xylem structure efficient for water transport, and concurrently provide capacity to withstand the risks of drought-induced embolism.

We present the results of a dendrochronological study carried out on timbers from the monastic abbey Grancia of Brindisi di Montagna in Southern Italy. Our objective was to date cross-sections of oak (Quercus spp.) taken from structural timbers to determine the felling dates, the time span covered by the series and to evaluate whether the retrieved tree-ring data could be used to extend an existing living trees chronology of oak from Southern Italy. Dendrochronological analyses were performed on samples collected from eight oak timbers in 2006 during the restoration of the abbey. Raw tree-ring series were crossdated and grouped into a floating chronology that was compared with an absolute reference chronology, specifically constructed from living Quercus pubescens (Willd.) trees, from the nearby Pollino National Park. Seven of eight samples could be absolutely dated in the early 19th, late 18th and mid late 17th Centuries, providing a chronology that reaches back to AD 1545.

This study aimed to evaluate the effects of long-term repeated aerial nitrogen (N) and sulphur (S) misting over tree canopies of a Sitka spruce plantation in Scotland. We combined δ13C and δ18O in tree rings to evaluate the changes in CO2 assimilation (A) and stomatal conductance (gs) and to assess their contribution to variations in the intrinsic water-use efficiency (WUEi, i.e., the A/gs ratio). Measurements of δ15N enabled shifts in the ecosystem N cycling following misting to be assessed. We found that: (i) N applications, with or without S, increased the ratio between A and gs in favour of A, thus supporting a fertilizer effect of added N. (ii) After the treatments ceased, the trees quickly adjusted to the reductions of N deposition, but not to the reduction in S deposition, which had a negative effect on WUEi by reducing A. This indicates that the beneficial role of N deposition may be negated in forests that previously received a high load of acid rain. (iii) δ15N in tree rings reflected the N dynamics caused by canopy retention, with the fingerprint also present in the litter, after the experiment stopped. (iv) Both our results (obtained using canopy applications) and a collection of published data (obtained using soil applications) showed that generally WUEi increased in response to an increase of N applications, with the magnitude of the changes related to soil conditions and the availability of other nutrients. The shifts observed in δ15N in tree rings also suggest that both the quantity of the applied N and its quality, mediated by processes occurring during canopy N retention, are important determinants of the interactions between N and C cycles. Stable isotopes are useful probes to understand these processes and to put the results of short-term experiments into context.

A partire dagli studi condotti da Pavari sulla coltivazione delle specie esotiche in Italia, il lavoro esplora alcuni aspetti dell’autoecologia delle piante soffermandosi sull’analisi dei concetti di plasticita fenotipica e acclimatazione

Si mostra come le ricerche degli ultimi vent’anni sul bilancio del carbonio delle foreste abbiano consentito: l’individuazione di rilevanti processi di assorbimento dell’anidride carbonica atmosferica negli ecosistemi forestali, comprese le foreste primarie; il riconoscimento della respirazione ecosistemica come componente decisiva del bilancio del carbonio; l’apprezzamento della variabilita interannuale dei processi di scambio e della loro regolazione da parte delle condizioni ambientali; il riconoscimento che la capacita di assorbimento delle foreste e della biosfera puo essere indebolita da fattori di disturbo e che alcune componenti ecosistemiche, come i suoli, sono vulnerabili e potrebbero restituire all’atmosfera parte della gran quantita di carbonio accumulata nel corso dei secoli. Si evidenzia, peraltro, che diversi aspetti del funzionamento ecosistemico e delle interazioni fra i fattori del cambiamento globale, in primo piano la relazione fra i cicli del carbonio e dell’azoto, richiedono una migliore interpretazione, e che i modelli di circolazione generale rappresentano in modo ancora inadeguato alcuni processi che potrebbero essere decisivi nella regolazione degli scambi di materia ed energia fra biosfera e atmosfera. Per questi motivi esiste ancora incertezza sul ruolo che, negli anni a venire, le foreste e la biosfera svolgeranno nella mitigazione dell’effetto serra e del cambiamento climatico.

The importance that nitrogen (N) deposition has in driving the carbon (C) sequestration of forests has recently been investigated using both experimental and modeling approaches. Whether increased N deposition has positive or negative effects on such ecosystems depends on the status of the N and the duration of the deposition. By combining delta(13)C, delta(18)O, delta(15)N and dendrochronological approaches, we analyzed the impact of two different sources of NO(x) emissions on two tree species, namely: a broad-leaved species (Quercus cerris) that was located close to an oil refinery in Southern Italy, and a coniferous species (Picea abies) located close to a freeway in Switzerland. Variations in the c(i)/c(a) ratio and the distinction between stomatal and photosynthetic responses to NO(x) emissions in trees were assessed using a conceptual model, which combines delta(13)C and delta(18)O, delta(15)N in leaves, needles and tree rings was found to be a bioindicator of N input from anthropogenic emissions, especially at the oil refinery site. We observed that N fertilization had a stimulatory effect on tree growth near the oil refinery, while the opposite effect was found for trees at the freeway site. Changes in the c(i)/c(a) ratio were mostly related to variations in delta(13)C at the freeway site and. thus, were driven by photosynthesis. At the oil refinery site they were mainly related to stomatal conductance, as assessed using delta(18)O. This study demonstrates that a single method approach does not always provide a complete picture of which physiological traits are more affected by N emissions. The triple isotope approach combined with dendrochronological analyses proved to be a very promising tool for monitoring the ecophysiological responses of trees to long-term N deposition. (C) 2008 Elsevier Ltd. All rights reserved.