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Old-growth forests have an important role in maintaining animal and plant diversity, are important carbon (C) reservoirs and are privileged sites to study long-term plant physiological responses, long-term forest dynamics and climate change impact on forest ecosystems. Several studies have highlighted how old-living trees undergo age-related declines with hydraulic limitations and reduction in photosynthesis, though some recent works have suggested that such a decline is not always observed. Our study aims at understanding the role of atmospheric CO2 increase on tree C uptake and stomatal conductance (gs) in old-living trees by analysing the long-term patterns of tree growth and intrinsic water use efficiency (iWUE) in three old-growth forests in the Balkans (Bosnia-Herzegovina and Montenegro), using dendrochronology and isotopic analysis. We hypothesised a long-term increase in iWUE in the studied old-growth forests, mostly related to enhanced photosynthesis rather than reduced stomatal conductance. Tree cores were sampled from dominant silver fir (Abies alba Mill.) trees in each forest. Tree-ring widths were measured and basal area increments (BAI) were assessed for each sampled tree and, from the six longest chronologies, five decades were chosen for cellulose extraction, its isotopic analysis (δ13C, δ18O), iWUE and leaf water 18O evaporative enrichment above the source water (Δ18OL) determination. We observed a continuous and significant increase in iWUE from 1800 to 2010 in the sampled dominant trees at all the three old-growth forests. Our BAI data and our estimates of Δ18OL across the study period support the idea that enhanced photosynthesis rather than reduced stomatal conductance is the major driver of the measured iWUE increase. Thus, our results support some recent findings challenging the hypothesis that iWUE in forests is primarily the result of a CO2-induced reduction in stomatal conductance as well as the so called hydraulic limitation hypothesis. [ABSTRACT FROM AUTHOR]

During the last millennia, all forests of the Italian Alps have been heavily affected by human land-use. Consequently, forest structures have been modified, and there are no old growth remains. In the last decades, however, many forests have been withdrawn from regular management, because wood production was unprofitable, and left to develop naturally. At the same time, in currently managed forests, silvicultural systems able to develop or maintain old-growth characteristics are being required. The aim of this paper was to assess the status and developmental dynamics of old-growth characteristics in mixed beech, silver fir, and Norway spruce montane forests of the eastern Italian Alps. We selected along a naturalness gradient (a) three old-growth forests in Bosnia and Montenegro (due to the lack of old-growth forests in the Italian Alps), (b) two forests withdrawn from regular management for at least 50 years, and (c) three currently managed forests. In each forest, we analysed 17 structural attributes, in order to assess their value as indicators of old-growth condition. Old-growth forests were characterized by significantly higher amounts of live and dead biomass, share of beech in the dominant and regeneration layers, and number of large trees. The diameter distribution was best described as a rotated sigmoid, differently from currently and formerly managed forest. We discuss the differences in old-growth characteristics across the management gradient and use our results to evaluate the effectiveness of retention prescriptions currently applied in the studied regions in maintaining or promoting old-growth structural attributes in managed forests. [ABSTRACT FROM AUTHOR]

Climate forcing is the major abiotic driver for forest ecosystem functioning and thus significantly affects the role of forests within the global carbon cycle and related ecosystem services. Annual radial increments of trees are probably the most valuable source of information to link tree growth and climate at long-term time scales, and have been used in a wide variety of investigations worldwide. However, especially in mountainous areas, tree-ring studies have focused on extreme environments where the climate sensitivity is perhaps greatest but are necessarily a biased representation of the forests within a region. We used tree-ring analyses to study two of the most important tree species growing in the Alps: Norway spruce (Picea abies) and silver fir (Abies alba). We developed tree-ring chronologies from 13 mesic mid-elevation sites (203 trees) and then compared them to monthly temperature and precipitation data for the period 1846-1995. Correlation functions, principal component analysis and fuzzy C-means clustering were applied to 1) assess the climate/growth relationships and their stationarity and consistency over time, and 2) extract common modes of variability in the species responses to mean and extreme climate variability. Our results highlight a clear, time-stable, and species-specific response to mean climate conditions. However, during the previous-year's growing season, which shows the strongest correlations, the primary difference between species is in their response to extreme events, not mean conditions. Mesic sites at midaltitude are commonly underrepresented in tree-ring research; we showed that strong climatic controls of growth may exist even in those areas. Extreme climatic events may play a key role in defining the species-specific responses on climatic sensitivity and, with a global change perspective, specific divergent responses are likely to occur even where current conditions are less limited. [ABSTRACT FROM AUTHOR]

Knowledge on the range of variability of montane European forests is hampered by limited data on the natural disturbance regime and by the small size of old-growth remnants. We studied the mixed -- Lom forest reserve (55.8 ha) in Bosnia and Herzegovina at three different scales: a grid of 40 sampling points to describe the structural characteristics and their range of variability, three transects to analyse gap size and gap fraction, and a 1.1 ha permanent plot to reconstruct age structure and disturbance history. The forest is characterized by a high volume of living trees (763 m3·ha-1 in the 55.8 ha core area and 1160 m3·ha-1 in the permanent plot) and of coarse woody debris (327 and 383 m3·ha-1, respectively). The percentages of forest area in canopy and expanded gaps are 19% and 41%, respectively. The median canopy gap size is 76.9 m2 and ranges from 11.1 to 708.0 m2. There are large (up to 120 cm diameter at breast height) and very old trees (441, 432, and 416 years for silver fir ( Mill.), Norway spruce ( (L.) Karst.), and European beech ( L.), respectively). During the last three centuries, the disturbance patterns have been characterized by single-tree or small group mortality. In central Europe, this forest is at the end of a gradient from forests characterized by intermediate disturbances to those where very small-scale processes predominate. [ABSTRACT FROM AUTHOR]

Spatiotemporal development and human impact on dynamic processes were investigated in the mixed European larch (Larix decidua Mill.) and Swiss stone pine (Pinus cembra L.) subalpine forest of Lago Perso (Piedmont, Italy). We mapped and measured all 295 trees (DBH ≥4 cm) and 914 saplings (>10 cm height, <4 cm DBH) in a permanent plot (1 ha). One core per tree was extracted upslope at 50 cm height, and dendrochronological techniques were applied to reconstruct age structure and growth patterns. All of the data collected were stored in a GIS, and tree and stem crown maps were generated and analysed to quantify spatial patterns. Ripley's K(t) univariate and bivariate point pattern analyses were employed to assess the degree of spatial autocorrelation. Documentary research was conducted to reconstruct human land use. The stand is uneven-aged, and there were no obvious age cohorts or other evidence of major disturbances in the past. Stone pine saplings and trees and larch saplings exhibited a clumped structure. The same clumping was not so evident in larch trees. The observed structural changes are mainly related to human land use and grazing regime. Although human influence is still manifest, in the recent decades natural dynamics have become the predominant influence on the forest's structure and processes. [ABSTRACT FROM AUTHOR]

Abstract. A study of the forest lines, tree lines and the structures of the sub-alpine forest was performed in Vallone Vallanta and in Alevé forest in the Varaita Valley (Cottian Alps, Piedmont, Italy). Forest- and tree lines were analysed over 1728 ha while forest structures were studied on six 3000-m 2 plots located at the tree line (2), at the forest line (2) and inside the sub-alpine forest (2). Dendro-ecological analysis of living plants and stumps showed that Larix decidua was more abundant in the past than today and that Pinus cembra has expanded, both upwards and within sub-alpine forests. Age structure analysis revealed that the current sub-alpine forest stands were established 200 - 220 yr ago, probably following a clearcut. At the forest lines the tree density decreases, and some trees are more than 500 yr old, whereas at the tree lines most of the trees (almost exclusively Pinus cembra) are younger than 100 yr. Growth dynamics were investigated both by observing Basal Area Increment (BAI) in the old and dominant trees, and by comparing the BAIs of classes of trees with a given cambial age range in different time periods. The results showed that the growth rates of mature Pinus cembra and Larix decidua had increased. These increments are more substantial for Pinus than for Larix. The growth rate of young trees (100 yr) of both species has decreased over recent decades. This could be due to competition caused by increased tree densities that have resulted from a decrease in grazing. [ABSTRACT FROM AUTHOR]

Tree regeneration is a key demographic process influencing long‐term forest dynamics. It is driven by climate, disturbances, biotic factors and their interactions. Thus, predictions of tree regeneration are challenging due to complex feedbacks along the wide climatic gradients covered by most tree species. The stress gradient hypothesis (SGH) provides a framework for assessing such feedbacks across species ranges, suggesting that competition between trees is more frequent under favourable conditions, whereas reduced competition (i.e. positive interactions) is more likely under climatic stress. Moreover, tree life‐history strategies (LHS) may shed light on how and whether the SGH explains regeneration of different tree species.To address these topics, we developed statistical models based on >50,000 recruitment events observed for 24 tree species in an extensive permanent plot network (6540 plots from 299 unmanaged European temperate, boreal and subalpine forests) covering a wide climatic gradient.We found that the effects of Leaf Area Index (as a proxy for competition) on tree recruitment changed along climatic gradients but in a species‐specific manner. Competition predominates, with its intensity decreasing under stressful conditions for most species, as predicted by the SGH. However, positive interactions were only evident for a few species. Additionally, the ability of the SGH to explain patterns of competition and positive interactions across the gradients differed among species, with some differences and exceptions that may be related to varying LHS.Synthesis. Our study shows that competition between trees toward climatic stress decreases systematically but depends on species stress tolerance to climate and shade. These findings explain within‐ and between‐species differences in tree recruitment patterns in European temperate forests. Moreover, our findings imply that projections of forest dynamics along wide climatic gradients and under climate change must accommodate both competition and positive interactions, as they strongly affect rates of community turnover. [ABSTRACT FROM AUTHOR]

Forest biomass is a renewable energy source, more climate-friendly than fossil fuels and widely available in Europe. The wood energy chain has been suggested as a means to re-activate forest management and improve the value of forest stands in marginalized rural areas. However, wall-to-wall estimates of forest biomass, needed to design the location and size of power and heat biomass plants in any given territory, are notoriously difficult to obtain. This paper tests an algorithm to predict forest biomass using publicly available Landsat satellite imagery in the Liguria region, northern Italy. We used regional forest inventory data to train and validate an artificial neural network (ANN) classifier that uses remotely-sensed information such as three principal components of Landsat-5 TM spectral bands, the Enhanced Vegetation Index (EVI), and topography, to retrieve aboveground live tree volume. Percent root mean square error was -9% and -23% for conifers and broadleaves respectively in the calibration dataset, and -27% and -24% in the validation dataset. The reconstructed volume map was updated to present day using current volume increment rates reported by the Italian National Forest Inventory. A wall-to-wall map of forest biomass from harvest residues was finally produced based on species-specific wood density, biomass expansion factors, volume logged for timber assortments, forest accessibility, and topography. Predicted aboveground forest volume ranged from 81 to 391 m³ ha-1. In forests available for wood supply (70% of the total), planned volume removals averaged 25.4 m³ ha-1, or 18.7% of the average standing stock across. Biomass available for bioenergy supply was 1.295.921 million Mg dry matter or 8.95 Mg ha-1. This analysis workflow can be replicated in all mountain regions with a predominant broadleaved coppice component. [ABSTRACT FROM AUTHOR]

We present the first high-resolution Holocene pollen, plant-macrofossil, and charcoal records from the upper-montane zone in the central Dinaric Alps. Drawing on these new records from well-dated lacustrine sediments of Zminje Jezero (ca. 1500 m a.s.l.; Montenegro) and on independent chironomid-inferred summer temperatures, we explore long-term ecosystem responses to variations in climate, fire disturbances and land use, as well as legacy effects of past environmental changes. A mixed spruce-fir forest established in the upper-montane zone around 9500 cal BP, and Fagus sylvatica became co-dominant with the two conifers after 5000 cal BP. Prehistoric land-use pressure was overall remarkably low, but increased since 2000 cal BP and was highest after the Middle Ages. We found a significant positive relationship between biomass burning and summer temperature, indicating that fires were mostly climate driven. Picea abies was insensitive to summer temperature, biomass burning and human impact, which supports the view that spruce forests may not be significantly impacted by fire. In contrast, Abies alba and other disturbance-sensitive trees (Tilia, Ulmus, Fraxinus excelsior -type) show significant negative responses to land-use pressure and positive responses to summer temperature. This supports the notion that these species may be well-adapted to warmer-than present summer temperatures and that their populations declined in recent millennia due to land-use activities. Conversely, F. sylvatica was sensitive to summer temperatures but was promoted by low biomass burning, indicating that its expansion in the spruce-fir dominated forest was enhanced by the onset of cooler and possibly also moister climatic conditions as well as by fire disturbances. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "The largest European forest carbon stocks are in the Dinaric Alps old-growth forests: comparison of direct measurements and standardised approaches" published in the journal Carbon Balance & Management. The correction addresses errors in the article title and the author group. The corrected article can be found at the provided link. The publisher, Springer Nature, remains neutral in terms of jurisdictional claims and institutional affiliations. The authors of the article are Alessia Bono, Giorgio Alberti, Roberta Berretti, Milic Curovic, Vojislav Dukic, and Renzo Motta. [Extracted from the article]

In the southern part of the Alps the intensive use of forests for domestic animals has declined this century and particularly during the last few decades. After the Second World War wild ungulates, rare or absent at the beginning of this century, increased in number and expanded their range. Mountain forests are very vulnerable to ungulate damage owing to the long periods needed for regeneration processes. In this study, the impact of ungulate browsing on forest regeneration was investigated in 10 areas of the Italian Alps. The incidence of browsing damage on forest regeneration (10-150 cm height) was found to vary between 52.8% in the most severely damaged area and 6.9%, in the least affected area. The lethality of browsing damage (used as index of browsing intensity) was found to he nil in 4 areas out of ten and up to 17.2170 in the areas with the highest ungulate density. Ungulate density is not the only factor influencing degree of browsing damage; winter tourism and land and road settlements in potential ungulatewinter ranges also play an important role. Naturalistic silvicultureis the most profitable system for the conservation and the sustainability of the whole forest ecosystem but high ungulate densities prevent its application. [ABSTRACT FROM AUTHOR]

Silver fir Abies alba is an indigenous tree species present in many southern European mountain forests. Its distribution area and its adaptive capacity to climate variability, expressed in tree-ring growth series, make it a very suitable target species for studying responses to climate particularly in a complex area like the Mediterranean basin where significant changes are expected. We used a set of 52 site chronologies (784 trees) in the Italian Alps and Apennines (38.1°– 46.6°N and 6.7°– 16.3°E) and temperature and precipitation monthly data for the period 1900–1995. Principal component analyses of the tree-ring site network was applied to extract common modes of variability in annual radial growth among the chronologies. Climate/growth relationships and their stationarity and consistency over time were computed by means of correlation and moving correlation functions. Tree-ring chronologies show a clear distinction between the Alpine and the Mediterranean sites and a further separation of the Alpine region in western and eastern sectors. Accordingly, we found different transient and contrasting regional responses in time with the trends found in the Mediterranean sites marking a relaxation of some of the major climate limiting factors recorded prior to the last decades. Species’ sensitivity to global change may result in distinct spatial responses reflecting the complexity of the Mediterranean climate, with large differences between various areas of the basin. It is still unclear if these contrasting tree-ring growth to climate responses of Abies alba are due to the corresponding separation between the Alpine and Mediterranean climate modes, the atmospheric CO2 fertilization effect, the environmentally most fitted genetic pools of the southern fir ecotypes or a combination of all factors. Climate–growth analysis based on a wide site network and on long-term weather records confirmed to be excellent tools to detect spatial and temporal variability of species’ responses to climate. [ABSTRACT FROM AUTHOR]

Questions: What is the structure of the anthropogenic upper forest-grassland ecotone and are there differences in the spatial relationships between the tree species involved? Location: Valfurva Valley, Italian central Alps. Methods: We conducted a spatial distribution and structure analysis in three 1-ha permanent plots along an altitudinal gradient, from the treeline to the sub-alpine forest. We reconstructed the age structure from cores from each individual with diameter > 4 cm at 50 cm height. Results: All tree species and age classes examined had a clumped structure. The cluster tendency was more evident at the treeline where the environmental conditions are more severe. In the sub-alpine forest there was a repulsion between Pinus cembra and Pious mugo but at the treeline P. cembra was frequently found downslope from P. mugo. Conclusions: Although human influence has been the main driving force in shaping the present forest structure, in the last few decades natural dynamics have become the predominant force acting on forest structure and processes, showing a higher magnitude as altitude increases. Our results emphasize the existence of facilitating and interfering mechanisms between different species. P. cembra seems to be favoured compared to the other tree species. [ABSTRACT FROM AUTHOR]

In the European Alps, subalpine forests are important for lichen diversity conservation at multiple levels. However, the potential role of coarse woody debris (CWD) has been only marginally considered in the previous literature. The aims of this case study are (i) to provide a first evaluation of the effects of different types of CWD (stumps, logs, and snags) and wood decay on lichen diversity in Pinus-Larix forests in the Italian Alps, and (ii) to increase the knowledge of the lichen biota on CWD in Italy. Seventy-eight species were found, including 12 nationally rare and 10 calicioid species; Placynthiella hyporhoda is new to Italy. Different types of CWD in different decay stages had significantly different lichen communities. Snags seem to be particularly effective for conservation, since they host the highest number of nationally rare species. Our survey suggests that CWD could be an important substratum for several nationally rare species, indicating that further surveys at a regional scale are urgently required in order to evaluate the role of CWD for lichen diversity conservation in the Alps. [ABSTRACT FROM PUBLISHER]

Aims: Primary forests are critical for forest biodiversity and provide key ecosystem services. In Europe, these forests are particularly scarce and it is unclear whether they are sufficiently protected. Here we aim to: (a) understand whether extant primary forests are representative of the range of naturally occurring forest types, (b) identify forest types which host enough primary forest under strict protection to meet conservation targets and (c) highlight areas where restoration is needed and feasible. Location: Europe. Methods: We combined a unique geodatabase of primary forests with maps of forest cover, potential natural vegetation, biogeographic regions and protected areas to quantify the proportion of extant primary forest across Europe's forest types and to identify gaps in protection. Using spatial predictions of primary forest locations to account for underreporting of primary forests, we then highlighted areas where restoration could complement protection. Results: We found a substantial bias in primary forest distribution across forest types. Of the 54 forest types we assessed, six had no primary forest at all, and in two‐thirds of forest types, less than 1% of forest was primary. Even if generally protected, only ten forest types had more than half of their primary forests strictly protected. Protecting all documented primary forests requires expanding the protected area networks by 1,132 km2 (19,194 km2 when including also predicted primary forests). Encouragingly, large areas of non‐primary forest existed inside protected areas for most types, thus presenting restoration opportunities. Main conclusion: Europe's primary forests are in a perilous state, as also acknowledged by EU's "Biodiversity Strategy for 2030." Yet, there are considerable opportunities for ensuring better protection and restoring primary forest structure, composition and functioning, at least partially. We advocate integrated policy reforms that explicitly account for the irreplaceable nature of primary forests and ramp up protection and restoration efforts alike. [ABSTRACT FROM AUTHOR]

In a context of progressive expansion of the Italian forest area, we present the results of a national survey exploring public perception of forests across different geographical scales in Italy. Perceptions of forests are assessed in relation to popular beliefs on relevant environmental issues such as countering climate change, protecting biodiversity, and promoting social cohesion and environmental education. Participants (N = 1059) living in five different regions of Northern (Trentino-Alto Adige/Südtirol, Piemonte), Central (Lazio, Molise) and Southern Italy (Puglia), were recruited in the survey and completed a paper-and-pencil questionnaire. Survey questions regarded the estimated percentage of forest cover, the perceived importance of different environmental issues and of different material and non-material forest products, as well as participants' perceptions regarding connectedness to nature. Results revealed a generalized tendency to overestimate the extension of forest surface area in the participants' region, in Italy, and in the European Union. Results also showed high scores for participants' perceived importance of environmental issues, such as climate change and biodiversity protection, and in their belief that forests could play a positive role in addressing these issues and providing important outcomes and benefits for the quality of human life, such as health and well-being or social cohesion. [ABSTRACT FROM AUTHOR]

Biogradska Gora National Park in Montenegro is part of the Dinaric Mountains mixed forest, which belongs to the montane region of the Dinaric Alps. This paper presents some of the main structural and ecological characteristics of the mixed broadleaved old-growth forest with beech [Fagus moesiaca (Domin, Maly) Czecz.], sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelsior L.) from the preserve area of the Biogradska Gora. These forest ecosystems are characterized by the high species richness and potential productivity. In the study area, 58 vascular plant species were recorded in 4 sample plots of 0.25 ha each. The average timber volume found in the sample plots was 814 m3/ha. This value is twice as high as that of similar pure beech forests in the same preserve area. The results are confirmed the biodiversity and production potential of mixed broadleaved forests, which rarely occur spontaneously. A better understanding of the processes of the pristine forest ecosystems could form a realistic basis for close-tonature management of similar stands. The obtained data provides overview of the structural characteristics of these forests, which have developed without anthropogenic influence. Exploring the structure of forests in permanent preservation areas could be an excellent basis for close-to-nature forest management. [ABSTRACT FROM AUTHOR]

Synchronous pulses of seed masting and natural disturbance have positive feedbacks on the reproduction of masting species in disturbance‐prone ecosystems. We test the hypotheses that disturbances and proximate causes of masting are correlated, and that their large‐scale synchrony is driven by similar climate teleconnection patterns at both inter‐annual and decadal time scales.Hypotheses were tested on white spruce (Picea glauca), a masting species which surprisingly persists in fire‐prone boreal forests while lacking clear fire adaptations. We built masting, drought and fire indices at regional (Alaska, Yukon, Alberta, Quebec) and sub‐continental scales (western North America) spanning the second half of the 20th century. Superposed Epoch Analysis tested the temporal associations between masting events, drought and burnt area at the regional scale. At the sub‐continental scale, Superposed Epoch Analysis tested whether El Niño‐Southern Oscillation (ENSO) and its coupled effects with the Atlantic Multidecadal Oscillation (AMO) in the positive phase (AMO+/ENSO+) synchronize drought, burnt area and masting. We additionally tested the consistency of our synchronization hypotheses on a decadal temporal scale to verify whether long‐term oscillations in AMO+/ENSO+ are coherent to decadal variation in drought, burnt area and masting.Analyses demonstrated synchronicity between drought, fire and masting. In all regions the year before a mast event was drier and more fire‐prone than usual. During AMO+/ENSO+ events sub‐continental indices of drought and burnt area experienced significant departures from mean values. The same was observed for large‐scale masting in the subsequent year, confirming 1‐year lag between fire and masting. Sub‐continental indices of burnt area and masting showed in‐phase decadal fluctuations led by the AMO+/ENSO+. Results support the 'Environmental prediction hypothesis' for mast seeding.Synthesis. We provide evidence of large‐scale synchronicity between seed masting in Picea glauca and fire regimes in boreal forests of western North America at both inter‐annual and decadal time scales. We conclude that seed production in white spruce predicts changes in disturbance regimes by sharing the same large‐scale climate drivers with drought and fire. This gives new insides in a mechanism providing a fire‐sensitive species with higher than expected adaptability to changes in climate. [ABSTRACT FROM AUTHOR]

The assessment of fire severity is a fundamental step required in the definition of post-disturbance management activities and priorities. Detecting and mapping the spatial heterogeneity of different severity classes within the fire perimeter allows to better distributing in time and space eventual post-fire restoration interventions. The present study describes the assessment of fire severity realized following the nine big fire events that burned almost 10000 ha in the Piedmont region during autumn 2017 (burned area per each fire ranging from 164 to 3974 ha). Two distinct methodologies, Burn Remote Sensing involving remote sensing data and a complementary field sampling approach, were integrated to characterize first and second order fire effects on the different components of the burned forest stands. Two timeframes of acquisition were applied to identify effects soon after fire and during the next growing season for Initial and Extended Assessments, respectively. The latter includes vegetative recovery potential and delayed mortality. Change detection techniques able to catch the difference of spectral signals from forests after the fire were applied. The applied methodology utilizes multispectral images acquired before and after the fire by the MSI sensor (MultiSpectral Instrument) on the Sentinel-2 satellites (European spatial programme Copernicus). The Normalized Burn Ratio (NBR), the standard index currently used for the detection of the fire perimeter and the assessment of fire severity, was computed. This index uses the Near infrared (NIR) and the Shortwave infrared (SWIR) spectral bands. The B8a (NIR) and the B12 (SWIR2) bands with a 20 m spatial resolution were used to compute the NBR values for the pre and post-fire scenarios. We then derived the delta Normalized Burn Ratio (dNBR) by subtracting the NBR post-fire from the NBR pre-fire values for each pixel. In order to reduce the noise produced by the phenological differences between the pre and post-fire periods, dNBR values have been calibrated with a value obtained from unburned stands. Burn indices based on field data were tested (e.g. CBI – Composite Burn Index e GeoCBI – Geometrically Structured Composite Burn Index), applying a stratified sampling design according to forest categories and severity classes (as defined with the dNBR). These indices were used to calibrate and validate remote sensing results, relating detected radiometric change to actual fire effects on the ground. [ABSTRACT FROM AUTHOR]

• Soil amelioration practices were tested to accelerate vegetation restoration. • Zeolitite addition improved some soil properties but weakly affected vegetation. • Herbaceous layer establishment increased soil properties and seedling performances. • Meteorological conditions and time since restoration affected restoration trajectory. • Proper site preparation can accelerate recovery rate of soil properties. Zeolitites, rocks with a content of zeolite group minerals greater than 50%, can serve as support for plant nutrients uptake, by enabling the slow release of macro- and micronutrients over time. Zeolitites equally improve soil cation exchange and water holding capacity. We analyzed the effect of zeolitite addition to the soil in forest restoration. We hypothesized that zeolitite ameliorated soil quality and consequently improved sward restoration and seedling establishment. Soil treatments were applied in 2014 and consist of: ploughed and ripped soil (non-amended) and ploughed, ripped and amended with zeolitite soil (amended). After application of the soil treatments, a herbaceous mixture was hand sown. Oak (Quercus robur L.), hawthorn (Crataegus monogyna Jacq.) and elm (Ulmus minor Mill.) seedlings were planted twice in the area, in autumn 2014 and autumn 2015. We monitored soil, sward and seedlings from 2015 to 2017. Seedling survival, which was generally above 50%, was never affected by zeolitite addition. The effect on seedling growth was significant only for hawthorn planted in 2015 that was approximately 5 cm taller in the amended soil. Herbaceous vegetation was also slightly affected by zeolitite addition. The zeolitite increased nitrogen (N) and phosphorus (P) Olsen in 2015, and exchangeable potassium (K) during the whole study period. Other parameters, such as year and growing season had significant effects on soil, sward and seedling dynamics. Time since restoration, plant-plant interactions, mechanical site preparation and meteorological conditions all together influenced the restoration dynamics more than zeolitite application. [ABSTRACT FROM AUTHOR]

Climatically controlled allocation to reproduction is a key mechanism by which climate influences tree growth and may explain lagged correlations between climate and growth. We used continent‐wide datasets of tree‐ring chronologies and annual reproductive effort in Fagus sylvatica from 1901 to 2015 to characterise relationships between climate, reproduction and growth. Results highlight that variable allocation to reproduction is a key factor for growth in this species, and that high reproductive effort ('mast years') is associated with stem growth reduction. Additionally, high reproductive effort is associated with previous summer temperature, creating lagged climate effects on growth. Consequently, understanding growth variability in forest ecosystems requires the incorporation of reproduction, which can be highly variable. Our results suggest that future response of growth dynamics to climate change in this species will be strongly influenced by the response of reproduction. [ABSTRACT FROM AUTHOR]

Human activities have the potential to enhance carbon sequestration by the world's forests and contribute to climate change mitigation. Voluntary carbon trading is currently the only option to pursue and reward carbon sequestration by forestry activities. Carbon credits for enhanced sequestration can be sold to partners wishing to offset their own emissions. Here we illustrate the steps taken to design guidelines for the generation of voluntary carbon credits by improved forest management in Piemonte, Italy. The guidelines have been developed in a joint effort by academia, regional administrations, forest owners and professional consultants. In particular, we show how to compute the baseline and the additionality of credit-generating forest management activities, and how to reconcile the generation of forest carbon credits with law requirements, technical limitations, and the provision of other ecosystem services. To illustrate the profitability of carbon credit generation, we simulated the application of carbon credit guidelines to two forest-rich mountain watersheds in the southern part of the Piemonte region. The two dominating tree species are beech (Fagus sylvatica L.) and chestnut (Castanea sativa Mill.). We computed current forest carbon stock and carbon credits generated in 20 years under business as usual and an alternative biomass retention scenario. The IFM resulted in an avoided harvest of 39,362 m³ for a net total of 64,014 MgCO2e after subtracting harvest emissions, or 38 Mg ha-1 throughout the permanence period of 20 years. These steps can be replicated in other mountain regions where there is interest in promoting this ecosystem service as an alternative or an addition to production-oriented forest management. [ABSTRACT FROM AUTHOR]

Human activities have the potential to enhance carbon sequestration by the world's forests and contribute to climate change mitigation. Voluntary carbon trading is currently the only option to pursue and reward carbon sequestration by forestry activities. Carbon credits for enhanced sequestration can be sold to partners wishing to offset their own emissions. Here we illustrate the steps taken to design guidelines for the generation of voluntary carbon credits by improved forest management in Piemonte, Italy. The guidelines have been developed in a joint effort by academia, regional administrations, forest owners and professional consultants. In particular, we show how to compute the baseline and the additionality of credit-generating forest management activities, and how to reconcile the generation of forest carbon credits with law requirements, technical limitations, and the provision of other ecosystem services. To illustrate the profitability of carbon credit generation, we simulated the application of carbon credit guidelines to two forest-rich mountain watersheds in the southern part of the Piemonte region. The two dominating tree species are beech (Fagus sylvatica L.) and chestnut (Castanea sativa Mill.). We computed current forest carbon stock and carbon credits generated in 20 years under business as usual and an alternative biomass retention scenario. The IFM resulted in an avoided harvest of 39,362 m3 for a net total of 64,014 MgCO2e after subtracting harvest emissions, or 38 Mg ha-1 throughout the permanence period of 20 years. These steps can be replicated in other mountain regions where there is interest in promoting this ecosystem service as an alternative or an addition to production-oriented forest management. [ABSTRACT FROM AUTHOR]

Interest in coppices is growing due to the need to replace fossil fuels with renewable energy sources. In Italy, beech covers one million hectares, half of which originated by coppicing. This study tested which factors drive the presence and growth of beech resprouts, with a focus on fertility, cutting intensity, age, and size at time of coppicing. We analyzed 509 stools in 24 stands coppiced between 1 and 26 years before sampling. We fitted Generalized Linear Mixed Models of the probability of sprouting and height of the tallest resprout for each stool as a function of elevation, slope, aspect, bedrock, precipitation, temperature, age at coppicing, time since coppicing, residual shoot density, the sum, average and coefficient of variation of the diameter of cut shoots, and type of stool treatment. Of all harvested stools, 249 (49%) had sprouted with an average of 7.6 resprouts per stool. Height of the tallest resprout on each stool ranged from 3 to 800 cm, mainly as a function of time since coppicing. Resprout mortality was on average 1.4% per plot. Sprouting decreased with decreasing site fertility, increasing precipitation, and increasing size of cut stems. Leaving one or more shoots on the stool after felling produced a high proportion of sprouting stools (82%). Although based on a limited sample, our quantitative analysis of the driving factors of sprouting in beech can be used to support silvicultural decisions in over-mature beech coppices, and to optimize trade-offs between ecosystem services such as biomass production, biodiversity, and hydro-geologic protection. [ABSTRACT FROM AUTHOR]

Mast seeding is a crucial population process in many tree species, but its spatio-temporal patterns and drivers at the continental scale remain unknown ., Using a large dataset (8000 masting observations across Europe for years 1950-2014) we analysed the spatial pattern of masting across the entire geographical range of European beech, how it is influenced by precipitation, temperature and drought, and the temporal and spatial stability of masting-weather correlations., Beech masting exhibited a general distance-dependent synchronicity and a pattern structured in three broad geographical groups consistent with continental climate regimes. Spearman's correlations and logistic regression revealed a general pattern of beech masting correlating negatively with temperature in the summer 2 yr before masting, and positively with summer temperature 1 yr before masting (i.e. 2T model). The temperature difference between the two previous summers (DeltaT model) was also a good predictor. Moving correlation analysis applied to the longest eight chronologies (74-114 yr) revealed stable correlations between temperature and masting, confirming consistency in weather cues across space and time., These results confirm widespread dependency of masting on temperature and lend robustness to the attempts to reconstruct and predict mast years using temperature data. [ABSTRACT FROM AUTHOR]

Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species' proportions estimated with this method are best approximated by the proportions of the species' leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach. [ABSTRACT FROM AUTHOR]

Aerial LiDAR (Light Detection and Ranging) derived data are widely adopted for the study and characterization of forests. In particular, LiDAR derived-CHM (Canopy Height Model) has proved essential in identifying tree height variability and estimating many forest features such as biomass and wood volume. However, CHM quality may be affected by internal limits and anomalies caused by raw data (point cloud) processing (i.e., vertical errors), which are quite often disregarded by users, thus generating potentially erroneous results in their applications. In this work, an auto-consistent procedure for the fast evaluation of CHM accuracy has been developed based on the assessment of internal anomalies affecting CHM data obtained by differencing gridded DSM (Digital Surface Model) and DTM (Digital Terrain Model). To this purpose, a CHM was generated using the gridded DTMs and DSMs provided by the Cartographic Office of the Piemonte Region (north-western Italy). We estimated the local potential CHM error over the whole region, and demonstrated its strictly dependence on the terrain morphometry, particularly slope. The relationship between potential CHM error and slope was modeled separately for mountain, hill and flat terrain contexts, and used to produce a potential error map over the whole region. Our results showed that approximately 20% of the regional territory suffers from CHM uncertainty (in particular high elevation areas, including the treeline), though the majority of regional forest categories was affected by negligible CHM error. The potential consequences of CHM error in forest applications were evaluated, concluding that the tested LiDAR dataset provide a reliable basis for forest applications in most of the regional territory. [ABSTRACT FROM AUTHOR]

Mountain forests provide important ecosystem services, such as protection against natural hazards, carbon sequestration, and plant and animal biodiversity. Natural disturbances occurring in forests can alter the provision of ecosystem services to local and offsite communities, but their influence on multiple service tradeoffs has rarely been analyzed. Our aim is to analyze the effect of avalanche frequency on the provision of ecosystem services in a mountain forest in the Italian Alps. We sampled tree and understory vegetation, soil carbon, and intensity of the browsing damage at 10 plots at each of the following observation sites: (1) an active avalanche track (“recent disturbance”), (2) an area last disturbed in 1959 by avalanches (“old disturbance”), occupied now by a dense aspen forest, and (3) the regularly managed spruce–fir stand (“control”). We computed metrics of plant diversity (Shannon and evenness indices), aboveground and belowground carbon stocks, and a browsing index on regeneration and shrubs as a proxy for ungulate habitat. Finally, we assessed the ability of forests in each site to mitigate rockfall hazard. In our study, higher avalanche frequency was associated with lower carbon stock, higher species diversity, and lower protection against rockfall. Of all species found in the avalanche track, 54% were exclusive to that site. After 50 years, the post-disturbance stand provided a very high protection effect against rockfall, but was temporarily unsuitable for wild ungulate habitat, due to the high tree density and lack of open areas. Species richness and diversity were lower in older than in more recently disturbed sites, and not significantly different than the control stand. The control stand fulfilled the requirements for minimal protection against rockfall, but may lose its effectiveness in the near future due to senescence or disturbance-related mortality of canopy trees. Elucidating the tradeoffs between ecosystem services and disturbance frequency will support managers in planning management actions (e.g., avalanche protection measures), and assess tradeoffs between the need to mitigate risks in the most vulnerable areas and the opportunity to improve the provision of ecosystem services where some disturbance can be allowed to occur. [ABSTRACT FROM AUTHOR]

Aim Climate change is expected to modify growth trends of forests around the world. However, this modification may vary in strength and intensity across a species' biogeographical range. Here, we study European populations of silver fir ( Abies alba) across its southern distribution limits in Spain, Italy and Romania. We hypothesized that growth trends of silver fir will differ across its distribution range, with a marked decline in growth in drought-prone regions near the species' southernmost biogeographical limits. Location Europe (Spain, Italy, Romania). Methods We collected tree-ring data from at least 1300 silver fir trees located in 111 sites. The dataset was used to assess and model growth trends, quantified as changes in basal area increment, and to determine how growth responds to climate. Results We found contrasting patterns of basal area increments among countries and sites. Populations of silver fir located outside the Mediterranean area (e.g. northern Italy, Romania) have shown a clear increase in growth over the last two decades, whereas most populations in Spain and southern Italy have displayed a marked decline in growth since the 1980s. The growth of silver fir forests at the south-western distribution limit is severely constrained by low spring-summer water availability, whereas growth of silver fir forests in non-Mediterranean areas is limited by cold conditions in late winter to early spring. Main conclusions Climate warming is distinctly modifying growth patterns and responses to climate in silver fir across most of the species' European distribution area. In south-western Europe the reduction in growth of many populations is related to an observed increase in aridity, whereas in more temperate areas warming is enhancing growth. Our results confirm a decline in the growth of silver fir at its south-western distribution limits as a consequence of climate warming. [ABSTRACT FROM AUTHOR]

Deriving burn severity from multispectral satellite data is a widely adopted approach to infer the degree of environmental change caused by fire. Burn severity maps obtained by thresholding bi-temporal indices based on pre- and post-fire Normalized Burn Ratio (NBR) can vary substantially depending on temporal constraints such as matched acquisition and optimal seasonal timing. Satisfying temporal requirements is crucial to effectively disentangle fire and non-fire induced spectral changes and can be particularly challenging when only a few cloud-free images are available. Our study focuses on 10 wildfires that occurred in mountainous areas of the Piedmont Region (Italy) during autumn 2017 following a severe and prolonged drought period. Our objectives were to: (i) generate reflectance composites using Sentinel-2 imagery that were optimised for seasonal timing by embedding spatial patterns of long-term land surface phenology (LSP); (ii) produce and validate burn severity maps based on the modelled relationship between bi-temporal indices and field data; (iii) compare burn severity maps obtained using either a pair of cloud-free Sentinel-2 images, i.e. paired images, or reflectance composites. We proposed a pixel-based compositing algorithm coupling the weighted geometric median and thematic spatial information, e.g. long-term LSP metrics derived from the MODIS Collection 6 Land Cover Dynamics Product, to rank all the clear observations available in the growing season. Composite Burn Index data and bi-temporal indices exhibited a strong nonlinear relationship (R 2 > 0.85) using paired images or reflectance composites. Burn severity maps attained overall classification accuracy ranging from 76.9% to 83.7% (Kappa between 0.61 and 0.72) and the Relative differenced NBR (RdNBR) achieved the best results compared to other bi-temporal indices (differenced NBR and Relativized Burn Ratio). Improvements in overall classification accuracy offered by the calibration of bi-temporal indices with the dNBR offset were limited to burn severity maps derived from paired images. Reflectance composites provided the highest overall classification accuracy and differences with paired images were significant using uncalibrated bi-temporal indices (4.4% to 5.2%) while they decreased (2.8% to 3.2%) when we calibrated bi-temporal indices derived from paired images. The extent of the high severity category increased by ~19% in burn severity maps derived from reflectance composites (uncalibrated RdNBR) compared to those from paired images (calibrated RdNBR). The reduced contrast between healthy and burnt conditions associated with suboptimal seasonal timing caused an underestimation of burnt areas. By embedding spatial patterns of long-term LSP metrics, our approach provided consistent reflectance composites targeted at a specific phenological stage and minimising non-fire induced inter-annual changes. Being independent from the multispectral dataset employed, the proposed pixel-based compositing approach offers new opportunities for operational change detection applications in geographic areas characterised by persistent cloud cover. • We mapped burn severity using Sentinel-2 paired images and reflectance composites. • Bi-temporal indices benefit from a reduction in non-fire induced spectral changes. • Reflectance composites exhibit spectral consistency in space and time. • Our approach increased the overall classification accuracy up to 5.2%. • Gaining contrast between healthy and burnt vegetation improves burn severity maps. [ABSTRACT FROM AUTHOR]

Abstract: Regeneration of non fire-adapted conifers following crown fires on the European Alps is often delayed or unsuccessful. Fire may limit establishment by eliminating seed trees, altering soil properties, or modifying microsite and soil conditions via disturbance legacies. However, the effect of soil legacies on post-fire establishment has rarely been discussed. We analyzed the abundance of Scots pine regeneration in a 257ha wildfire in an inner-alpine forest. Our aims were (1) to model fire intensity at the soil surface and topsoil heating along a gradient of increasing fire severities; (2) to assess the differences in soil properties along the fire severity gradient; (3) to model the effect of disturbance and soil legacies on the density of pine seedlings. We reconstructed fire behavior and soil heating with the First Order Fire Effects Model (FOFEM), tested the effect of fire severity on soils by nonparametric distributional tests, and modeled seedling density as a function of site, disturbance and soil legacies by fitting a GLM following a variable selection procedure. Topsoil heating differed markedly between the moderate and high severity fires, reaching temperatures high enough to strongly and permanently alter soil properties only in the latter. High fire severity resulted in decreased soil consistency and wet aggregate stability. Burned soils had lower organic matter and cations than those unburned. Pine seedlings favored low-fertility, eroded, and chemically poor sites. Establishment was facilitated by the presence of coarse woody debris, but hampered by increasing distance from the seed source. These results suggest that in dry, inner-alpine valleys, fire residuals and soil legacies interact in determining the success of Scots pine re-establishment. High severity fire can promote favorable soil conditions, but distance from the seed source and high evaporation rates of bare soils must be mitigated in order to ensure a successful restoration. [Copyright &y& Elsevier]

Norway spruce is one of the most important conifer tree species in Europe, paramount for timber provision, habitat, recreation, and protection of mountain roads and settlements from natural hazards. Although natural Norway spruce forests exhibit diverse structures, even-aged stands can arise after disturbance or as the result of common silvicultural practice, including off-site afforestation. Many even-aged Norway spruce forests face issues such as senescence, insufficient regeneration, mechanical stability, sensitivity to biotic disturbances, and restoration. We propose the use of Density Management Diagrams (DMD), stand-scale graphical models designed to project growth and yield of even-aged forests, as a heuristic tool for assessing the structure and development of even-aged Norway spruce stands. DMDs are predicated on basic tree allometry and the assumption that self-thinning occurs predictably in forest stands. We designed a DMD for Norway spruce in temperate Europe based on wide-ranging forest inventory data. Quantitative relationships between tree- and stand-level variables that describe resistance to selected natural disturbances were superimposed on the DMD. These susceptibility zones were used to demonstrate assessment and possible management actions related to, for example, windfirmness and effectiveness of the protective function against rockfall or avalanches. The Norway spruce DMD provides forest managers and silviculturists a simple, easy-to-use, tool for evaluating stand dynamics and scheduling needed density management actions. [ABSTRACT FROM AUTHOR]

Scots pine ( Pinus sylvestris L.) forests of many inner Alpine valleys have recently displayed a quick loss of vitality. A decline disease has been suggested as the cause, with drought as the main predisposing factor and the additional contribution of biotic agents inciting tree dieback. This study is focused on Valle d'Aosta, a dry, inner-Alpine region in NW Italy. We inferred vitality changes between years 2000 and 2007 by computing reductions in enhanced vegetation index (EVI). Image differencing was carried out on pre-processed Moderate Resolution Imaging Spectroradiometer (MODIS) imagery taken in late springtime and validated against ancillary ground truth. We: (1) tested whether EVI reductions in Scots pine forests were significantly higher than those of a control species and of a wetter region for the same species, (2) analyzed decline incidence as a function of site and topographic variables, and (3) assessed the relative influence of site and stand structure on decline probability by means of path analysis. Mean EVI in the study area increased due to an early onset of the 2007 growing season. Nevertheless, the incidence of decline was 6.3% and significantly greater for Scots pine than the control species and site. Low-elevation, northerly exposed sites exhibited the highest incidence of decline. Path analysis suggested that the most important determinants of decline probability were slope, solar radiation, and stand sparseness. [ABSTRACT FROM AUTHOR]

In a forest stand, competition plays a central role, affecting individual growth. The size-growth relationship (SGR) indicates whether large trees grow proportionally more than (asymmetric SGR), equal to (symmetric), or less than (inversely asymmetric) smaller trees. SGR is thus an indicator of the growth partitioning and competition intensity within a stand. Using tree-ring analysis, we investigated long-term trends and interannual variability of SGR in several Norway spruce ( Picea abies (L.) Karst.) stands in the Paneveggio Forest (eastern Italian Alps) over a 100-year period. The study plots were characterized by different stand structures (one multilayered and two monolayered) and disturbance histories (different dates of logging). Logging conducted until the 1940s induced an inversely asymmetric SGR in all the plots. During the successive five decades, in the monolayered plots, it shifted to direct asymmetric (plot 1) and to symmetric (plot 2). In the multilayered plot (plot 3), SGR remained inversely asymmetric. A direct effect of climate on SGR interannual variability was not found. However, fast-growing trees had a stronger climatic signal than slow-growing trees, indicating that growth rate affects tree response to climate. Moreover, we observed that sensitivity to climate was reduced in the monolayered plots over the study period, possibly as a consequence of increased competition. [ABSTRACT FROM AUTHOR]

a consequence of land abandonment and marginalization, open areas and traditionally managed wood pastures are disappearing from many alpine valleys. Landscape and stand scale dynamics were analyzed in two neighboring inner valleys of central Italian Alps (Valmalenco, SO) dominated by larch ( Larix decidua Mill.) forests and experiencing different historical land use intensities. Land cover mapping obtained from object-oriented analysis of aerial photographs was used to quantify land cover changes between 1961 and 2003. Spatial statistics were used to quantify landscape patterns, and intensive sampling in permanent plots was employed to perform point pattern analysis at the stand scale. Expansion of forested area at the expense of wood pastures was the main land cover transition observed. Differences in land use intensities were responsible for different patterns at the landscape scale: (1) heavier grazing and human pressure created a more diverse and fragmented mosaic of meadows, open woodlands, forests and wood pastures, (2) lower human impact favored a more homogeneous and stable system. A decline in grazing pressure in the late 1970s favored the establishment of larch and spruce in a clustered pattern, typical of the subalpine belt. Subalpine wood pastures, likewise many other semi-natural environments, are in danger of disappearing and lose their productive and cultural characteristics, because they are developing into more closed and dense stands. [ABSTRACT FROM AUTHOR]

Abstract: It is frequently believed that a post-fire environment requires immediate actions in order to be restored. Salvage logging followed by plantation is a common post-fire restoration practice in many forests of the northwestern Italian Alps. The objectives of this study were to assess the impact of active and passive management techniques on the restoration of a burned area of the Aosta Valley and to determine which approach is the most suitable for enhancing Pinus sylvestris regeneration after stand replacing wildfires. The influence of five management options (no intervention; salvage logging; broadleaves plantation; Larix decidua plantation; P. sylvestris or Pseudotsuga menziesii plantation) and environmental variables on natural regeneration structure and composition was evaluated through direct gradient analysis. Pinus sylvestris and Populus tremula were the dominant tree species (40 and 29%, respectively) in the regeneration layer. Density, size, and structural diversity of natural regeneration were higher in the no intervention area. The proximity to forest edge was found to be the most important environmental variable. This study provided evidence that taking advantage of natural restoration processes may be a suitable alternative strategy to the active restoration practices adopted according to the Aosta Valley policy of post-fire management. [ABSTRACT FROM AUTHOR]

1. The tree-ring growth response of stone pine ( Pinus cembra L.) to climatic variability was studied in the Alps. The aims were (i) to assess tree-ring growth patterns at different spatial-temporal scales; (ii) to identify the climate parameters that explain most of the variability in radial growth at different time domains; and (iii) to study past and current trends in radial growth and climate–growth relationships at different locations. 2. High- and low-frequency stone pine chronologies were compiled for 30 treeline sites on the French and Italian Alps. We used gridded climate data computed from 200 years of instrumental records from an extensive Alpine network. Climate–growth relationships were computed with bootstrap correlation functions and their stationarity and consistency over time assessed with moving correlation. 3. No spatial patterns were detected in stone pine chronology statistics despite the regional clustering observed in tree-ring series and climate responses. This can be attributed to (i) local weather variability; (ii) different biophysical conditions caused by soil moisture, solar radiation, snowmelt dynamics and growing season length; and (iii) forest stand history and age structure, the expression of long-term land use and disturbances. 4. The exceptionally long-term climate records allowed significant stone pine growth response changes to be assessed at both annual and decadal time scales. Winter conditions and spring–summer temperatures mainly affected the growing season length, in addition to site carbon and water balance. Most of these limiting factors varied spatially and temporally along the latitudinal and longitudinal gradients in response to the corresponding changes in local conditions. 5. Our results show evidence of a clear response variability of Pinus cembra to climate limiting factors, at both spatial and temporal scale. Such knowledge extended to other species and regions will provide better estimates of the effect of climate variability on species distribution and dynamics within global change scenarios and more accurate past climate reconstruction and forest ecosystem modelling. [ABSTRACT FROM AUTHOR]

• Intra-annual radial growth rates and durations in trees are reported to differ greatly in relation to species, site and environmental conditions. However, very similar dynamics of cambial activity and wood formation are observed in temperate and boreal zones. • Here, we compared weekly xylem cell production and variation in stem circumference in the main northern hemisphere conifer species (genera Picea, Pinus, Abies and Larix) from 1996 to 2003. Dynamics of radial growth were modeled with a Gompertz function, defining the upper asymptote ( A), x-axis placement (β) and rate of change (κ). • A strong linear relationship was found between the constants β and κ for both types of analysis. The slope of the linear regression, which corresponds to the time at which maximum growth rate occurred, appeared to converge towards the summer solstice. • The maximum growth rate occurred around the time of maximum day length, and not during the warmest period of the year as previously suggested. The achievements of photoperiod could act as a growth constraint or a limit after which the rate of tree-ring formation tends to decrease, thus allowing plants to safely complete secondary cell wall lignification before winter. [ABSTRACT FROM AUTHOR]

Large crown fires in the Aosta Valley mostly occur in south-facing slopes where xeric conditions favour the presence of highly flammable conifer stands dominated by Pinus sylvestris. North-facing slopes are less affected by the occurrence of wildfires but the availability of large fuel amounts and prolonged drought periods can raise the fire risk also in these areas. Although stand-replacing wildfires affected about 20% of the total burned forest area from 1989 to 2017, the scarce fire adaptations of Pinus sylvestris pose serious problems for the regeneration of this species and a suitable post-fire management strategy is thus required to enhance this process. Long and mid-term forest regeneration dynamics of Pinus sylvestris were explored using both field surveys and remote sensing techniques in 12 stand-replacing wildfires occurred between 1989 and 2006 in the Aosta Valley. Tree regeneration at different development stages was sampled during 2017 and its fractional cover was also assessed. Time series of Landsat derived spectral vegetation indices were employed to track forest regeneration over time and temporal trajectories were modelled using robust regression methods to assess the magnitude and the direction of spectral changes throughout the years. [ABSTRACT FROM AUTHOR]

Tree masting is one of the most intensively studied ecological processes. It affects nutrient fluxes of trees, regeneration dynamics in forests, animal population densities, and ultimately influences ecosystem services. Despite a large volume of research focused on masting, its evolutionary ecology, spatial and temporal variability, and environmental drivers are still matter of debate. Understanding the proximate and ultimate causes of masting at broad spatial and temporal scales will enable us to predict tree reproductive strategies and their response to changing environment. Here we provide broad spatial (distribution range-wide) and temporal (century) masting data for the two main masting tree species in Europe, European beech ( Fagus sylvatica L.) and Norway spruce ( Picea abies (L.) H. Karst.). We collected masting data from a total of 359 sources through an extensive literature review and from unpublished surveys. The data set has a total of 1,747 series and 18,348 yearly observations from 28 countries and covering a time span of years 1677-2016 and 1791-2016 for beech and spruce, respectively. For each record, the following information is available: identification code; species; year of observation; proxy of masting (flower, pollen, fruit, seed, dendrochronological reconstructions); statistical data type (ordinal, continuous); data value; unit of measurement (only in case of continuous data); geographical location (country, Nomenclature of Units for Territorial Statistics NUTS-1 level, municipality, coordinates); first and last record year and related length; type of data source (field survey, peer reviewed scientific literature, gray literature, personal observation); source identification code; date when data were added to the database; comments. To provide a ready-to-use masting index we harmonized ordinal data into five classes. Furthermore, we computed an additional field where continuous series with length >4 yr where converted into a five classes ordinal index. To our knowledge, this is the most comprehensive published database on species-specific masting behavior. It is useful to study spatial and temporal patterns of masting and its proximate and ultimate causes, to refine studies based on tree-ring chronologies, to understand dynamics of animal species and pests vectored by these animals affecting human health, and it may serve as calibration-validation data for dynamic forest models. [ABSTRACT FROM AUTHOR]