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International audience; AbstractKey messageSpecies interactions implicate a complex balance of facilitation and competition, which may shift during community development, thus structuring the subalpine ecotone of Mediterranean mountain ranges through time and space. This study highlights that encroachment of grasslands and simultaneous downward/upward movement of forest tree species involve species interferences and environmental feedbacks, with differential effects on mountain pine and European beech, and the grassland communities of the Majella Massif.ContextThe transitional ecotone from the European beech closed forest to the mountain pine krummholz vegetation in the Majella Massif (Apennines, Italy) is a sensitive area to climate and land-use changes. Vegetation shifts in these ecotonal zones may cause a negative impact on the spatial distribution and survival of rare or endemic herbaceous species, thus influencing the appearance, structure, and productivity of the subalpine ecotone of the Majella National Park.AimsWe focused on determining the structures and dynamics of this Mediterranean tree line, and the climate–growth relationships of European beech and mountain pine. We investigated the upward and downward movement of pine into areas potentially suitable for beech expansion, and the concurrent beech encroachment upward.MethodsGrowth dynamics and canopy cover of European beech closed forest and mountain pine krummholz vegetation were analyzed in relation to disturbances at four different sites.ResultsSpring and summer temperatures and summer precipitation affected stem radial growth of both species. In details, spring and summer temperatures negatively affected tree ring width (TRW) of European beech, except for the highest site, whereas spring temperatures affected positively and summer temperatures negatively TRW of mountain pine. Mountain pine expanded upward, encroaching formerly grazed pastures and harvested areas, especially where the soil is shallow and rocky; downward expansion is also occurring, following progressive abandonment of forest management practices. At the same time, European beech recruitment is moving upward, interspersed within mountain pine krummholz, taking advantage from canopy shelter and higher temperature.ConclusionClimate and land-cover simultaneous changes induce species interactions and a complex balance of facilitation and competition, which may shift during community development and structure the subalpine European beech-mountain pine ecotone of the Majella Massif through time and space.

The dynamics of Pinus mugo krummholz during concomitant change in pastoral land use and climate in central Italy since the mid-20th century was investigated. Krummholz dynamics were detected using sequential aerial photography and fitted to a logistic regression model with elevation, grazing, proximity to beech forest, and proximity to krummholz as explanatory variables. Dendrochronological series were correlated with temperature and precipitation and fitted to a linear model. During this period krummholz doubled in extent and migrated 35–65 m upslope. Expansion was positively associated with krummholz proximity, residual pastoral grazing, and proximity to beech forest beyond 10 m and negatively associated with elevation and beech forest closer than 10 m. The logistic regression model forecasts krummholz migration by an additional 30 m upslope by 2060. During the 20th century, winter and spring minimum temperatures increased but did not result in increased radial stem growth of P. mugo. The combined evidence suggests that krummholz dynamics can be explained by the legacy of summer pastoralism and the dispersal limitations of P. mugo, rather than by climate change.

International audience; AbstractKey messageComparisons between compression and opposite wood formation in prostratingPinus mugoindicate that the secondary meristem can produce more tracheids with thicker walls by also increasing the number of contemporaneously differentiating cells, rather than only increasing the duration or the rate of cell formation.ContextAlthough cambium tissues within a stem experience the same climatic conditions, the resulting wood structure and properties can strongly differ. Assessing how meristem differently regulates wood formation to achieve different anatomical properties can help understanding the mechanisms of response and their plasticity.AimsWe monitored the formation of compression (CW) and opposite (OW) wood within the same stems to understand whether achieved differences in wood structure are caused by modifications in the process of cell formation.MethodsWe collected weekly microcores of compression and opposite wood from the curved stem of ten treeline prostrating mountain pines (Pinus mugo Turra ssp. mugo) at the Majella massif in Central Italy.ResultsResults indicate that cambium formed approximately 1.5 times more cells in CW than OW, despite that CW cell differentiation only extended 2 weeks longer and the residence time of CW cells in the wall-thickening phase was only 20% longer. Differences in their formation were thus mainly related to both the rates and the width of the enlarging and wall-thickening zones (i.e., the number of cells simultaneously under differentiation) and less to duration of cell formation.ConclusionWe conclude that to achieve such a different wood structures, the efficiency of the secondary meristem, in addition of altered rate of cell division and differentiation, can also modify the width of the developing zones. Thus, deciphering what rules this width is important to link environmental conditions with productivity.

Changes in tree growth and insect distribution are projected due to climate warming. The expected effects of climate change on forest disturbance (e.g., insect outbreak) regime call for a better insight into the growth responses of trees to varying environmental conditions over geographical regions in eastern North America. In this study, the effects of a latitudinal thermal gradient and spruce budworm (SBW) outbreaks on the tree growth of black spruce (Picea mariana Mill.) were investigated along a 400 km transect from 48 degrees N to 51 degrees N across the continuous boreal forest in Quebec, Canada. Time series data were analyzed to synchronize climatic factors (temperature and precipitation trends), insect dynamics (SBW population frequency) and tree growth (ring-width chronology). Radial growth resulted as being synchronized with climate patterns, highlighting a positive effect of maximum temperatures on tree growth, especially in the northernmost site. Increasing temperatures and precipitation had a more positive effect on tree growth during epidemic periods, whereas the detrimental effects of SBW outbreaks on tree growth were observed with climate patterns characterized by lowered temperature. The lag between time series, synchrony and/or frequency of synchrony between tree growth and SBW outbreak were considered in order to link the growth of host trees and the dynamics of insect populations. The proposed analytical approach defined damage severity on tree growth in relation to population dynamics and climate fluctuations at the northern distribution limit of the insect. Overall, a decline in tree growth was observed in these boreal forests, due to SBW outbreaks acting in combination with other stress factors.

Understanding to what extent species mixtures modify the growth of trees and their responses to climate, in comparison with pure stands, is important to support forest adaptation and mitigation strategies. In this sense, information stored in tree rings can be useful to evaluate whether the positive relationship between species diversity and tree productivity holds true under disturbance (e.g., drought). This paper aimed at assessing (i) how radial growth of trees responded to local variation in climate patterns (Standardised Precipitation-Evapotranspiration Index; SPEI), and (ii) whether there was a relationship with intrinsic water use efficiency (WUEi) and tree-ring δ18O in two important tree species, occurring in pure and mixed forest stands. Three sites with similar topographic and pedo-climatic conditions were identified in a single location in the Italian Alps. The first two are characterized by pure stands, respectively dominated by European beech (Fagus sylvatica L.) and Scots pine (Pinus sylvestris L.). The third site refers to a mixed stand of both previous species. In particular, in order to assess the annual changes in WUEi, we analysed δ13C in tree rings. The influence of the stomatal conductance was also investigated through δ18O. Our results indicated that: (i) Basal Area Increments (BAI) consistently increased in all stands except for the pure Scots pine stand, in the 1994–2003 period; (ii) SPEI highlighted a drought period between 1991 and 2007 (62.2% of the average precipitation); and (iii) the WUEi values were generally higher in pure than in mixed stands, especially for European beech. The divergence between BAI and SPEI values in the 1990s and early 2000s could be a consequence of moderate thinning. We conclude that past forest management (namely thinning) can be more influential on tree growth than current climatic oscillations.

Mountain ecosystems are, however, fragile and particularly vulnerable to the adverse impacts of climate change, deforestation and forest degradation, land-use change, land degradation and natural disasters.

L‟analisi dei cambiamenti dell‟uso del suolo e la conseguente valutazione degli effetti che essi generano verso le diverse matrici (ambientale, paesaggistica, socia- le, di sicurezza e salute pubblica) assumono importanza sempre più riconosciuta nell‟ambito di una corretta pianificazione del territorio. All‟evidente urgenza di porre in atto misure di contrasto al consumo di suolo nei territori montani, si af- fianca, pertanto, la necessità di poter disporre di basi informative confrontabili che consentano il monitoraggio del fenomeno nello spazio e nel tempo. Con questo la- voro si esaminano i risultati desunti dall‟Inventario dell‟Uso delle Terre in Italia (IUTI), considerando anche potenzialità e limiti di utilizzo di questa base inventa- riale per analisi a scala regionale. Un particolare approfondimento riguarda i terri- tori montani della regione Veneto, per i quali si dispone di una base diacronica più estesa e di altre fonti di dati utilizzate per il confronto dei trend emersi.

A change in climate would be expected to shift plant distribu-tion as species expand in newly favourable areas and decline in increasingly hostile locations (Kelly and Goulden 2008). Even under conservative scenarios, future climate changes are likely to include further increases in mean temperature with significant drying in some regions, as well as increases in the frequency and severity of extreme droughts, and heat waves (Allen et al. 2010 ). As climate changes rapidly with height over relatively short horizontal distances, so does vegetation and ecohydrology (Beniston 2003), and alpine regions have been suggested to be particularly vulnerable to climate change (Elkin etal. 2013 ). If the treeline moves up in elevation, the increased carbon storage and evapotranspiration from this effect may provide a partial negative feedback to climate change. Nevertheless, vegetation influences the absorption of energy by the surface via modification of the surface albedo. A shift to evergreen forest at the mountain treeline would amplify the alteration of the physical characteristics of the land surface induced by forest expansion, decreasing surface albedo, while increasing net evaporation and surface roughness.In the present issue of

Global change is leaving a fingerprint on the appearance, structure and productivity of the treeline ecotone, modifying patterns of mountain ecosystems. In order to implement correct policies for managing natural resources, we examine how climate change interrelated with land-use abandonment could shape mountain forests at their upper limit in a Mediterranean environment, and how patterns of tree growth and periods of tree establishment guide the interpretation of global change effects on treeline dynamics. We reconstructed the population dynamics of mountain pine (Pinus mugo Turra spp. mugo) in the subalpine belt of the Majella National Park (Italy). In a test area of 14,440 ha, proposed as a pilot study site for long-term ecological monitoring, temporal and spatial mountain pine distribution were examined since 1954 by historical aerial ortophotos. Multitemporal maps documented the expansion upwards (1 m/year) and downwards (3 m/year) of mountain pine. Mountain pine started to expand upwards into the fo...

Seasonal analyses of cambial cell production and day-by-day stem radial increment can help to elucidate how climate modulates wood formation in conifers. Intra-annual dynamics of wood formation were determined with microcores and dendrometers and related to climatic signals in Norway spruce (Picea abies (L.) Karst.). The seasonal dynamics of these processes were observed at two sites of different altitude, Savignano (650 m a.s.l.) and Lavaze (1800 m a.s.l.) in the Italian Alps. Seasonal dynamics of cambial activity were found to be site specific, indicating that the phenology of cambial cell production is highly variable and plastic with altitude. There was a site-specific trend in the number of cells in the wall thickening phase, with the maximum cell production in early July (DOY 186) at Savignano and in mid-July (DOY 200) at Lavaze. The formation of mature cells showed similar trends at the two sites, although different numbers of cells and timing of cell differentiation were visible in the model shapes; at the end of ring formation in 2010, the number of cells was four times higher at Savignano (106.5 cells) than at Lavaze (26.5 cells). At low altitudes, microcores and dendrometers described the radial growth patterns comparably, though the dendrometer function underlined the higher upper asymptote of maximum growth in comparison with the cell production function. In contrast, at high altitude, these functions exhibited different trends. The best model was obtained by fitting functions of the Gompertz model to the experimental data. By combining radial growth and cambial activity indices we defined a model system able to synchronize these processes. Processes of adaptation of the pattern of xylogenesis occurred, enabling P. abies to occupy sites with contrasting climatic conditions. The use of daily climatic variables in combination with plant functional traits obtained by sensors and/or destructive sampling could provide a suitable tool to better investigate the effect of disturbances on response strategies in trees and, consequently, contribute to improving our prediction of tree growth and species resilience based on climate scenarios.

In questo lavoro sono riportati i risultati della stima della disponibilita di biomassa per uso energetico ottenibile dalle risorse agro-forestali a seguito dell’applicazione di criteri di sostenibilita. Le analisi sono state effettuate a due differenti scale geografiche: la prima a livello nazionale e la seconda a livello regionale, basata su strati informativi di maggior dettaglio, e con risultati aggregati a livello comunale. In entrambi i casi sono stati applicati dei vincoli alla produzione di biomassa strettamente connessi alle caratteristiche morfologiche, tecnico-strutturali e gestionali dell’area di studio e all’uso di criteri che garantiscono la sostenibilita della gestione delle risorse forestali basati sulla provvigione minimale.

High-mountain ecosystems, located at the geographical distribution limit of the species, may provide valuable information about tree-growth responses to changes in climate conditions and land uses. In order to provide a first description of a mountain pine ecotone, at the alpine treeline, three plots were sampled along an altitudinal gradient in the Monti del Sole (Dolomiti Bellunesi National Park, Veneto, Italy) on a northwestern slope from 1850 to 2000 m a.s.l. In order to reconstruct recent dynamics of Pinus mugo Turra ssp. mugo (mountain pine) at this altitudinal range dendroecological methods were used,which allowed reconstructing the age structures of tree populations. Raw mean chronologies showed the long-term variability, related to non-climatic signals due to age, size and stand dynamics. The raw mean chronology of Plot 1 followed the typical exponential negative trend, while raw mean chronologies of Plot 2 and Plot 3 depicted an increasing growth trend, starting from early fifties of 20th century. There was a greater ring width in Plot 2,than the other two plots. These mountain pine scrublands belong the Sorbo chamaemespili - Pinetum mugi association and form persistent woodlands.

Questions:Could mountainpine (Pinus mugo Turra subsp. mugo) located abovethe timberline and at the southern limit of its potential geographic distributionbea promising speciestomonitorclimatic changeinspecificenvironmentssuchas the Mediterranean mountains? Does mountain pine krummholz upwardexpansion result from current climate change? Has the relationship betweenclimate and tree ring growth of mountain pine changed? To what extent doesclimatic variability affect tree ring growth? Could mountain pine upwardexpansion contribute to loss of biodiversity in the undisturbed tree line ecotoneon the Majella massif?Location:MajellaNationalPark,Apennines,Italy.Methods: Dendroclimatological analysis was performed to examine the rela-tionshipbetweentreeringsofmountainpineandclimaticparametersatthetreeline. Climate–growth relationships were analysed using correlation function(CF)analysisandmovingCF(MCF).Results: In the Majella massif, climate variables affected mountain pine treegrowth at the tree line ecotone. Significant correlations were found with springtemperatures and summer precipitation. Essentially, 3 mo played a key role inmountain pine growth: April and May of the current year and October of theprevious year. MCF showed that mountain pine is a sensitive species, in termsoftreeringgrowth.Conclusions: Growing above the limit of tree vegetation, mountain pineproved to be a promising species for monitoring climate- and land use-driveninfluences over tree ring growth at high elevations. Our results show thatmountain pine is particularly sensitive to climate at the beginning and at theendofthegrowingseason.IntroductionIn the central Apennines (Italy), the low altitudinal rangeand marked influence of mediterranean climate set theboundary between alpine and sub-alpine bioclimatic beltsat 2550 m a.s.l. Within the Mediterranean Basin, theApennine range represents a temperate mountain climatic‘island’withinwhichthecentralApenninesformanarchi-pelago of arctic-alpine ‘islands’ (van Gils et al. 2012). TheApennine chain acted as refugia for trees during theW€urmian Late Glacial (Watson 1996), playing an impor-tant role in preservation of endemic high-altitude vegeta