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ABSTRACTXylem phenology has been widely recognised as an ecological indicator of the impact of environmental changes on forest ecosystems, especially at the edge of a species distribution. We investigated xylem phenology of silver fir (Abies alba Mill.) in three sites in Italy, between the 38th and 46th parallels. The phases of xylem phenology were assessed weekly on wood microcores collected from March to November 2015 to calculate timing and duration of xylem cell production. The effect of temperature and precipitation on xylem phenology were sequentially included in stepwise regressions and used to predict the duration of each phenological phase under three future climatic scenarios at different concentrations of greenhouse gases (RCP 2.6; 4. 5; 8. 5). A growing season of 163 days was detected in the southern site that was longer compared to the central (132 days) and northern (120 days) sites. A longer duration of xylogenesis was mostly related to a delayed completion of xylem differentiation in autumn rather than an earlier onset of cambium reactivation in spring. Overall, 67–76% of the duration of phenological phases was controlled by growing season precipitation, while 24 –33% was influenced by minimum temperature. Inclusion of both the above factors in the modelling exercise simulated a lengthening of the silver fir growing season during the 21st century. A longer duration of xylogenesis was envisaged in the scenario RCP 8. 5, especially in the central site. Population and climate gradients need to be considered when addressing phenological shifts and growth dynamics of silver fir in Mediterranean mountains.

Cudlín, Pavel et. al.- 16 páginas.- Ilustraciones.- Se acompaña suplemento de 3 páginas.- © The autors 2017. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are unrestricted. Authors and original publication must be credited. A growing body of evidence suggests that processes of upward treeline expansion and shifts in vegetation zones may occur in response to climate change. However, such shifts can be limited by a variety of non-climatic factors, such as nutrient availability, soil conditions, landscape fragmentation and some species-specific traits. Many changes in species distributions have been observed, although no evidence of complete community replacement has been registered yet. Climatic signals are often confounded with the effects of human activity, for example, forest encroachment at the treeline owing to the coupled effect of climate change and highland pasture abandonment. Data on the treeline ecotone, barriers to the expected treeline or dominant tree species shifts due to climate and land use change, and their possible impacts on biodiversity in 11 mountain areas of interest, from Italy to Norway and from Spain to Bulgaria, are reported. We investigated the role of environmental conditions on treeline ecotone features with a focus on treeline shift. The results showed that treeline altitude and the altitudinal width of the treeline ecotone, as well as the significance of climatic and soil parameters as barriers against tree species shift, significantly decreased with increasing latitude. However, the largest part of the commonly observed variability in mountain vegetation near the treeline in Europe seems to be caused by geomorphological, geological, pedological and microclimatic variability in combination with different land use history and present socio-economic relations. This paper is based firstly upon work from the COST Action ES 1203 SENSFOR, supported by COST (European Cooperation in Science and Technology; www.cost.eu). This international work was further supported by projects granted by the Ministry of Education Youth and Sports of the Czech Republic, grant NPU I LO1415 and LD 14039, by the agency APVV SR under projects APVV-14-0086 and APVV-15-0270. We acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (www.ecad.eu) Peer reviewed

AbstractDespite growing interest in predicting plant phenological shifts, advanced spring phenology by global climate change remains debated. Evidence documenting either small or large advancement of spring phenology to rising temperature over the spatio‐temporal scales implies a potential existence of a thermal threshold in the responses of forests to global warming. We collected a unique data set of xylem cell‐wall‐thickening onset dates in 20 coniferous species covering a broad mean annual temperature (MAT) gradient (−3.05 to 22.9°C) across the Northern Hemisphere (latitudes 23°–66° N). Along the MAT gradient, we identified a threshold temperature (using segmented regression) of 4.9 ± 1.1°C, above which the response of xylem phenology to rising temperatures significantly decline. This threshold separates the Northern Hemisphere conifers into cold and warm thermal niches, with MAT and spring forcing being the primary drivers for the onset dates (estimated by linear and Bayesian mixed‐effect models), respectively. The identified thermal threshold should be integrated into the Earth‐System‐Models for a better understanding of spring phenology in response to global warming and an improved prediction of global climate‐carbon feedbacks.

Global changes push to set up strategies able to mitigate and adapt agricultural and forest crops to environmental variability, and the sustainable intensification of production processes under agricultural and forestry systems is one of the approaches mainly supported. In Italy biomass and biogas are the renewable energy sources that have shown the greatest potential for growth in recent years. In this context, during the XV National Congress held in Bolzano in February 2018, the Italian Association of Agricultural Scientific Societies has promoted an analysis about potential and limits of the sustainable intensification of agricultural and forestry systems for bioenergy production. This document reports the outcome, in the form of a commented discussion on the main evidences and proposals from technical-scientific and operational points of view.

AbstractThe allocation and stoichiometry of plant nutrients in leaves reflect fundamental ecosystem processes, biotic interactions, and environmental drivers such as water availability. Climate change will lead to increases in drought severity and frequency, but how canopy nutrients will respond to drought, and how these responses may vary with community composition along aridity gradients is poorly understood. We experimentally addressed this issue by reducing precipitation amounts by 66% during two consecutive growing seasons at three sites located along a natural aridity gradient. This allowed us to assess drought effects on canopy nitrogen (N) and phosphorus (P) concentrations in arid and semiarid grasslands of northern China. Along the aridity gradient, canopy nutrient concentrations were positively related to aridity, with this pattern was driven primarily by species turnover (i.e., an increase in the relative biomass of N‐ and P‐rich species with increasing aridity). In contrast, drought imposed experimentally increased N but decreased P concentrations in plant canopies. These changes were driven by the combined effects of species turnover and intraspecific variation in leaf nutrient concentrations. In addition, the sensitivity of canopy N and P concentrations to drought varied across the three sites. Canopy nutrient concentrations were less affected by drought at drier than wetter sites, because of the opposing effects of species turnover and intraspecific variation, as well as greater drought tolerance for nutrient‐rich species. These contrasting effects of long‐term aridity vs. short‐term drought on canopy nutrient concentrations, as well as differing sensitivities among sites in the same grassland biome, highlight the challenge of predicting ecosystem responses to future climate change.

Abstract A spatially explicit knowledge of forest resources is essential to support the sustainable use of wood as a fuel for producing energy (firewood). This paper describes the integrated use of remotely sensed data and sample based forest inventories to derive a biomass map for coppice forest, resulted estimated potential biomass available is contrasted with local domestic consumptions at the municipality level. The test was carried out in an environmentally and socially homogeneous district of Apennine Mountains (Alto Molise, south-central Italy) coupling multispectral high resolution Landsat 7 ETM+ satellite imagery and a local forest inventory trough the application of the non-parametric estimation procedure k -Nearest Neighbours ( k -NN). Several forest management scenarios were applied in order to evaluate their impact on the potential availability of firewood from coppice forests. The paper introduces data and methods used and presents the achieved results both in terms of the accuracy of the biomass map produced by k -NN and of the relationship between the potential availability and demand for firewood. These results demonstrated that k -NN is able to estimate the biomass of coppice forest in the test area with an accuracy level comparable with recent similar application of k -NN carried out in Boreal regions (RMSE of 25.6%). The application of different forest management scenarios have a significant impact on local estimated firewood balance between potential supply from coppice forests and demand for domestic consumption, depending of the scenarios the net balance changed up to 84%.

Significance Forest trees can live for hundreds to thousands of years, and they play a critical role in mitigating global warming by fixing approximately 15% of anthropogenic CO 2 emissions annually by wood formation. However, the environmental factors triggering wood formation onset in springtime and the cellular mechanisms underlying this onset remain poorly understood, since wood forms beneath the bark and is difficult to monitor. We report that the onset of wood formation in Northern Hemisphere conifers is driven primarily by photoperiod and mean annual temperature. Understanding the unique relationships between exogenous factors and wood formation could aid in predicting how forest ecosystems respond and adapt to climate warming, while improving the assessment of long-term and high-resolution observations of global biogeochemical cycles.