The FLUXNET2015 dataset provides ecosystem-scale data on CO 2 , water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.

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Atmospheric nitrogen (N) inputs in the Mediterranean Basin are projected to increase due to fossil fuel combustion, fertilizer use, and the exacerbation of agricultural production processes. Although increasing N deposition is recognized as a major threat to ecosystem functioning, little is known about how local environmental conditions modulate ecosystem function response to N addition, particularly in the context of Mediterranean-Basin ecosystems. Here, we assess how N addition affects important ecosystem properties associated with litter decomposition, soil physical-chemical properties, soil extracellular enzymatic activity and microbial abundance across three long-term N addition experimental sites in the Mediterranean Basin. Sites were located in El Regajal (Madrid, Spain), Capo Caccia (Alghero, Italy), and Arrábida (Lisbon, Portugal) and are all representative of Mediterranean shrublands. No common pattern for litter decomposition process or other studied variables emerged among the control plots of the studied sites. Nitrogen supply only affected soil pH, a major driver of decomposition, in two out of three experimental sites. Moreover, when we explored the role of N addition and soil pH in controlling litter decay, we found that the effects of these factors were site-dependent. Our results point out to local ecosystem features modulating N addition effects in controlling litter decomposition rates in Mediterranean ecosystems, suggesting that the responses of soil functioning to N deposition are site-dependent. These findings provide further knowledge to understand contrasting ecosystem responses to N additions based on a single field experiments.

In the Mediterranean region, ecosystems are severely affected by climate variability. The Italian Peninsula is a hot spot for biodiversity thanks to its heterogeneous landscape and the Mediterranean, Continental, and Alpine climates hosting a broad range of plant functional types along a limited latitudinal range from 40 ′ to 46 ′ N. In this study we applied a comparative approach integrating descriptive statistics, time series analysis, and multivariate techniques to answer the following questions: (i) do the climatic variables affect Gross Primary Productivity (GPP), Reco, Water Use Efficiency (WUE), and ET to a similar extent among different sites? (ii) Does a common response pattern exist among ecosystems along a latitudinal gradient in Italy? And, finally (iii) do these ecosystems respond synchronically to meteorological conditions or does a delayed response exist? Six sites along a latitudinal, altitudinal, and vegetational gradient from semi-arid (southern Italy), to a mountainous Mediterranean site (central Italy), and sub-humid wet Alpine sites (northern Italy) were considered. For each site, carbon and water fluxes, and meteorological data collected during two hydrologically-contrasting years (i.e., a dry and a wet year) were analyzed. Principal Component Analysis (PCA) was adopted to identify temporal and spatial variations in GPP, Ecosystem Respiration (Reco), WUE, and Evapotranspiration (ET). The model outlined differences among Mediterranean semi-arid, Mediterranean mountainous, and Alpine sites in response to contrasting precipitation regimes. GPP, Reco, WUE, and ET increased up to 16, 19, 25, and 28%, respectively in semi-arid Mediterranean sites and up to 15, 32, 15, and 11%, respectively in Alpine sites in the wet year compared to the dry year. Air temperature was revealed to be one of the most important variables affecting GPP, Reco, WUE, and ET in all the study sites. While relative air humidity was more important in southern Mediterranean sites, Conte et al. Forest Responses to Rainfall Variability global radiation was more significant in northern Italy. Our work suggests that a realistic prediction of the main responses of Italian forests under climate change should also take in account delayed responses due to acclimation to abiotic stress or changing environmental conditions.

The cork oak shows a good resistance to fire events due to the properties of its bark and a high capacity to resprout after intense fire events from basal suckers. Two experimental trials aiming to evaluate post fire recovery techniques enclosing the influence of the grazing disturbance were conducted in Sardinia. In the first trial, where the experimental activities started in the 1985 in northern hills of Sardinia, a traditional coppicing of severe damaged cork oak trees was compared with the branch pruning.. The coppicing, suggested when high damage levels due to the fire occur, showed a percentage of recovered plants higher than 95%. The early sucker thinning did not produce any significant advantage. The branch pruning showed lower percentages of living trees, going from 20% to 77% in relation to the number of the bark stripping the plants have before the fire. The second case study (Sardinia, central hills) was mainly addressed to the evaluation of the grazing effects after fire. As in the first case, the fire event occurred two years after the bark stripping. The results reveal that the intense grazing after fire causes the death of all coppiced trees. On the other hand, almost all plants recovered after the fire in not grazed plots. The trials showed that a preliminary evaluation of the degree of the trees damage due to the fire is necessary before to apply any recovery technique. Finally, the results give useful information for the management of cork oak stands after fire events, a very common situation in the Mediterranean areas where cork oak is diffuse.

Quantifying actual evapotranspiration (ETa) over natural vegetation is crucial in evaluating the water status of ecosystems and the water-use patterns in local or regional hydrological basins. Remote sensing-based surface energy balance models have been used extensively for estimating ETa in agro-environments; however, the application of these models to natural ecosystems is still limited. The surface energy balance algorithm for land (SEBAL) physical-based surface energy balance model was applied to estimate the actual evapotranspiration over a heterogeneous coverage of Mediterranean maquis in a natural reserve in Sardinia, Italy. The model was applied on 19 Landsat 5 and 8 images from 2009 to 2014, and the results were compared to the data of a micrometeorological station with eddy covariance flux measurements. Comparing the SEBAL-based evaporative fraction (ΛS) to the corresponding tower-derived evaporative fractions (ΛT) showed good flux estimations in the Landsat overpass time (Coefficient of determination R2 = 0.77, root mean square error RMSE = 0.05 and mean absolute error MAE = 0.076). Three methods were evaluated for upscaling instantaneous latent heat flux (λE) to daily actual evapotranspiration (ETa,D). The upscaling methods use the evaporative fraction (Λ), the reference evapotranspiration fraction (EFr) and the ratio of daily to instantaneous incoming shortwave radiation (Rs24/Rsi) as upscaling factors under the hypothesis of diurnal self-preservation. A preliminary analysis performed using only in-situ measured data demonstrated that the three factors were relatively self-preserved during the daytime, and can yield good ETa,D estimations, particularly when obtained at near the Landsat scene acquisition time (≈10:00 UTC). The upscaling factors obtained from SEBAL retrieved instantaneous fluxes, and some ancillary measured meteorological data were used to upscale SEBAL-estimated instantaneous actual λ to daily ET. The Λ EFr and Rs24/Rsi methods on average overestimated the measured ETa,D by nearly 20, 61 and 18%, respectively. The performance of the Λ and Rs24/Rsi methods was considered satisfactory, bearing in mind the high variable ground cover and the inherent variability of the biome composition, which cannot be properly represented in the Landsat moderate spatial resolution. In this study, we tested the potential of the SEBAL model application in a complex natural ecosystem. This modeling approach will be used to represent the spatial dynamics of ET, which will be integrated into further environmental and hydrological applications.