• Energy Research

A methodological approach based on detailed land-use map, high-resolution LiDAR data and field surveys was developed to categorize productive and non-productive mixed forests, both in term of stand attributes and structural diversity. In 2011, leaf-off dedicated airborne LiDAR data were collected in a 20,000 ha inland patchy area which was representative of soil land use in the Apennines mountains of southern Italy. By combining field and LiDAR data in 5574 ha of forests with coexisting evergreen and deciduous species, wemodelled common forest stand variables (height, diameter, volumeand biomass)with high accuracy (0.60 <= Adj.R2 <= 0.89).Moreover, a moderate correlation (0.425 <= ? <= 0.462) between field- and LiDAR-derived diversity indices was found. About 3393 ha of forests are enclosed in protected areas of the Natura 2000 network, which in turn possesses 77% (~ 576,286 Mg) of total aboveground dry biomass. Overall, eight forest types were identified, one of which, the European beech, is only found in the Natura 2000 sites,while other forest types are also found elsewhere. This is the first study to undertake a LiDAR analysis ofMediterranean forests in the Campania Region and might help better evaluate trade-off, especially in protected areas, in order to enhance multiple benefits and support sustainable management of forests.

AbstractAimThe aim was to decipher Europe‐wide spatio‐temporal patterns of forest growth dynamics and their associations with carbon isotope fractionation processes inferred from tree rings as modulated by climate warming.LocationEurope and North Africa (30‒70° N, 10° W‒35° E).Time period1901‒2003.Major taxa studiedTemperate and Euro‐Siberian trees.MethodsWe characterize changes in the relationship between tree growth and carbon isotope fractionation over the 20th century using a European network consisting of 20 site chronologies. Using indexed tree‐ring widths (TRWi), we assess shifts in the temporal coherence of radial growth across sites (synchrony) for five forest ecosystems (Atlantic, boreal, cold continental, Mediterranean and temperate). We also examine whether TRWi shows variable coupling with leaf‐level gas exchange, inferred from indexed carbon isotope discrimination of tree‐ring cellulose (Δ13Ci).ResultsWe find spatial autocorrelation for TRWi and Δ13Ci extending over a maximum of 1,000 km among forest stands. However, growth synchrony is not uniform across Europe, but increases along a latitudinal gradient concurrent with decreasing temperature and evapotranspiration. Latitudinal relationships between TRWi and Δ13Ci (changing from negative to positive southwards) point to drought impairing carbon uptake via stomatal regulation for water saving occurring at forests below 60° N in continental Europe. An increase in forest growth synchrony over the 20th century together with increasingly positive relationships between TRWi and Δ13Ci indicate intensifying impacts of drought on tree performance. These effects are noticeable in drought‐prone biomes (Mediterranean, temperate and cold continental).Main conclusionsAt the turn of this century, convergence in growth synchrony across European forest ecosystems is coupled with coordinated warming‐induced effects of drought on leaf physiology and tree growth spreading northwards. Such a tendency towards exacerbated moisture‐sensitive growth and physiology could override positive effects of enhanced leaf intercellular CO2 concentrations, possibly resulting in Europe‐wide declines of forest carbon gain in the coming decades.

AbstractAs major terrestrial carbon sinks, forests play an important role in mitigating climate change. The relationship between the seasonal uptake of carbon and its allocation to woody biomass remains poorly understood, leaving a significant gap in our capacity to predict carbon sequestration by forests. Here, we compare the intra-annual dynamics of carbon fluxes and wood formation across the Northern hemisphere, from carbon assimilation and the formation of non-structural carbon compounds to their incorporation in woody tissues. We show temporally coupled seasonal peaks of carbon assimilation (GPP) and wood cell differentiation, while the two processes are substantially decoupled during off-peak periods. Peaks of cambial activity occur substantially earlier compared to GPP, suggesting the buffer role of non-structural carbohydrates between the processes of carbon assimilation and allocation to wood. Our findings suggest that high-resolution seasonal data of ecosystem carbon fluxes, wood formation and the associated physiological processes may reduce uncertainties in carbon source-sink relationships at different spatial scales, from stand to ecosystem levels.

AbstractDeciphering the spatial patterns of alpine treelines is critical for understanding the ecosystem processes involved in the persistence of tree species and their altitudinal limit. Treelines are thought to be controlled by temperature, and other environmental variables but they have rarely been investigated in regions with different land‐use change legacies. Here, we systematically investigated treeline elevation in the Apennines (Italy) and Southern Alps (New Zealand) with contrasting human history but similar biogeographic trajectories, intending to identify distinct drivers that affect their current elevation and highlight their respective peculiarities. Over 3622 km of Apennines, treeline elevation was assessed in 302 mountain peaks and in 294 peaks along 4504 km of Southern Alps. The major difference between the Southern Alps and Apennines treeline limit is associated with their mountain aspects. In the Southern Alps, the scarcely anthropized Nothofagus treeline elevation was higher on the warmer equator‐facing slopes than on the pole‐facing ones. Contrary to what would be expected based on temperature limitation, the elevation of Fagus sylvatica treelines in the Apennines was higher on colder, pole‐facing slopes than on human‐shaped equator‐facing, warmer mountainsides. Pervasive positive correlations were found between treeline elevation and temperature in the Southern Alps but not in the Apennines. While the position of the Fagus and Nothofagus treelines converge on similar isotherms of annual average temperature, a striking isothermal difference between the temperatures of the hottest month on which the two taxonomic groups grow exists. We conclude that actual treeline elevation reflects the ecological processes driven by a combination of local‐scale topoclimatic conditions, and human disturbance legacy. Predicting dynamic processes affecting current and future alpine treeline position requires further insight into the modulating influences that are currently understood at a regional scale.

Abstract There is a current concern that the capacity of urban forests to recover from the effects of climate change may be diminishing. New management options are needed so that they can continue to provide ecosystem services to local communities. After a windstorm occurred on June 2014 pre- and post-disturbance stand conditions (years 2010 and 2015, respectively) of the historical old-growth holm oak forest of Parco Gussone were analysed by combining ground- and satellite-based methodologies. Results highlighted that Parco Gussone was primarily valued for its historical importance and, despite the phytosanitary conditions of the trees, no silvicultural treatments were made since 1986, most probably due to conflicts arisen between different stakeholders. Therefore in 2014, the windstorm damaged 406 trees (8.1% of the total aboveground forest dry biomass) and it was stand-replacing on 1.53 ha (9.3 % of the total forest area). Windthrows, heterogeneously distributed and unequally sized (103 canopy gap ranging between ∼6 to 1632 m2), caused, overall, a significant reduction of LAI (∼19%). The presence of large gaps promoted the invasion of non-native herbaceous species whereas native species of the shrubs and herbaceous layers were favoured when felled trees were left on the ground or removed mechanically during harvest, respectively. In this context, urban forests should be considered as ‘complex adaptive systems’, therefore natural processes can be simulated by applying a ‘close-to-nature’ silviculture (e.g. by opening small gaps), vulnerability assessed (e.g. using a tree-by-tree VTA), biodiversity and ecological resilience improved and short- and long term disturbance effects evaluated (e.g. analysis of disturbance attributes and stand dynamics) so that specific conservation goals can be adapted to a specific landscape and biotic community. By implementing and applying the proposed guidelines in urban forest planning, we are confident that the resilience of those Mediterranean urban forest ecosystems could be effectively restored and improved.