ALBERT

Description: Key message Atmospheric deposition of nitrogen compounds and soil and foliar variables related to N deposition resulted important factors accounting for the variability of defoliation in European forest plots. Context Nitrogen (N) deposition has increased in the northern hemisphere because of anthropogenic-related emission of N compounds. Increased N availability may have an adverse impact on forest sustainability. Aims This study aims to test the importance of throughfall N (N thr ) deposition in explaining the variability of the frequency of trees with defoliation 〉25 % ( F 25 ), an indicator of forest condition. Methods A pan-European data set (71 plots) with enhanced quality control was considered. The additive effect of N thr -related predictors (identified conceptually and by rank correlation) in explaining F 25 was investigated by partial least square regression in comparison with a reference model based on site, stand, management and climate data. Reported damage to foliage, N thr deposition, foliar N ratios and mineral top-soil variables were added stepwise to the reference model. Results N-related variables improved defoliation models. Higher N thr deposition led to higher F 25 for beech and Norway spruce, while the effect was opposite for Scots pine. Higher foliar N ratios led to higher F 25 for all species. Conclusion N thr deposition, damage to foliage, foliar N/P, N/Ca, N/Mg, N/K, top-soil pH, C/N and exchangeable base cation resulted important factors (although with possible diverse effect) in explaining the variability of F 25 among plots.

Description: • Key message Pruning one third of crown length in summer produced the least number of epicormic branches after two growing seasons. Epicormic branches can be removed without compromising tree growth. • Context The formation of epicormic shoots is often observed following pruning treatments, but their role in the overall tree growth is unknown. • Aims The objectives of this study were to examine how pruning intensity and season affect the production of epicormic branches and how their presence (or removal) affects tree growth and total non-structural carbohydrate reserves in the roots. • Methods Trees from four hybrid poplar clones were pruned in fall, spring, and summer at two intensities 1/3 and 2/3 of the crown length and an unpruned control. Produced epicormic branches were removed from half the trees. • Results Pruning intensity and season were the most important factors affecting the number and biomass of epicormic shoots while clone was not. Pruning 1/3 crown length in summer reduced the emergence of epicormic shoots compared to 2/3 and spring or fall pruning. Two years after pruning, the removal of epicormic shoots did not affect height or diameter at breast height of trees, and their presence did not restore root total non-structural carbohydrates reserves to unpruned levels. • Conclusion We concluded that pruning should be done in summer at 1/3 of the crown length to reduce epicormic shoot formation and to avoid decreases in stem growth. If epicormic shoots appear, they can be removed without compromising tree growth.

Description: • The key message N addition decreased soil inorganic P availability, microbial biomass P, and acid phosphatase activity in the larch plantation. Soil inorganic P availability decreased after N addition due to the changes in both microbial properties and plant uptake. • Context Soil phosphorus (P) availability is considered an important factor in influencing the biomass production of plants. Sustained inputs of nitrogen (N) through atmospheric deposition or N fertilizers, particularly in temperate forests, may change the composition and availability of P and thus affect long-term forest productivity. • Aims The objective of this study was to assess soil P availability, P fractions, and microbial properties including microbial biomass P and acid phosphatase activity after 9 consecutive years of N addition in a larch ( Larix gmelinii ) plantation, northeastern China. • Methods From 2003 to 2011, NH 4 NO 3 was added to replicate plots (three 20 m × 30 m plots) in the larch plantation each year at a rate of 100 kg N ha −1  year −1 . Soil samples from 0–10-cm and 10–20-cm depths were collected in N addition plots and control (no N addition) plots. • Results N addition significantly decreased soil NaHCO 3 -Pi (Pi is inorganic P), microbial biomass P, and acid phosphatase activity but increased the NaOH-Pi concentration. N addition appeared to induce a decrease in soil inorganic P availability by changing pH and P uptake by trees. In addition, N addition significantly decreased the NaOH-Po (Po is organic P) concentration, possibly because of increased P mineralization. However, the total P and other P fractions were unaffected by N fertilization. • Conclusion Our results suggested that N addition enhanced P uptake by trees, whereas it reduced soil inorganic P availability as well as microbial biomass and activity related to soil P cycling in the larch plantation.

Description: Key message Warming will induce an upward displacement of Scots pine, but this can be partially mitigated by maintaining a more intense land use. Context Scots pine is currently declining in most inner alpine sectors of southern Europe. The relative contribution of climate, land use change, and disturbances on the decline is poorly understood. What will be the future distribution of the species? Is vegetation shifting toward oak-dominated forests? What is the role of extreme drought years? Aims The aims of the study were to determine drivers of current distribution of Scots pine and downy oak in Aosta valley (SW Alps), to extrapolate species distribution models to year 2080 (Special Report on Emissions Scenarios (SRES) A1B), and to assess the correlation between pine vitality after the extreme droughts of 2003 and 2006, and modeled longterm vegetation changes. Methods Ensemble distribution models were created using climate, topography, soil, competition, natural disturbances, and land use. Species presence was derived from a regional forest inventory. Pine response to drought of 2003–2006 was assessed by Normalized Difference Vegetation Index (NDVI) differencing and correlated to modeled cover change between 2080 and present. Results Scots pine and downy oak were more likely to occur under higher climatic aridity. Scots pine was also associated to higher wildfire frequency, land use intensity, and lack of competition. In a warming scenario, pine experienced an elevational displacement. This was partially counteracted if no land abandonment was hypothesized. Downy oak cover increased in all scenarios. Short- and long-term drought responses of pine were unrelated. Conclusion Warming will induce an upward displacement of pine, but this can be partially mitigated by maintaining a more intense land use. The drought-induced decline in pine vitality after extreme years did not overlap to the modeled species response under climate warming; responses to short-term drought must be more thoroughly understood in order to predict community shifts.

Description: Key message Forest maturity benefits biodiversity by providing positive effects on key arthropod assemblages such as spider and ground beetles, which play a fundamental role in the ecosystem. Context Sustainable forest management is a widely held international goal, and more knowledge is needed on invertebrate assemblages, essential to the ecological functioning of forest ecosystems. Aims We aim at evaluating the effects of microsite conditions on spider, centipede, and ground beetle assemblages living in an unmanaged protected beech forest within the Natural Park of Alpi Marittime (SW Alps, Italy). In view of our results, we provide insights on the successional pathways of the focal assemblages in relation to future management of the forest, recommended by the local authorities for conservation purposes. Methods We placed 50 pitfall traps along four transects crossing the forest and emptied them monthly, from July to October 2011. We characterized the four arthropod assemblages in terms of abundance, species richness, diversity, and biomass and related them to leaf cover, rock cover, wood debris cover, litter depth, number of trees, mean tree size, and light conditions at ground level using generalized linear mixed models (GLMM) and canonical correspondence analysis (CCA). Results Thirty-one species of spiders (1,212 individuals), 12 of centipedes (262 individuals), and 11 of ground beetles (2,177 individuals) were collected. In all groups, mature-forest species highly dominated the samples. Tree size proved to be one of the most important parameters conditioning the assemblages, in particular spiders and ground beetles. A minor effect of light conditions and ground cover (presence of wood debris) was also detected. Conclusions In view of our results, the recent guidelines for the management of the forest seem in accordance with an effective conservation of the forest arthropod assemblages. Interventions aimed at stabilizing and renovating critical areas within the forest go along with a progressive amelioration of the forest arthropod community. With respect to the maintenance of a large degree of arthropod diversity, stand thinning may not be the most effective management, and reaching a more mature stage might be of interest.

Description: Key message Few integration steps (adding low-cost ozone measurements, link to existing conventional monitors, joint data processing) transformed the traditional forest monitoring network into a multifunctional infrastructure producing information relevant for estimating risk to vegetation and human health Context Traditionally, forest monitoring networks have been designed to assess status and trends of forest condition. We argue that they can help providing answers to a much broader range of questions for science, policy, and society. Here, we concentrate on the example of ground-level ozone pollution. Aims The aim of this study is to demonstrate the value of present forest monitoring networks as infrastructures that—with few integration steps—can provide important data and information to estimate the risk posed by ground-level ozone to vegetation and human health. Methods We measured ozone concentration by passive samplers at the local (Trentino, northern Italy) plots of the ICP Forests Level I network over the period 2007–2011. By integrating these data with those from conventional ozone monitors (mostly located in urban areas), we (i) obtained an even distribution of air quality measurements over the investigated area, (ii) estimated international exposure indicators for vegetation and human population, and (iii) obtained data allowing geostatistical modeling and mapping of ozone concentrations, exposure, and associated potential risk. Results Mean May–July ozone concentration ranged from 58 to 169 μg m −3 , depending on forest site and year. Modeling and mapping (root-mean-square deviation (RMSD) = 12.31 μg m −3 ) provided evidence that the risk threshold for vegetation in terms of AOT40 was exceeded in large parts (90 %) of the study area, and frequently even by two times, depending on the year. With respect to population, up to 43 % of the dwellers were exposed to medium–high risk of exceedances of the information threshold. Conclusion Ozone measurements carried out at the ICP Forests Level I forest monitoring network permitted mapping ozone levels and the estimation of possible risk for vegetation and human health. Forest monitoring networks can be seen as infrastructures that can be useful to address a wide range of environmental issues and with a much broader scope than their original one.