The fingerprint of tropospheric ozone on broadleaved forest vegetation in Europe

Tropospheric ozone (O3) increased globally in the 20th century, contributes to climate change and can have adverse effects on terrestrial ecosystems. The response of forest vegetation to ozone is modulated by species- and site-specific factors and visible foliar symptoms (VFS) are the only direct evidence of ozone effects on vegetation. VFS have been observed and reproduced under (semi-) controlled conditions and their field assessment has been largely harmonized in Europe. We analyzed ozone concentration and VFS data as measured at (respectively) 118 and 91 intensive monitoring sites of the International Co-Operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) spanning over five European biogeographic regions from 2005 to 2018. Average values for VFS were calculated accounting for the number of species present and their observed frequency. Spatial and temporal variation of ozone concentrations, VFS, and their relationships across Europe were then investigated by applying Generalized Linear Mixed Models (GLMMs) and combined GLMMs. Ozone concentrations exceeded 40 ppb on 37.3 % of the sites and were significantly higher (p < 0.05) in the Alpine and the Mediterranean regions. Over the 2005–2018 period there was a substantial stagnation of ozone concentrations with a tendency towards decreasing values in the Alpine-Boreal sites and increasing values in the Atlantic sites. Ozone left a “fingerprint” in terms of VFS on 38 % of the observed broadleaved woody species across Europe, with no significant difference among biogeographic regions. Overall, and again with the exception of an increase at the Atlantic sites, the frequency of VFS remained unchanged or has been slightly declining over the investigated period. We found positive relationship between ozone concentrations and VFS across Europe (p < 0.05), while their temporal trends (both insignificant) were not related. The species with the highest frequency of VFS were those classified as sensitive species under controlled/semi-controlled experimental conditions. Frequency of VFS tends to be modulated by vegetation traits such as specific leaf area and leaf thickness (p < 0.10). Our results showed that, although ozone levels suggested a North-to-South gradient of increasing potential risk to vegetation with hot spots in the Alps and in the Mediterranean, VFS observed on the actual species assemblage at the sites modifies this picture. According to frequency of VFS, ozone risk for vegetation may be higher in parts of the Alpine and Continental Europe than in the Mediterranean regio

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

201

Harmful impact of exceptional cold air outbreak in april 1997 on silver fir in Croatia

After a severe outbreak of cold air in mid and late April in 1997, locally occurring damages on twigs and needles of silver fir were recorded in some forests in Croatia. Field examinations in the first half of July 1997 revealed the damages on one-year and older needles while fully developed twigs of current year growth were left intact. Southern and western slopes with fir growing forests rep­ resented typically affected sites. Further laboratory analyses confirmed the field observation that no harmful insect or pathogens were the cause of these damages. Spread of symptoms, expressed more heavily at lower elevations, indicated a prob­ able connection with recent exceptionally cold air outbreak in mid-April. Physiological disturbances caused by potassium deficiency are discussed in the light of specific occurrences of damage symptoms on silver fir trees

Phosphorus nutrition of beech (Fagus sylvatica L.) is decreasing in Europe

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The Effect of Environmental Factors on the Nutrition of European Beech (Fagus sylvatica L.) Varies with Defoliation

Despite being adapted to a wide range of environmental conditions, the vitality of European beech is expected to be significantly affected by the projected effects of climate change, which we attempted to assess with foliar nutrition and crown defoliation, as two different, yet interlinked vitality indicators. Based on 28 beech plots of the ICP Forests Level I network, we set out to investigate the nutritional status of beech in Croatia, the relation of its defoliation and nutrient status, and the effects of environmental factors on this relation. The results indicate a generally satisfactory nutrition of common beech in Croatia. Links between defoliation and nutrition of beech are not very direct or very prominent; differences were observed only in some years and on limited number of plots. However, the applied multinomial logistic regression models show that environmental factors affect the relationship between defoliation and nutrition, as climate and altitude influence the occurrence of differences in foliar nutrition between defoliation categories.publishedVersio

Part IV Visual assessment of crown condition and damaging agents

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Forest condition and environmental drivers in Europe: Recent evidence from selected studies

202

Dégradation de la nutrition des arbres en phosphore : un signal confirmé à l'échelle européenne

En Europe, la productivité des forêts a augmenté durant les dernières décennies suite à l’effet combiné de la concentration croissante en CO2 dans l’atmosphère et des dépôts atmosphériques d’azote. Les dépôts d’azote étant restés élevés dans différentes régions d’Europe et la concentration en CO2 dans l’atmosphère continuant de s’accroître, cette productivité pourrait encore augmenter sauf si elle devient limitée par la disponibilité d’autres ressources, notamment les nutriments. Les objectifs de cette étude étaient de décrire le statut nutritionnel foliaire des principales essences forestières en Europe (hêtre commun, chênes sessile et pédonculé, épicéa commun, pin sylvestre, sapin pectiné), d’identifier les nutriments limitants pour la croissance pour chacune de ces essences et de détecter les évolutions temporelles de la nutrition foliaire. Elle s’est basée sur les données d’analyses foliaires collectées entre 1992 et 2009 dans les placettes de suivi des écosystèmes forestiers de niveau II du programme international concerté sur les forêts (PIC Forêts). Il s’agit d’un jeu de données unique qui couvre l’entièreté de l’Europe sur deux décennies et qui a été produit selon des méthodes harmonisées entre les différents pays. Le niveau de nutrition en azote est généralement bon (suboptimal à optimal) pour les feuillus, mais sous le seuil de déficit pour environ la moitié des placettes résineuses. En revanche, une déficience en phosphore est constatée pour une part notable des placettes de chaque essence (de 22 à 74 %). Toutes les essences sont aussi affectées par des déficiences en cations basiques (calcium, magnésium, potassium) mais dans une moindre proportion de leurs placettes (de 5 à 40 %). L’analyse des tendances a permis de mettre en évidence une augmentation significative de la masse des feuilles ou des aiguilles chez le hêtre et l’épicéa commun. Au niveau des teneurs foliaires, la grande majorité des évolutions détectées sont des tendances à la baisse (20 sur 22). Parmi les évolutions les plus préoccupantes, on note une dégradation nette de la nutrition en phosphore pour la plupart des essences, ce qui confirme le signal mis en évidence précédemment à l’échelle des placettes de France, de Wallonie et du Luxembourg (Jonard et al., 2009). Les teneurs foliaires en azote, soufre et potassium diminuent également significativement pour certaines essences. En ce qui concerne le calcium et le magnésium, des tendances à la baisse sont observées pour les essences feuillues et à la hausse pour les essences résineuse