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•High summer ozone and foliar symptoms were frequent in European forests.•They had stagnating, slightly declining time trends and different spatial pattern.•Ozone was higher in the ...Mediterranean and the Alpine biogeographic regions.•Symptoms tend to be driven by functional leaf traits.•Ozone had a significant effect on symptoms on the most sensitive species.
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 region.
Measuring density of wood samples with mercury volumemeter is a standard throughout the world. To find out the reliability of another less toxic density measuring technique, samples were measured in ...a mercury medium and in a water medium as well. This study is a revision of the previously published results (Finžgar et al., 2013), since the determination of decay phases was questionable and correct results are presented here. New data is also presented herewith. For water measurements, the MSA 323S scale (Sartorius, Germany) with YDK01 Density Determination Kit (Sartorius, Germany) was used for the first time in our labs. We measured density of coarse woody debris from the secondary virgin forest reserve Rajhenavski Rog, Slovenia. Results of the two methods employed were not comparable due to different density definitions. Also, lower densities in higher decay phases were not detected, although expected. Nevertheless, the scale MSA 323S proved to be a reliable method of measuring wood sample density in water. However, some optimizations will have to be considered in the future.
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