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Scarce evidence of ozone effect on recent health and productivity of Alpine forests – a case study in Trentino, N. Italy

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We investigated the significance of tropospheric ozone as a factor explaining recent tree health (in terms of defoliation) and productivity (in terms of Basal Area Increment, BAI) in 15 ICP Forests Level I and one Level II plots in Alpine forests in Trentino (N. Italy). Mean daily ozone summer concentrations varied between 30-72 parts per billion (ppb) leading to large exceedance of concentration-based Critical Levels set to protect forest trees. Phytoxic Ozone Dose (POD0) estimated at the Level II plots over the period 1996-2009 was 31-61 mmol m-2 Projected Leaf Area (PLA). Significance of ozone was investigated taking into account other site and environmental factors. Simple linear regression, multiple linear regression (MLR, to study mean periodical defoliation and mean periodical basal area increment) and Linear Mixed Models (LMM, to study annual defoliation data) were used. Our findings suggest thatregardless the metric adopted - tropospheric ozone is not a significant factor in explaining recent status and trends of forest health and growth in the Alpine region examined, which are in turn driven by biotic/abiotic damage, nutritional status, age and site characteristics. These results contrast with available ozone-growth Dose Response Relationship (DRR) and other observational studies. This may be due to a variety of concurrent reasons: (i) DRRs, developed for individual saplings under controlled condition are not necessarily valid for mature trees into real forests ecosystems; (ii) some observational studies may have suffered from biased design; and (iii) since Alpine forests have been exposed to high ozone levels (and other oxidative stress) over decades possible acclimation mechanisms cannot be excluded.
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OZONE AND PLANT LIFE: THE ITALIAN STATE-OF-THE-ART
Scarce evidence of ozone effect on recent health and productivity
of alpine forestsa case study in Trentino, N. Italy
Marco Ferretti
1,2
&Giovanni Bacaro
3
&Giorgio Brunialti
2
&Mauro Confalonieri
4
&Fabiana Cristofolini
5
&
Antonella Cristofori
5
&Luisa Frati
2
&Angelo Finco
6
&Giacomo Gerosa
6
&Simona Maccherini
2,7
&Elena Gottardini
5
Received: 18 April 2017 / Accepted: 2 January 2018 /Published online: 20 January 2018
#Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
We investigated the significance of tropospheric ozone as a factor explaining recent tree health (in terms of defoliation) and
productivity (in terms of basal area increment, BAI) in15 ICP Forests level I and one level II plots in alpine forests in Trentino (N.
Italy). Mean daily ozone summer concentrations varied between 30 and 72 parts per billion (ppb) leading to large exceedance of
concentration-based critical levels set to protect forest trees. Phytoxic ozone dose (POD
0
) estimated at the level II plot over the
period 19962009 was 3161 mmol m
2
projected leaf area (PLA). The role of ozone was investigated taking into account other
site and environmental factors. Simple linear regression, multiple linear regression (MLR, to study mean periodical defoliation
and mean periodical BAI), and linear mixed models (LMM, to study annual defoliation data) were used. Our findings suggest
thatregardless of the metric adoptedtropospheric ozone is not a significant factor in explaining recent status and trends of
defoliation and BAI in the alpine region examined. Both defoliation and BAI are in turn driven by biotic/abiotic damage,
nutritional status, DBH (assumed as a proxy for age), and site characteristics. These results contrast with available ozone-
growth dose response relationships (DRRs) and other observational studies. This may be due to a variety of concurrent reasons:
(i) DRRs developed for individual saplings under controlled condition are not necessarily valid for population of mature trees into
real forest ecosystems; (ii) some observational studies may have suffered from biased design; and (iii) since alpine forests have
been exposed to high ozone levels (and other oxidative stress) over decades, possible acclimation mechanisms cannot be
excluded.
Keywords Defoliation .Basal area increment .Linear mixed models .Multiple regression models .Stomatal flux .Tree rings
Introduction
Tropospheric ozone (O
3
) concentrations have increased glob-
ally during the twentieth century (Cooper et al. 2014). In rural
European environments, concentration has doubled from
about 1015 ppb at the end of the nineteenth century to 20
30 ppb in the 1980s (Volz and Kley 1988; Vingarzan 2004),
with further increase in many areas since then (Staehelin and
Schnadt Poberaj 2008;Cooperetal.2014). Such an increase
was attributed to an augmented net chemical production in the
troposphere due to increased precursor emissions, although
increases in the stratospheric source of ozone may also have
contributed (The Royal Society 2008). More recently, trends
have varied by region (Cooper et al. 2014; Tørseth et al.
2012), and in Western Europe mean summer concentration
at forested sites leveled off or decreased slightlysince the year
2000 (EEA 2014; Schaub et al. 2016a). Concentrations of 50
80 ppb, however, are still frequent in many rural and remote
Responsible editor: Philippe Garrigues
*Marco Ferretti
marco.ferretti@wsl.ch
1
Swiss Federal Research Institute for Forests, Snow, and Landscape
Research WSL, Züricherstrasse 111, 8903 Birmensdorf, Switzerland
2
TerraData environmetrics, Spin-Off Company of the University of
Siena, Via L. Bardelloni 19, 58025 Monterotondo Marittimo,
Grosseto, Italy
3
Department of Life Sciences, University of Trieste, Via L. Giorgieri
10, 34127 Trieste, Italy
4
Provincia Autonoma di Trento, Servizio Foreste e Fauna, Via G.B.
Trener 3, 38121 Trento, Italy
5
Research and Innovation Centre,Fondazione Edmund Mach (FEM),
Via E. Mach 1, 38010 San Michele allAdige, Italy
6
Università Cattolica del Sacro Cuore, via Musei 41,
25121 Brescia, Italy
7
Department of Life Science, University of Siena, Via P.A. Mattioli 4,
53100 Siena, Italy
Environmental Science and Pollution Research (2018) 25:82178232
https://doi.org/10.1007/s11356-018-1195-z
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Nelle foreste delle Alpi, i valori di pH delle precipitazioni sono aumentati in relazione alla significativa riduzione delle concentrazioni di solfati e nitrati nelle deposizioni atmosferiche, conseguenza del generale calo di emissioni di anidridi di zolfo e azoto (Salvadori et al. 2009). Al Passo Lavazè, in Val di Fiemme, non è emersa una relazione significativa fra lo stato di salute ed accrescimento delle piante ed i valori di ozono troposferico, nonostante questi siano risultati superiori ai livelli definiti per la protezione della vegetazione (Ferretti et al. 2018). Nelle ultime due decadi, fino al 2018, la pecceta subalpina è cresciuta con ritmo abbastanza stabile e piuttosto elevato, soprattutto se rapportato all'altitudine del sito (1800 m s.l.m.) e all'età del soprassuolo. ...
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Tropospheric ozone is a serious air-pollutant, with large impacts on plant function. This study demonstrates that tropospheric ozone, although it damages plant metabolism, does not necessarily reduce ecosystem processes such as productivity or carbon sequestration because of diversity change and compensatory processes at the community scale ameliorate negative impacts at the individual level. This study assesses the impact of ozone on forest composition and ecosystem dynamics with an individual-based gap model that includes basic physiology as well as species-specific metabolic properties. Elevated tropospheric ozone leads to no reduction of forest productivity and carbon stock and to increased isoprene emissions, which result from enhanced dominance by isoprene-emitting species (which tolerate ozone stress better than non-emitters). This study suggests that tropospheric ozone may not diminish forest carbon sequestration capacity. This study also suggests that, because of the often positive relationship between isoprene emission and ozone formation, there is a positive feedback loop between forest communities and ozone, which further aggravates ozone pollution.
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Key message Daily stem growth was reduced by drought with high significance, but not affected by ozone uptake or drought–ozone interaction. Increasing air temperature showed capacity of compensating negative drought effects. Abstract Future increases in stress on forest trees due to rising ozone deposition and/or exacerbating drought are one of many contemporary climate change concerns. European beech (Fagus sylvatica L.) is known to be sensitive to both stressors. To date, there is limited evidence concerning the impact of ozone uptake, or its combined effect with drought, on the growth of forest trees. This study emanated from the hypothesis that high daily ozone influx potentially limits daily radial stem increment. A secondary hypothesis intimated that not only prolonged, but also short-term water limitation has the capacity for reducing intra-annual growth performance. To address these hypotheses, the concerted impacts of drought and O3 on radial stem growth were analyzed as components of multi-factorial field scenarios comprising gradients in altitude, temperature, precipitation and ozone exposure. Linear mixed models, adjusting for meteorological factors and nutrition, were fit to daily growth measurements in nine beech forest sites across Bavaria/Germany during three consecutive growing seasons. During individual years, daily ozone influx did not statistically significantly limit daily stem growth. However, short-term drought was associated with statistically significant, but minor and reversible limitations of intra-annual radial stem growth. Distinctive levels of plant-available soil water and soil water potential limited growth. Increases in air temperature were conducive to beech stem growth across the study region, apparently offering the capacity for buffering drought impact on the stem growth of beech.