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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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Scarce evidence of ozone effect on recent health and productivity
of alpine forestsa case study in Trentino, N. Italy
Marco Ferretti
&Giovanni Bacaro
&Giorgio Brunialti
&Mauro Confalonieri
&Fabiana Cristofolini
Antonella Cristofori
&Luisa Frati
&Angelo Finco
&Giacomo Gerosa
&Simona Maccherini
&Elena Gottardini
Received: 18 April 2017 / Accepted: 2 January 2018 /Published online: 20 January 2018
#Springer-Verlag GmbH Germany, part of Springer Nature 2018
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
) estimated at the level II plot over the
period 19962009 was 3161 mmol m
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
Keywords Defoliation .Basal area increment .Linear mixed models .Multiple regression models .Stomatal flux .Tree rings
Tropospheric ozone (O
) 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
Swiss Federal Research Institute for Forests, Snow, and Landscape
Research WSL, Züricherstrasse 111, 8903 Birmensdorf, Switzerland
TerraData environmetrics, Spin-Off Company of the University of
Siena, Via L. Bardelloni 19, 58025 Monterotondo Marittimo,
Grosseto, Italy
Department of Life Sciences, University of Trieste, Via L. Giorgieri
10, 34127 Trieste, Italy
Provincia Autonoma di Trento, Servizio Foreste e Fauna, Via G.B.
Trener 3, 38121 Trento, Italy
Research and Innovation Centre,Fondazione Edmund Mach (FEM),
Via E. Mach 1, 38010 San Michele allAdige, Italy
Università Cattolica del Sacro Cuore, via Musei 41,
25121 Brescia, Italy
Department of Life Science, University of Siena, Via P.A. Mattioli 4,
53100 Siena, Italy
Environmental Science and Pollution Research (2018) 25:82178232
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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The LTER-Italy network encompasses 79 sites distributed in terrestrial, freshwater and marine domains and reflects the great variety and biodiversity of environments present in Italy and in two extraterritorial areas under Italian responsibility. The research activities carried out at these sites allow following and understanding the short and long term ecosystem dynamics. This chapter provides a synthetic overview of the results achieved by researches focused on the environmental changes detected in the different types of ecosystems. Studies of the terrestrial sites have shown changes, even on relatively short scales, due to the increase in temperature and the variation in the rainfall regime, and the decrease in snow cover. It has been observed an increase in: i) vegetation cover at medium and high altitudes, ii) distribution of thermophilic species, and iii) microbial biomass in the soil. In addition, variations have been recorded in the composition of insect communities and aquatic fauna. On the other hand, variations observed in the fragile environments of coastal dunes seem to be caused more by anthropogenic activities than by climate change. In the freshwater ecosystems, the most evident effect in large and medium-sized lakes is related to temperature increase, which has affected the winter mixing, especially in large lakes, and the production and seasonal cycle of plankton. In contrast, the decreased impact of reduced acid and non-acid atmospheric depositions and the appearance of alien species, especially in the benthic systems, are connected to the anthropic activities. In marine and transitional ecosystems, plankton seem to respond to the climatic variation with changes in phenology and variations in production, which is, however, also linked to anthropogenic impact such as external nutrient supply. Benthic systems show a more marked response, likely due to a tight interplay of climatic variation and anthropogenic pressure, such as the introduction and establishment of alien species mainly linked to commercial use. Terrestrial and aquatic systems, especially the marine ones, respond differently to climate change and anthropogenic activity even if both systems show responses to the temperature increasing. However, it is still difficult to completely disentangle anthropogenic from natural factors that tightly interplay and affect ecosystem components and dynamics.
... Periodical tree growth is based on the diameter measured at breast height (DBH; conventionally at 1.30 m above ground) and expressed in terms of diameter increments during 2001-2005, 2005-2009, and 2001-2009. Implausible values (i.e., negative incremental values, implausible growth rates) were identified, checked and discarded (see Ferretti et al., 2018 for details). ...
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Although several manipulative experiments provided evidence for a negative effect of defoliation on tree growth, results from observational studies were less univocal. This may be due to the ability of observed defoliation to reflect the health status of individual trees, to the influence of site condition and to the amplitude of time window used for growth assessment. Here, we investigated the relationship between two tree health indicators (crown defoliation, damage symptoms) and annual (measured by tree-ring width on 69 Norway spruce trees) and periodical (5-year and 10-year diameter increments, 346 trees from five coniferous species) tree growth. Data originated from 14 (seven for tree rings) ICP Forests Level I plots in Trentino, northern Italy. Diameter, defoliation and damage were measured between 1997 and 2011 as part of the annual crown condition survey, while cores for tree-rings were collected on a sub-sample of trees in 2012. We carried out regression modeling combined with model selection in one-step (periodical data) and two-step (annual data) approaches, using moving averages for the annual data with varying time window widths. Our results indicated an overall negative correlation between defoliation and annual or periodical stem diameter growth. The relationship between defoliation and growth changes in relation to the time window considered, and becomes stronger when data are aggregated over longer time windows (>3 years), when also the occurrence of damage symptoms plays a significant role. The effect of the amplitude of the time windows for data aggregation is probably due to the mechanisms behind the defoliation-growth relationship, which may change according to the causal factors involved. In particular, when larger time windows are considered, short-term fluctuations are likely to be smoothed out, and more general patterns may emerge. We concluded that radial growth is significantly negatively related to defoliation, and this supports the use of defoliation as a rapid indicator for forest health and vitality.
... There are, however, also some downside effects such as increase of fire frequency and the closure of open areas with the homogenization of the landscape [3]. To mitigate these negative effects and to safeguard the economic and ecological functions of forests, it is necessary to implement sustainable management of secondary forests [4]. ...
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Species interactions in mixed plantations can influence tree growth, resources capture and soil fertility of the stands. A combined approach of tree-ring analyses and carbon stable isotope was used to check tree growth and water use efficiency of two species, Populus alba L. and Juglans regia L., intercropped with each other and with N-fixing or competitive production species. Furthermore, soil analyses were performed to understand how the different intercropping systems can influence soil characteristics, in particular soil carbon stock. Dendrochronological data showed that during the first years, the growth of principal species was favored by intercropping. This positive effect decreased in the following years in most of intercropped stands, due to light competition with the crown of companion species. Carbon isotope data showed that P. alba and J. regia had the highest intrinsic water use efficiency when growing with Elaeagnus umbellata Thunb, a shrubby species with a shallow root system that favors a non-competitive exploitation of soil water resources. Finally, the intercropping of the principal species with Corylus avellana L. promoted the highest soil C stock. Our findings confirmed the importance to consider the plantation dynamics and wood formation in the long-run and to apply appropriate thinning and pruning interventions to counteract interspecific competition.
... The frequency of symptoms of damage recorded on different tree's compartments (foliage, branches, stem, collar) was reported closely related to defoliation for all the species considered in this study, in France and elsewhere (e.g. Ferretti et al., 2014Ferretti et al., , 2018Gottardini et al., 2020;Carnicer et al., 2011). Gottardini et al. (2016) found a consistent pattern between crown transparency (a proxy for crown defoliation), visible damage on trees, reduction of shoot length, needle weight, photosynthetic potential and ẟ 18 O (an oxygen isotope useful to evaluate plant responses to environmental variables that influence leaf stomatal functioning, see e.g. ...
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Climate and weather fluctuations and changes are the most important environmental driver of tree canopy defoliation, an indicator of forest health. We examined the relationship between tree defoliation and Basal Area Increment (BAI), a dimension of tree growth related to wood biomass increment, carbon sequestration and therefore to the climate change mitigation potential of forests. We analysed data from mostly even-aged, single-species permanent monitoring plots in France over two growing periods (1995-2004: 47 plots, 2008 trees; 2000-2009: 63 plots, 3116 trees) and for which precipitation deficit was identified as the main environmental driver of defoliation. Trees from ten different species were assessed annually for defoliation and measured periodically for growth, from which we derived periodical (10-year) BAI (BAIperiod). We investigated (i) direction and significance of defoliation-BAIperiod relationship and (ii) occurrence, size and significance of BAI deviation of progressively defoliated trees in proportion to the BAI of undefoliated trees (BAIrel). Analyses were first carried out at the level of individual plots, with results subsequently evaluated using meta-analysis, and further aggregated at different levels (all species, functional groups, individual species). BAIperiod resulted negatively and significantly related to defoliation, with a significant reduction detected already at slight (15%) defoliation level. A generalized statistically significant reduction of BAIrel was obvious, leading to an estimated reduction of 0.7 - 0.8% per unit increase of defoliation for conifers, and 0.9% for broadleaves. Considering the observed distribution of trees along the defoliation range, our results indicate an overall growth reduction of ca. 42% in comparison to a theoretical population of undefoliated trees. Shifts in such a distribution can result into loss or gains of growth, which in turn may have cascading effects on carbon sequestration and therefore on land-climate interactions. In the context of the significant increase in defoliation observed in Europe in recent decades, our results suggest that even slight and moderate variations in defoliation may have had a significant impact on tree and forest growth.
... The analyses carried out by Ferretti et al., 2018 showed that neither AOT40 nor POD0 were significantly related to the annual radial growth of the Alpine forests. However, our results on Mediterranean species showed that growth was positively and negatively related to radiation and humidity, respectively. ...
Given the high ozone concentrations observed in the Mediterranean region during summer, it is crucial to extend our knowledge on the potential ozone impacts on forest health with in situ studies, especially to protect typical endemic forests of the Mediterranean basin. This study is focused on ozone measurements and exposures over the Eastern Adriatic coast and on the calculation of different O3 metrics, i.e., accumulated exposure AOT40 (AOT40dir, AOT40ICP, AOT40pheno) and stomatal O3 fluxes with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (PODY, with Y = 0, 1, 2 nmol O3 m⁻² s⁻¹) used for forest protection. Finally, we provide an assessment of the relationships between the forest response indicators and environmental variables. Passive ozone measurements and monitoring of forest health indicators, namely growth and crown defoliation, were performed for Quercus ilex, Quercus pubescens, Pinus halepensis, and Pinus nigra forests. Results showed that, for all the analysed species, ozone levels were close to reached the upper plausibility limits for passive monitoring of air quality at forest sites (100 ppb), with the highest values found on P. halepensis in the summer period. O3 metrics based on exposure were found to be higher in pine plots than in oak plots, while the highest values of uptake-based metrics were found on P. nigra. Regarding relationships between environmental variables and forest-health response indicators, the crown defoliation was significantly correlated with the soil water content at various depth while the tree growth was correlated with the different O3 metrics. The most important predictors affecting tree growth of Q. pubescens and Q. ilex were AOT40pheno and AOT40dir and POD0 for P. nigra.
... For example, flux has been identified as a better predictor of the distribution and scale of damage for bio-monitoring and beech growth across Europe [62,81]. By contrast, neither flux-based nor AOT40 metrics could explain forest defoliation and declines in basal area increment in an Alpine region in northern Italy [82]. ...
The damage and injury that ground level ozone (O3) causes vegetation has become increasingly evident over the past half century with a large body of observational and experimental evidence demonstrating a variety of effects at ambient concentrations on crop, forest and grassland species and ecosystems. This paper explores the use of experimental data to develop exposure-response relationships for use in risk assessment studies. These studies have typically identified the USA mid-West, much of Europe, the Indo Gangetic Plain in South Asia and the Eastern coastal region of China as global regions where O3 is likely to threaten food supply and other ecosystems. Global risk assessment modelling estimates yield losses of staple crops between 3 to 16% causing economic losses of between US$14 to 26 billion in the year 2000. Changes in anthropogenic emissions of O3 precursors in recent decades have modified O3 concentration profiles (peaks versus background O3) and global distributions with the Northern Hemisphere seeing increases in O3 levels of between 1 and 5 ppb/decade since the 1950s and the emergence of Asia as the region with the highest O3 concentrations. In the future, O3 mitigation could focus on methane (CH4) and nitrogen oxide (NOx) emissions; these will differentially influence global and local/regional O3 concentrations and influence daily and seasonal profiles. The consequent effects on vegetation will in part depend on how these changes in O3 profile alter the exceedance of detoxification thresholds for plant damage. Adaptation options may play an important role in enhancing food supply while mitigation strategies are being implemented. An improved understanding of the mechanisms by which O3 affects plants, and how this might influence detoxification thresholds and interactions with other environmental variables such as water stress and nutrients, would help develop O3 deposition and impact models to support the development of crop, land-surface exchange and ultimately earth system models for holistic assessments of global change. This article is part of a discussion meeting issue 'Air quality, past present and future'.
... From an operational point of view, within the population of trees examined in our study we detected significant and common relationships between defoliation and symptoms of damage, either overall (cumulated number of damage symptoms on trees), on branches (all species) and foliage (European beech only). Although in many cases the causes of damage were not identified, the observed relationship between defoliation and tree damage confirmed the complementarity (and perhaps the link of causality) of these two indicators (see also Ferretti et al., 2014Ferretti et al., , 2018. It is worth noting that, although monitored at different levels (defoliation at tree level; forest damage at forest area level) both defoliation and forest damage are adopted under Forest Europe (2015), and connection / integration between these two indicators are worthwhile to be explored further. ...
Tree crown defoliation is the most widespread indicator of forest health and vitality in Europe. It is part of the ICP Forests Pan-European survey and it is adopted for reporting under Forest Europe. It is readily understandable and can count on fairly harmonized, long-term, large-scale data series across Europe. On the other hand, it is unspecific with respect to possible causes of damage, and its relation with tree functioning remains unclear. This study focused on European beech (Fagus sylvatica L.), Turkey oak (Quercus cerris L.), and holm oak (Quercus ilex L.), three important broadleaved forest species in southern Europe. We investigated whether and to what extent morpho-physiological (functional) leaf traits and other indicators of foliar, branch and stem health condition are associated with tree defoliation. We tested the relationship between defoliation and leaf-, branch- and stem attributes, and whether indicators of damage and functional leaf traits significantly differ (Mann-Whitney U Test) between defoliated (defoliation > 25%) and undefoliated trees (defoliation ≤ 25%). For each species, we considered one site (three to five plots each) and n = 11–19 randomly selected trees. For each tree, the following indicators were measured: crown condition (defoliation; leaf-, branch- and stem damage, in terms of extent and intensity of damage), leaf morphology (leaf thickness, leaf area, lamina length, fluctuating asymmetry, specific leaf area, damaged leaf surface), leaf physiology and chemistry (chlorophyll a fluorescence, chlorophyll content, carbon and nitrogen stable isotopes composition δ¹³C, δ¹⁵N, carbon/nitrogen ratio). Results show that, for the selected trees of all the three species, defoliation was positively related to the extent of damage on branches. While increasing defoliation in European beech was also accompanied by several significant differences at leaf level (i.e., leaf damage, leaf volume, dry weight, carbon/nitrogen ratio and photosynthetic efficiency), for Turkey oak and holm oak the significant differences between defoliated and undefoliated trees were limited to damage on branches (both species).
Tropospheric ozone (O3) is the third most important greenhouse gas that is transported from the stratosphere or formed locally by photochemical reactions among precursors such as nitrogen oxides (NOx), carbon monoxide (CO), methane (CH4), volatile organic compounds (VOCs), and peroxyacetyl nitrate (PAN). The lifetime of tropospheric O3 is long enough, i.e. a few days in the boundary layer to a few months in the free troposphere, allowing its (and its precursors) long–range transport from regional to hemispheric scale through trans–Atlantic, trans–Pacific, and trans–Eurasian transport. Therefore, remote areas such as the Arctic region can be affected. The current annual mean background O3 concentrations at surface–layer are 35–50 ppb in North Hemisphere and 15–25 ppb in South Hemisphere. At regional and local scales, the O3 production depends on the VOCs/NOx ratio. Since the 1990s, anthropogenic O3 precursor emissions decreased in North America and Europe, while eastern Asian emissions have increased. Therefore, both mean and peak O3 concentrations decreased in North America and Europe and increased in East Asia. The reduction in O3 mean concentrations and higher percentiles is associated with reductions in NOx and VOCs emissions in the EU and North America since the 1990s. The increase in lower concentrations and percentiles can be attributed to a reduction in local NOx emissions, due to e.g. vehicle emission controls, resulting in lower O3 titration by NO. Generally, the global background O3 increase can be driven by the net impacts of climate change, i.e. increase in stratospheric O3 inputs, higher CH4 emissions, changing lightning NOx emissions, weakened NO titration and impacting reaction rates, through sea surface temperatures and relative humidity changes. (note: the final abstract might slightly differ due to copy editing)
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The ponderosa pine (Pinus ponderosa, Douglas ex C. Lawson) is a climate-sensitive tree species dominant in the mixed conifer stands of the San Bernardino Mountains of California. However, the close proximity to the city of Los Angeles has resulted in extremely high levels of air pollution. Nitrogen (N) deposition, resulting from nitrous oxides emitted from incomplete combustion of fossil fuels, has been recorded in this region since the 1980s. The impact of this N deposition on ponderosa pine growth is complex and often obscured by other stressors including climate, bark beetle attack, and tropospheric ozone pollution. Here I use a 160-year-long (1855–2015) ponderosa pine tree ring chronology to examine the annual response of tree growth to both N deposition and climate in this region. The chronology is generated from 34 tree cores taken near Crestline, CA. A stepwise multiple regression between the tree ring chronology and various climate and air pollution stressors indicates that drought conditions at the end of the rainy season (March) and NO2 pollution during the water year (pOct-Sep) exhibit primary controls on growth (r2-adj = 0.65, p < 0.001). The direct correlation between NO2 and tree growth suggests that N deposition has a positive impact on ponderosa pine bole growth in this region. However, it is important to note that ozone, a known stressor to ponderosa pine trees, and NO2 are also highly correlated (r = 0.84, p < 0.05). Chronic exposure to both ozone and nitrogen dioxide may, therefore, have unexpected impacts on tree sensitivity to climate and other stressors in a warming world.
Although nitrogen deposition and tropospheric ozone have impacted California forests for decades, broad scale studies of these impacts on forest growth and mortality are lacking. Because of the summer-dry climate over most of the state, forest responses to air pollution are expected to differ from more mesic climates. In this study, data from US Forest Service Forest Inventory and Analysis (FIA) permanent (remeasured) plots were combined with modelled atmospheric N and S deposition and an ozone exposure index to evaluate tree growth and mortality responses in California. Seven of 18 species exhibited significantly greater carbon increment (CI) in tree boles as N deposition increased, though the magnitude of the effect was quite small in most California forests. However, increases in CI were substantial in the coastal ecosections of central and northern California where precipitation and fog exposure are greatest. Redwood (Sequoia sempervirens (D. Don) Endl.) trees exhibited the strongest CI response to N deposition. Our model results imply a mean CI increase of 4.2 kg ha⁻¹ yr⁻¹ of C per kg ha⁻¹ yr⁻¹ of N deposition statewide versus 13.6 in the Central and Northern California Coast ecosections, where > 50% of the trees are redwood or tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.). Increased carbon sequestration rates in response to N deposition in these California coastal regions were similar to increases reported for Europe and global estimates. Nitrogen and S deposition significantly increased the odds of top damage and trees with crown damage exhibited higher mortality, although the effect was small. Elevated ozone exposure was associated with significantly larger rates of overall tree growth. However, for ozone-sensitive ponderosa pine at moderate ozone levels (ozone index values of ca. 20–30 ppb) and moderately-elevated N deposition (15–25 kg ha⁻¹ hr⁻¹), CI begins to decline, before increasing at higher pollution levels, presumably because of the fertilizing effect of N deposition; although data are limited for these more polluted conditions. Sulfur deposition in California forests was low, ranging from 0.3 to 3.1 kg ha⁻¹ yr⁻¹, but was associated with positive growth response in seven coniferous species. The combined effect of N and S deposition and ozone exposure statewide is a net increase in bole CI. However, aridity reduces the stimulatory growth effect of N deposition, and alters the threshold, capacity and sometimes the direction (e.g., S deposition) of the CI response to deposition, factors that need to be considered in global change models.
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The estimation of the ozone (O3) stomatal dose absorbed by a forest is a crucial step for O3 risk assessment. For this purpose, data on O3 concentrations at the forest top-canopy are needed. However, O3 is barely measured at that height, while more often it is measured at a lower height above a different surface, typically a grassland near to the forest edge. The DO3SE model for O3 stomatal flux calculation estimates the top-canopy O3 concentration in near neutral stability conditions. However, near-neutrality is quite rare in the field, particularly in southern Europe. In this work, we present a modification of the DO3SE gradient calculation scheme to include the atmospheric stability. The performance of the new calculation scheme was tested against the direct measurements above a mature forest. Different gradient estimation options were also tested and evaluated. These options include simplified gradient calculation schemes and the techniques of the tabulated gradients described in the UN/ECE Mapping Manual for O3 risk assessment. The results highlight that the inclusion of the atmospheric stability in the DO3SE model greatly improves the accuracy of the stomatal dose estimation. However, the simpler technique of the tabulated gradients had the best performance on a whole-season time frame.
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Global biodiversity and productivity The relationship between biodiversity and ecosystem productivity has been explored in detail in herbaceous vegetation, but patterns in forests are far less well understood. Liang et al. have amassed a global forest data set from >770,000 sample plots in 44 countries. A positive and consistent relationship can be discerned between tree diversity and ecosystem productivity at landscape, country, and ecoregion scales. On average, a 10% loss in biodiversity leads to a 3% loss in productivity. This means that the economic value of maintaining biodiversity for the sake of global forest productivity is more than fivefold greater than global conservation costs. Science , this issue p. 196
For human health studies, epidemiology has been established as important tool to examine factors that affect the frequency and distribution of disease, injury, and other health-related events in a defined population, serving the purpose of establishing prevention and control programs. On the other hand, gradient studies have a long tradition in the research of air pollution effects on plants. While there is no principal difference between gradient and epidemiological studies, the former address more one-dimensional transects while the latter focus more on populations and include more experience in making quantitative predictions, in dealing with confounding factors and in taking into account the complex interplay of different factors acting at different levels. Epidemiological analyses may disentangle and quantify the contributions of different predictor variables to an overall effect, e.g. plant growth, and may generate hypotheses deserving further study in experiments. Therefore, their use in ecosystem research is encouraged. This article provides a number of recommendations on: (1) spatial and temporal aspects in preparing predictor maps of nitrogen deposition, ozone exposure and meteorological covariates; (2) extent of a dataset required for an analysis; (3) choice of the appropriate regression model and conditions to be satisfied by the data; (4) selection of the relevant explanatory variables; (5) treatment of interactions and confounding factors; and (6) assessment of model validity.
The frequency of Viburnum lantana L. plants showing visible foliar symptoms (VFS) was assessed in Trentino, north Italy in 2010, 2012, 2014 and 2015. The assessment was based on a sub-sample (n = 10) of the ViburNeT observation plots network installed in 2010 according to a stratified random design. Depending on the year, a range of 193–232 plants were assessed during August. The frequency of symptomatic plants varied from 20.7 to 50.6%. Mean May-July hourly ozone concentration measured by conventional monitors over the same area and period varied from 37.9 to 45.8 ppb. There was a consistent time pattern between ozone and VFS. Consistency is confirmed if also a pilot survey carried out in 2009 is taken into account. Results are promising and supportive of the use of V. lantana as in-situ bioindicator for monitoring ozone impact on vegetation in forest areas.
The European Forest Institute (EFI) has five Research and Development priority ar­ eas: forest sustainability, forestry and possible climate change, structural changes in markets for forest products and services, policy analysis, and forest sector informa­ tion services and research methodology. In the area of forest sustainability our most important activity has been the project "Growth trends of European forests", the re­sults of which are presented in this book. The project was started in August 1993 under the leadership of Prof. Dr. Heinrich Spiecker from the University of Freiburg, Germany, and it is one of the first EFI's research projects after its establishment in 1993. The main purpose of the project was to analyse whether site productivity has changed in European forests during the last decades. While several forest growth studies have been published at local, re­ gional and national levels, this project has aimed at stimulating a joint effort in iden­ tifying and quantifying possible growth trends and their spatial and temporal extent at the European level. Debate on forest decline and possible climate change, as well as considerations re­ lated to the long term supply of wood underline the importance of this project, both from environmental and industrial points of view. Knowledge on possible changes in growth trends is vital for the sustainable management of forest ecosystems.
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.
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.