This Tropospheric Ozone Assessment Report (TOAR) on the current state of knowledge of ozone metrics of relevance to vegetation (TOAR-Vegetation) reports on present-day global distribution of ozone at over 3300 vegetated sites and the long-term trends at nearly 1200 sites.TOAR-Vegetationfocusses on three metrics over vegetation-relevant time-periods across major world climatic zones: M12, the mean ozone during 08:00–19:59; AOT40, the accumulation of hourly mean ozone values over 40 ppb during daylight hours, and W126 with stronger weighting to higher hourly mean values, accumulated during 08:00–19:59.Although the density of measurement stations is highly variable across regions, in general, the highest ozone values (mean, 2010–14) are in mid-latitudes of the northern hemisphere, including southern USA, the Mediterranean basin, northern India, north, north-west and east China, the Republic of Korea and Japan. The lowest metric values reported are in Australia, New Zealand, southern parts of South America and some northern parts of Europe, Canada and the USA. Regional-scale assessments showed, for example, significantly higher AOT40 and W126 values in East Asia (EAS) than Europe (EUR) in wheat growing areas (p< 0.05), but not in rice growing areas. In NAM, the dominant trend during 1995–2014 was a significant decrease in ozone, whilst in EUR it was no change and in EAS it was a significant increase.TOAR-Vegetation provides recommendations to facilitate a more complete global assessment of ozone impacts on vegetation in the future, including: an increase in monitoring of ozone and collation of field evidence of the damaging effects on vegetation; an investigation of the effects on peri-urban agriculture and in mountain/upland areas; inclusion of additional pollutant, meteorological and inlet height data in the TOAR dataset; where not already in existence, establishing new region-specific thresholds for vegetation damage and an innovative integration of observations and modelling including stomatal uptake of the pollutant.

. 2011 Evidence of widespread effects of ozone on crops and (semi-)natural vegetation in Europe (1990Europe ( -2006 in relation to AOT40-and flux-based risk maps. Global Change Biology, 17. 592-613. 10.1111Biology, 17. 592-613. 10. /j.1365Biology, 17. 592-613. 10. -2486Biology, 17. 592-613. 10. .2010 Contact CEH NORA team at noraceh@ceh.ac.ukThe NERC and CEH trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. and an international biomonitoring experiment coordinated by the ICP Vegetation. 5The latter involved ozone-sensitive (NC-S) and ozone-resistant (NC-R) biotypes of 6 white clover (Trifolium repens L.) grown according to a common protocol and 7 monitored for ozone injury and biomass differences in 17 European countries, from 8 1998 to 2006. Effects were separated into visible injury or growth/yield reduction. 9Of the 644 records of visible injury, 39% were for crops (27 species), 38.1 % were for 10 (semi-)natural vegetation (95 species) and 22.9% were for shrubs (49 species). Due 11 to inconsistencies in reporting effort from year to year it was not possible to determine 12 geographical or temporal trends in the data. Nevertheless, this study has shown 13 effects in ambient air in 18 European countries from Sweden in the north to Greece in 14 the south. These effects data were superimposed on AOT40 (accumulated ozone 15 concentrations over 40 ppb) and POD3 gen (modelled accumulated stomatal flux over a 16 threshold of 3 nmol m -2 s -1 ) maps generated by the EMEP Eulerian model (50 km x 50 17 km grid) that were parameterised for a generic crop based on wheat and NC-S/NC-R 18 white clover. Many effects were found in areas where the AOT40 (crops) was below 19 the critical level of 3 ppm h. In contrast, the majority of effects were detected in grid 20 squares where POD3 gen (crops) were in the mid-high range (> 12 mmol m -2 ). Overall, 21 maps based on POD3 gen provided better fit to the effects data than those based on 22 AOT40, with the POD3 gen model for clover fitting the clover effects data better than 23 that for a generic crop. 24 25

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Global change drivers (GCDs) are expected to alter community structure and consequently, the services that ecosystems provide. Yet, few experimental investigations have examined effects of GCDs on plant community structure across multiple ecosystem types, and those that do exist present conflicting patterns. In an unprecedented global synthesis of over 100 experiments that manipulated factors linked to GCDs, we show that herbaceous plant community responses depend on experimental manipulation length and number of factors manipulated. We found that plant communities are fairly resistant to experimentally manipulated GCDs in the short term (<10 y). In contrast, long-term (≥10 y) experiments show increasing community divergence of treatments from control conditions. Surprisingly, these community responses occurred with similar frequency across the GCD types manipulated in our database. However, community responses were more common when 3 or more GCDs were simultaneously manipulated, suggesting the emergence of additive or synergistic effects of multiple drivers, particularly over long time periods. In half of the cases, GCD manipulations caused a difference in community composition without a corresponding species richness difference, indicating that species reordering or replacement is an important mechanism of community responses to GCDs and should be given greater consideration when examining consequences of GCDs for the biodiversity–ecosystem function relationship. Human activities are currently driving unparalleled global changes worldwide. Our analyses provide the most comprehensive evidence to date that these human activities may have widespread impacts on plant community composition globally, which will increase in frequency over time and be greater in areas where communities face multiple GCDs simultaneously.

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