Theme 1 : Quantifying ozone impacts on Mediterranean Forests (original) (raw)
Related papers
Modelling ozone fluxes to forests for risk assessment: status and prospects
Annals of Forest Science, 2009
Risk assessment of ozone effects on forests is gradually moving from concentration-based exposure metrics to a more complicated approach that requires modelling of ozone fluxes to trees. • This study reviews the status of the DO 3 SE stomatal flux model employed within the Convention on Long-range Transboundary Air Pollution, describing a range of applications and identifying major research needs, especially in the context of support that could be provided by the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests. • The most urgent development need for DO 3 SE is the modelling of the soil moisture status and its effect on stomatal conductance. Furthermore, the data related to the physical characteristics and the seasonal dynamics of physiological activity of vegetation continue to pose problems. • There is a clear need for more extensive validation of models and risk estimates using more rigorous statistical procedures and comparisons with flux networks and satellites. • The current large-scale forest monitoring activities provide only limited possibilities for flux modelling, but could be enhanced by introducing a new monitoring strategy outlined here.
Atmospheric Environment, 2005
Ozone (O 3) induces deleterious effects on plants by its oxidising capacity. Efforts have aimed at defining O 3 critical loads which are based on O 3 penetrating into the plant through the stomata, being an important mechanism of O 3 removal. Recently, papers have proposed the use of process-based models for estimating the O 3 dose at the community level. These models should define the stomatal O 3 flux (F st) on vegetation, correlating it to O 3-induced injury and hence to improve the database available for decision makers. A process-based model has been utilised for the quantification of O 3 flux (F) toward a Holm oak forest and its repartition in F st and non-stomatal flux (F nost) during daylight. The model outputs have been compared with eddy covariance measurements. Simulation of O 3 fluxes under the climatic limitations of summer 2003 showed that the mean values of F st represented only 28.9% of F, which was similar to eddy covariance (31.5%). The use of LAI effective to link the leaf F st to the canopy scale O 3 stomatal flux (F effectjve ; on ground unit) is shown to be useful not only for the model validation but also for upscaling purposes from leaf to canopy. Forest acts as a LAI ¼ 1; i.e. a ''real'' big leaf for canopy O 3 uptake. Changes in O 3 fluxes were more closely related to the factors that control O 3 deposition than to the factors controlling O 3 concentration. Simulations showed that Holm oak forest was most effective at taking up O 3 under moderate to high irradiance and high physiological activity, but not in limiting environmental conditions. The model used here does not require a great number of input variables and it is based on simple assumptions with respect to other more recognised models. So, the use of this model can have useful applications for the risk assessment of level II for the forests.
• We develop new flux-based critical levels CLef for forest protection against visible O 3 injury. • We recommend the use of POD0 calculated for hours with a non-null global radiation. • We propose CLef = 19 & 32 mmol m − 2 for high & moderate O 3 sensitive conifers respectively. • We propose CLef = 19 & 25 mmol m − 2 for high & moderate O 3 sensitive broad-leaves respectively. Southern forests are at the highest ozone (O 3) risk in Europe where ground-level O 3 is a pressing sanitary problem for ecosystem health. Exposure-based standards for protecting vegetation are not representative of actual field conditions. A biologically-sound stomatal flux-based standard has been proposed, although critical levels for protection still need to be validated. This innovative epidemiological assessment of forest responses to O 3 was carried out in 54 plots in Southeastern France and Northwestern Italy in 2012 and 2013. Three O 3 indices, namely the accumulated exposure AOT40, and the accumulated stomatal flux with and without an hourly threshold of uptake (POD1 and POD0) were compared. Stomatal O 3 fluxes were modeled (DO3SE) and correlated to measured forest-response indicators, i.e. crown defoliation, crown discoloration and visible foliar O 3 injury. Soil water content, a key variable affecting the severity of visible foliar O 3 injury, was included in DO3SE. Based on flux–effect relationships, we developed species-specific flux-based critical levels (CLef) for forest protection against visible O 3 injury. For O 3 sensitive conifers, CLef of 19 mmol m −2 for Pinus cembra (high O 3 sensitivity)
New flux based dose–response relationships for ozone for European forest tree species
Environmental Pollution, 2015
To derive O 3 doseeresponse relationships (DRR) for five European forest trees species and broadleaf deciduous and needleleaf tree plant functional types (PFTs), phytotoxic O 3 doses (PODy) were related to biomass reductions. PODy was calculated using a stomatal flux model with a range of cutoff thresholds (y) indicative of varying detoxification capacities. Linear regression analysis showed that DRR for PFT and individual tree species differed in their robustness. A simplified parameterisation of the flux model was tested and showed that for most non-Mediterranean tree species, this simplified model led to similarly robust DRR as compared to a species-and climate region-specific parameterisation. Experimentally induced soil water stress was not found to substantially reduce PODy, mainly due to the short duration of soil water stress periods. This study validates the stomatal O 3 flux concept and represents a step forward in predicting O 3 damage to forests in a spatially and temporally varying climate.
2014
Questions to be discussed: Can we add new flux parameterisations for additional tree species to the Modelling and Mapping Manual? Can we set critical levels for new tree species? Is amendment of current critical levels required? Is there new field-based evidence of predicted impacts? 09:00-10:30: session 1 (10 min per presentation, 5 min discussion per paper) 09:00 Alexandra De Marco et al.-Ozone stomatal flux-based critical levels translated into real-world forest impacts. 09:15 Silvano Fares et al.-Ball-Berry vs Jarvis approaches to model stomatal ozone deposition in Mediterranean forests: validation using the test sites of Castelporziano and San Rossore forests. 09:30 Beat Rihm et al.-Mapping of ozone flux in Switzerland with high spatial resolution for epidemiological analysis. 09:45 Patrick Büker et al.-The effect of ozone on the C sequestration potentials of European forests. 10:00 General discussion. 10:30-11:00 Coffee/tea 11:00-12:30: session 2 (10 min per presentation, 5 min discussion per paper) 11:00 Per Erik Karlsson et al.-Further developments of the concept of the Simplified Phytotoxic Ozone Dose, S-POD, to assess the risk for ozone impacts on trees on the regional scale. 11:15 Sabine Braun-Validation of stomatal flux in Quercus species. 11:30 Patrick Büker et al.-DO 3 SE parameterisation for new forest tree species and revision of flux-response relationships for eight European trees species (note: 15 min presentation). 11:45 Harry Harmens-Structured discussion on questions, conclusions & recommendations on trees.
Environmental Pollution, 2009
Ozone fluxes to a Holm oak coastal forest show inter-annual variations depending on meteorological conditions and water availability. a b s t r a c t Ozone and energy fluxes have been measured using the eddy covariance technique, from June to December 2004 in Castelporziano near Rome (Italy), and compared to similar measurements made in the previous year. The studied ecosystem consisted in a typical Mediterranean Holm oak forest. Stomatal fluxes have been calculated using the resistance analogy and by inverting the Penmann-Monteith equation. Results showed that the average stomatal contribution accounts for 42.6% of the total fluxes. Non-stomatal deposition proved to be enhanced by increasing leaf wetness and air humidity during the autumnal months. From a comparison of the two years, it can be inferred that water supply is the most important limiting factor for ozone uptake and that prolonged droughts alter significantly the stomatal conductance, even 2 months after the soil water content is replenished. Ozone exposure, expressed as AOT40, behaves similarly to the cumulated stomatal flux in dry conditions whereas a different behaviour for the two indices appears in wet autumnal conditions. A difference also occurs between the two years.
Ozone and particle fluxes in a Mediterranean forest predicted by the AIRTREE model
Science of The Total Environment, 2019
Mediterranean forests are among the most threatened ecosystems by the concurrent effects of climate change and atmospheric pollution. In this work we parameterized the AIRTREE multi-layer model to predict CO 2 , water, ozone, and fine particles exchanges between leaves and the atmosphere. AIRTREE consists of four different modules: (1) a canopy environmental module determines the leaf temperature and radiative fluxes at different levels from above to the bottom of the canopy; (2) a hydrological module predicts soil water flow and water availability to the plant's photosynthetic apparatus; (3) a photosynthesis module estimates the net photosynthesis and stomatal conductance, and (4) a deposition module estimates ozone and PM deposition sinks as a function of the resistances to gas diffusion in the atmosphere, and within the canopy and leaf boundary layer. We describe the AIRTREE model framework, accuracy and sensitivity by comparing modeling results against longterm continuous Eddy Covariance measurements of ozone, water, and CO 2 fluxes in a Mediterranean Holm oak forest, and we discuss potential application of AIRTREE for ozone-risk assessment in view of availability of a large observational database from ecosystems distributed worldwide.