| 1. |
- Buker, P., et al.
(author)
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DO3SE modelling of soil moisture to determine ozone flux to forest trees
- 2012
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:12, s. 5537-5562
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Journal article (peer-reviewed)abstract
- The DO3SE (Deposition of O-3 for Stomatal Exchange) model is an established tool for estimating ozone (O-3) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O-3 precursor emission scenarios for use in policy formulation. A key limitation of regional flux-based risk assessments has been the assumption that soil water deficits are not limiting O-3 flux due to the unavailability of evaluated methods for modelling soil water deficits and their influence on stomatal conductance (g(sto)), and subsequent O-3 flux. This paper describes the development and evaluation of a method to estimate soil moisture status and its influence on g(sto) for a variety of forest tree species. This DO3SE soil moisture module uses the Penman-Monteith energy balance method to drive water cycling through the soil-plant-atmosphere system and empirical data describing g(sto) relationships with pre-dawn leaf water status to estimate the biological control of transpiration. We trial four different methods to estimate this biological control of the transpiration stream, which vary from simple methods that relate soil water content or potential directly to g(sto), to more complex methods that incorporate hydraulic resistance and plant capacitance that control water flow through the plant system. These methods are evaluated against field data describing a variety of soil water variables, g(sto) and transpiration data for Norway spruce (Picea abies), Scots pine (Pinus sylvestris), birch (Betula pendula), aspen (Populus tremuloides), beech (Fagus sylvatica) and holm oak (Quercus ilex) collected from ten sites across Europe and North America. Modelled estimates of these variables show consistency with observed data when applying the simple empirical methods, with the timing and magnitude of soil drying events being captured well across all sites and reductions in transpiration with the onset of drought being predicted with reasonable accuracy. The more complex methods, which incorporate hydraulic resistance and plant capacitance, perform less well, with predicted drying cycles consistently underestimating the rate and magnitude of water loss from the soil. A sensitivity analysis showed that model performance was strongly dependent upon the local parameterisation of key model drivers such as the maximum g(sto), soil texture, root depth and leaf area index. The results suggest that the simple modelling methods that relate g(sto) directly to soil water content and potential provide adequate estimates of soil moisture and influence on g(sto) such that they are suitable to be used to assess the potential risk posed by O-3 to forest trees across Europe.
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| 2. |
- Calfapietra, Carlo, et al.
(author)
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Challenges in elevated CO2 experiments on forests
- 2010
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In: Trends in Plant Science. - : Elsevier BV. - 1360-1385. ; 15:1, s. 5-10
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Research review (peer-reviewed)abstract
- Current forest Free Air CO2 Enrichment (FACE) experiments are reaching completion. Therefore, it is time to define the scientific goals and priorities of future experimental facilities. In this opinion article, we discuss the following three overarching issues (i) What are the most urgent scientific questions and how can they be addressed? (ii) What forest ecosystems should be investigated? (iii) Which other climate change factors should be coupled with elevated CO2 concentrations in future experiments to better predict the effects of climate change? Plantations and natural forests can have conflicting purposes for high productivity and environmental protection. However, in both cases the assessment of carbon balance and how this will be affected by elevated CO2 concentrations and the interacting climate change factors is the most pressing priority for future experiments.
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| 3. |
- Fischer, R, et al.
(author)
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Towards a transnational system of supersites for forest monitoring and research in Europe - an overview on present state and future recommendations
- 2011
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In: IForest. - : Italian Society of Sivilculture and Forest Ecology (SISEF). - 1971-7458. ; 4:1, s. 167-171
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Journal article (peer-reviewed)abstract
- Science based approaches in addressing future risks and challenges for forests require close collaboration among the communities operating different monitoring and research networks as well as experts in process and large-scale modelling. Results of the COST FP0903 conference which took place in October 2010 in Rome, reveal valuable results from different European forest monitoring and research networks. However, the need for closer integration of these activities is obvious. In this paper, representatives from major European networks recommend a new approach for forest monitoring and research in Europe, based on a reasonable number of highly instrumented "supersites" and a larger number of intensive monitoring plots linked to these. This system needs to be built on existing infrastructures but requires increased coordination, harmonisation and a joint long term platform for data exchange and modelling.
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| 4. |
- Uddling, Johan, 1972, et al.
(author)
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Biomass reduction of juvenile birch is more strongly related to stomatal uptake of ozone than to indices based on external exposure
- 2004
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 38:28, s. 4709-4719
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Journal article (peer-reviewed)abstract
- In order to test the hypothesis that ozone-induced limitation of biomass production in juvenile silver birch (Betula pendula Roth) is driven by stomatal uptake of ozone (O-3) rather than external exposure, biomass reduction was related to the cumulative uptake of O-3 through stomata over an uptake cut-off threshold of x nmol O-3 m(-2) s(-1) (CUO > x), to the accumulated exposure to O-3 over a threshold of y nmol mol(-1) during daylight hours (daylight AOTy) or during 24 h (24 h AOTy), and to the sum of daytime concentrations exceeding 60 nmol mol(-1) (SUM06). The analysis included data from nine different experiments conducted in Sweden, Finland and Switzerland. Stomatal uptake of O-3 was estimated using a stomatal conductance (g,) model including g, response functions for photosynthetic photon flux density, water vapour pressure deficit of the air and air temperature. Experiment-specific maximum g(s) (g(max)) as well as g(s) in darkness (g(dark)) were assessed through local measurements. Biomass reduction Was more strongly related to CUO > x than to SUM06 and daylight or 24 h AOTy, but the difference between CUO > x and 24 h AOTy was small. The better performance of CUO > x was dependent on the use of site- and experiment-specific g(max) and g(dark) values, and there was a positive relationship between g(max) and biomass reduction per unit AOT40. Daylight AOTy and SUM06 could not account for the growth limiting impact of nocturnal O-3 uptake in the Swiss experiments. A sensitivity analysis revealed that the CUO > x estimates were largely insensitive to the estimate of the conductance for non-stomatal leaf surface deposition of O-3, as a result of turbulent conditions at the experimental plots. In summary, we conclude that CUO > x was more successful in accounting for the variation in biomass reduction in juvenile birch as compared to indices based on external exposure, if g(max) and g(dark) were locally parameterised. (C) 2004 Elsevier Ltd. All rights reserved.
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