Impacts of ozone on the carbon sequestration in Swedish forests
This report shows that model simulations, based on empirical information about negative impacts of ozone on photosynthesis and leaf senescence on young trees under experimental conditions, show that forest growth ( NPP) is reduced by 4-16 percent and 1-4 percent for conifers and deciduous trees respectively under current, ambient ozone levels across Sweden, as compared to pre-industrial, low ozone levels.
Carbon sequestration by terrestrial vegetation is important for the budget of greenhouse gas (GHG) fluxes to and from the atmosphere, globally as well as for Sweden. The carbon sequestrations to Swedish forest ecosystems corresponded to approximately 38 M ton CO2-e (CO2 equivalents) while Sweden´s net emissions of GHG from all other sectors the same year 2011 corresponded to approximately 61 M ton CO2-e. Most of the increase in the Swedish forest carbon stocks was in the living biomass. The high rates of carbon sequestration to Swedish forests depend on the fact the forests annual growth rates have been substantially exceeding annual harvest rates. Any factor that tends to reduce growth rates also potentially will reduce forest carbon sequestration rates. Ozone has the potential to negatively affect tree biomass increment growth.
The aim of this study was to estimate to what extent the occurrence of elevated ground level ozone concentrations will negatively affect the growth and carbon sequestration of Swedish forests. This was achieved by the following procedure:
• An assessment was made of which physiological processes influencing forest growth that could be particularly vulnerable to negative ozone impacts
• Ozone dose – response relationships were established for these vulnerable processes
• The occurrence of different ozone levels in each county of Sweden was mapped for a relevant time period
• The net primary production (NPP) for the Swedish forests was modelled with the 3-PG model for forest stand representative for six different geographical zones across Sweden, with or without the assumed negative ozone impacts derived for the dose – response relationships IVL-report C 60 Impacts of ozone on the carbon sequestration in Swedish forests
• The modelled NPP for the forests in the different zones, with and without ozone, was used to estimate the ozone impacts on the carbon sequestration for the forest living biomass carbon stocks.