Long term carbon dioxide and water vapour fluxes of European forests and interactions with the Climate System
EUROFLUX programme will address the following specific objectives:
- to characterize fluxes and energy exchange at the surface in order to provide useful parameters to global and regional climate modellers and to analyze the variables that determine energy partitioning by forests in different climatic conditions, including extreme events and stress limitations.
- to determine the sink strength of European forests for carbon and analyze the variables that determine the gains and the losses of carbon from forests of differing vegetation composition and in different climate regions.
- to analyze the response of water and carbon fluxes from European forest to climatic factors in order to aid regional scale modelling designed to predict impacts of global environmental change on forest ecosystem function.
- to provide objective data for the validation of forest models, related to growth, partitioning of primary production, water cycling and hydrology.
- to provide information for the development and testing of schemes designed to elaborate forest-atmosphere interactions based on remotely sensed data.
- to recommend management strategies for the conservation of carbon stores in forests.
Rationale :
There is a pressing need for information concerning the influence of terrestrial ecosystems and particularly of forests on biosphere-atmosphere interactions and their impact on the Climate System (Fung 1992) . Climate modellers require this information in order to parameterize mass and energy exchanges between vegetation and atmosphere to improve the predictions of Mesoscale and General Circulation Models (Sellers 1991). In particular, quantitative flux estimates are needed to develop surface parameterizations and aggregation schemes in order to scale up from the patchwork of landscapes, evident in Europe, to regional and, ultimately, global scales (Dolman and Blith 1995).
Atmospheric exchanges of European forest ecosystems deserve special attention due first to their potential mesoscale effects on rainfall distribution and soil water storage (Blith et al. 1994), and also because of their potential role in the long-term CO2 uptake from the atmosphere and carbon storage (Jarvis 1994). A number of recent studies suggest a sink of carbon in regrowing Northern Emisphere forests. Estimates of this term range from essentially zero to 0.7 Gt C y-1 (Melillo et al. 1988; Houghton 1993; Dixon et al. 1994). The uncertainty of this magnitude arises from the wide disparities in the published data and assumption employed, particularly when inventory-based estimates are used (Schimel 1995).
In addition European forests, due to the increase in nitrogen deposition, can represent a big transient carbon sink as recently suggested by Schulze et al. (1994).
Thus, it is essential to examine the role of forests on carbon sources and sinks in the biosphere and their role in the regional carbon balance for future political considerations. On the other hand, the impact of climate on forests and the effects of forest management on the atmospheric exchanges deserve particular attention.
Project Methodology :
The study of the interactions between forests and atmosphere has recently been made more routine by new developments in the eddy covariance technique (Leuning and Moncrieff 1990). This technique has primarily been used in intensive short-term land surface experiments and has provided new opportunities for estimating fluxes at larger spatial scales (Kanemasu et al. 1992). Within EUROFLUX, eddy covariance will be used for long term continuous measurements of mass and energy fluxes, to capture seasonal dynamics and allow for a meaningful scaling with respect to time. Indeed, many of the processes driving water and carbon fluxes at ecosystem level are strongly dependent on seasonal changes in climate. Seasonal changes of phenology and biomass production affect significantly the rates and properties of water and carbon exchanges in the atmosphere. Furthermore, extreme events (temperature, high wind velocity, drought conditions) are not often considered during short term field campaings but can have a strong impact on the hydrological and carbon cycles.
The technology is available for continuous measurement of carbon dioxide and water fluxes on a seasonal basis with hourly discrimination (Wofsy et al. 1993). Within EUROFLUX the equipment and methodology is standardized using a common software and instrumentation design in order to have a solid basis for site intercomparisons (Moncrieff et al. 1995). The present project proposal is a unique case to combine flux measurements on a continuous multi-year time basis with ecological process interpretation and modelling. Long-term measurements of the fluxes of CO2, water vapour and energy exchange are carried out at 15 representative forest sites encompassing the entire range in European climate, species distribution, and site conditions. The selected sites are representative of the regional features of the European basin (Mediterranean, Boreal, Continental, Atlantic) and form a unique integrated system for the analysis of climate-related ecosystem processes, their impact on hydrological and carbon cycles and will represent test cases for validation of environmental policies. Features of EUROFLUX sites :
click on GRAPHICS to expand them
Y = Latitude N
X = Longitude E
Y = Mean annual temperature (°C)
X = Euroflux sites
Y = Mean annual precipitation (mm.)
X = Euroflux sites
