The relationship between climate parameters and the carbon stable isotope composition (δ13C), of annual tree ring cellulose is examined for three native British tree species; Common beech (Fagus sylvatica L.), Pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylvestris L.). The last 100 annual tree rings of six trees, two of each species, were cut into slivers and the a-cellulose extracted. Annual δ13C values of each species were averaged to produce three species δ13C chronologies. These were compared with climate parameters from a nearby meteorological station. The carbon stable isotope discrimination (Δ13C) of pine is consistently lower, by approximately 2.5‰, than that of beech and oak. Although the exact cause of this offset cannot be identified, similar differences in carbon isotope ratios have been noted between other gymnosperm and angiosperm species and attributed to inherent physiological differences. As this offset is consistent, once centred around the same mean δ13C and Δ13C chronologies from these 3 species can be combined. Δ13C chronologies of the three species demonstrate strong cross-correlations in both high and low frequency fluctuations. Low frequency fluctuations, although consistent between species, show no direct climate relationship, and may be linked with physiological responses to increasing CO2 concentrations. Significant correlations do exist between the high frequency δ13C fluctuations and climate parameters. The high frequency δ13C series of all three species are most significantly correlated with the same two climate parameters and have the same seasonal timing; July — October average maximum temperature and June — September average relative humidity. Pine δ13C is the most responsive species to climate changes and displays the most significant correlations with all the climate parameters studied. However, an average series of all three high frequency species δ13C series shows the most significant correlations with climate. Assuming these relationships are consistent spatially and temporally,high frequency δ13C chronologies from the three species studied are climatically comparable and can be combined to reconstruct the same climatic information.
Funding for a large-scale ecosystem research has been notoriously difficult to secure and sustain over more than a few years. Yet it is this information that is, and will become even more vital in order to understand and tackle global environmental changes and their impacts on societies. The measurements of stable isotope ratios present in the important elements of life (hydrogen, carbon, oxygen, nitrogen, and sulphur) provide unique information on the structure and processes associated with ecosystem and biome functioning. To sustain large-scale isotopic monitoring into the future, it is important to identify the key advantages of these networks, particularly when combined with socioeconomic indicators and to explore how these advantages may be maximized in order to secure long-term funding. This chapter addresses these points by giving a brief overview of existing large-scale stable isotope networks, emphasizing some of the key information available from these and discussing the possible application of these data to key international policy issues. While the importance of targeting research toward the current international policy agenda is emphasized, it is also considered essential to balance this with fundamental research that provides vision toward the future potential applications of large-scale isotope data and a focus for the development of new technologies that introduce novel and more accurate information. By successfully integrating these aspects, it is hoped that large-scale stable isotope networks will be an important part of a well-developed and vibrant ecological research field that will be sustained into the future.
Abstract. The JULES-crop model (Osborne et al., 2015) is a parameterisation of crops within the Joint UK Land Environment Simulator (JULES), which aims to simulate both the impact of weather and climate on crop productivity and the impact of crop-lands on weather and climate. In this evaluation paper, observations of maize at three FLUXNET sites in Nebraska (US-Ne1, US-Ne2, US-Ne3) are used to test model assumptions and make appropriate input parameter choices. JULES runs are performed for the irrigated sites (US-Ne1 and US-Ne2) both with the crop model switched off (prescribing leaf area index (LAI) and canopy height) and with the crop model switched on. These are compared against GPP and carbon pool FLUXNET observations. We use the results to point to future priorities for model development and describe how our methodology can be adapted to set up model runs for other sites and crop varieties. The implications of our results on the choice of parameters and settings to be used in global runs of JULES-crop are also discussed.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
