Environment in time and space: Opportunities from tree-ring isotope networks

Light stable isotopes in plants have been related to various climate parameters such as temperature, precipitation, relative humidity, and soil moisture, and to ecophysiological variables such as photosynthetic rate, stomatal conductance and intrinsic water-use efficiency. By collecting radial growth rings of trees in networks, it is not only possible to characterize these variables around the geographical area, but also to reconstruct the variation of these parameters through time. The real power of dendrochronologically dated tree rings is in providing certainty in assignment of an isotopic value to a particular year and perhaps even a sub-annual period. Additionally, the growth rings integrate isotopic signals from around the tree crown and may smooth out some of the high intra-crown variability associated with microenvironments. Furthermore, woody plants are widespread on six of seven continents, thereby supporting widespread opportunities for network development. Examples of existing and emerging tree-ring isotope networks on three continents are used to illustrate the findings, successes and limitations of this methodology. The goals of such studies will ultimately determine the methods used in developing the network, but analysis of multiple, dendrochronologically dated trees at each site, sampling of the same species at all sites, and analysis of the same wood component in all trees would be ideal in most cases.