Evaluating the time-dependent behavior of ecological models
based on dendrochronological data
or:
What if we know climate but not its large-scale ecological response?

by H. Bugmann¹, T. Kittel², D. Schimel^2,3, C. Woodhouse⁴ & C. Bigler<sup>1


1</sup> Mountain Forest Ecology, Swiss Federal Institute of Technology, ETH-Zentrum,
CH-8092 Zurich, Switzerland

² Ecosystem Dynamics and the Atmosphere, National Center for Atmospheric Research, Boulder, CO 80307-3000, USA

³ Max-Planck-Institute for Biogeochemistry, Carl-Zeiss-Promenade 10, D-07745 Jena, Germany

² Paleoclimatology Program, National Oceanic and Atmospheric Administration,
Boulder, CO 80303-3328, USA

Dynamic models of ecosystem structure and function are increasingly used to address questions relating to the large-scale (continental to global) and long-term (decades to centuries) behavior of ecosystems, with the aim of assessing biogeochemical fluxes between the land surface and the atmosphere as well as structural changes of the vegetation.

A spatially explicit climate data set covering the conterminous United States for the period 1895-1993 has recently become available, and this allows us to explore the response of the ecosystem models to climate variability on a variety of time scales. Few data sets are available, however, to evaluate the realism of the simulated spatial and temporal patterns of ecosystem properties.

Dendrochronological data have the potential to become a major resource for evaluating such ecosystem model predictions. Large archives of ring-width data exist from many regions of the world, the data have annual resolution over time periods of years to millennia, and tree rings record not only proxies for growth (diameter increments and density) but other factors via carbon (¹²C, ¹⁴C) and oxygen isotopes. Hence, we are confronted with the “inverse” problem of classical dendroclimatology: We have a climate reconstruction and are looking for the biotic response patterns, whereas much of dendrochronology is concerned with reconstructing climate from biotic variables.

In this poster, the methodological challenges of using dendrochronological data for evaluating ecosystem models will be discussed, and several case studies from the western United States will be presented, where data from the International Tree Ring Data Bank were re-analyzed and compared against indices from ecosystem model simulations.