The International Tree-Ring Data Bank
Dendrochronology and its related subfields (e.g., dendroecology and dendroclimatology) have proven invaluable disciplines for investigating spatial and temporal aspects of processes in the earth sciences that operate at annual to centennial time scales. Dendrochronology is currently practiced worldwide in laboratories at academic, government-funded, and private institutions by nearly one thousand practitioners, which has resulted in the development of thousands of tree-ring chronologies from sites around the world. These data sets are increasingly being used to assess past changes in Holocene climate to place the global dynamics of present and future climate change in historical context. Recent, intensive efforts have focused on the development of millennium-length tree-ring chronologies to investigate not only short-term, intradecadal (<10 years) trends in past climate, but also longer-term, centennial scale (>100 years) secular trends. Spatial networks or grids of tree-ring chronologies have been or are currently being developed to provide information about past climate on regional and global spatial scales. These efforts allow researchers to (1) develop and test new hypotheses that investigate the effects changes in regional and global-scale atmospheric circulation processes could have on human behavior, pattern, adaptation, and response, and (2) place current changes in global climate processes, often attributed to anthropogenic influences, in context with previous changes in past climate.
The rapid development of large numbers of tree-ring chronologies across the globe was addressed by dendrochronologists attending a workshop in 1974, who subsequently established the International Tree-Ring Data Bank (ITRDB), a professional organization that provides the only central repository for all types of dendrochronological data from around the world. For years, the ITRDB operated exclusively as a "grass roots" organization, largely dependent on the time and efforts of volunteers. Modest funding was supplied by the United States National Science Foundation as a supplement to research support for Dr. Harold C. Fritts, the founder of the ITRDB, at the Laboratory of Tree-Ring Research, The University of Arizona. In 1990, the Paleoclimatology Program of the National Oceanic and Atmospheric Administration (NOAA) took over the operation of the ITRDB with the establishment of the World Data Center - A for Paleoclimatology at the National Geophysical Data Center (NGDC) in Boulder, Colorado, USA. This center houses many different types of paleoclimatic data, such as ice core, sedimentary, tree-ring, palaeobiological, pollen, and documentary data. With continued support from the Paleoclimatology Program, the ITRDB has established itself firmly in the scientific community as one of the premier paleoclimatic databases.
The primary purpose for the ITRDB is to provide a permanent location for the storage of well-dated, high-quality dendrochronological data from around the world. This central repository protects data from loss due to: (1) mishandling of tree-ring data, (2) the relocation or termination of laboratories, (3) scientists who move to other projects or retire, or (4) the death of scientists. Besides providing secure storage of the original basic tree-ring information (the actual dated measurements and derived chronologies), the ITRDB is also an increasingly valuable archive of well-dated baseline information on the world's oldest trees, thus providing environmental information before anthropogenic changes became pervasive. As more forests are harvested or restructured due to human intervention, the information in such a database could provide the only surviving long-term record from some of the world's more threatened regions. Such information may be critical for evaluating anthropogenically-induced climatic change, its magnitude, and extent, as well as for reconstructing past climates. Thus, expansion and maintenance of the basic tree-ring data housed in the ITRDB could well assume a greater importance in the coming years.
Tree-ring data submitted to the ITRDB must meet certain requirements before assimilation into the holdings. First, each tree-ring chronology must have been developed from at least 10 trees. Second, the minimum length of the final chronology should be at least 100 years. Third, the ITRDB requests contributions of the original tree-ring measurements used to develop the final master chronologies. We make this request to ensure that original measurements are available in the future should new methods and techniques be developed. Fourth, it is expected that the series have undergone intense scrutiny by the principal investigator to ensure all individual series are correctly crossdated, and that errors during measurement have been minimized. Finally, all necessary documentation must be delivered to the ITRDB (for example, all site data or information on publications that used the data) to ensure as much information is archived as possible. Under special circumstances, these requirements can be waived when samples are too few and scarce (as, for example, with archaeological tree-ring material), or when the data were developed for extremely detailed analyses (as, for example, in stem growth analyses).
In the mid- to late 1990s, the ITRDB completed a massive, two-year quality control assessment of its holdings of raw measurement data sets for nearly 1,300 sites. This assessment was necessary to ensure that (1) all data files were completely and accurately documented, (2) all data files were in standard Decadal (measurement) and Index (chronology) formats, and (3) all individual series were accurately crossdated. Using a modified version of the computer program COFECHA (Holmes 1983), results of the crossdating accuracy tests were output to separate text files that will provide non-dendrochronologists with an impartial assessment of the quality of the data sets. These text files are now included in the holdings of the ITRDB. The ITRDB is currently developing guidelines for crossdating accuracy to be used by NOAA personnel, and will soon be confirming the accuracy of crossdating for all new contributions.
Holdings of the ITRDB
Currently, the ITRDB contains over 6,000 data sets, including 2,804 raw measurement files, 3,275 tree-ring chronologies, and numerous climate reconstructions derived from these tree-ring data. These data were collected from over 1,500 sites around the world representing over 100 tree and shrub species. All final chronology files contain necessary site information and documentation, such as location (site name, state/province, country, latitude and longitude), elevation, species analyzed, specific site characteristics, source of materials (living trees, historical sites), number of trees sampled, type of samples (cores, cross-sections), type and unit of measurement, general chronology statistics (if submitted), and names of the principal investigators. The contribution of separate text files containing even more detailed information is especially encouraged. The tree-ring measurements represent mostly total ring widths, but numerous data sets consist of earlywood and latewood widths, as well as minimum earlywood and maximum latewood densities, and new ring characteristics have been contributed derived from digital image analyses.
As part of the World Data Center system, the ITRDB makes its holdings freely available to any and all researchers. It is more important to stress that the collective data are shared around the world when they are submitted to the ITRDB. All newly-contributed tree-ring data are archived by personnel at the National Geophysical Data Center in Boulder, Colorado. Membership in the ITRDB is automatic for those individuals and institutions that contribute dendrochronological data. Currently, the ITRDB has 139 members from 21 countries: Argentina, Australia, Belgium, Canada, The Czech Republic, Finland, France, Germany, Italy, Japan, Lithuania, Mexico, The Netherlands, New Zealand, Poland, Russia, Slovenia, Sweden, Switzerland, the United Kingdom, and the United States.
Administration of the ITRDB
An Advisory Committee of dendrochronologists administers the ITRDB and consists of a chairperson and individuals selected from its members. In 1994, committee membership was expanded to provide a wider geographic coverage among dendrochronologists, and to also provide representation for the numerous subdisciplines within the science. This Advisory Committee assures that the ITRDB keeps pace with new developments in dendrochronology, and has the special function of reporting annually to NOAA on the functioning of the organization.
The Future of the ITRDB
The primary purpose of the ITRDB is to assimilate tree-ring measurement and chronology data into a central location for permanent archiving. In the past, solicitation efforts concentrated on tree-ring data useful for climate reconstruction purposes. As scientists applied tree-ring data to more and more different types of studies, however, the ITRDB realized this view was too narrow - tree-ring data developed for non-climatic purposes were being overlooked. The ITRDB has since relaxed this requirement to allow contributions of all types of tree-ring data. New data types that have been or will be assimilated include: (1) isotopic measurements of hydrogen, carbon, and oxygen, (2) information on cellular structure (e.g., cell wall thickness and cell wall area measurements), (3) data from stem analyses, (4) data gathered from image analyses, and (5) data from event chronologies (e.g., frost ring chronologies). Tree-ring chronologies developed for reconstructions of disturbance regimes (for example, spruce budworm outbreaks) will also be included in the holdings of the ITRDB. These data files should have special text files included that discuss the unique nature of the study for which these data were developed. The ITRDB will also increase its solicitation for actual climate reconstructions developed from tree-ring data.
Another major goal of the ITRDB is to increase awareness among dendrochronologists concerning the role of the ITRDB in its relationship with the World Data Center system and the International Council of Scientific Unions (ICSU). We would like to clarify to the worldwide dendrochronological community the guidelines established for the WDCs, and how these guidelines apply to the ITRDB and to the availability of tree-ring data. In the coming years, the Advisory Committee of the ITRDB will begin developing preliminary guidelines for the ITRDB that clearly state its mission and purpose, responsibilities, requirements, and policies regarding data submission and distribution. Hopefully, these guidelines will be published in a future edition of the Guide to the World Data Center System by the ICSU. We feel this is a critically important step to facilitating the steady flow of tree-ring data to the ITRDB and the WDC-A for Paleoclimatology. The proposed improvements to the ITRDB will initiate and facilitate processes that will lead to mutually agreeable guidelines representing the consensus of dendrochronologists worldwide.
The ITRDB graciously thanks those who, over the years, provided continuous support for our efforts by contributing their valuable tree-ring data, which will serve generations of future researchers in years to come. We especially thank Richard Holmes for his continuous involvement with development of the ITRDB Program Library, often on his own time, and for his steadfast support for the ITRDB mission. Special thanks to Mariette Seklecki who laboriously executed nearly two thousand runs of COFECHA, and prepared all documentation and computer files during the quality control assessment. Generous support for the ITRDB database efforts was supplied for many years by the Paleoclimatology Program of the National Oceanic and Atmospheric Administration, and to them we are very grateful. Finally, we would be remiss if we did not acknowledge the long standing and continued support of the Laboratory of Tree-Ring Research, The University of Arizona, since the inception of the ITRDB. The ITRDB would not have survived these many years without this backing, and the Laboratory has and continues to play a significant part through supporting facilities, faculty salaries, and other personnel time for many different aspects of this undertaking.