MARKER DATES AND TREE RINGS

            One of the many ways to validate the interpretation of the tree-ring record is through the use of anecdotal data and marker dates (Baillie, 1995) .  Information may sometimes come from unusual sources such as the writings of Ammianus.  Ammianus wrote a survey of Dacia, a province of Rome, and noted that the Alamanni villas were rich in livestock and crops in the year AD 357 (Ammianus, Ammianus Marcellinus) (Dixon, 1976) .  Comparing this to the master tree-ring record from the same area, it shows the average growth rate from AD 354 to 359 being 109, 177, 104, 102, 99, 102 with AD 357 being 102.  The mean growth rate of the master chronology is 100, so AD 357 is surrounded by years with growth rates above the mean with AD 358 being just barely under the average at 99 (Figure 4.1).  This not only suggests that Ammianus was correct, but that the tree ring record could be reflecting the productivity of the area.

Procopius describes a volcanic eruption in AD 536, which is also reflected in the master tree-ring chronology with an average value recorded of 80.6 (the mean being 100) (Procopius, Secret history of the court of the Emperor Justinian).  Some anecdotal information may be useful to some studies, but is difficult to make a direct application to the master chronology.  An example is found in Livy’s History of Rome.  Found in section 9.36 is “the Ciminian forest was more frightful and impassable than the German forests were recently found to be, not a single trader had ventured through it.  Only the general himself was brave enough to enter it” (Livy, The History of Rome).  This may suggest a denser forest or maybe just there was some stigma applied to the forest that the documentation does not describe.  Although the exact date for this event could be narrowed down, it does not assist in the verification of the tree-ring record.

            Some marker dates are even harder to apply.  Documented evidence of the river Rhine freezing solidly in December 31, AD 406, is the same date as a major invasion where Mainz, Trier, Worms, Strasbourg, Tournai, Boulogne, Theims and Amiens are all sacked (Dixon, 1976) .  However, the tree ring record shows this year with a value of 102 and the following year at 106 (mean value of 100).  Events in the winter months are not necessarily valuable to the correlation of the tree-rings and documented climate events.  This may be of greater use for the ice core record.