• Removing Biological Trends From Tree-Ring Series: Testing Modified Hugershoff Curves

      Fang, Keyan; Gou, Xiaohua; Peters, Kenneth; Li, Jinbao; Zhang, Fen; MOE Key Laboratory of Western China’s Environmental Systems, Lanzhou University; Tree-Ring Lab, Lamont-Doherty Earth Observatory of Columbia University (Tree-Ring Society, 2010-01)
      The performance of the Hugershoff curve on fitting the growth trends of tree-ring series was tested using ring-width series with different starting years. The fitted values tend to be biased by tree-ring series close to pith, a phenomenon that was referred to as the ‘‘start-fitting problem’’. We determined three parameters with specific biological age-related meanings for the Hugershoff growth curve, i.e. the maximum growth, the maximum slope and the maximum changing ratio of slopes. A set of modified Hugershoff curves with different starting years was proposed to mitigate the start-fitting problem. Behavior of the modified Hugershoff curves on tree-ring series standardizations was tested and discussed. The ‘‘end-fitting problem’’ suggests that deviations in one interval could bias the fitted values of other time periods by using the Hugershoff curve.