Removing biological trends from tree-ring series: Testing modified hugershoff curves

Abstract

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. Copyright © 2010 by The Tree-Ring Society.