• 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.
    • Stable-Carbon Isotope Time Series From Tropical Tree Rings Indicate A Precipitation Signal

      Fichtler, Esther; Helle, Gerhard; Worbes, Martin; Georg August Universität Göttingen, Department of Crop Sciences, Agronomy in the Tropics; Institute of Chemistry and Dynamics of the Geosphere, Research Centre Jülich (Tree-Ring Society, 2010-01)
      Although studies on stable-carbon isotopes in trees from temperate zones provide abundant paleoclimatic data, tropical trees are still understudied in this context. Therefore this study examined the variability of intra- and inter-annual stable-carbon isotopic pattern in several tree species from various tropical climates. The 𝛿¹³C values of samples of 12 broadleaved trees (seven species) from various paleotropical and neotropical sites along a climatic moisture gradient were investigated. The inter-annual variability between species and sites was studied. Further the relationship between 𝛿¹³C and precipitation time series was analyzed. Results show that tropical tree species show a similar variability in carbon isotopic composition as temperate tree species. Significant correlations between annual precipitation and tree-ring 𝛿¹³C time series were negative. Successful crossdating of a tree-ring 𝛿¹³C time series highlights the potential of carbon isotope measurements for tropical tree-ring analytical studies. Tropical broadleaved trees are able to capture a carbon isotopic signal in their annual rings even under everwet conditions and show good potential for paleoclimatic research.
    • Technique To Improve Visualization Of Elusive Tree-Ring Boundaries In Aspen (Populus tremuloides)

      DeRose, R. Justin; Gardner, Richard S.; Department of Wildland Resources and Ecology Center, Utah State University; Department of Wildland Resources, Utah State University (Tree-Ring Society, 2010-01)
      A simple, quick, and inexpensive technique to improve visualization of aspen (Populus tremuloides) tree rings under the microscope, the ‘shadow technique’, is described. The technique assumes appropriate preparation of increment cores or cross-sections and works well on the lighter portions of the sample with fungus- and bacteria-free wood. The shadow technique was used successfully to elucidate tree-ring boundaries in small diameter (<5 cm DBH) aspen from northern Utah that commonly had >100 annual rings. Crossdating verified whether the elusive rings were missing or false rings. Aspen tree-ring measurement will be greatly enhanced with the shadow technique and preliminary investigation suggests it could be used on other species such as curlleaf mountain mahogany (Cercocarpus ledifolius).