Browsing Tree-Ring Research, Volume 66 (2010) by Title
Now showing items 13-16 of 16
The Meteorological Significance Of False Rings In Eastern Redcedar (Juniperus Virginiana L.) From The Southern Great Plains, U.S.A.The growth rings of eastern redcedar (Juniperus virginiana L.) often contain a high frequency of false intra-annual growth bands, which complicates the dendrochronology of this species. However, exactly dated false rings replicated among many trees can reflect major weather changes during the growing season. Sixty-one trees from two sites (Oklahoma and Kansas) were dated and used to compile replicated chronologies of false rings at both locations extending from AD 1700–2000. False-ring events during the modern instrumental era were compared with the daily weather data from nearby stations. Significant false-ring events occurred at both locations during years that experienced a dramatic late-growing season weather reversal, when an extended period of high temperatures and drought was followed by prolonged cool and wet conditions. Synoptic weather maps for these events indicate that all ten replicated false-ring events in the instrumental era occurred during the highly unseasonable penetration of a cold front into the region. However, none of the significant false-ring events occurred in the same year at both sites. These separate false-ring chronologies indicate that there may be phenological differences in the timing of radial growth in redcedar between Kansas and Oklahoma, and that the weather conditions responsible for false-ring formation often occur at the mesoscale and do not often impact central Kansas and northcentral Oklahoma simultaneously.
Removing Biological Trends From Tree-Ring Series: Testing Modified Hugershoff CurvesThe 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 SignalAlthough 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)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).