Abstract
The “two-third spline” (2/3S) is a frequently applied method to detrend tree-ring series. It fits a spline with a 50% frequency cutoff at a frequency equal to two-thirds of each sample length in a dataset. It was introduced to ensure a minimum loss of low-frequency variance, which is resolvable during the detrending of ring-width series.In this paper I show potential problems that arise when rusing this method. The 2/3S runs counter the strengths of using a digital filter to detrend – i.e. one is giving up full control over the frequency-removing characteristics of the growth curve and each individual time series retains a different amount of low frequency. Thus, the 2/3S is less suitable for reconstructing climate or to compare environmental impacts on tree growth between groups – both of which comprise the majority of dendrochronological analyses – as it will likely introduce a temporal frequency bias. Within a long chronology it will result in decreasing power to resolve low frequencies towards present in a living-only trees setting, especially when the youngest segment lengths are 100 years and shorter, and more generally during the period where the chronology is constructed from samples with shorter segment lengths compared to the period with longer segment lengths. The frequency bias will also significantly impact regression slopes and correlation coefficients, possibly distorting analyses investigating multiple groups with different mean segment lengths. Highlighting these potential biases, I recommend the community to not use this method on an individual basis but rather to use a fixed spline stiffness for all samples based on the n% criterion (n = 67) of e.g. the mean segment length of the entire dataset.
Highlights
Detrending is inherent to the dendrochronology discipline
To over come the so-called segment length curse, i.e. low-frequency climate variability cannot be investigated on time-scales longer than the segment lengths of the studied tree-ring series (Cook et al, 1995), one can follow the biological approach, i.e. regional curve standardization (RCS; Briffa et al, 1992a; Briffa and Melvin, 2011; Esper et al, 2003)
Part 1: Temporal frequency bias within a chronology affecting climate reconstructions. Amplitude ratios of both the 100-year and 200-year frequency domain are stable in all chronologies detrended with the 100-year spline (Fig. 4)
Summary
Detrending is inherent to the dendrochronology discipline. Removal of the age trend in ring widths is standard practice and a required pro cedure prior to any statistical analysis to infer climate-growth re lationships. The most commonly used deterministic growth trend models are the modified negative exponential curve, and the generalized negative exponential “Hugershoff” curve. These growth models fit a monotonic decreasing or unimodal curve to the ring-width series and are typically used to detrend open-canopy stands with undisturbed trees. To over come the so-called segment length curse, i.e. low-frequency climate variability cannot be investigated on time-scales longer than the segment lengths of the studied tree-ring series (Cook et al, 1995), one can follow the biological approach, i.e. regional curve standardization (RCS; Briffa et al, 1992a; Briffa and Melvin, 2011; Esper et al, 2003). Through systematic (temporally clustered) over- or under-estimating of the actual growth values the resulting mean chro nology is capable of resolving lower frequencies that a determin istic approach would not be able to retain
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
