A Closer Look at Regional Curve Standardization of Tree-Ring Records: Justification of the Need, aWarning of Some Pitfalls, and Suggested Improvements in Its Application - Dendroclimatology - page 119

Fig. 5.2 A schematic representation of how the simple regional curve standardization (RCS)
recovers long-timescale trend from the mean values of index series but with potential distortions
within, and particularly at the ends, of the chronology: ( a ) an idealized chronology signal composed
of an overall negative slope with superimposed medium-frequency variance; ( b ) five overlapping
200-year-long series representing simulated measurements; ( c ) the five series aligned by ring age;
( d ) the smoothed RCS curve generated by averaging these series; ( e ) the series of indices gener-
ated through division by the RCS curve; ( f ) the averages of these indices that make up the resultant
chronology ( solid line ), which is shown superimposed on the ideal chronology ( dashed line )

situations where there is a good overlap in many series, this potential bias could
be averaged out. However, this cannot happen at the start and end of the chronol-
ogy. In the case of a long-term declining signal, the chronology will, respectively,
under- and overestimate the ideal chronology at the beginning and end. With a
long-term positive forcing trend, the signs of the biases will be reversed.
Figure 5.3 illustrates a somewhat more realistic example of this problem than
that shown in Fig. 5.2 . The underlying forcing signal that is used here is similar to
that used in Fig. 5.1 , but rescaled to resemble ring measurements (white noise with
mean of 1.0 and range 5% was smoothed with a 10-year low-pass filter added

to the three sine waves, each of which has an amplitude of 0.34). This aggregated
sine wave signal series was sub-sampled to produce forty-one 334-year pseudo-
measurement series. Their start dates are evenly distributed between year 1 and year
668, providing the potential for a 1002-year chronology with a maximum repli-
cation of 20 series (see shaded area in Fig. 5.3d ) . Figure 5.3a shows five of the
sample series. Figure 5.3b shows the average of age-aligned measurements of all

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