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 127

Fig. 5.8 Based on 1024 trees from AD portions of the Torneträsk and Finnish Lapland chronolo-
gies. ( a ) The simple regional curve standardization (RCS) chronology ( black line ) and associated
tree counts ( gray shading ), truncated before AD 400. Simulated 'modern sample type' chronolo-
gies were created by averaging eight selected groups of tree indices (all produced by using the
same single RCS curve and only where sample counts exceed 2). Each sub-chronology is made
up of samples that would have been collected by using modern sampling practice with selections
made on a series of specific dates (the first is AD 580 and subsequent selections are made every
200 years until 1980) and only including trees alive and with a diameter greater that 14 cm on the
sampling date. ( b ) Shaded areas showing sample counts by year for each simulated chronology,
plotted alternatively from the bottom and top of the figure for clarity. Approximately 43% of the
total ring measurements are included in the 'selected' samples
with the growth rate/longevity phenomenon, imparts negative bias in the start of a
chronology and positive bias in the recent period. The systematic continuous over-
laps between slower- and faster-grown trees in this example compensate throughout
the chronology for these biases. That is, of course, except for the early section
and, most noticeably, in the most recent 100 years of the overall chronology, which
appears to follow what is likely to be a biased trajectory due to an absence of small
indices from young, slow-growing trees that would have gone on to become the
early sections of old trees.
5.5 Particular Problems Associated with the Application of RCS
to Modern (i.e., Living-Tree) Sample Data
In practice, the underlying assumption of RCS, that the averaging of measurement
series aligned by ring age and subsequent smoothing of the resulting mean curve will
remove all the climate-related variance, may not always be valid. This assumption
cannot be true when all samples span the full length of the chronology. In such a
case, the overall climate signal will be contained within the RCS curve and will be
completely removed by standardization. In a modern chronology where trees are
of unequal length, the average overall slope of the chronology is contained in the
RCS curve and is thus removed from every tree in the final chronology. In a long