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 139

is manifest only at the ends, but it can be a substantial bias affecting the whole
length of a short, modern chronology. Differences in the growth rates of contem-
poraneously growing trees, and the inadvertent acquisition of data from younger
trees that are more vigorous rather than slower-growing trees in recent times, both
lead to the possibility of chronologies in which more recent chronology trends may
not accurately represent the influence of climate variability. This contemporaneous-
growth-rate bias will cancel in all but the ends of long chronologies, but may
be a serious end-effect problem manifest equally in long subfossil and modern
chronologies.
Having discussed the various sources of potential bias, we now turn to the ques-
tion as to relative magnitudes. No generalizations can be made, because the specific
characteristics of sample data and underlying climate signal will vary in different
situations. However, in an attempt to provide some illustrative indication, we offer
Table 5.2 . This table lists the sources and possible relative magnitudes of different
biases, and makes a guess at the overall bias for a hypothetical, but not untypical,
example chronology (the detailed makeup of which is described in the caption to
Table 5.2 ) that was assumed to have been subject to a notable increase in tree growth
forcing about 50-60 years ago. All the biases are manifest at the recent end and tend
to reduce the expression of the expected recent growth increase over the last century
of the chronology. The net biases act to produce a spurious positive trend 400 200

years from the end of the chronology, but the relatively large negative bias, mostly
associated with non-random sampling practices, is likely to dominate in the most
recent centuries.

−

Table 5.2 Relative sizes of individual and net bias effects a

Effective duration
(years)

Approximate
magnitude Type of RCS bias General slope of bias

Absence of pith-offset estimates 200 Negative 0.1

Trend-in-signal bias
Solely modern chronology 200 Negative 0.1

Longer subfossil chronology 200 Negative Negligible

Contemporaneous-growth-rate bias
Modern sample bias 400 Positive 0.2

Dominancy of fast-growth
indices

100 Negative 0.2

Net effect 400 − 200 Positive 0.1

100 − 0 Negative 0.2

a These effects are implicit in the application of simple regional curve standardization (RCS) for a
hypothetical chronology. These figures are 'guesstimates' of the magnitude and effective duration
of RCS biases discussed in this review. These figures are expressed for a hypothetical set of data
from trees with the following characteristics: the longest trees are about 400 years old; the shortest
trees are around 100 years old; the chronology indices have a range from 0.5 to 1.5; and the trees
experienced a 40% growth increase, which occurred around the middle of the twentieth century.
These biases are manifest as 'end effects' (i.e., all terminating at the end of the chronology). All
biases, with the exception of trend-in-signal bias, will apply equally to modern and sub-fossil
chronologies.