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 121

5.4.2 'Differing-Contemporaneous-Growth-Rate' Bias
The second potential end-effect bias arises because, even within one region, there
is often a variation in the growth rates of contemporaneously growing trees. The
problem that a single RCS curve may not be relevant for trees with widely varying
growth rates has been widely recognized (e.g., Erlandsson 1936 ; Nicolussi et al.
1995 ; Briffaetal. 1996 ; Rathgeber et al. 1999a ; Esper et al. 2002 ) . In a restricted
geographical range where trees might be expected to experience the same regional
climate, localized elevation or aspect differences can lead to variations in the cli-
mates of specific tree locations. Even where trees do experience the same common
history of climate forcing during their lifetime, invariably, some trees will exhibit
greater or less radial growth than others because they are influenced by non-climatic
factors such as differences in soil quality or competition for light or other resources.
A simple RCS approach uses a single (average) model of expected tree growth
(e.g., radial ring increment or maximum latewood density) as a function of tree
age, applied to all trees in one region. If trees are drawn from a wide region or one
with diverse ecological conditions, differences in growth rate in contemporaneously
growing trees is virtually inevitable. Within such a sample, the slope of a single
average RCS curve will be systematically too shallow for relatively fast-growing
trees and too steep for relatively slow-growing trees (Fig. 5.4 ) .
Fig. 5.4 Based on 207 measurement series, for which pith-offset estimates are available (Kershaw
2007 ) , from the AD portion of the Swedish Torneträsk chronology (Grudd et al. 2002): ( a )curve
of mean ring width by ring age, bracketed by thin lines showing the plus and minus one standard
deviation limits of the mean values; ( b ) separate curves of mean ring width by ring age for all trees
( middle line —as in a ), the fastest-growing third of trees ( upper line ), and the slowest-growing third
of trees ( lower line ); ( c ) mean ring width indices (produced by dividing the measurements by the
appropriate age values on the overall-mean regional curve standardization curve), plotted by ring
age for the fastest-growing third of trees ( upper line ) and the slowest-growing third of trees ( lower
line ). The gray shading in ( a )and( b ) shows sample replication for the fastest- and slowest-growing
trees, respectively, where rate of growth is based on time to reach 20 cm diameter