How Well Understood Are the Processes that Create Dendroclimatic Records? A Mechanistic Model of the Climatic Control on Conifer Tree-Ring Growth Dynamics - Dendroclimatology - page 53

2. At high latitudes, tree-ring width variations correlate well with average summer
(June-August) temperature, but maximum density shows a significant correla-
tion with temperature for a larger part of the growing season—for example,
May-September (Briffa et al. 1990 , 1992 , D'Arrigo et al. 1992 ) . A longer grow-
ing season due to high temperatures will definitely increase the percentage of
latewood in tree rings (Larson 1964 ) .
3. Denne ( 1971 ) , in experiments with Scots pine ( Pinus sylvestris ) seedlings,
showed that a temperature increase from 17.5 to 27.5 ◦ C produced only a 10%
increase in tracheid diameter. Contrary to this, we found a significant increase of
tracheid diameter in the earlywood of larch tree rings near the northern timber-
line associated with a long-term summer temperature increase (Vaganov 1996c ) .
Note that these effects of early summer temperature on earlywood tracheid diam-
eter occur in the temperature range 5-14 ◦ C. In more southerly sites where the
early summer temperatures were higher (between 12 and 19 ◦ C), the effect of
temperature on tracheid diameter was diminished because the temperature was
no longer in the range where it was clearly limiting (Vaganov 1996c ) . Under
conditions close to optimal temperature (as in Denne's experiments), the limiting
effect of temperature on tracheid diameter is probably small.
4. Temperature and tracheid wall thickness were inversely correlated in several
conifer species (Wodzicki 1971 ) . Similar data were obtained by Antonova and
Stasova ( 1993 , 1997 ) . This result contradicts results from maximum latewood
density, which is mainly determined by cell wall thickness. At the upper ele-
vations or northern timberlines, rings with thin-walled cells in the latewood
(so-called 'light rings'), are produced by a cold autumn or sharp cooling at the
end of summer (Filion et al. 1986 ; Schweingruber 1993 ) .
Many of the contradictions in publications on the effect of temperature on tra-
cheid dimensions (diameter, wall thickness) are caused by other uncontrolled but
important external factors, such as water supply or light intensity, and by uncer-
tainties in the ranges of strong limitation of one factor and alteration of the limit
by another factor. For example, Denne ( 1971 ) chose a temperature range that is
close to optimal for growth. Thus there is no pronounced effect of temperature on
anatomical structure. In the case of Antonova and Stasova ( 1993 , 1997 ) , there was
no control of the soil water content during the production and formation of late-
wood tracheids. Hence the apparent negative effect of temperature could come from
its indirect effect on water loss from soil due to increased evapotranspiration.
3.5.2 Water
The availability of soil water may affect the growth rate and formation of wood,
both at long timescales and within a season (Zahner and Oliver 1962 ; Kozlowski
1968 ; Zahner 1968 ; Creber and Chaloner 1984 ; Bräuning 1999 ) . For example, pine
in marshy conditions forms not only narrower tree rings, but rings with smaller
absolute size and proportion of latewood. In periods of suppressed growth, a tree