Geoscience Reference
In-Depth Information
differentiation. This hypothesis of 'independent' external control of wood forma-
models for dendroclimatology.
The hypothesis of 'independent control' can be illustrated by the following. In a
period of active wood formation, cells are in all three main stages (but at different
locations within the forming tree ring); i.e., the external signal may affect cells in
all stages at the same time. According to this we may write that
d
N
d
t
=
f
1
{
x
i
(t
j
)
}
d
D
d
t
=
f
2
{
x
i
(t
j
)
}
(3.1)
d
CWT
d
t
=
f
3
{
x
i
(t
j
)
}
Where
i
indicates the factors or processes affected, and all three functions are
assumed to be different and have a different time dependence. Then in the final tree
ring, each of its subdivisions (portions) will contain the climatic signal, integrated
in time, accumulated in cell number (N), cell dimension (D), and cell wall thickness
(CWT).
TR
portion
=
f
{
f
1
[
x
i
(
t
j
),
f
2
[
x
i
(
t
j
+
k
)],
f
3
[
x
i
(
t
j
+
m
)]
}
(3.2)
Here,
j
,
k
, and m are the time intervals between the processes of production, cell
enlargement, and wall thickening. The values of
j
,
k
, and m vary significantly during
a season, and show a significant relation with the total number of cells in the cambial
zone and total production (tree-ring width). Taking into account that the process of
enlargement of a single cell can continue up to 3 weeks, and that wall thickening
takes 2-3 weeks, leads to the conclusion that each portion of a tree ring integrates
the growth conditions over about 1.5 months (without any delays in passing the
hormonal signal from apical meristem to cambium). The most complex aspect of
are assumed to be different.
According to this statement, the maximum density of the last forming por-
tion of a tree ring must be determined only by the climatic conditions at the
end of the growing season because all processes involved occur at this particular
time. This means that even in strong temperature-limited conditions, the maxi-
mum density must be related strongly to August-September temperatures, when
the last forming tracheids enlarge and thicken. But almost all results in dendro-
climatic interpretation of maximum density show that maximum density is better
than even the tree-ring width as an indicator of the whole summer temperature
because of significant correlation with the early season as well as with late season
An alternative hypothesis is that the main target of environmental control in tree-
ring seasonal formation is the cambial zone, and then this signal is transformed into
further processes of cell differentiation (enlargement and cell wall thickening). This
hypothesis suggests that the main target of environmental control is the first process;
