Geoscience Reference
In-Depth Information
Optical
lower
Optical
upper
Growth (Environmental) Block [Daily Time Step]
G(t) = g
E
(
t
) ยท min [g
T
(
t
), g
W
(
t
)]
1
Temperature Sum
(Growing Degrees)
Minimum
Maximum
Temperature or Soil Moisture
Temperature
Precipitation
Latitude
Growing season
begins?
Daylength
YES
No
Soil Moisture
Environmental
Growth Rate
G(t)
Cambial Block, for each cell in annual file
f{
j
, G(
t
)}
Position specific
growth rate
V(j,G(t))
Cell in
Dormancy?
or Differentiated?
N
o
N
o
Cell growing
faster than
Vmin(j) ?
Cell large enough
to divide?
YES
YES
No
Large enough
to complete
mitosis?
No
Cell Enters
Mitosis
Cell Grows
Proportion to
V(j,t)
YES
Cell Divides
Fig. 3.2
Vaganov-Shashkin growth and cambial model block processes. Daily external (environ-
mental) growth rates are determined by comparing daily temperature and soil moisture (calculated
from precipitation, transpiration, and soil drainage) to piecewise linear approximations of parabolic
growth functions (see
inset
) in the Growth (Environmental) Block. This growth rate is used in the
Cambial Block to calculate the cellular growth rate
V
(
j
,
G
(
t
)),which is a function of the envi-
ronmental growth rate and the position of the cell in the radial file. Each cell is permitted to be
dormant, differentiate, grow, or divide on an intraday time interval. When a nondifferentiated cell
reaches a critical size, it enters and completes the mitotic cycle, continuing its subsequent growth
at a constant, environmentally independent growth rate until division occurs, resulting in two cells,
each half the size of the original mother cell. Once differentiated, cells can no longer divide and go
on to complete the subsequent stages of expansion and cell wall thickening
