Agriculture Reference
In-Depth Information
a
b
E
F
G
EG
H
L
a
L
a
L
b
L
c
L
b
L
c
A
B
C
D
C
B
D
A
t
P
t
P
t
t
t
L
t
L
Time of leaf production or loss (d)
Time of leaf production or loss (d)
c
G
E
H
A
C
B
D
t
P
t
t
L
Time of leaf production or loss (d)
Fig. 3.3
A framework for assessing the determinants of variation in leaf longevity (after Navas
et al. 2003). The
panels
illustrate different patterns for the relative timing of leaf emergence and
leaffall. This graphical framework relates the duration of the period of leaf emergence (
t
p
, the time
from the appearance of the first leaf to the last), the duration of the period of leaffall (
t
L
, the
time from the first fallen leaf to the last), and the length of the stable period
t
from the end of
leaf emergence to the start of leaffall. If leaffall starts within the period of leaf emergence (i.e., the leaf
emergence line and leaffall line overlap), then
t
is scored as a negative value. (
a
) The case when
there is a time interval between the periods of leaf emergence and leaffall. (
b
), (
c
) Cases in which
the emergence and fall of leaves overlap in time:
t
is long in (
b
) but short in (
c
). In (
b
),
t
p
and
t
L
are equivalent, but in (
c
)
t
L
is far longer than
t
p
,
L
a
,
L
b
, and
L
c
in (
a
) indicate the leaves in the same
cohort having different longevity as a result of differences in the timing of leaffall. Symbols and
calculations are explained further in the text
where
t
p
is the duration of the period of leaf emergence (i.e., the time from the
appearance of the first leaf to the last),
t
L
is the duration of the period of leaffall
(i.e., the time from the first fallen leaf to the last), and
t
is the length of the period
from the end of leaf emergence to the start of leaffall when leaf numbers are stable.
If leaffall starts within the period of leaf emergence (i.e., the leaf emergence line
and leaffall line overlap), then
t
is scored as a negative value. Craine et al. (1999)
adopt essentially the same framework. When leaf longevity is too long for the
continuous observation of all the leaves on a shoot to be practical from emergence
