Agriculture Reference
In-Depth Information
Fig. 9.5
Relationships between favorable period length and leaf longevity in three alpine plant
species: deciduous
Sieversia pentapetala
(
a
), evergreen
Phyllodoce aleutic
a (
b
), and evergreen
Rhododendron aureum
(
c
). (From Kikuzawa and Kudo 1995)
their construction costs within the short favorable period, so extended leaf longevity
leads to an evergreen habit (see Fig.
9.3c
). This rationale is supported by the
contrasting trends in the leaf longevity of evergreen versus deciduous species
reported by Wright et al. (2005a) along global temperature gradients associated
with length of the growing season. Leaf longevity of evergreen species decreased
with mean annual temperature whereas that of deciduous species increased. In
summary, deciduous plants are unable to retain their leaves over an unfavorable
period but do prolong leaf longevity when the favorable period lengthens.
Conversely, evergreen species have to prolong leaf longevity when the unfavorable
period lengthens to pay back the construction and maintenance costs of leaves
unproductive during the unfavorable period. Although these patterns are in accord
with intuitive arguments provided by Kikuzawa (1991, 1995a, 1996) to account for
the bimodal distribution of evergreen habit on latitude, the development of relevant
analytical theory is desirable.
In principle, these arguments should apply not only to interspecific behavior on
latitudinal gradients but also to variation in leaf longevity for species at local spatial
scales. We can illustrate and test the ideas using situations such as topographic
variation in the timing of spring snowmelt caused by differences in winter snow
depth on Mount Daisetsu in northern Japan. Kudo and Kikuzawa (Kudo 1992, 1996;
