Agriculture Reference
In-Depth Information
Chapter 5
Phylogenetic Variation in Leaf Longevity
Tree fern canopy
(Cyathea arborea)
There are broad patterns of variation in leaf longevity associated with plant growth
form (Fig.
5.1
), and leaf longevity spans more than two orders of magnitude
(Fig.
5.2
). Longevities as little as a few weeks are recorded for some herbaceous
species and 20 years or more for some woody species (Wright et al. 2004). Lusk (2001)
reported leaf longevities for a conifer in south-central Chile as long as 26.2 years in
shaded sites and 21.5 years in open sites. The extensive compilation of leaf longevi-
ties by Wright et al. (2004) is primarily for woody species (79%), mostly shrubs and
trees, with only a few vines; the herbaceous plants in this compilation include
graminoids as well as forbs. The median value of leaf longevity in this data set is
8.5 months. Biologically noteworthy longevities are illustrated by the temporary
flattening of the rank-order diagram (see Fig.
5.2
) at about 3.5 months and again at
6 months. Although there is in general a highly regular and continuous variation in
longevity across species, these clusters of species with similar longevities suggest
the existence of some sort of limiting factor on leaf viability associated with longevities
of these durations. We can speculate that the 6-month longevity reflects the typical
