Agriculture Reference
In-Depth Information
Fig. 9.2 Global distribution of evergreen trees. (From Woodward et al. 2004)
south to temperate broad-leaved deciduous forests transits a “mixed-wood” zone
with evergreen and deciduous trees in more or less equal proportions. South of the
deciduous broad-leaved forests, broad-leaved forests of evergreen oaks predominate,
and further south give way to evergreen as well as deciduous forests in the sub-
tropics and tropics. Mesic tropical forests are basically evergreen, but in seasonally
dry regions tropical deciduous forests predominate. These and many other examples
spanning widely divergent spatial scales illustrate a pattern of evergreen predomi-
nance at both ends of the latitudinal gradient in contemporary vegetation that,
although not inviolate, is common enough to demand general explanation. We
clearly need a theory addressing the fundamental basis for spatiotemporal variation
in foliar habit.
Theory for the Geography of Foliar Habit
Our premise is that a theoretical analysis of the geographic distribution of the ever-
green and deciduous habits should be based on a theory of leaf longevity. Evergreen
and deciduous habits are defined at the canopy level but set by the temporal
dynamics of leaf turnover and leaf longevity. Previous theories with their intel-
lectual heritage in the canopy-level perspectives of Monsi and Saeki (1953)
have not really tried to predict conditions favoring evergreen versus deciduous spe-
cies. Because this issue was an explicit motivation for the seminal review by
Chabot and Hicks (1982), at least some of the existing theory for leaf longevity
Search WWH ::




Custom Search