Agriculture Reference
In-Depth Information
Box 1.2 (continued)
Semievergreen : Immediately after new leaf emergence, old leaves fall; leaf
longevity is essentially 1 year, and a leafless period is not very apparent.
Brevideciduous : Some leaves are shed during part of the year, but never
more than 50% of the leaves, so the plant canopy appears evergreen.
Semideciduous : More than 50% of leaves are lost at some time in the year,
but the plant canopy is never completely bare.
Heteroptosis : Some branches of a tree become completely leafless during
unfavorable periods but others retain leaves throughout the year.
Variations on the deciduous habit
Summergreen : Leaves are shed in autumn, and in woody plants the canopy
is completely bare through winter; this is a typical deciduous habit in
temperate regions.
Wintergreen : Leaf emergence occurs at the end of summer and leaves are
retained through winter, but are shed at the onset of the next summer,
and the plant is completely bare during summer.
Drought deciduous : Leaves are shed during the dry season in tropical
forests and deserts.
Spring ephemeral : Plants have leaves only in early spring that wither by
summer. This habit is usually found in herbaceous plants but has been
recorded in a small tree ( Aesculus sylvatica ) in North America
(DePamphilis and Neufeld 1989).
It is important to recognize that the distinction between evergreen and deciduous
species applies at the level of the entire plant canopy, not individual leaves. It is
possible for a plant canopy to be evergreen by replacing relatively short-lived leaves
frequently throughout the year. Of 13 evergreen species in California chaparral, 5
had leaves that survived less than a year but which maintained an evergreen canopy
through a prolonged period of leaf production from early spring into summer
(Ackerly 2004). Although the basic evergreen-deciduous dichotomy at the canopy
level is reasonably clear, some intermediate terms have arisen to describe pecu-
liarities in leaf turnover that can lead to differing degrees of evergreenness (Sato
and Sakai 1980; Eamus 1999; Eamus et al. 1999a; Eamus and Prior 2001; Franco
et al. 2005; Saha et al. 2005; Negi 2006; Williams et al. 2008). Primary among
these alternative terms is the recognition of a brevideciduous habit in which there
is a brief period in the year when old leaves are falling and new leaves are emerging
simultaneously. This intermediate habit also is referred to as “leaf exchanger”
(Whitmore 1990), “incomplete deciduousness” (Hatta and Darnaedi 2005), and
“semievergreen (Singh and Kushwaha 2005). The canopy in such species is never
entirely leafless, even briefly, and therefore cannot be considered truly deciduous,
but then neither can it be considered any more than marginally evergreen. From
developmental, phylogenetic, and functional points of view, this brevideciduous
 
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