2.3.1.2 Some deciduous tropical trees
Some deciduous tropical tree species behave very counterintuitively in
producing fresh foliage before a dry season ends (e.g. Frankie et al.
1974; Borchert and Rivera 2001; Kushwaha et al. 2015). A specific case
is Faidherbia albida A. Chev. (apple-ring acacia), a widely
distributed, deep-rooting tropical tree species of Africa, found with
annual rainfall of 200−500 mm. It flushes vegetatively during the dry
season, but sheds its leaves during the rains (Huxley 2001), yet it
flowers at the end of the wet season. Accounting for such
counterintuitive behaviour is a challenge, but it is hard to see a
convincing alternative to the postulate of pathogens driving a shift to
deciduousness. Actual support for the postulate would come if, when such
species are grown with no dry season, the new foliage suffered from
pathogens. The success of such a study, however, would depend on both
the presence of the appropriate pathogens and the nature of the triggers
for shedding old leaves and producing new ones. An alternative driver,
namely increased herbivory pressure during the wet season, seems very
unlikely in these cases.
Suggesting a similar explanation are some results of Frankie et al.
(1974), for “Wet” forests in Costa Rica, where dry seasons would not
be severe and not generally associated with actual deciduousness. They
noted “Most Wet forest species flushed large quantities of new leaves
during the first dry season.”