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.”