Denis Loubry’s scientific contributions

The early shedding of fruits while developing and maturing has been observed among two Caesalpiniaceae trees in the forest of French Guiana. Parasitism had no effect upon the shedding of fruits since Vouacapoua americana has a one large seed. Significative effects of parasitism on Dicorynia guianensis small seeds were observed at the time of emergence of insects adults occurs. Abscission of parasited fruits seems not to be a direct consequence of the presence of seed-eater insects but a non direct consequence of complete destruction of the seed.

The French Guianan forest is an evergreen rain forest that contains approximately 100 deciduous tree species. The taxonomical distribution of the deciduous character is widely spread, and its presence or absence among some taxa, as well as its ancient origin, are arguments in favour of an endogenous origin. Leaf-fall periodicity was studied on a sample of 500 trees during a 2-year period. Periodicity is annual and seasonal. It is not correlated to rainfall and not linked to the occurrence of a dry season. It seems closely correlated to photoperiodical variations, even though those variations are weak (35 min at latitude 5°30′N). However, each tree has its own periodicity for leaves shedding. Therefore, there is a paradox between seasonality and individual periodicity of leaf fall. The existence of this paradox leads us to consider the hypothesis of an integration of endogenous and exogenous components in the determination of leaf-fall periodicity. Key words: deciduousness, French Guiana, phenology, photop...

Dicorynia guianensis (Caesalpiniaceae) is an emergent forest tree from French Guiana. Its fruits and seeds have many morphological features in common with wind-dispersed species. The indéhiscent pods contain 1, 2 or 3 seeds. The farthest scattering distance observed did not exceed 30 m away from the parent tree. Seeds suffered from high rates of predispersal predation by seed-eating insects, and their reproductive potential was higher in pods containing 2 or 3 seeds (see Table I). Seeds from multiseeded pods made up most of the regeneration potential. 70 % of pods containing viable seeds fell straight under the tree crown, since multiseeded fruits have a restricted dispersal distance (Fig. 2). D. guianensis is an unusual example of a species whose regeneration strategy is modified by predispersal parasitism. Seed predation could be a significant factor in maintaining multiseeded fruits in D. guianensis populations. Moreover, the aggregative distribution of the adult trees of this species could result from the predispersal parasitism of its seeds.