Saisonnalité et déterminisme du pic de fructification en forêt guyanaise

Abstract

The phenology of flowering and fruiting of trees was studied from June 1980 to the end of March 1982 in the lowland rain forest of Piste Saint Elie, French Guiana. All flowering and fruiting trees over 2 cm DBH overhanging a trail 1000 to 1500 m long and 1 m wide were noted every second week, and all flowers and fruits which fell on the trail were collected and weighed. The following results were obtained : Fertility was always low, less than 50 % of the trees over 45 cm DBH bearing fruit during the two yearly cycles. Fertility also varied from one year to the next, being higher during the second yearly cycle. However, some trees which flowered normally never bore fruit. Most tree species (from 76 to 80 %, depending on the year) flowered during the «dry» season and bore fruit during the rainy season (86 to 88 %). The seeds of most of the species (56 %) germinated in less than one month in experimental conditions, and 22,2 % in more than 4 months. Seasonality in reproduction occured in all species of dicotyledonous trees, whatever their size or age (from 2 to > 60 cm DBH). It was far less marked in understorey trees, epiphytes and woody lianas. Seasonality in fruiting was particularly marked among species bearing fleshy fruits disseminated by animals, although some were produced at any time of the year. Seasonality was also marked among wind-dispersed and autochorous tree species. Among trees bearing fleshy fruits, those with the larger seeds were much more seasonal than those with smaller seeds. Finally, the species which were moderately abundant on the sampling transect were more seasonal than both the scarcer and the most abundant ones. Mast fruiting was observed in 8 species of Eschweilera and Lecythis (Lecythidaceae). In the rain forest studied, the fruiting peak mostly results, at the species level, from the adjustment of the maturation period to the flowering time. Biotic factors undoubtedly play an important role in determining fruiting peaks at the community level.