Timing Frequency of Flowering and Seed Production

It is important to conduct phenological studies, i.e. to know when during the year the trees start flowering, fruiting, and producing seed, so that one can collect seeds of desired species that will be later planted in enrichment plantings or in plantations or for agroforestry. In tropical forests, flowering, fruiting, and seed production are most frequent in the dry season. Generally, each species flowers at a certain interval, with regularity. Continuous flowering after the juvenile period is over is found in some secondary forest tree species, for example, Trema orientalis, and also in some mangroves, such as Riz-hophora mangle. However, periodic flowering is more common (Longman and Jenik 1987). Frequency of flowering periods may be 3-4 months to 1015 years. Many common forestry species flower once a year (for example, Ce-drela odorata, Gmelina arborea, Tectona grandis, Terminalia ivorensis). Many canopy trees in the rain forest of Surinam have a biennial flowering habit (Longman and Jenik 1987).

Many species of dipterocarps, important timber species in SE Asia, flower every 3-8 years, a pattern that is called "mast" flowering (general or gregarious flowering) and fruiting. In those years, the majority of dipterocarps of the whole region flower profusely and gregariously over a period of a few months, often accompanied by flowering of species of other families as well. Mast flowering also occurs in plantation trees of these species. The environmental trigger for mast flowering is thought to be an increase in the diurnal fluctuation of temperature associated with drier spells of weather with clearer skies (Yap and Chan 1990). Although the pattern is not as marked as in the dipterocarps, several species of the Vochysiaceae family in the Neotropics have an irregular flowering pattern, which is affected by variations in annual rainfall: there may be no flowering at all in some years, some trees may flower at different times during the year, and, in some cases, trees may flower but will not produce viable seeds (Flores 1993). Several species of Vochysiaceae are important timber species; therefore this pattern also influences the success of management in enrichment planting or in plantations utilizing these species.

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