Phenological Behavior of Habit and Habitat Classes on Barro Colorado Island (Panama Canal Zone)

Abstract

Phenological patterns of flowering and fruiting are presented for species of phanerogams on Barro Colorado Island. The phenological patterns represent overall averages rather than for any single year or for any individual. Flowering and fruiting graphs were prepared by calculating the total number of species which might be in flower or fruit for any month. Species were divided according to both habit and habitat. Aquatic and suffruticose herbs were found to be aseasonal as were the arborescent plants of clearings. Clearing herbs, herbaceous vines, epiphytic herbs, as well as lianas and trees, are seasonal with a peak of activity in the dry season. Forest herbs including herbs of forest trails, lightgaps and edges, as well as shrubs, have a peak of activity in the rainy season. In contrast to the clearing herbs, these groups appear to be relatively unaffected by conditions of drought, and flowering is probably cued by the onset of the rainy season. The average length of flowering time is least for those groups which were markedly seasonal such as lianas and larger trees. Species studied were divided into 20 seasonal groups, 6 nonseasonal groups, and 1 bimodal group. A total of 295 species flower and fruit all year. The largest seasonal categories include those species which flower and fruit in the wet season (171 spp.) and those which flower and fruit in the dry season (132 spp.). More species flower and fruit in the rainy season than in the dry season, despite the fact that the overall flowering and fruiting curves peak in the dry season. THE DATA PRESENTED HERE are the result of field observations and herbarium studies made between 1967 and 1974, and include observations made during more than three years in Panama and a survey of more than 50,000 herbarium specimens from Barro Colorado Island and adjacent areas. The study has been an integral part of the new Barro Colorado Island Flora which is now being completed and which attempts to determine the phenological behavior of flowering and fruiting for all species of flowering plants that occur on the Island. In these data no attempt has been made to outline the phenology of individual plants, though numerous individuals were repeatedly observed. Instead the data represent what are thought to be the normal phenological variation for each species. This might be termed its historical pattern of flowering. No attempt has been made to include the broad outlier especially when the phenology of the species involved is well-known. In the well-known species an estimated 95 percent or more of the flowering or fruiting probably falls within the time span indicated in the studies. The flowering or fruiting period given for most species is broader than that for any single year. However, since weather patterns are in general consistent and since plants have probably evolved a phenology which is compatible with a particular climatic condition, I have chosen to look at overall phenological patterns rather than what might happen in any one year. Variation in phenological patterns from year to year for any species is considerable and can also be great between individuals in a given year both in terms of timing and duration. Although other phenological studies have been made (Rovirosa 1892; Fournier and Salas 1966; Janzen 1967; Smythe 1970; Foster, unpublished; Frankie, Baker, and Opler 1974), this is the only known attempt to define an entire flora in a phenological