Impact of Global Changes on the
Reproductive Biology of
Trees in Tropical Dry Forests
Kamaljit S. Bawa
The most spectacular feature of tropical dry forests of Guanacaste is perhaps the mass flowering of many tree species during the dry season. As the dry season begins toward the end of December, a number of species start to bloom, displaying flowers of various shapes, sizes, and colors in the leafless canopy until the end of April (Janzen 1967; Frankie et al. 1974). The seasonal progression of flowering of various species is also mirrored in the daily rhythms, as flowers of various species start opening at dawn, progress through the morning, and then are replaced by nocturnally flowering species at dusk. Since almost all tree species are animal-pollinated, the activity of various pollinators—insects, birds, and mammals—is tied to the phenology of flowers of their host plants, providing a kaleidoscope of plant-pollinator interactions resulting from millions of years of coevolution (Frankie et al. 1983; chapter 2). Flower-pollinator interactions are only one of many interactions involved in the reproductive processes of tropical plants. Before flowers mature and after fruits initiate development, many insects protect reproductive parts of the plants (Bentley 1977). Following seed and fruit development, a wide variety of animals disperse seeds (Howe and Smallwood 1982). Immature and mature seeds and fruits are subject to predation by a diverse array of invertebrates and vertebrates, and such interactions in turn have profound effects on the structure and diversity of tropical forests (Janzen 1970; Connell 1971).
The complex plant and animal interactions are being affected by global environmental change, resulting principally from deforestation and forest fragmentation, climate change, and invasive species. In particular, mutualistic interactions between plants and animals, so vital to the reproduction and survival of both groups of organisms, are likely to be disrupted with severe consequences on the composition of tropical biota. Here, I focus on the effects of deforestation and forest fragmentation on reproductive processes of forest trees in tropical dry forests of