Seed dormancy in trees of climax tropical vegetation types

This review includes data on classes of seed dormancy, or of nondormancy, for 2040 species of trees in climax tropical forests: evergreen, 1098; semievergreen, 515; deciduous, 133; savanna, 223; and montane, 71. In evergreen, semievergreen, deciduous, savanna, and montane forests, 57.3, 52.0, 34.8, 37.8, and 33.8% of the species, respectively, had nondormant seeds. Overall, there was an increase in dormancy with decreases in temperature and precipitation across the gradient of forest types from evergreen to montane forests, but deciduous, savanna, and montane forests had about the same proportion of species with dormant seeds. Depending on the family, there were increases, decreases, or no change in proportion of species with dormant seeds across the gradient. Considering only the species with dormant seeds, physiological dormancy decreased from evergreen to deciduous forests but increased slightly in savanna and montane forests. On the other hand, physical dormancy increased from evergreen to savanna forests but decreased in the montane. Morphological dormancy decreased from evergreen to savanna forests but increased in montane forests. Morphophysiological dormancy decreased from evergreen to deciduous forests but increased in savanna and montane forests. Combinational dormancy (physical + physiological), which never exceeded 2%, was found only in evergreen and montane forests. Much research remains to be done to understand the evolutionary origins and biogeography of seed dormancy in tropical trees, and it is suggested that working on members of plant families that occur across the gradient of forest types may be a rewarding approach.