Interpreting long-term exponential growth of plant populations in a 250000-year pollen record from Valle di Castiglione (Roma)

their doubling times vary from a few to many hundreds of years. The durations of exponential growth last up to 6000 years. The interpretation of this phenomenon takes into account the close relation between climate, soil and vegetation. Under climatic conditions suitable for the expansion of a given population, growth depends on soil fertility, which, in turn, increases as the population grows. The process may be self-fertilizing, producing in the long run a sum of nutrients greater than their consumption. Competition does not seem decisive in determining patterns and times of increase of plant populations.; The pollen concentration diagram of a long core drilled in the lacustrine sediments of Valle di Castiglione (Roma) indicates that the increase of different plant populations is often exponential. Increases of trees, shrubs, herbs, aquatic plants and pteridophytes have been examined