LATE-QUATERNARY CHANGES OF PLANT BIOMASS AS RECORDED BY POLLEN-STRATIGRAPHICAL DATA - A DISCUSSION OF THE PROBLEM AT VALLE-DI-CASTIGLIONE, ITALY

The possibility is discussed of interpreting fossil data in terms of changes of past plant biomass, by means of examination of percentages and concentrations of arboreal (AP) and non-arboreal pollen (NAP), and of the AP/NAP quotient. Changes in the pollen concentration by up to three orders of magnitude in a single core are interpreted as dramatic changes of the plant biomass through time; they are consistent with the variations of present-day phytomass and of modern pollen influx in different ecosystem of the world. The AP/NAP quotient can also provide general information on changes of forest biomass, when the non-forest vegetation does not significantly change its pollen production. In contrast, pollen percentages, by their inherent numerical properties, cannot adequately represent the variations in the vegetational density, particularly when the AP percentages are high. The possibility is considered that marked changes of biomass occur during forested periods, even if no significant changes of vegetation composition are recorded.