Landscape openness and pollen records: a simulation approach

Quantitative reconstruction of the area cleared of forest in the past is es sential to assess the possible indirect anthropogenic impacts on the past e nvironment of Europe, including past climate. We apply a simulation model o f pollen dispersal and deposition (1) to re-examine the relationship betwee n pollen and landscape openness, often uncritically inferred from non-arbor eal pollen (NAP) percentages done, and (2) to predict the relevant source a rea of pollen, the smallest spatial scale of vegetation that can be reconst ructed from pollen records. The simulations use landscapes simplified from the modem open agricultural and semi-open forested regions in southern Swed en where traditional cultural landscapes still remain. The model is appropr iate, because the simulated pollen assemblages resemble the pollen assembla ges observed in each of the two landscape types, and because the simulated relationships between NAP percentages and percentage cover of open land wit hin 1000 m agree with the empirical relationships. The simulated relevant s ource area of pollen is the area within 800-1000 m from both small hollows and 3-ha ponds. NAP percentages give only a rough first approximation of th e percentage cover of open land. More comprehensive methods will be require d to obtain quantitative estimates of open land from fossil pollen.