Modelled and observed surface soil pollen deposition distance curves for isolated trees of Carpinus betulus, Cedrus atlantica, Juglans nigra and Platanus acerifolia

Source-distance relationships for pollen deposited directly into surface soil have been rarely undertaken, particularly for a single or isolated source, rather than a forest, grove or plantation. This study aimed to determine surface soil pollen deposition patterns from single, isolated source trees and to compare the results to Gaussian model curves for the same trees. Four isolated tree pollen sources were chosen in Worcester, UK: Carpinus betulus, Cedrus atlantica, Juglans nigra and Platanus acerifolia. Surface soil samples were collected at 1, 5 and then every 10 m, up to 100 m distance from the main trunk of each source along the prevailing wind direction during flowering. A Gaussian dispersion model was used to estimate source strength using tree height and width and wind speeds on days when flowering was occurring and when the wind direction flowed along the sampling transect. This model simulated the expected concentration and deposition along the sampling transect. Modelled and observed results showed that most pollen was deposited beneath the canopy (range 63-94%) in an exponentially decreasing curve and the tailing off started from around the outer edge of the canopy in most cases. The amount of pollen deposited at 50 m was no more than 2.6% of total deposition in the samples for any tree and at 100 m no more than 0.2%. Tree height, width and wind speed during the pollination period were found to be the main parameters affecting deposition away from the source.