RAINFALL ESTIMATES DERIVED FROM THE POLLEN CONTENT OF MODERN HYRAX DUNG - AN EVALUATION

Pollen-rich fossil hyrax middens have been used to reconstruct changes in Holocene Karoo plant cover and precipitation. However, rainfall es timates depend on a set of untested assumptions that link annual sprin g-summer rains to grass/Karoo shrublet ratios in the ground cover and to Poaceae/Compositae ratios in atmospheric pollen. Here, rainfall, gr ound cover and pollen discharge records collected in the eastern Karoo from 1952-55 are compared. There is a very strong correlation between mean monthly rainfall and mean monthly grass/Composite ratios in atmo spheric pollen. In theory, past rainfall can be estimated from fossil pollen spectra near the sampling station by the formula rainfall (mm) = Poaceae/Compositae x 4,6. Applied to monthly pollen counts from mode rn hyrax pellets collected from 1989-91, this formula revealed clear s easonal rainfall patterns. Also reflected were the catchment differenc es between sampling stations, and contrasting drought conditions durin g the two sampling periods. The airborne pollen spectrum was not signi ficantly altered by incorporation into the dung. Seasonal changes in t he concentration and composition of pollen in the pellets were so pron ounced, however, that an assay of the seasonal mix of pellets in any f ossil dung sample is recommended before calculating prehistoric rainfa ll from its grass/Composite pollen content.