The new presentation of the results in this report focuses on a comparison of the fossil data with an extensive modern data set (118 spectra) covering all the vegetation types encountered on an altitudinal gradient from 500 to 4000 meters elevation. Statistical Factorial Analysis was carried out both on the modern (118) and the fossil pollen spectra (18), with the fossil data being considered as supplementary elements. In this procedure, local aquatics and grasses are excluded, and the statistical treatment is applied to the pollen counts for the 189 identified taxa. The statistical results show a distribution of the modern samples into four distinct altitudinal vegetation zones, with the fossil samples from Hadar linked to modern samples taken from vegetation existing now at altitude above 500 meters. Therefore, the statistical analysis confirms previous interpretation of the past vegetation interpreted as similar to that presently known in the Ethiopian mountains. However, the interpretation of the pollen record should take into account possible rifting that might have occurred since the deposition of the Hadar Formation, and could produce, in the pollen assemblages, the same changes as those indicating a noticeable cooling. Although the Pliocene pollen data can be interpreted as indicating conditions much more humid than the arid climate that prevails in the Hadar region today, the factorial analysis indicates close affinities with modern pollen data from the dry forests of northeastern Ethiopia but not with the wettest forests of southwestern Ethiopia. This is a clear indication of the eastern limit of humid lowland and highland forests, and that they did not reach the 40o longitude at that time.
Palynologists have developed a statistical methodology which enables the quantitative reconstruction of climatic parameters. We have been successful in reconstructing such parameters for the Holocene and Late Glacial pollen data in Central Africa. Because the Pliocene pollen can be identified by comparison with the modern taxa, an attempt was made to apply such a quantitative reconstruction of climatic parameters to the Pliocene record, using the modern pollen data set from Eastern Africa. The results of this essay show that a possible short cooling event associated to more humid conditions could have occurred around 3.4 Ma ago. But quantitative estimate of this cooling would need a better evaluation for the amplitude of the Ethiopian plateau uplift in the Hadar area. The modern pollen data set from Ethiopia expresses a clear pattern for the decreasing temperature gradient with increasing altitude, nevertheless a more reliable result can only be achieved when pollen data from the Last Glacial Period in Ethiopia are obtained, in order to constrain the coefficients for evaluating the climatic parameters.