Modern pollen dispersal in Argentina

Extensive analyses were made of surface soil samples and extant vegetation from Argentina, where palynological reconstructions of paleoenvironments over the last 15,000 years is underway. The major vegetation zones in the desert northwest and the sub‐antarctic southwest and south of Argentina are discernible in the relative frequency of their respective pollen assemblages. Where quantitative comparisons of plant and pollen data are possible, representation factors for the pollen taxa are calculated. In addition to the conventional approach using percentage values, principal component and cluster analysis prove to be excellent and complementary techniques in that they reduce the data set into definite groups of representative taxa, both for plants and pollen. The comparison of these groups and their respective dominance along transects indicate that, for example, in the treeless vegetation zones of the desert northwest of Argentina, the transition zone between the grassland and desert scrub (Puneña) occupies a broader range, regionally, in the pollen data than in the vegetation. An explanation for this phenomenon is that the plant taxa representing this transition zone are predominantly wind pollinated, thus they are overrepresented in the pollen rain. Predominance of wind pollination also explains the relative over‐representation of human disturbance zones in the pollen data compared to the vegetation data. It is important to recognize over‐representation when changes are interpreted in fossil pollen assemblages which include transition or disturbance type pollen spectra, as these spectra evidently mask the other vegetation types. In the temperate forest region this problem does not occur, inasmuch as even the transition from forest to steppe can be recognized in the pollen assemblages. However, the upper timberline in the temperate region cannot be precisely defined. For several hundred meters above the treeline a species of Nothofagus that is present below the treeline occurs as dwarf shrub, thus maintaining relatively high pollen percentages both above and below the tree‐line. Thus, the limit can only be defined with a precision of about two hundred meters, above which increasing percentages of herbaceous pollen taxa indicate the increasing openness of the vegetation in the pollen spectra.