Modern pollen-vegetation relationships along an altitudinal transect in the central Pyrenees (southwestern Europe)

Modern proxy-calibration studies are a powerful tool for paleoecological interpretation. This paper analyzes the relationships among modern pollen rain, vegetation and altitude in the central Pyrenees, where several paleo-palynological studies have been developed, but a modern analog survey is still unavailable. The work analyzes the pollen content of moss polsters from different vegetation communities along an altitudinal transect, as well as the flora and vegetation using the Braun-Blanquet system. DCCA showed that altitude satisfactorily explains both vegetation (r(2) = 0.988) and pollen (r(2) = 0.841) gradients. Besides the complexity of pollen-vegetation relationships, some regularities were found to be useful for paleoecological and paleoenvironmental interpretation. In general, altitudinal vegetation and pollen patterns show similarities, but pollen belts and boundaries are less well defined, likely because of the homogenizing effect of upward wind transport. Palynological differentiation of montane from subalpine/alpine belts is straightforward from the trends of the more significant pollen types, mainly the low-altitude deciduous trees and the high-mountain herbs. Palynological differences between subalpine and alpine belts, which boundary coincides with the treeline, are more subtle and need quantitative criteria and complementary proxies. From an individual point of view, four main groups of pollen were distinguished, in relation to their usefulness as vegetation and altitudinal indicators: (1) very good indicators, (2) good indicators, (3) non indicators, and (4) allochthonous pollen types. The first two groups resulted to be useful as indicator taxa for modern analogs for paleovegetational and paleoaltitudinal reconstruction, while the latter two groups should be interpreted with caution in paleoenvironmental studies.