Trapping pollen in the tropics — Comparing modern pollen rain spectra of different pollen traps and surface samples across Andean vegetation zones

Abstract

The analysis of modern pollen rain is an important prerequisite for detailed and comprehensive studies on fossil pollen assemblages, as it is necessary for obtaining valuable information about present pollen spectra in a more quantitative way. At present, several sampling media are used for modern pollen rain collection in tropical environments, without knowing a lot about their trapping properties. We compared modern pollen rain spectra of different pollen rain sampling media along an altitudinal gradient from ca. 1000 to ca. 3300m a.s.l. in southern Ecuador. The vegetation types covered are premontane forest, lower montane forest, upper montane forest and páramo. Pollen assemblage composition, representation, diversity and palynological abundance in the modern pollen spectra of Behling traps, modified Oldfield traps, reference traps and soil samples were assessed in comparison to the vegetation. All sampling media showed distinguishable pollen spectra for each vegetation type. For the páramo, the most characterising taxa are Poaceae and Melastomataceae, accompanied by other, less frequent taxa such as Arcytophyllum, Valeriana and Ericaceae. The pollen spectrum of the upper montane forest is dominated by Melastomataceae, Hedyosmum and Weinmannia. The lower montane and premontane forests both have similar spectra, with high proportions of Moraceae/Urticaceae, Melastomataceae, Alchornea and Cecropia. Soil samples had a bias towards an over-representation of pollen and spore taxa with a thick exine, such as Poaceae, whereas taxa with fragile pollen grains, as Moraceae/Urticaceae, were represented to a lesser extent than in the pollen traps. Behling traps and modified Oldfield traps show similar patterns in taxa composition, pollen accumulation rates and pollen taxa proportions, as well as in representation of pollen spectra in comparison with the vegetation. However, especially in the páramo samples, modified Oldfield traps were disintegrated after one year in the field, due to temporarily dry and windy conditions, as well as strong radiation. We therefore recommend the use of Behling traps for the collection of modern pollen rain in areas with open vegetation, which are subjected to drought periods and strong radiation. In forested areas, modified Oldfield and Behling traps show similar results.