Trapping pollen in the tropics - Comparing modern pollen rain spectra of differen 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 envi- ronments, 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. 3300 m a.s.l. in southern Ecuador. The vegetation types covered are premontane forest, lower montane forest, upper montane forest and paÌramo. 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 com- parison to the vegetation. All sampling media showed distinguishable pollen spectra for each vegetation type. For the paÌramo, 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 domi- nated 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, pol- len accumulation rates and pollen taxa proportions, as well as in representation of pollen spectra in comparison with the vegetation. However, especially in the paÌramo 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 rec- ommend 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.