Representativeness of tree diversity in the modern pollen rain of Andean montane forests

Abstract

Questions To assess the relationship between modern pollen rain and Andean montane forest vegetation for diversity, and provide a basis for interpretations of palaeoecological data in the northern Andes, we asked: (1) can the reduction of plant and pollen data to family level preserve information about diversity in both data sets; (2) how precisely do tree pollen and spore types represent richness patterns along an altitudinal gradient on tropical mountains; and (3) how similar are tree pollen and spore family richness in relationship to tree family richness? Location Tropical montane rain forests, Podocarpus National Park in the Andes of South Ecuador (3 degrees S, 79 degrees W, 1000-3000m a.s.l.). Methods We analysed tree diversity and species composition in three different rain forest types: Premontane (PMF), lower montane (LMF) and upper montane (UMF). We investigated modern pollen rain using pollen traps. After testing the reliability of a taxonomic surrogacy on the plant data, we compared abundance and representation, as well as diversity of the two data sets at family level. This was done using rarefaction and Sorensen indices. Results The correlation between tree species and families was high (r=0.81, P<0.001). Sample rarefaction on tree pollen and plant family data revealed highest pollen diversity on sites of the UMF, but highest tree diversity on LMF and PMF sites. The Sorensen indices indicate down-drift of pollen from higher altitudes in PMF and LMF and up-drift in UMF. Between 1% and 50% of pollen taxa of each sample originate from outside the plot. Conclusions Taxonomic surrogacy at family level is a good tool for comparing presence-absence patterns of plant and pollen data in tropical regions with high tree diversity. On a family basis, pollen presence-absence data represent the corresponding tree vegetation data, but uncertainties increase with decreasing altitude. The higher diversity in pollen data of the UMF, but slightly lower diversity in the LMF and PMF, can at least partly be explained by wind patterns, local abundance of shrubs and herbs and differences in evenness.