Pollen rain, vegetation and connectivity in the Tacaná volcano, Southern Mexico

Abstract

The Tacaná volcano in southern Mexico, is one of the most important areas for conservation in the Mesoamerican biodiversity hotspot. Yet, traditional floristic inventories in the area have been limited by access to remote zones along its 4000 m elevation gradient. To achieve an accurate view of vegetation structure and spatial dynamics, we sampled moss pollsters from elevation locations along the entire Tacaná elevation gradient. We observed a strong correlation between pollen spectra and elevation variations, reflecting general vegetation patterns. Main vegetation types along the elevation gradient included tropical rain forest (from 500 to 1500 m), with relative high abundance of Moraceae, Ficus, Alchornea, Fabaceae and Bombacaceae. Montane rain forests were distributed from 2000 to 2500 m, and pollen spectra were dominated by Alnus, Clethra, Cyathea, Quercus, Alchornea, Ilex and Bombacaceae. Temperate forests were located at elevations ranging from 2800 to 3000 m, in association with Pinus-Alnus forests. Pinus forests were recorded at highest elevations from 3000 to 4000 m. In addition, relative humidity was the main factor determining elevation distribution and vegetation change in the area. We argue that up-climbing warm winds favor the distribution of tropical taxa towards higher elevations, thus allowing landscape plant connectivity. Biogeographic and local/regional factors –likely volcanism activity- might govern temperature fluctuations and immediate and long-term effects of the climatic distribution on the associated flora and on biodiversity as a whole.