Recent pollen spectra from the deciduous and coniferous-deciduous forests of Northeastern Minnesota: a study in pollen dispersal

Pollen samples were taken along nine transects across local vegetational belts bordering bogs or ponds in overall deciduous and coniferous-deciduous forest regions. Three types of pollen rain are distinguished: local, extralocal, and regional. Local pollen rain is derived from plants that grow at or very close to the sampling point. High local values are common in all sorts of vegetation types: lakes, bogs, marshes, and forests. Extralocal pollen rain is derived largely from trees that grow on the slopes and upland adjacent to the sampling site, but not extensively over larger areas. When excluded from the pollen sum along with the local types, its curves increase slightly, but noticeably, along the transect as the source of dispersal is approached. The regional pollen rain is derived from plants common far beyond the immediate basin slopes. When the extralocal and local types are excluded from the sum of upland pollen types, the regional pollen rain differs little from site to site. Its recognition permits comparison of modern and presettlement pollen rain with the composition of the recent regional vegetation