Aerobiological Clines: The Role of Topography As a Barrier for Establishing Dispersal Corridors

Abstract

Cline is a largely known and studied concept in ecology, but is not part of the aerobiological vocabulary. Some attempts have been undertaken in the past to put in evidence aerobiological clines, but their true significance, especially in relation to dispersal, remains unknown. One of the ideal situations to visualise clines is a dispersal corridor. Looking at the geomorphological and phytogeographical localization of Montreal island, the Hudson River corridor (with its continuation through Lake George, Champlain canal & Lake and Richelieu River), seems to be a natural corridor linking the Oak–Chestnut Forest region (which present a tongue on the Hudson river up to Albany, New York, USA) to the Hemlock – White Pine – Northern Hardwoods region of the St-Lawrence lowlands (Quebec, Canada), through the Adirondacks and the Green Mountains. Pollen and spores were collected in the early summer of 2001 (June 13 to July 17) in a mountain (Five Mile Mountain, 685 m.a.s.l) situated on the west ridge of Lake George. Sampling was repeated for a total of 5 sites, through the western slope (out of the corridor) and eastern slope (Lake George side, into the corridor). In this preliminary analysis, the differences in concentration into and out of the corridor of 5 pollen types (Poaceae, Pinus, Juglans, Carya and Ambrosia) and 6 spore types (Alternaria, Cladosporium, Epicoccum, Ganoderma, Ustilago and Ascospores) in addition to Myxomycetes spores and microscopic algae were investigated. Preliminary results indicate that:(1) there are some significant differences in pollen and spores concentrations out and into the corridor (western and eastern slopes); (2) along the transect, the differences were lower between sampling sites located at the same slope than between sites at different slopes; (3) high concentrations of pollen grains of flowering species several kilometres southward were found on the eastern slope. This could confirm the role of the corridor as an ‘aerobiological conveyor belt’ or cline from South to North.