EXTENSIVE POLLEN FLOW MAY COUNTERACT THE EFFECTS OF LANDSCAPE FRAGMENTATION

MARCHELLI, P; MORENO, C; GALLO, L

San Carlos de Bariloche, Río Negro, Argentina

Workshop; Understanding biodiverity loss: an overview on forest fragmentation in South America; 2006

Gene flow, and especially pollen flow, might constitute a fundamental factor in balancing some of the negative effects of forest fragmentation. Wind pollinated species in Patagonia can overcome the isolation of populations by mechanisms of extensive pollen flow favored by the strong directional winds of the region.Measuring contemporary levels of effective pollen flow is essential to analyze if fragmented populations are on risk. A recently developed method called TWOGENER allows the estimation of current pollen flow through the analysis of mother trees and their offspring. The method consists of using the mothers as pollen tramps and to determine if pollen clouds are overlapped or not. It also permits an estimation of effective pollination distance and effective pollination neighborhood.Several species of Patagonia have passed through a fragmentation process since European colonization. The most evident are those that extend their ranges into the Patagonian steppe like Austrocedrus chilensis and Araucaria araucana. But also some Nothofagus species have suffered overexploitation and drastically reduction of their historical distribution ranges.In order to evaluate the degree of connectivity between populations and therefore the effect of fragmentation, pollen flow studies are being conducted in Nothofagus nervosa, A. chilensis and A. araucana.In N. nervosa, we began with an intrapopulation pollen flow study in order to establish the pollen dispersal curve (and the effective pollination distance). We collected buds and seeds from 25 mother trees and we are analyzing between 10 to 20 seedlings per mother, by means of five microsatellite loci.For A. chilensis and A. araucana we have recently began a project in order to study pollen flow in fragmented populations in the steppe. For that purpose we have collected mother and seeds from different locations with a spatially explicit design (total of 140 mothers and 30 seeds/mother). At the moment we are analyzing the material with isozyme markers and setting up the protocols for microsatellites.Preliminary results, problems and perspectives of both studies will be presented and discussed