Clonal and spatial genetic structures of aspern (Populus tremuloides Michx.).
Marie-Claire Namroud, Andrew Park, Francine Tremblay, Yves Bergeron.
To portray aspen clonal and spatial genetic structures, we mapped and genotyped trees in
two 1-ha plots, each containing three aspen cohorts originating from fire or subsequent
secondary disturbances. We used four microsatellite loci to identify aspen clones and increment
core analysis to determine tree age. Clonal dimensions were measured by the maximum
distance between two ramets and the number of ramets per genet. Standard normal deviate
(SND) was used to assess the spatial distribution of aspen genets and cohorts, and multivariate
spatial genetic autocorrelations to assess the spatial distribution of aspen genetic variation.
Most aspen genets consisted of only one ramet (> 75%). Median clonal dimensions
were 19 and 29 m (maxima: 104 and 72 m in the two plots). No segregation was observed
between clones. Aspen cohorts were spatially segregated but trees were spatially aggregated
within old and medium-aged cohorts. In contrast, trees were more randomly distributed
within the youngest cohorts. This coincided with a spatial genetic autocorrelation at small
scales (up to 30 m) in the older cohorts and a more random genetic distribution in the
youngest ones. Our results suggest that aspen spatial genetic structuring reflects the spatial
patterns produced by the regeneration of discrete cohorts at different stages of succession.
Vegetative reproduction leads to aspen genetic spatial structuring at small scales (few metres)
until midsuccession. However, as the stand gets older, the spatial distribution of aspen
trees and genetic structure evolve from a structured pattern to a more random one under a gap disturbances regime.