Relationships between genetic diversity, clonal structure and sudden apsen decline in Kaibab National Forest, Arizona

Rapid and extensive dieback of aspen stands in the western United States, termed ‘Sudden Aspen Decline,’ has been attributed to combinations of predisposing inciting and contributing factors. A recent study in the Kaibab National Forest near Flagstaff, AZ conducted by Zegler (2011) was intended in part to examine the relationships between aspen crown dieback and mortality with predisposing stand factors and contributing damaging agents. However, the genetic diversity and clonal structure of the sample sites used in this study had not been estimated. This provided a unique opportunity to combine a genetic dataset with preexisting measurements of stand degradation and environmental conditions to test for relationships between them. The objectives of this study were 1) to estimate the genetic diversity of aspen in the study area, 2) to assess clonal structure to make inferences of historical reproductive patterns, and 3) to test for relationships between genetic diversity, clonal structure, and signs of SAD. To accomplish this, microsatellite multilocus genotypes were generated from tissue samples taken from a subset of sample sites from Zegler (2011). Analysis of the genotypes from these sites revealed an association between genotypic diversity and northerly aspect, and levels of site degradation showed a positive relationship with mean heterozygosity. I speculate that the association between genotypic diversity and northerly aspect may be due to higher rates of aspen seedling recruitment among northerly aspects, and that the relationship between heterozygosity and stand degradation results from ancient clonal lineages with both high levels of heterozygosity and poor fitness under current conditions. I conclude that conservation efforts encouraging the propagation of seedlings and younger clones would improve resistance of the greater aspen population in Kaibab National Forest to Sudden Aspen Decline