The effect of cytotype on radial growth rate in quaking aspen (<i> Populus tremuloides </i>) across environmental gradients

Abstract

Quaking aspen (Populus tremuloides) trees are a foundation species that is widely distributed across all North America. Since the early 2000s, high levels of mortality have been observed in these forests. In recent decades, many quaking aspen forests have been experiencing high mortality rates. This large-scale mortality has been the subject of many studies attempting to ascertain the cause and gather knowledge which could aid in future forest management efforts. There have been observed differences between aspen ramets’ (individual stems) drought-response at small spatial scales under similar environmental conditions, which suggests intraspecific (within species) variation in drought mortality risk. Aspen ramets grow in genetically identical clones (genets) that have either two (diploid) or three (triploid) copies of each chromosome. My project investigated the effect of ploidy level on drought response in quaking aspen and sought to gather data on aspen cytotype growth rate differences across a larger environmental gradient. I collected stem core samples from both aspen cytotypes, compared their radial growth for each year, and analyzed their responses to drought years using historical drought data for the area. While my data analysis did show cytotype to be a significant factor in aspen radial growth, the diploids sampled were measured to have a wider average ring width than triploids in the same areas, counter to the original hypothesis. Elevation, aspect, and slope were all found to have a significant impact on aspen growth rates for both cytotypes, These findings and future studies into polyploidy’s impact on growth rates could prove useful in future forest management efforts through an understanding of which aspen trees may be more vulnerable, or more successful, in future droughts.

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