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Figure 6: Section of experimental trial alpha design set up with replicates and blocks of clone 5 and clone 8.
Data Collection
This project used a long-term Aspen trial (est. 2002) dataset, from Alberta, Canada (Figure 7, 8, 9), containing height measurements of 688 Aspen trees across 38 clones and 7 provenances. Data was collected over 22 years and included individual tree height, provenance, clone, and sex. Seasonal climate data, including mean temperature (Figure 8) and precipitation (Figure 9), was obtained through the ClimateNA software (Wang et al., 2016), and merged based on the corresponding measurement years.
Figure 7: Worldwide distribution of different Aspen species with pinned location of the trial in Alberta, Canada. (Coordinates: N 53.23342°, W 114.57100°)
Figure 8: Mean annual temperature in North America. (Wang et al., 2016)
Figure 9: Mean annual precipitation in North America. (Wang et al., 2016)
Experimental and Statistical Design
Clone-level height performance was analyzed in R by calculating mean height of every clone, as well as the overall mean height of clones (baseline) at trial age 22. Clones were ranked in descending order to identify the top 5, top 10 and top 15 best performing clones. Subsequently, the average height of each groups was calculated and one-sample t-tests were used to determine weather the height estimates of the groups differ significantly from the baseline. The mean heights of the top-performing groups were further compared to the baseline mean height at trial age 22 to estimate the gain.
Height measurements were analyzed to assess clone performance under three distinct climate periods: Cold & Dry (2003–2005), Warm & Dry (2005–2007), and Cold & Wet (2010–2014). Measurement year 3 , year 5, and year 12 heights were used to represent growth during these periods as those measurements were taken at the end of the respective climate period. For each climate class, the top 5 clones were identified based on their mean height, and their performance was compared to the baseline mean height of all clones for the respective year. One-sample t-tests were conducted to evaluate whether the mean height of each top-performing clone significantly differed from the baseline mean. Gains were calculated as the difference between each clone’s mean height and the baseline. Statistical metrics, including t-values, p-values, and degrees of freedom, were reported for each comparison to quantify the significance of clone performance within each climate class.
Lastly, to evaluate sex-based height differences within provenances at year 22, separate linear regression models were fitted for each provenance, with sex as the predictor. Confidence intervals were used to assess height differences.
References Wang, T., Hamann, A. Spittlehouse, D.L. and Carroll, C. 2016. Locally downscaled and spatially customizable climate data for historical and future periods for North America. PLoS One 11: e0156720.
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