DATA

Data Exploration

Climate data for White spruce breeding regions were collected from spatially interpolated climate data for the 1961–1990 climate normal period generated using the software package ClimateWNA v4.62 (Hamann et al., 2013) freely available at http://tinyurl.com/ClimateWNA. The variables selected for this study were biologically relevant for the adaptation of the species population to climatic differences. The climate variables are mean annual temperature (MAT), mean coldest month temperature (MCMT), mean warmest month temperature (MWMT), continentality (TD), mean annual precipitation (MAP), growing season precipitation (MSP), climate moisture deficit (CMD), frost-free period (FFP), number of frost-free days (NFFD), and growing degree days above 5 °C (DD5). ​Data exploration and analysis were carried out using R statistical package v4.1.1 software (Table 2 and 3).

Box plots of the sites by region reflected the variations within the regions (Figure 8). The Lower and upper limits of the boxes represent the 25th and 75th percentiles, respectively. The line within the box represents the median of the data. Whiskers represent the largest value no further than 1.5 interquartile range. The data showed that there were no outliers as there was no data plotted as circles above any of the boxes. Generally, the box plots reveal the planting sites in regions NM and SM have high variance and low height. All the other regions seem to do well in all the sites except at site C where the height measurements were of lower values. We can also see that site regions E1 and E2 have relatively stable height in site C while all other regions dipped below. Low height measurements were recorded for region E1 in sites D, C, F, and G. Gi seemed to be most resilient and did well

The principal component analysis of the climate data revealed strong correlations between the climate data of the breeding regions, the color of ellipses represents regions. Region D and G1 are associated with relatively warm and dry climates (MAT). The climate of Southern Montane (SM) and SNorthern montane (NM) possess very similar climatic characteristics. These regions have higher moisture and are relatively warm as indicated by the overlay of MAP and MSP vectors. In contrast, regions H and E1 are from the northern part of Alberta and have drier and warmer summers and very cold winter exhibiting strong seasonality (TD). G2 shows strong continentality. E1 and G2 have low to medium precipitation while G2, E2 and D1 have relatively less precipitation (Figure 9).

Exploration of the data using scatter plots below shows the average height measurements of the trees by region on each planting site. each point’s horizontal position indicates the average tree height (cm) and the vertical position indicates the mean annual temperature, MAT (°C ), or mean annual precipitation, MAP (mm). From the plot, we can see a positive correlation between height and MAT in sites D, H, and P, while negative correlations were observed in sites B and J We also did not observe any definite clustering. The exponential curves fitted showed a generally negative correlation between height and MAP. The optimum precipitation for most of the sites appears to be 400-500 mm/yr as we noticed a clustering here. Linear models were fitted in growth versus MAT because they have a lesser Akaike Information Criterion(AIC). A linear model was fitted in the scatterplots of height in relation to MAP of the sites while the polynomial quadratic model was fitted in height versus MAP because they resulted in a lower AIC. Similar results were observed in the higher elevation sites.

References

Hamann A, Wang T, Spittlehouse DL, Murdock TQ (2013) A comprehensive, high-resolution database of historical and projected climate surfaces for western North America. Bull Am Meteorol Soc 94: 1307–1309