Results
Variation in Heating across the range of White Spruce
Heat sum requirements varied significantly across provenances (Figure 1). Populations in the North had the lowest overall heating requirements. Southern populations had less clear genetic differentiation from about the same latitude (Figure 2).
Heating Requirement Variance Partitioning
Variance partitioning was performed for the variables identified as having the highest correlation with heating requirements during our exploratory data analysis (Figure 3). Spring frost period independently explained 18.2% of variance in spring heating requirements (p=0.011). Number of frost free days explained -2.2% (p=0.88) of the variance which indicates some interference with the other predictor variables. The region of origin explained 9.0% of total variance (p=0.007) (Table 1).
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Variation in the Chilling Requirements of White Spruce
For our second objective we sought to detect differences in chilling requirements by white spruce in different regions. First we explored the proportion of buds that began growing at different amounts of chilling. No consistent regional pattern can be seen in proportion of successful budbreak (Figure 4). In addition we examined the effects that different amounts of chilling had on the heating required to force budbreak. In all provenances there was a sharp increase in heating required for budbreak as chilling decreased, however there was once again no consistent region pattern (Figure 5).