Phenotypic Variation
Consistent with our first hypothesis, we found significant within and among population variation for traits at each of the three common gardens (Table 1, Fig. 3), with phenology traits exhibiting higher differentiation at the population than the genotype level in all but one case. For example, most of the variation in bud flush in Yuma and Agua Fria was explained by population. For the morphological and growth traits, the relative contribution of population vs. genotype varied among gardens. Traits measured in the hottest common garden exhibited stronger population than genotype effects in four out of the five traits (SLA had a higher genotype variance). This garden thus produced higher values of QST (the proportion of the genetic variance that is found among rather than within populations, see next section).