Many forest tree species distributed across large geographic ranges are composed of genetically distinct populations that are adapted to the segment of climate in which they inhabit. Forestry provenance studies, i.e. common gardens, provide evidence of local adaption to climate when associations between fitness traits and the population home climate are observed. When grown in a common environment, populations from warmer climates, exhibit larger growth potential compared to populations from colder climates. Most studies that measured tree height as fitness trait, do so at a point in time, usually age 10. In this study we model juvenile height growth up to age 19 to elucidate differences in early growth patterns. We use provenance tests data from the mid-1980’s for black walnut, a tree species with significant economic and ecological importance that has been shown to have ample intra-specific genetic variation. The data comprised height measurements for 50 populations tested in several of 10 common gardens, totaling 360 observations. We develop nonlinear mixed effects models of populations’ height growth. These models test whether populations differ in growth patterns by incorporating populations’ home climate into the model.
Results/Conclusions
We hypothesized that populations from warmer climates will exhibit a growth pattern that will enhance their competitive ability early on as these populations are more likely to inhabit resource rich environments, while populations from colder climates may display more gradual growth patterns. Preliminary analyses indicate that by age four, populations from warmer climates begin exhibiting higher growth rates than those of populations from colder environments and that those differences increase with age. Our results have important implications for understanding species and populations responses to a changing climate and for seed source selection under a changing climate.