Journal
ECOLOGY AND EVOLUTION
Volume 11, Issue 12, Pages 7399-7410Publisher
WILEY
DOI: 10.1002/ece3.7571
Keywords
adaptation to climate; ecological genetics; Juglans nigra; juvenile growth patterns; provenance tests
Categories
Funding
- USDA Forest Service Northern Research Station [03-JV11242328-001]
- Pennsylvania State University [03-JV11242328-001]
- USDA National Institute of Food and Agriculture [PEN04700, 1019151]
- USDA National Institute of Food and Agriculture Hatch Appropriations [PEN04700, 1019151]
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This study examines early growth patterns in black walnut populations and finds that populations from warmer climates exhibit higher cumulative growth, maximum absolute growth rate, and relative growth rates compared to populations from colder climates. This suggests that natural selection may favor fast early growth rates in milder environments where competition is the dominant selection pressure.
Many boreal and temperate forest tree species distributed across large geographic ranges are composed of populations adapted to the climate they inhabit. Forestry provenance studies and common gardens provide evidence of local adaptation to climate when associations between fitness traits and the populations' home climates are observed. Most studies that evaluate tree height as a fitness trait do so at a specific point in time. In this study, we elucidate differences in early growth patterns in black walnut (Juglans nigra L.) populations by modeling height growth from seed up to age 11. The data comprise tree height measurements between ages 2 and 11 for 52 natural populations of black walnut collected through its geographic range and planted in one or more of 3 common gardens. We use the Chapman-Richards growth model in a mixed effects framework and test whether populations differ in growth patterns by incorporating populations' home climate into the model. In addition, we evaluate differences in populations' absolute growth and relative growth based on the fitted model. Models indicated that populations from warmer climates had the highest cumulative growth through time, with differences in average tree height between populations from home climates with a mean annual temperature (MAT) of 13 degrees C and of 7 degrees C estimated to be as high as 80% at age 3. Populations from warmer climates were also estimated to have higher and earlier maximum absolute growth rate than populations from colder climates. In addition, populations from warm climates were predicted to have higher relative growth rates at any given tree size. Results indicate that natural selection may shape early growth patterns of populations within a tree species, suggesting that fast early growth rates are likely selected for in relatively mild environments where competition rather than tolerance to environmental stressors becomes the dominant selection pressure.
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