Principal investigators: C. Dana Nelson, project leader/research geneticist, USDA Forest Service, Southern Research Station (charles.d.nelson@usda.gov); Ellen V. Crocker, assistant professor of Forest Health Extension, University of Kentucky (e.crocker@uky.edu)
Co-author: Austin Thomas, ORISE postdoctoral scholar, USDA Forest Service Southern Research Station
A preferred strategy for white oak reforestation is enhancement planting in forest gaps. These gaps vary in size and therefore light availability on the forest floor. The Hardwood Tree Improvement and Regeneration Center (HTIRC) and White Oak Genetics and Tree Improvement Program (WOGTIP) are working to improve the performance of white oak seedlings through selection and breeding.
To provide the best testing environment for selecting genotypes that will perform well in variably shaded conditions, researchers need to know the extent to which families respond differently to light conditions to determine the best level of light for testing families’ performance in gap plantings.
To answer these questions, researchers with the U.S. Forest Service Southern Research Station Forest Health Center (FHC) at the University of Kentucky and the HTIRC at Purdue University are evaluating the performance of white oak families (seedlings from individual mother trees) grown under varying light conditions (experimental shade treatments).
Traditionally, progeny tests are grown under open-field or full sunlight conditions, but white oak (Quercus alba) typically regenerates under at least partially shaded conditions, necessitating the need for determining optimal light conditions for testing white oak families.
“This research will provide needed information to tree improvement programs,” principal investigator Dana Nelson said. “Specifically, should they test white oak families in traditional full-sun (open field conditions) for performance in gap plantings, or do they need to test families under lower or variable light conditions? The outcome of this research will begin to answer this question and lead to refinements in the progeny testing strategies developed by tree breeders.”
White oak acorns collected from several mother trees in three areas of the Central Hardwoods Region (central Missouri, Indiana and eastern Kentucky) are being grown into seedlings for testing the families’ responses to light conditions ranging from full sun to 80% shade. Survival, growth, biomass and photosynthesis rates will be measured to determine the performance of each family and test for family/ light level interactions.
Significant interactions will suggest the need for testing families under conditions most like the intended regeneration light environment. Alternatively, lack of interactions will simplify future testing protocols, as a single light level will provide appropriate performance data for any anticipated light condition.
The acorns for this research were collected in fall 2024, with the shade treatments being planned for the 2025 and possibly the 2026 growing seasons. Additional families may be collected and entered into testing in fall 2026, depending on funding and acorn mast availability.
Goals:
This project aims to examine the growth responses of white oak seedlings under varying shade conditions using 0%, 20%, 50% and 80% shade netting, simulating varying shade levels in forest gaps.
White oaks will represent about 20 open-pollinated families collected from across a west-to-east (wet-to-dry) gradient of the Central Hardwood Region. Survival, height growth, tree biomass and photosynthetic rates will be quantified across seed sources, families and shade treatments.
The findings of this study will result in a better understanding of the genetic contribution to shade tolerance and how variation in the physiological response to shade translates to gap silviculture.
Methods:
Objective 1 of this research is to develop a light response curve for white oak. Researchers will evaluate how seedlings from 20 half-sib families representing three seed sources (central Missouri, Indiana and eastern Kentucky) respond to different levels of light. Approximately 40 acorns per family were sown in 2024 with a goal of achieving 15 healthy seedlings per family in each shade treatment. Measurements of photosynthesis rates and above- and below-ground biomass will provide insight into genetic variation in shade tolerance and help refine recommendations for forest gap silviculture.
Objective 2 will evaluate half-sib family performance under high and low light conditions. Researchers will test the performance of the same 20 families from Objective 1 under high (full sun) and low-moderate (50% shade) light. They will evaluate genetic parameters such as heritability, genetic correlations and genotype-by-environment interactions for important seedling traits.
Germination (emergence), growth (height, diameter) and biomass will be measured over two growing seasons to assess family performance and refine breeding strategies.
Key Findings in 2024:
Researchers collected acorns from 20 families representing central Missouri, Indiana non-selected and elite (seed orchard source) and eastern Kentucky seed sources.
The acorns were sown into two studies; a third study is pending sowing once conditions permit at the Morgan County Tree Nursery in eastern Kentucky. The first two experiments were sown in containers at UK’s South Farm greenhouse facility due to excessive rain and snow. Field conditions permitting, researchers plan to sow a second experiment in the nursery for Objective 2.
Future Research:
Assuming researchers show that light conditions matter for selecting families, larger-scale validation trials will need to be established, further refining the approach. Second, validation of family performance in actual gap plantings will need to be tested. And finally, an efficient protocol will need to be developed and implemented as part of operational tree improvement programs.
Key Partners/Collaborators:
Primary partners: HTIRC, Kentucky Division of Forestry, University of Kentucky Departments of Forestry and Natural Resources and Horticulture, U.S. Forest Service Southern Research Station.
Secondary partners: White Oak Genetics and Tree Improvement Program (WOGTIP), the Daniel Boone National Forest and the University of Missouri School of Forest Resources.