The float test as a method to determine acorn viability and activity of insect herbivores during masting and non-masting years in Quercus garryana

Oak habitats are declining globally, creating concern for the biodiversity they support. The acorn float test is a widely relied-upon technique for oak conservationists to identify damaged acorns due to its simplicity and speed. However, the biological basis and accuracy of the float test are not well studied. This study used acorns from Oregon white oaks (Quercus garryana Douglas ex Hook.) collected in both masting (2019, 2023) and non-masting (2021) years to examine the biological basis and accuracy of the test for application in oak habitat conservation efforts. Acorns were float tested, examined for damage and presence of insects, and germinated to determine whether the test could detect insect damage and acorn viability. The test accurately predicted 84–89 % of germination in both masting and non-masting years. External and internal examinations for damage yielded significant associations between damage and float test results, damage and acorn density, and insect infestation and float test results. Our data indicate that the float test does have a biological basis in insect-caused damage and is a legitimate method to rely on for quickly determining acorn viability. This technique holds practical applications for ecologists and managers in estimating viable acorn crop size, insect predation rates, and wildlife food availability in oak ecosystems.