Should we use the float test to quantify acorn viability?: Improving the Float Test

The float test is the most widely used method to discriminate between viable and nonviable acorns. It provides an objective, simple, rapid, and inexpensive test to inform experiments and management strategies dependent on quantification of viable acorns. However, the accuracy of the float-test method is understudied. To test the accuracy of the float-test method, during autumn of 2013 we collected 300 acorns from white oak (Quercus alba), native to our study area within the city limits of Raleigh, North Carolina, USA, and sawtooth oak (Q. acutissima), not native to the study area. An untrained observer visually inspected acorns (visual test) to assign viability subjectively and then float-tested the respective acorn. After conducting visual and float tests, we planted the acorns in a test plot protected from predation. In the test plots, 56% of white oak acorns and 60% of sawtooth acorns germinated. Both the float test and visual methods accurately predicted viability in both oak species. However, the visual test (white R-2=0.83, sawtooth R-2=0.85) explained more variation in observed germination than the float test explained (white R-2=0.65, sawtooth R-2=0.70). Our data indicate the float test, though objective, is less accurate than an untrained observer at predicting the viability of acorns. We tested the potential for the methods to be paired to further improve prediction accuracy and determined the float test provided no additional information to visual inspections. When dissecting or germinating acorns is not possible, our data indicate that visually inspecting acorns is better than float-testing to determine viability. (c) 2017 The Wildlife Society.