Oklahoma Deciduous Trees Differ in Chilling Enhancement of Budburst

In many tree species, winter chilling accelerates budburst in response to spring warmth. Global climate change has already accelerated budburst in deciduous tree species around the world. But as global climate change leads to milder winters, tree species also experience less chilling, which may actually delay spring budburst in some species. We hypothesized that reduced duration of winter chilling would delay spring budburst in sycamore (Platanus occidentalis) and pecan (Carya illinoinensis), but would not delay it in sweetgum (Liquidambar styraciflua). We tested this hypothesis experimentally by manipulating the number of weeks of chilling from 0 to 6 weeks. Lack of winter chilling did not delay budburst in sweetgum but did delay it in sycamore and pecan, in agreement with the hypothesis. Mild winters in Oklahoma may eventually favor the growth of sweetgums at the expense of sycamores and pecans