Biologically effective UV-B exposures of an oak-hickory forest understory during leaf-out

Canopy transmittance during leaf-out was not dependent on cloud cover. Greater penetration of solar radiation in longer wavelengths within the UV was probably a result of scattering of direct beam radiation off tree bark in the canopy. The effective canopy transmittance from 15 March through the canopy leaf-out was 47%. For an expected period of UV exposure for the herbaceous layer of 15 March through 15 May, the tree seedlings and herbaceous plants received 41 kJ m−2 of biologically effective UV-B radiation. It is projected that the herbaceous layer vegetation will receive approximately 27% more UVBBE radiation on clear days with a decreased stratospheric ozone of 20 DU and approximately 3% more UVBBE radiation with increased temperatures causing leaf-out to begin 10 days earlier than 2004. More research is needed to understand the potential interactions of these and other climate change components on the deciduous forest.