Effects of light regimes on the growth of cherrybark oak seedlings

Light regimes vary significantly within small forest openings, ranging from full sunlight to total shade, and they may affect the establishment and ea rly growth of oak seedlings. We designed modified shadehouses to simulate t he complex light conditions within forest openings and tested the effects o f daily photosynthetically active radiation (PAR), time of direct light exp osure, and the ratio of direct light to day length (direct-sunlight ratio) on height, diameter, and periodic growth of cherrybark oak (Quercus pagoda Raf,) seedlings through 2 yr, Five treatments representing the time of expo sure to direct sunlight were created: NO, NOON, MORNING,AFTERNOON, and FULL . Treatments significantly affected both the height and root-collar diamete r of seedlings, especially during the second growing season. The direct-sun light ratio was linearly related to periodic height growth for the NOON tr eatment but not related to height growth for the other treatments. However, periodic height growth in the AFTERNOON and FULL treatments was highly cor related to mean daily PAR. Maximum periodic height growth occurred at moder ate daily PAR levels, This research showed that light conditions for maximu m growth of cherrybarh oak seedlings change through time, with adequate sha ding being most favorable during the early stages of establishment.