Forest cover as a solar camera: penumbral effects in plant canopies.
Presents photos taken during and after a solar eclipse in the University of Wisconsin Arboretum, on 10th July 1972, giving examples of solar images under a densely leaved branch of Acer saccharum and under a similar branch of Quercus velutina. Skyward photos of the areas of canopy producing images are given for comparison. The photos indicate that the finite angular size of the sun must be taken into account when modelling light under many plant canopies. Penumbral effects increase the effective sunlit area under plant canopies, reducing heat and water stress, and making available more photosynthetically active radiation.