Methods
Twice annually, preferably in January and July, a photograph of each of the four plots was taken from gridpoint G4. G4 is at a corner of each plot and the photos were taken with the camera directed toward gridpoint F3 for Plot A, H3 for Plot B, F5 for Plot C, and H5 for Plot E. In 2007-date, pictures were made with a Canon EOS 20D single-lens-reflex, 8 megapixel digital camera. The camera was mounted on a SLIK Universal U-210 tripod, which allowed adjusting all aspects of the camera position. Camera height was adjusted so that the viewfinder eyepiece was at eyelevel (about 5 ft. above the ground). To make sure the camera was still when each picture was taken, the camera's self-timer was used to insert a delay of 10 seconds between the press of the shutter button and the exposure. The lens opening was kept at f/16 by using the aperture-priority, automatic-exposure mode. Auto focusing was set manually to the middle focusing point. This point was used to adjust the angle of elevation of each shot. For plots A, C, and D the focusing point was aimed at the top flag on the 9-9.5 ft pole at gridpoints F3, F5, and H5. For plot B the focusing point was adjusted upward to compensate for gridpoint H3 being well below the level of Plot D. Image quality was set at "Large Fine," which records an 8.2 million pixel image in a low-compression jpeg file. ISO light-sensitivity value was generally set at 100 or 200 depending on the amount of light. In 2007, a 50mm, auto-focus, Canon lens was used. In 2008-date, a 35mm, auto-focus, Canon lens was used. (On a digital camera a 50mm lens is equivalent to a modest telephoto lens on a film camera. The 35mm lens was purchased to yield a field of view approximately equivalent to a 50mm lens on a film camera.)