Abstract This study examines basal area and three measures of canopy cover as predictors of both throughfall and light in an Arizona ponderosa pine forest. Overhead canopy cover, as measured with canopy photographs, accounted for the largest proportion of the variance in throughfall. The amountof open canopy in the east, south, and west directions (ESW canopy open), as measured with the spherical densiometer, accounted for the largest proportion of the variance in light penetration. Basal area was the poorest predictor of both throughfall and light penetration. Statistical fittingof each of these overstory attributes with understory cover or production should be an important aid in determining whether moisture, light, or root competition are limiting growth. Forest Sci. 24:550-553.