Potential factors affecting the estimation of light availability using hemispherical photography in oak forest understories

With advances in computer technology, the use of hemispherical photography to assess forest canopy cover and understory light environments has become increasingly simplified. Numerous investigators have utilized this technique and employed Various protocols for photo acquisition. Several studies have noted the potential for subjective bias at various stages throughout the procedure. However, it remains unclear as to what influence either the identity of the investigator or camera height may have on the outcome of the analysis. Based on considerations derived from the literature, we evaluated two aspects of the hemispherical photography technique (camera height and experimenter error) to determine if decisions made at various points in the process contribute additional variance that may ultimately affect the interpretation or comparability of studies. The first consideration was camera height. A variety of camera heights have been used in the Literature. We found no significant differences (P > 0.50) in either estimates of percent open sky or available global radiation obtained at heights of either 30 or 150 cm in a mixed oak forest in southern Ohio. The second consideration was to assess how different experimenters analyzed the same set of hemispherical photographs. We found no significant differences among ten experimenter's measures of either percent open sky or available global radiation (P > 0.75). Based on our results, we feel more confident about the comparison of results from independent studies done by different investigators using a variety of photo acquisition protocols.