Dusan Rozenbergar, Uros Kolar, Matjaz Čater, Jurij Diaci
Comparison of four methods for estimating relative solar radiation in managed and old-growth silver fir-beech forest
Dendrobiology 2011, vol. 65: 73-82
Abstract: Methods based on the principle of hemispherical canopy projection, including hemispherical photography (digital and film), sensors like LAI 2000 (zenith cutoff anle 74,1°) and stable horizontoscope, represent less accurate, yet significantly less expensive and time-consuming techniques for radiation measurements compared to long-term measurement with a network of photosynthetically active radiation (PAR) sensors. With measurements taken at a single point in time they can provide reliable estimates of relative diffuse and direct solar radiation and can also be used to estimate the light climate in different times of the year. The four above mentioned methods for solar radiation estimation were applied at the same points in gaps and under adjacent canopies in unevenaged, mixed Dinaric fir-beech and pure beech montane forests. Locations covered a range of radiation and stand structure conditions. Data analyses showed good reliability of all four methods over the whole range (2–80%) of radiation conditions. The most comparable results come from LAI 2000 and film hemispherical photography (all R > 0.90). Digital hemispherical photography is an accurate and reliable (R = 0.89) replacement for film hemispherical photography, but the higher values estimated for direct radiation should be taken into account. Compared to the other three methods, the stable horizontoscope gives less accurate results, especially under canopies with poorly defined gaps. Our study showed that all four methods tested are suitable for estimating the solar radiation climate in gaps and stands with heterogeneous vertical structures, and have potential value as a tool in decision making when practicing silviculture.
Additional key words: light conditions, small-scale forestry, hemispherical photography