Measurement of Solar Radiation Under Forest Canopies by Use of Chlorophyll Extracts

Abstract

The purpose of this study was to determine the reproducibility of measurements of solar radiation by the degradation of petroleum ether-chlorophyll extracts under oak and pine canopies at 100 evenly spaced points over 5 days. The use of extracts permitted a large number of simultaneous measurements of solar radiation at different heights up to 4-5 m above the ground. Chlorophyll extracts were judged more practical than solarimeters and pyranometers in giving inexpensive simultaneous measurements of light sums over a day in natural vegetation, but less effective in giving reproducible results. On each day, there was a linear relationship over time between changes in absorbance at 660 nm of the chlorophyll extracts and cumulative light sums in g cal/cm2 as measured by an Eppley pyrheliometer. Transmittance of the oak stand was 590% less than that of the pine stand; the oak stand's basal area was 150% greater. Daily average light sums in the pine stand were 33-509 % greater than those in the oak stand, and seedlings, mostly of hardwoods, were twice as dense in the pine stand as in the oak stand. The average range of daily light sums in the pine stand was 2 6 times greater. On three of the five days, light sums at points under pine tree canopies alone were significantly higher than those at points under other combinations of tree, sapling, and large seedling canopies. All species of seedlings showed random distribution in relation to light measurements, except red maple in the pine stand.