Partitioning of solar and net irradiance in mixed and chamise chaparral in southern California.

The partitioning of solar and net total irradiances between the canopy and soil was measured in mixed and chamise chaparral in southern California. The solar and net total irradiance absorbed within the canopy was a relatively constant fraction throughout the year. Variations can be explained by the changing path length of the solar beam as the solar altitude varies. The increased fraction of solar irradiance in winter, combined with the lower incident solar irradiance, produced a wide fluctuation of solar irradiance at the soil surface through the year. Although incoming solar irradiance on the bare soil surface is less on the north-facing slope than on the south-facing slope, the absorption of solar irradiance is greater in the canopy of the mixed chaparral on the north-facing slope because greater leaf and stem area has developed.