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This article in SSSAJ

  1. Vol. 45 No. 2, p. 423-427
    Received: Jan 17, 1980



Soil Moisture Use by Mixed Conifer Forest in a Summer-Dry Climate1

  1. Rodney J. Arkley2



Soil moisture regimes under a mixed conifer forest were measured at 16 sites in the San Bernardino Mountains of southern California for 5 years. Soil moisture depletion was found to occur to depths of 274 cm from coarse loamy and sandy-skeletal soils and underlying decomposed granite. Available soil moisture storage ranged from 128 mm, where hard rock was encountered at 121 cm, to as high as 496 mm, where the underlying material was grus (strongly decomposed granitic rock). Water use (soil moisture depletion plus rainfall) during the growing season appeared equal to available moisture storage during long dry summers but was considerably increased in years with summer precipitation. The evidence suggests that water use by the trees extends to depths considerably deeper than the 274 cm sampled. The productivity and indeed the survival of the forest trees in this summer-dry climate appear to depend on moisture stored at considerable depth in fractured or decomposed rock. Tree use of such deep moisture may explain the relatively small runoff measured in southern California streams compared with that estimated by the water balance method.

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