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Rates and Patterns of Water Uptake in a Douglas‐Fir Forest
Author(s) -
Nnyamah Joe U.,
Black T. A.
Publication year - 1977
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1977.03615995004100050033x
Subject(s) - evapotranspiration , environmental science , soil water , water balance , water content , hydrology (agriculture) , neutron probe , douglas fir , water potential , dns root zone , soil science , geology , botany , ecology , biology , neutron cross section , physics , geotechnical engineering , quantum mechanics , neutron temperature , neutron
The forest water balance was studied in a thinned (840 stems/ha) and an unthinned (1,840 stems/ha) Douglas‐fir forest [ Pseudotsuga menziesii (Mirb.) Franco] during two consecutive summers. Soil water content was measured with the neutron meter. Soil water potential was measured with tensiometers and dew‐point hygrometers over a range of 0 to −15 bars. These data were used to compute water extraction rates and patterns for the root zone over a four‐week drying period. The results showed a gradual downward shift of the zone of maximum root water uptake as the soil dried. The fully developed root system of Douglas fir showed less hydrotropic response than the developing root systems of annuals reported in the literature. There was good correlation between water uptake rate and rooting density. During the drying period, water flux into the bottom of the root zone, estimated by the use of Darcy's law, increased from 8 to 15% of the evapotranspiration at the thinned site and from 2 to 8% at the unthinned site. Soil profile water depletion corrected for flux out of or into the bottom of the root zone agreed well with evapotranspiration computed from micrometeorological energy balance data. Water with‐drawal from trunk storage accounted for only 2% of the total evapotranspiration over the four‐week drying period.