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Sapwood water content of lodgepole pine Rothwell, Richard L.

Abstract

Breast height sapwood water content fluctuations of lodgepole pine (Pinus contorta var. latifolia Engelm) were studied with the objective of relating them to conducting xylem area, and to environmental and plant variables. Also gamma radiation attenuation was tested as a method for in situ sapwood water content measurement. Sapwood water content fluctuations and upward sap velocity indicated a conducting xylem area 3.25 cm wide from the cambium. For the trees studied, such an area would occupy between 60-80% of total cross-sectional stem area. Multiple regression analyses indicated significant correlation coefficients of 0.36-0.85 between sapwood water content and environmental and plant variables. The most important group of variables included soil water content, heat pulse velocity, and precipitation, and these gave a multiple correlation coefficient of 0.85, and a standard error of estimate of 4% o.d.w. with a sample size of 27. Laboratory tests indicated that gamma radiation attenuation is a feasible method for wood water content measurement. In the laboratory no significant differences were observed between gamma and gravimetric measurements of wood water content for prepared samples. In the field, in situ measurements showed similar monthly and diurnal fluctuations for gamma and gravimetric estimates. However, gamma water contents were significantly higher than gravimetric, with a mean difference of 17% o.d.w. The higher gamma values were attributed to the inclusion of bark moisture content and measurement of a larger volume of wood.

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