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SAPWOOD WATER CONTENT IS INSENSITIVE TO CHANGES IN SOIL MOISTURE
Citation:
Beedlow, P A., D T. Tingey, AND R B. McKane. SAPWOOD WATER CONTENT IS INSENSITIVE TO CHANGES IN SOIL MOISTURE. Presented at 4th North American Forest Ecology Workshop, Corvallis, OR, June 16-20, 2003.
Description:
Changes in sapwood water content of large Douglas fir (Pseudotsuga menziesii) trees were measured throughout the year at two sites: a low elevation (600-m) site where precipitation occurs primarily as rain, and a high elevation (1200-m) site that receives significant snowfall. Both sites are located on ridge crests where soil moisture content is dependent on precipitation rather than lateral movement. An increment borer was used to collect sample cores at breast height (1.37 m) at approximately monthly intervals. Cores were immediately separated into bark, phloem, sapwood and heartwood components and placed into separate tared, sealed glass vials. Relative water content of each component was calculated from measured fresh and oven-dry weights and fresh sample volume. During the year, volumetric soil water content decreased from field capacity in the late spring to ~5-10% in early fall before rewetting. Despite this large change in soil water content, sapwood relative water content remained high (70-80%) and was essentially constant (changed less than 10% over the same time period). In contrast to sapwood relative water content, the bole diameter (measured via a band dendrometer) decreased when soil water content was lowest. At these sites, trees apparently regulate water loss to maintain sapwood water content at relatively high values despite large changes in soil water content. This response is consistent with theories of cavitation avoidance in water-stressed plants.