© 1998 Heron Publishing—Victoria, Canada
Hydraulic properties of Douglas-fir (Pseudotsuga menziesii) branches and branch halves with reference to compression wood
Rachel Spicer (1) and Barbara L. Gartner (1)
1. Forest Research Laboratory, Oregon State University, Corvallis, OR 97331, USA / Received January 14, 1998
Summary
Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) branch segments were used to test the hypothesis that compression wood reduces xylem transport efficiency.
Whole 3-year-old segments were first measured for specific conductivity (ks, m2 s–1 MPa–1), then split lengthwise into upper and lower halves, the latter containing all or most of the compression wood in the segment.
Halves were then remeasured for ks using a new technique that prevents leakage of permeating fluid during measurements. Lower branch halves had significantly
lower ks than upper halves (6.4 ± 0.3 versus 9.3 ± 0.3 m2 s–1 MPa–1 × 10–4, respectively; n = 36), and despite their larger size, significantly lower hydraulic conductivity (kh, m4 s–1 MPa–1) than upper halves. Lower branch halves had higher specific gravity (0.51 ± 0.01 versus 0.45 ± 0.01; n = 36), lower water content (123 ± 2% versus 155 ± 3%; n = 36), and larger proportions of volume occupied by both cell wall and air than upper halves. Lower halves had more tracheids
per annual ring than upper halves (73 ± 3 versus 63 ± 2 per radial transect, respectively; n = 36), but tracheids were shorter and had narrower lumens than those of upper branch halves. Differences in hydraulic properties
between upper and lower halves suggest that compression wood does reduce xylem transport efficiency. In contrast, the amount
of compression wood in each sample did not explain any variation in whole unsplit sample hydraulic properties.
Keywords:
compression wood, hydraulic conductivity, leaf-specific conductivity, specific conductivity.
