© 2000 Heron Publishing—Victoria, Canada
Coarse root elongation rate estimates for interior Douglas-fir
Andrew Richardson (1)
1. Yale University, School of Forestry and Environmental Studies, 370 Prospect St., New Haven, CT 06511, USA (andrew.richardson@yale.edu) / Received July 6, 1999
Summary
Accurate estimates of root growth rates are important for root system modeling, and the spread of root systems may be an important
determinant of belowground site occupancy. Estimating root system growth rates is complicated because missing, discontinuous,
and false annual growth rings make root cross sections difficult to age. These irregularities can occur even in roots of dominant
conifers with rare or absent stem growth ring abnormalities. Incomplete rings were noted in the root growth rings of nine
co-dominant interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) trees. Coarse root (> 1.0-cm diameter) elongation rates were estimated by fitting a geometric mean regression
line to ring count and lateral distance data. In all nine roots examined, the geometric mean regression slope was well within
the range of the 95% confidence interval for the ordinary least squares regression of lateral distance versus age, suggesting
that measurement error may have been negligible. Coarse root elongation rates (which ranged from 2.8 to 15.3 cm year–1 and averaged 7.4 cm year–1) in the interior Douglas-fir trees studied were much lower than those reported by others. This discrepancy may be a result
of limited soil water availability, soil heterogeneity (both soil water content and soil texture were highly variable across
short distances) and fragmentation of belowground growing space.
Keywords:
annual growth rings, geometric mean regression, incomplete rings, measurement error, Pseudotsuga menziesii, root growth.
