Authors: Kuehne, Christian¹; Kohnle, Ulrich²; Bauhus, Jürgen¹

Source: Canadian Journal of Forest Research, Volume 42, Number 10, October 2012 , pp. 1858-1864(7)

Publisher: NRC Research Press

Abstract:

Long regeneration periods, which result in two-layered or multilayered forest stands, are an important element of the close-to-nature forest management paradigm in central Europe. Such extended regeneration periods, however, may lead to undesirable development of advance regeneration, specifically in species such as Douglas-fir (<named-content content-type="species" xlink:type="simple">Pseudotsuga menziesii</named-content> (Mirb.) Franco) where root growth is strongly curtailed under competition. We hypothesized that root systems of naturally regenerated Douglas-fir that had grown under closed canopy for prolonged periods would be inhibited in their capacity to develop adequate structural root systems following release through removal of the canopy. Complete root systems of six approximately 25-year-old Douglas-fir that had grown for at least 12 years underneath a closed canopy before overstory removal were excavated using subterranean explosives. Root elongation, radial increment of primary lateral and vertical roots, and aboveground stem growth were investigated using retrospective analysis of growth rings. Structural roots of the previously suppressed Douglas-fir were capable of strongly responding to release from competition relative to growth prior to removal, but this response, particularly in the form of root elongation, was delayed. However, since the growth response of roots was not stronger than that above ground, an imbalanced root to shoot ratio, likely developed in trees when grown under the canopy, was not reverted. Generalizing interpretation of the derived findings of this study is limited because of the small sample size and the lack of freely grown control trees. Whether or not previously suppressed trees can develop the same physical stability as open-grown individuals therefore deserves further investigation.

Document Type: Research article

DOI: http://dx.doi.org/10.1139/x2012-123

Affiliations: 1: Faculty of Forest and Environmental Science, Institute of Silviculture, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany; Waldbau-Institut Universität Freiburg Tennenbacherstr. 4-79085 Freiburg im Breisgau, Germany. 2: Forest Research Institute of Baden-Wuerttemberg. Wonnhaldestr. 4-79100 Freiburg im Breisgau, Germany.

Publication date: 2012-10-10

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