Root structure of western hemlock and western redcedar in single- and mixed-species stands

Abstract

Root structure of western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata Donn. ex D. Don) was studied in single- and mixed-species stands of hemlock and western redcedar in Capilano River watershed, University of British Columbia Malcolm Knapp Research Forest, and Mission, southern coastal British Columbia. We sampled roots using a tree-to-tree trench excavation method. In each stand, roots were collected from three randomly located trenches using a 20 × 20 × 10 cm template along (i) a soil depth gradient: forest floor (FF), 0- to 10-cm (MS1), and 10- to 20-cm mineral soil layers (MS2) and (ii) a lateral soil gradient (tree-to-tree trenches). Hemlock–redcedar mixtures had the greatest root density, followed by pure hemlock and redcedar stands. In both pure hemlock stands and hemlock-redcedar mixtures, root density of all size classes (fine, medium, and coarse roots) decreased with increasing soil depth, whereas that of pure redcedar stands peaked at the MS1 layer. Density of roots along the lateral gradient varied among stand types and root size classes. Density of coarse roots was higher towards tree stems, while that of fine and medium roots was more evenly distributed. In the forest floor of the hemlock–redcedar mixtures, root density of all sizes except that of redcedar coarse roots was not related to the distance to stems, but fine root density of hemlock was greater than that of redcedar. The highest root density in the hemlock–redcedar mixtures may indicate the presence of overlapping and intermingling roots and intense competition for available soil resources.

Adaptation to exploit nitrate in surface soils predisposes yellow-cedar to climate-induced decline while enhancing the survival of western redcedar: A new hypothesis

“…There is some evidence that redcedar is not uniformly shallow rooted (Bennett et al, 2002). Fine-root biomass of redcedar was located in both surface organic and deeper mineral horizons compared to western hemlock and salal (Gaultheria shallon Pursh) in mixed stands (Bennett et al, 2002) and peaked in the upper most mineral soil in pure cedar stands (Wang et al, 2002). Redcedar foliar Ca concentrations are less than those for co-existing yellowcedar (Fig.…”

Do limited cold tolerance and shallow depth of roots contribute to yellow-cedar decline?

“…There is evidence that western redcedar is not uniformly shallow rooted. Bennett et al (2002) reported that western redcedar fine root biomass was located in both surface soils and deeper mineral horizons in mixed conifer stands, and Wang et al (2002) found that redcedar root mass was concentrated in the upper most mineral soil horizon in pure cedar stands. Despite important differences in the cold tolerance and depth of roots that seem to place yellow-cedar at a uniquely elevated risk of injury, the cold tolerance and rooting depths of yellow-cedar and western redcedar are similar enough that one might expect western redcedar to show some, though more limited, vulnerability to root freezing injury.…”

Windthrow and recruitment of large woody debris in riparian stands

“…Forest policies require retention of treed buffer strips along relatively small stream channels if they have fish populations (Wang et al, 2002). These unharvested strips are intended to minimize impacts of forest management activities on water quality, aquatic ecosystems and riparian community diversity (BCMOF, 1995).…”