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

2002 ◽  
Vol 32 (6) ◽  
pp. 997-1004 ◽  
Author(s):  
X L Wang ◽  
K Klinka ◽  
H Y.H Chen ◽  
L de Montigny
Keyword(s):  
British Columbia ◽  
Forest Floor ◽  
Soil Depth ◽  
Root Density ◽  
Western Hemlock ◽  
Root Structure ◽  
Mixed Species ◽  
Coarse Roots ◽  
Western Redcedar ◽  
Size Classes

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.

Overturning resistance of western redcedar and western hemlock in mixed-species stands in coastal British Columbia

2007 ◽  
Vol 37 (5) ◽  
pp. 931-939 ◽  
Author(s):  
Kenneth E. Byrne ◽  
Stephen J. Mitchell
Keyword(s):  
British Columbia ◽  
Tsuga Heterophylla ◽  
Western Hemlock ◽  
Thuja Plicata ◽  
Specific Information ◽  
Mixed Species ◽  
Stem Form ◽  
Western Redcedar ◽  
Applied Forces ◽  
Coastal British Columbia

Specific information about the applied forces that cause trees to fail is required to validate mechanistic models of windthrow in different forest types. Static tree-pulling tests were conducted to examine the overturning resistance of western redcedar ( Thuja plicata Donn ex D. Don) and western hemlock ( Tsuga heterophylla (Raf.) Sarg.) in a mixed species second-growth stand in coastal British Columbia. Although widely used, tree-pulling techniques are not standardized. Data from three inclinometers were used to estimate stem deflection, which was found to increase with tree slenderness. Differing methods of fitting stem curvature had a small effect on estimates of self-loading at failure. The distance of the pivot point from the centre of the stem base increased with tree diameter. Accounting for the correct self-loading at failure produced a small difference in the overall turning moment regressions but did not improve the fit of these regressions. However, this difference increased with tree size and warrants consideration in future tree-pulling tests with large or plate-rooted trees. The stem mass – overturning resistance relationship had the best fit and was not significantly different for these species in spite of their differences in wood density and stem form.

scholarly journals The potential of mixing timber assets to financially offset negative effects of deer browsing on western redcedar

2015 ◽  
Vol 91 (04) ◽  
pp. 436-443 ◽  
Author(s):  
Verena C. Griess ◽  
Rajat Panwar ◽  
Julie Cool
Keyword(s):  
Western Hemlock ◽  
Investment Risk ◽  
Financial Indicators ◽  
Negative Effects ◽  
Mixed Species ◽  
Financial Return ◽  
Protective Measures ◽  
Western Redcedar ◽  
Risk Return ◽  
Mixed Species Forest

Western redcedar (WRC) is a highly desirable species in British Columbia's Coastal Western Hemlock zone, both from a management and a conservation perspective. However, it is also highly palatable for ungulates. Existing countermeasures against browsing all have high costs and imperfect results in common. We used the portfolio method to display how diversification can help to lower investment risk. Using risk-return ratios of a WRC and Douglas-fir (DF), we derived species portfolios that yield maximum financial return per unit of risk. Financial indicators were calculated based on Monte Carlo simulations, which consider timber price fluctuation and browsing risk. Results show how economic risks of a forest investment could be reduced by creating a species portfolio. The optimum portfolio leading to most beneficial risk-return combination is 75% WRC and 25% DF if browsing is lowered using protective measures that double planting costs; and 30% WRC and 70% DF if no protective measures are applied. Accordingly, the most desirable risk-return combination is that of a mixed-species forest, whereas the 2 species don't have to be grown in intimate mixtures. Our research sketches a path forward that can help to ensure WRC will remain an important asset in BC's timber portfolio.

Tree-size diversity between single- and mixed-species stands in three forest types in western Canada

2005 ◽  
Vol 35 (3) ◽  
pp. 593-601 ◽  
Author(s):  
Pàl Varga ◽  
Han YH Chen ◽  
Karel Klinka
Keyword(s):  
Lodgepole Pine ◽  
Structural Diversity ◽  
Single Species ◽  
Tree Size ◽  
Western Hemlock ◽  
Stand Age ◽  
Western Canada ◽  
Mixed Species ◽  
Western Redcedar ◽  
Size Diversity

Mixed-species stands are hypothesized to be more structurally diverse because of inherent differences in growth rates between tree species. We investigated three combinations of even-aged, single- and mixed-species coniferous stands in western Canada: (i) shade-tolerant western hemlock (Tsuga heterophylla (Raf.) Sarg.) and western redcedar (Thuja plicata (Donn ex D. Don) Spach), (ii) shade-intolerant lodgepole pine (Pinus contorta Dougl. ex Loud.) and western larch (Larix occidentalis Nutt.), and (iii) shade-intolerant lodgepole pine and shade-tolerant black spruce (Picea mariana (Mill.) BSP). We quantified stand structural diversity based on tree diameter and height by using Shannon's index and the coefficient of variation. Regression analysis was applied to examine the relationships between structural diversity, species composition, and stand age. Mixed-species stands of western hemlock and western redcedar had similar structural diversity to their respective single-species stands. Pine–larch and pine–spruce mixed-species stands had higher tree-size diversity than their respective single-species stands. Stand age was a significant factor for tree-size diversity, but its effect changed in different ways depending on the type of mixtures and index used to measure diversity.

scholarly journals Western redcedar population dynamics in old-growth forests: Contrasting ecological paradigms using tree rings

2003 ◽  
Vol 79 (3) ◽  
pp. 517-530 ◽  
Author(s):  
Lori D Daniels
Keyword(s):  
British Columbia ◽  
Population Dynamics ◽  
Western Hemlock ◽  
Thuja Plicata ◽  
Silver Fir ◽  
Old Growth ◽  
Western Redcedar ◽  
Old Growth Forests ◽  
Gap Phase ◽  
Coastal British Columbia

In coastal British Columbia, late-successional forests dominated by western redcedar (Thuja plicata Donn ex D. Don) are structurally complex, with deep multi-layered canopies, large trees that are > 250 years old, and abundant coarse woody debris (CWD). These forests are presumed to be "old-growth" forests in which fine-scale gaps are the dominant disturbance regime, accounting for their structural diversity. In this study, I have used tree-ring analyses to investigate western redcedar regeneration dynamics in these old-growth forests. Western redcedar dominates canopies of many stands, but is rare in the understorey although it tolerates shade. The traditional interpretation is that western redcedar depends on catastrophic disturbance to regenerate and that it is replaced through succession by western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Pacific silver fir (Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes), which are abundant in the understorey. Dominant trees are perceived to represent an even-aged, post-disturbance cohort and the lack of regeneration indicates a population decline in the absence of catastrophic disturbances. In this paper, I investigate four assumptions underlying this interpretation: (1) Tree size indicates age. (2) Populations establish as even-aged, post-disturbance cohorts. (3) Abundant CWD represents recent mortality. (4) Regeneration is insufficient to maintain canopy dominance. Using tree-ring evidence, I show that population dynamics of western redcedar are a combination of gap-phase establishment and a continuous mode of recruitment from the sub-canopy to the canopy. Specifically, size is a poor surrogate for tree age. Age distributions from 15 sites revealed uneven-aged populations, rather than single post-disturbance cohorts. Both logs and snags of western redcedar may persist more than 270 years; they do not represent recent mortality that is disproportionate to the number of live western redcedar in canopy. The regeneration niches of western redcedar and western hemlock overlap. For both species, gap-phase disturbances result in substrate suitable for successful seedling establishment. Preliminary results from dendroecological analysis of radial growth rates of trees in the subcanopy and canopy strata suggest that western hemlock and Pacific silver fir depend on gaps to recruit to the upper canopy, but recruitment of western redcedar may be independent of canopy gaps. I propose that differences in mode of recruitment to the canopy may explain the differences in population structures between western redcedar, western hemlock, and Pacific silver fir in the old-growth forest. These results provide an ecological precedent for use of a range of silvicultural systems, including clearcuts through single-tree harvesting and protection forests, when managing western redcedar in coastal British Columbia. Key words: Coastal British Columbia, disturbance regimes, regeneration dynamics, Thuja plicata, variable retention silviculture

Vertical fine root distributions of western redcedar, western hemlock, and salal in old-growth cedar–hemlock forests on northern Vancouver Island

2002 ◽  
Vol 32 (7) ◽  
pp. 1208-1216 ◽  
Author(s):  
Jennifer N Bennett ◽  
Ben Andrew ◽  
Cindy E Prescott
Keyword(s):  
Forest Floor ◽  
Fine Roots ◽  
Fine Root ◽  
Mineral Soil ◽  
Vancouver Island ◽  
Western Hemlock ◽  
Old Growth ◽  
Total N ◽  
Western Redcedar ◽  
Vertical Distributions

The vertical distributions of fine roots of western hemlock (Tsuga heterophylla (Raf.) Sarg.) western redcedar (Thuja plicata Donn ex D. Don), and salal (Gaultheria shallon Pursh) were characterized in old-growth cedar–hemlock forests on northern Vancouver Island. Total biomasses of cedar, hemlock, and salal roots in the forest floor and upper mineral soil were 817, 620, and 187 g·m–2, respectively. Hemlock and salal fine roots were concentrated in the upper forest floor, while cedar fine roots were evenly distributed through the profile. Salal and hemlock fine root densities (g·m–3) in the forest floor and mineral soil were positively correlated, as were salal and cedar root biomass distributions (g·m–2). Only salal and hemlock root densities were significantly correlated with N concentrations. Hemlock root densities were negatively correlated with total N, and salal root densities were negatively correlated with total N and soluble organic N. Based on fine root densities, hemlock and salal probably compete for resources in the upper forest floor, whereas cedar accesses resources in the lower organic and mineral soil horizons. The differences in the vertical distributions of cedar, hemlock, and salal fine roots may partly explain the co-occurrence and different productivities of the three species in cedar-hemlock forests.

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