Factors limiting the early survivorship ofThuja plicataon northern Vancouver Island, British Columbia

Abstract

Western redcedar (Thuja plicata Donn ex D. Don), a late successional species on northern Vancouver Island, has a low seedling survival in mature hemlock (Tsuga heterophylla (Raf.) Sarg.) – amabilis fir (Abies amabilis (Dougl. ex Loud.) Dougl. ex J. Forbes) (HA) stands. Shade, moss competition, and substrate were tested as causes of low cedar establishment. Cedar seeds were sown on reference and local soils isolated from surrounding soil, on nonisolated local soil, and on forest floor with moss removed. Western hemlock, amabilis fir, and cedar seeded on forest floor acted as controls. Treatments were implemented in the HA interior and the HA–clearcut edge, with soil treatments also implemented in clearcuts. Germinants and very young seedlings of cedar have a low leaf area of needle-like primary foliage. Cedar development of secondary foliage (the scale foliage normally associated with this species) was correlated with greater vigour and growth. Secondary foliage developed in the rankings forest edge and clearcut > forest interior, and reference isolated soil > local isolated soil > nonisolated local soil. Seedling survival rankings were edge > interior, and amabilis fir > hemlock > cedar on soil and with moss removed > cedar on forest floor. Cedar and amabilis fir showed a smaller growth response to light than hemlock. The results indicate that cedar, normally considered a late successional species, needs disturbance for early seedling establishment and survival and thus has some characteristics of an early seral species.

The role of salal in forest regeneration problems in coastal British Columbia: problem or symptom?

“…A GIS study of northern Vancouver Island (Lavery and Albani 2000) demonstrated that abundance of cedar (hence CH sites) increases near swamps and bogs. Finally, it was found that cedar is actually not a late-successional species (Weber et al 2003). As such the dominance of cedar on CH sites may be related to these sites being wetter, and not to their being older and undisturbed, as previously thought.…”

Thuja plicata exclusion in ectomycorrhiza-dominated forests: testing the role of inoculum potential of arbuscular mycorrhizal fungi

“…The current landscape reflects this historical influence, with two distinct forest types occupying mesic sites: the hemlock-amabilis fir (HA) and the red cedar-hemlock (CH) forests (Lewis 1982). These forest types tend to have clear boundaries with little or no red cedar regeneration inside HA stands (Prescott and Weetman 1994;Weber et al 2003), but abundant hemlock regeneration in both stand types. Researchers have attempted to explain the exclusion of red cedar from HA stands based on shade tolerance (Weber et al 2003) and disturbance history (Prescott and Weetman 1994).…”

“…These forest types tend to have clear boundaries with little or no red cedar regeneration inside HA stands (Prescott and Weetman 1994;Weber et al 2003), but abundant hemlock regeneration in both stand types. Researchers have attempted to explain the exclusion of red cedar from HA stands based on shade tolerance (Weber et al 2003) and disturbance history (Prescott and Weetman 1994). Although the processes responsible for maintaining two distinctive forest types on apparently similar sites are not fully understood, initial research suggests that red cedar is excluded from HA stands by an interaction between low light and an incompatibility with the HA substrate (Weber et al 2003).…”

“…Researchers have attempted to explain the exclusion of red cedar from HA stands based on shade tolerance (Weber et al 2003) and disturbance history (Prescott and Weetman 1994). Although the processes responsible for maintaining two distinctive forest types on apparently similar sites are not fully understood, initial research suggests that red cedar is excluded from HA stands by an interaction between low light and an incompatibility with the HA substrate (Weber et al 2003). Measurements taken within intact CH and HA stands showed that soil chemical or physical properties were not substantially different among the two stands; mineral soils in CH stands had lower amounts of total N, but were similar with respect to organic C, C:N, available P, aluminium, and soil texture (De Montigny 1992;reviewed in Prescott and Weetman 1994).…”

Caractérisation de la régénération et des lits de germination des semis de Thuja occidentalis dans une vieille cédrière en Gaspésie, Québec, Canada /

“…dans les litières de feuilles pourrait être due à ses graines qui sont plus grosses que celles de Thuja sp. (Weber et al 2003).…”