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Thinning plays a major role in forest soil carbon cycling. However, the mechanisms governing soil C fluxes, i.e., C input through litterfall and fine root (FR) production and C output through soil heterotrophic respiration (R h), remain unclear. To fill this gap, we quantified the C fluxes in the topsoil layer (0–20 cm) by measuring litterfall, FR production and total soil respiration (R s) (R a (autotrophic respiration) and R h) at three thinning intensities (control; low-intensity thinning: extraction of 30% of individual trees; high-intensity thinning (HIT): extraction of 70% of individual trees) in a 26-year-old Chinese fir plantation in southern China. In the control plots, the total C input (110 g C m−2 year−1) via litterfall (59 g C m−2 year−1) and FR production (51 g C m−2 year−1) was much lower than the C output via R h (518 g C m−2 year−1). This finding demonstrated that the soil is a C source (407 g C m−2 year−1). Furthermore, the C source increased with increasing thinning intensity, particularly under HIT, due to the decreased litterfall return and increased soil CO 2 emissions through R h ; this increase occurred despite the increased C input from FR production. In addition, the C output via R s significantly increased by 42% under HIT due to the stimulation of R a and R h. Consequently, thinning reduced the topsoil C pool by 7–8%. Redundancy analysis indicated that the soil C fluxes following thinning were driven by increased FR mortality, understory plant biomass and diversity, and microbial biomass carbon (MBC). Overall, our results indicate that heavy thinning increases soil C loss by increasing soil CO 2 emissions and decreasing litterfall return, even under substantially increased FR production. This finding suggests that thinning practices should consider the trade-off between soil C inputs and outputs to reduce the impact of thinning on forest soil carbon sequestration. Unlabelled Image • Thinning increases soil CO 2 emission by increasing auto- and heterotrophic respiration. • Fine root production significantly increased with increasing thinning intensity. • Litterfall production decreased with increasing thinning intensity. • High thinning intensity increases soil C loss and causes a decrease in the topsoil C pool. [ABSTRACT FROM AUTHOR]

Analyzes the structural pattern of roots in pure hemlock, pure redcedar and mixed-stands in British Columbia. Variations in the density of roots along the lateral gradient among stand types and root size classes; Potential of some forest sites to support mixed-species stands; Use of the vertical and horizontal distributions of root density in describing the root structural pattern.

Much of Canada's terrestrial biodiversity is supported by boreal forests. Natural resource development in boreal forests poses risks to this biodiversity. This paper reviews the scientific literature to assess the effects of natural resource development on terrestrial biodiversity in Canadian boreal forests. We address four questions: (1) To what extent have Canadian boreal forests changed due to natural resource development? (2) How has biodiversity responded to these changes? (3) Will the biodiversity of second-growth forests converge with that of primary boreal forests? (4) Are we losing species from boreal forests? We focus on trees, understory plants, insects, fungi, selected mammals, and songbirds because these groups have been most studied. We review more than 600 studies and found that changes in community composition are prevalent in response to large-scale conversion of forest types, changes in stand structures and age distributions, and altered landscape structure resulting from forest management and habitat loss associated with other developments such as oil and gas, hydroelectric, and mining. The southern boreal forest has been more highly impacted than the north due to more extensive forest management and the cumulative effects of multiple forms of development. There is abundant evidence that most species are not in danger of being extirpated from the boreal forest due to these anthropogenic changes. A few species, including woodland caribou ( Rangifer tarandus) and grizzly bear ( Ursus arctos), have, however, undergone long-term range contractions. Significant gaps in our ability to assess the effects of natural resource development on biodiversity in the boreal zone are the lack of long-term spatial and population data to monitor the impact of forest changes on ecosystems and species. [ABSTRACT FROM AUTHOR]