Open Collections

Boyer, Christophe Richard

University of British Columbia

Western redcedar (Thuja plicata) is a major component of native forests on Haida Gwaii, British Columbia, Canada, and a culturally indispensable species to the Haida people. However, its natural regeneration is unachievable due to intensive grazing by the island’s overabundant population of Sitka black-tailed deer. Forest fertilization with nitrogen (N)-urea has been shown to increase the growth rate of western redcedar in the Pacific Northwest, thus increasing aboveground carbon (C) sequestration. N-urea fertilization can also increase soil C storage by increasing litter inputs and decreasing the rate of soil organic matter decomposition. Using a paired-tree design, we tested the effects of N-urea fertilization (200 kg N/ha⁻¹) on western redcedar growth, soil C, N, and microbial biomass C in the forest floor and mineral soil one year following fertilization at six replicate plots in 14–19-year-old stands on Graham Island, Haida Gwaii. We also measured soil greenhouse gas fluxes (CO₂, CH₄, N₂O) for a period of 56 days and one year after fertilization to evaluate the net benefit of fertilization on forest C storage. N-urea pellets were rapidly mineralized, releasing a flush of CO₂ in the first 4 days after application. A sustained increase in CO₂ emissions was observed for 2 months after application, but emissions reverted to levels of controls after 12 months. Fertilization had no effect on CH₄ or N₂O emissions. N-urea had no effect on the change in soil C or N in any soil fraction from 2021-2022 but did increase microbial biomass C in the mineral soil in 2 of the 6 plots. Fertilized trees showed a significant increase in biomass, and thus C sequestration, compared to controls in 2 of the 6 plots, which was greater than the amount of C lost via increased CO₂ emissions. Increases in the growth rate of tree height and diameter after one year suggest that western redcedar is responding to fertilization, which may lead to an increase in aboveground C storage. However, further studies will be crucial in determining the long-term response of western redcedar growth to N-urea fertilization and evaluating changes in soil C storage.

Text; Still Image; Dataset

2023-04-04

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/84137

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/