Carbon stocks in managed and unmanaged old-growth western redcedar and western hemlock stands of Canada’s inland temperate rainforests

In the inland temperate rainforests (ITRs) of east-central British Columbia (BC), there is a lack of baseline carbon (C) stocks information for managed and unmanaged stands of old-growth western redcedar and hemlock. To fill the knowledge gap, we estimated C stocks of live trees, snags, coarse woody debris and forest floor (excluding mineral soil) and evaluated impacts of harvesting on these C stocks. We also accounted for heart-rot in stem wood of live cedar and hemlock, and identified uncertainties in live-tree C stocks estimation for more accurate assessment of the C. Forests stands were selected from three previously established silvicultural systems trials that contrasted three levels of harvesting intensity (clear-cut (CC, 0% retention), group retention (GR, 30%), group selection (GS, 70%)), and uncut old-growth (100%). Despite a high incidence of heart-rot, live-tree and total forest (minus mineral soil) C stocks (348 ± 155 and 455 ± 156 Mg C ha−1, respectively) in uncut old-growth ITR stands were within the range of regional averages for old-growth forests in the Pacific Northwest (US) and coastal cedar and hemlocks forests of BC. Intensive harvesting (CC and GR) resulted in significant reductions in total forest C stocks (78% and 64%) relative to uncut old-growth stands. By contrast, total forest C stocks in stands where high-retention harvesting (GS) occurred were reduced by only 13% (not significant) relative to uncut old-growth stands. Analysis of uncertainty identified allometric equations to be the largest contributor to total uncertainty in live-tree C stocks, indicating the need to develop more robust equations to reduce the uncertainty for more accurate evaluation of harvesting impacts in old ITRs. Although heart-rot had no significant effects on forest C stocks in this study, we need a better scientific understanding of their contribution to live-tree C in this ecosystem. Nonetheless, these results underscore the importance of conserving C-rich old ITRs where possible and the potential for high-retention harvesting to maintain C stocks in this forest type.

► Forest carbon stocks with counting heart-rot were estimated in old-growth stands.
► We evaluated variable retention harvesting practices on forest carbon stocks.
► Old-growth stands represent important carbon reservoirs at the landscape level.
► High retention harvesting show the potential to mitigate the loss of carbon.
► Heart-rot had no significant effects on forest carbon stocks.