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Forests in the northern Sierra Nevada of California, USA, store large amounts of carbon in different patterns

Mattson, Kim G., Zhang, Jianwei
Ecosphere 2019 v.10 no.6 pp. e02778
altitude, carbon, carbon sequestration, carbon sinks, coniferous forests, conifers, fires, forest litter, mountains, old-growth forests, site preparation, soil carbon, soil depth, California
To better understand forest carbon (C) storage patterns, C budgets were constructed and contrasted among four stands of different vegetation, elevation, and disturbance histories from the northern Sierra Nevada of California, USA. The True‐fir stand, considered to be undisturbed and at a higher elevation (1820 m), stored substantially more C than the three stands at lower elevation (1360–1430 m) and that had sustained various levels of disturbance. The Mixed Conifer stand was minimally disturbed by thinning 27 yr ago. The Oak stand was moderately disturbed by two fires in the past 17 yr. The Pine Plantation stand was considered the most disturbed having been cleared and subjected to site preparation and windrowing 50 yr ago and thinned again 17 yr ago. Total C mass to a 30 cm soil depth (Mg C/ha) was True‐fir 531, Mixed Conifer 317, Oak 310, and Pine Plantation 253. Adding in soil C to 1 m depth increased total C mass to 595, 349, 404, and 345, respectively. True‐fir had significantly larger C mass than the other three stands in nearly all pools measured. The three low‐elevation stands, while similar to each other in total C, stored C differently in patterns that reflected their disturbance histories. Oak and Pine Plantation were very similar in detrital C stores, whereas Mixed Conifer had at least twice the C mass in both the forest floor and woody debris pools. Mixed Conifer had higher concentrations of soil C but had very low soil C mass due to considerably lower fine‐soil bulk densities and higher rock contents. C pools in the forest floor and soil showed observable patterns over distances of 10–100 m that paralleled the patterns of C in the live vegetation. Total C in True‐fir was equal to the large masses of old‐growth conifer forests of the U.S. Pacific Northwest and likely represents a high‐equilibrium level of C storage for forests of this region. The three low‐elevation stands represent typical forests in various states of recovery from disturbance that are in C accumulating stages.