Carbon stores and flux in Redwood National and State Parks

Madej, Mary Ann; van Mantgem, Phillip; Seney, Joseph

Globally, soil is the third largest store of carbon (after the atmosphere and ocean). Nevertheless, in old-growth redwood forest the high volume of living and dead biomass constitutes another large store of carbon. Here we examine carbon stores and flux in Redwood National and State Parks (RNSP) and include the effect of restoration activities on C emissions and storage. The first phase of our study was to quantify the store of soil organic carbon (SOC). SOC ranges from 11 Mg C ha-1 in floodplain soils to 468 Mg C ha-1 in moist redwood forest, with an average of 213 Mg C ha-1 , based on soil survey data from RNSP. Total SOC in RNSP is 12 x 106 Mg. The second step focused on estimating C stored in vegetation. Simple estimates of above-ground C stored in vegetation in RNSP ranged from <0.1 Mg C ha-1 in dune vegetation to 415 Mg C ha-1 in old-growth redwood forests. As more detailed studies of biomass in redwood forests are conducted, the estimate of living and dead biomass is likely to rise. The next step was to measure the export of organic carbon from terrestrial environments in watersheds via transport by rivers. We computed the flux of fine particulate organic carbon in Prairie Creek, based on collection and analysis of suspended sediment samples. Carbon content, determined through loss-on-ignition tests, was strongly correlated with turbidity, and continuous turbidity records from three gaging station were used to estimate annual carbon exports of 1.6 to 4.2 Mg km-2 yr-1. These values, representing 13 to 33% of the suspended sediment load, are some of the highest percentages reported in the global literature. Finally, we determined the effect of RNSP’s road restoration program on carbon sources and sinks. Treatment of 425 km of abandoned logging roads from 1979 to 2009 saved 72,000 Mg C through on-site soil erosion prevention, revegetation, and soil development on formerly compacted roads. The carbon cost for this road decommissioning work, based on heavy equipment and vehicle fuel emissions, short-term soil loss, and clearing of vegetation, was 23,000 Mg C, resulting in a net carbon savings of 49,000 Mg C to date. Carbon sequestration will increase in time as forests and soils develop more fully on the restored sites. Rates of SOC accumulation following timber harvest and two types of restoration of unpaved roads were compared to SOC in undisturbed old-growth forests. Several environmental variables, including aspect, vegetation, soil depth, lithology, distance from ocean, and time since road treatment, explain about half of the variation in SOC content within the upper half meter of soil on restored roads in RNSP.

Carbon stores and flux in Redwood National and State Parks

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