Evaluating carbon storage in restoration plantings in the Tasmanian Midlands, a highly modified agricultural landscape

In recent years there have been incentives to reforest cleared farmland in southern Australia to establish carbon sinks, but the rates of carbon sequestration by such plantings are uncertain at local scales. We used a chronosequence of 21 restoration plantings aged from 6 to 34 years old to measure how above- and belowground carbon relates to the age of the planting. We also compared the amount of carbon in these plantings with that in nearby remnant forest and in adjacent cleared pasture. In terms of total carbon storage in biomass, coarse woody debris and soil, young restoration plantings contained on average much less biomass carbon than the remnant forest (72 versus 203 Mg C ha^–1), suggesting that restoration plantings had not yet attained maximum biomass carbon. Mean biomass carbon accumulation during the first 34 years after planting was estimated as 4.2 ± 0.6 Mg C ha^–1 year^–1, with the 10th and 90th quantile regression estimates being 2.1 and 8.8 Mg C ha^–1 year^–1. There were no significant differences in soil organic carbon (0–30-cm depth) between the plantings, remnant forest and pasture, with all values in the range of 59–67 Mg ha^–1. This is in line with other studies showing that soil carbon is slow to respond to changes in land use. Based on our measured rates of biomass carbon accumulation, it would require ~50 years to accumulate the average carbon content of remnant forests. However, it is more realistic to assume the rates will slow with time, and it could take over 100 years to attain a new equilibrium of biomass carbon stocks.