Tree restoration and ecosystem carbon storage in an acid and metal impacted landscape: Chronosequence and resampling approaches

Abstract

Tree restoration on degraded land has been identified as an effective and affordable capture carbon strategy but it is unclear if carbon sequestration rates are comparable to rates on non-industrially impacted silvicultural forests. To this end, we resampled a jack pine (Pinus banksiana) and red pine (P. resinosa) chronosequence 16 years after the initial measurement to quantify carbon pools following ca. 40 years of regreening on an acid and metal impacted landscape. Measured carbon pools were then compared to those reported in an unpublished study to determine how carbon sequestration rates have changed over time and if repeated sampling at the stand level validates temporal trends estimated by the chronosequence. Total ecosystem carbon (TEC) within the stands ranged from 55 to 136 Mg ha−1 with a regional mean of 90.2 ± 9.6 Mg ha−1. On average, tree and soil organic pools (SOC) were the two largest carbon pools, representing 47% and 42% of TEC, respectively. Compared with unplanted sites, tree restoration resulted in a significant increase in the mean TEC among all sites of 54.4 ± 10.2 Mg ha−1 with a corresponding sequestration rate of 1.7 ± 0.3 Mg ha−1 yr−1. The chronosequence approach was only able to consistently detect a change in the tree carbon pool. In contrast, repeated sampling at the stand level identified changes in carbon sequestration rates within SOC, LFH and shrub carbon pools and showed that the chronosequence tree carbon sequestration rate was underestimated by a factor of 2.3. Chronosequence studies assume study sites have similar landscape history and environmental conditions, which may not be reasonable in highly degraded landscapes where past events (e.g., pollution, erosion, restoration) influence multiple landscape characteristics (e.g., local hydrology and topography). We conclude that tree restoration on impacted landscapes can sequester carbon at a rate comparable to silvicultural plantations in a similar climatic region and that reforestation of industrially damaged landscapes could be part of an effective carbon capture strategy.