Soil amendment improves carbon sequestration by trees on severely damaged acid and metal impacted landscape, but total storage remains low

Landscape carbon storage is a key component of climate change mitigation. Tree planting on degraded land has been identified as an effective carbon capture strategy, but it is unclear how various associated restoration treatments influence carbon sequestration. In this study, we measured carbon pools in jack pine (Pinus banksiana Lamb.) stands subject to different restoration treatments within severely damaged upland areas in the metal mining region of Sudbury, Ontario, Canada. Treatments included: i) soil amendment (liming, fertilizing and grass/legume seeding) followed by jack pine planting, ii) jack pine planting alone, iii) soil amendment only, and iv) untreated plots with some natural regeneration as a result of improving air quality in the region. Twenty-four years after the initial treatments, we measured the carbon storage in coarse and fine woody debris, herbs, shrubs, forest floor (LFH), mineral soil, and trees. The carbon pool in planted trees was 1.5 times higher in plots when soil amendments were applied. This increase in the tree carbon pool was the result of greater carbon sequestration per individual jack pine tree rather than changes in tree density or arrival of new species. Similarly, naturally regenerated white birch (Betula papyrifera Marshall) in the amended plots stored 1.7 times more carbon than white birch in the untreated plots. Tree planting proved essential on this landscape with natural tree regeneration rates very low even 50 years after local pollution was massively reduced. However, tree planting surprisingly did not significantly affect total carbon storage in these exposed upland sites. Total ecosystem carbon varied from 21.4 Mg ha(-1) to 124.5 Mg ha(-1) across all plots (mean of 67.6 +/- 4.8 Mg ha(-1)) but no statistically significant differences were observed among the treatments. Soil organic carbon (SOC) proved to be the largest carbon pool across plots and stored on average 66% of total ecosystem carbon. However, at this early stage the restoration treatments had no influence on SOC pools on this highly degraded landscape, which still appears to be severely affected by ongoing erosion of surface soil and metal contamination. The restoration treatment also did not significantly affect the understory or downed woody debris carbon pools. This study demonstrates that the current restoration treatments used in Sudbury do influence the amount of carbon sequestrated mainly through tree restoration on this industrially degraded landscape, but long-term storage potential is still limited by poor soil conditions.

Automated summary

This study in Sudbury, Canada, found that tree planting on degraded upland areas significantly increased carbon sequestration, while soil amendment treatments did not have a significant impact on soil organic carbon pools.