Woodland creation scheme in the Yorkshire Dales successfully focuses tree planting on soils with lower soil organic carbon stocks

1. Tree planting is a key climate mitigation strategy, but afforestation on organo-mineral soils may cause soil organic carbon (SOC) losses, limiting long-term ecosystem carbon gains over decadal timescales. New woodland creation guidance aims to avoid tree planting on high-carbon soils to protect existing SOC stocks.

2. We measured topsoil SOC stocks (0–15 cm) at a new native woodland in the Yorkshire Dales, UK, with highly variable organo-mineral soils typical of many UK uplands. The woodland design was based on peat depth, vegetation classification, archaeological features and breeding bird surveys.

3. Our study had two aims. First, to test whether the woodland design resulted in tree planting in areas with lowest SOC stocks at a site scale. Second, to assess whether low-disturbance, hand-planting techniques avoided high SOC stocks at plot scale. Five replicate 10 × 10 m plots were established for each of three treatments: unplanted, low-density and high-density tree planting. Each planted plot was paired with a topographically similar unplanted control. Soil cores were sampled randomly across each plot as well as close to planted trees. Fieldwork occurred 9–13 months after planting began.

4. We found SOC stocks were significantly lower in high-density plots (median = 75.60 t C ha−1; IQR = 66.44–87.95) than in unplanted (97.70 t C ha−1; 80.74–115.59) and low-density plots (91.47 t C ha−1; 78.67–99.98; p < 0.05), indicating that areas selected for tree planting preferentially targeted lower carbon soils as planned. No evidence was found to suggest avoidance of higher carbon soils at the 10-m plot scale.

5. Practical implications. Our results show that careful woodland design can avoid tree-planting on high-carbon organo-mineral soils. Our work shows that new woodland creation guidelines in England are likely to reduce the potential for SOC losses by targeting high-density tree planting on soils with lower SOC stocks.