4.6. Future of soil carbon changes
It is unclear if the SOC losses from tree establishment on grassland, 14 years after planting, will continue into the future. Huang et al. (2011) noted that the SOC beneath Eucalyptus trees planted on pasture in New Zealand started to recover within ten years of planting. Conversely, in a modelling study based on 100 observations from 16 papers, Poeplau et al. (2011) did not find a recovery in SOC as much as 140 years after tree planting on grassland. In this study, SOC measurements were taken from an adjacent mature grazed woodland (Fig. 7) indicate that a recovery of SOC may be possible.
5. Conclusions
In agreement with many studies in the literature, we found that tree planting on pasture was associated with a loss of SOC in the uppermost soil layer. Whilst this study did not directly consider the cause of soil carbon losses, two explanations are the loss of perennial grasses in the understorey and an increase in soil respiration due to lower soil water contents.