The removal of carbon dioxide from the atmosphere by trees is central to current plans to expand forest and woodland cover in the UK and international efforts to mitigate the impacts of climate change. Understanding the carbon balances of different forest types in the UK and how these are impacted by both management and the climate is essential for the development of effective climate change mitigation strategies. This Research Note summarises recent research on the carbon balances of two forest stands: an upland Sitka spruce plantation in Harwood Forest in the northeast of England, and a lowland deciduous oak plantation in Alice Holt Forest in southeast England. Overall total carbon stocks, including tree stems, roots, litter and soils, were higher at the spruce forest compared with the oak forest and soils at the spruce forest contained a larger proportion of the total carbon (62%) compared with the oak site (49%). The evergreen spruce forest remained photosynthetically active all year round, including over the winter period when the deciduous oak forest was leafless. The average overall long-term net ecosystem carbon dioxide uptake was 53% higher at the spruce forest compared with the oak forest. There were also differences between the two sites in the balance between carbon dioxide absorbed through photosynthesis and that lost to the atmosphere via respiration. Annual carbon dioxide emissions from the forest floor were larger at the oak forest compared with the spruce forest, which also accounted for a larger fraction of total ecosystem respiration (67% vs 40%).