The impact of restoring management to undermanaged forests in the UK: Comparing stand level assessments to the impact at a National Greenhouse gas inventory scale.

Approximately 54% of woodlands in the UK are undermanaged meaning they have not had a Woodland Management Plan, grant or felling licence in the last 15 years. There is policy interest in restoring management to these woodlands to enhance biodiversity, ecosystem function and ecosystem resilience, however it is well known that management can influence forest carbon stocks by both removing carbon in harvested material and by shifting carbon into the deadwood pool where it decomposes. Therefore, there are expected to be trade-offs between managing forests for biodiversity and carbon objectives.

This paper outlines research showing that the carbon losses from woodland restoration could be long lasting on both a regional and national scale when applied to the GHG inventory.

We examined this from a top-down and bottom-up approach. The top-down approach applies a restoration target to the UK National Greenhouse Gas inventory by transitioning areas reported as unmanaged areas to low intensity silvicultural management. The transition takes place over a 10-year period to either achieve a target of 65% or 75% of total UK woodland into active management. The GHG Inventory and inventory projections applied the CARBINE-R forest sector carbon accounting model to model carbon sequestration in trees, transfers to and between deadwood, litter, soil, and the atmosphere due to turnover, mortality, harvesting, and decay, and allocation of harvested timber to the raw wood products of bark, roundwood, and sawlogs. This was used to project the change in national carbon stocks over the next 100 years, which showed a modest decline that increased with the area of forest restored.

The GHG Inventory assumes growth without disturbance in the baseline, and the restoration is applied agnostically to all unmanaged woodland types, therefore a bottom-up method stand-level assessment was performed for a number of unmanaged woodland case studies that ranged in species composition, management history, and targeted management interventions for either biodiversity or commercial objectives. This approach allowed us to consider the impact of different stocking levels, species mixes, as well as comparing the impacts of different levels of management. Also, a business-as-usual scenario was developed that considered disturbance from common tree diseases (ash dieback, acute oak decline, Dothistroma needle blight), that could affect the baseline.

The results show that in most of the unmanaged woodland types modelled, introducing management leads to large carbon stock losses which do not recover by 2150, except areas of woodland that are young and have failed to establish, resulting in understocked or overly browsed woodland. These consistently gained land carbon due to introducing management. For other woodland types, the carbon losses can be reduced if there is considerable mortality due to natural disturbance in the baseline, suggesting that targeting restoration to areas at high risk of disturbance would mitigate the carbon losses. We can use these results to refine the GHG inventory projections by focusing on suitable tree species mixes and ages of stands and to identify the potential impact of a more targeted management restoration policy.