## Materials and Methods  
### Site Description  
The Straits Inclosure GHG flux measurement site, with its eddy covariance tower, is in the centre of a managed oak plantation of approximately 90 ha in the SE of England (51\({}^{\circ}\)09\({}^{\prime}\) N, 0\({}^{\circ}\)51\({}^{\prime}\) W), with an elevation of 80 m AMSL. The Inclosure is a flat area with an annual precipitation of 877 mm and temperature of 10.3 \({}^{\circ}\)C averaged over the period simulated, 1995 to 2014, and was replanted in the 1930s. It is located at the SW corner of the larger Alice Holt Forest (850 ha) and is surrounded on three sides by agricultural land (both arable and sheep pasture). The forest is a site for the UK Environmental Change Network (www.ecn.ac.uk (accessed on 29 October 2021)) and has a long-term forest health observation plot within the European 'Level II' Network (ICP Forests, www.icp-forests.net (accessed on 29 October 2021); further details are given in [29], and site characteristics used for model input are shown in Table 1.  
The tree species in the Straits Inclosure are mainly pedunculate oak (_Quercus robur_ L.) with about 10% basal area and a number of other deciduous species including ash (_Faxiculus exexelsior_ L.), sessile oak (_Q. pertaea_) (Mattuschka) Liebl. and Turkey oak (_Q. cerris_ L.).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Property** & **Value** \\ \hline Latitude & 51\({}^{\circ}\) 09\({}^{\prime}\) N \\ Longitude & 0\({}^{\circ}\) 51\({}^{\prime}\) W \\ Average annual rainfall & 877 mm \\ Average annual temperature & 10.3 \({}^{\circ}\)C \\ Annual N deposition as NH\({}_{4}\) & 0.89 g m\({}^{-3}\) \\ Annual N deposition as NO\({}_{3}\) & 0.51 g m\({}^{-3}\) \\ Total annual N deposition & 1.4 g m\({}^{-3}\) \\ Slope & 0\({}^{\circ}\) \\ Altitude & 80.0 m AMSL \\ \hline Upper storey trees: main species & Pedunculate oak (_Q. robur_) \\ Number of trees per hectare & 442 \\ Height & 16.5 m \\ Diameter at breast height & 0.233 m \\ \hline Understorey trees: species & European Ash (_F. execsior_) \\ (aggregated, for PSIM only) & (representing hazeel, hawthorn, ash and holly) \\ Number of trees per hectare & 8000 \\ Height & 3.0 m \\ Diameter at breast height & 0.03 m \\ \hline Modelling start date & 1/1/1995 \\ Thinning event (eastern half of Inclosure) & 20/9/2007 \\ Proportion of stemwood removed by thinning & 0.3 for upper storey; \\  & 0.6 for understorey \\ \hline \hline \end{tabular}
\end{table}
Table 1: Site and vegetation properties in 1995 with average climate and air chemistry data (1995–2014) input to initiate the LandscapeDNDC model specifically for the Straits Inclosure, Alice Holt Forest.  
There is a small area of mixed conifers (_Pinus nigra_ subsp. _laricio [PERSON]_.) and Scots Pine (_P. sylvestris_ L.) on the NW edge of the plantation. The understorey is substantial, dominated by hazel (_Corylus avellana_ L.), hawthorn (_Crataegus monogyna_ Jacq.) and regenerating canopy species. There are also climbers and ground flora, including grasses, sedges and herbs [30].  
The forest soil is a surface water stagno-gley [31], classified by the FAO as a eutric vertisol, silty clay in texture, 80 cm in depth, and developed on a bedrock of Cretaceous Gault Clay. Table 2 summarises the site soil information used in the modelling, derived from previous measurements at the site. With prevailing winds from the SW, wet and dry N deposition of 12.3 kg N ha\({}^{-1}\) year\({}^{-1}\) averaged over 1995-2002 [28] is relatively low for northern Europe.