## 2 Methods  
### Site Description  
The site is situated at the Stordalen ombrotrophic peat mite in northern Sweden (68 deg21.4280' N, 19 deg03.1810' E, 351 m.a.s.l.). The site lies within the zone of discontinuous permafrost, but permafrost degradation over recent decades has left the area being more characteristic of the sporadic permafrost zone [45]. At the lower elevations, permafrost typically only occurs in the elevated palsas within the peat mires with wet and non-permafrost depressions covering much of the mite [45, 46]. The elevated palsas are usually covered by mosses, lichens, sedges, and dwarf shrub [40, 47]. Maximum thaw depth in the palsas is typically 45-50 cm [40] with the volume of soil accessible to plant roots increasing over the course of the growing season. Peat thickness can be up to 3 m. Mean annual temperature has been increasing over recent decades and has fluctuated around 0 \({}^{\circ}\)C since the 1990's [48]. As a result, permafrost thaw and vegetation shifts have occurred in some areas, replacing palsa with bogs or fens [47, 49]. For a more detailed description of observations and changes in Abisko, see [46].  
We used data from a belowground nitrogen fertilisation experiment that [40] carried out at Stordalen to identify the potential impact of increased nitrogen availability at the permafrost thaw front on subarctic peatland vascular-plant production and species performance. Table 1 summarises the observed characteristics of the two main vegetation types at the site. Table 1 shows that only _Rubus chamaemorus_ (Cloudberry) has roots present at the 45-cm thaw front. Roots of the other species (mainly _E. hermaphroditium_, or Mountain Crowberry) were confined to the upper 25 cm of the soil.  
Slow-release nitrogen fertiliser grains were added at two different depths within the soil (at 10 cm depth denoted near-surface and at 45 cm depth denoted thaw-front) through an aluminium tube in grids of nine points, which was then monitored by [35] over a three-year period. This was done in randomly selected plots of 60 \(\times\) 60 cm dominated by _E. hermaphroditium_ and _R. chamaemorus_ (78% and 12% of total biomass, respectively, Table 1). Fertiliser grains work through adding nutrients to the soil by naturally breaking down and decomposing due to moisture and temperature at a steady rate. Grains consisted of a nitrogen:phosphorus:potassium ratio of 17:3:11, respectively, with the 17% nitrogen consisting of 8.9% NH\({}_{4}\)-N and 8.1% NO\({}_{3}\)-N. Fertiliser was applied to give four different treatments: near-surface fertilisation (\(N^{+}_{NearSurfaced}\)), thaw-front fertilisation (\(N^{+}_{ThawFront}\)), both near-surface and thaw-front fertilisation (\(N^{+}_{Both}\)), and a control simulation with no fertilisation (_Control_). The authors of [35] found that the three-year fertilisation resulted in increased plant biomass and increased plant nitrogen content. Although all species responded to near-surface fertilisation (\(N^{+}_{NearSurface}\)), only the deep-rooting species responded to the fertilisation at the thaw-front (\(N^{+}_{ThawFront}\)). Here, we evaluate the ability of JULES to represent this response of vegetation to application of nitrogen fertiliser both near the surface, at the thaw front, and at both depths.