Site characteristics
For full site characteristics, see Table S1. The ground vegetation was
dominated by typical Subarctic dry heath dwarf shrubs, particularlyEmpetrum hermaphroditum, Vaccinium myrtillus and Vaccinium
vitis-idea , with higher coverage of graminoids and forbs at the
relatively wetter and more fertile sites and mosses and (rarely) lichens
at the low fertility end (Table S1). The mean annual soil temperature
(averaged from summer 2016 to summer 2017) across all sites ranged
between 1.7±0.06 and 3.5±0.1 °C, while the mean annual growing season
(averaged from 15/6 to 15/9 2017) soil temperature ranged between
6.7±0.1 and 11.1±0.2 °C. These figures are slightly lower but comparable
to the coarse scaled (4x4 km) modelled Luftweb record for the mean
growing season air temperature per transect for the period 2000-2014
(mean: 10.7±0.2 °C, Table S1), so we believe the variance in mean
growing season soil temperature reflects the site air temperature
variance relatively well. Early growing season volumetric soil moisture
content ranged from 11±1.1 to 38±2.5 % across sites (Table S1). All
sites were characterised by relatively acid (mean pH: 4.5±0.06) and
nutrient poor soils. Dissolved inorganic N-content was low, and at the
same level as dissolved P, while dissolved base cations (calcium,
magnesium, sodium and potassium) were an order of magnitude more
abundant than N and P (Table S1), suggesting no scarcity of other
macronutrients than N.