*2.2. Litterbag Experiment*

Foliar litter of *A. faxoniana* in this study area was collected using a litter trap method in late autumn (October 2011). Only freshly fallen leaves (without signs of galls, herbivory or atypical coloration) were collected and air-dried for two weeks. Nylon litterbags (20 cm × 20 cm, mesh size: 1 mm top vs. 0.5 mm bottom) were used to fill 10 g of dried litter. Litterbags were placed on the top of existing litter layer in each plot on November 21, 2011. In total, we applied 3 elevations × 4 gap sizes × 3 replicates × 3 bags × 16 samplings = 1728 litterbags. The snow depth in each plot was obtained by averaging the direct measurements from 9 random locations, and the measurements were performed immediately after each sampling event using a ruler. The temperatures of the litter layers were recorded every 2 h by iButton DS1923-F5 recorders (Maxim Inc., Sunnyvale, CA, USA), which were placed in the litterbags.

Based on previous field investigations, the growing season was from April to October every year [31]. In order to explore litter decay processes comprehensively, the bags were retrieved at the end of each period: these were in December (OF, onset of freezing stage), February (DP, deep freezing stage), April (TS, thawing stage), June (EGS, early snow-free stage), August (MGS, middle snow-free stage) and October (LGS, late snow-free stage) of the initial two decomposing years (2011–2013). For the latter two years (2014–2015), bags were only retrieved in April (NGS, non-growing season) and October (GS, growing season), which were defined according to the phenological characteristics of the vegetation

in the study area. After carefully removing the roots, mosses and foreign materials from the litter, each sample was oven-dried at 65 ◦C for 48 h to a constant weight to determine the litter's remaining mass. Litter carbon content was determined using the dichromate oxidation–ferrous sulfate titration method [41].
