Litter interception and water storage
To upscale the effect of litter interception across our study site, we sampled three randomly selected 1 m2 plots of broadleaf and needle litter, obtaining oven-dried litter weights of about 400 +/- 120 g m-2 for broadleaf litter and 1230 +/- 152 g m-2 for needle litter. Previous studies have reported litter weights of 785 g m-2 (Li et al., 2013) and 1090 g m-2 (Zagyvai-Kiss et al., 2019) for broadleaf litter and 115 g m-2 (Van Stan et al., 2017) to 1890 g m-2 (Zagyvai-Kiss et al., 2019) for needle litter in temperate mixed forests. Scaling our litter weights by the median specific storage capacities (g water per g dry weight) reported in section 3.1 yields a potential total water storage of 1.9 mm for beech litter and 3.1 mm for spruce litter. However, these figures are derived from laboratory experiments in which the litter was fully saturated by being submerged in water. Assuming that the litter layer actual storage capacities are 70% of these laboratory values (resulting in specific storage capacities of 3.4 and 1.8 times the dry weight for broadleaf and needle litter, respectively), we estimate the storage capacity of the broadleaf and needle litter layers to be 1.3 mm and 2.2 mm respectively (Table 1).
Table 1: To estimate the mean storage potential of the forest-floor litter layer at our field site, we combine laboratory and field measurements (in bold) with assumptions on the typical saturation reached during precipitation events (in italics) as summarized below.