Figure 1:Location of the “Waldlabor Zürich” in Zurich (a) and a
schematic of our experimental site at its eastern border (b) ,
indicating the locations of trees (spruce, beech and other species shown
in green, orange, and gray, respectively), two litter plots (orange
squares EX I and EX II), the monitored deadwood pieces and spruce cones
(blue ovals), and the small temperature/relative humidity towers (yellow
crosses). The weather station is located outside the forest,
approximately 150 m from our experimental site.
Laboratory estimation of litter storage capacity
We estimated the storage and retention behavior of the forest‑floor
litter layer both in the laboratory and in situ. In laboratory
saturation experiments, we filled 63-µm-mesh laboratory sieves (area of
0.0308 m2) with a 5 cm layer of broadleaf litter or a
2.5 cm layer of needle litter (both collected from the site), dried them
at 70 °C for 24 hours and measured the dry weight, as suggested in
Carnol and Bazgir (2013). The thickness of the litter layer corresponds
to the mean thickness across our field site, as estimated from collected
grab samples. We then submerged the sieves with litter into water for 24
hours, let the water drain gravitationally, and then weighed the sieves
after 30 minutes and again after 4 hours to calculate the litter’s water
retention capacity (Sato et al., 2004; Li et al., 2013). During these
steps, the litter was not removed from the sieves, to preserve the
litter structure and the water captured within it. We then removed the
litter from the sieve and weighed the sieve to account for water that
was captured in the sieve itself (Helvey and Patric, 1965). Afterwards
the litter was again dried at 70 °C for 24 hours to verify the
conservation of the original dry mass of the leaf litter. This procedure
was repeated for 40 samples each of broadleaf and needle litter. To
evaluate the impact of litter-layer thickness and structure, we also
measured the retention capacity of doubled and quadrupled litter
thicknesses (10 cm and 20 cm for broadleaf litter layer and 5 cm and 10
cm for needle litter), with four replicates each.