Figure 5: Daily fluctuations in deadwood moisture content (grey
lines), measured by pressure cushions for four deadwood pieces (CB1 –
CB4), normalized between 0 and 1 (a) , compared to precipitation
events (blue bars) and daily variations in vapor pressure deficit (VPD;
red line) (b) . Deadwood absorbed moisture from the air during
the night, when VPD was low, and evaporated moisture to the subcanopy
atmosphere during the day, when VPD was high.
Water storage and retention capacity in forest floor deadwood
(and spruce cones)
We assessed the water storage dynamics of 40 pieces of deadwood (divided
between two sites, one under beech and the other under spruce canopies
– see Figure 1b) and 20 spruce cones (only under spruce canopy) by
weighing them daily for eight weeks. The temporal patterns of water
retention capacity and the timescale of water storage recession were
broadly similar for deadwood (at both sites) and for the spruce cones,
as indicated by the boxplots in Figure 6. The median storage capacity of
deadwood pieces is 1.7 times their dry weight, and for spruce cones is
1.3 times their dry weight. Overall, deadwood - even when not fully
saturated - retains moisture for more than 7 days, and spruce cones
retain moisture over even longer time periods, as indicated by the
duration of declining water-content values in Figure 6. The mean time
between the highest saturation following each precipitation event, and
the time when 50 % of the moisture was lost, was approximately 2.5 to
3.5 days for deadwood and 3.5 to 4.5 days for the spruce cones.