| 23 Jan 2026
Water storage and redistribution effect evaporation, retention, and infiltration of forest floor sites
Abstract. The forest floor (FF) possesses a significant water retention capacity, facilitating the transfer of water between the atmosphere and the soil. However, knowledge on the water retention characteristics and water redistribution effects of the FF remain limited. Due to the dominance of laboratory data regarding the storage capacity of a forest’s litter layer, we used a combined FF weighted grid-lysimeter and soil moisture network to directly and in-situ measure the dynamics of water storage of the FF and fluxes from and into the FF. The objective was to quantify storage capacities, retention durations, and resulting water redistribution patterns, as well as evaporation from the FF. We present the results of our network at three sites with different altitudes located in the Black Forest, southwest Germany. The three sites have an annual mean temperature gradient from 6.3 °C to 10.3 °C, leading to humus forms that vary from typical F-Mull to typical Moder. Throughout the monitored period in 2024–2025, the storage capacity of the FF ranged between 1.4 and 4.2 g/g FF and was not only influenced by the type of litter but also by the rainfall characteristics themselves. With our field setup we could show that longer, low intensity rainfall events fill the FF storage more efficiently than shorter heavy rainfall events (−24 %). Our gridded lysimeter design revealed small-scale spatio-temporal infiltration patterns, caused by a redistribution of rainfall along the passage through the FF. The findings of the lysimeter network provide a comprehensive understanding of the influence of the FF mass on the water cycle within forest ecosystems.
This manuscript reports on experiments to quantify storage, drainage, and evaporation from the forest floor, using innovative instrumentation to obtain rare observations of these processes. The experiment and analysis are simple and the interpretations are clear, providing a remarkably clean story about the controls on water storage and release from this important store. I have only a few suggestions to improve the manuscript.
There is an inconsistency in how Cmax is defined. In Fig 8 and many other places in the results, Cmax is the same as or less than Cmin. I expected Cmax to be defined as in Fig 2 and L150, where it is defined as an absolute amount of water, not as excess above Cmin as it seems to be in most of the Results. I hope you will choose to define and report it as in Fig 2 and L150.
The methods and discussion unfortunately gloss over how much mineral soil is in these lysimeters. Are there data available on organic volume or mass vs mineral volume or mass? Though it might be difficult to compare across humus forms, this kind of analysis would help in extrapolating results to other settings.
In Fig 9A, why are there large hourly oscillations between high evaporation and zero? Can we be sure this is due to sunflecks and not to an error in the data logger or analysis? Even if there are no data errors, it may be worth explaining the limitations of Fig 9 when estimating evaporation at the ha or catchment scale; i.e., sunflecks affect these installations differently than they affect catchments.
I think Fig 10 is one of the most important figures in the manuscript. We almost never get to see spatially resolved estimates of infiltration, and I found the variation to be strikingly high. It’s interesting to see that the forest floor appears to be a stronger source of variability than redistribution by the canopy. Is it possible to add some discussion on how these magnitudes compare to spatial redistributions caused by other sources of heterogeneity?
I appreciate the discussion comparing intensity effects on storage capacity in the canopy vs forest floor, but I think there is a missing element, namely the contrasting mechanisms in how those two stores become wetted. Unlike in canopies, the role of drop velocity in wetting the forest floor is low, and wetness depends more on low-velocity flow into detrital pores. This difference (momentum vs van der Waals dominance) seems to me a more obvious explanation than the laboratory vs. field distinction emphasized in the manuscript. I do agree that the duration is
Figure 3 given that evaporation is always near zero and the details are also in Table 3, I suggest replacing that uninformative line with a time-varying estimate of C, as in Figure 2.
Table 5 last rows should be mm per … h?
Line 293: what does “saturated” mean here? This word must be chosen carefully.