Contributions of throughfall, forest and soil characteristics to near-surface soil water-content variability at the plot scale in a mountainous Mediterranean area

Abstract

Soil water-content (SWC) variability in forest ecosystems is affected by complex interactions between climate, topography, forest structure and soil factors. However, detailed studies taking into account the combined effects of these factors are scarce. This study's main aims were to examine the control that throughfall exerts on local spatial variation of near-surface soil water-content and to combine this information with forest structure and soil characteristics, in order to analyze all their effects together. Two stands located in the Vallcebre Research Catchments (NE Spain) were studied: one dominated by Quercus pubescens and the other by Pinus sylvestris. Throughfall and the related shallow SWC were monitored in each plot in 20 selected locations. The main characteristics of the nearest tree and soil parameters were also measured. The results indicated that mean SWC increment at the rainfall event scale showed a strong linear relationship with mean throughfall amount in both forest plots. The % of locations with SWC increments increased in a similar way to throughfall amount in both forest plots. The analyses considering all the effects together indicated again that throughfall had a significant positive effect in both forest plots, while soil litter depth showed a significant negative effect for the oak plot but lower statistical significance for the pine plot, showing a comparable -although more erratic- influence of the organic forest floor for this plot. These results, together with lower responses of SWC to throughfall than expected in rainfall events characterized by low preceding soil water-condition and high rainfall intensity, suggest that litter layer is playing an important role in controlling the soil water-content dynamics. The biometric characteristics of the nearest trees showed significant but very weak relationships with soil water-content increment, suggesting that stemflow and throughfall may act at lower distances from tree trunk than those presented in our study.

The Demographics of Water: A Review of Water Ages in the Critical Zone

“…Water age estimates are challenged by the natural multiscale heterogeneity of hydraulic conductivity (e.g., soil matrix vs. macropores in the subsurface) (Bachmair & Weiler, ; Troch et al, ), which can lead to long tails of the water age distribution functions (Kirchner et al, ). Additionally, heterogeneity in infiltration and percolation results from vegetation (e.g., interception and throughfall—e.g., Molina et al, —and root water uptake volumes and depths—e.g., Dick et al, ), snow accumulation and melt patterns (e.g., Garvelmann et al, ), and other spatially variable environmental characteristics.…”

Particulate Matter Fluxes in a Mediterranean Mountain Forest: Interspecific Differences Between Throughfall and Stemflow in Oak and Pine Stands

“…Prior to the experiment, canopy coverage and diameter at breast height distributions were measured in both stands via hemispherical photography and forestry measurements, respectively (Llorens & Gallart, 2000;Molina et al, 2019). A total of 10 throughfall and 4 stemflow collectors were deployed in each forest stand, covering different representative canopy coverages (from 30% to 88% in the pine stand, and from 30% to 95% in the oak stand) and the diameter at breast height distributions (~15, 20, 25, and 30 cm; Cayuela et al, 2018).…”

Mechanisms of consistently disconnected soil water pools over (pore)space and time

“…The dry winters and negative water balance during summer result in a succession of wet and dry periods with soils usually wetting up in early spring and early fall (Gallart et al, 2002). The studied soils are of silty loam texture (4% sand, 30 72% silt, 24% clay) with about 3% gravel content and 6% organic matter content (Molina et al, 2019). The soil's bulk density is 0.99 g cm -3 and its porosity is 62% (Molina et al, 2019).…”

“…The studied soils are of silty loam texture (4% sand, 30 72% silt, 24% clay) with about 3% gravel content and 6% organic matter content (Molina et al, 2019). The soil's bulk density is 0.99 g cm -3 and its porosity is 62% (Molina et al, 2019). The study area was terraced before and during the 19 th and abandoned in the second half of the 20 th century.…”

“…The vegetation is Scots pine (Pinus sylvestris). The Scots pine trees are about 17 m high, basal area is 45 m 2 ha -1 and their canopy cover is 70% (Molina et al, 2019).…”