Swiss Federal Institute for Forest, Snow and Landscape Research

About: Swiss Federal Institute for Forest, Snow and Landscape Research is a facility organization based out in Birmensdorf, Switzerland. It is known for research contribution in the topics: Climate change & Soil water. The organization has 1256 authors who have published 3222 publications receiving 161639 citations. The organization is also known as: WSL.

New Tree-Ring Evidence from the Pyrenees Reveals Western Mediterranean Climate Variability since Medieval Times

Abstract: Paleoclimatic evidence is necessary to place the current warming and drying of the western Mediterranean basin in a long-term perspective of natural climate variability. Annually resolved and absolutely dated temperature proxies south of the European Alps that extend back into medieval times are, however, mainly limited to measurements of maximum latewood density (MXD) from high-elevation conifers. Here, the authors present the world’s best replicated MXD site chronology of 414 living and relict Pinus uncinata trees found >2200 m above mean sea level (MSL) in the Spanish central Pyrenees. This composite record correlates significantly (p ≤ 0.01) with May–June and August–September mean temperatures over most of the Iberian Peninsula and northern Africa (r = 0.72; 1950–2014). Spanning the period 1186–2014 of the Common Era (CE), the new reconstruction reveals overall warmer conditions around 1200 and 1400, and again after around 1850. The coldest reconstructed summer in 1258 (−4.4°C compared to 1961...

Macroroughness and variations in reach-averaged flow resistance in steep mountain streams

Abstract: [1] Steep mountain streams typically feature macroroughness elements like large immobile boulders or channel-spanning bedforms such as step-pool sequences. The effects of macroroughness on resistance and flow velocity are not well understood and appropriate field parameters for representing macroroughness in flow velocity equations have not been identified. The prediction of flow velocity in rough and steep streams therefore remains challenging. We measured flow velocity and several macroroughness parameters, i.e., boulder concentration, boulder diameter and protrusion, and roughness of longitudinal channel profiles in six reaches of steep mountain streams with plane bed/riffle, step-pool, and cascade channel morphologies. The between-site variations in flow resistance can be explained to a large degree by nondimensionalization of discharge and flow velocity using channel slope and a characteristic roughness length. Using any of our roughness parameters as the characteristic roughness length, this nondimensionalization leads to a similarity collapse of the entire data set. The remaining differences in flow resistance among the streams are related to dimensionless measures of macroroughness that describe the concentration of boulders or step density in a reach. Boulder concentration represents the measure best describing the data and is used in a simple regression equation for flow velocity. The predictions were better than predictions by the variable power law equation proposed by Ferguson. Although the regression might not be statistically significant, the observed trends suggest that boulder concentration partly explains the residual variance of between-site variation of flow resistance.

Topographic Controls on the Extension and Retraction of Flowing Streams

Abstract: Flowing stream networks extend and retract as their surrounding landscapes wet up and dry out, both seasonally and during rainstorms, with implications for aquatic ecosystems and greenhouse gas exchange. Some networks are much more dynamic than others, however, and the reasons for this difference are unknown. Here we show that the tendency of stream networks to extend and retract can be predicted from down‐valley changes in topographic attributes (slope, curvature, and contributing drainage area), without measuring subsurface hydrologic properties. Topography determines where water accumulates within valley networks, and we propose that it also modulates flow partitioning between the surface and subsurface. Measurements from 17 mountain stream networks support this hypothesis, showing that undissected valley heads have greater subsurface transport capacities than sharply incised valleys downstream. In catchments where broad valley heads rapidly transition to sharply incised valleys, subsurface transport capacity decreases abruptly, stabilizing stream length through wet and dry periods. Plain Language Summary Although stream networks are represented as fixed blue lines on maps, the actual extent of flowing water dynamically adjusts as landscapes become wetter and drier. This is an old observation, but one without a satisfying physical explanation. Intuitively, flowing streams extend during wetter periods, as smaller parts of the landscape are able to supply enough water to support streamflow. But the supply of water is only part of the story, because some parts of the landscape may have greater capacity to move supplied water through the subsurface without streamflow, affecting where water ultimately emerges. In this study, we use observations from 17 mountainous landscapes to show that topography can be used to predict both the supply of water and the capacity to move that water through the subsurface. Consequently, topographic maps can tell us how much a stream network will extend as its surrounding landscape becomes wetter. This helps us predict how dynamic (or, conversely, stable) stream networks will be during rainstorms, droughts, and longer‐term climatic shifts.

Importance of tree height and social position for drought-related stress on tree growth and mortality

Abstract: Key message A higher mortality of dominant trees under drought stress is explained by impacts of tree size, canopy- and root structure and the hydraulic transport system.

Below-ground complementarity effects in a grassland biodiversity experiment are related to deep-rooting species

Abstract: Summary 1.Belowground resource partitioning is often proposed as the underlying mechanism for the positive relationship between plant species richness and productivity. For example, if species have different root distributions, a mixture of plant species may be able to use the available resources more completely than the individual species in a monoculture. However, there is little experimental evidence for differentiation in vertical root distributions among species and its contribution to biodiversity effects. 2.We determined species-specific root standing biomass over depth using molecular techniques (real time-qPCR) in a large grassland biodiversity experiment (1-8 plant species mixtures), in two years. Species-specific root biomass data were used to disentangle the effects of positive interactions between species (complementarity effects) and effects due to dominance of productive species (selection effects) on root biomass in mixtures. In a next step, these biodiversity effects were linked to the diversity of rooting depths and the averaged rooting depth of the community. 3.Root biomass increased with species richness. This was mainly due to positive interactions (the complementarity effect), which increased with species richness belowground. In contrast, the selection effect decreased with species richness. Although there was considerable variation in vertical root distribution between species in monocultures, the diversity of rooting strategies did not explain the complementarity effect. Rather, the abundance of deep-rooting species in mixtures (i.e. high community weighted mean) was significantly related to the complementarity effect. Comparing the ‘predicted’ root distribution (based on monocultures) to the actual distribution in mixtures, we found that mixtures rooted deeper than expected, but this did not better explain the complementarity effect. 4.Synthesis: This study demonstrates that vertical root distributions of species provide only subtle evidence for resource partitioning. We found no evidence that functional diversity in vertical rooting patterns was important for the complementarity effect, in contrast to our expectation that the enhancement of productivity was due to resource partitioning. Alternatively, we found significant but weak relationships between the complementarity effect and deep-rooting communities, based on the community weighted mean root distribution. This suggests that factors other than belowground resource partitioning alone may drive the biodiversity-productivity relationship. This article is protected by copyright. All rights reserved.