Large areas worldwide have been affected by farmland abandonment and subsequent plant colonization with significant environmental consequences. Although the process of farmland abandonment has slowed ...down, vegetation recovery in abandoned lands is far from complete. In addition, agricultural areas and pasture lands with low-intensity activities could be abandoned in the near future. In this foreword, we review current knowledge of the impacts of farmland abandonment on water resources and soil conservation, and we highlight the open questions that still persist, in particular regarding terraced landscapes, afforested areas, abandonment of woody crops, traditional irrigated fields, solute yields, long-term trends in the response of abandoned areas, and the management of abandoned farmland. This Special Issue includes seven contributions that illustrate recent research into the hydrological, geomorphological, and edaphological consequences of farmland abandonment.
Scree cones and slopes are common sedimentary landforms created by rock fall and rock particle fall in mountainous environments. These formative processes are attributed to various weathering and ...particle detachment mechanisms. However, the aeolian contributions to the weathering of rock faces and formation of scree sediments are poorly understood and often underestimated. A case study in the southern highlands of Iceland provided a geological setting in a subarctic environment where the contribution of various erosion and deposition mechanisms to the development of scree deposits could be studied. Here, moderately-cohesive subglacial volcanic eruption products are continuously undercut by local streams, creating exposed and steep-sided canyon walls where scree cones and slopes are formed by dominant influences of freeze–thaw cycles and the wind on rock particle fall. The stratigraphy and the morphometry of these sedimentary landforms indicate that wet formative processes can contribute but are not as dominant. Avalanching of accumulated material occurs in dry conditions and creates distinct stratified sediments. The aeolian contribution to the scree development was studied by determining the physical requirements of particle detachment using wind tunnel simulations. Simulated threshold wind speeds of the removal of fines show that these wind and gust conditions are common in these areas in Iceland. A detailed particle analysis of the sediment from an isolated scree cone and the contributing rock face showed that sediments were depleted in the silt fractions. Field observations confirmed the influence of deflation where fine material is removed by the wind from exposed sediments whereas larger particles are excavated by the deflation of the surrounding matrix on the overlying rock face. The outcomes highlight the role that aeolian processes can fulfil in subarctic environments. As similar glassy materials are also found on other planets, the studied processes can for example offer insights in hillslope processes at the surface of planet Mars.
► Scree formation below rock faces of subglacially formed volcanic glass ► Formation dominated by freeze and thaw cycles and wind in dry conditions ► Wind excavates coarse material on rock face and modifies texture of sediments. ► Relevance for landforms in various dry and windy environments on Earth and Mars
This study describes the effect of soil fauna and vegetation on the development of landscapes and how these actually control soil formation, geomorphological development and hydrological response. ...The study area is located in a semi-natural deciduous forest on marl in Luxembourg, with a strong texture contrast in the soil at 15–25 cm depth (luvic planosols).
The methodology applied is both based on hydrological and geomorphological field measurements on runoff, sediment yield, perched water table dynamics, geomorphological survey, pedological survey and measurements related to in situ ectorganic horizon dynamics and litter decay, soil animal activity, as well as measurements of dynamic soil properties such as soil moisture and swelling and shrinkage.
The results show that there is a positive feedback between tree type, soil fauna activity and the development of pipes, partial areas, soils and geomorphology. The landscape can be divided into two main types: Areas where Stellario-Carpinetum vegetation and partial areas are common and areas with Milio-Fagetum vegetation on dry slopes, which are differentiating more and more over time as a result of ongoing geo-ecosystem processes, and which also reflected in their sediment yield. The hydrological response is highly different for both landscape compartments as they are dominated by matrix (Beech) and pipe flow (Hornbeam) respectively. Soil fauna and tree type drive both soil and geomorphological evolution and they both can be considered as important ecosystem engineers.
Blowouts can mitigate the negative effects of acidification in the topsoil, especially in industrialized countries with high atmospheric nitrogen (N) deposition. However, blowout activity may differ ...between lime‐rich and lime‐poor dunes, which creates different regional responses and interactions between processes and patterns.
To further explore this, five Dutch dune sites were selected over the gradient from lime‐rich and lime‐poor dunes. We mapped blowout activity in 5 years between 1996 and 2017 with aerial photographs, and used transport potential, atmospheric N‐deposition and rabbit density as explanatory variables. We also studied soil and plant parameters in the field in different stages of succession.
All sites showed fluctuations, but blowout activity net increased in the lime‐rich sites, and decreased in the lime‐poor sites. Differences in blowout activity could not be explained by sand transport potential, which differed between years, but not sites. Differences in blowout activity could to some extent be explained by rabbit density and exceedance of the critical N load, although the transition site between lime‐rich and lime‐poor dunes showed high blowout activity despite low rabbit density.
Differences in blowout activity between lime‐rich and lime‐poor dunes were also related to differences in topsoil chemistry, especially with respect to lime content, Fe content and different forms of phosphorus (P). High pH was a key factor, which reduced sensitivity to high N deposition through reduced P‐availability to the vegetation, higher proportion of arbuscular mycorrhizal plants, which may improve food quality for rabbits, and lower root biomass, which may increase erodibility of the dune soil. High pH and low P availability may even occur in lime‐poor dunes with a little lime, as long as blowouts stay active and counteract acidification. However, when pH values drop below 6.5, P availability to the vegetation will increase and start feedback processes leading to blowout stabilization.
Differences in blowout activity between lime‐rich and lime‐poor dunes in the Netherlands over the period 1996–2017 could not be explained by sand transport potential, but may have been due to differences in rabbit density and exceedance of the critical atmospheric nitrogen (N) load, together with differences in topsoil chemistry. High pH was a key factor, which decreased sensitivity to high N deposition through reduced phosphorus‐availability to the vegetation, lower root biomass, and more edible plant species.
High mountain environments are among the most fragile on Earth. Due to anthropogenic disturbances and the exposure to extreme weather events, the rates of soil erosion have recently been ...accelerating, resulting in ecological degradation and geological hazards. Ecological restoration of mountains and an improved understanding of nature-based solutions to mitigate land degradation is therefore of utmost urgency. Identifying hotspots of soil erosion is a first step towards improving mitigation strategies. A promising methodology to identify erosion hotspots is sediment source fingerprinting, that differentiates the properties of soil from different sources, using signatures such as elemental geochemistry or radionuclides. However, in areas with complex lithologies or shallow and poorly developed soils, geochemical fingerprints allow only a rough distinction between erosion hotspots. In this opinion paper, we explore the relevance of environmental DNA (eDNA) that originates from plant litter and fixes onto fine soil particles, as a targeted sediment fingerprinting method sensitive to vegetation that could potentially allow the identification of erosion hotspots and their relative importance from sedimentary deposits. Pioneering studies indicate that eDNA allows not only the detection of specific vegetation communities, but also the identification of individual plant species. Supported by the increasing availability and quality of vegetation maps and eDNA reference libraries, we argue that sediment source fingerprinting using eDNA from plant litter, will evolve into a valuable method to identify hotspots of soil erosion and allow stakeholders to prioritize areas where ecological restoration is necessary in high mountain environments.
The Mediterranean mountainous landscapes have undergone large-scale exploitation for millennia. In the Central Pyrenees, land abandonment has occurred since the 1950s, leading to a process of woody ...encroachment. The main objective of this paper is to shed light on the effects of different land use and land covers (LULCs) on soil organic carbon (SOC) and nitrogen (N) stocks, and on the composition of soil organic matter (SOM) after land abandonment in the Central Pyrenees. Five LULCs (8 specific sites) were selected through detailed land use change mapping. Soil and litter samples (n = 160) were collected and analyzed, including Tetramethylammonium hydroxide pyrolysis–gas chromatography. Organic carbon (Corg)/N ratios, Carbon Preference Index and Average Chain Length indices were calculated based on the distribution of fatty acids in order to determine the molecular composition and degradation of SOM. The results showed: (i) an increase in the dominance index and forest cover, at the expense of shrublands and agricultural fields, and a decrease in Shannon’s Diversity and Evenness indexes; (ii) LULC and depth had significant effects on SOC and N contents and stocks; (iii) SOC and N contents and stocks were higher in the meadows and young forests; (iv) significant differences were observed between meadows and young forests and the first stages of land abandonment considering the soil profile; (v) total decomposition of lignins and an omnipresence of unsaturated and saturated straight-chain fatty acids; and (vi) Corg/N values indicate that the origin of SOM is microbial. This study confirms that SOC accumulation after abandonment is a slow process, and the first stages of the woody encroachment decrease SOC stocks. Woody encroachment should be managed with measures based on scientific knowledge, but also considering the historic adaptation of agro-pastoral activities to the environment to ensure the proper functioning of ecosystem services and promote SOC storage in Mediterranean mountain soils.
•The long-term observed sediment yield of forests is lower than reported so far.•The index of connectivity (IC) was calculated using vegetation as target sinks.•Subplot sediment yields did not ...correlate with vegetation cover.•They significantly correlated with IC and its hot/cold spots relative areas.•The important roles of structural and functional connectivity are highlighted.
Semi-arid (semi-)natural terrestrial ecosystems are often vulnerable to soil erosion, but long-term comparable observations are relatively scarce. We measured erosion for thirteen years on a hillslope dominated by tussock grass and pine trees in the Mediterranean region and conducted multiple aerial surveys of landscapes. At plot scales, we found sediment yields of 3.1 g m−2 yr−1 for open forest, and around 35 g m−2 yr−1 for tussock grasslands, probably attributed to differences in vegetation type and cover related to exposition. Furthermore, erosion rates in the forest were lower than reported so far. The values obtained could act as a baseline for achieving land degradation neutrality. The tussock grass plots were divided into ten natural subplots. Subplot sediment yields were not sensitive to vegetation cover but significantly negatively correlated with the maximum value of the index of connectivity (IC). This metric, calculated for bare areas not directly connected to measurement gutters for subplots, measures structural connectivity between bare areas and vegetation. Furthermore, spatial clusters of high and low connectivity - hot and cold spots of IC were identified. Sediment yields decreased significantly with a higher percentage of IC hot spots in bare areas, due to vegetation obstruction. However, sediment yields increased significantly with the relative area of IC cold spots plus bare areas adjacent to gutters, which could be useful hints for functional connectivity. At broader catchment scales, the IC cold spot showed promise in identifying potential sediment sources, demonstrating its stability and potential in the upscaling analysis. Our findings support the role of vegetation and topography and the importance of structural and functional connectivity in erosional processes.
1. Litter quality is an important ecosystem factor, which may affect undergrowth species richness via decomposition and organic layers directly, but also via longer-term changes in soil pH and ...moisture. The impact of beech trees with low-degradable and hornbeam trees with highdegradable litter on biodiversity and soil characteristics was studied in ancient forests on decalcified marl, a parent material sensitive to changes in pH and clay content, and characteristic of large parts of western Europe. 2. Vegetation analysis clearly separated beech and hornbeam plots, and showed that species richness was consistently lower under beech. Low species richness under beech was associated with low pH, high mass of the organic layer and low soil moisture, which were all interrelated. 3. Development of the organic layer was affected by, not only litter quality, but also by pH levels and soil moisture. Under hornbeam, older organic matter increased from almost zero to 1 kg m⁻² in drier and more acid soil. Under beech tree litter decay was generally slow, but slowed further in acid soils, where older organic matter amounted to 4 kg m⁻² . 4. Soil moisture and pH levels were strongly related, possibly due to long-term soil development. Under hornbeam, which is more palatable to soil organisms, moisture, bulk density, clay content and pH were high. Acidification and clay eluviation may be counteracted by earthworms, which bring base cations and clay particles back to the surface, and stimulate erosion, so that the impermeable, clay-rich subsoil remains close to the surface. Soils remain base-rich and moist, which further stimulates litter decay and species richness. 5. The unpalatable beech showed low pH and clay content, and high porosity, air-filled pore space and depth to the impermeable subsoil. Acidification and clay eluviation may proceed uninhibited, because earthworm activity is low, and erosion limited by protective litter covers. This may lead to drier and more acid soils, which reduce litter decay and species richness even further. 6. Trees with low and high litter quality may thus act as an ecosystem engineer, and not only affect ecosystem functioning via mass of the organic layer, but also via longer-term changes in soil characteristics, which in turn affect species richness of the understorey.
•Cropland abandonment significantly affects soil physico-chemical properties.•Differences between revegetated practices after farmland abandonment occurred.•Afforestation triggered higher soil ...organic carbon than natural revegetation.•Grassland sites enhance the accumulation of soil organic carbon.•Labile fractions are higher in both vegetated sites than in grasslands.
Mediterranean mountains are sensitive agroecosystems that have suffered intense land use and land cover changes (LULCC) during the last century. From the middle of the twentieth century, most of the cultivated lands in Mediterranean mountains were abandoned, allowing the recovery of vegetation (through natural revegetation and afforestation programmes). To examine the effects of farmland abandonment, secondary succession (natural revegetation) and afforestation, an intensive soil sampling was carried out in the Araguás catchment (Central Spanish Pyrenees) including sparsely vegetated areas (badlands), grasslands, shrublands and afforested sites. LULCC were mapped, and soil physico-chemical properties were analysed in reference sites (unaltered areas during the last centuries) and in the different land uses. Likewise, the soil organic carbon (SOC) content in the bulk soils and in the fractions separated by density fractionation have been studied. This study evidenced that farmland abandonment led to a mosaic landscape with different land use and land covers. Results show that LULCC significantly affect soil physico-chemical properties (soil texture, stoniness, pH, SOC, total carbon, CorgN ratio, bulk density and field capacity). Significant differences were observed between secondary and afforested sites following farmland abandonment. Afforestation triggered higher SOC than shrubland sites (natural revegetation) (1.4 and 1.1% respectively), suggesting a slower process of organic matter accumulation after farmland abandonment in the natural revegetation compared to afforestation. The significant role of grassland sites for enhancing the accumulation of SOC has been also confirmed. The results showed also significant differences in the relative contribution of each organic fraction to the bulk SOC: the amount of labile fraction (free and occluded labile fractions) is significantly higher in afforested and shrubland sites (58.1 and 51.2% respectively) than in grassland sites (36.8%). Understanding the effects of LULCC on soil properties and SOC dynamics is essential when planning post-land management practices after farmland abandonment.
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