SSS8.2

Small natural features (SNFs) are small landmarks that differ in their abiotic characteristics from the surrounding landscape. SNFs, such as road verges, midfield islets, rocky outcrops and ancient burial mounds, provide safe havens for grassland specialist species in human-modified landscapes; therefore, their great ecological importance is in contrast to their small size. SNFs often have a high topographical heterogeneity and a related high variability in abiotic conditions; therefore, they provide a unique opportunity for establishing links between environmental heterogeneity (EH) and biodiversity. We investigated the EH components of topographically heterogeneous SNFs in a comprehensive framework, by linking environmental and biotic parameters. We studied ancient millennia-old burial mounds built by nomadic steppic tribes that are covered by semi-natural grasslands in the Pannonian (Hungary) and Continental (Bulgaria) biogeographical regions. We designated 16 study sites, each containing a few-metre-high mound with five microsites (top, north-, east-, south- and west-facing slopes) and a nearby plain grassland. At each microsite, we measured soil moisture, soil chemical properties, solar radiation and microclimate; and recorded the list and cover of vascular plants in a total of 480 plots. On the mounds, topographical heterogeneity was associated with sharp differences in microclimate and soil properties. Besides the contrast between mild north-facing and harsh south-facing slopes, east- and west-facing slopes also sustained unique microsites characterised by dynamic diurnal changes in air temperature and vapour pressure deficit. Various combinations of the EH components resulted in unique plant species compositions within the microsites, and supported the co-occurrence of species typical of contrasting habitat types, even within a couple of metres. By combining high-resolution measurements of abiotic factors with fine-scale vegetation sampling, our study provides evidence that widespread SNFs with complex topography harbour several grassland-specialist plant species and introduce a high level of EH to otherwise homogeneous plain landscapes, which cover one third of the global land area.

How to cite: Deák, B., Kovács, B., Rádai, Z., Apostolova, I., Kelemen, A., Kiss, R., Lukács, K., Palpurina, S., Sopotlieva, D., Báthori, F., and Valkó, O.: Heterogeneity in microclimate and soil parameters support diverse and unique vegetation on small natural features, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-598, https://doi.org/10.5194/egusphere-egu21-598, 2021.

Drylands are one of the largest biomes over the Earth, covering around 40% of land surface. These are water limited ecosystems where vegetation occupies the most favourable positions over the landscape. Less favourable areas are frequently covered by other biotic and abiotic components such as biological soil crusts, bare soil, or stones. During most rainfall events, runoff is generated in open areas (runoff sources) and redistributed through vegetation patches (runoff sinks), therefore increasing water and nutrient availability for plants. Water redistribution feedbacks determine vegetation coverage and productivity, modulate changes in its spatial distribution, and could ameliorate the predicted negative effects of climate change over these ecosystems.

The principal aim of this study was to quantify the impact of water redistribution processes on vegetation performance, and to evaluate how this effect varies in response to aridity. To achieve it, we analysed the relationships between runoff redistribution from open areas and vegetation productivity, by combining satellite information on vegetation state and topography. More precisely, we calculated Normalized Difference Vegetation Index (NDVI) dynamics during three hydrological years in 17 study sites along an aridity gradient in the SE of the Iberian Peninsula using SENTINEL 2 images. Then we used a DEM and a high spatial resolution vegetation map to derive a water redistribution index that simulate source-sinks interactions between vegetation and open areas. Finally, we analyse the relationship between, potential water redistribution and vegetation dynamics and how it varies along the aridity gradient.

We found a non-linear relationship between potential water redistribution and vegetation productivity. Overall, vegetation NDVI increases as potential water redistribution did, which demonstrated the importance of water redistribution processes on drylands vegetation performance. However, vegetation capacity to retain runoff water is limited and there is a clear threshold above which increased potential water redistribution does not promote vegetation productivity. Thresholds are caused by the limit capacity of vegetation to infiltrate run off when preferential flows are forming, increasing ecosystem connectivity, and involving local water losses for vegetation.  Therefore, an increase in open areas between vegetation patches could have a positive effect over vegetation through hydrological connectivity but until to a certain point in which global connectivity supposed water losses for plants. This process could have important effects under climate change, by controlling the resistance and resilience of vegetation in drylands ecosystems.

Acknowledgements. This research was supported by the FPU predoctoral fellowship from the Educational, Culture and Sports Ministry of Spain (FPU17/01886) REBIOARID (RTI2018-101921-B-I00) projects, funded by the FEDER/Science and Innovation Ministry-National Research Agency, and the RH2O-ARID (P18-RT-5130) funded by Junta de Andalucía and the European Union for Regional Development.

How to cite: Rodríguez Lozano, B., Rodriguez-Caballero, E., and Cantón, Y.: Open areas in patchy ecosystems: key spaces for vegetation survival., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15022, https://doi.org/10.5194/egusphere-egu21-15022, 2021.

The Brazilian semiarid have a diversity of soils and parent material, and this influences its flora. We observed different landscapes, and we revised papers about the vegetation surveys and their relationship with the landscape elements and their evolution. Brazil's semiarid area is between average latitudes 2º and 17º South, and longitudes 35º and 46º West, on the same latitude position of Amazon Forest and Savanna biomes, and one of the few sub-equatorial dryland regions. The semiarid biome is named Caatinga and characterized by Seasonally Dry Forests and Woodlands (SDFW), one of Brazil's most degraded and least studied biomes. It was considered low in species diversity and endemism for a long time, mainly because of the semiarid climate and low research quantities. Recent studies indicated high biodiversity, surpassing the Amazon concerning the number of plant species per area. The landscape presents vast rocky pediments scattered with Proterozoic crystalline massifs and elevated sedimentary basins forming table-like plateaus. Caatinga shows an average annual rainfall of around 600mm/year; marked by seasonal irregularity, the dry season occurs between August and October, and the rainy season concentrates during the summer. Orography effects are significant, and in the higher areas such as Plateaus, the precipitation can exceed 1000mm/year, and the lack of rainfall is distributed among depressions. Dry conditions started in the Miocene when the SDTFW arrived at the Brazil northeastern by connecting with two large SDTFW of South America. The crystalline shield is the basement of the Sertaneja Depression and the Borborema Plateau, both own soils related to semiarid conditions like Luvisols, Planosols, Phaeozems, Vertisols, and shallow soils, besides Lixisols at the colluvium materials at the foot of the hills.  These soils are mainly above granites, gneisses, and schists exposed during the notching of the Sertaneja surface, with some elevated areas by most resistant rocks. These areas harbor the most typical SDTFW of the Caatinga with deciduous and spiny woodlands or small forests, in the high altitude also influenced the vegetation assembly. On the Sedimentary regions, distinct floristic communities show seasonal dynamics not controlled exclusively by the rainfall supply; at least 50% of them maintain their leaves throughout the year. Flora presents independent events of ecological speciation over the last 1,5 Ma. Predominant soils are Ferrasols and Arenosols; the latter, in some cases, may represent an advanced stage of the Ferrasol with high clay loss. These soils did not form under current climatic conditions as they demand more and regular precipitation. We noted the close relationship between parent materials, soils, and vegetation controlling the landscape characteristics and their time and space evolution.

How to cite: Alves, G.: Dryland landscapes in Brazil: the relationship between soils and vegetation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12761, https://doi.org/10.5194/egusphere-egu21-12761, 2021.

Textural layering of soil plays an important role in distributing and regulating resources for plants in many semiarid and arid landscapes. However, the spatial patterns of textural layering and the potential effects on soil hydrology and water regimes are poorly understood, especially in arid sandy soil environments like the desert-oasis ecotones in northwestern China. This work aims to determine the distribution of textural layered soils, analyze the effects of different soil-textural configurations on water regimes, and evaluate which factors affect soil water infiltration and retention characteristics in such a desert-oasis ecotone. We measured soil water content and mineral composition in 87 soil profiles distributed along 3 transects in the study area. Constant-head infiltration experiments were conducted at 9 of the soil profiles with different texture configurations. The results showed that textural layered soils were patchily but extensively distributed throughout the study area (with a combined surface area percentage of about 84%). Soil water content in the profiles ranged from 0.002 to 0.27 g/cm³ during the investigation period, and significantly and positively correlated with the thickness of a medium-textured (silt or silt loam) layer (P < 0.001). The occurrence of a medium-textured layer increased field capacity (FC) and wilting point (WP), and decreased available water-holding capacity in soil profiles. Burial depth of the medium-textured layer had no clear effects on water retention properties, but the layer thickness tended to. In textural layered soils, smaller water infiltration rate and cumulative infiltration, and shallower depths of wetting fronts were detected, compared with homogeneous sand profiles. The thickness and burial depth of medium-textured layers had obvious effects on infiltration, but the magnitude of the effects depended on soil texture configuration. The revealed patterns of soil textural layering and the potential effects on water regimes may provide new insight into the sustainable management of rainfed vegetation in the desert-oasis ecotones of arid northwestern China and other regions with similar environments around the world.

How to cite: Sun, C., Zhao, W., Liu, H., Zhang, Y., and Zhou, H.: Effects of textural layering on water regimes in sandy soils in a desert-oasis ecotone, Northwestern China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9324, https://doi.org/10.5194/egusphere-egu21-9324, 2021.

Rocky desertification induced by severe deforestation has caused the water loss and soil erosion in karst regions in southeast China, limiting local social and economic developments. To prevent further rocky desertification, the farmland which had obtained by deforestation were abandoned for recovery. As soil quality improved by agriculture abandonment should be examined, it is necessary to investigate the dynamics of physical and chemical properties of soil in different ages after abandonment. In this study, 38 investigation sites were selected for soil sampling on the slopes in Longtan trough valley in Youyang County, Chongqing Municipality, China. The dominant plant species of the investigation sites were also noted during soil sampling. The sites were divided into seven age classes according to their abandonment time. Dynamics of water content, bulk density, pH, and concentration of available potassium, available phosphorus, available nitrogen, total nitrogen and organic matters were examined. It suggests that soil quality might be deteriorated right after abandonment and then improved from around 20 years after abandonment. Deterioration of soil quality may be induced by lack of plant coverage and exposure of rock outcrops which may accelerate water loss and swelling and shrinkage cycles of soil. After the formation of plant communities and litter layer above the ground, soil quality was then apparently improved. These findings can provide a potential guideline for recovery management in karst regions in southwest of China.

How to cite: Wang, K., Wang, Z., Wang, J., Li, J., Sun, B., Yang, H., and Zhang, P.: Dynamics of physical and chemical properties of soil after agricultural abandonment in a karst region in Southwest China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10468, https://doi.org/10.5194/egusphere-egu21-10468, 2021.

Recent detailed investigations of landforms, soils and surface deposits of the Borisoglebsk Upland northeastern slope within the Nero Lake basin (Central European Russia, Yaroslavl Region) allowed deciphering co-evolution of the major landscape components of the case study area since the Late Pleistocene. The Late Pleistocene to Holocene transition in the gully network was represented by relatively short but high-magnitude (up to 12 m) incision phase followed by significant infill till 6.5 ka. Absence of the well-developed early Holocene paleosols in the studied sections and cores suggests dominantly negative sediment budget. There is so far limited evidence of sedimentation over the first half of the Holocene. Discontinuous deposition with certain interruptions (but without distinct buried soil formation) occurred only within closed depressions and on gully fans. The second part of the Holocene prior to the widespread human settlement left more substantial traces in soil and sediment record. Despite the common perception of the pristine boreal forest landscapes to be geomorphologically stable due to erosion-protective role of woodland vegetation, several phases of dramatically increased soil and gully erosion rates have been identified. It is identified in soil bodies and sediments, both at locations dominated by denudation (evidences of multiple topsoil truncation in Atlantic and Subatlantic) and at zones of alternating incision and infill of small linear erosion features. Such extremes were most likely associated with combination of several triggers including natural forest fires and high-magnitude rainfall or snowmelt runoff events. There are several ¹⁴C dated layers of pyrogenic charcoal indicating pre-anthropogenic wildfire-induced incision and infill cycles during the middle and late Holocene.

The last phases of increased hillslope and fluvial activity within the study area can be related to increased human interference, starting from about 1600-900 years ago. The onset of cut-and-burn cultivation is independently established from available archeological evidences, dating of cut and burnt tree logs remnants, organic material buried by agrogenic colluvium and gully fans. Latest period of intensive gully growth can most likely be attributed to the XIX^th Century land tenure reform, when most of the study area gullies experienced significant linear growth, bottom incisions and appearance of several new gully branches. The most recent trend of soil and gully erosion has been evaluated by ¹³⁷Cs sediment tracing, soil empirical modeling and comparison of historical and modern maps, airborne photos and satellite images. Rates of soil redistribution on slopes decreased significantly over the last several decades due to combination of natural and anthropogenic impacts: 1) decreased spring snowmelt runoff caused mainly by generally lowered thickness of seasonally frozen topsoil layer; 2) arable land abandonment or shift from row crops and cereals to perennial grass-dominated crop rotations in the post-Soviet period. In addition, local short-term (from several years to within-year) cycles of relatively low-magnitude (not exceeding ±1 m range) incision and infill in gullies are often triggered by biogenic activities, namely beaver dam constructions and breaches and local log jams.

The study is supported by the Russian Science Foundation (Project No. 19-77-10061) and Russian Foundation for Basic Research (Project No. 19-29-05238).

How to cite: Belyaev, V., Shorkunov, I., Garankina, K., Mergelov, N., Shishkina, Y., Lobkov, V., Semochkina, A., and Van, V.: Holocene history of boreal forest landscapes of the Central European Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14681, https://doi.org/10.5194/egusphere-egu21-14681, 2021.

Vegetation protects soil against erosion by intercepting rain, increasing flow resistance, promoting soil infiltration and improving soil strength. However, the representation of vegetation dynamics in Landform Evolution Models (LEMs) is very simplified, which could result in over/under estimations of erosion rates. Here we use a new model framework to study the differences in erosion rates when considering different processes associated with vegetation protection. We analysed the changes in erosion rates by considering: (1) the effect of root biomass on soil erodibility, (2) the effect of leaf cover on soil diffusivity, (3) the effect of litter on flow resistance, and (4) the effect of soil carbon on soil infiltration. We implemented the model in an open-forest savannah catchment situated in Howard Springs (Northern Territory, Australia) and ran simulations using daily time step for 100 years. The modelling framework comprises a coupled Landform Evolution Model (LEM) with dynamic biochemical vegetation and biomass pools dynamics. Our results show that bare soil conditions generate a 100% increase in erosion compared to those using the full dynamic vegetation (that include protection from all carbon pools). We find that the effects from vegetation protection and rainfall are asynchronous, with substantial vegetation growth typically lagging behind substantial rainfall events. This means that rainfall events at the beginning of the rainy season contribute heavily to erosion. For the specific case of Howard Springs, leaves and roots are the most important factors that control erosion except when they are not fully recovered after the dry season. At this time the effect of the litter, and to a lesser extent the soil carbon, turn out to be determinant. Overall, this study highlights the importance of including dynamic vegetation and the effects of the biomass pools on controlling erosion in order to estimate erosion rates.

How to cite: Quijano Baron, J., Saco, P., and Rodriguez, J.: Asynchronous effects of vegetation protection on landform evolution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14037, https://doi.org/10.5194/egusphere-egu21-14037, 2021.