Soil Heterogeneity Research Articles

Unsaturated soil nailing wall system reliability analysis using random finite element

This study focuses on the evaluation of stability for a typical unsaturated Soil Nailing Wall System (SNWS), considering variations in soil shear strength, suction, and elasticity modulus. The Random Finite Element Method (RFEM) is employed to derive the reliability indices for stability modes, including Global Stability (GS), Lateral Displacement Stability (LDS), Tensile Strength Stability (TSS), and Pullout Resistance Stability (PRS), which serve as essential components of the SNWS. Finally, the Sequential Compounding Method (SCM) is utilized to combine these modes of stability and their direct influence on the system reliability index. The results show although the maximum Coefficient of Variation (COV) of the soil parameters was 11%, the COV of lateral displacements at the top of the wall was obtained as 19%, which shows the significant influence of considering the soil heterogeneity. Furthermore, uncertainties of elasticity modulus and matric suction lead to an increase in GS, LDS, and PRS. The calculated system reliability index was found to be lower than the lowest reliability index of the individual components. The findings indicate that while the inclusion of matric suction and elasticity modulus may enhance the mean values of stability modes, there is a possibility that the system reliability index could decrease.

In situ visualization on the mobility of mineral associated organic matter in a microfluidics-based heterogeneous soil aggregate structure

The mobility of different types of soil organic matter (SOM), including dissolved organic matter (DOM) and mineral associated organic matter (MAOM), along the soil profile in response to infiltration flow can significantly affect the carbon pools in subsoil. In addition, the soil heterogeneity on the pore-scale, comprising pore spaces within the intra-aggregate matrix and preferential pathways within inter-aggregate zones, can also affect the mobility of SOM. This is especially the case for clay-sized MAOM. However, the quantitative understanding of the clay-sized MAOM mobility in presence of pore-scale heterogeneity remains elusive. This study designed a novel microfluidic device to track the pore-scale distribution and mobility of fluorescence labeled clay-sized MAOM in heterogeneous soil pore structures. Results showed that the MAOM mobility was significantly lower in the intra-aggregate zones compared with in the inter-aggregate zones. Only 4.8 % to 47.9 % of MAOM in the intra-aggregate region was mobilized at high leaching flow rates of 81 to 163 mm/d. Moreover, colloid mobilization induced by shearing rather than solute desorption followed by solute dilution is expected to be the major factor facilitating the mobilization of clay-sized MAOM. This study demonstrated a new experimental protocol allowing the in-situ visualization and quantification of OMs mobility in presence of pore-scale heterogeneity. Moreover, our findings also highlighted the potential importance of heterogeneous mobility of clay-sized MAOMs that facilitated by the colloid transport on the SOM turnover and distribution.

Time domain reflectometry coil probes for measuring thin surface layer soil moisture: Field tests over 21 years (2002–2022) under highly variable climate conditions in Mongolia

A coil probe (CP) for time-domain reflectometry (TDR) with a sensor length of 40 mm (CP40) was developed for long-term field soil moisture measurements in a thin surface soil layer (0–3 cm depth). In laboratory, soil moisture measurements of CP40 were nearly identical to those of a traditional two-rod type TDR (2RTDR) probe (rod length: 15 cm, diameter: 0.3 cm, spacing: 3 cm). The CP40 measurement accuracy was between 0.01 m3/m3 and 0.03 m3/m3. For long-term field soil moisture measurements, five CP40 units were installed in the highly wetted soil at the Sanzai site (SS), which is in the permafrost area of the Taiga, and dry soil at the Mandalgobi site (MGS) in the semi-arid area of Mongolia. Four units accurately measured soil moisture at both sites over six years (2002–2007and 2008–2009). Three units succeeded in conducting precisely continuous soil moisture measurements between 2008 and 2022 at the MGS. Two units successfully measured soil moisture over 21 years at both the sites. The representativeness of the CP40 soil moisture measurements in highly wetted soils was low because of heavy rainfall and soil heterogeneity. The accuracy of CP40 soil moisture measurements in highly wetted soils was slightly lower than that of the traditional 2RTDR probe. However, the accuracy of the CP40 soil-moisture measurements in the dry soil was comparable to that of the traditional 2RTDR probe. CP40 units are durable and their field soil moisture measurements demonstrate stable and precise performance (bias, RMSE), even under severe environmental conditions.

Growing on patch boundaries of heterogeneous soils promotes root growth but not the total biomass of naturalized alien and native plants

Growing on patch boundaries of heterogeneous soils promotes root growth but not the total biomass of naturalized alien and native plants

Effects of nZVI on the migration and availability of Cr(VI) in soils under simulated acid rain leaching conditions

Hexavalent chromium, Cr(VI), is a ubiquitous toxic metal that can be reduced to Cr(III) by nano-zero-valent iron (nZVI). Finding out effects of continuous rainfall leaching on the Cr(VI) release and availability remains a problem, needing to be addressed. Whether the Cr(VI) reduction by nZVI and continuous rainfall leaching lead to localized heterogeneity in soil is unclear. Therefore, two in situ high-resolution (HR) techniques of the diffusive gradients in thin-films (DGT) and planar optode were combined with ex situ sampling experiments here. Results demonstrate that nZVI decreased Cr(VI) leaching by 5.60–8.50 % compared to control soils. DGT-measured concentrations of Cr(VI), CDGT-Cr(VI), ranged from 7.31 to 19.4 μg L-1 in the control soils, increasing with depth while CDGT-Cr(VI) in nZVI-treated soils (2.41–6.18 μg L-1) decreased or remained stable with depth. However, simulated acid-rain leaching increases CDGT-Cr(VI) by 1.61-fold in nZVI-treated soils, negatively affecting the remediation. DGT measurements in bulk soils using disc devices are better at capturing the change of Cr(VI) availability at different conditions, whereas 2D-HR DGT mappings did not characterize significant mobilization of Cr(VI) at the micro-scale. These findings emphasize the importance of monitoring Cr(VI) release and availability in remediated soil under acid-rain leaching conditions for effective environment management.

Mapping agricultural soil water content using multi-feature ensemble learning of GPR data

Soil water content (SWC) is significant for understanding and evaluating the conditions of soils and plants. Since traditional methods such as time domain reflectometry (TDR) and neutron probes have significant drawbacks such as limitations in spatial resolution, detection depth, efficiency, and non-destruction, ground penetrating radar (GPR) has become a potential method in SWC estimation. Many features extracted from GPR data in the time and frequency domain have been proven to be sensitive to the SWC and can further achieve the estimation of it. However, the methods based on these features are easy to be interfered with by noise and the heterogeneity in soils. This article aims to solve this problem by including more features and integrating these features for a joint estimation. Firstly, we study the relationships between SWC and seven features extracted from GPR data. Consequently, we propose to include new features, i.e. the loss tangent feature and the time-frequency features, in the SWC inversion. Secondly, we achieve the multi-feature ensemble learning based on the Adaboost R. method, which largely enhances the accuracy of SWC inversions compared to the single-feature estimations. During the numerical test, we establish the stochastic medium to model the heterogeneity in the real soil. The test verifies the effectiveness and the robustness of the proposed method. Finally, a field experiment is performed on the transition zone of no-tillage and deep-ploughing croplands. A 2-D SWC map is obtained which distinctly presents the SWC difference between the two regions. Our study provides a new approach to improve the accuracy of SWC estimation using GPR.

Mosaic coexistence of two subalpine grassland types as a consequence of soil nutrient heterogeneity

High-mountain areas often exhibit high soil heterogeneity, which allows for the close coexistence of plant species and communities with contrasting resource requirements. This study investigated the nutritional factors driving the mosaic distribution of Nardus stricta L. grasslands and chalk grasslands dominated by forbs in the subalpine southern Pyrenees (Spain). The concentrations of C, N, P, S, K, Ca and fiber fractions in herbage were analyzed in relation to soil nutrient availability; soil β-glucosidase, urease, phosphatase and arylsulfatase activities; and plant species and functional type compositions. The chalk grassland showed higher N:P ratios in herbage and higher enzyme demand for P relative to N in the soil, which indicates a greater limitation of P versus N compared to Nardus grassland. This limitation was related to the higher soil and plant Ca levels in the chalk grassland, where the calcareous bedrock lies close to the soil surface. In the Nardus grasslands, the alleviation of P limitation translated into increased productivity and the replacement of forbs with taller graminoids rich in structural carbohydrates, which was mirrored by greater β-D-glucosidase activity. The plant N:K and P:K ratios indicated potential K deficiency in both grasslands, which resulted from decreased uptake of K in competition with Ca, as indicated by the correlation between plant K and the soil K+:Ca2+ ratio. Our results highlight the effect of the heterogeneity of soil nutrient constraints, mediated by stoichiometry and dependent on microtopography, on the biodiversity of high-mountain ecosystems.

Neighbour effects on plant biomass and its allocation for forbs growing in heterogeneous soils

Abstract Focal plants are considerably affected by their neighbouring plants, especially when growing in heterogeneous soils. A previous study on grasses demonstrated that soil heterogeneity and species composition affected plant biomass and above- and belowground allocation patterns. We now tested whether these findings were similar for forbs. Three forb species (i.e. Spartina anglica, Limonium bicolor and Suaeda glauca) were grown in pots with three levels of soil heterogeneity, created by alternatively filling resource-rich and resource-poor substrates using small, medium or large patch sizes. Species compositions were created by growing these forbs either in monocultures or in mixtures. Results showed that patch size × species composition significantly impacted shoot biomass, root biomass and total biomass of forbs at different scales. Specifically, at the pot scale, shoot biomass, root biomass and total biomass increased with increasing patch size. At the substrate scale, shoot biomass and total biomass were higher at the large patch size than at the medium patch size, both in resource-rich and resource-poor substrates. Finally, at the community scale, monocultures had more shoot biomass, root biomass and total biomass than those in the two- or three-species mixtures. These results differ from earlier findings on the responses of grasses, where shoot biomass and total biomass decreased with patch size, and more shoot biomass and total biomass were found in resource-rich than resource-poor substrates. To further elucidate the effects of soil heterogeneity on the interactions between neighbour plants, we advise to conduct longer-term experiments featuring a variety of functional groups.

Nonlinear Static Soil-Structure Interaction Analysis of Time-Dependent Soil Deformation Effects on RC Structures

Soil response and superstructure behavior are two major factors influencing the long-term performance of reinforced concrete (RC) structures. Maintaining the structural integrity of these structures over time is crucial due to the complex static interactions between the soil and the structure. This study uses a finite element model to examine the stability of RC structures, considering the long-term static interactions between the nonlinear behavior of the soil and the structure. Numerical simulations are performed on real RC beam constructions at serviceability limit states (SLS) under various loading scenarios in both homogeneous and heterogeneous soil conditions. The parametric study's results indicate that soil heterogeneity and static soil-structure interactions significantly influence the design of RC structures. The nonlinear behavior of the soil over time intensifies these impacts further. This study shows how important it is to think about different types of soil and how they interact with structures when they are not moving. This is especially true when it comes to soil that is easily compressed and changes shape over time in a nonlinear way. By incorporating these factors, the research highlights the critical need to integrate soil heterogeneity and static interaction into the design process to ensure the stability and safety of RC structures. Ultimately, the results demonstrate that accounting for these complex interactions can greatly improve the durability and reliability of RC structures in diverse soil conditions.

Two-phase system model to predict hydrophobic organic compound partition to heterogeneous soil dissolved organic matter across China

Soil dissolved organic matter (SDOM) is an important part of the DOM pool in terrestrial systems, influencing the transport and fate of many pollutants. In this study, SDOMs from different regions across China were compared by a series of spectroscopic methods, including UV–vis spectroscopy, fluorescence spectroscopy, and Fourier transform infrared (FTIR) spectroscopy, and the hydrophobicity was quantified by partition coefficients of SDOM in the aqueous two-phase system (KATPS). The molecular weight, aromaticity, and hydrophobicity of SDOM from different regions exhibited strong heterogeneity, KATPS combined with UV–vis and fluorescence indices can be readily used for differentiating heterogeneous SDOM, and SDOMs were compositionally and structurally different from DOMs in aquatic systems based on spectral characterization. Importantly, the two-phase system (TPS) model has only been validated by DOMs in freshwater systems, and good organic carbon‒water partition coefficient (KOC) predictive power (RMSE = 0.11) could be provided by the TPS model when applied to heterogeneous SDOM without calibration, showing its broad applicability. Our results demonstrate the applicability of the TPS model for predicting the sorption behavior of terrestrial DOM, broadening the application scope of the TPS model and indicating its potential as a routine model for the risk assessment of hydrophobic organic compounds (HOCs) in organic contaminated sites.

A hyperbolic–elliptic PDE model and conservative numerical method for gravity-dominated variably-saturated groundwater flow

Richards equation is often used to represent two-phase fluid flow in an unsaturated porous medium when one phase is much heavier and more viscous than the other. However, it cannot describe the fully saturated flow for some capillary functions without specialized treatment due to degeneracy in the capillary pressure term. Mathematically, gravity-dominated variably saturated flows are interesting because their governing partial differential equation switches from hyperbolic in the unsaturated region to elliptic in the saturated region. Moreover, the presence of wetting fronts introduces strong spatial gradients often leading to numerical instability. In this work, we develop a robust, multidimensional mathematical model and implement a well-known efficient and conservative numerical method for such variably saturated flow in the limit of negligible capillary forces. The elliptic problem in saturated regions is integrated efficiently into our framework by solving a reduced system corresponding only to the saturated cells using fixed head boundary conditions in the unsaturated cells. In summary, this coupled hyperbolic–elliptic PDE framework provides an efficient, physics-based extension of the hyperbolic Richards equation to simulate fully saturated regions. Finally, we provide a suite of easy-to-implement yet challenging benchmark test problems involving saturated flows in one and two dimensions. These simple problems, accompanied by their corresponding analytical solutions, can prove to be pivotal for the code verification, model validation (V&V) and performance comparison of simulators for variably saturated flow. Our numerical solutions show an excellent comparison with the analytical results for the proposed problems. The last test problem on two-dimensional infiltration in a stratified, heterogeneous soil shows the formation and evolution of multiple disconnected saturated regions.

Multiscale pore‐network reconstruction of a fine‐textured heterogeneous soil

AbstractDigital samples offer many opportunities to study subsurface fluid flow and contaminant transport processes. The pore size distribution of especially fine‐textured porous media often covers many orders of magnitude in the length scale, which makes accurate microCT scanning and modeling of the underlying processes difficult. When a single‐resolution image is not capable of capturing all relevant details of a sample, one should scan the sample, or selected parts of it, at different resolutions. Combining multiple resolutions into one single sample for subsequent pore‐scale modeling is generally not possible due to limitations in computer memory and speed, thus making it necessary to create a simpler sample containing relevant information from the parent networks. We imaged four samples using different resolutions to capture the multiscale heterogeneity of a fine‐textured soil and combined them into one overall digital sample based on the original pore networks. The parent networks were characterized using their geometrical properties, correlations between these properties, and connectivity functions describing the network topologies. Our approach creates stochastic networks of arbitrary size with the same flow properties as the parent network. The method, implemented using the PoreStudio pore network model, repeatedly integrates information at two subsequent scales, with the resulting digital sample having the same hydraulic properties as the original samples. The procedure leads to more useful three‐dimensional digital models, facilitating basic analyses of underlying pore size distributions. Porosity calculations were compared with direct measurements, while those for the hydraulic conductivity were compared with estimates based on the particle size distribution and nearby field data.

Evapotranspiration estimation using high-resolution aerial imagery and pySEBAL for processing tomatoes

AbstractThe use of high-resolution aerial imagery for assessing actual crop evapotranspiration $$ \left({ET}_{a}\right)$$ holds the potential to optimize the use of limited water resources in agriculture. Despite this potential, there is a shortage of information regarding the effectiveness of energy balance algorithms, initially designed for satellite remote sensing in estimating $$ {ET}_{a}$$ using aerial imagery. This study addresses this gap by employing the remote sensing model pySEBAL (Surface Energy Balance Algorithm for Land) in conjunction with high-resolution aerial imagery to estimate $$ {ET}_{a}$$ for processing tomatoes. Throughout the 2021 growing season, an aircraft captured multispectral and thermal imagery over a processing tomato field near Esparto, California, USA. Simultaneously, an eddy covariance flux tower within the field measured high-frequency turbulent fluxes and low-frequency biometeorology variables essential for evaluating the energy balance. The comprehensive assessment of energy balance components, including $$ {ET}_{a}$$, yielded compelling evidence that pySEBAL accurately estimated $$ {ET}_{a}$$ at high spatial resolution. The root mean square error (RMSE) and normalized RMSE for various energy balance components were as follows: 33 W m− 2 (12%) for latent heat flux, 29 W m− 2 (35%) for sensible heat flux, 24 W m− 2 (4%) for net radiation, and 10 W m− 2 (15%) for soil heat flux. Additionally, $$ {ET}_{a}$$ exhibited an RMSE and NRMSE of 0.26 mm d− 1 (6%). Moreover, the spatial mapping of $$ {ET}_{a}$$ across the processing tomato field visually depicted the spatial variability associated with irrigation scheduling, crop development, areas affected by disease, and soil heterogeneity. This research underscores the value of high resolution spatial aerial imagery and pySEBAL algorithm for estimating $$ {ET}_{a}$$ variability in the field, a crucial aspect for guiding precision irrigation management and ensuring the optimal use of limited water resources in agriculture.

A Numerical Analysis of the Non-Uniform Layered Ground Vibration Caused by a Moving Railway Load Using an Efficient Frequency–Wave-Number Method

The ground vibration caused by the operation of high-speed trains has become a key challenge in the development of high-speed railways. In order to study the train-induced ground vibration affected by geotechnical heterogeneity, an efficient frequency–wave-number method coupled with the random variable theory model is proposed to quickly obtain the numerical results without losing accuracy. The track is regarded as a composite Euler–Bernoulli beam resting on the layered ground, and the spatial heterogeneity of the ground soil is considered. The ground dynamic characteristics of an elastic, layered, non-uniform foundation are investigated, and numerical results at three typical train speeds are reported based on the developed Fortran computer programs. The results show that as the soil homogeneity coefficient increases, the peak acceleration continuously decreases in the transonic case, while it gradually increases in the supersonic case, and the ground acceleration spectrum at a far distance obviously decreases; the maximum acceleration occurs at the track edge, and a local rebound in vibration attenuation occurs in the supersonic case.

Spatial-temporal variability in nitrogen use efficiency: Insights from a long-term experiment and crop simulation modeling to support site specific nitrogen management

Within-field soil heterogeneity can lead to large variation in nitrogen use efficiency (NUE). Crop simulation models provide a multi-faceted approach to management considering both soil and plant interactions. However, research using crop models for investigating within field variation in NUE is limited, in part because of challenges quantifying spatially variable soil model parameters. Here soil apparent electrical conductivity (ECa) and measured soil properties were used to map spatial variations in soil characteristics across a Long-Term Experiment in Norfolk, England. The relationship between plot ECa across the 3 ha experiment and agronomic data across three different nitrogen rates (0, 110, and 220 kg N ha-1) over five wheat years (2010–2020) was quantified. The Sirius crop model was parameterized for two soils representing the extremes of ECa. Sirius was validated using recorded plot data. Site-specific optimal nitrogen and associated leaching risks were simulated across 29 years of weather data. Variation in soil properties had significant impact on measured NUE. At 220 kg N ha-1 mean observed yields across 5 years ranged from 9.0 to 10.7 t ha-1 and grain protein from 11.6% to 11% on the low EC and high EC plots, respectively. On average fertiliser grain N recovery was 19.7 kg N ha-1 lower on the low ECa plots. Sirius simulated the variation in yield, grain protein and grain N recovery to a good level of accuracy with RRMSE of 19.5%, 15.4% and 19.5%, respectively. Simulated optimal nitrogen on the low EC soils was on average 12 kg N ha-1 lower, with >1 in 4 years with optimal nitrogen <200 kg N ha-1. Our work demonstrated that using a combination of proximal soil EC scans and targeted soil sampling we can optimize the data requirements for model parameterisation to support site-specific N management.

Microtopography effects on pedogenesis in the mudstone-derived soils of the hilly mountainous regions

Topography is a critical factor that determines the characteristics of regional soil formation. Small-scale topographic changes are referred to microtopographies. In hilly mountainous regions, the redistribution of water and soil materials caused by microtopography is the main factor affecting the spatial heterogeneity of soil and the utilization of land resources. In this study, the influence of microtopography on pedogenesis was investigated using soil samples formed from mudstones with lacustrine facies deposition in the middle of the Sichuan Basin. Soil profiles were sampled along the slopes at the summit, shoulder, backslope, footslope, and toeslope positions. The morphological, physicochemical, and geochemical attributes of profiles were analyzed. The results showed that from the summit to the toeslope, soil thickness increased significantly and profile configuration changed from A–C to A–B–C. The total contents of Ca and Na decreased at the summit, backslope, and footslope, while the total contents of Al, Fe and Mg showed an opposite trend. On the summit and shoulder of the hillslope, weathered materials were transported away by gravity and surface erosion, exposing new rocks. As a result, soil development in these areas was relatively weak. In flat areas such as the footslope and toeslope with sufficient water conditions, the addition of weathered components and the prolonged contact between water, soil, and sediment led to further chemical weathering, resulting in highly developed characteristics. Microtopography may influence physicochemical properties, chemical weathering, and redistribution of water and materials, causing variations in pedogenic characteristics at different slope positions.

Effective strategies for reclaiming soda-saline soils: Field experimentation and practical applications in Southeast Kazakhstan

Soda-saline soils pose significant challenges to agricultural productivity, particularly in regions like the foothill plain of the Ili Alatau in southeast Kazakhstan. In this study, we examined the effectiveness of different ameliorants, including phosphogypsum, elemental sulfur, and sulfuric acid, in reclaiming soda-saline soils and enhancing crop yields. The study was conducted under real climatic and production conditions at the "Amiran" LLP farm. Using a randomized complete block design, we assessed the impact of these ameliorants on soil composition and alfalfa yield over two cutting cycles. The experiment involved the application of phosphogypsum, elemental sulfur, and sulfuric acid to designated plots within the farm, each covering an area of 15m2. Soil samples were collected before and after treatment to assess changes in soil composition and salinity. Alfalfa, a resilient perennial crop, was selected for cultivation due to its tolerance to adverse soil conditions. Our findings reveal that all tested ameliorants successfully neutralized the toxic environment of soda-saline soils, resulting in improved soil conditions and increased crop productivity. Phosphogypsum treatment led to a reduction in bicarbonate and carbonate ions, an increase in sulfate ion concentration, and improved soil structure. Elemental sulfur incubation decreased bicarbonate and carbonate ions, further reducing absorbed sodium levels and enhancing soil fertility. Sulfuric acid treatment provided rapid results in reducing alkalinity and increasing sulfate ion concentration, leading to significant improvements in soil quality and crop yield. However, the reclamation of soda-saline solonetzes presented challenges related to soil heterogeneity and poor water permeability. To address these challenges, we recommend the implementation of mechanical destruction of the solonetz soil horizon and deep soil loosening, accompanied by the addition of ameliorants. In conclusion, our study demonstrates the potential of phosphogypsum, elemental sulfur, and sulfuric acid as effective ameliorants for reclaiming soda-saline soils and improving agricultural productivity in challenging environments. By adopting recommended reclamation strategies, farmers can overcome soil limitations and achieve sustainable crop production in regions affected by soda-saline soil degradation.

Large deformation assessment of the bearing capacity factor for rigid footing: effect of soil heterogeneity

Large deformation assessment of the bearing capacity factor for rigid footing: effect of soil heterogeneity

Subsurface flow model for estimating 2D wetting pattern in drip irrigation

AbstractNumerical model using 2D Richard’s equation in cylindrical polar coordinate system was developed to assess the soil wetting patterns in a drip irrigation system. A fully implicit finite‐difference scheme was used to solve equations with suitable initial and boundary conditions. The developed model was validated with an experimental result available in the literature, which shows a high level of concordance with low values of RMSE and R2 greater than 0.93 for all discharge rates. Furthermore, the versatility and applicability of the model were demonstrated for complex subsurface conditions considering homogeneous and heterogeneous soil profiles. Water ponding on the surface was observed in clay loam soil, contrasting with deep percolation in sandy loam soil. This underscores the significance of adjusting both discharge rate and irrigation frequency in accordance with prevailing soil conditions.

Influence of Picea Abies Logs on the Distribution of Vascular Plants in Old-Growth Spruce Forests

The deadwood contributes to an increase in soil heterogeneity due to the changing the microrelief (by the formation of windthrow-soil complexes), as well as changes in physical and chemical characteristics of decaying wood directly during xylolysis. We hypothesized that fallen logs as an element of microrelief influence the species composition and cover structure of vascular plants. We studied the influence of Picea abies (L.) Karst fallen logs of moderate and advanced decay stages on the horizontal distribution and heterogeneity of vascular plant cover in different microsite types (small boreal grass type, blueberry type, small boreal grass-blueberry type, herbs, and blueberry type) in old-growth middle taiga spruce forest in the Kivach State Nature Reserve (Republic of Karelia, Russia). The fallen deadwood acts as a factor of heterogeneity, causing reversible changes in the homogeneity of the original plant cover. The decaying logs influence the horizontal distribution of small herbs by changing the occurrence and density of shoots of Oxalis acetosella L., Maianthemum bifolium (L.) F.W. Schmidt, Vaccinium myrtillus L., and Vaccinium vitis-idaea L., as well as the occurrence of Luzula pilosa (L.) Willd. and Calamagrostis arundinacea (L.) Roth. Its impact on the heterogeneity parameters can be traced up to 20 cm from the log. The differences in vascular plant cover between fallen logs and the surrounding forest floor depend on the soil conditions of the microsite. The heterogeneity of conditions created by the logs smoothed out with increasing decay class, resulting in decreasing differences in the heterogeneity parameters of vascular plant cover between deadwood and forest floor. The changes in the homogeneity of the initial vascular plant cover by deadwood and the gradual smoothing of heterogeneity between the logs and the forest floor in rich and poor conditions have different, mainly opposite, trends. Finally, the structure of the vegetation cover reaches a state that is typical of particular growth conditions beyond deadwood.