Conditional reconstruction: An alternative strategy in digital rock physics

Digital rock physics (DRP) is a newly developed method based on imaging and digitizing of 3D pore and mineral structure of actual rock and numerically computing rock physical properties, such as permeability, elastic moduli, and formation factor. Modern high-resolution microcomputed tomography scanners are used for imaging, but these devices are not widely available, and 3D imaging is also costly and it is a time-consuming procedure. However, recent improvements of 3D reconstruction algorithms such as crosscorrelation-based simulation and, on the other side, the concept of rock physical trends have provided some new avenues in DRP. We have developed a modified work flow using higher order statistical methods. First, a high-resolution 2D image is divided into smaller subimages. Then, different stochastic subsamples are generated based on the provided 2D subimages. Eventually, various rock physical parameters are calculated. Using several subsamples allows extracting rock physical trends and better capturing the heterogeneity and variability. We implemented our work flow on two DRP benchmark data (Berea sandstone and Grosmont carbonate) and a thin-section image from the Grosmont carbonate formation. Results of realization models, pore network modeling, and autocorrelation functions for the real and reconstructed subsamples reveal the validity of the reconstructed models. Furthermore, the agreement between static and dynamic methods indicates that subsamples are representative volume elements. Average values of the subsamples’ properties follow the reference trends of the rock sample. Permeability trends pass the actual results of the benchmark samples; however, elastic moduli trends find higher values. The latter can be due to image resolution and voxel size, which are generated by imaging tools and reconstruction algorithms. According to the obtained results, this strategy can be introduced as a valid and accurate method where an alternative method for standard DRP is needed

Image-Based Modeling of Granular Porous Media

We propose a new method of modeling granular media that utilizes a single two- or three-dimensional image and is formulated based on a Markov process. The process is mapped onto one that minimizes the difference between the image and a stochastic realization of the granular medium and utilizes a novel approach to remove possible unphysical discontinuities in the realization. Quantitative comparison between the morphological properties of the realizations and representative examples indicates excellent agreement

Conditional reconstruction: An alternative strategy in digital rock physics

Digital rock physics (DRP) is a newly developed method based on imaging and digitizing of 3D pore and mineral structure of actual rock and numerically computing rock physical properties, such as permeability, elastic moduli, and formation factor. Modern high-resolution microcomputed tomography scanners are used for imaging, but these devices are not widely available, and 3D imaging is also costly and it is a time-consuming procedure. However, recent improvements of 3D reconstruction algorithms such as crosscorrelation-based simulation and, on the other side, the concept of rock physical trends have provided some new avenues in DRP. We have developed a modified work flow using higher order statistical methods. First, a high-resolution 2D image is divided into smaller subimages. Then, different stochastic subsamples are generated based on the provided 2D subimages. Eventually, various rock physical parameters are calculated. Using several subsamples allows extracting rock physical trends and better capturing the heterogeneity and variability. We implemented our work flow on two DRP benchmark data (Berea sandstone and Grosmont carbonate) and a thin-section image from the Grosmont carbonate formation. Results of realization models, pore network modeling, and autocorrelation functions for the real and reconstructed subsamples reveal the validity of the reconstructed models. Furthermore, the agreement between static and dynamic methods indicates that subsamples are representative volume elements. Average values of the subsamples’ properties follow the reference trends of the rock sample. Permeability trends pass the actual results of the benchmark samples; however, elastic moduli trends find higher values. The latter can be due to image resolution and voxel size, which are generated by imaging tools and reconstruction algorithms. According to the obtained results, this strategy can be introduced as a valid and accurate method where an alternative method for standard DRP is needed

Ecological sustainability in rangelands : the contribution of dung beetles in secondary seed dispersal (case study: Chaharmahal and Bakhtiari province, Iran)

Ecological sustainability has been recognized as one of the main aspects of sustainable development of rangelands, at which different kinds of animal including insects, make substantial contributions. Dung beetles, known as dung-visiting insects, play several key roles in many ecological functions from which benefit both terrestrial ecosystems and human population. Specifically, they benefit rangelands through reducing greenhouse gas emission, nutrient cycling, plant growth enhancement, trophic regulation and pollination and secondary seed dispersal. This study examined secondary seed dispersal as one of the ecological functions of dung beetles, in Chaharmahal and Bakhtiari province, Iran. We applied an experimental approach to measure ecological function (i.e. seed removal) by functional groups of dung beetles. We tested whether functional dung beetle groups influence secondary seed dispersal differently. Through repeated standardized samples of sheep dung, data obtained regularly during two different months August and November in 2013. The results show that dung beetles play a role in secondary seed dispersal. However, it is affected by seed size, so that seed removal increased in the order of, large, medium and small size, respectively. The significant differences between treatments were found for small seeds in the both months. More seeds were dispersed from treatment t02 (all combinations of functional groups except large rollers) in August, while in November more seeds from treatments t01 (dwellers plus large and small tunnelers plus large and small rollers) and t03 (the combinations of dwellers plus small tunnelers, and small rollers) were removed. As a conclusion, it is suggested that if it is to guarantee the ecological sustainability of rangelands, paying attention to the ecological functions of dung beetles is crucial

Functionally richer communities improve ecosystem functioning: Dung removal and secondary seed dispersal by dung beetles in the Western Palaearctic

Aim: In several ecosystems, the diversity of functional species traits has been shown to have a stronger effect on ecosystem functioning than taxonomic diversity alone. However, few studies have explored this idea at a large geographical scale. In a multisite experiment, we unravelled the relationship between ecosystem function and functional completeness of species assemblages using dung beetles as a model group, focusing on dung removal and secondary seed dispersal. Location: Seventeen grassland locations across the Western Palaearctic. Methods: We used a randomized block design with different exclosure types to control the dung and seed removing activities of individual functional groups of the local dung beetle assemblage. We classified dung beetle species according to resource specialization and into functional groups based on dung processing behaviour (dwellers, tunnellers, rollers) and body size (small, large). Additionally, we assessed the role of other soil macro‐invertebrates. By sampling the dung beetle community and measuring the remaining dung and seeds after the experiment, the impact of each functional group was estimated. Results: Dung beetle assemblages differed along a north–south and east–west gradient. Dwellers dominated northernmost sites, whereas at lower latitudes we observed more tunnellers and rollers indicating a functional shift. Resource specialists were more abundant in southern and eastern areas. Overall, functional group diversity enhanced dung removal. More dung (+46.9%) and seeds (+32.1%) were removed in the southern sites and tunnellers and rollers were more effective. At the northernmost sites, where tunnellers were scarce or absent, other soil macro‐invertebrates removed the majority of dung. Main conclusions: The conservation of functionally complete dung beetle assemblages is crucial to maintain the ecosystem functions provided by dung beetles. Given the latitudinal variation in functional group diversity, it is reasonable to expect compositional changes due to climate change. These changes could lead to increased dung removal and a higher secondary seed dispersal rate in northern regions

Dung beetle assemblages, dung removal and secondary seed dispersal: data from a large-scale, multi-site experiment in the Western Palaearctic

By manipulating faeces during feeding and breeding, dung beetles (Coleoptera: Scarabaeidae) fulfil important ecosystem functions in terrestrial ecosystems throughout the world. In a pan-European multi-site experiment (MSE), we estimated the ecosystem functions of dung removal and secondary seed dispersal by differing combinations of dung beetle functional groups. Therefore, we classified dung beetles into five functional groups according to their body size and dung manipulation method: dwellers, large and small tunnelers, and large and small rollers. Furthermore, we set up a dung beetle sampling database containing all sampled dung beetles during the project. By identifying dung beetle specimens to the species level, we obtained a detailed insight into the dung beetle communities at each study location. By establishing experimental plots allowing and inhibiting specific combinations of functional groups in the local dung beetle assemblage from removing dung and seeds, we estimated the role of each group in dung removal and secondary seed dispersal during a 4-week period. We performed all experiments in grazed (semi-)natural grasslands, and used different dung types (cattle, horse, sheep, goat or red deer) to match the herbivore species grazing in close vicinity of each of the study areas. Simultaneously, we sampled dung beetle assemblages by using pitfalls baited with the same dung types as used in the experiments. This data paper documents two datasets collected in the framework of this MSE project. All the experiments took place between 2013 and 2016 at 17 study sites in 10 countries and 11 biogeographic zones. The entire dung beetle sampling dataset was published as a sampling event dataset at GBIF. The dataset includes the sampling results of all 17 study sites, which contain 1,050 sampling events and 4,362 occurrence records of 94 species. The second dataset contains the results of the dung removal and secondary seed dispersal experiments in which we used 11 experimental treatments and the five dung types mentioned above. This experimental results dataset holds all experimental results of the MSE project (11,537 records), and was published in the online data repository Zenodo

Grazer induced changes in dry, low-productive grassland plant communities

Grazing by larger herbivores is widely used as a management tool to preserve and enhance plant diversity of the vegetation and structural heterogeneity of the landscape. In the late 1990s, different large herbivores species were introduced in several dune reserves along the Belgian coast to avoid further expansion of dominant grasses and woody species. Given the scarcity of information of grazing effects in nutrient-poor grasslands systems and in order to generate generalisations on plant community development in the grazed areas, it is important to have insight into the effects of grazing on the abundance of plant functional types. Although, there is a rich literature on the effects of grazing on vegetation, much controversy still exists on the (likely) effects of the introduction of larger herbivores on plant species composition and diversity in different environmental conditions. The main objective of this study is to investigate the large herbivore effects on plant community composition and diversity among dry coastal dune grasslands. Since the dune grasslands treated in the present study occurred in a gradient of soil conditions (i.e. nutrient availability), the interaction between grazing effect and soil conditions on plant community composition and diversity was investigated at different spatial scales. Furthermore, the mechanisms involved in shifts in plant community composition was also assessed by analyzing tolerance ability of different plant species under both greenhouse and field conditions. In the greenhouse experiment, we tested whether difference in herbivory tolerance of plant species (Arrhenatherum elatius, Holcus lanatus, Lotus corniculatus and Prunella vulgaris) can be related to their abundance in grassland communities and how herbivory and nutrient availability affect competitive balances among plant species through changes in their tolerance. In the field, we tested whether variation in response of four dominant grass species (Festuca arundinacea, Holcus lanatus, Agrostis stolonifera and Poa pratensis) to a high grazing intensity by large herbivores can be attributed to different responses of their vegetative and reproductive components. The results showed that grazing was responsible for important and significant shifts in plant community composition in dune grasslands. Grazing caused a shift in plant composition towards an annual life history, seasonal regeneration by seed, small size, early reproduction strategy and an increasing relative abundance of forbs and annual grasses in dune grasslands. The impact of grazing on plant diversity depended both on the spatial scale and soil conditions. Grazed plots had an overall higher local species richness than the ungrazed plots within the entire pH range. In contrast, site species richness(8× 8 m²) was influenced by grazing and its interaction with soil acidity. Site species richness increased with pH at grazed sites while the opposite pattern was observed in ungrazed situations. This resulted in larger differences in the species richness between grazed and ungrazed sites at higher soil pH compared to sites with a lower pH. Results on the greenhouse experiment showed that species replacement in function of herbivory is partially depending on the individual plant tolerance to herbivory and on competitive relations between competitive plant species and subordinate species and that both were different under different environmental conditions. Although grazing disturbance significantly influenced competitor-non-competitor relations in favour of less competitive species, increasing nutrient levels (expressed in pH-differences) contract the effect of grazing on dominant competitive plant species. The increased investment in vegetative biomass by A. stolonifera and P. pratensis under grazing ensures their persistence. Stimulatory effects of grazing resulted in a dense population of smaller plants of A. stolonifera and P. pratensis. However, for all species studied grazing had negative effects on the reproductive outputs. Vegetative reproduction may hence partially compensate for the loss of reproductive output of A. stolonifera and P. pratensis, but not for H. lanatus and F. arundinacea. Although grazing seems an appropriate management tool to maintain and even enhance plant biodiversity under many circumstances, it may negatively affect plant species richness, where soil resources limit plant biomass production (i.e. under more or less acid soil conditions). We may also conclude that different responses of plant species in term of their ability to have a higher tolerance to herbivory and vegetative production to the direct detrimental effect of grazing are likely to be the primary mechanisms, contributing to persistence of plant species under high grazing intensity

A Hierarchical Sampling for Capturing Permeability Trend in Rock Physics

Among all properties of reservoir rocks, permeability is an important parameter which is typically measured from core samples in the laboratory. Due to limitations of core drilling all over a reservoir, simulation of rock porous media is demanded to explore more scenarios not seen in the available data. One of the most accurate methods is cross correlation based simulation (CCSIM) which recently has broadly applied in geoscience and porous media. The purpose of this study is producing realizations with the same permeability trend to a real sample. Berea sandstone sample is selected for this aim. Permeability results, extracted from smaller sub-samples of the original sample, showed that classic Kozeny–Carman permeability trend is not suitable for this sample. One reason can be due to lack of including geometrical and fractal properties of pore-space distribution in this equation. Thus, a general trend based on fractal dimensions of pore-space and tortuosity of the Berea sample is applied in this paper. Results show that direct 3D stochastic modeling of porous media preserves porous structure and fractal behavior of rock. On the other hand, using only 2D images for constructing the 3D pore structures does not reproduce the measured experimental permeability. For this aim, a hierarchical sampling is implemented in two and three steps using both 2D and 3D stochastic modeling. Results showed that two-step sampling is not suitable enough, while the utilized three-step sampling occurs to be show excellent performance by which different models of porous media with the same permeability trend as the Berea sandstone sample can be generated