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An improved version of ORCA's automated generator environment (ORCA-AGE II) is presented. The algorithmic improvements and the move to C++ as the programming language lead to a performance gain of up to two orders of magnitude compared to the previously developed P YTHON toolchain. Additionally, the restructured modular design allows for far more complex code engines to be implemented readily. Importantly, we have realised an extremely tight integration with the ORCA host program. This allows for a workflow in which only the wavefunction Ansatz is part of the source code repository while all actual high-level code is generated automatically, inserted at the appropriate place in the host program before it is compiled and linked together with the hand written code parts. This construction ensures longevity and uniform code quality. Furthermore the new developments allow ORCA-AGE II to generate parallelised production-level code for highly complex theories, such as fully internally contracted multireference coupled-cluster theory (fic-MRCC) with an enormous number of contributing tensor contractions. We also discuss the automated implementation of nuclear gradients for arbitrary theories. All these improvements enable the implementation of theories that are too complex for the human mind and also reduce development times by orders of magnitude. We hope that this work enables researchers to concentrate on the intellectual content of the theories they develop rather than be concerned with technical details of the implementation. [ABSTRACT FROM AUTHOR]

Aim : To provide the first syntaxonomic, plot-based classification of the dry grasslands and thorn-cushion communities in Armenia. Study area : Armenia. Methods : We sampled 111 vegetation plots (10 m2) and recorded environmental and structural parameters. We collected additional 487 relevés from surrounding countries for a broad-scale comparison. We used modified TWINSPAN to derive a syntaxonomic classification system, whose units were then compared among each other regarding species composition, structure, site conditions and distribution. Results : The classification of Armenian vegetation plots resulted in a 12-cluster solution. Unsupervised classification of the broad-scale dataset yielded five main groups, which were used for the high-level syntaxonomic assignments of the Armenian data. We assigned about half of the plots of the Armenian dataset to the Festuco-Brometea, while the remaining represented a potential new class, preliminarily called "Ziziphora tenuior-Stipa arabica grasslands". Most of the syntaxa below class level are new to science, therefore we provide formal descriptions of three orders (Plantagini atratae-Bromopsietalia variegatae, Onobrychido transcaucasicae-Stipetalia pulcherrimae, Cousinio brachypterae-Stipetalia arabicae), four alliances (Acantholimono caryophyllacei-Stipion holosericeae, Artemision fragrantis, Onobrychido michauxii-Stipion capillatae, Onobrychido transcaucasicae-Stipion pulcherrimae) and six associations. We found significant differences in the topographic, climatic and soil characteristics, and structural parameters, species life forms and distribution range types between the grassland types at different syntaxonomic levels. The mean species richness was 47.3 (vascular plants: 46.8, bryophytes: 0.4, lichens: 0.1). Conclusions : We found remarkable differences of the Armenian dry grasslands from the previously known units and described most of the higher syntaxa and all the associations as new to science. Our study provides arguments for a potential new class of Ziziphora tenuior-Stipa arabica grasslands separate both from the Euro-Siberian Festuco-Brometea and the Anatolian Astragalo-Brometea. Finally, we found plot scale richness of vascular plants clearly above the Palaearctic average of dry grasslands and that of non-vascular plants clearly below, which calls for further biodiversity analyses. Taxonomic reference : Euro+Med (2023) for vascular plants, Hodgetts et al. (2020) for bryophytes, Nimis et al. (2018) for lichens except for Xanthoparmelia camtschadalis (Ach.) Hale. Abbreviations : EDGG = Eurasian Dry Grassland Group; DCA = detrended correspondence analysis; ICPN = International Code of Phytosociological Nomenclature (Theurillat et al. 2021); TWINSPAN = two-way indicator species analysis. [ABSTRACT FROM AUTHOR]

In this contribution to the special software-centered issue, the ORCA program package is described. We start with a short historical perspective of how the project began and go on to discuss its current feature set. ORCA has grown into a rather comprehensive general-purpose package for theoretical research in all areas of chemistry and many neighboring disciplines such as materials sciences and biochemistry. ORCA features density functional theory, a range of wavefunction based correlation methods, semi-empirical methods, and even force-field methods. A range of solvation and embedding models is featured as well as a complete intrinsic to ORCA quantum mechanics/molecular mechanics engine. A specialty of ORCA always has been a focus on transition metals and spectroscopy as well as a focus on applicability of the implemented methods to "real-life" chemical applications involving systems with a few hundred atoms. In addition to being efficient, user friendly, and, to the largest extent possible, platform independent, ORCA features a number of methods that are either unique to ORCA or have been first implemented in the course of the ORCA development. Next to a range of spectroscopic and magnetic properties, the linear- or low-order single- and multi-reference local correlation methods based on pair natural orbitals (domain based local pair natural orbital methods) should be mentioned here. Consequently, ORCA is a widely used program in various areas of chemistry and spectroscopy with a current user base of over 22 000 registered users in academic research and in industry. [ABSTRACT FROM AUTHOR]

The coupled cluster method with single-, double-, and perturbative triple excitations [CCSD(T)] is considered to be one of the most reliable quantum chemistry theories. However, the steep scaling of CCSD(T) has limited its application to small or medium-sized systems for a long time. In our previous work, the linear scaling domain based local pair natural orbital CCSD variant (DLPNO-CCSD) has been developed for closed-shell and open-shell. However, it is known from extensive benchmark studies that triple-excitation contributions are important to reach chemical accuracy. In the present work, two linear scaling (T) approximations for open-shell DLPNO-CCSD are implemented and compared: (a) an algorithm based on the semicanonical approximation, in which off-diagonal Fock matrix elements in the occupied space are neglected [referred to as DLPNO-(T0)]; and (b) an improved algorithm in which the triples amplitudes are computed iteratively [referred to as DLPNO-(T)]. This work is based on the previous open-shell DLPNO-CCSD algorithm [M. Saitow et al., J. Chem. Phys. 146, 164105 (2017)] as well as the iterative (T) correction for closed-shell systems [Y. Guo et al., J. Chem. Phys. 148, 011101 (2018)]. Our results show that the new open-shell perturbative corrections, DLPNO-(T0/T), can predict accurate absolute and relative correlation energies relative to the canonical reference calculations with the same basis set. The absolute energies from DLPNO-(T) are significantly more accurate than those of DLPNO-(T0). The additional computational effort of DLPNO-(T) relative to DLPNO-(T0) is a factor of 4 on average. We report calculations on systems with more than 4000 basis functions. [ABSTRACT FROM AUTHOR]

In this communication, an improved perturbative triples correction (T) algorithm for domain based local pair-natural orbital singles and doubles coupled cluster (DLPNO-CCSD) theory is reported. In our previous implementation, the semi-canonical approximation was used and linear scaling was achieved for both the DLPNO-CCSD and (T) parts of the calculation. In this work, we refer to this previous method as DLPNO-CCSD(T0) to emphasize the semi-canonical approximation. It is wellestablished that the DLPNO-CCSD method can predict very accurate absolute and relative energies with respect to the parent canonical CCSD method. However, the (T0) approximation may introduce significant errors in absolute energies as the triples correction grows up in magnitude. In the majority of cases, the relative energies from (T0) are as accurate as the canonical (T) results of themselves. Unfortunately, in rare cases and in particular for small gap systems, the (T0) approximation breaks down and relative energies show large deviations from the parent canonical CCSD(T) results. To address this problem, an iterative (T) algorithm based on the previous DLPNO-CCSD(T0) algorithm has been implemented [abbreviated here as DLPNO-CCSD(T)]. Using triples natural orbitals to represent the virtual spaces for triples amplitudes, storage bottlenecks are avoided. Various carefully designed approximations ease the computational burden such that overall, the increase in the DLPNO- (T) calculation time over DLPNO-(T0) only amounts to a factor of about two (depending on the basis set). Benchmark calculations for the GMTKN30 database showthat compared to DLPNO-CCSD(T0), the errors in absolute energies are greatly reduced and relative energies are moderately improved. The particularly problematic case of cumulene chains of increasing lengths is also successfully addressed by DLPNO-CCSD(T). [ABSTRACT FROM AUTHOR]

The Coupled-Cluster expansion, truncated after single and double excitations (CCSD), provides accurate and reliable molecular electronicwave functions and energies for many molecular systems around their equilibrium geometries. However, the high computational cost, which is well-known to scale as O(N6) with system size N, has limited its practical application to small systems consisting of not more than approximately 20-30 atoms. To overcome these limitations, low-order scaling approximations to CCSD have been intensively investigated over the past fewyears. In our previouswork, we have shown that by combining the pair natural orbital (PNO) approach and the concept of orbital domains it is possible to achieve fully linear scaling CC implementations (DLPNO-CCSD and DLPNO-CCSD(T)) that recover around 99.9% of the total correlation energy [C. Riplinger et al., J. Chem. Phys. 144, 024109 (2016)]. The production level implementations of the DLPNO-CCSD and DLPNO-CCSD(T) methods were shown to be applicable to realistic systems composed of a few hundred atoms in a routine, black-box fashion on relatively modest hardware. In 2011, a reduced-scaling CCSD approach for high-spin open-shell unrestricted Hartree-Fock reference wave functions was proposed (UHF-LPNOCCSD) [A. Hansen et al., J. Chem. Phys. 135, 214102 (2011)]. After a few years of experience with this method, a few shortcomings of UHF-LPNO-CCSD were noticed that required a redesign of the method, which is the subject of this paper. To this end, we employ the high-spin open-shell variant of the N-electron valence perturbation theory formalism to define the initial guess wave function, and consequently also the open-shell PNOs. The new PNO ansatz properly converges to the closed-shell limit since all truncations and approximations have been made in strict analogy to the closed-shell case. Furthermore, given the fact that the formalism uses a single set of orbitals, only a single PNO integral transformation is necessary, which offers large computational savings. We show that, with the default PNO truncation parameters, approximately 99.9% of the total CCSD correlation energy is recovered for open-shell species, which is comparable to the performance of the method for closedshells. UHF-DLPNO-CCSD shows a linear scaling behavior for closed-shell systems, while linear to quadratic scaling is obtained for open-shell systems. The largest systems we have considered contain more than 500 atoms and feature more than 10 000 basis functions with a triple-ζ quality basis set. [ABSTRACT FROM AUTHOR]

Domain based local pair natural orbital coupled cluster theory with single-, double-, and perturbative triple excitations (DLPNO-CCSD(T)) is a highly efficient local correlation method. It is known to be accurate and robust and can be used in a black box fashion in order to obtain coupled cluster quality total energies for large molecules with several hundred atoms. While previous implementations showed near linear scaling up to a few hundred atoms, several nonlinear scaling steps limited the applicability of the method for very large systems. In this work, these limitations are overcome and a linear scaling DLPNO-CCSD(T) method for closed shell systems is reported. The new implementation is based on the concept of sparse maps that was introduced in Part I of this series [P. Pinski, C. Riplinger, E. F. Valeev, and F. Neese, J. Chem. Phys. 143, 034108 (2015)]. Using the sparse map infrastructure, all essential computational steps (integral transformation and storage, initial guess, pair natural orbital construction, amplitude iterations, triples correction) are achieved in a linear scaling fashion. In addition, a number of additional algorithmic improvements are reported that lead to significant speedups of the method. The new, linear-scaling DLPNO-CCSD(T) implementation typically is 7 times faster than the previous implementation and consumes 4 times less disk space for large three-dimensional systems. For linear systems, the performance gains and memory savings are substantially larger. Calculations with more than 20 000 basis functions and 1000 atoms are reported in this work. In all cases, the time required for the coupled cluster step is comparable to or lower than for the preceding Hartree-Fock calculation, even if this is carried out with the efficient resolutionof- the-identity and chain-of-spheres approximations. The new implementation even reduces the error in absolute correlation energies by about a factor of two, compared to the already accurate previous implementation. [ABSTRACT FROM AUTHOR]

A nearly linear scaling implementation of coupled‐cluster with singles and doubles excitations (CCSD) can be achieved by means of the domain‐based local pair natural orbital (DLPNO) method. The combination of DLPNO‐CCSD with implicit solvation methods allows the calculation of accurate energies and chemical properties of solvated systems at an affordable computational cost. We have efficiently implemented different schemes within the conductor‐like polarizable continuum model (C‐PCM) for DLPNO‐CCSD in the ORCA quantum chemistry suite. In our implementation, the overhead due to the additional solvent terms amounts to less than 5% of the time the equivalent gas phase job takes. Our results for organic neutrals and open‐shell ions in water show that for most systems, adding solvation terms to the coupled‐cluster amplitudes equations and to the energy leads to small changes in the total energy compared to only considering solvated orbitals and corrections to the reference energy. However, when the solute contains certain functional groups, such as carbonyl or nitrile groups, the changes in the energy are larger and estimated to be around 0.04 and 0.02 kcal/mol for each carbonyl and nitrile group in the solute, respectively. For solutes containing metals, the use of accurate CC/C‐PCM schemes is crucial to account for correlation solvation effects. Simultaneously, we have calculated the electrostatic component of the solvation energy for neutrals and ions in water for the different DLPNO‐CCSD/C‐PCM schemes. We observe negligible changes in the deviation between DLPNO‐CCSD and canonical‐CCSD data. Here, DLPNO‐CCSD results outperform those for Hartree‐Fock and density functional theory calculations. [ABSTRACT FROM AUTHOR]

Psychosocial factors in general, and the social and psychological conditions of work and occupation in particular, have attracted little attention to the epidemiological investigation into the occupational-related causes of lung cancer. There is some evidence available concerning the impact of loss events - including job losses - on cancer development. During our research presented in this article, we examined job changes and job transitions in the occupational biography of men with regard to their circumstances in terms of (in-)voluntariness both as individual events and the job-changing histories of individuals. We expected the job-changing histories of lung cancer cases to be more involuntary than those of population controls, and vice versa. Our sample contains 391 male case-control pairs. Cases are defined as newly-diagnosed men of German nationality with a histologically- or cytologically-confirmed diagnosis of primary lung cancer. Population controls were drawn randomly from the municipality records of residents and individuals matched to cases 1:1 by age and region. Occupational histories were reconstructed, and information about other classical and suspected risk factors was collected during standardized interviews by trained interviewers. We categorized the reported reasons for job changes, and classified them with respect to voluntariness on a seven-stepped rating scale from -3 'very involuntary' to +3 'very voluntary', defining relations within the empirically established categories. The job-changing histories of individuals are described by using the average score of voluntariness. We measured the degree of voluntariness for the occupational history: (1) by the rounded average score; and (2) by the quintiles of the average score. On the basis of individuals matched odds ratios (OR) estimates are derived for the score of voluntariness unadjusted and adjusted for smoking, asbestos exposure and socio-economic group by conditional logistic regression. The investigation into job-changing histories using the average score of voluntariness lead to similar results for both measuring methods for the total study group. When the rounded score was used, job-changing histories which were assessed as 'very involuntary' and 'involuntary' (score -3 and -2) showed an elevated odds ratio of adjusted 1.41 (95%-CI: 0.57; 3.48), and when they were assessed as 'moderately involuntary' (score -1) the adjusted odds ratio was 1.59 (95%-CI: 1.02; 2.48), as compared with job-changing histories assessed as neutral (score 0). When the degree of voluntariness was measured by quintiles, the first quintile (score -3-< -0.6) showed an elevated risk of adjusted OR 1.36 (95%-CI: 0.79; 2.36) as compared to the third quintile (score -0.2-< -0.1). The observed protective effects of either positively assessed job-changing histories ('moderately voluntary' (score +1): OR 0.78 and 'voluntary' (score +2) or 'very voluntary' (score +3: OR 0.58) or those in the fourth quintile (score -0.01-0.6: OR 0.73) and fifth quintile (score >0.6-3: OR 0.63) were insignificant. The analysis was also conducted for three broad age groups, and for biographies reduced by the five years prior to the interview or the diagnosis of lung cancer respectively. Methodological limitations of the case-control design and methodical implications - missing values and recall-bias in particular - as well as possible explanations for these findings are discussed. Key words - psychosocial factors, case-control study, lung cancer. male, job-changing history, life event approach, occupational life course

Festuca valesiaca Schleich. ex Gaudin subsp. valesiaca is acknowledged as one of the most characteristic grasses of the continental grasslands and steppes of Eurasia. In Italy, the species was known almost only from the continental valleys of the Alpine chain (with the exception of two small populations at the northernmost edge of the Apennines). Here, we report on the first confirmed finding of F. valesiaca subsp. valesiaca in the surroundings of the Fucino Basin, Central Apennines. This finding expands by c. 400 km southwards the species' range in Italy. The identity of the species was first ascertained by means of leaf cross-sections and stomata measurements, and then confirmed by chromosome count. Its habitat preferences within the area were found to match well with those described in the literature for C-Europe. After discussing some identification issues and the population's ecological niche, we present the main biogeographic implications of our finding. By recalling and discussing similar examples, we conclude that during the Holocene forest spread some Apennine "dry valleys" performed as refugia for a number of Pleistocene steppic taxa. The grasslands of these areas may thus be ancient and valuable ecosystems maintained by climate and disturbance throughout the Holocene. [ABSTRACT FROM AUTHOR]

Local correlation theories have been developed in two main flavors: (1) “direct” local correlation methods apply local approximation to the canonical equations and (2) fragment based methods reconstruct the correlation energy from a series of smaller calculations on subsystems. The present work serves two purposes. First, we investigate the relative efficiencies of the two approaches using the domain-based local pair natural orbital (DLPNO) approach as the “direct” method and the cluster in molecule (CIM) approach as the fragment based approach. Both approaches are applied in conjunction with second-order many-body perturbation theory (MP2) as well as coupled-cluster theory with single-, double- and perturbative triple excitations [CCSD(T)]. Second, we have investigated the possible merits of combining the two approaches by performing CIM calculations with DLPNO methods serving as the method of choice for performing the subsystem calculations. Our cluster-in-molecule approach is closely related to but slightly deviates from approaches in the literature since we have avoided real space cutoffs. Moreover, the neglected distant pair correlations in the previous CIM approach are considered approximately. Six very large molecules (503-2380 atoms) were studied. At both MP2 and CCSD(T) levels of theory, the CIM and DLPNO methods show similar efficiency. However, DLPNO methods are more accurate for 3-dimensional systems. While we have found only little incentive for the combination of CIM with DLPNO-MP2, the situation is different for CIM-DLPNO-CCSD(T). This combination is attractive because (1) the better parallelization opportunities offered by CIM; (2) the methodology is less memory intensive than the genuine DLPNO-CCSD(T) method and, hence, allows for large calculations on more modest hardware; and (3) the methodology is applicable and efficient in the frequently met cases, where the largest subsystem calculation is too large for the canonical CCSD(T) method. [ABSTRACT FROM AUTHOR]

In this paper, various implementations of the analytic Hartree–Fock and hybrid density functional energy second derivatives are studied. An approximation-free four-centre implementation is presented, and its accuracy is rigorously analysed in terms of self-consistent field (SCF), coupled-perturbed SCF (CP-SCF) convergence and prescreening criteria. The CP-SCF residual norm convergence threshold turns out to be the most important of these. Final choices of convergence thresholds are made such that an accuracy of the vibrational frequencies of better than 5 cm−1compared to the numerical noise-free results is obtained, even for the highly sensitive low frequencies (<100–200 cm−1). The effects of the choice of numerical grid for density functional exchange–correlation integrations are studied and various weight derivative schemes are analysed in detail. In the second step of the work, approximations are introduced in order to speed up the computation without compromising its accuracy. To this end, the accuracy and efficiency of the resolution of identity approximation for the Coulomb terms and the semi-numerical chain of spheres approximation to the exchange terms are carefully analysed. It is shown that the largest performance improvements are realised if either Hartree–Fock exchange is absent (pure density functionals) and otherwise, if the exchange terms in the CP-SCF step of the calculation are approximated by the COSX method in conjunction with a small integration grid. Default values for all the involved truncation parameters are suggested. For vancomycine (176 atoms and 3593 basis functions), the RIJCOSX Hessian calculation with the B3LYP functional and the def2-TZVP basis set takes ∼3 days using 16 Intel® Xeon® 2.60GHz processors with the COSX algorithm having a net parallelisation scaling of 11.9 which is at least ∼20 times faster than the calculation without the RIJCOSX approximation. [ABSTRACT FROM PUBLISHER]

Predictability of gas flows through leak elements in various conditions (geometry of leak elements, gas species, pressure) from the results of only a few measurements in a specific configuration is an issue for the gas dynamics theory. This paper aims to provide results of leak flow rate measurements performed by national metrology institutes (NMIs) in the framework of the European project JRP IND12. Leak artefacts made of different materials with well defined geometry, were calibrated by means of primary standards with different gas species flowing to vacuum or atmospheric pressure. The numerous collected data are made available to allow the experts in gas dynamics to use this large database to improve the knowledge of gas flow in narrow ducts in terms of predictability for different gas species and find a simple model to describe the gas flow inside microchannels. [ABSTRACT FROM AUTHOR]

Short tubes with diameters of the order of 200 nm were drilled into silicon nitride (Si 3 N 4 ) membranes of 200 nm thickness by focused ion beam technology and examined as leak elements for vacuum technology applications. These nano-holes exhibit molecular flow in the pressure range from high vacuum up to 10 kPa and can therefore be used as predictable leak elements for any non-condensable gas species. The geometrical dimensions were determined by SEM, STEM and AFM techniques. By Direct Simulation Monte Carlo method the conductances of these short tubes were calculated from the measured dimensions. The calculated conductance agreed with the value measured by comparison with a primary gas flowmeter within their respective uncertainties. [ABSTRACT FROM AUTHOR]

Abstract: Non-timber forest products (NTFPs) strongly contribute to livelihood security in the semi-arid tropics. There is increasing concern about the population status of NTFP-providing trees and therefore a need for their sustainable use. Thus, this study examines the impact of land-use type on the multipurpose baobab tree (Adansonia digitata L.) in Burkina Faso, combined with rates and patterns of bark- and leaf-harvesting, and their impact on fruit production. We compared stands in a protected area (W National Park of Burkina Faso) with those of surrounding communal area (fallows, croplands and villages) to obtain an indication on the status of the baobab population, to assess its harvesting tolerance and to estimate to what extent their actual use is sustainable. Our results reveal that land-use type has an impact on the population structure of the baobab. The size class distribution curve of park stands was inverse J-shape which indicates good rejuvenation, while the curve of fallows, croplands and villages stands was bell-shaped, indicating a lack of recruitment. However, a high number of seedlings were recorded in villages. Nearly all baobabs were pruned and debarked in villages, croplands and fallows while half of the individuals were harvested in the park. Most of the trees were pruned and debarked moderately. Debarking and pruning were slightly size specific. Pruning in interaction with tree-size had a significant impact on fruit production. In contrast, debarking had no effect on fruit production. We conclude that despite the land-use impact and the intense harvesting, baobabs are still well preserved in the communal area due to their longevity, extremely low adult mortality rates and traditional management practices. However, land-use intensifications may lead to increasing pressure on baobab populations in the future. Therefore, adapted management strategies are needed to guarantee the persistence of this important species and to avoid a shortage of baobab products. [Copyright &y& Elsevier]

Abstract: Cities are well known as rich in vascular plant species. To evaluate the importance of this richness for global biodiversity it is necessary to know the degree of homogenization of the city flora at a continental or even worldwide scale. Therefore, we looked for a habitat type that is typical urban and which is represented in nearly all cities of the world: the area around street trees (“Baumscheiben”). The spontaneous flora of this habitat was recorded in seven West and Central European metropolises situated in six countries and in Baltimore (USA). To test for floristic homogenization, the dissimilarity among the Baumscheiben Flora in the European cities was compared with dissimilarity among relevés of the potential natural vegetation in the cities. On average 81 species were found growing on Baumscheiben in each of the European cities. 29 species (i.e. more than one third of the total) were found in every city, 59 species (i.e. 74%) were represented in at least four of the seven cities. The obvious homogenization of the flora of this habitat is confirmed by low total variation among European Baumscheiben. Furthermore, the dissimilarity among Baumscheiben was much lower than among the potential natural vegetation (forests) around these cities. There is not only low variation between the Baumscheiben flora of the seven European metropolises analyzed, but also great similarity to the Baumscheiben flora of Baltimore: 80% of the species found on Baumscheiben in Baltimore also belong to the spontaneous flora of most European cities and 26% even belong to the group of the most common species of West and Central European tree bases. [Copyright &y& Elsevier]

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Large areas of northern and western China are covered with steppe vegetation which is grazed with different intensities. Areas which are not or only slightly grazed are rare and mostly exist in nature reserves. We investigated floristic composition and species diversity of the steppe vegetation of the autonomous region Ningxia Hui with emphasis on the Yunwushan dry steppe nature reserve in relation to grazing intensity; all 77 plots were analyzed using ordination techniques, and the relationship between the variation in species composition and environmental conditions was analyzed. In Ningxia, two types of loess grass steppes prevail: in areas with lower altitudes from approximately 1650–1950 m a.s.l., the Stipa bungeana steppe occurs whereas the Stipa grandis steppe is typical for higher altitudes between 1900 and 2100 m a.s.l. For both vegetation types, three subtypes can be distinguished according to different levels of grazing intensity. With increasing grazing intensity, the number of plant species per plot strongly declines and the typical steppe vegetation types are dominated by Artemisia species ( A. frigida in the Stipa grandis community and A. sacrorum in the Stipa bungeana community). In contrast to studies carried out in neighboring areas, in our study area the Artemisia steppes do not represent the final state of degradation. Instead, Convolvulus ammanii dominates in heavily grazed areas of both Stipa steppe types. Detrended correspondence analysis confirms the classification and shows that the heavily grazed subtypes of the Stipa grandis and the Stipa bungeana steppe with Convolvulus ammanii are more similar to each other than the other vegetation types. The first axis of the detrended correspondence analysis is strongly related to the grazing intensity ( r = 0.93). Our results show that grazing intensity is an important factor for the differentiation of the steppe grasslands and a severe threat to species diversity. [ABSTRACT FROM AUTHOR]