The theoretical underpinnings of the assessment of invasive alien species impacts need to be improved. At present most approaches are unreliable to quantify impact at regional scales and do not allow for comparison of different invasive species. There are four basic problems that need to be addressed: (1) Some impacted ecosystem traits are spatially not additive; (2) invader effects may increase non-linearly with abundance or there may be effect thresholds impairing estimates of linear impact models; (3) the abundance and impact of alien species will often co-vary with environmental variation; and (4) the total invaded range is an inappropriate measure for quantifying regional impact because the habitat area available for invasion can vary markedly among invasive species. Mathematical models and empirical data using an invasive alien plant species (Heracleum mantegazzianum) indicate that ignoring these issues leads to impact estimates almost an order of magnitude from the real values. Thus, we propose a habitatsensitive formula for regional impact assessment that is unaffected by non-linearity. Furthermore, we make some statistical suggestions on how to assess invader effects properly and we discuss the quantification of the invaded range. These improvements are crucial for impact assessment with the overall aim of prioritizing management of invasive species.

Questions: Are negative invasion–diversity relationships due to biotic resistance of the invaded plant community or to post‐invasion displacement of less competitive species? Do invasion–diversity relationships change with habitat type or resident traits? Location/species: Lowlands and uplands of western and southern Germany, Heracleum mantegazzianum; mountain range in central Germany, Lupinus polyphyllus; and coastal dunes of northwest Germany, Rosa rugosa. Methods: We tested the significance and estimated regression slopes of invasion–diversity relationships using generalized linear (mixed effects) models relating invader cover and habitat type to species richness in different plant groups, stratified based on size, life cycle and community association. Results: We found negative, positive and neutral relationships between invader cover and species richness. There were negative linear correlations of invader cover with small plant species throughout, but no negative linear correlation with tall species. Invasion–diversity relationships tended to be more negative in early‐successional habitats, such as dunes or abandoned grasslands, than in late‐successional habitats. Conclusions: Invasion diversity–relationships are complex; they vary among habitat types and among different groups of resident species. Negative invasion–diversity relationships are due to asymmetric competitive displacement of inferior species and not due to biotic resistance. Small species are displaced in early‐successional habitats, while there is little effect on persistence of tall species.

Land-use intensification is a major driver of biodiversity loss. However, understanding how different components of land use drive biodiversity loss requires the investigation of multiple trophic levels across spatial scales. Using data from 150 agricultural grasslands in central Europe, we assess the influence of multiple components of local- and landscape-level land use on more than 4,000 above- and belowground taxa, spanning 20 trophic groups. Plot-level land-use intensity is strongly and negatively associated with aboveground trophic groups, but positively or not associated with belowground trophic groups. Meanwhile, both above- and belowground trophic groups respond to landscape-level land use, but to different drivers: aboveground diversity of grasslands is promoted by diverse surrounding land-cover, while belowground diversity is positively related to a high permanent forest cover in the surrounding landscape. These results highlight a role of landscape-level land use in shaping belowground communities, and suggest that revised agroecosystem management strategies are needed to conserve whole-ecosystem biodiversity.

Remote sensing by Unmanned Aerial Systems (UAS) is a dynamic evolving technology. UAS are particularly useful in environmental monitoring and management because they have the capability to provide data at high temporal and spatial resolutions. Moreover, data acquisition costs are lower than those of conventional methods such as extensive ground sampling, manned airplanes, or satellites. Small fixed-wing UAS in particular offer further potential benefits as they extend the operational coverage of the area under study at lower operator risks and accelerate data deployment times. Taking these aspects into account, UAS might be an effective tool to support management of invasive plant based on early detection and regular monitoring. A straightforward UAS approach to map invasive plant species is presented in this study with the intention of providing ready-to-use field maps essential for action-oriented management. Our UAS utilizes low-cost sensors, free-of-charge software for mission planning and an affordable, commercial aerial platform to reduce operational costs, reducing expenses with personnel while increasing overall efficiency. We illustrate our approach using a real example of invasion by Acacia mangium in a Brazilian Savanna ecosystem. A. mangium was correctly identified with an overall accuracy of 82.7% from the analysis of imagery. This approach provides land management authorities and practitioners with new prospects for environmental restoration in areas where invasive plant species are present.

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In the permafrost region of northeastern China, vegetation and soil environment have showed response to permafrost degradation triggered by global warming, but the corresponding variation of the soil microbial communities remains poorly investigated. Here, a field investigation in the continuous permafrost region was conducted to collect 63 soil samples from 21 sites along a latitudinal gradient to assess the distribution pattern of microbial communities and their correlation with environmental factors. High-throughput Illumina sequencing revealed that bacterial communities were dominated by Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria. Both microbial richness and phylogenetic diversity decreased initially and then increased as the latitude increased. UniFrac analysis of microbial communities detected significant differences among latitudes. Variation partitioning analysis and structural equation models revealed that environmental variables, including geographic factors, plant-community factors and soil physicochemical factors, all played non-negligible roles in affecting the microbial community structures directly or indirectly. Redundancy analysis and boosted regression tree analysis further highlighted the influences of soil pH and plant richness on microbial community compositions and diversity patterns. Taken together, these results suggest that the distribution pattern of soil microbial communities shows distinct changes along the latitudinal gradients in northeastern China and is predominantly mediated by soil pH and plant diversity.

The aim of the present study was to analyse Heracleum mantegazzianum's habitat preference and to identify recipient communities in its invasive range in Central Europe with regard to the species' effects on resident vegetation and potential implications for nature conservation. Field investigations were carried out in 20 study areas (each 1 ¥ 1 km 2 ) in Germany. In all encountered stands of H. mantegazzianum the vegetation composition and various site parameters were sampled. Additionally, time series of aerial photographs of study areas were analysed to reconstruct the history of invaded sites.H. mantegazzianum occurs in a variety of different habitat types, such as grasslands, roadsides, riverbanks, woodland margins etc. Stand densities of the species vary widely from scattered individuals to dominant stands. Primary constraining factors for H. mantegazzianum densities are land use, shading and low-productive site conditions. Site conditions of preferred habitats are more or less uniform, and are characterised by high productivity in combination with lack of land use and recent or historic disturbances or habitat changes. H. mantegazzianum is a successful invader and a potentially dominant species only if these particular habitat requirements are met. However, even then most stands of the species are not dominant.The majority of invaded sites have been subject to human caused habitat changes within the last 50 years which have enabled or facilitated invasion. The most important process here is land-use decline, especially abandonment of grasslands.The prevailing vegetation types with H. mantegazzianum are ruderal Arrhenatherion grasslands and Galio-Urticetea tall-forb stands which represent stages of secondary successions from grasslands to woodlands after abandonment of land use. Successional age seems to play a role with respect to stand densities of H. mantegazzianum as maximum densities occur prevalently at sites which represent young successional stages.The results of the present study suggest that high densities of H. mantegazzianum can decrease native diversity of invaded stands, especially in abandoned grasslands. However, a loss in diversity is a typical effect of the processes that facilitate the invasion of H. mantegazzianum, i. e. abandonment of grassland management and severe disturbances or even habitat destruction (e. g. due to mining), and can be brought about by native species, such as Urtica dioica, as well. From this point of view H. mantegazzianum can be seen rather as a symptom of diversity loss than the cause of it.Further, the results suggest that H. mantegazzianum does not seriously threaten to conflict with nature conservation as preferred habitats and plant communities are very common today and habitats which are of special conservation interest present no favourable conditions for this species.

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