Using remote sensing to characterize riparian vegetation: A review of available tools and perspectives for managers.

Riparian vegetation is a central component of the hydrosystem. As such, it is often subject to management practices that aim to influence its ecological, hydraulic or hydrological functions. Remote sensing has the potential to improve knowledge and management of riparian vegetation by providing cost-effective and spatially continuous data over wide extents. The objectives of this review were twofold: to provide an overview of the use of remote sensing in riparian vegetation studies and to discuss the transferability of remote sensing tools from scientists to managers. We systematically reviewed the scientific literature (428 articles) to identify the objectives and remote sensing data used to characterize riparian vegetation. Overall, results highlight a strong relationship between the tools used, the features of riparian vegetation extracted and the mapping extent. Very high-resolution data are rarely used for rivers longer than 100 km, especially when mapping species composition. Multi-temporality is central in remote sensing riparian studies, but authors use only aerial photographs and relatively coarse resolution satellite images for diachronic analyses. Some remote sensing approaches have reached an operational level and are now used for management purposes. Overall, new opportunities will arise with the increased availability of very high-resolution data in understudied or data-scarce regions, for large extents and as time series. To transfer remote sensing approaches to riparian managers, we suggest mutualizing achievements by producting open-access and robust tools. These tools will then have to be adapted to each specific project, in collaboration with managers.

Multi-temporal monitoring of a regional riparian buffer network (>12,000 km) with LiDAR and photogrammetric point clouds.

Riparian buffers are of major concern for land and water resource managers despite their relatively low spatial coverage. In Europe, this concern has been acknowledged by different environmental directives which recommend multi-scale monitoring (from local to regional scales). Remote sensing methods could be a cost-effective alternative to field-based monitoring, to build replicable "wall-to-wall" monitoring strategies of large river networks and associated riparian buffers. The main goal of our study is to extract and analyze various parameters of the riparian buffers of up to 12,000 km of river in southern Belgium (Wallonia) from three-dimensional (3D) point clouds based on LiDAR and photogrammetric surveys to i) map riparian buffers parameters on different scales, ii) interpret the regional patterns of the riparian buffers and iii) propose new riparian buffer management indicators. We propose different strategies to synthesize and visualize relevant information at different spatial scales ranging from local (<10 km) to regional scale (>12,000 km). Our results showed that the selected parameters had a clear regional pattern. The reaches of Ardenne ecoregion have channels with the highest flow widths and shallowest depths. In contrast, the reaches of the Loam ecoregion have the narrowest and deepest flow channels. Regional variability in channel width and depth is used to locate management units potentially affected by human impact. Riparian forest of the Loam ecoregion is characterized by the lowest longitudinal continuity and mean tree height, underlining significant human disturbance. As the availability of 3D point clouds at the regional scale is constantly growing, our study proposes reproducible methods which can be integrated into regional monitoring by land managers. With LiDAR still being relatively expensive to acquire, the use of photogrammetric point clouds combined with LiDAR data is a cost-effective means to update the characterization of the riparian forest conditions.

Effect of a static magnetic field on Escherichia coli adhesion and orientation.

This preliminary study focused on the effect of exposure to 0.5 T static magnetic fields on Escherichia coli adhesion and orientation. We investigated the difference in bacterial adhesion on the surface of glass and indium tin oxide-coated glass when exposed to a magnetic field either perpendicular or parallel to the adhesion surface (vectors of magnetic induction are perpendicular or parallel to the adhesion surface, respectively). Control cultures were simultaneously grown under identical conditions but without exposure to the magnetic field. We observed a decrease in cell adhesion after exposure to the magnetic field. Orientation of bacteria cells was affected after exposure to a parallel magnetic field. On the other hand, no effect on the orientation of bacteria cells was observed after exposure to a perpendicular magnetic field.

Classification of riparian forest species and health condition using multi-temporal and hyperspatial imagery from unmanned aerial system.

Riparian forests are critically endangered many anthropogenic pressures and natural hazards. The importance of riparian zones has been acknowledged by European Directives, involving multi-scale monitoring. The use of this very-high-resolution and hyperspatial imagery in a multi-temporal approach is an emerging topic. The trend is reinforced by the recent and rapid growth of the use of the unmanned aerial system (UAS), which has prompted the development of innovative methodology. Our study proposes a methodological framework to explore how a set of multi-temporal images acquired during a vegetative period can differentiate some of the deciduous riparian forest species and their health conditions. More specifically, the developed approach intends to identify, through a process of variable selection, which variables derived from UAS imagery and which scale of image analysis are the most relevant to our objectives.The methodological framework is applied to two study sites to describe the riparian forest through two fundamental characteristics: the species composition and the health condition. These characteristics were selected not only because of their use as proxies for the riparian zone ecological integrity but also because of their use for river management.The comparison of various scales of image analysis identified the smallest object-based image analysis (OBIA) objects (ca. 1 m(2)) as the most relevant scale. Variables derived from spectral information (bands ratios) were identified as the most appropriate, followed by variables related to the vertical structure of the forest. Classification results show good overall accuracies for the species composition of the riparian forest (five classes, 79.5 and 84.1% for site 1 and site 2). The classification scenario regarding the health condition of the black alders of the site 1 performed the best (90.6%).The quality of the classification models developed with a UAS-based, cost-effective, and semi-automatic approach competes successfully with those developed using more expensive imagery, such as multi-spectral and hyperspectral airborne imagery. The high overall accuracy results obtained by the classification of the diseased alders open the door to applications dedicated to monitoring of the health conditions of riparian forest. Our methodological framework will allow UAS users to manage large imagery metric datasets derived from those dense time series.

Conserving wildlife amongst the cotton fields. A third of a century of experience at the Nazinga Game Ranch, Burkina Faso.

Established in the early 1970 as a participatory wildlife production area, the Nazinga Game Ranch turned into an island of conservation surrounded by cultivation. We asked ourselves how long-term ungulate trends are affected in a context of continuous human pressure. To find out, we compiled and analysed the data of yearly line-transect counts of mammals carried out since 1985. Results showed that large species such as the elephant (Loxodonta africana) and large antelopes increased or showed stable populations. In contrast, medium and small ungulates showed continuously decreasing trends. During the same period, rainfall, water availability from artificial water points and the crop encroaching outside Nazinga Game Ranch increased. After an initial significant reduction, illegal human signs increased. However, we showed that human signs were positively correlated with the abundance of large ungulates but negatively correlated with the abundance of medium and small ones. In conclusion, this study showed that some isolated mammal populations could be restored and maintained in the long term, in spite of being surrounded by highly cultivated areas.

Keep the nest clean: survival advantages of corpse removal in ants.

Sociality increases exposure to pathogens. Therefore, social insects have developed a wide range of behavioural defences, known as 'social immunity'. However, the benefits of these behaviours in terms of colony survival have been scarcely investigated. We tested the survival advantage of prophylaxis, i.e. corpse removal, in ants. Over 50 days, we compared the survival of ants in colonies that were free to remove corpses with those that were restricted in their corpse removal. From Day 8 onwards, the survival of adult workers was significantly higher in colonies that were allowed to remove corpses normally. Overall, larvae survived better than adults, but were slightly affected by the presence of corpses in the nest. When removal was restricted, ants removed as many corpses as they could and moved the remaining corpses away from brood, typically to the nest corners. These results show the importance of nest maintenance and prophylactic behaviour in social insects.

Harmonised statistics and maps of forest biomass and increment in Europe.

Forest biomass is an essential resource in relation to the green transition and its assessment is key for the sustainable management of forest resources. Here, we present a forest biomass dataset for Europe based on the best available inventory and satellite data, with a higher level of harmonisation and spatial resolution than other existing data. This database provides statistics and maps of the forest area, biomass stock and their share available for wood supply in the year 2020, and statistics on gross and net volume increment in 2010-2020, for 38 European countries. The statistics of most countries are available at a sub-national scale and are derived from National Forest Inventory data, harmonised using common reference definitions and estimation methodology, and updated to a common year using a modelling approach. For those counties without harmonised statistics, data were derived from the State of Europe's Forest 2020 Report at the national scale. The maps are coherent with the statistics and depict the spatial distribution of the forest variables at 100 m resolution.

The nucleoid-associated protein Fis directly modulates the synthesis of cellulose, an essential component of pellicle-biofilms in the phytopathogenic bacterium Dickeya dadantii.

Bacteria use biofilm structures to colonize surfaces and to survive in hostile conditions, and numerous bacteria produce cellulose as a biofilm matrix polymer. Hence, expression of the bcs operon, responsible for cellulose biosynthesis, must be finely regulated in order to allow bacteria to adopt the proper surface-associated behaviours. Here we show that in the phytopathogenic bacterium, Dickeya dadantii, production of cellulose is required for pellicle-biofilm formation and resistance to chlorine treatments. Expression of the bcs operon is growth phase-regulated and is stimulated in biofilms. Furthermore, we unexpectedly found that the nucleoid-associated protein and global regulator of virulence functions, Fis, directly represses bcs operon expression by interacting with an operator that is absent from the bcs operon of animal pathogenic bacteria and the plant pathogenic bacterium Pectobacterium. Moreover, production of cellulose enhances plant surface colonization by D. dadantii. Overall, these data suggest that cellulose production and biofilm formation may be important factors for surface colonization by D. dadantii and its subsequent survival in hostile environments. This report also presents a new example of how bacteria can modulate the action of a global regulator to co-ordinate basic metabolism, virulence and modifications of lifestyle.

Game over! Wildlife collapse in northern Central African Republic.

The wildlife populations of northern Central African Republic (CAR) have long suffered intense uncontrolled hunting. Socio-political turmoil in northern CAR that started in 2002 resulted in a rebellion in 2006. An aerial sample count was carried out in northern CAR after the ceasefire to assess the impact of this troubled period on wildlife. The survey was flown at the end of the dry season in February-March 2010. It covered a landscape complex of 95,000 km² comprising national parks, hunting reserves and community hunting areas. Comparison with earlier surveys revealed a dramatic decline of wildlife: the numbers of large mammals fell by 94% in 30 years, probably due to poaching, loss of habitat and diseases brought by illegal movements of cattle. Elephant (Loxodonta africana), Reduncinae and topi (Damaliscus lunatus) populations showed the greatest decline (each over 90%). Other species declined by 70-80% during the same period. The future of wildlife in this area is dark without a strong commitment to provide adequate funding and quickly implement of determined field management. Reinforced cooperation with neighbouring Chad and Sudan is required since they are facing similar problems.

A regional inventory and monitoring setup to evaluate bark peeling damage by red deer (Cervus elaphus) in coniferous plantations in Southern Belgium.

Bark peeling by red deer (Cervus elaphus L.) has become a serious issue for productive forests in western Europe. The damage is particularly severe on species such as spruce, as these become vulnerable to fungus attacks that result in considerably depreciated timber. This article presents a monitoring setup for recent bark peeling damage in spruce plantings in Wallonia (southern part of Belgium). This setup implies to collect data annually from a survey involving cluster sampling. It has been employed since 2004 in coniferous stands amounting to 165,000 ha of land, where Norway spruce is the predominant species. The study area was divided into blocks delineated along features preventing deer migrations. A set of indicators was computed either at the whole study area level or at block level. The resulting set of indicators enabled forest managers to follow up debarking intensity in productive forests. Additional analyses were carried out in order to assess the relationship between the social position of trees in the stand and the debarking probability on the one hand, and the relationship between the variation in damage magnitude and seasonality, namely summer versus winter, on the other hand.

Which environmental factors control extreme thermal events in rivers? A multi-scale approach (Wallonia, Belgium).

Managers need to know how to mitigate rising stream water temperature (WT) due to climate change. This requires identifying the environmental drivers that influence thermal regime and determining the spatial area where interventions are most effective. We hypothesized that (i) extreme thermal events can be influenced by a set of environmental factors that reduce thermal sensitivity and (ii) the role played by those factors varies spatially. To test these hypotheses, we (i) determined which of the environmental variables reported to be the most influential affected WT and (ii)identified the spatial scales over which those environmental variables influenced WT. To this end, the influence of multi-scale environmental variables, namely land cover, topography (channel slope, elevation), hydromorphology (channel sinuosity, water level, watershed area, baseflow index) and shade conditions, was analyzed on the three model variables (day thermal sensitivity, night thermal sensitivity, and non-convective thermal flux) in the model developed by Georges et al. (2021) of the temporal thermal dynamics of daily maximum WT during extreme events. Values were calculated on six spatial scales (the entire upstream catchment and the associated 1 km and 2 km circular buffer, and 50 m wide corridors on each side of the stream with the associated 1 km and 2 km circular buffer). The period considered was 17 extreme days during the summer identified by Georges et al. (2021) based on WT data measured every 10 min for 7 years (2012-2018) at 92 measurement sites. Sites were located evenly throughout the Wallonia (southern Belgium) hydrological network. Results showed that shade, baseflow index (a proxy of the influence of groundwater), water level and watershed area were the most significant variables influencing thermal sensitivity. Since managers with finite financial and human resources can act on only a few environmental variables, we advocate restoring and preserving the vegetation cover that limits solar radiation on the watercourse as a cost-effective solution to reduce thermal sensitivity. Moreover, management at small spatial scale (50 m riparian buffer) should be strategically promoted (for finance and staffing) as our results show that a larger management scale is not more effective in reducing thermal sensitivity to extreme events.

Nickel promotes biofilm formation by Escherichia coli K-12 strains that produce curli.

The survival of bacteria exposed to toxic compounds is a multifactorial phenomenon, involving well-known molecular mechanisms of resistance but also less-well-understood mechanisms of tolerance that need to be clarified. In particular, the contribution of biofilm formation to survival in the presence of toxic compounds, such as nickel, was investigated in this study. We found that a subinhibitory concentration of nickel leads Escherichia coli bacteria to change their lifestyle, developing biofilm structures rather than growing as free-floating cells. Interestingly, whereas nickel and magnesium both alter the global cell surface charge, only nickel promotes biofilm formation in our system. Genetic evidence indicates that biofilm formation induced by nickel is mediated by the transcriptional induction of the adhesive curli-encoding genes. Biofilm formation induced by nickel does not rely on efflux mechanisms using the RcnA pump, as these require a higher concentration of nickel to be activated. Our results demonstrate that the nickel-induced biofilm formation in E. coli is an adaptational process, occurring through a transcriptional effect on genes coding for adherence structures. The biofilm lifestyle is obviously a selective advantage in the presence of nickel, but the means by which it improves bacterial survival needs to be investigated.

Malaria risk assessment and mapping using satellite imagery and boosted regression trees in the Peruvian Amazon.

This is the first study to assess the risk of co-endemic Plasmodium vivax and Plasmodium falciparum transmission in the Peruvian Amazon using boosted regression tree (BRT) models based on social and environmental predictors derived from satellite imagery and data. Yearly cross-validated BRT models were created to discriminate high-risk (annual parasite index API > 10 cases/1000 people) and very-high-risk for malaria (API > 50 cases/1000 people) in 2766 georeferenced villages of Loreto department, between 2010-2017 as other parts in the article (graphs, tables, and texts). Predictors were cumulative annual rainfall, forest coverage, annual forest loss, annual mean land surface temperature, normalized difference vegetation index (NDVI), normalized difference water index (NDWI), shortest distance to rivers, time to populated villages, and population density. BRT models built with predictor data of a given year efficiently discriminated the malaria risk for that year in villages (area under the ROC curve (AUC) > 0.80), and most models also effectively predicted malaria risk in the following year. Cumulative rainfall, population density and time to populated villages were consistently the top three predictors for both P. vivax and P. falciparum incidence. Maps created using the BRT models characterize the spatial distribution of the malaria incidence in Loreto and should contribute to malaria-related decision making in the area.

Microbiological disinfection of water and air by photocatalysis.

This article is aimed at presenting (i) a fundamental research on the efficiency of photocatalysis in water disinfection and (ii) the efficiency of a photocatalytic prototype, developed by Buxair firm, to remove avian influenza virus in air. In water disinfection, two model strains of Escherichia coli (K12 PHL849 and K12 PHL1273) were selected and a comparison of the efficiencies of TiO2 Degussa P-25 versus TiO2 Millennium PC500 were estimated. A more important inactivation of E. coli PHL1273 was obtained on TiO2 Millennium PC500, in line with its better adherence on this solid. An experimental study was performed using a dialysis membrane to investigate the impact of the contact between the microorganisms and the photocatalyst and to determine the role of H2O2 generated in situ. In air disinfection, a total inactivation of virus A/H5N2, close to avian influenza virus A/H5N2, was obtained in a single pass in the Buxair® gas phase dynamic photoreactor using a contaminated air flow rate of 40 m3/h.

Dans cette publication, nous rapportons une étude fondamentale sur l'efficacité du procédé photocatalytique pour éliminer les bactéries présentes en solution aqueuse ainsi qu'une étude préliminaire concernant l'efficacité d'un prototype photocatalytique, développé par la société Buxair, pour éliminer le virus de la grippe aviaire présent dans l'air. En phase aqueuse, deux souches de E. coli ont été sélectionnées (la souche K12 PHL849 et la souche K12 PHL1273) et inactivées en présence de deux photocatalyseurs. Une inactivation beaucoup plus importante de la souche adhérente (PHL1273) se produit en présence du photocatalyseur TiO2 PC500. L'importance du contact entre photocatalyseur et bactérie et le rôle du peroxyde d'hydrogène susceptible d'être produit lors du procédé photocatalytique sont étudiés en utilisant une membrane de dialyse.

UAS imagery reveals new survey opportunities for counting hippos.

INTRODUCTION: The common hippopotamus Hippopotamus amphibius L. is a vulnerable species that requires efficient methods to monitor its populations for conservation purposes. Rapid evolution of civil drones provides new opportunities but survey protocols still need development. This study aims to determine the optimal flight parameters for accurate population estimates. A second objective is to evaluate the effects of three environmental factors: wind speed, sun reflection and cloud cover. METHOD: We estimated the population of two main hippo schools (Dungu and Wilibadi II) located in Garamba National Park in Democratic republic of Congo. Eight observers reviewed 252 photos taken over the Dungu school, representing a total of 2016 experimental units. A detection rate and a level of certainty were associated with each experimental unit, and five parameters were related to each count: flight height, three environmental parameters (sun reflection on water surface, cloud cover, and wind speed), and observers' experience. RESULTS: Flight height reduced the observers' confidence in their detection ability, rather than the detection itself. For accurate counts of large groups an average height of 150 m was shown to be a good compromise between animal detection without zooming in and the area covered in one frame. Wind speed had little influence on the counts, but it affected the performance of the UAS. Sun reflection reduced the detection rate of hippos and increased level of certainty, while cloud cover reduced detection rates slightly. Therefore, we recommend flying when the sun is still low on the horizon and when there is little cloud, or when cloud cover is light and even. This last point reinforces our recommendation for flights early in the day. The counts also showed large differences between groups of inexperienced and experienced observers. Experienced observers achieved better detection rates and were generally more confident in their detection. Experienced observers detected 86.5% of the hippos on average (confidence interval = ±0.76%). When applied to data from the second site, the detection was 84.3% (confidence interval = ±1.84%). Two correction factors were then calculated, as the inverse of the detection rate, based on the estimated number of hippos present during one flight (Factor 1) or in the general population respectively (Factor 2). Factor 2 especially was consistent with previous studies using traditional aerial counts (1.22 vs 1.25). Factor 2 was found to be appropriate for use by experienced observers. These results confirm the use of correction factor 2 for hippo surveys, regardless of the study site, as it accounts for hippo behavior. Optimum counting and cost efficiency were achieved with two trained observers counting 7 pictures. CONCLUSION: This study is a promising approach for routine surveys of the hippopotamus which is a species usually ignored in wildlife counts. Drone technology is expected to improve rapidly; therefore UAS could become a very useful and affordable survey tool for other species requiring specific monitoring.

Present-day central African forest is a legacy of the 19th century human history.

The populations of light-demanding trees that dominate the canopy of central African forests are now aging. Here, we show that the lack of regeneration of these populations began ca. 165 ya (around 1850) after major anthropogenic disturbances ceased. Since 1885, less itinerancy and disturbance in the forest has occurred because the colonial administrations concentrated people and villages along the primary communication axes. Local populations formerly gardened the forest by creating scattered openings, which were sufficiently large for the establishment of light-demanding trees. Currently, common logging operations do not create suitable openings for the regeneration of these species, whereas deforestation degrades landscapes. Using an interdisciplinary approach, which included paleoecological, archaeological, historical, and dendrological data, we highlight the long-term history of human activities across central African forests and assess the contribution of these activities to present-day forest structure and composition. The conclusions of this sobering analysis present challenges to current silvicultural practices and to those of the future.

The Cpx system of Escherichia coli, a strategic signaling pathway for confronting adverse conditions and for settling biofilm communities?

Amongst the thirty or so two-component systems known in Escherichia coli, the Cpx system has been described as being a stress response system the main function of which is to respond to damage to the cell envelope via activation of proteases and folding catalysts. Nevertheless, the size of the Cpx regulon (several dozens of target genes) and the diversity of the physiological functions associated with it (resistance to hostile conditions, mobility, adherence factors, metabolism, etc.) indicate that the role of Cpx in cell physiology is undoubtedly more complex. The range of cellular functions affected by activation of the Cpx pathway corresponds quite closely to the description of the physiological state of cells grown in biofilms. We suggest that Cpx is a strategic signaling pathway for facing adverse conditions and for settling biofilm communities. Current knowledge of the regulatory mechanisms of the CpxR response (transcriptional and post-transcriptional) and the interactions between CpxR and the other bacterial regulatory systems are presented.

Dealing with paralogy in RADseq data: in silico detection and single nucleotide polymorphism validation in Robinia pseudoacacia L.

The RADseq technology allows researchers to efficiently develop thousands of polymorphic loci across multiple individuals with little or no prior information on the genome. However, many questions remain about the biases inherent to this technology. Notably, sequence misalignments arising from paralogy may affect the development of single nucleotide polymorphism (SNP) markers and the estimation of genetic diversity. We evaluated the impact of putative paralog loci on genetic diversity estimation during the development of SNPs from a RADseq dataset for the nonmodel tree species Robinia pseudoacacia L. We sequenced nine genotypes and analyzed the frequency of putative paralogous RAD loci as a function of both the depth of coverage and the mismatch threshold allowed between loci. Putative paralogy was detected in a very variable number of loci, from 1% to more than 20%, with the depth of coverage having a major influence on the result. Putative paralogy artificially increased the observed degree of polymorphism and resulting estimates of diversity. The choice of the depth of coverage also affected diversity estimation and SNP validation: A low threshold decreased the chances of detecting minor alleles while a high threshold increased allelic dropout. SNP validation was better for the low threshold (4×) than for the high threshold (18×) we tested. Using the strategy developed here, we were able to validate more than 80% of the SNPs tested by means of individual genotyping, resulting in a readily usable set of 330 SNPs, suitable for use in population genetics applications.

Contamination of abiotic surfaces: what a colonizing bacterium sees and how to blur it.

Many microbes are able to interfere with solid surfaces and trigger highly sophisticated colonization responses that include expression of specific properties such as increased resistances to antimicrobial agents. An anticontamination strategy might be to prevent adhesion by interfering with the surface-sensing processes and repelling the pioneering cells, to maintain the cellular sensitivity to antimicrobial agents. Recent studies have shown that differences in the physiological state of free-floating and attached bacteria, which could explain the increased levels of resistance, are triggered very early during attachment. Two-component-mediated signalling mechanisms are involved in these surface-sensing processes. Drugs and surface treatments able to interfere with the stimulation factors of these sensing systems (water activity and accumulation of proteins within the periplasm) could "blind" the colonizing bacteria and delay surface contamination.

Designing the European Road Safety Observatory.

The unavailability of consistent traffic accident data and road safety information limits the opportunities to provide target approaches to reduce road crashes. The European commission has decided to meet the demand for this data by establishing a new Road Safety Observatory. The structure and much of the initial content is being developed within the SafetyNet Integrated Project. This paper describes the structure of its key components.