With a few exceptions, comprehensive lists of alien plants that invade natural ecosystems are lacking in sub-Saharan Africa. Some available lists are either preliminary or localised, or focus on ...agricultural weeds. This study set out to compile a list of alien plant species that are invading natural ecosystems and rangelands in five countries in eastern Africa, and to map the distribution of the species that threaten ecosystem integrity and productivity. The location of all alien plant species seen during surveys between 2008 and 2016 was recorded using a hand-held GPS device, as well as their status in terms of either being present and/or naturalised, or invasive and spreading. Individual occurrence records were summarised at the scale of half degree grid cells (∼55 km × 55 km). The survey covered almost half (522) of the 1063 grid cells in Ethiopia, Kenya, Tanzania, Uganda and Rwanda. We recorded 164 invasive alien species in 110 genera and 47 families. We provide further information on the distribution and impacts of 30 species considered to have the greatest impacts in terms of transforming natural ecosystems, as well as on a further 21 species with limited distributions that could potentially become ecosystem transformers. Invasive alien plants are clearly a widespread and growing problem in eastern Africa, and capacity to manage them effectively remains a problem. A great deal of work needs to be done to raise awareness of the problem, and to identify appropriate responses that will be effective in resource-poor countries.
•We compared three OBIA programs for mapping invasive alien plants (IAP) along roadsides.•We mapped IAP species with a sequential process, masking first non-vegetation classes.•eCognition hold better ...classification results in mapping land cover and IAP.•OTB/Monteverdi and ArcGIS showed good performance in land-cover mapping and poorer performance in IAP mapping.•Spectral and phenological species traits should be considered when monitoring IAP.
Roads and roadsides provide dispersal channels for non-native invasive alien plants (IAP), many of which hold devastating impacts in the economy, human health, biodiversity and ecosystem functionality. Remote sensing is an essential tool for efficiently assessing and monitoring the dynamics of IAP along roads. In this study, we explore the potentialities of object based image analysis (OBIA) approach to map several invasive plant species along roads using very high spatial resolution imagery. We compared the performance of OBIA approaches implemented in one open source software (OTB/Monteverdi) against those available in two proprietary programs (eCognition and ArcGIS). We analysed the images by two sequential processes. First, we obtained a land-cover map for 15 study sites by segmenting the images with the algorithms Mean Shift Segmentation (MSS) and Multiresolution Segmentation (MRS), and by classifying the segmented images with the algorithms Support Vector Machine (SVM), Nearest Neighbour Classifier (NNC) and Maximum Likelihood Classifier (MLC). We created a mask using the polygons classified as non-vegetation to crop the images of the 15 study sites. Second, we repeated the previous segmentation and classification steps over the 15 masked images of vegetated areas using the same algorithms. OTB/Monteverdi, with MSS and SVM algorithms, showed to be a good software for land-cover mapping (OA = 87.0%), as well as ArcGIS, with MSS and MLC algorithms (OA = 84.3%). However, these two programs, using the same segmentation algorithms, did not achieve good accuracy results when mapping IAP species (OAOTB/Monteverdi = 63.3%; OAArcGIS = 45.7%). eCognition, with MRS and NNC algorithms, reached better classification results in both land-cover and IAP maps (OALand-cover = 95.7%; OAInvasive-plant = 92.8%). ’Bare soil’ and ‘Road’, and ‘A. donax’ were the classes with best and worst overall accuracy, respectively, when mapping land-cover classes in the three programs. ‘Other trees’ was the class with the most accurate and significant differences in the three programs when mapping IAP species. The separation of each invasive species should be improved with a phenology-based design of field surveys. This study demonstrates the effectiveness of sequential segmentation and classification of RS data for mapping and monitoring plant invasions along linear infrastructures, which allows to reduce the time, cost and hazard of extensive field campaigns along roadsides.
Invasive alien plants (IAPs) can negatively affect plant taxonomic diversity, community stability, and invasibility in the invaded habitats. This study aimed to assess the degree of influence of the ...IAP Solidago canadensis L. under various levels of invasion (i.e., light, moderate, and heavy invasion based on its relative abundance in the invaded communities) on plant taxonomic diversity, community stability, and invasibility. In addition, we determined the contribution of plant taxonomic diversity to community stability and invasibility under various levels of S. canadensis invasion. The degree of influence of S. canadensis on plant taxonomic diversity and community stability increases as the level of S. canadensis invasion increases. Community invasibility increases as the level of S. canadensis invasion increases. The competitive advantage of S. canadensis is negatively associated with all indexes of plant taxonomic diversity and community stability but positively connected with community invasibility. Community stability is positively related to Shannon's diversity and Simpson's dominance indexes but negatively associated with community invasibility. Inversely, communities were more likely to be invaded when they had less plant taxonomic diversity. Thus, plant communities with lower values of plant taxonomic diversity and community stability are more vulnerable to S. canadensis invasion. Plant diversity causes a greater pressure on community stability than the other indexes of plant taxonomic diversity under various levels of S. canadensis invasion. However, the contribution intensity of the number of plant species to community invasibility is higher than the other indexes of plant taxonomic diversity under various levels of S. canadensis invasion.
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•Community invasibility increases as the level of S. canadensis invasion increases.•Community invasibility is negatively associated with plant taxonomic diversity.•Community invasibility is negatively associated with community stability.•Community stability is mainly affected by plant diversity.•Community invasibility is chiefly affected by the number of plant species.
Many alien plant species are introduced to urban areas to create, augment or restore ecosystem services (ES). However, many of these species spread beyond original plantings, sometimes causing ...negative effects on existing ES or creating novel ecosystem disservices (EDS). An understanding of the perceptions of urban residents regarding invasive alien plants (IAPs) and the ES and EDS they provide is needed for the effective prioritisation of IAP management efforts in cities. Using the city of Cape Town, South Africa as a case study, we conducted questionnaire-based surveys (online and face-to-face) to determine the perceptions of urban residents regarding IAPs and their capacity to provide ES and EDS.
Most urban residents perceive IAPs negatively (i.e. agreeing that they create EDS), but many recognise their importance in providing ES. Although most residents are not opposed to the management of IAPs, such actions are not perceived as a high priority relative to other environmental problems. Socio-demographic variables such as age, education, environmental awareness, and ethnicity shape urban residents' perceptions of IAPs. Older, more educated respondents were more likely to perceive IAPs negatively, while respondents with greater environmental awareness were aware of the benefits provided by IAPs. This study highlights the need to integrate public perceptions into the planning and management of IAPs and emphasises the importance of including ES assessments into the decision-making process, particularly in urban areas.
•Most urban residents perceive invasive alien plants negatively, but many also recognise their importance.•The management of invasive alien plants is not perceived as a high priority relative to other environmental problems.•Age, education, environmental awareness and ethnicity shape urban residents' perceptions of invasive alien plants.
Biological invasion poses a major threat to biodiversity and conservation efforts in protected areas. The Greater Shennongjia Area (GSA) is one of China's 16 key areas for biodiversity, as stated in ...the China National Biodiversity Conservation Strategy and Action Plan. However, the local authorities lack appropriate data on the extent and impact of exotic species in protected areas, as well as lack the capacity and motivation to properly plan for exotic species strategy and action plan to support both prevention, control as well as management of exotic plants in their jurisdiction. In addition, while most previous studies have focused on exotic species in protected areas, little effort has been devoted to specifying which environmental factors contribute to the difference between protected and non-protected areas. Here, we explored the current distribution pattern of the richness and abundance of exotic species in relation to environmental variables within the GSA. In total, we found 84 exotic plant species, of which 41 exotic species within the protected areas, in 64 genera and 27 families, predominately from Asteraceae, Fabaceae, and Poaceae. The generalized linear mixed models (GLMMs) revealed that the protection status and the distance to human settlements were the most important predictors of exotic plant richness and abundance in the GSA. Our results showed that the average exotic plant richness and coverage in the protected areas were 22% and 31% lower than outside the protected areas, respectively. Such differences were probably the result of anthropogenic activities (e.g., proximity to human settlements and the proportion of cropland). Although protected areas provide an important barrier against plant invasions, invasion may be a tricky issue for protected area management in the future. The Alliance of Protected areas in Western Hubei and Eastern Chongqing will need to further consider stringent control and management strategies for the entry of exotic species into protected areas to effectively maintain the continuity and integrity of the GSA's biodiversity and ecosystems. Our results provided guidance and support to enhance the capacity of scientific and effective management and sustainable development of the Shennongjia World Natural Heritage Site and other protected areas.
•41 exotic plants, 68.3% of which are invasive inside the protected areas in the GSA.•Protected areas are lower on the richness and abundance of exotic plants.•The less anthropogenic pressures in protected areas, the less exotic plants invasion.•Exotic plants are threatening the OUV of Shennongjia World Natural Heritage Site.•The Alliance of Protected Areas should proactively defend against exotic species.
The preparation of biochar capped magnetic nanoparticles as adsorbents for the removal of methylene blue (MB), bromophenol blue (BPB) and rhodamine B (RhB) dyes is reported. Morphological studies of ...the untreated magnetic biochar nanoadsorbent showed monodispersed particles of about 20 nm. Brunauer, Emmett and Teller (BET) analysis revealed surface area of 138.28 m2/g while saturation magnetization was 12.61 emu/g. The energy bandgap of pure magnetite was reduced from 4.03 to 2.70 eV after capping with biochar. Maximum adsorption capacity (Qo) of the dyes onto the magnetic biochar are 14.39, 16.47 and 2.65 mg/g for MB, RhB and BPB respectively. The Langmuir equation best interpreted the sorption of methylene blue while Freundlich equation was more suitable for the sorption of bromophenol blue and Rhodamine B dyes. FTIR spectra of the magnetic biochar nanoadsorbent after adsorption indicated that uptake of the organic dyes occurred through physisorption. Competitive adsorption studies indicate the sorption of methylene blue, and bromophenol blue dyes occurred in acidic medium in comparison to neutral and alkaline media. The result from the study also shows that ethanol is the best eluent for the desorption of the organic dyes and eluted about 70% of adsorbed dyes in the first run.
We tested the insecticidal efficacy of different powders as surface treatment against the rice weevil (Sitophilus oryzae) adults. We have applied dusts from five invasive alien plant species ...(Solidago canadensis, Solidago gigantea, Amorpha fruticosa, Rhus typhina, Ailanthus altissima) and two inert dusts, i.e. wood ash from Norway Spruce (Picea abies) and commercial product SilicoSec® (as diatomaceous earth). Mortality was evaluated from 1st till 7th day after exposure, at 20 and 25 °C, two values of relative humidity and two doses (20 and 40 g/m2). After Day 7, alive beetles were placed into clean Petri dishes, and mortality counts were measured from 8th till 14th day. In general, we have detected poor efficacy of plant powders against S. oryzae. SilicoSec® at 20 g/m2 caused 100 % mortality at 25 °C and 55% RH, after seven days. Wood ash (13.46% SiO2) was less effective in comparison to SilicoSec® (79.48% SiO2), as approx. 60% mortality was recorded at the same conditions. We have detected that leaves of A. altissima and flowers od S. gigantea are rich with polyphenols (like catechin hydrate), on average almost 17 mg/g in S. gigantea flowers. Flowers and leaves of Solidago species are also rich with essential oil, like beta-copaene. The results of our research indicate that the powders of invasive plants are closer to fragrant roses in controlling S. oryzae adults, while the gun for this pest is only diatomaceous earth. To improve the effectiveness of invasive plant products, we suggest testing their independent effectiveness in liquid form as well as combinations of their essential oils with inert dusts.
•Insecticidal efficacy of powders of tested invasive alien plant species is very low.•The highest insecticidal efficacy against the rice weevil adults has diatomaceous earth.•We suggest testing the efficacy of simultaneous use of essential oils of invasive alien plants and inert dusts.
•A system for categorizing biocontrol outcomes is explained.•The outcomes of biocontrol against 54 weed species in South Africa are tabled.•Categorization allows for a detailed, overall view of what ...has been achieved.•The procedures adopted may be suitable for acceptance and use more widely.
The biological control of weeds, i.e. invasive alien plant species, depends on the release and establishment of host-specific plant-damaging insect, mite, or pathogen species from the country of origin of the target weed. These ‘natural enemies’ (agents) variously damage their target hosts and may reduce their vigor and invasiveness. Over time, populations of the target weed may be influenced and these outcomes can be observed and/or measured. The impacts of biocontrol agents and the outcomes of biological control are usually summarized using brief descriptive terms which have been previously defined and widely applied but are unsatisfactory from several viewpoints. Recently, a conceptual model was put forward that illustrates and categorizes the possible results of agent impacts at a plant population level. The details of releases of agents and their impacts against 54 species of target weeds in South Africa, since 1913, are given as elaborations of that system. Outcomes are categorized for different regions and habitats, according to measures of changes in density, biomass, area occupied, and rate of spread of the targeted weed species. The categorizations have been updated and verified through extensive consultations with local experts. The traditional descriptive assessments of outcomes in weed biological control have now been replaced in South Africa by implementing this more-rigorous system which may, with modifications, have wider applicability, in other regions or countries.
•We assess seed dispersal rates of invasive Lantana across canopy cover gradient.•Fruit crop size of Lantana shrubs was higher under low canopy cover.•Higher number of seed dispersers visited Lantana ...under low canopy cover.•Open-canopy habitats would be more prone to Lantana invasion.•Similarly, canopy openings via lopping, may enable invasion in forest habitats.
Lantana camara (hereafter, Lantana) is among the worst invasive alien plants spread extensively across Africa, Australia and Asia at an alarming rate, posing significant challenges to conservation of native biodiversity. While, Lantana invasion is widely recognised to be more pronounced in open-canopy habitats (including deciduous forests, forest edges and gaps), the potential role of variation in seed dispersal across habitats varying in overstory canopy cover is poorly understood.Avian frugivores are among primary seed dispersers of the fleshy-fruited Lantana. We monitored 45 Lantana shrubs across a gradient of overstory canopy cover to determine the relationship between fruiting intensity and canopy cover. We watched 80 Lantana shrubs (240 h) across a canopy cover gradient to determine 1) differences in frugivore assemblage visiting Lantana across open- and closed-canopy habitats, 2) drivers of frugivore visitation on Lantana, and 3) relationship between seed disperser visitation rate and overstory canopy cover. We found that Lantana shrubs under low overstory canopy cover had higher fruit abundance than those in high canopy cover. Frugivore assemblage differed between Lantana shrubs in open- versus closed-canopy cover habitats. Drivers of frugivore visitation on Lantana varied across different frugivore species with a greater probability of occurrence of bulbuls (the primary seed dispersers of Lantana) on shrubs under low overstory canopy cover.Visitation rates of the effective seed dispersers were higher on shrubs under low overstory canopy cover. Thus, there was greater chances of dispersal of seeds in habitats with low overstory canopy cover.The study demonstrates variable fruiting intensity and fruit removal rate as a driver of differences in dispersal of seeds across habitats. It highlights greater vulnerability of open habitats to invasion and the need to prioritise Lantana management efforts in open habitats. Anthropogenic activities that lead to canopy openings (e.g. tree lopping and logging) likely facilitate Lantana invasion through greater fruit production and seed dispersal.
Invasive alien species are among the main global drivers of biodiversity loss posing major challenges to nature conservation and to managers of protected areas.
The present study applied a ...methodological framework that combined invasive Species Distribution Models, based on propagule pressure, abiotic and biotic factors for 14 invasive alien plants of Union concern in Italy, with the local interpretable model-agnostic explanation analysis aiming to map, evaluate and analyse the risk of plant invasions across the country, inside and outside the network of protected areas.
Using a hierarchical invasive Species Distribution Model, we explored the combined effect of propagule pressure, abiotic and biotic factors on shaping invasive alien plant occurrence across three biogeographic regions (Alpine, Continental, and Mediterranean) and realms (terrestrial and aquatic) in Italy. We disentangled the role of propagule pressure, abiotic and biotic factors on invasive alien plant distribution and projected invasion risk maps. We compared the risk posed by invasive alien plants inside and outside protected areas.
Invasive alien plant distribution varied across biogeographic regions and realms and unevenly threatens protected areas. As an alien's occurrence and risk on a national scale are linked with abiotic factors followed by propagule pressure, their local distribution in protected areas is shaped by propagule pressure and biotic filters. The proposed modelling framework for the assessment of the risk posed by invasive alien plants across spatial scales and under different protection regimes represents an attempt to fill the gap between theory and practice in conservation planning helping to identify scale, site, and species-specific priorities of management, monitoring and control actions. Based on solid theory and on free geographic information, it has great potential for application to wider networks of protected areas in the world and to any invasive alien plant, aiding improved management strategies claimed by the environmental legislation and national and global strategies.
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•Plant invasions vary across realms, biogeographic regions and protection regimes.•On a national scale invasion is promoted by abiotic factors and propagule pressure.•On protected areas, low anthropic pressure and biotic filters, regulate invasions.•Terrestrial plants represent a higher threat to protected areas than aquatic ones.•Spatial modelling aid tailored management across spatial and administrative scales.
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