Madagascar's burned area from Sentinel-2 imagery (2016-2022): Four times higher than from lower resolution sensors

Madagascar is one of the most burned regions in the world, to the point that it has been called the 'Isle of fire' or the 'Burning Island'. An accurate characterization of the burned area (BA) is crucial for understanding the true situation and impacts of fires on this island, where there is an active scientific debate on how fire affects multiple environmental and socioeconomic aspects, and how fire regimes should be in a complex context with differing interests. Despite this, recent advances have revealed that BA in Madagascar is poorly characterised by the currently available global BA products. In this work, we present, validate, and explore a BA database at 20 m spatial resolution for Madagascar covering the period 2016-2022. The database was built based on 75,010 Sentinel-2 images using a two-phase BA detection algorithm. The validation with independent long-term reference units showed Dice coefficients ≥79 %, omission errors ≤24 %, commission errors ≤18 %, and a relative bias ≥ - 8 %. An intercomparison with other available global BA products (GABAM, FireCCI51, C3SBA11, or MCD64) demonstrated that our product (i) exhibits temporal consistency, (ii) represents a significant accuracy improvement, as it reduces BA underestimations by about eightfold, (iii) yields BA estimates four times higher, and (iv) shows enhanced capability in detecting fires of all sizes. The observed BA spatial patterns were heterogeneous across the island, with 32 % of the grasslands burning annually, in contrast to other land cover types such as the dense tropical forest where <2 % burned every year. We conclude that the BA characterization in Madagascar must be addressed using imagery at spatial resolution higher than MODIS or Sentinel-3 (≥250 m), and temporal resolution higher than Landsat (16 days) to deal with cloudiness, the rapid attenuation of burn scars signals, and small fire patches.

Madagascar's fire regimes challenge global assumptions about landscape degradation

Narratives of landscape degradation are often linked to unsustainable fire use by local communities. Madagascar is a case in point: the island is considered globally exceptional, with its remarkable endemic biodiversity viewed as threatened by unsustainable anthropogenic fire. Yet, fire regimes on Madagascar have not been empirically characterised or globally contextualised. Here, we contribute a comparative approach to determining relationships between regional fire regimes and global patterns and trends, applied to Madagascar using MODIS remote sensing data (2003-2019). Rather than a global exception, we show that Madagascar's fire regimes are similar to 88% of tropical burned area with shared climate and vegetation characteristics, and can be considered a microcosm of most tropical fire regimes. From 2003-2019, landscape-scale fire declined across tropical grassy biomes (17%-44% excluding Madagascar), and on Madagascar at a relatively fast rate (36%-46%). Thus, high tree loss anomalies on the island (1.25-4.77× the tropical average) were not explained by any general expansion of landscape-scale fire in grassy biomes. Rather, tree loss anomalies centred in forests, and could not be explained by landscape-scale fire escaping from savannas into forests. Unexpectedly, the highest tree loss anomalies on Madagascar (4.77×) occurred in environments without landscape-scale fire, where the role of small-scale fires (<21 h [0.21 km² ]) is unknown. While landscape-scale fire declined across tropical grassy biomes, trends in tropical forests reflected important differences among regions, indicating a need to better understand regional variation in the anthropogenic drivers of forest loss and fire risk. Our new understanding of Madagascar's fire regimes offers two lessons with global implications: first, landscape-scale fire is declining across tropical grassy biomes and does not explain high tree loss anomalies on Madagascar. Second, landscape-scale fire is not uniformly associated with tropical forest loss, indicating a need for socio-ecological context in framing new narratives of fire and ecosystem degradation.

Consensus and controversy in the discipline of invasion science

Approaches, values, and perceptions in invasion science are highly dynamic, and like in other disciplines, views among different people can diverge. This has led to debate in the field specifically surrounding the core themes of values, management, impacts, and terminology. Considering these debates, we surveyed 698 scientists and practitioners globally to assess levels of polarization (opposing views) on core and contentious topics. The survey was distributed online (via Google Forms) and promoted through listservs and social media. Although there were generally high levels of consensus among respondents, there was some polarization (scores of ≥0.39 [top quartile]). Relating to values, there was high polarization regarding claims of invasive species denialism, whether invasive species contribute to biodiversity, and how biodiversity reporting should be conducted. With regard to management, there were polarized views on banning the commercial use of beneficial invasive species, the extent to which stakeholders' perceptions should influence management, whether invasive species use alone is an appropriate control strategy, and whether eradication of invasive plants is possible. For impacts, there was high polarization concerning whether invasive species drive or are a side effect of degradation and whether invasive species benefits are understated. For terminology, polarized views related to defining invasive species based only on spread, whether species can be labeled as invasive in their native ranges, and whether language used is too xenophobic. Factor and regression analysis revealed that views were particularly divergent between people working on different invasive taxa (plants and mammals) and in different disciplines (between biologists and social scientists), between academics and practitioners, and between world regions (between Africa and the Global North). Unlike in other studies, age and gender had a limited influence on response patterns. Better integration globally and between disciplines, taxa, and sectors (e.g., academic vs. practitioners) could help build broader understanding and consensus.

Integrated Methods for Monitoring the Invasive Potential and Management of Heracleum mantegazzianum (giant hogweed) in Switzerland

Biological invasions are a major driver of human-induced global environmental change. This makes monitoring of potential spread, population changes and control measures necessary for guiding management. We illustrate the value of integrated methods (species distribution modelling (SDM), plant population monitoring and questionnaires) for monitoring and assessing invasions of Heracleum mantegazzianum (giant hogweed) over time in Switzerland. SDMs highlighted the potential spread of the species, uncovered ecological mechanisms underlying invasions and guided monitoring at a regional level. We used adaptive and repeat plant sampling to monitor invasive population status and changes, and assess the effectiveness of H. mantegazzianum management over three periods (2005, 2013 and 2018) within the pre-Alps, Vaud. We also conducted questionnaire surveys with managers and the public. Multiscale modelling, and integrating global and regional SDMs, provided the best predictions, showing that H. mantegazzianum can potentially invade large parts of Switzerland, especially below 2 000 m a.s.l. Over time, populations of invasive H. mantegazzianum in the Vaud pre-Alps have declined, which is most likely due to a sharp rise in management uptake post 2007 (7% of municipalities before 2007 to 86% in 2018). The level of known invasive populations has decreased by 54% over time. Some municipalities have even successfully eradicated H. mantegazzianum within their borders. However, a few areas, particularly in the rural, higher-altitude municipalities, where management was not implemented effectively, populations have expanded, which could hamper control efforts at lower altitudes. We provide encouraging evidence that control measures can be effective in reducing plant invasions with long-term commitment, as well as a good template for using integrated methodological approaches to better study and monitor invasive alien species.

Explaining people's perceptions of invasive alien species: A conceptual framework

Human perceptions of nature and the environment are increasingly being recognised as important for environmental management and conservation. Understanding people's perceptions is crucial for understanding behaviour and developing effective management strategies to maintain, preserve and improve biodiversity, ecosystem services and human well-being. As an interdisciplinary team, we produced a synthesis of the key factors that influence people's perceptions of invasive alien species, and ordered them in a conceptual framework. In a context of considerable complexity and variation across time and space, we identified six broad-scale dimensions: (1) attributes of the individual perceiving the invasive alien species; (2) characteristics of the invasive alien species itself; (3) effects of the invasion (including negative and positive impacts, i.e. benefits and costs); (4) socio-cultural context; (5) landscape context; and (6) institutional and policy context. A number of underlying and facilitating aspects for each of these six overarching dimensions are also identified and discussed. Synthesising and understanding the main factors that influence people's perceptions is useful to guide future research, to facilitate dialogue and negotiation between actors, and to aid management and policy formulation and governance of invasive alien species. This can help to circumvent and mitigate conflicts, support prioritisation plans, improve stakeholder engagement platforms, and implement control measures.

From killing lists to healthy country: Aboriginal approaches to weed control in the Kimberley, Western Australia

The Australian Government's funding of land management by Aboriginal communities aims to enable them to manage natural and cultural resources according to their values and aspirations. But this approach is countered in the case of weed management, where the emphasis is on killing plants that are identified on invasive alien species lists prepared by government agencies. Based on field research with Bardi-Jawi, Bunuba, Ngurrara, Nyikina Mangala and Wunggurr land managers in the Kimberley region of Western Australia, we observed that 27 of 35 weed control projects followed the government agency weed lists for species-led control. Of these 27 projects, only two were considered successful in meeting Aboriginal cultural aspirations. In most of the other cases, the list-based approach generated frustration among Aboriginal rangers who felt they were engaged in purposeless killing. In contrast, we found that elders and rangers preferred site-based approaches that considered landscape and vegetation management from their culturally specific and highly contextual geographies of 'healthy country'. We outline instances where ranger groups have adopted site-based management that has been informed by geographies of healthy country and argue that such an approach offers a better alternative to current list-based weed control and produces positive outcomes for Aboriginal communities.

Divergent perceptions of the 'neo-Australian' forests of lowland eastern Madagascar: Invasions, transitions, and livelihoods

Grevillea banksii (Proteaceae), a non-native shrubby tree, has in the past five decades expanded to cover hundreds of thousands of hectares in lowland eastern Madagascar, accompanied by other Australian and pan-tropical species, including Melaleuca quinquenervia, Acacia mangium, and Eucalyptus spp. We investigate contrasting perceptions of this new landscape with view to facilitate future management. Field research was based on 290 surveys, key informant interviews, and ecological inventories at six sites from Farafangana in the south to Fenerive Est in the north. After documenting the ecology and usage of grevillea, we analyse differing ways in which it can be perceived. Perceptions promoted by scientists and administrators include the contrasting ideas of beneficial landscape greening, rampant biological invasion, novel ecosystems, and forest transition. Perceptions held by local actors are highly determined by practical livelihood concerns. These local views are largely positive due to the major role of grevillea firewood and charcoal sales in livelihoods; however, context plays a major role and a number of disadvantages are perceived as well, including difficulty of removal, competition with crop and pasture land, and the respiratory health impacts of involvement in charcoal production. We conclude that policymakers and managers - in this case and in similar cases around the world - need to be more reflexive on the ways in which environmental problems are framed and to put those frames more in conversation with local people's experiences in order to productively resolve invasive species management dilemmas.

The role of invasive alien species in shaping local livelihoods and human well-being: A review

Invasive alien species are a well-recognised driver of social-ecological change globally. Much research has focused on ecological impacts, but the role of invasive species for livelihoods and human well-being is less well known. Understanding the effects (benefits and costs) of invasive species on livelihoods and human well-being is important for guiding policy formulation and management. Here we review the literature on the role of invasive species in livelihoods to assess what is known, identify knowledge gaps and provide recommendations for future research. Literature was collected using key word searches and included both journal publications and grey literature. Slightly less than half (48%) of species studied had both substantial positive and negative impacts on local livelihoods (e.g. Australian Acacia spp. species; Camelus dromedaries; Lantana camara; Prosopis spp.), with 37% inducing mainly costs (Chromolaena odorata; Lissachatina fulica; Opuntia stricta) and 16% producing mainly benefits (Opuntia ficus-indica; Acacia spp.). Some species, such as Acacia dealbata, fell into different categories depending on the social-ecological context. Key benefits or services included the provision of fuelwood, fodder, timber and food products for local households communities and to a lesser extent supporting and regulating services such as soil improvement and shade. A number of species also provided cultural services such as recreation and spiritual values and provided many with an opportunity to earn a cash income. However, invasive species also harm livelihoods and increase vulnerability through encroaching on land and reducing mobility or access. They can also decrease the supply of natural resources used by households and reduce agricultural production (livestock and/or crops) which can result in losses of income and increased vulnerability. Furthermore, some invasive species were seen to have negative implications for human health and safety and reduce the cultural value of landscapes. Economic impacts on livelihoods as a result of invasive species were highly variable and very dependent on the social-ecological contexts. These negative implications can reduce resilience and adaptive capacity of households and communities thus increasing their vulnerability to change. Drawing on case studies we highlight that efforts for managing invasive species need to safeguard livelihood benefits while mitigating negative impacts. In concluding we highlight future research and policy needs on the topic of invasive species, livelihoods and human well-being.

The human and social dimensions of invasion science and management

Biological invasions are a leading cause of global environmental change given their effects on both humans and biodiversity. Humans introduce invasive alien species and may facilitate their establishment and spread, which can alter ecosystem services, livelihoods, and human well-being. People perceive the benefits and costs of these species through the lens of diverse value systems; these perspectives influence decisions about when and where to manage them. Despite the entanglement of humans with invasive alien species, most research on the topic has focused on their ecological aspects. Only relatively recently have the human and social dimensions of invasions started to receive sustained attention in light of their importance for understanding and governing biological invasions. This editorial draws on contributions to a special issue on the "Human and Social Dimensions of Invasion Science" and other literature to elucidate major trends and current contributions in this research area. We examine the relation between humans and biological invasions in terms of four crosscutting themes: (1) how people cause biological invasions; (2) how people conceptualise and perceive them; (3) how people are affected - both positively and negatively - by them; and (4) how people respond to them. We also highlight several ways in which research on the human and social dimensions of invasion science improves understanding, stakeholder engagement, and management.

The progress of interdisciplinarity in invasion science

Interdisciplinarity is needed to gain knowledge of the ecology of invasive species and invaded ecosystems, and of the human dimensions of biological invasions. We combine a quantitative literature review with a qualitative historical narrative to document the progress of interdisciplinarity in invasion science since 1950. Our review shows that 92.4% of interdisciplinary publications (out of 9192) focus on ecological questions, 4.4% on social ones, and 3.2% on social-ecological ones. The emergence of invasion science out of ecology might explain why interdisciplinarity has remained mostly within the natural sciences. Nevertheless, invasion science is attracting social-ecological collaborations to understand ecological challenges, and to develop novel approaches to address new ideas, concepts, and invasion-related questions between scholars and stakeholders. We discuss ways to reframe invasion science as a field centred on interlinked social-ecological dynamics to bring science, governance and society together in a common effort to deal with invasions.

Chance long-distance or human-mediated dispersal? How Acacia s.l. farnesiana attained its pan-tropical distribution

Acacia s.l. farnesiana, which originates from Mesoamerica, is the most widely distributed Acacia s.l. species across the tropics. It is assumed that the plant was transferred across the Atlantic to southern Europe by Spanish explorers, and then spread across the Old World tropics through a combination of chance long-distance and human-mediated dispersal. Our study uses genetic analysis and information from historical sources to test the relative roles of chance and human-mediated dispersal in its distribution. The results confirm the Mesoamerican origins of the plant and show three patterns of human-mediated dispersal. Samples from Spain showed greater genetic diversity than those from other Old World tropics, suggesting more instances of transatlantic introductions from the Americas to that country than to other parts of Africa and Asia. Individuals from the Philippines matched a population from South Central Mexico and were likely to have been direct, trans-Pacific introductions. Australian samples were genetically unique, indicating that the arrival of the species in the continent was independent of these European colonial activities. This suggests the possibility of pre-European human-mediated dispersal across the Pacific Ocean. These significant findings raise new questions for biogeographic studies that assume chance or transoceanic dispersal for disjunct plant distributions.

The history of introduction of the African baobab (Adansonia digitata, Malvaceae: Bombacoideae) in the Indian subcontinent

To investigate the pathways of introduction of the African baobab, Adansonia digitata, to the Indian subcontinent, we examined 10 microsatellite loci in individuals from Africa, India, the Mascarenes and Malaysia, and matched this with historical evidence of human interactions between source and destination regions. Genetic analysis showed broad congruence of African clusters with biogeographic regions except along the Zambezi (Mozambique) and Kilwa (Tanzania), where populations included a mixture of individuals assigned to at least two different clusters. Individuals from West Africa, the Mascarenes, southeast India and Malaysia shared a cluster. Baobabs from western and central India clustered separately from Africa. Genetic diversity was lower in populations from the Indian subcontinent than in African populations, but the former contained private alleles. Phylogenetic analysis showed Indian populations were closest to those from the Mombasa-Dar es Salaam coast. The genetic results provide evidence of multiple introductions of African baobabs to the Indian subcontinent over a longer time period than previously assumed. Individuals belonging to different genetic clusters in Zambezi and Kilwa may reflect the history of trafficking captives from inland areas to supply the slave trade between the fifteenth and nineteenth centuries. Baobabs in the Mascarenes, southeast India and Malaysia indicate introduction from West Africa through eighteenth and nineteenth century European colonial networks.

Farmer-managed natural regeneration enhances rural livelihoods in dryland west Africa

Declining agricultural productivity, land clearance and climate change are compounding the vulnerability of already marginal rural populations in West Africa. 'Farmer-Managed Natural Regeneration' (FMNR) is an approach to arable land restoration and reforestation that seeks to reconcile sustained food production, conservation of soils, and protection of biodiversity. It involves selecting and protecting the most vigorous stems regrowing from live stumps of felled trees, pruning off all other stems, and pollarding the chosen stems to grow into straight trunks. Despite widespread enthusiasm and application of FMNR by environmental management and development projects, to date, no research has provided a measure of the aggregate livelihood impact of community adoption of FMNR. This paper places FMNR in the context of other agroforestry initiatives, then seeks to quantify the value of livelihood outcomes of FMNR. We review published and unpublished evidence about the impacts of FMNR, and present a new case study that addresses gaps in the evidence-base. The case study focuses on a FMNR project in the district of Talensi in the semi-arid Upper East Region in Ghana. The case study employs a social return on investment analysis, which identifies proxy financial values for non-economic as well as economic benefits. The results demonstrate income and agricultural benefits, but also show that asset creation, increased consumption of wild resources, health improvements, and psycho-social benefits created more value in FMNR-adopting households during the period of the study than increases in income and agricultural yields.

New genetic and linguistic analyses show ancient human influence on baobab evolution and distribution in Australia

This study investigates the role of human agency in the gene flow and geographical distribution of the Australian baobab, Adansonia gregorii. The genus Adansonia is a charismatic tree endemic to Africa, Madagascar, and northwest Australia that has long been valued by humans for its multiple uses. The distribution of genetic variation in baobabs in Africa has been partially attributed to human-mediated dispersal over millennia, but this relationship has never been investigated for the Australian species. We combined genetic and linguistic data to analyse geographic patterns of gene flow and movement of word-forms for A. gregorii in the Aboriginal languages of northwest Australia. Comprehensive assessment of genetic diversity showed weak geographic structure and high gene flow. Of potential dispersal vectors, humans were identified as most likely to have enabled gene flow across biogeographic barriers in northwest Australia. Genetic-linguistic analysis demonstrated congruence of gene flow patterns and directional movement of Aboriginal loanwords for A. gregorii. These findings, along with previous archaeobotanical evidence from the Late Pleistocene and Holocene, suggest that ancient humans significantly influenced the geographic distribution of Adansonia in northwest Australia.

The human dimension of fire regimes on Earth

Humans and their ancestors are unique in being a fire-making species, but 'natural' (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from 'natural' background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke-related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas-induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre-human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.

Proposition d'un cadre de représentation des bioinvasions en milieu rural : cas de

Dans certaines situations rurales où se conjuguent pauvreté des populations et rareté des ressources, l'analyse des conséquences de l'invasion d'une espèce ligneuse nécessite l'emploi d'un cadre d'approche large et objectif, qui inclue les interactions entre les paysans et les espaces envahis. L'article tire parti d'une courte étude conduite dans la commune d'Ambatofitorahana, au sud d'Ambositra, dans la région des Hautes Terres. Introduit d'Australie à Madagascar, où il est devenu invasif, le mimosa (Acacia dealbata) y constitue aujourd'hui une ressource renouvelable pour le paysannat. Les types d'usages relatifs à cet arbuste ont été préalablement sommairement caractérisés. La discussion des résultats, qui représente l'essentiel du corps de cet article, donne lieu à la proposition d'un cadre de représentation à différentes échelles pour appréhender correctement une bioinvasion en milieu rural. L'investigation de l'ensemble de l'impact socio-économique et écologique de ce processus nécessite de recourir à une gamme de niveaux d'organisation etd'échelle allantde la parcelle à l'ensemble du pays. Les avantages et inconvénients que recouvre l'invasion du mimosa à Madagascar se révèlent en effet spécifiques de chacun de ces niveaux d'analyse. À l'échelle des espaces ruraux, la valorisation apparaît essentiellement centrée sur la réalisation de jachères ligneuses et la production de combustibles (bois de feu et charbon de bois). L'analyse montre qu'au niveau des territoires ruraux, l'invasion de A. dealbata obéit à des phases de stabilisation suivies d'extensions, en lien étroit avec des périodes de valorisation suivies d'un relâchement dans l'utilisation de cette ressource. Les incidences socio-économiques de cette bioinvasion varient dès lors avec la période historique considérée. De manière permanente, la valorisation paysanne et l'occupation agricole des espaces ruraux demeurent le meilleur rempart à l'extension des surfaces envahies par le mimo sa dans les Hautes Terres malgaches. (Résumé d'auteur)

Fire in the Earth system

Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

Evaluation préliminaire des risques d'invasion par les essences forestières introduites à Madagascar

Il est désormais admis que l'introduction d'une espèce exotique en milieu insulaire s'accompagne toujours d'un risque environnemental, représenté par l'éventuel déclenchement d'une invasion biologique. À Madagascar, ce risque est d'autant plus élevé que les introductions de matériel végétal s'accroissent à un degré très supérieur à celui des actions de lutte préventive, que la fréquence et l'intensité des perturbations humaines facilitent les invasions, et que la biodiversité à protéger est remarquable. Un examen préliminaire des 406 introductions d'arbres et arbustes effectuées sur cette île à des fins forestières ou agroforestières révèle que 12,8% de ces espèces se sont avérées nuisibles dans d'autres pays, et que 39,2% présentent un risque potentiel pour Madagascar dans la mesure où elles sont au moins susceptibles de s'y naturaliser. Une liste de 19 espèces présentant un risque élevé d'invasion est présentée. Sept d'entre elles sont connues pour avoir, à la fois, une reproduction sexuée et une multiplication végétative par drageonnage importantes. Face à une telle menace, un plan de gestion s'impose sur le plan national de manière à hiérarchiser, puis mettre en oeuvre les actions de communication, de recherche, de lutte préventive et de détection précoce qui s'imposent. (Résumé d'auteur)