Writing review & editing, Affiliation The Data behind Deforestation Causes of Deforestation A study conducted by the Food and Agriculture Organization (FAO) of the United Nations in 1985 (based on 90 tropical countries reporting forest fallow areas within the FAO/UNEP Tropical Forest Resources Assessment Project 1982 [49]) estimated the worldwide extent of shifting cultivation in the early 1980s at 400 Mha [50], and an assessment made in 2011 with the aim of estimating greenhouse gas emissions arrived at 260 Mha for the 2000s [1]. Furthermore, it should be noted that the large difference between the two spatial data sets (Fig 6) in arid and semiarid parts of Africa (Sahelian and Sudanian zones of northern Africa as well as parts of southern Africa) is partly due to the fact that Butler included other, non-shifting smallholder farming systems in his map. Spencer [45] indicates an approximate area under shifting cultivation (currently cultivated fields plus all stages of fallows) of around 110 million hectares (Mha) for Asia. These approaches, however, are still in the making and will require substantial resources. Laos, Vietnam) over the past 15 to 25 years is not reflected in this comparison. This number certainly requires further validation before it can be claimed to be an adequate estimate of the global area under shifting cultivation. First, we compared the Butler [13] map (Fig 4) with our own spatial estimate (Fig 5) of areas that were under shifting cultivation around 2010. The impacts of traditional agriculture on Environment are discussed below: 1. Yucatan Peninsula [66], northern South America (e.g. - India and Bangladesh: Shifting cultivation is estimated to disappear by 2030. Yes In Asia, we expect that continued rapid economic development and the related changes in agricultural practices and, more importantly, in the economic structure (from the primary to the secondary and tertiary sectors) may cause shifting cultivation to disappear faster than in Africa or the Americas. The difference appears plausible if we consider that Spencers estimate is based on a hand-drawn map and that Asia has seen considerable decreases in shifting cultivation since that map was created (see section on recent trends below). For Central and South America, the survey shows a mixed picture, with some areas being quite stable or even likely to experience expansion in the near future, and other areas (e.g. Environment; Why poison ivy is an unlikely climate change winner. Trends in humid tropical Africa vary widely. The period of cultivation is usually terminated when the soil shows signs of exhaustion or, more commonly, when the field is overrun by weeds. However, there are a number of other negative effects related to irrigation. The earlier 15-20 years cycle of shifting cultivation on a particular land has reduced to 2-3 years now. Visual interpretation has well-known limitations in terms of subjectivity and potentially limited reproducibility [29], but there are two main reasons why a visual approach has been chosen: Firstly, while a number of approaches has recently been developed to detect shifting cultivation based on automated approaches at the regional and national level using remote sensing data (e.g. To get a first estimation of the occurrence of shifting cultivation, we classified each cell under investigation into one of five shifting-cultivation occurrence classes: none, very low, low, moderate, or high. Intensive agriculture has dominated the global food production . Centre for Development and Environment, University of Bern, Bern, Switzerland, Roles Accordingly, they emphasized that the need for global data on annual global gridded land-use transitions from past-to-future presents a large and underdetermined problem [2]. Writing review & editing, Roles The selection process ensured that all are experts in the field, but there may be disciplinary or personal differences in the way that especially the future of shifting cultivation was assessed. As our aim was to provide, in a timely manner, a global-scale overview of landscapes showing signs of shifting cultivation for use in global land userelated earth system modeling scenarios [27], we worked at an aggregated level using one-degree cells, which corresponds approximately to the scale of current earth system model analyses. Overall, a decrease after 2030 and disappearance after 2060 is expected. The analysis presented is primarily qualitative with a supplementary quantitative analysis of the causes of forest . 2], while long cycles comprise fallow periods of more than 15 years (Villa et al., 2020; Villa et al., 2017 . No, Is the Subject Area "Agriculture" applicable to this article? Recent international efforts to compare and synthesize different earth system models have come with a strong focus on quantifying the past, current, and future contributions of land use to climate change [14]. Using the data and approach described above, each one-degree cell was examined visually at various zoom levels (roughly 1:100000 but, if necessary, occasionally at larger scales) to determine whether it showed the very specific spatio-temporal signature of shifting cultivation (see Fig 1). Extreme weather events like wildfires (which are responsible for an estimated 10% of degradation annually), droughts, and storm surges destroy millions of hectares of forest every year and their intensity is only increasing with global warming. There is a need to transform shifting cultivation to sustainable intensification. Hence, the occurrence level was estimated and not measured and the classification was based on a coarse assessment of the landscape (also see accuracy assessment below). Taking into consideration the stratification criteria, 328 one-degree cells were randomly selected to be validated. Shifting Cultivation Shifting Cultivation Agricultural Geography Agricultural Hearths Agricultural Production Regions Agricultural Revolutions Agriculture and Climate Agriculture and Pollution Agrochemicals Community Supported Agriculture Extensive Farming Feeding the World Food Desert Food Insecurity Food Movements Green Revolution Climate Change. The accuracy levels of our classification were high with an overall accuracy above 87%. The 270 first authors of these papers were listed and their email addresses were found. (Fig 2A): the global distribution of the stratified sample of the 328 one-degree cells used in the validation data set. Click through the PLOS taxonomy to find articles in your field. Secondly, the detection and monitoring of complex shifting cultivation mosaics using automated remote sensing approaches remains challenging [33,38,39] and the mentioned small spatio-temporal signature of vegetation clearings and regrowth is very specific to shifting cultivation and visual interpretation is therefore suitable [40]. We used a search string similar to the one used for the literature review: [Title]: "Shifting cultivation" or swidden or "slash-and-burn" or "slash and burn" or "shifting agriculture" AND [Year published]: 20052015. The analysis presented is primarily qualitative with a supplementary quantitative analysis of the causes of forest . (Fig 2C): One-degree cell with a mesh of 1/100 degree cells as a basic unit for the validation data set, green cells having a shifting cultivation occurrence class of >1% in our global classification. However, the expert survey confirms that shifting cultivation has fully disappeared between the 1970s and the 2000s in various areas of mainland Southeast Asia, such as southern Thailand, Peninsular Malaysia, and China. Yes 2.2). - Shifting cultivation also destroys the habitat of wild animals at large. The global food system is in crisis. Australia, the Gulf States, arid areas in Africa) or where it disappeared several decades ago (e.g. An online questionnaire was designed and sent to these 270 authors in September 2015 using survey monkey. The history of shifting cultivation is as old as the history of agriculture itself. South America shows mixed trends: Areas under shifting cultivation have clearly decreased in the southern Brazilian Amazon, whereas survey responses indicate that they are expanding in other parts of the Brazilian Amazon and in Peru. We are very grateful to Laura Ebneter, Manuel Abebe, Lukas Wuersch and Boris Fuhrer for their support in interpreting the satellite imagery and to Marlne Tibeault for the language editing. Extreme weather. Extreme precipitation events can disturb plant growth, particularly in recently burned forests, and make plants more vulnerable to flooding and soils to erosion. The spatio-temporal pattern of the annual deforestation data from 2000 to 2014 at a resolution of 30 meters provides the basis for our approximation. If the survey provided information about when (i.e. The area approximation of actual shifting cultivation landscapes was performed based on the average occurrence rates in the one-degree cells for each of the five classes above (>1% class: 0%; 19%: 5%; 1019%: 15%; 2039%: 30%; 40%:70%). The period of cultivation is usually terminated when the soil shows signs of exhaustion or, more commonly, when the field is overrun by weeds. Lastly, it is also problematic that shifting cultivation has been subject to recycling of statements about its importance that have no basis in thorough empirical research. The author has visited the entire Mizoram state and observed that shifting cultivation has a severe adverse impact on the environment, forest depletion and landscape degradation. The ranges are based on the expert survey and observed trends between the Butler map and our 2010 classification (Fig 5). Livestock may be at risk, both directly from heat stress and indirectly from reduced quality of their food supply. Omissions? Mosaic landscapes under shifting cultivation, with their dynamic mix of managed and natural land covers, often fall through the cracks in remote sensingbased land cover and land use classifications, as these are unable to adequately capture such landscapes dynamic nature and complex spectral and spatial signatures. PLoS ONE 12(9): Venezuela [67]), and Madagascar [68]. In soil-based agriculture, soil health is the most important foundation of a healthy farm ecosystem. For more information about PLOS Subject Areas, click However, it is important to underline that this assessment is based on very few survey responses (Fig 3) due to the small number of existing studies on shifting cultivation in Africa. In Central America, shifting cultivation is still widespread, and both Fig 6 and the survey results indicate an increase in some areas (e.g. No, Is the Subject Area "South America" applicable to this article? decadal), the areas newly classified as having shifting cultivation (blue in Fig 6) should be added to the original Butler map, thereby producing an updated estimated extent of shifting cultivation for this earlier period. Centre for Development and Environment, University of Bern, Bern, Switzerland, Roles Validation, This figure was elaborated by the first author using ArcGIS 10.4. https://doi.org/10.1371/journal.pone.0184479.g007. Supervision, By zooming into areas where these clearings indicate possible shifting cultivation, we were able to determine visually whether they were accompanied by the pattern of fallows characteristic of shifting cultivation (Fig 1E) or not (Fig 1D). in parts of Southeast Asia). Is the Subject Area "Land use" applicable to this article? Analysis of Landsat data back to Landsat4 (launched in 1982) could provide more than 30 years of pan-tropical records, covering a time of significant change in the distribution of shifting cultivation across the humid tropics and perhaps also in the length of fallow periods.
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