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Tropical forest and swidden agriculture are declining, while industrial tree plantations are continuously expanding due to a robust global demand for timber and pulp. However, little is known about the processes, trends and mechanisms of the tropical forest-swidden-plantation (TFSP) nexus. Global ongoing initiatives including the United Nations Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation in Developing Countries (UN-REDD Programme), not only have repeatedly emphasized the significance of conserving forests, reforestation and afforestation, but also pushed swidden agriculture to the forefront of a long-standing international debate of climate change and biodiversity. Many facets limit our understanding of swidden agriculture and its roles in forest loss and plantations expansion.The lack of geographic and demographic data and their dynamics across the tropics undoubtedly further aggravates this situation since the first appeals for eradication of shifting cultivation by the Food and Agriculture Organization (FAO) in the late 1950s. Although recent studies have significantly enriched our knowledge of forest loss and plantation expansion, previous research has proceeded separately and has yet to be integrated under the umbrella of 'sustainable development of swidden agriculture'. Efforts are needed to investigate the dynamics of the TFSP nexus for the sake of a synergetic goal of climate mitigation, biodiversity conservation, and poverty alleviation.industrial plantation expansion, natural forest loss, swidden agriculture transformation, the UN-REDD Programme, tropical forest-swidden-plantation (TFSP) nexus | INTRODUCTIONSwidden agriculture (called many things, including shifting cultivation or slash-and-burn farming), has a variable length of fallow period and slash-and-burn intensity and is continuously evolving with much change since the mid-20th century (FAO Staff, 1957), some forms of swidden can be sustainable in human-environment that do not cause reduced fallow through population increase and/or commercial demand for crops/ produce context (Kukla et al., 2019). It remains a widespread but controversial farming practice and/or land use category especially in the hilly areas and low-medium mountains of the tropics [the Figure 1(A)] (Cairns, 2015;Heinimann et al., 2017;van Vliet et al., 2012). Sometimes, swidden is a straw to clutch for millions of impoverished upland ethnic groups facing constantly changing markets and meteorological disasters (e.g., floods and droughts caused by El Niño and La Niña) 2009;Smith & Dressler, 2019). The evolution and/or transformation not only matter the livelihoods and ethnic identity of swiddendependent uplanders, but it also trigger endless debates about swidden agriculture and how it relates to carbon emission or sequestration and biological diversity gain or loss (Fox

Currently, the historical archive images of Landsat family sensors are probably the most effective data products for tracking global longitudinal changes since the 1970s. However, the issue of the degree and extent of cloud coverage is always a challenge and varies distinctively worldwide. So far, acquisition probability (AP) analyses of cloud cover (CC) of Landsat observations have been conducted with different sensors at regional scale. To our knowledge, CC probability analysis for the newly-launched Landsat-8 Operational Land Imager (OLI) across China is not reported. In this paper, monthly, seasonal, and annual APs for Landsat OLI (44,228 in total) images over China acquired from April 2013 to October 2016 with various CC thresholds were analyzed. The results showed that: first, the cumulative average APs of all OLI data over China at the CC thresholds ≤30% was about 49.6% which illustrated the availability of OLI imagery across China. Second, the spatial patterns of 10%, 20%, and 30% CC thresholds of OLI observations, coincided well with the precipitation distributions separated by the respective 200 mm, 400 mm, and 800 mm isohyetal lines. Third, the APs of images with the 30% CC threshold are the highest in autumn and winter especially in October of 58.7%, while the corresponding lowest probability occurred in June of 41.0%. Finally, the spatial differences in APs of targeted images with ≤30% CC thresholds were quite significant. At regional scales, the arid and semi-arid areas, Inland River and Songliao River basins, and northwestern side of the Hu Huanyong population line had the larger probabilities of obtaining high-quality images. Our study suggested that OLI imagery satisfy the data requirements needed for land surface monitoring, although there existed obvious spatio-temporal differences in APs over China at the 30% CC threshold.

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The release of global gridded population datasets, including the Gridded Population of the World (GPW), Global Human Settlement Population Grid (GHS-POP), WorldPop, and LandScan, have greatly facilitated cross-comparison for ongoing research related to anthropogenic impacts. However, little attention is paid to the consistency and discrepancy of these gridded products in the regions with rapid changes in local population, e.g., Mainland Southeast Asia (MSEA), where the countries have experienced fast population growth since the 1950s. This awkward situation is unsurprisingly aggravated because of national scarce demographics and incomplete census counts, which further limits their appropriate usage. Thus, comparative analyses of them become the priority of their better application. Here, the consistency and discrepancy of the four common global gridded population datasets were cross-compared by combing the 2015 provincial population statistics (census and yearbooks) via error-comparison based statistical methods. The results showed that: (1) the LandScan performs the best both in spatial accuracy and estimated errors, then followed by the WorldPop, GHS-POP, and GPW in MSEA. (2) Provincial differences in estimated errors indicated that the LandScan better reveals the spatial pattern of population density in Thailand and Vietnam, while the WorldPop performs slightly better in Myanmar and Laos, and both fit well in Cambodia. (3) Substantial errors among the four gridded datasets normally occur in the provincial units with larger population density (over 610 persons/km2) and a rapid population growth rate (greater than 1.54%), respectively. The new findings in MSEA indicated that future usage of these datasets should pay attention to the estimated population in the areas characterized by high population density and rapid population growth.

Investigating the spatio-temporal transmission features and process of novel coronavirus disease 2019 (COVID-19) mitigation strategies are of great practical significance to understand the development of COVID-19 and establish international cooperation for prevention and control. In this paper, the cumulative number of confirmed cases, number of confirmed cases per day and cumulative number of deaths, were used to compare transmission paths, outbreaks timelines, and coping strategies of COVID-19 in China and the US. The results revealed that: first, the COVID-19 outbreaks in both China and the US exhibited a 6-week initiation stage. In China, the COVID-19 erupted in late January. It lasted only a short period of time and was almost completely contained within 6–8 weeks. But the COVID-19 erupted in early March in the US and was still in the peak or post-peak stage. Second, in China, the COVID-19 emerged in Wuhan and spread to other regions of Hubei Province and then nationwide, exhibiting a cross(“+”)-shaped of spread with Wuhan city as the center. Importantly, the COVID-19 in China had a large concentration and there were no national outbreaks. In contrast, the COVID-19 in the US first spread through New York and the western and eastern coasts but has since emerged throughout the entire country. Third, the lack of emergency response planning in both countries in the early stage (about 6-week) hampered COVID-19 prevention. However, actively high-pressure prevention and control measures were used to basically control COVID-19 in early March in China. And then China has gradually resumed business and production activities. Unfortunately, the US government missed the best opportunity to contain the epidemic. Faced with the choice between economic recovery and coronavirus containment, the US removed the quarantine and restriction measures too early. The COVID-19 is continuing to spread in the country and blossom everywhere, still showing no signs of receding.