Mainland Southeast Asia Research Articles

Agricultural drought conditions over mainland Southeast Asia: Spatiotemporal characteristics revealed from MODIS-based vegetation time-series

Drought is a reoccurring slow-onset hazard event and has a tremendous impact on agricultural production and ecosystem health. Mainland Southeast Asia is a major rainfed crop-producing area of the world, and this region is increasingly vulnerable to drought hazards. However, the monitoring and characterization of agricultural and vegetative droughts in this region remains understudied. This paper presented the first comprehensive analysis of spatiotemporal characteristics and trends of agricultural and vegetative droughts across the region using the Vegetation Condition Index (VCI) based on the reconstructed MODIS-based vegetation time-series data between 2000 and 2021. This study also developed an approach for identifying severe drought years using annual extreme pixels. Results showed that vegetation-based drought characteristics and trends varied in space and time across the region. Central Myanmar suffered from the most frequent droughts (nearly 60%), but prolonged events were less common. By contrast, the Lower Mekong area suffered from frequent and prolonged drought conditions. Most of the recent severe droughts were observed in Cambodia, and this area is characterized by a drying trend. Regionally, the severe drought years were detected in 2000, 2004, 2005, 2010, 2016, 2019, and 2020, and they were commonly found in Central Myanmar, Thailand, and Cambodia. The analysis of drought years indicated that the temporal change pattern of drought has shifted from the northern regions (e.g., Central Myanmar) in 2010 to the Lower Mekong region in recent years. The findings of this study provide valuable information for drought early warning management and agricultural planning across mainland Southeast Asia.

Long journey of Indonesian Homo erectus: Arrival and dispersal in Java Island

The presence of Homo erectus in the Archipelago was identified very early when human remains were found in various ancient deposits on Java Island. The widespread distribution in the global Old World indicates their long migration route since they left Africa around 1.8 million years ago, spreading to Europe, East, and Southeast Asia, until finally reaching Java Island as the easternmost end of their migration route. Sea level regression during the Ice Age, which formed a land bridge across the Sunda Shelf, allowed migration during the Pleistocene from mainland Southeast Asia to islands Southeast Asia. Interpreted to have reached Java in the early Lower Pleistocene, their oldest fossils were found at Bumiayu, Sangiran, and Mojokerto. Their dispersal occurred for more than 1.5 million years on Java, with the discovery of younger Homo erectus sites in chronology. Discovery of the Middle Pleistocene Period were mainly deposited in volcanic layers of the Kabuh Formation in Sangiran, as well as Trinil, Kedungbrubus, Semedo, Rancah, and Patiayam. While related to younger chronologies, their fossil remains were found in the alluvial deposits of the Bengawan Solo at the sites of Ngandong, Sambungacan, and Ngawi. This assemblage of Javanese Homo erectus fossils consists of various anatomical components, mostly cranial and its fragments, complemented by maxilla-mandibular components, isolated teeth, and post-cranial fragments. Morphological, metric, geologic-stratigraphic, and radiometric dating analyses applied to these Homo erectus fossils indicate three evolutive stages among Javanese Homo erectus during the Pleistocene, namely – from the oldest to the youngest ones – archaic Homo erectus, typical Homo erectus, and progressive Homo erectus. The variability of earlier taxonomic names, such as Pithecanthropus (erectus, robustus, dubius, modjokertensis, soloensis) and Meganthropus paleojavanicus, are merely historical names given by researchers at the time and do not indicate genus or species differences. Within the evolutionary scope of Homo erectus in Java, there is only one genus (Homo) and one species (erectus).

Glacial changes in sea level modulated millennial-scale variability of Southeast Asian autumn monsoon rainfall

Most paleoclimate studies of Mainland Southeast Asia hydroclimate focus on the summer monsoon, with few studies investigating rainfall in other seasons. Here, we present a multiproxy stalagmite record (45,000 to 4,000years) from central Vietnam, a region that receives most of its annual rainfall in autumn (September-November). We find evidence of a prolonged dry period spanning the last glacial maximum that is punctuated by an abrupt shift to wetter conditions during the deglaciation at ~14 ka. Paired with climate model simulations, we show that sea-level change drives autumn monsoon rainfall variability on glacial-orbital timescales. Consistent with the dry signal in the stalagmite record, climate model simulations reveal that lower glacial sea level exposes land in the Gulf of Tonkin and along the South China Shelf, reducing convection and moisture delivery to central Vietnam. When sea level rises and these landmasses flood at ~14 ka, moisture delivery to central Vietnam increases, causing an abrupt shift from dry to wet conditions. On millennial timescales, we find signatures of well-known Heinrich Stadials (HS) (dry conditions) and Dansgaard-Oeschger Events (wet conditions). Model simulations show that during the dry HS, changes in sea surface temperature related to meltwater forcing cause the formation of an anomalous anticyclone in the Western Pacific, which advects dry air across central Vietnam, decreasing autumn rainfall. Notably, sea level modulates the magnitude of millennial-scale dry and wet phases by muting dry events and enhancing wet events during periods of low sea level, highlighting the importance of this mechanism to autumn monsoon variability.

Perspective on Particulate Matter: From Biomass Burning to the Health Crisis in Mainland Southeast Asia.

Air pollution, notably particulate matter pollution, has become a serious concern in Southeast Asia in recent decades. The combustion of biomass has been recognized to considerably increase air pollution problems from particulate matter in this region. Consequently, its effect on people in this area is significant. This article presents a synthesis of several datasets obtained from satellites, global emissions, global reanalysis, and the global burden of disease (GBD) to highlight the air quality issue and emphasize the health crisis in mainland Southeast Asia. We found that the death rates of people have increased significantly along with the rise of hotspots in mainland Southeast Asia over the last two decades (2000-2019). In comparison, most countries saw a considerable increase in the predicted fatality rates associated with chronic respiratory illnesses during those two decades. Several reports highlight the continued prevalence of chronic respiratory diseases likely related to poor air quality in Southeast Asia.

Satellite observed response of fire dynamics to vegetation water content and weather conditions in Southeast Asia

Fires greatly affect terrestrial ecosystems, climate, human health, and economy. Under the threat of global warming, assessing fire occurrence frequency and fire danger is critical to mitigate fire’s negative impacts. The state-of-the-art satellite microwave observation provides the unique opportunity to monitor vegetation water content (VWC) for multiple vegetation strata, yet still lacks associated investigation in fire dynamics. Here, we applied the multiple microwave Emissivity Difference Vegetation Indexes (EDVIs) as VWC proxies of different vegetation strata to explore their influence on fire occurrence frequency (given by the number of fires, NOF) and the cumulative fire radiant energy (FRE) in mainland Southeast Asia during 2015–2019; and compared to that with the commonly used fire weather indices from the Canadian Forest Fire Weather Index system. Then, we identified the optimal regression models to depict the relationship of fires with EDVIs and fire weather indices, respectively; and incorporated both kinds of indices in models to retrospectively predict NOF and FRE. Results show that: (1) the monthly mean NOF and FRE nonlinearly decrease with EDVI in mainland Southeast Asia, and 40–60% of the variances are explained by EDVI, which further improve to 60–70% by incorporating EDVIs of two different vegetation layers. (2) In comparison, NOF and FRE nonlinearly increase with fire weather indices, and connections are stronger than that with EDVI; nevertheless, combing fire weather indices with EDVI, especially with EDVIs of two vegetation layers provides almost the highest explanation for fires. (3) The log-linear and/or log-quadratic models are identified to outperform the other models in depicting the fire-EDVI and fire-fire weather indices relationships; and incorporating EDVI and fire weather indices in models generally improves the prediction accuracy. These findings reveal the differentiated VWC effects on NOF and FRE among vegetation strata and quantify the strong nonlinear response of fires to VWC and weather conditions in mainland Southeast Asia, which could provide new insight for fire prediction and fire danger assessments with the utility of microwave observations.

A Partial Prehistory of the Southwest Silk Road: Archaeometallurgical Networks along the Sub-Himalayan Corridor

Historical phenomena often have prehistoric precedents; with this paper we investigate the potential for archaeometallurgical analyses and networked data processing to elucidate the progenitors of the Southwest Silk Road in Mainland Southeast Asia and southern China. We present original microstructural, elemental and lead isotope data for 40 archaeological copper-base metal samples, mostly from the UNESCO-listed site of Halin, and lead isotope data for 24 geological copper-mineral samples, also from Myanmar. We combined these data with existing datasets (N = 98 total) and compared them to the 1000+ sample late prehistoric archaeometallurgical database available from Cambodia, Laos, Thailand, Vietnam and Yunnan. Lead isotope data, contextualized for alloy, find location and date, were interpreted manually for intra-site, inter-site and inter-regional consistency, which hint at significant multi-scalar connectivity from the late second millennium bc. To test this interpretation statistically, the archaeological lead isotope data were then processed using regionally adapted production-derived consistency parameters. Complex networks analysis using the Leiden community detection algorithm established groups of artefacts sharing lead isotopic consistency. Introducing the geographic component allowed for the identification of communities of sites with consistent assemblages. The four major communities were consistent with the manually interpreted exchange networks and suggest southern sections of the Southwest Silk Road were active in the late second millennium bc.

Impact of human and climate factors on vegetation changes in mainland southeast asia and yunnan province of China

Currently, although the greening is prevalent, it is unclear whether greening can truly improve vegetation productivity in the tropics and its main influence factors. To effectively manage vegetation, it is necessary not only to have a deep understanding of its characteristics but also to have a clear understanding of the main influencing factors. Based on Enhanced Vegetation Index (EVI) and Gross primary productivity (GPP) indexes in Mainland Southeast Asia and Yunnan province (China), we analyzed vegetation greenness and productivity, and revealed the main influencing factors. We found that:1) greening and productivity showed significant increase larger than significant decrease; the relative increase rate of productivity (0.26%/year) was higher than greenness (0.11%/year); the inconsistency between greenness and productivity appeared prevalent, accounting for 57.23%. 2) temperature and precipitation were the important factors for vegetation changes, with a greater impact on greenness than productivity in most regions. 3) for the total vegetation regions, about 56%–60% of the areas were dominated by human activities for greenness and productivity, and 38%–40% of the areas were dominantly affected by climate factors. For vegetation change, the 60.69% of the EVI significant increase region and 55.74% of the GPP significant increase region mainly influenced by climate factors; the 67.34% of the EVI significant decrease region and 86.28% of the GPP significant decrease region mainly influenced by human factors. In addition, productivity was inconsistent with greenness originating not only from climate factors, but also from high land use intensity. The results suggested simultaneous monitoring of vegetation greenness and productivity can serve as indicators for comprehensive understanding of vegetation dynamics to attain vegetation sustainable development in the tropics.

Le Hoabinhien et la reconstruction de la paléogéographie du Nord de Sumatra

The Hoabinhian is a Late Pleistocene and Holocene technocomplex in northern Sumatra and mainland Southeast Asia, characterized by the presence of unifacial pebbles (sumatraliths). In North Sumatra Hoabinhian sites are present as shell-middens in coastal areas and, in caves in mountainous areas. These sites have been established upstream and downstream of the river system since the Pleistocene. Recent 14C dating of several Hoabihian sites in North Sumatra show occupation between 12,000 and 3,000 years BP. At Loyang Mendale, Mabitce Cave, and Gedong Cave new data provide additional information on Hoabinhian sites in North Sumatra. Lithic tool morphology and technology show similarities to other Hoabinhian sites and indicate a process of adaptation to environmental conditions related to raw material sources and subsistence strategies. The new Hoabinhian sites in North Sumatra must now be reviewed and correlated with environmental aspects.

The savannization of tropical forests in mainland Southeast Asia since 2000

The savannization of tropical forests in mainland Southeast Asia since 2000

Reanalyzing the genetic history of Kra-Dai speakers from Thailand and new insights into their genetic interactions beyond Mainland Southeast Asia

Thailand is a country where over 60 languages from five language families (Austroasiatic, Austronesian, Hmong-Mien, Kra-Dai, and Sino-Tibetan) are spoken. The Kra-Dai language family is the most prevalent, and Thai, the official language of the country, belongs to it. Previous genome-wide studies on Thailand populations revealed a complex population structure and put some hypotheses forward concerning the population history of the country. However, many published populations have not been co-analyzed, and some aspects of population history were not explored adequately. In this study, we employ new methods to re-analyze published genome-wide genetic data on Thailand populations, with a focus on 14 Kra-Dai-speaking groups. Our analyses reveal South Asian ancestry in Kra-Dai-speaking Lao Isan and Khonmueang, and in Austroasiatic-speaking Palaung, in contrast to a previous study in which the data were generated. We support the admixture scenario for the formation of Kra-Dai-speaking groups from Thailand who harbor both Austroasiatic-related ancestry and Kra-Dai-related ancestry from outside of Thailand. We also provide evidence of bidirectional admixture between Southern Thai and Nayu, an Austronesian-speaking group from Southern Thailand. Challenging some previously reported genetic analyses, we reveal a close genetic relationship between Nayu and Austronesian-speaking groups from Island Southeast Asia (ISEA).

New species of the dancing semislug Cryptosemelus Collinge, 1902 (Eupulmonata, Ariophantidae) from Loei Province, northeastern Thailand with a key to genera of mainland Southeast Asian semislugs and a key to species of the genus.

In this study, we describe a new dancing semislug from a limestone hill area in northeastern Thailand. Cryptosemelusnigersp. nov. differs from the three recognized congener species from western and southern Thailand, due to differences in their body and shell lobes coloration, appearance of penial caecum, shape and surface texture of penis and epiphallus, and radula formula and morphology.

Molecular Characterization of Dengue Virus Strains from the 2019-2020 Epidemic in Hanoi, Vietnam.

Dengue virus (DENV), which has circulated in Vietnam for several decades, has multiple serotypes and genotypes. A 2019 dengue outbreak resulted in a larger number of cases than any other outbreak. We conducted a molecular characterization using samples collected in 2019-2020 from dengue patients in Hanoi and nearby cities located in northern Vietnam. The circulating serotypes were DENV-1 (25%, n = 22) and DENV-2 (73%, n = 64). Phylogenetic analyses revealed that all DENV-1 (n = 13) were genotype I and clustered to local strains circulating during the previous outbreak in the 2017, whereas DENV-2 consisted of two genotypes: Asian-I (n = 5), related to local strains from 2006-2022, and cosmopolitan (n = 18), the predominant genotype in this epidemic. The current cosmopolitan virus was identified as having an Asian-Pacific lineage. The virus was closely related to strains in other recent outbreaks in Southeast Asian countries and China. Multiple introductions occurred in 2016-2017, which were possibly from maritime Southeast Asia (Indonesia, Singapore, and Malaysia), mainland Southeast Asia (Cambodia and Thailand), or China, rather than from an expansion of localized Vietnamese cosmopolitan strains that were previously detected in the 2000s. We also analyzed the genetic relationship between Vietnam's cosmopolitan strain and recent global strains reported from Asia, Oceania, Africa, and South America. This analysis revealed that viruses of Asian-Pacific lineage are not restricted to Asia but have spread to Peru and Brazil in South America.

Prehistory and Ideology in Cold War Southeast Asia: The Politics of Wartime Archaeology in Thailand and the Democratic Republic of Vietnam, 1954–1975

The two decades comprised within the partition of Vietnam and the end of the Indochina Wars surprisingly saw major advances in prehistoric archaeology in the region. This article examines the political context and implications of archaeological investigations conducted in Thailand and the Democratic Republic of Vietnam under the guidance of, respectively, American and Soviet specialists, as an aspect of the cultural Cold War. Archaeological discoveries in both countries debunked colonial archaeology’s account of prehistoric Southeast Asia as a passive recipient of Chinese cultural influence by documenting autonomous technological development. The article argues that the new image of mainland Southeast Asia’ prehistory that formed by the early 1970s reflected the superpowers’ objective of empowering the region’s postcolonial nation-states notwithstanding their political contrasts, yet it was not equally congruent with the nationalist narratives of Thailand and North Vietnam.

Restoring Asia’s roar: Opportunities for tiger recovery across the historic range

Wildlife conservation in the Anthropocene requires bold conservation solutions including restoration of ecosystems and species. The recovery of large carnivore populations is a conservation goal which can generate significant benefits in terms of ecosystem services, ecological functionality, and human well-being. Tigers Panthera tigris, Asia’s most iconic species, are currently restricted to less than 10% of their historic range with recent national extinctions from a number of countries in mainland Southeast Asia. Tiger recovery through range expansion requires suitable habitat, a robust prey base, and high levels of institutional support for conservation. We explored government support for conservation to produce a ranking of the political opportunities for tiger restoration across current and former tiger range countries. We used this analysis, in combination with globally remotely sensed data-sets on human impact, to show that there is potential for significant tiger range expansion. We identified large expanses of currently unoccupied, but potentially suitable, habitat in at least 14 countries including all extant tiger range countries and four countries with extirpated tiger populations – Cambodia, Lao PDR, Viet Nam, and Kazakhstan. Thirty-two percent of expansion areas were within 50-km, and 50% within 100-km, of current tiger populations highlighting that in many landscapes range expansion could be driven by the natural dispersal of tigers provided connectivity is maintained or enhanced. The proportion of potential range within existing protected areas varied between <5% in India, Indonesia, and China, to >60% in Thailand and Cambodia. As such socially appropriate conservation approaches, in collaboration with local communities, will be necessary to support tiger recovery in many areas. We recommend that some of the areas which we have identified should be highlighted as significant for future tiger conservation by tiger range country governments. Whilst the landscapes and sites which we identify will require detailed ground-truthing, and all tiger reintroductions need extensive planning and feasibility assessments, safeguarding these areas for human-carnivore coexistence could provide significant planetary benefits and support both tiger recovery and Global Sustainable Development Goals.

Chinese Word Order in the Comparative Sino-Tibetan and Sociotypological Contexts

The present study discusses typology and variation of word order patterns in nominal and verb structures across 20 Chinese languages and compares them with another 43 languages from the Sino-Tibetan family. The methods employed are internal and external historical reconstruction and correlation studies from linguistic typology and sociolinguistics. The results show that the head-final tendency is a baseline across the family, but individual languages differ by the degree of head-initial structures allowed in a language, leading to a hybrid word order profile. On the one hand, Chinese languages consistently manifest the head-final noun phrase structures, whereas head-initial deviants can be explained either internally through reanalysis or externally through contact. On the other hand, Chinese verb phrases have varied toward head-initial structures due to contact with verb-medial languages of Mainland Southeast Asia, before reinstalling the head-final structures as a consequence of contact with verb-final languages in North Asia. When extralinguistic factors are considered, the typological north-south divide of Chinese appears to be geographically consistent and gradable by the latitude of individual Chinese language communities, confirming the validity of a broader typological cline from north to south in Eastern Eurasia.

Twenty-meter annual paddy rice area map for mainland Southeast Asia using Sentinel-1 synthetic-aperture-radar data

Abstract. Over 90 % of the world's rice is produced in the Asia–Pacific region. Synthetic-aperture radar (SAR) enables all-day and all-weather observations of rice distribution in tropical and subtropical regions. The complexity of rice cultivation patterns in tropical and subtropical regions makes it difficult to construct a representative data-relevant rice crop model, increasing the difficulty in extracting rice distributions from SAR data. To address this problem, a rice area mapping method for large regional tropical or subtropical areas based on time-series Sentinel-1 SAR data is proposed in this study. Based on the analysis of rice backscattering characteristics in mainland Southeast Asia, the combination of spatiotemporal statistical features with good generalization ability was selected and then input into the U-Net semantic segmentation model, combined with WorldCover data to reduce false alarms, finally the 20 m resolution rice area map of five countries in mainland Southeast Asia in 2019 was obtained. The proposed method achieved an accuracy of 92.20 % on the validation sample set, and the good agreement was obtained when comparing our rice area map with statistical data and other rice area maps at the national and provincial levels. The maximum coefficient of determination R2 was 0.93 at the national level and 0.97 at the provincial level. These results demonstrate the advantages of the proposed method in rice area mapping with complex cropping patterns and the reliability of the generated rice area maps. The 20 m annual paddy rice area map for mainland Southeast Asia is available at https://doi.org/10.5281/zenodo.7315076 (Sun et al., 2022b).

Contesting patriarchy: Employment and gender roles of East Asian middle-class marriage migrants in Taiwan

ABSTRACT Studies of trans-local marriages in Taiwan focused on Mainland Chinese and Southeast Asian women married to Taiwanese men, documenting how they had joined the lower rungs of the work force, and shouldered a major amount of family responsibilities that included reproductive roles. They were projected in literature and the media as subjugated women and objects of commodified marriages and exploitation. In contrast, marriage migration of middle-class women was seldom studied. This paper explores East Asian middle-class marriage migrants’ embodied experiences in their work and family roles, exposing them to the patriarchal structures and unequal power relations that exist in Taiwan. Twenty in-depth interviews were conducted from 2019 to 2021 on participants from Greater China (Mainland China, Hong Kong, and Macau), Korea, Japan, and Singapore. Advanced education, professional performance, and feminist consciousness have empowered these women to become agents of change in the family and the workplace and shall benefit Taiwan’s economy in the long run as highly skilled human resources.

Middle Pleistocene Pongo from Ganxian Cave in southern China with implications for understanding dental size evolution in orangutans

The Pongo fossil record of China extends from the Early Pleistocene to the Late Pleistocene, but to date, no late Middle Pleistocene samples of Pongo with precise absolute dating have been identified in southern China. Here, we report the recovery of 106 fossil teeth of Pongo from Ganxian Cave in the Bubing Basin, Guangxi, southern China. We dated the speleothems using Uranium-series and dated the two rhinoceros teeth using coupled electron spin resonance/Uranium-series dating methods to between 168.9 ± 2.4 ka and 362 ± 78 ka, respectively. These dates are consistent with the biostratigraphic and magnetostratigraphic age estimates. We further describe the fossil teeth from Ganxian Cave and compare them metrically to samples of fossil Pongo (i.e., Pongo weidenreichi, Pongo duboisi, Pongo palaeosumatrensis, Pongo javensis, and Pongo sp.) from the Early, Middle, and Late Pleistocene and to extant Pongo (i.e., Pongo pygmaeus and Pongo abelii) from Southeast Asia. Based on overall dental size, a high frequency of lingual cingulum remnants on the upper molars, and a low frequency of moderate to heavy wrinkling on the molars, we attribute the Ganxian fossils to P. weidenreichi. Compared with Pongo fossils from other mainland Southeast Asia sites, those from Ganxian confirm that dental size reduction of Pongo occurred principally during the Early and Middle Pleistocene. From the Middle to Late Pleistocene, all teeth except the P3 show little change in occlusal area, indicating that the size of these teeth remained relatively stable over time. The evolutionary trajectory of the Pongo dentition through time may be more complex than previously thought. More orangutan fossils with precise dating constraints are the keys to solving this issue.

New lithic evidence from Terminal Pleistocene-Early Holocene Zhongshan Rockshelter, Guangxi, southern China

The archaeological materials recovered during the 2018 excavation of Zhongshan Rockshelter (ZSRS) in Bubing Basin, Guangxi, southern China helps to fill a cultural gap during the terminal Paleolithic in the region. The evidence from the ZSRS, dated to ∼14,523–8,472 cal. BP, is comparable to other parts of southern China and mainland Southeast Asia where grinding techniques, complex settlement patterns and broad-spectrum subsistence strategies appeared. What distinguishes the ZSRS from other sites in the region however is the widespread use of flaked stone tools and ochre utilization, but with an absence of pottery. This is an excellent example of variation in foraging behavior in this spatio-temporal facies, where one size does not fit all. Regional differences suggest a more complex human foraging strategy rather than a single and fixed behavioral model across southern China during the Terminal Pleistocene to Early Holocene transition.

Autumn migration tracks of Helopsaltes grasshopper-warblers from Northeast Asia support recent taxonomic assignments.

Migration strategies are genetically inherited in most songbirds, and closely related species can exhibit markedly contrasting migration programs. Here, we investigate the autumn migration of one Helopsaltes grasshopper-warbler from a population near Magadan, North East Russia, based on light-level geolocation. Although often considered to belong to Middendorff's Grasshopper-warbler H. ochotensis, recent genetic studies suggest that birds from this population are more closely related to Pallas's Grasshopper-warbler H. certhiola. We compare the migratory behavior of the Magadan bird with two Pallas's Grasshopper-warblers tracked from populations in the Kolyma River valley and the Amur region, Russia. We found similar migration patterns in all three tracked individuals, with stopover sites in eastern China and wintering sites in mainland Southeast Asia, within the known range for Pallas's Grasshopper-warbler. Furthermore, based on morphological data compiled during bird ringing, we were able to confirm the presence of potential "Magadan grasshopper-warblers" during spring and autumn migration in Thailand. Our scant data provide further evidence that Magadan Helopsaltes, notwithstanding their morphological resemblance to Middendorff's Grasshopper-warbler, constitute a population of Pallas's Grasshopper-warbler.