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Rubber plantations are among the most important in the world's tropical regions. They play a positive role in carbon sequestration and in delaying climate change, supplying strategic resources of natural rubber (NR), and aiding in poverty alleviation and rural revitalisation. This paper reviews six methods of research on carbon sinks in rubber plantations: the biomass inventory method, the biomass conversion factor continuous function method, the trade potential of carbon sinks method, the calculation method for carbon storage of rubber latex, the eddy covariance method, and the remote sensing image model method. This study clarifies the carbon sink assessment and enhancement model for rubber plantations and describes the composition of the carbon pool, which includes the aboveground and belowground vegetation biomass carbon pools, litter carbon pool, latex carbon pool, and soil carbon pool. It also examines influencing factors such as tree age, global climate change, and human disturbance, as well as improvement pathways including afforestation, fertilisation, irrigation, and tapping, and evaluation methods like field surveys, positional observations, remote sensing monitoring, and model simulation. Research on carbon sequestration in rubber plantations faces challenges, including the unclear dynamics of carbon sources and sequestration, uncertain spatial and temporal patterns, and the long-term lack of accurate monitoring of carbon sinks and technologies for increasing sinks and reducing emissions. Future research should focus on the methodology of rubber plantation carbon sequestration projects, the dynamics of carbon sequestration, and the spatial allocation pattern of carbon sequestration in rubber plantations. [ABSTRACT FROM AUTHOR]

Understanding the dynamic relationships between soil organic carbon (SOC) and stand age are essential to quantify and predict the terrestrial carbon sequestration potential. However, the spatial patterns in the response of rubber plantation SOC to stand age and their driving factors remain unclear. Based on SOC and its components measurement at different soil depths (0–40 cm) in rubber plantations under five different age classes (0–5, 5–10, 10–20, 20–30, and >30 years) in three major rubber cultivation regions in China, distribution pattern and controlling factors of SOC were investigated. We found that SOC and its components showed significant spatial variability vertically with soil depth and laterally across sampling sites. SOC contents in three major rubber cultivation regions range from 4.48 to 20.13 g kg−1 at a depth of 0–40 cm. Among the sampling sites, Jinghong had the highest SOC content at a depth of 0–10 cm (20.13 g kg−1). On a large‐scale, the relationship between SOC and stand age in rubber plantations did not show a consistent pattern among different sampling sites. Additionally, annual rainfall, soil moisture content, and soil pH had a stronger impact on SOC in rubber plantations compared to stand age. The results indicated that the spatial variability of SOC in rubber plantations with stand age could be influenced by specific soil properties and climate‐related variables at each sampling site. This study emphasized the significance of conducting multi‐site, multi‐scale studies to enhance our understanding of SOC dynamics and its influencing factors, and help to more accurately predict the dynamic changes of soil carbon storage in rubber plantations. [ABSTRACT FROM AUTHOR]

Background: Studying green manure decomposition in various returning methods can establish a scientific foundation for farmland nutrient management. Methods: In a rubber plantation on Hainan Island, China, utilized the nylon mesh bag method to imitate the decomposition of kudzu (whole plant, stem, and leaf) under two returning methods (mulching and burying) in two different sites (young and mature rubber plantations). The study examined the decomposition rate and nutrient release dynamics of kudzu, as well as the effects of kudzu reintroduction on several soil properties including soil pH, soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO3−-N), ammonium nitrogen (NH4+-N), available phosphorus (AP), and enzyme activities. Results: Compared with mulching, the burying returning method significantly increased the kudzu decomposition rate and nutrient release proportions. After 270 days, more than 80% of the C, N, and P in different components of kudzu were released. The decomposition rate was found to be more affected by the initial soil factors than by the endogenous nutrients of kudzu. Compared with CK, all kudzu treatments led to significant increases in soil enzyme activities and soil pH, SOC, NO3−-N, and AP concentrations in two rubber plantations. The TN and NH4+-N concentrations were significantly increased in mature rubber plantations, while the TP was the opposite. Conclusion: The kudzu returned can effectively alleviate soil acidic, improve soil nutrient availability, regulating soil enzyme activities of the rubber plantation in the short-term. These results provide a scientific basis for the rational application of kudzu in rubber plantations. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) demonstrated a new ecological factor that influences organisms through a multi-approach. Yet, the impacts of ALAN on understory plants remain largely unknown. We evaluated whether ALAN would affect the leaf mass per area (LMA) of understory plants through a two-year field light experiment in a tropical rubber plantation in south China. We hypothesized that ALAN could impact the understory in two ways: by directly supplementing light to aboveground plant parts (which increases LMA) and indirectly affecting soil nutrient composition by attracting insects (which decreases LMA). We selected two species: Colocasia gigantea, representing shade-tolerant species, and Melastoma candidum, representing light-demanding species. We measured canopy openness, LMA, soil nutrients, and individual distance away from light resources. Our Bayesian linear mixed model showed a negative relationship between LMA and the strength of ALAN, indicating that ALAN may influence LMA more indirectly by enhancing soil nutrient availability rather than directly acting as a light resource. This relationship was significant for Colocasia gigantea but not for Melastoma candidum. These results suggest that ALAN might have complex and species-specific impacts on the understory ecosystem. Our study underscores the need for continued research and informed management of anthropogenic ecosystems. [ABSTRACT FROM AUTHOR]

In the last 2 years, rubber tree abnormal leaf fall occurred over large area in Xishuangbanna rubber plantation, and the symptoms were similar to those of rubber tree Phytophthora leaf fall disease. In order to clarify the pathogenic species and screen fungicides for effective control of this disease, the pathogen was isolated and purified by tissue isolation and mycelia cusp purification method, and the pathogenicity was determined by Koch' s postulates test, morphological and physiological characteristics, rDNA-ITS and COX II gene sequence analysis. The results showed that the pathogen caused rubber tree abnormal leaf fall was identified as Phytophthora botryosa, which was a new record pathogen of rubber tree Phytophthora leaf fall disease in China. The antibiotic activities of 15 fungicides was tested in vitro with mycelial growth rate method. 48% dimethomorph-cyazofamid SC (suspension concentrate), 80% dimethomorph WG (water dispersible granule), 30% metalaxyl-dimethomorph WG, 35% dimethomorph-cymoxanil SC, 30% floridomide-metalaxyl WG and 0.3% tetramycin AS (aqueoces solution) could effectively inhibit the mycelial growth of the pathogen, with EC50 of 0.137 1, 0.175 9, 0.201 7, 0.2577, 0.265 1, 0.351 0 mg⋅L-1, respectively, which could be used as candidates for control of the disease in the field. [ABSTRACT FROM AUTHOR]

Rubber tree plantations (Hevea brasiliensis) are expanding into the tropical regions of southwest China to ensure production to meet the growing demand for latex. The effects of long-term plantations on soil carbon processes are still unclear. Also, the effects of the plant's rhizosphere on the decomposition of soil organic matter (SOM) play a crucial role in predicting soil carbon dynamics. The rhizosphere and soils corresponding to a chronosequence of ages (4, 15 and 30 years) of rubber plantations were collected and incubated to determine the effect of the rhizosphere (RE) on SOM decomposition. We also examined the soil physicochemical properties; bacterial community structure; and root morphological, chemical, and physiological traits to further explore the underlying mechanisms of the RE on SOM decomposition. The REs on SOM decomposition varied significantly in the different age classes of the rubber plantations, and the higher the REs on SOM decomposition in an older plantation might limit the accumulation of organic carbon in the soil. Root traits, including the specific root length, root nitrogen content, and root carbon/nitrogen ratio, varied significantly in response to the plantation age and explained more of the variance in the RE on SOM decomposition than the soil and microbial properties. Due to the changing root morphological and chemical traits along the age chronosequence, the rhizosphere bacterial community composition tended to shift the carbon utilisation strategy and the bulk soil nitrogen content decreased. These variations also affected the RE on SOM decomposition. Our results indicate that the development of rubber plantations would prevent soil carbon accumulation, especially in the rhizosphere, by increasing the RE on SOM decomposition, which would be predicated by root morphological and chemical traits. [ABSTRACT FROM AUTHOR]

Soil quality is a critically important component of soil within ecosystems, and our understanding of soil quality variation and its driving factors in tropical forests is limited. This study collected soil samples at 0–20 cm depths from two typical tropical forests (tropical rainforest and rubber plantation) on Hainan Island, China's largest tropical island, during dry and rainy seasons. A soil quality index (SQI) using principal component analysis was applied to measure soil quality based on 21 soil properties. The soil properties' spatial and seasonal changes and their driving factors were simultaneously collected for a holistic analysis of the ecosystems. The results were summarized as follows: (i) The SQI of the rubber plantation decreased by 26.48% compared to the tropical rainforest on the island, while four soil properties investigated (soil pH, total phosphorus, cellulose decomposition, and actinomycetes) increased. (ii) The SQI of different soil types in the two tropical forests displayed an apparent discrepancy. Within the same soil type, the SQI of tropical rainforests showed no obvious differences, while there was a notable spatial discrepancy among rubber plantations in dispersed geographical positions belonging to varied climatic zones. (iii) The SQI of the tropical rainforest was significantly higher in the wet season than in the dry season. In contrast, there were no significant differences between the two seasons for rubber plantations, indicating that soil quality in the tropical rainforest was more sensitive to seasonal changes than soil quality in rubber plantations. Overall, we concluded that except for land use and soil type, spatial variability and seasonal pattern also played essential roles in soil quality on the tropical island. The results from the SQI are expected to provide novel information regarding the sustainable use of tropical forests on Hainan Island. [ABSTRACT FROM AUTHOR]

Rubber (Hevea brasiliensis Müll. Arg.) is a major economic crop grown in tropical areas. However, the various service functions of rubber plantations and their benefit to society, the economy and the environment are still unclear. Data on rubber planting areas, dry rubber and wood yields, carbon sequestration and oxygen release capacities, biodiversity, employment, and market prices for natural rubber and rubber wood were collected. Observations of land use patterns and functions were carried out. The results showed that the capacity of average annual carbon stock capacity of rubber plantations in China was 36.51 million tonnes. The accumulation values of carbon sequestration and oxygen release, 416.89 million tonnes and 304.42 million tonnes, respectively. A total of 849 plant species, 60 bird species, 5 species of ground beetle, 25 species of wild bees, 27 ant species, 10 termite species, 87 spider species and 38 hemipterous species were found in rubber plantations. The average annual dry rubber and rubber wood yields were 676,300 tonnes and 1.29 million m3. From 2000 to 2020, 14.20 million tonnes of dry rubber were produced and 27.02 million m3 of wood were harvested. The average annual output of dry rubber and rubber wood was US$1.86 billion, while total output value summed to US$ 39.08 billion from 2000 to 2020. Rubber cultivation and plantation operation activities employed an average of 1.11 million people annually. Land use management and natural disasters may affect the service functions of rubber plantations, which are carbon sequestration and oxygen release, maintaining biodiversity, providing dry rubber and rubber wood, maintaining water and conserving water sources, absorbing employment, changing unsustainable agricultural practices and habits of smallholders and ethnic minorities, and promoting transfer of technologies. In the future, on the basis of recognising and rationally weighing the various functions of rubber plantations and their main driving factors, smallholders are expected to maximise the social, economic and ecological functions of rubber plantations through effective crop management and utilisation of resources. [ABSTRACT FROM AUTHOR]

Rubber (Hevea brasiliensis) plantations have high water consumption through evapotranspiration, which can contribute to water scarcity. In addition, there is a lack of spatial observation data and estimation methods for evapotranspiration (ET) for rubber plantations. To alleviate the water stress of expanding rubber plantations caused by seasonal drought in Xishuangbanna, Southwest China, an up to 7 days crop evapotranspiration (ETc) forecast method, "Kc-ET0" for rubber plantations with limited meteorological data, was proposed by using rubber crop coefficient Kc and public weather forecasts. The results showed that the average absolute error (MAE) of forecasted ETc was 0.68 mm d−1, the root mean square error (RMSE) was 0.85 mm d−1, and the average correlation coefficient (R) was 0.69 during the rainy season, while during the dry season these metrics were 0.52 mm d−1, 0.68 mm d−1, and 0.85, respectively. The accuracy of ETc forecast in the dry season was higher. Additionally, Kc was the main factor influencing the accuracy of rubber plantations ETc forecast, while the accuracy of the temperature forecast and the chosen Hargreaves-Samani (HS) model were also considerable. Our results suggested that the "Kc-ET0" short-term rubber plantation ETc forecasting method shows good performance and acceptable accuracy, especially in the dry season. The study provides an important basis for creating ET-based irrigation scheduling for improving regional-scale water management in high water consumption rubber plantations. [ABSTRACT FROM AUTHOR]

The continuous transformation from biodiverse natural forests and mixed-use farms into monoculture rubber plantations may lead to a series of hazards, such as natural forest habitats fragmentation, biodiversity loss, as well as drought and water shortage. Therefore, understanding the spatial distribution of rubber plantations is crucial to regional ecological security and a sustainable economy. However, the spectral characteristics of rubber tree is easily mixed with other vegetation such as natural forests, tea plantations, orchards and shrubs, which brings difficulty and uncertainty to regional scale identification. In this paper, we proposed a classification method combines multi-source phenology characteristics and random forest algorithm. On the basis of optimization of input samples and features, phenological spectrum, brightness, greenness, wetness, fractional vegetation cover, topography and other features of rubber were extracted. Five classification schemes were constructed for comparison, and the one with the highest classification accuracy was used to identify the spatial pattern of rubber plantations in 2014, 2016, 2018 and 2020 in Xishuangbanna. The results show that: (1) the identification results are in consistent with field survey and rubber plantations area generally shows a first increasing and then decreasing trend; (2) the Overall Accuracy (OA) and Kappa coefficient of the proposed method are 90.0% and 0.86, respectively, with a Producer's Accuracy (PA) and User's Accuracy (UA) of 95.2% and 88.8%, respectively; (3) cross-validation was employed to analyze the accuracy evaluation indexes of the identification results: both PA and UA of the rubber plantations stay stable over 85%, with the minimum fluctuation and best stability of UA value. The OA value and Kappa coefficient were stable in the range of 0.88–0.90 and 0.84–0.86, respectively. The method proposed provides reliable results on spatial distribution of rubber, and is potentially transferable to other mountainous areas as a robust approach for rapid monitoring of rubber plantations. [ABSTRACT FROM AUTHOR]

Pandanus amaryllifolius Roxb. is a special tropical spice crop resource with broad development prospects. It is widely cultivated under a Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg. canopy to improve the comprehensive benefits to Hevea brasiliensis plantations in Hainan Provence, China. However, the effects of intercropping with Hevea brasiliensis on the component number and relative contents of volatile substances in different categories in the Pandanus amaryllifolius leaves are still unknown. Therefore, a Hevea brasiliensis and Pandanus amaryllifolius intercropping experiment was set up to clarify the differences between several cultivated patterns on volatile substances in the Pandanus amaryllifolius leaves, and the key regulatory factors of volatile substances. The results showed that the soil pH was significantly decreased, while soil bulk density, alkali-hydrolyzable nitrogen and available phosphorus contents were significantly increased under the intercropping pattern. The component numbers of esters in volatile substances were increased by 6.20%, while the component numbers of ketones were decreased by 4.26% under the intercropping pattern. Compared with the Pandanus amaryllifolius monoculture, the relative contents of pyrroles, esters and furanones were significantly increased by 8.83%, 2.30% and 8.27%, respectively, while the relative contents of ketones, furans and hydrocarbons were decreased by 1.01%, 10.55% and 9.16% under the intercropping pattern, respectively. The relative contents of pyrroles, esters, furanones, ketones, furans and hydrocarbons were associated with changes in soil pH, soil available phosphorus content and air temperature. The results indicated that the reduction in soil pH and enhancement in soil-available phosphorus may be the main reasons for promoting the relative content of pyrroles and reducing the relative content of hydrocarbons under an intercropping pattern. Overall, Hevea brasiliensis intercropping with Pandanus amaryllifolius could not only improve soil properties, but also significantly increase the relative contents of the main volatile substances in Pandanus amaryllifolius leaves, which could provide a theoretical basis for the application and promotion of high-quality production patterns of Pandanus amaryllifolius. [ABSTRACT FROM AUTHOR]

In 2021, an unprecedented major movement of Asian elephants in China aroused the curiosity of hundreds of millions of people around the world. For research objectives, we firstly reproduce the movement route of Asian elephants and reveal their geographical spatial characteristics and landscape characteristics using multisource data; secondly, we reveal the reason for this Asian elephant movement. We found Asian elephants went far beyond the northernmost movement boundary from past years. Most of the areas along the movement route fell within the higher accessibility to road traffic. Over the past 20 years, the rubber and tea areas of Xishuangbanna and Pu'er have increased by 91.1% and 120.1%, respectively, from 2005 to 2019. Asian elephants spent 18 days in areas with suitable food, but relatively low vegetation coverage. The 2021 movement was most likely a "purposeful" trip rather than a "detour". The elephants chose the most rewarding way to move forward, which showed they are far smarter than we thought. They may have left to find food due to exhausted food supply. The expansion of rubber and tea plantations has caused the habitat of Asian elephants to shrink, which was one of the reasons for the northward movement of them. [ABSTRACT FROM AUTHOR]

The rapid expansion of rubber plantations in Xishuangbanna, China, has severely decreased rubber prices in the last several years. The income loss and other adverse environmental impacts have brought livelihood challenges and opportunities to develop and adopt more diversified and environmental-friendly income-generating activities (IGAs). To better understand the constraints and opportunities for smallholder rubber farmers to sustain or improve their livelihoods, this study investigates which IGAs are applied by local farmers and the factors that determine their adoption, using the sustainable livelihood framework as the theoretical guideline. The qualitative approach is applied using semi-structured interviews and thematic analysis. Five directions of changes in IGAs (i.e., intercropping, other cash crops, livestock raising for marketing, part-time job, and land renting) are identified, and local farmers are categorized into three groups (i.e., rejective, affirmative, and hesitate groups) based on their attitudes towards these IGAs. The results reveal that the main adoption motivations of certain IGAs are closely related to price shock, economic return, information, and extension service. Based on the results, suggestions are provided to enhance farmers' motivation to make changes and improve the adoption of emerging IGAs with attention given to vulnerability contexts, livelihood assets and institutional assistance. [ABSTRACT FROM AUTHOR]

Identification of the effect of anthropogenic threats on ecosystem is crucial. We used molecular tools and remote sensing to evaluate the population status of an isolated Asian elephant population in southwestern China in response to changes in habitat suitability between 1989 and 2019. A total of 22 unique genotypes were identified from 117 dung samples collected between March and June 2018 using microsatellite DNA analysis, including 13 males and 9 females. Based on the size of fecal boli, 1 animal was a juvenile, 9 were subadults, and 12 were adults, indicating that recruitment was limited. The effective population size was small (15.3) but there was no signature of a recent population bottleneck. We observed a low genetic diversity (He = 0.46 ± 0.05) and a high level of inbreeding (Fis of 0.43 ± 0.11), suggesting low population viability and high risk of extinction. In total, these elephants lost nearly two thirds (62%) of their habitat in 3 decades. The expansion of agriculture and rubber plantations followed by an increase in human settlements after 1989 increased the isolation of this population. We recommend that resettlement of 800 inhabitants of 2 villages and the abandonment of associated farmland and rubber plantations would make an additional 20 km2 of suitable habitat available. This could allow a population increase of 14 elephants, possibly by translocating individuals from elsewhere in China. Our findings can be applied to the management and conservation of other fragmented populations in China or in other range countries of Asian elephants. [ABSTRACT FROM AUTHOR]

Corynespora cassiicola is an anamorphic pathogenic fungus belonging to the phylum Ascomycota with a broad host range. It causes the Corynespora leaf fall (CLF) disease, in rubber trees for which it badly affects natural rubber production. A small phytotoxic protein named cassiicolin derived from the cassiicolin gene (Cas gene) of the fungus was thought to be inducing the pathogenicity in rubber tree; however, some of the isolates that do not possess cassiicolin gene shows aggressiveness on the host. The present study intends to identify the effect of cassiicolin and other putative effectors involved in CLF disease. Comparative screening of the crude toxin extracted from 30 isolates was carried out for cassiicolin activity and the Cas isoform was determined. The isolate named HV showed maximum aggressiveness and the presence of a Cas gene isoform (Cas2). It was sequenced, assembled, and confirmed for the presence of Cas2 isoform of the Cassiicolin gene. This is the first report of an Indian isolate having a Cas-2 isoform from Hevea brasiliensis. The phylogenetic analysis reveals the similarity of Cas gene from HV to Cas2 gene of CC004 strain of China. The effector proteins present in the isolate (HV) were identified. A total of 1035 effector proteins were predicted, among them 1026 were matched with the DFVF database, and in which 229 are classified as leaf spot-associated virulence factors. The predicted gene and proteins were mostly associated with carbohydrate and amino acid metabolism. Identification of specific effectors involved in the pathogenicity helps to step towards the understanding of C. cassiicola virulence and host–pathogen interaction. The data of this work and its future aspects will furnish the facts behind the interaction between the Hevea and Corynespora. [ABSTRACT FROM AUTHOR]

Clarifying the effects of rubber‐tapping and natural growth weed cover on the variations in the concentrations of soil organic carbon (SOC) and nitrogen (N) may be beneficial to rubber plantation management via optimizing soil N and C accumulations and reducing the risk of environmental pollution due to NO3− leaching. This study aims to compare the concentrations of soil total‐N, available‐N, NH4+‐N, NO3−‐N, and SOC for addressing N and C variations as affected by rubber‐tapping or weed covering in a 14‐year‐old rubber (Hevea brasiliensis cv. GT1) plantation in Xishuangbanna, southwest China. The soil samples at 0–20, 20–40, and 40–60 cm depths between July and December 2018 were examined monthly from no‐rubber‐tapping tree belt (NRTB) or rubber‐tapping tree belt and no‐rubber‐tapping weed zone (NRTWZ) or rubber‐tapping weed zone. The concentrations of SOC, total‐N, available‐N, NH4+‐N, and NO3−‐N vary with soil depths and sampling date. The average concentrations of SOC, total‐N, available‐N, NH4+‐N, and NO3−‐N at 0–60 cm soil depth are significantly higher for the NRTWZs than for the NRTBs. Soil total‐N was positively correlated with SOC; either positive or negative relationships are found among different soil N forms. More soil available‐N and NO3−‐N accumulate for tree growth under weed covering or no‐rubber‐tapping. These findings indicate that the variations in soil N and SOC concentrations should be taken into account as a part of rubber plantation management to improve soil N and C accumulations. [ABSTRACT FROM AUTHOR]

Phylogenies are crucial for understanding historical patterns of genetic biodiversity, but very few are incorporated practically into existing conservation programs. Xishuangbanna, a tropical–subtropical forest transition, is a key biodiversity hotspot in Southwest of China; however, gaps between practical protection and national planning need to be bridged, as ongoing, rapid expansion of rubber plantations in the region increasingly threatens local diversity. Here, we used administrative regions as study units to identify spatial patterns for 158 threatened woody species and investigate the ratio of tropical floristic to temperate floristic in the transition zone. We used all-subsets regression analysis to test the impacts of environments (climatic, edaphic, topographic) on biodiversity patterns. Spatial patterns using several conservation metrics gave different results, with species richness, phylogenetic diversity, and evolutionary distinctiveness and global endangerment highly consistent spatially, while either standardized phylogenetic diversity and phylogenetic structure performed differently from others for spatial patterns. The biodiversity patterns of threatened woody species in Xishuangbanna are affected by the combined impact of rubber plantations and abiotic environments, but their evolutionary history is not, with only c. 69% of phylogenetic diversity currently protected by traditional nature reserves. Although the Menglong and Xiangming townships show high conservation values, they are not in the reserves. Eleven threatened woody species were required for ex situ conservation due to threats from clearance for rubber plantations and in all, 21 regionally and internationally important species are currently unprotected. We recommend incorporating the phylogenetic component of biodiversity in improving current and establishing new reserves. [ABSTRACT FROM AUTHOR]

The specific impact of ecological environment quality at a regional scale due to the rubber plantations expansion is still unclear in Xishuangbanna, Yunnan province, China. First, we used a pixel and phenology-based multiple normalization approach to map rubber plantations over six time periods during 1995–2018 with the available high-quality Landsat imagery. Second, a pixel-based optimized algorithm was developed to reduce the commission and omission errors of the rubber plantations maps and we mapped the rubber plantations expansion area. Third, a remote sensing-based ecological index (RSEI) was employed to assess the rubber plantations expansion area ecological environment quality. RSEI value decreased with the lowest value in 2007 (0.511) and increased with the highest value in 2016 (0.727). This study demonstrated that the ecological environment quality degraded from 1995 to 2007 with an increase of rubber plantations expansion, but improved gradually from 2007 to 2018 with the slow growth of rubber. [ABSTRACT FROM AUTHOR]

The expansion of agroforestry crops in South Asia has resulted in the reallocation of local agricultural resources, including labor force. Based on two‐wave panel data collected from more than 600 smallholder rubber farmers in southwest China, this study examines the impacts of rubber expansion on the migration of rural labor. The results show that smallholders planting more rubber plantations have significantly fewer migrant family members and lower likelihood of migration, revealing a significantly negative effect of rubber cultivation on the migration of rural labor. Given that the migration of rural labor is a major trend in rural economic transformation, rubber farming appears to result in the resource curse in rubber planting areas. In addition, a positive interaction effect between rubber cultivation and the price of natural rubber on the migration of rural labor reveals that the resource curse effect of natural rubber decreases with the decrease in the price of natural rubber. A period with a relatively low price of natural rubber provides an opportunity to foster the migration of rural labor in rubber planting areas. [ABSTRACT FROM AUTHOR]

The expansion of rubber (Hevea brasiliensis) cultivation plantation over the past few decades has been significantly explosive in Xishuangbanna, southwest China. More and more evidences concerning the expansion of rubber plantations lead to the negative influence to local regional hydrology. It is vital to explore the impact of climate change and rubber (Hevea brasiliensis) plantation expansion on reference evapotranspiration (ET0) for the sustainable and efficient use of regional water resources. In this study, the spatiotemporal variation of ET0 as well as its relationship in rubber plantations area in Xishuangbanna from 1970–2017 were analyzed by using trend, correlation and contribution analysis. The results showed that the rubber plantation was 12,768 ha yr–1 from 1990 to 2017 in Xishuangbanna, and nearly 40.8% of new rubber plantations expanded above 900 m in altitude from 2000 to 2017. Sunshine duration and average relative humidity were the key meteorological factors that affect ET0 in Xishuangbanna, with the sensitivity coefficient of 0.51 and 0.35, respectively. The multiyear relative change of ET0 in Xishuangbanna was 9.18%, and the total contribution of major climate factors was 7.87% during 1970 and 2017. The average relative humidity in the plantation area decreases, which directly leads to the increase of ET0. The amount of ET0 change from 2000 to 2017 affected by climate change increased at 3.13 mm/10a, whereas it was 2.17 mm/10a affected by the expansion of rubber plantations by quantitative separation. ET0 was significantly affected by climate change but intensified by the expansion of rubber plantation. [ABSTRACT FROM AUTHOR]

Soil microbial communities play a crucial role in ecosystem functioning. Past research has examined the effects of forest conversion on soil microbial composition and diversity, but it remains unknown how networks within these communities respond to forest conversion, including when tropical rainforests are replaced with rubber plantations. Microbial networks are viewed as critical indicators of soil health and quality. They consist of two parts: nodes and edges. In this study, we used data from Illumina sequencing and shotgun metagenome sequencing to analyze bacterial and fungal community network structure in a large number of soil samples from tropical rainforests and rubber plantation sites on Hainan Island, China. Our results showed that only 5 %–10 % of shared network edges (i.e., links between species A and B existing in both rubber plantations and rainforests) were observed in both bacterial and fungal communities, which indicates that forest conversion altered the soil microbial network structure. The identity of keystone operational taxonomic units (OTUs) differed entirely between rubber plantation and rainforest sites, further underscoring the altered network structure. More edges and more negative correlations within the soil bacterial–fungal networks were observed at rubber plantation sites (dry season: 4284 total edges, 844 negative; rainy season: 7257 total edges, 1744 negative) than at rainforest sites (dry season: 3650 total edges, 149 negative; rainy season: 6018 total edges, 489 negative), demonstrating that soil bacterial–fungal network structure was more complex and stable in rubber plantations than in rainforests. For bacteria, a larger number of network edges were observed among bacterial networks in samples from tropical rainforest than in samples from rubber plantations, indicating that rainforest bacterial networks were more complex than those from rubber plantations. However, soil fungal networks from rubber plantations showed more links, suggesting that forest conversion increased fungal network complexity. More edges of network and more links between species and functions were observed in the rainy season than in the dry season, indicating that seasonal changes had a strong effect on network structure and function. Further analysis shows that soil pH, potassium (AK), and total nitrogen (TN) had more links with species of some phyla. In conclusion, forest conversion results in an increase in soil pH as well as a decrease in AK and TN, and these changes as well as seasonal variations had a great impact on soil microbial composition, network structure and function. [ABSTRACT FROM AUTHOR]

Rubber tree (Hevea brasiliensis) is important economic agroforestry with high water demand during its growth. Evapotranspiration as the main component of water and energy balance in forest ecosystem which is a vital link between its ecological and hydrological processes. Therefore, it is of extreme significance to study the energy balance and evapotranspiration of rubber plantations for in-depth study of the regional water vapor cycle, scientific and efficient management of water resources. Based on the meteorological and energy data measured by the Bowen ratio system in 2016 at Xishuangbanna, the energy balance and evapotranspiration characteristics of rubber plantations were analyzed by Bowen ratio-energy balance. The result showed that: (1) The daily variations of net radiation (Rn), latent heat flux (LE), sensible heat flux (H) and soil heat flux (G) in rubber plantation were high value in rainy season and low in dry season; (2) The annual ET of the rubber plantation was 1035.91 mm, the average daily ET was 2.83 mm/d in 2016. The ET was about 114%-140% of precipitation in the dry season which indicated that ET of rubber plantation was mainly dependent on the volumetric soil water content (VWC); (3) The dominant environmental factors were Rn, vapour pressure deficit (VPD) and VWC which affect ET of rubber plantation. [ABSTRACT FROM AUTHOR]

Litter decomposition influences the nutrient cycle and the availability of soil nutrient resources in rubber plantation ecosystem. This study aimed to analyze effects of different factors such as soil layer depths, root accessibility and soil fertility levels on dynamic decomposition of leaf litter in rubber plantations, as well as physico-chemical properties and microbiological parameters of the soil. We performed decomposition experiments to analyze the effect of these factors on leaf litter decomposition in a rubber plantation in Danzhou, South China. The results showed that the rubber leaf litter decomposition activity increased with the depth of the soil layer. The fertility level of soil affected the decomposition process, with higher soil fertility level restraining litter decomposition. The litter decomposition was affected by the root accessibility, but the roots turned out to not be decisive factors in the decomposition process. The microorganism abundance differed seasonally in the above-ground and underground soil layers during the rubber leaf litter decomposition. The number of actinomycetes, bacteria and fungi changed most dramatically between March and May. The fastest rate of rubber leaf litter decomposition also occurred during this period. The microorganisms played a key role in the rubber litter decomposition underground. Enzymes sucrase, urease, polyphenol oxidase and cellulase contributed in regulating the decomposition of rubber leaf litter. These results may provide further insight into the potential of using leaf litter resources in tropical plantations. This study also provides valuable information about the decomposition mechanism of leaf litter as part of the nutrient cycle. [ABSTRACT FROM AUTHOR]

Land-use changes can alter soil properties and thus affect soil quality. Our understanding of how forest conversion (from tropical rainforest to rubber plantations) affects soil properties and soil quality is limited. An ideal testing ground for analyzing such land-use change and its impacts is Hainan Island, the largest tropical island in China. Based on 21 soil physicochemical and biological properties, a soil quality index (SQI) employed principal component analysis to assess soil quality changes from the conversion of tropical rainforests to rubber plantations. The results showed that (i) soil available potassium, available phosphorus, microbial biomass carbon, cellulose decomposition, acid phosphatase, and urease were vital soil properties for soil quality assessment on Hainan Island. (ii) The SQI of rubber plantations decreased by 26.48% compared to tropical rainforests, while four investigated soil properties (soil pH, total phosphorus, cellulose decomposition, and actinomyces) increased. (iii) The SQI of both the tropical rainforests and rubber plantations showed significant spatial differences, which, under tropical rainforests, was more sensitive to seasonal changes than those under rubber plantations. (iv) Structural equation modeling suggested that forest conversion directly impacted soil quality and, indirectly impacted soil qualities' spatial variation by their interaction with soil types and geographical positions. Overall, though the conversion of tropical rainforest to rubber plantation did not decrease all soil properties, the tropical rainforest with its high soil quality should be protected. [ABSTRACT FROM AUTHOR]

Information on where rubber plantations are located and when they were established is essential for understanding changes in the regional carbon cycle, biodiversity, hydrology and ecosystem services. Here, we proposed a simple and modified phenology-based method to map rubber plantations and evaluate the effectiveness of this method in Xishuangbanna in southwest China, the second largest area of natural rubber cultivation. Our phenological algorithm is supported by local meteorological data and involves the re-normalization of two Landsat-8 Operational Land Imager-derived vegetation moisture indices (i.e. the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Moisture Index (NDMI)). We then applied air temperature data (daily records from 1981 to 2015) and periodic in situ observations of rubber plantations (weekly records from 2017 to 2018) to determine the phenological stages of rubber tree growth with the goal of selecting the most effective Landsat images. The re-normalization algorithm was able to highlight the temporal differences in the vegetation canopy and moisture content of rubber plantations, because rubber trees in Xishuangbanna display unique defoliation-foliation signals during the dry season. The resultant map of rubber plantations showed a high overall accuracy of 92.3% and a Kappa coefficient of 0.846. The developed phenological re-normalization method with meteorological data greatly enriches remote sensing-based approaches for mapping rubber plantations. [ABSTRACT FROM AUTHOR]

Knowledge of the location, area and extent of rubber plantations is a prerequisite for assessing their ecological and environmental impacts. Mainland Southeast Asia (MSEA) and Yunnan province (MSEA&YN) in China are globally important rubber-planting regions. Rubber cultivation in areas at moderate and low altitudes (<1000 m) within these regions has expanded rapidly in recent years. However, datasets of maps generated at a fine spatial resolution are still unavailable for MSEA&YN. Because of this, three relevant and important questions remain unanswered: what are the northern most boundary for rubber production in these regions, what is the highest altitude at which rubber is produced, and how are the plantations distributed in (cross-) border regions? An approach of the phenology- and Landsat-based re-normalized vegetation index (RNVI), originally developed for Xishuangbanna in southern China, is used in this study to verify the feasibility of mapping mature rubber plantations in MSEA & YN using the Landsat 8Operational Land Imager data products acquired from January to April, 2013 to 2018. Characteristics of the vertical and horizontal distributions of mature rubber plantations in MSEA&YN, as well as national differences especially in the (cross-) borders, were examined using the generated map. The results showed that the RNVI method, although tailored to the northern edge of the tropics, is useful for detecting mature rubber plantations in MSEA & YN. The latest map of mature rubber plantations indicated that they occupied a total area of 7.69 -106 ha, accounting for 3.32% of the study area. Spatial analyses showed three typical features of the distribution: new plantations at higher (over 1000 m) and lower (below 200 m) elevations, more cultivation in the borderlands (over a half within 60 km buffers), and their north ward movement (as far as 25 N). The results of this study have important implications for phenological methods verification in the tropics, and provide valuable information on mature rubber plantations in MSEA & YN. [ABSTRACT FROM AUTHOR]

Phylogenetic analyses can provide an accurate identification for endangered species, which is a prerequisite for their conservation. Understanding how threats shape the current realized niche of declining species can effectively improve conservation policies. In this study, we used molecular data to identify the real Eleutharrhena macrocarpa, a critically endangered species in Yunnan, China. A niche reduction approach was used to model its range change by predicting the historic and current distributions. Our subfamily‐wide phylogenetic analyses based on five plastid DNA regions indicate that the E. macrocarpa with pinnate‐nerved leaves is real and is a member of Tiliacoreae, whereas the so‐called E. macrocarpa with triplinerved leaves is actually Haematocarpus subpeltatus, which is for the first time reported to be distributed in China. Our subsequent analyses of Tiliacoreae using seven plastid and two nuclear DNA regions further support Eleutharrhena as a distinctly monotypic genus and as sister to Pycnarrhena. Among the four prevalent barcodes in plants, three plastid DNA fragments (rbcL, matK, trnH‐psbA) failed to discriminate E. macrocarpa from Pycnarrhena; however, nuclear ribosomal internal transcribed spacer (ITS) regions could well recognize this endangered species. The distributional range of E. macrocarpa has undergone a dramatic contraction over the last 100 years and may further shrink southwestwards in the future. This dramatic range contraction might be associated with habitat loss due to increasing drought and expansion of rubber plantation. We point out the need for in situ conservation of E. macrocarpa populations, and suggest to establish a large nature reserve in southern and western Yunnan to effectively protect E. macrocarpa and other declining species that exhibit similar distribution and habitat requirements. This study highlights the significance of taxonomy and molecular phylogenetics in biological conservation. [ABSTRACT FROM AUTHOR]

Purpose: In rural areas, geographic location is key to market access and labor mobility of farm households. This paper aims to investigate the opportunities and constraints of smallholder rubber farmers in southwest China to adjust to the changes in economic and institutional conditions, namely the declining rubber prices, emerging land rental markets and growing off-farm job opportunities. Design/methodology/approach: The empirical basis is a dataset of some 600 rubber farmers in Xishuangbanna Dai Autonomous Prefecture, Yunnan Province, collected in March 2015. The study uses instrumental variable and recursive bivariate probit models to account for possible endogeneity and selection bias. Findings: With rubber prices in decline, the elevation of rubber plantations is an essential factor for the costs of access to the local factor markets and influences farm households' possibilities to adopt coping strategies. Notably, we find a U-shape type of relationship between the location and renting-out land due to the decline in rubber profitability. Rubber producers in low elevations are better bestowed with access to local markets. Households in high elevations, where rubber planting came in later, can shift to new crops like tea. However, the economic resilience of farmers in middle elevations is low due to their higher adjustment costs. Originality/value: The paper provides a constructive basis for designing more location-specific development policies and can help avoid the past often ineffective blanket measures. Its implications have significant relevance for areas with similar conditions, for example, the remote, ethnic minority–dominated and mountainous rural areas in China. [ABSTRACT FROM AUTHOR]

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Hunting and deforestation are the two biggest threats to vertebrates in Southeast Asia. In the last 50 years, monoculture rubber plantations replaced large areas of tropical rainforests in Xishuangbanna, southwest China. We set up camera traps at 109 stations (57 in forest reserves and 52 in rubber plantations) to determine the distribution of mammal species in Menglun, Xishuangbanna. We also interviewed 37 experienced hunters (mean age: 54) in the study area to understand their perceptions of species abundance trends. We used hierarchical multispecies occupancy modelling to determine the effect of distance to village, distance to forest edge and elevation on mammal occupancy after accounting for imperfect detection. We used non‐parametric tests for the rank data to evaluate perceived species trends. Using a combination of historical literature (1954–1985), hunter interviews, direct observations and camera‐trap surveys, we only recorded 56% (15 out of 27) of the medium‐to‐large sized (>1 kg) mammal species known previously from the study region. Interviews suggested that current population densities of all extant mammal species are below historical levels. Our camera traps captured 11 mammal species in the forest reserve and only two species in rubber plantations. Low capture rates (10 captures) in rubber mean we could only determine mammal occupancy in forests. Environmental variables did not affect community level mammal occupancy in forests, but common muntjac (Muntiacus muntjak) and the northern pig‐tailed macaque (Macaca leonina) avoided forest edges. At the time of the survey, hunting was still prevalent in the region. Therefore, conservation interventions that end both hunting and deforestation are urgently needed to stabilize and increase mammal populations in the region. [ABSTRACT FROM AUTHOR]

Land degradation caused by deforestation seriously affects the soil environmental capacity (SEC), with potential risks to soil health. However, conventional SEC theory is unable to quantitatively describe the saturation capacity of different soil fractions and environmental pollution levels of a heterogeneous system. Thus, a new concept, the soil pool capacity (SPC), was introduced to fill this gap. We undertook space‐for‐time substitution to investigate the responses of SPCand soil safety capacity (SSC) to changes in the soil physiochemical properties, chemical species, and molecular characteristics of soil lead (Pb) in the conversion of tropical secondary rainforest (TSR) to rubber (Hevea brasiliensis) monoculture plantations with 15‐ and 60‐year histories (RP15/60). Conversion of TSR to RP15/60 caused adverse effects on soil properties (i.e., lower soil organic matter [SOM] and higher bulk density [BD]). The saturated SPC (SPCsat) for Pb in bulk soils under RP15 (2,203.17 g m−2) and RP60 (1,634.09 g m−2) decreased compared with that in TSR (2,227.10 g m−2). The contribution rates of SPCsat in the exchangeable (P1) and carbonate (P2) pools to the total capacity stabilized at approximately 94%. The contribution rate of potential SPCsat in P4 (OM‐bound Pb) significantly decreased with increasing agricultural intensity. The SSC of labile fractions (P1 + P2) accounted for 81–85% (a critical level) of the total SSC when the soil loading capacity for Pb reached the SSC in bulk soil regardless of land‐use type. Fourier transform infrared and X‐ray diffraction spectra revealed the Pb‐loaded species of SPCsat in TSR and RP15/60 (i.e., TSR: Pb2SiO4 in P2, (CH3COO)2Pb in P4, RP15/60: Pb5Si8O21 and Pb2(P4O12) in P2, and (CHOO)2Pb in P4). Correlation and factor analyzes showed that SOM and BD were key factors that had an opposite impact on SPCsat and SSC. These results are helpful to choose appropriate agronomic measurements to reduce land degradation and crop safety risks caused by deforestation. [ABSTRACT FROM AUTHOR]

Rubber powdery mildew caused by the foliar fungi Oidium heveae is one of the main diseases affecting rubber plantations (Hevea brasiliensis) worldwide. It is particularly serious in sub-optimal growing areas, such as Xishuangbanna in SW China. To prevent and control this disease, fungicides causing serious environmental problems are widely used. Strong correlations between the infection level and the temperature variables were reported previously, but they were related to monthly data that did not allow unraveling the patterns during the entire sensitive period. We correlated the infection level of powdery mildew of rubber trees recorded over 2003–2011 with antecedent 365 days daily temperature variables using partial least squares (PLS) regression. Our PLS regression results showed that the infection level of powdery mildew responded differently to the temperature variables of the defoliation and refoliation periods. Further analysis with Kriging interpolation showed that the infection level increased by 20% and 11%, respectively, per 1 °C rise of the daily maximum and mean temperature in the defoliation season, while it decreased by 8% and 10%, respectively, per 1 °C rise of the daily maximum and temperature difference in the refoliation season. This pattern was likely linked to the effects of temperature on leaf phenology. It seems highly possible that the infection level of powdery mildew increases, as increasing trends of maximum temperature and mean temperature during the defoliation continue. [ABSTRACT FROM AUTHOR]

In this article, we examine the modern Chinese state's efforts to consolidate control over land and people in its southwest borderlands via the development of rubber plantations. We examine these efforts via the lenses of the changes that ensued in the political, economic, and sociocultural life-worlds of certain indigenous Akha communities in post-1980s Yunnan, China, in conjunction with their transition from shifting rice to sedentary rubber cultivation. This livelihood shift, while initially a largely passive response on the part of Akha to the state, was, at later times, more actively driven by Akha as they sought to maintain some autonomy from the state. While this particular case is a fairly predictable outcome of broader sets of processes occurring in other resource frontiers in Asia and beyond, the Akha case is unique in highlighting the fact that resource frontiers are complex and dynamic spaces where one often encounters a diversity of distinct actors, objects, and practices at play that actively affect larger political systems and projects. [ABSTRACT FROM AUTHOR]

Extensive conversion of natural forest to monoculture rubber plantation in Xishuangbannan. It is the 'non-traditional' rubber plantation areas in southwest (SW) of China has resulted in the soil microbial community change. The aim of our study was to identify the impacts of conversion of natural forests into rubber plantations on soil microorganisms. Soil microbial community from 10 old years rubber plantation (10aRP), 20 old years rubber plantation (20aRP), 30 old years rubber plantation (30aRP), Lower hill seasonal rainforest (LRF) and tropical ravine rainforest (RRF) were analysed by Illumina MiSeq technology. The results showed that changes in soil physical and chemical properties were strongly correlated with available phosphorus (AP), total nitrogen (TN), available potassium (AK) and total potassium (TP) which were lower in natural forests than in rubber plantations. And the dominant phylum were Acidobacteria (44.67%), Proteobacteria (13.92%), Chloroflexi (13.13%), Verrucomicrobia (9.99%) and Planctomycetes (5.23%) in 45 soil microbial communities. Microbial community in rubber plantations were less abundant than in natural forests. In addition, TP, AK, TN and AN were the main environmental factors which affected soil microbial composition. The soil health of rubber plantations were impacted by soil bacterial community. [ABSTRACT FROM AUTHOR]

Niche differentiation has long been identified as an essential stabilizing mechanism for the coexistence of sympatric species. Using camera trapping data obtained during 2012–2016, we identified Macaca leonina and M. mulatta as the dominant macaque species in the Naban River Watershed National Nature Reserve (NRW‐NNR), a tropical forest in southwestern China. In general, M. leonina exhibited a wider distribution and greater niche breadth than co‐occurring M. mulatta. According to a fitted maximum entropy model (MaxEnt), M. leonina was predicted to predominantly occur in forest at higher elevation, whereas M. mulatta was predicted at lower elevation; the broadleaved evergreen forest was predicted as the most suitable vegetation for both species to inhabit, while the unsuitable area was bordered by rubber plantation, in which both food scarcity and human disturbance restricted the movement of macaques. Although the niches of these two species highly overlapped across space and time, we also found evidence for their spatiotemporal niche differentiation. When the two species inhabited independent areas with different elevations and vegetation, they maintained a similar activity pattern; however, in the zones of overlap, their activity patterns differed significantly. Further comparative field studies of these two macaques, considering other niche dimensions, are required to ensure their coexistence and long‐term conservation. Research Highlights: Macaca leonina generally has a larger distribution and niche breadth than M. mulatta.While niche differentiation occurs along at least one dimension, there is substantial overlap.Space limitation drives niche differentiation over time. [ABSTRACT FROM AUTHOR]

Context: Maintaining connectivity is critical for fragmented habitat networks to retain native species. The tropical forest in Xishuangbanna, Southwest China, is a biodiversity hotspot for China, but is also vulnerable to deforestation due to rapid expansion of rubber plantations, thus better understanding of connectivity may be crucial to species persistence. Objectives: To quantify the functional connectivity changes in the forest in Xishuangbanna from 1976 to 2014, and identify the conservation and restoration priorities for effective forest conservation and management. Methods: Using the graph theory (in Conefor sensinode 2.6), forest connectivity from 1976 to 2014 was quantified using probability of connectivity and number of components indexes. The importance of each forest patch during each period and the potential contribution of low-profit rubber plantation patches in 2014 was quantified and ranked by delta values for PC (dPC) index. Results: Connectivity of forest in Xishuangbanna has progressively decreased over the last 40 years. The ten forest patches which had the highest dPC value remained almost the same for all five periods between 1976 and 2014, though relative importance varied. The 50 most potentially important low-profit rubber plantation patches were identified and mapped, and provide a target for effective restoration efforts to facilitate efficient use of funding to best improve conservation outcomes. Conclusions: Targeted and effective interventions for landscape scale conservation and management can be made based on graph theory and connectivity analysis. Restoring low-profit rubber provides a mechanism for reconnecting the forest as an effective conservation tool. Here we show the application of this approach to restore forest and most effectively increase connectivity at minimum economic cost. [ABSTRACT FROM AUTHOR]

Temperature change is an important environmental variable for global change sciences since it largely affects the physiology of plants in forest ecosystems. Canopy temperature depression (CTD) - the result of the deviation of the air temperature (Ta) from the plant canopy surface temperature (Tc) - varies depending on the meteorological and environmental conditions of the forests. Here, we evaluated the differences in CTD between a rubber plantation (RP) and a tropical rainforest (TR) in Xishuangbanna, southwestern China across the various time series of the period of 2011 to 2015. The mean maximum CTD values at the TR site and the RP site were 2.4°C and 0.6°C at diurnal level, 1.3°C and -0.5°C at monthly level, 0.6°C and -0.8°C at seasonal level and 5.6°C and 0.2°C at yearly time series level, respectively, while they were only significant (p < 0.01) in the diurnal time series. There was a significant (p < 0.01) negative linear relationship between CTD and global radiation (Q) in both sites at diurnal level and a significant (p < 0.05) negative linear relationship in the RP site at monthly time series level. A significant (p < 0.05) positive linear relationship between CTD and precipitation (P) at the RP site was found at diurnal level, as well as a significant (p < 0.01) positive linear relationship in the TR site at monthly time series level. The variation of CTD was critical for these two sites and largely depended on the amount of global radiation and the precipitation, while it will mainly affect the physiological variables. This study may prove useful for assessing the physiological response in terms of high temperature and drought conditions to regional and global change. [ABSTRACT FROM AUTHOR]

The land use change from tropical forests to rubber plantations has had a great influence on ecosystem‐level carbon (C) exchange and soil C dynamics. This study aimed to assess the variation of soil respiration and its components in rubber plantations of different stand age. A trenching method was used to partition soil respiration (RS) into autotrophic respiration (RA) and heterotrophic respiration (RH) for 3 years in 12, 24, 32 and 49‐year‐old rubber plantations. Our results showed that RS changed significantly among rubber plantations, with the highest RS in the old‐growth rubber plantation (49‐year plantation, 147.30 ± 6.91 mg CO2‐C m−2 hr−1) followed by the mature (137.16 ± 7.68 and 108.10 ± 4.83 in 24‐year and 32‐year plantations, respectively) and the young (12‐year plantation, 78.43 ± 3.84 mg CO2‐C m−2 hr−1) rubber plantations. RS was significantly and exponentially related to soil temperature (p < .0001) rather than soil water content, which led to higher RS in the rainy season than in the dry season. The contribution of RA to RS was higher in the mature rubber plantation than in the young (27%) and the old‐growth (20%) rubber plantations. The sensitivity of RS to increasing temperature (Q10) was higher in 32‐ and 49‐year plantations than in 12‐ and 24‐year rubber plantations. The largest Q10 value of RH and RA was found in the old‐growth (49‐year plantation, 2.95) and the mature (32‐year plantation, 8.01) rubber plantations, respectively. Our results highlight the importance of environmental factors in determining the variation in RS in rubber plantations with different stand age. However, further studies are still required to elucidate the mechanisms impacting stand age‐related effects on soil respiration, such as the differences in photosynthesis in rubber plantations. Highlights: Soil respiration (RS) in four rubber plantations of different stand age was examined.RS tended to increase with the increasing stand age.The contribution of autotrophic respiration (RA) to RS was higher in the mature stands.Q10 values of heterotrophic respiration (RH) and RA were higher in old‐growth and mature stands, respectively. [ABSTRACT FROM AUTHOR]

Rubber plantations have experienced continuous expansion in Xishuangbanna, in southwestern China, since the 1950s. However, the question of how the establishment of adventive rubber trees has spatially expanded in the margin of the Asian tropics in recent decades is not clearly understood. Here, a robust phenology-based algorithm--namely the change rate of the Landsat-derived normalized burn ratio--was modified based on tri-windows (i.e., predefoliation, defoliation, and foliation) and then used to discriminate deciduous rubber plantations from other land cover types by applying a threshold of 1.0 and combining Landsat-based forest masks every five years during 1991-2016. Deciduous rubber plantations increased more than 6.6 times, approximately 3074 km2 in 2016, or at an annual rate of about 8% (104 km2/year) in Xishuangbanna over that period, showing two typical expansion trends toward both higher (over 1000 m) and lower (below 600 m) elevations and increasingly spread to borderlands with Laos and Myanmar. [ABSTRACT FROM AUTHOR]

The expansion of rubber plantations in northern Southeast Asia over the last 20 years displaced shifting cultivation and tropical forests. In Xishuangbanna, SW China, rubber occupied 22% of the area by 2010, reducing lowland forest to scattered fragments, with severe impacts on plants, animals, and ecosystem services. The rubber price has declined steeply since 2011, but consequences for forest biodiversity have not previously been explored. We use a new approach for vegetation mapping, combining phenological information with object-based classification, to produce land-use maps for 2002, 2010, 2014, and 2018. During 2002–2018, forest cover declined continuously, from 71 to 52% of the land area, while rubber increased from 11 to 24% by 2014, before declining to 21% by 2018. Other farmlands also declined while tea plantations increased. Forest patch number increased 8-fold during 2001–2014, while patch size decreased 10-fold, but these trends were partly reversed after 2014, with the loss of numerous small (< 1 ha) patches. Most larger (> 10 ha) patches in 2018 were forest throughout the study period, but many smaller patches are secondary. Currently, 20% of Xishuangbanna is in protected areas. Unprotected forest is disproportionately on steep slopes at high altitudes, while biodiversity is highest in valleys and at low altitudes, where only smaller patches remain, creating challenges for conservation planning. We recommend that all the largest patches are preserved, plus smaller patches selected for their biota, and that forest restoration is used to restore connectivity and buffer small patches of high conservation value. [ABSTRACT FROM AUTHOR]

Despite the extensive, ongoing conversion of tropical forests to rubber plantation, the effects of this land-use change on soil fungal community diversity and composition are still poorly known. We compared a network of sites of tropical forest in southern Yunnan, China, with a network of rubber plantation sites originally derived from this forest. Soil DNA was amplified for ITS2 and sequenced using Illumina MiSeq. We found that there was a major shift in community composition across all phyla, including a large reduction in ectomycorrhizal fungi likely related to the absence of hosts. Conversion from forest to rubber plantation had no effect on total fungal α-diversity, but rubber plantation had lower β-diversity, resulting in lower overall gamma diversity. Networks based on co-occurrence of operational taxonomic unit in each land-use type showed that network complexity decreased with land-use change from forest to rubber plantation. Further investigation of soil functionality is needed to investigate whether this lower network complexity is related to reduced soil ecosystem resilience. [ABSTRACT FROM AUTHOR]

Highlights • Intercropping decreased nutrient content in calla lily rhizosphere and non-rhizosphere soil. • Intercropping decreased nitrogen and potassium, but increased phosphorus uptaken by calla lily. • Intercropping altered conditions affected soil enzyme activity and the number of microbes. • Rubber and calla lily competition for nutrients lead to the change in soil microbial abundance and the plants roots architecture. • Soil microbes and root architecture of calla lily was adjusted as much as possible to meet the nutrient needs of calla lily. Abstract Rubber is a globally important crop species and is widely grown in Hainan, China; the development of efficient agricultural practices is essential when attempting to maximize productivity. The effects of interspecific competition for nutrients and calla lily (Alocasia macrorrhizos L.) intercropping on calla lily growth, development, and nutrient uptake were investigated in rubber tree (Hevea brasiliensis Müll. Arg.) plantations. The nutrient abundances, enzyme activity, and number of microbes present in rhizosphere and non-rhizosphere soil were determined. Barriers were inserted between the crops to separate their root systems and nullify belowground competition to facilitate the analysis of intercrop competition. We found that in the rubber tree/calla lily intercropping system, nutrient content and soil urease activities in rhizosphere and non-rhizosphere soil significantly decreased, and nitrogen (N) and potassium (K) taken up by calla lilies, and the growth and biomasses of calla lilies significantly decreased. In contrast, soil sucrase, acid phosphatase, and catalase activities and the quantity of fungi in rhizosphere and non-rhizosphere soil significantly increased, and phosphorus (P) uptake, root length, and the ratio of root to shoot dry weights in calla lilies also significantly increased. Intercropping significantly decreased the abundances of both bacteria and actinomycetes and decreased total microbial abundance in rhizosphere soil, but significantly increased their abundances in non-rhizosphere soil. The nutrient content (excluding organic matter content and pH) in rhizosphere soil was lower than in non-rhizosphere soil. These findings indicate that nutrient competition between rubber trees and calla lilies was significant in this intercropping system, with rubber trees holding a competitive advantage. Intercropping significantly inhibited calla lily growth by significantly decreasing soil nutrient content. The abundances of soil microbes and changes in root architectures correspond to the responses of calla lilies to nutrient competition, allowing the adjustment of the plants' nutritional needs during growth and development. [ABSTRACT FROM AUTHOR]

Highlights • A Re-Normalized Vegetation Index was firstly developed to map rubber plantations. • 32-year maps of rubber plantations were generated in Xishuangbanna during 1987–2018. • Annual area of rubber plantations reached its peak in 2014 and then decreased. • Rubber plantations expanded extensively in Sino-Lao and Sino-Myanmar border regions. Abstract Accurately monitoring rubber plantations dynamics is essential for assessing eco-environmental effects in soil, hydrology and biodiversity especially in the northern edge of the Asian tropics (e.g. Xishuangbanna, China). In this study, a novel phenology-based multiple normalization approach was firstly proposed to annually map rubber plantations between two critical phenological phase (defoliation and foliation) in Xishuangbanna during 1987–2018. It included three key steps, namely (1) Landsat non-visible bands normalization for calculating the Normalized Difference Moisture Index (NDMI) and Normalized Burn Ratio (NBR), (2) normalization of NDMI and NBR for the Normalized Vegetation Index (NVI), and (3) re-normalization of NVIs for the Re-Normalized Vegetation Index (RNVI). The NVI highlighted the temporal differences of NDMI in land surface moisture content and NBR in soil moisture as well as vegetation survival of rubber plantations during the shifting period of defoliation and foliation. The RNVI fully considered the inverse patterns of the NVIs between defoliation and foliation phase. Rubber plantations were featured by negative NVI and RNVI values within the two temporal windows, while the positive NVI and RNVI values or zero stood for other non-rubber land cover types. The average overall accuracy of five-year mature rubber plantations maps (2010, 2013, 2015, 2016, and 2018) was up to 94.7% with the average kappa coefficient of 0.88, showing the great potential of multiple normalization approach. The total area of rubber plantations increased about 5.9 times from 1987 to 2018, showing clear expansion trends from centralization to scattering in Xishuangbanna as well as continuous spread in Sino-Lao (near Luang Namtha) and Sino-Myanmar (near Mongphak of Shan) border regions on the Chinese side. In addition, annual average analysis showed that about 91.4% of rubber plantations were invariably distributed around Jinghong City and Mengla County in the past decades. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amino acid polymorphisms in SDH of Colletotrichum siamense impact susceptibility to SDHIs. • Double mutations (W85L and T86N) in SDHC reduce fitness and sensitivity to penthiopyrad. • Molecular docking reveals specific interactions between penthiopyrad and SDH residues. • SDHC polymorphisms arise from natural evolution, posing challenges for SDHI use in rubber plantations. Among succinate dehydrogenase inhibiter (SDHI) fungicides, penthiopyrad and benzovindiflupyr particularly inhibit Colletotrichum. Studying SDH amino acid polymorphism in Colletotrichum , along with its fungicide binding sites, is key to understanding their mechanisms of action. This study explores the SDH amino acid polymorphisms in Colletotrichum siamense strains from rubber trees in China and their interaction with SDHI fungicides, specifically penthiopyrad and benzovindiflupyr. Sequencing revealed most polymorphisms were in the SDHC subunit, particularly at positions 85 and 86, which are key to penthiopyrad resistance. Among 33 isolates, 33.3 % exhibited a substitution at position 85, and 9 % at position 86. A strain with W85L and T86N substitutions in SDHC showed reduced SDH activity, ATP content, mycelial growth, and virulence, and decreased sensitivity to penthiopyrad but not benzovindiflupyr. Molecular docking with Alphafold2 modeling suggested distinct binding modes of the two fungicides to C. siamense SDH. These findings underscore the importance of SDHC polymorphisms in C. siamense 's fitness and sensitivity to SDHIs, enhancing our understanding of pathogen-SDHI interactions and aiding the development of novel SDHI fungicides. [ABSTRACT FROM AUTHOR]

Cover crops are often intercropped in rubber plantations to improve utilization of understory space; however, how cover crops promote the growth rate (GR) of young rubber trees remains unclear, as these are largely dependent on the growth time and varieties of cover crops. We conducted a five-year experiment with five cover crop treatments of no cover crop (CK) and cover with four varieties of perennial leguminous crops, namely, Stylosanthes guianensis Reyan No. 2 (RY2), Reyan No. 5 (RY5), Reyan No. 7 (RY7), and Reyan No.10 (RY10). We analyzed changes in total organic carbon (TOC), total nitrogen (TN), and the fractions of labile organic carbon (LOC), mineral nitrogen (MN), and organic nitrogen (ON) in understory soil of young rubber plants (Hevea Brisiliensis cv. Reyan 7–33–97) in tropical China and their effects on the GR. The results showed that cover year and cover crop varieties significantly affected soil TOC, LOC fractions, TN, MN, and ON fractions, as well as GR. Compared to CK, the five-year average GRs of rubber trees covering the RY2, RY5, RY7, and RY10 increased by 12.8%, 41.5% 30.0%, and 43.1%, respectively. Compared with CK, the five-year average nutrients of RY5 and RY10 all increased after covering, whereas the soil NH 4 +-N of RY2 decreased by 0.3%. Meanwhile, the soil TOC, TN, acid-hydrolyzable ammonium nitrogen (AN), and amino acid nitrogen of RY7 decreased by 10.1%, 13.4%, 6.7%, and 21.3%, respectively. The soil nutrients all show a good linear relationship with GR. We identified TN and MN as the main nutrients for the growth of young rubber plants through linear regression and stepwise regression. In addition, structural equation modeling indicated that TOC was the carrier of nitrogen transformation and utilization in soil. The total effects of TOC, AN, and NH 4 +-N on GR of rubber trees were 0.55, 0.52, and 0.31, respectively. The results demonstrated that RY5 and RY10 are suitable for young rubber plantation in tropical China as these effectively improved soil nitrogen supply potential, improved soil fertility, and promoted the GR of young rubber trees. [Display omitted] • Covering S. guianensis significantly increase growth rate of young rubber trees. • Labile organic carbon decreased with increase in age of rubber tree. • Covering S. guianensis increased soil organic carbon and organic nitrogen. [ABSTRACT FROM AUTHOR]

Rural land rental markets in China play an increasingly important role in the transformation of the agricultural sector. This study focuses on the rural land rental market in the Xishuangbanna Dai Autonomous Prefecture in Southern China, a mountainous region, where rapid changes in land use have taken place with the transition from traditional agriculture and a tropical rainforest to rubber monoculture. Notably, we assess the impacts of population aging, land tenure security, and ethnicity on the participation of smallholders in the land rental market. The analysis suggests that a higher proportion of older people in a household increases the likelihood of renting out land and reduces the probability of renting in land, implying that population aging fosters land rental market development by transferring land from older to younger farmers. We also confirm that the availability of a land tenure certificate has a significant and positive impact on the renting out of land. Furthermore, ethnic minority groups are less likely to rent out land, indicating that land rental markets are ethnic sensitive. Additionally, specialization in rubber farming, household wealth and the altitude of household location also influence participation in the land rental market. [ABSTRACT FROM AUTHOR]

Transition from forest to rubber (Hevea brasiliensis Muell. Arg.) plantation has occurred in tropical China for decades. Rubber has been planted on 1 million ha to provide raw materials to the rubber industry. The role of various-aged rubber plantations in carbon (C) sequestration remains unclear. The biomass C accumulation including latex C and C distribution in soil of five different-aged stands (7, 13, 19, 25 and 47 years old) were examined. The total biomass C stock (TBC) and total net primary productivity (NPPtotal), whether with or without latex C, had a close quadratic relationship with stand age. Regardless of stand age, around 68% of the C was stored in aboveground biomass, and NPPlatex contributed to approximately 18% of C sequestration. Soil organic carbon stock in the 100-cm depth remained relatively stable, but it lost about 16.8 Mg ha-1 with stand age. The total ecosystem C stock (TEC) across stands averaged 159.6, 174.4, 229.6, 238.1 and 291.9Mg ha-1, respectively, of which more than 45% was stored in the soil. However, biomass would become the major C sink rather than soil over a maximal rubber life expectancy. Regression analysis showed that TEC for rubber plantation at 22 years is comparable to a baseline of 230.4 Mg ha-1 for tropical forest in China, and would reach the maximum value at around 54 years. Therefore, rubber plantation can be considered as alternative land use without affecting net forest ecosystem C storage. In addition to the potential C gains, a full set of ecosystem and economic properties have to be quantified in order to assess the trade-offs associated with forest-to-rubber transition. [ABSTRACT FROM AUTHOR]

Purpose The purpose of this paper is to examine the impact of farmers’ risk perceptions regarding rubber farming on their land use choices, including rubber specialization and crop diversification.Design/methodology/approach A cross-sectional survey data of some 600 smallholder rubber farmers in Xishuangbanna in Southwest China is employed. This paper develops a general conceptual framework that incorporates a subjective risk item into a model of farmers’ land use choices, thereby developing four econometric models to estimate the role of risk perceptions, and applies instrumental variables to control for the endogeneity of risk perceptions.Findings The results demonstrate that risk perceptions play an important role in smallholders’ decision-making regarding land use strategies to address potential risks in rubber farming. Smallholders with higher risk perceptions specialize in rubber farming less often and are more likely to diversify their land use, thereby contributing to local environmental conservation in terms of agrobiodiversity. The land use choices of smallholder rubber farmers are also associated with ethnicity, household wealth, off-farm employment, land tenure status, altitude and rubber farming experience.Originality/value This study contributes to a better understanding of the implications of farmers’ risk perceptions and shows entry points for improving the sustainability of rubber-based land use systems. [ABSTRACT FROM AUTHOR]

In order to investigate the influence of the litter layer and undergrowth intercrops on surface runoff and soil erosion, experimental field plots were monitored over one rainy season in a rubber monoculture and a rubber/tea agroforestry system. Results indicated that the cumulative runoff from plots with bare soil was 1.7 and 2.3 times higher than plots with a litter layer, and with a litter layer plus undergrowth, respectively. Overall, soil erosion from plots with bare soil, plots with a litter layer, and plots with a litter layer plus undergrowth was 4.73, 1.92 and 0.91 t ha − 1 , respectively. This suggests that rubber/tea agroforestry was more effective in runoff and erosion control than rubber monoculture. In contrast to runoff, soil erosion was found to be highly correlated with rainfall intensity, but weakly correlated with rainfall volumes. In the early rainy season when litterfall was considerably abundant (litter coverage > 70%), runoff and soil erosion in both the litter plots and litter plus undergrowth plots were significantly lower compared to the bare soil plots, or plots with only undergrowth. In the late rainy season when litter coverage < 40%, runoff and soil erosion in plots with litter layer or litter plus undergrowth were no longer significantly lower than those in the bare soil or undergrowth plots. These imply that the thick, intact leaf litter layer is an important soil protection agent. In addition, the results demonstrate that the direct influence of precipitation on surface erosion becomes less important as the number of protective layers increase. Solely from the point of view of erosion control, particular attention in practical soil conservation activities should be given to the capacity of tree litter to maintaining soil cover in a rubber plantation. [ABSTRACT FROM AUTHOR]

The partial substitution of chemical nitrogen (N) fertilizer with organic fertilizers is widely used to maintain soil fertility and enhance crop yield, although its effects on soil organic carbon (SOC) composition, mineralization and stability are not fully understood. For this study, a 12-year field experiment was conducted in a rubber plantation field of Hainan Island, China. Three fertilizer treatments included no fertilizer application as control (CK), chemical fertilizer application (NPK), and half of the chemical N fertilizer plus manure application equivalent to half of chemical N fertilizer (NPKM). We determined the soil physicochemical properties, four labile SOC compositions (microbial biomass carbon (MBC), light fraction organic carbon (LFOC), dissolved organic carbon, dissolved organic carbon extracted by hot water (HOC), particulate organic carbon (POC)), four C-associated soil enzymes (β -1, 4-glucosidase (BG), polyphenol oxidase (POX), catalase (CAT) and cellulase), and SOC mineralization (from a 46-day aerobic incubation experiment) in two soil layers (topsoil layer (0–10 cm) and subsoil layer (10–20 cm)). Compared with NPK, NPKM significantly increased soil pH, total nitrogen, total phosphorus, available phosphorus and potassium, NH 4 +-N, and NO 3 −-N contents, and SOC, LFOC, POC, HOC, and MBC concentrations. NPKM had higher cumulative CO 2 production but lower SOC mineralization potential (C p) than NPK, although the difference was not significant. In both soil layers, NPKM significantly increased POX activity, but decreased BG and CAT activities. Soil pH can regulate enzyme activities and synthesis in acidic soil in a tropical region with a significantly positive correlation with POX activity. Compared with NPK, the relatively lower C p /SOC and higher carbon quality index (CQI) indicated higher SOC stability (C p /SOC) in NPKM. The redundancy analysis results revealed that the dominant factors affecting SOC stability were NH 4 +-N, pH, POC and MBC in NPK, and available phosphorus, BG, and pH in NPKM. In the three fertilization treatments, the POX was the dominant factor affecting the CQI. Conclusively, half of the chemical N fertilizer plus half of the manure application could facilitate SOC stability by mediating soil C mineralization and enzyme activities in the rubber plantation of Hainan Island, China. • A 12-year field experiment was conducted in a rubber plantation in Hainan Island, China. • SOC content and labile composition (MBC, LFOC, DOC, HOC, and POC) were significantly increased by NPKM. • Compared with NPK, NPKM increased POX activity but decreased BG and CAT activities. • NPKM significantly increased SOC stability by increasing carbon quality index and decreasing C p /SOC. [ABSTRACT FROM AUTHOR]