Forests In Vietnam Research Articles

A new approach in soil organic carbon estimation using machine learning algorithms: a study in a tropical forest in Vietnam

ABSTRACT Soil organic carbon (SOC) dataset augmentation, which enables the comprehensive monitoring of carbon sinks at regional and global scales, is vital for global carbon cycle management and soil fertility. SOC maps built by conventional laboratory or field measurements are time- and cost-consuming and especially difficult in forests. A new approach to build SOC maps with good accuracy and time efficiency and promptly respond to changes in SOC dynamics is, therefore, being identified. This study aimed to evaluate the ability of SOC estimation using a multiple linear regression model (MLR) and four machine learning algorithms: artificial neural networks (ANN), support vector machine (SVM), random forest (RF), and extreme gradient boosting (XGBoost) with satellite data sources and soil nutrient indicator data to find the optimal method. The results indicate that the SVM and XGBoost models demonstrated the best predictive abilities (R2 = 0.70 and 0.74, %RMSE = 8.8 and 8.3, MAE = 0.176 and 0.155) when using remote sensing variables and soil property variables, respectively. Band7_IDM, Band 5, Band4_IDM, RVI, NSMI, NDVI, Band 6, Band 7, and Band 4 were the most valuable variables in the SVM model, while NDVI, DVI, GVMI, NSMI, and Band4_Dive in the XGBoost model. The SVM model using remote sensing data may be applied to build SOC maps in Vietnamese forests instead of using conventional methods with a high accuracy (R2 = 0.74).

Evaluation of statistical and machine learning models using satellite data to estimate aboveground biomass: A study in Vietnam Tropical Forests

The combination of machine learning models with satellite imagery is becoming a popular data-modeling tool for biomass prediction, supporting land cover management. This study aims to select the most suitable model to estimate tropical forest aboveground biomass in Vietnam, helping to manage and monitor changes in biomass at regional and local scales. The study identified the optimal model for estimating forest aboveground biomass and minimizing the number of input variables while achieving satisfactory model performance. A total of 59 input variables, including topography, texture features, and vegetation indices, from satellite data were used in four non-parametric algorithms and a conventional parametric model, Artificial Neural Networks (ANN), Support Vector Machine (SVM), Random Forest (RF), Extreme Gradient Boosting (XGBoost), and Multiple Linear Regression (MLR) to predict biomass and evaluate changes aboveground biomass over 10 years in two tropical forests in Vietnam. The results indicated that all models had good estimation performance with R2 ranging from 0.615 to 0.754. For RF, MLR, and XGBoost, vegetation indices contributed the highest model weights, occupying 77.71% – 92.48%. For ANN and SVM, textural and topographic features were the majority of the model weights (73.74 – 96.36%). The RF model performed the best using 59 variables (R2 = 0.754, MAE = 78.5 Mg·ha−1, and %RMSE = 13.57%) and ten variables (R2 = 0.745, MAE = 85.8 Mg·ha−1, and %RMSE = 16.17%). The biomass map using the RF and ten variables achieved a good degree of fitting of 0.76, so it was suitable for managing and monitoring forest biomass in Vietnam. The results indicated a sharp decrease in the areas of dense and very dense forests from 2013 to 2021 and a gradual increase in 2023.

Decentralization Of Vietnam'S forestlands: The policy process and impact

The decentralization of land is crucial for effective production, welfare improvement, and social development. However, the formulation, outcome, and impact of land decentralization policies are influenced by political regimes, policy processes, geographical areas, and socio-economic settings. This study focuses on Vietnam's forest and forestland allocation program over the past 30 years to investigate its impact on poverty dynamics. Retrospective policy analysis and an extended random effect treatment model with longitudinal panel data collected from 53,568 plots in 12 provinces across Vietnam from 2008 to 2018 were used. The findings suggest that while the forestland allocation policy has a positive effect on poverty alleviation, it has minimal impact on the poorest household groups. Additionally, actual tree planting is more beneficial to the non-poor group, indicating a lack of incentivized policies for tree planting and inadequate consideration of the genuine livelihood needs and investment capacities of land recipients, especially poor households. Policy improvements are recommended to better align with the rationale, aims, and social expectations.

Wild-type Caenorhabditis sinica, a model nematode for speciation and evolution, massively found in Vietnam

Caenorhabditis sinica is a male/female species, in which the genetic diversity is possibly high. Thus, the species is advantageous for the understanding of the mechanisms of diversity, evolution, and adaptation within the nematode genus Caenorhabditis. Previous studies reported the geographic distribution of C. sinica only in China; nonetheless, this should be more convincing for its ecology. We allegedly surveyed the Caenorhabditis species and their diversity in the forests of Vietnam. We found 59 C. sinica strains, and this therefore indicates the vast variation that is 85.88% and 100% identical within isolated wild-type strains. They unequally present in habitats and are enormous in the northern forest, and rarer in the southern forest. The comparison of 18S rDNA barcode sequences from 59 C. sinica isolates by nucleotide sequence alignment showed the consistent diversity among the strains in or off the same ecologies, and all are comparable with the ever-first isolated strain JU727.

Possible carnivory in the epiphytic liverwort Pleurozia acinosa (Mitt.) Trevis. is not confirmed

ABSTRACT Introduction. Although in all proven cases of carnivory in plants the relevant species are in the Angiospermae, it has been posited that this phenomenon occurs in two genera of liverworts, Colura and Pleurozia. The suggested occurence of zoophagy in these groups is largely based on their trap-like water sacs, leaf modifications, and the positive results of ‘feeding’ experiments; however, no evidence of nitrogen uptake has been presented. Methods. We measured δ13C, δ15N, %C and %N in Pleurozia acinosa (Mitt.) Trevis. from tropical montane forests in Vietnam, and in representatives from several reference plant groups, both carnivorous and non-carnivorous, and including epiphytes and terrestrial plants. Key results and conclusions. δ13C values in Pleurozia acinosa were significantly higher than in all other groups of plants studied. However, δ15N was significantly lower in P. acinosa than in both groups of true carnivorous plants, and it did not differ from that in non-carnivorous vascular epiphytes and phorophyte trees, being even lower than in other epiphytic bryophytes. Thus, our results do not support the suggestion of carnivory in the genus Pleurozia.

Phylogenetic diversity patterns of woody species across different tree sizes and spatial scales in a tropical forest community on Con Dao Islands

Understanding the maintenance of diversity and the assembly of communities is a primary concern in community ecology. This study explored the phylogenetic structure of an evergreen broadleaved tree community in Con Dao National Park, Vietnam. The survey, conducted in December 2023, encompassed all tree individuals with a diameter at breast height (DBH) ≥ 2.5 cm within a 4-ha study plot. These individuals were identified by species name, and their DBH was measured. Subsequently, a community phylogenetic tree was constructed using the Phylomatic online platform. The 4-ha study plot was subdivided into there different subplots based on three spatial scales (25 m × 25 m, 50 m × 50 m, and 100 m × 100 m) and all trees were classified into three different DBH classes (2.5 cm ≤ DBH < 10 cm representing small trees; 10 cm ≤ DBH < 20 cm as medium trees; and DBH ≥ 20 cm as large trees). The net relatedness index (NRI) and net nearest taxon index (NTI) were utilized to evaluate the phylogenetic structure and infer ecological processes. Our findings revealed a consistent decrease in both NRI and NTI with increasing spatial scales and tree sizes. These results suggest an overdispersed phylogenetic structure within the community across different spatial scales and tree sizes. Additionally, negative density dependence was found to have a pronounced effect on the phylogenetic structure, with a more significant impact on tree individuals from small and medium DBH classes than large ones. This study underscores the significance of phylogenetic density dependence as a primary mechanism governing species diversity and shaping the community structure of evergreen broadleaved forests in Vietnam.

Genetic population structure of the Vietnamese ginseng (Panax vietnamensis Ha et Grushv.) detected by microsatellite analysis.

Panax vietnamensis Ha et Grushv. is a precious medicinal species native to the tropical forests of Vietnam. Due to habitat loss and over-harvesting, this species is endangered in Vietnam. To conserve the species, we investigated genetic variability and population structure using nine microsatellites for 148 individuals from seven populations across the current distribution range of P. vietnamensis in Vietnam. We determined a moderate genetic diversity within populations (HO = 0.367, HE = 0.437) and relatively low population differentiation (the Weir and Cockerham index of 0.172 and the Hedrick index of 0.254) and showed significant differentiation (P < 0.05), which suggested fragmented habitats, over-utilization and over-harvesting of P. vietnamensis. Different clustering methods revealed that individuals were grouped into two major clusters, which were associated with gene flow across the geographical range of P. vietnamensis. This study also detected that ginseng populations can have undergone a recent bottleneck. We recommend measures in future P. vietnamensis conservation and breeding programs.

Classifying forest cover and mapping forest fire susceptibility in Dak Nong province, Vietnam utilizing remote sensing and machine learning

Forest fires can cause significant harm to the biodiversity, air quality, economy, and industries that depend on forests, which is particularly critical given the current climate change scenario. Therefore, it is crucial to predict potential fire risks, especially in Dak Nong, a province located in the highland region of Vietnam, where forest farming is prevalent. In this study, the utilization of remote sensing data from unmanned aerial vehicles (UAV) revealed a decline in forest areas while agricultural rubber and industrial crops witnessed an increase. Furthermore, the integration of SPOT satellite images with UAV and the eXtreme gradient boosting (XGBoost) classification algorithm proved highly efficient in mapping forest types in this province (OA = 81.446%, and Kappa = 0.803). To assess forest fire susceptibility in this study, a hybrid model known as Artificial bee colony-Adaptive neuro fuzzy inference system (ABC-ANFIS) was employed, which indicated that the majority of forests in the area face high to very high of fires, particularly in bamboo and dipterocarp forest areas. The present model is proposed to suggest better prevention and suppression strategies. These facts can help managers stop fires or deal with this disturbance more effectively that may occur in the future. Policymakers and researchers in different areas, such as the limestone forest in the north or the Dipterocarp forests in Vietnam, may consider replicating this study to evaluate specific wildfire risks and develop appropriate fire prevention strategies tailored to their local circumstances.

Initial assessment of the presence of plastic waste in some coastal mangrove forests in Vietnam

Abstract Plastic, valued for its low cost and durability, is widely used in various aspects of daily life. However, accumulative plastic waste (PW) has emerged as an increasing environmental concern that causes a negative impact on both public well-being and marine biodiversity. Studies on marine PW have focused primarily on the number of PW items collected without considering its accumulation in coastal areas. Hence, this study aims to address this gap by meticulously examining the mass and constitution of macro PW in the summertime mangrove ecosystems of Hau Loc, Cat Ba, and Nha Trang. This study revealed that the average densities of PW collected in Hau Loc, Cat Ba, and Nha Trang mangrove forests were 0.93, 0.23, and 0.18 items·m−2 in the morning collection, whereas the afternoon collection showed slightly lower densities of 0.31, 0.12, and 0.14 items·m−2 for the same locations. Although all PWs in the standard plots were collected in the morning, PWs were present in the afternoon after the rising tide. This initially proves that tide is one of the reasons for increasing the presence of PW in mangroves. The most common types of PWs collected included water bottles, plastic bags, ropes, freight lines, fishing nets, and sponge floats. When assessing the PW composition based on mass, low-density polyethylene was the dominant PW category in Hau Loc with 5.97 g·m−2. In Cat Ba, polypropylene was the highest with 11.87 g·m−2, while polyethylene terephthalate was the highest with 0.9 g·m−2 in Nha Trang during the morning sampling. The “Others” type of PW was not present in any of the three locations. This study provides useful information that can be a foundation for future studies to analyze the relationship between socio-economic activities and the presence of PW in mangroves. Additionally, they hold the potential to guide the formulation of targeted strategies aimed at curbing plastic pollution within Vietnam’s coastal regions.

Observations on Pluteaceae in Vietnam: Four New Species and New Records of Pluteus.

Eighteen specimens of Pluteus collected from the tropical forests of Vietnam were studied using morphological and molecular approaches. Pluteus podospilloides, P. semibulbosus, P. chrysaegis and P. septocystidiatus are registered as additional or new records for Vietnam. Four species (P. conformis, P. lucidus, P. subroseus, and P. ornatus) are proposed as new to science, and several other collections (Pluteus sp. 1, P. aff. septocystidiatus, P. aff. pauperculus and P. cf. velutinus) are given an inconclusive taxonomic status for now. The taxonomic positions of all specimens were confirmed using DNA data (nrITS and tef1). Descriptions of the macro- and microscopic features of the studied collections with a discussion of similar taxa are given.

Thinning, selective harvesting and mangrove protection forests: Lessons learned and recommendations from the Vietnamese Mekong Delta

To date, there have been controversies over the effects of thinning and selective harvesting (SH) on mangrove forests. Recently, thinning and SH regulations have been updated with limitation on intensity rates and the requirements for mangrove transplantation for mangrove protection forests of Vietnam. Crucial questions remain unanswered regarding whether upgraded thinning and SH have contributed to the mangrove loss, and whether they have resulted in longer-term negative effects on mangrove protection forests. We used the example of Kien Giang mangrove protection forest (KGMPF), Kien Giang, Vietnam as an appropriate case study to address the above questions. Modified Normalized Difference Water Index, Water Frequency Index, and Normalized Difference Vegetation Index were calculated to understand the effects of upgraded thinning and SH on mangrove protection within KGMPF. The findings reveal that upgraded thinning and SH did not contribute to the loss of mangrove forests in KGMPF between 2005 and 2015. Likewise, these two silvicultural techniques have not created any negative effects on vegetation cover in the districts between 2005 and 2015. In addition, these techniques have not resulted in longer-term effects on the vegetation cover in KGMPF, with the vegetation cover being gradually increased in all four districts between 2020 and 2022. The findings of this study provide solid evidence that the termination of upgraded thinning and SH in Vietnam, Kien Giang and wider region may not be required.

Restricting living space: Development and larval morphology in sticky frogs (Microhylidae: Kalophrynus) with different reproductive modes

We compare reproductive features, development, and larval morphology in three closely related species of sticky frogs (Kalophrynus Tschudi, 1838) inhabiting the lowland and mountain forests of Vietnam and displaying a variety of reproductive modes. While K. interlineatus breeds in open temporary ponds, K. honbaensis and K. cryptophonus are phytotelm-breeders using tree hollows and bamboo stems for reproduction. Their tadpoles also differ in trophic specialization: larval K. interlineatus are typical suspension-feeders, whereas K. honbaensis and K. cryptophonus are obligatorily oophagous. All three species differ in egg and clutch sizes, duration of embryonal period and hatching stage, and the structure of the larval digestive tract and skeleton. Based on external and internal morphology, we conclude that tadpoles of K. interlineatus and K. cryptophonus represent two “extremes” of the adaptive spectrum of microhylid larvae, while K. honbaensis displays a set of transitory traits. Relying on these new findings in anuran biology, we discuss reproductive, ontogenetic, and morphological rearrangements during the transition from pond breeding to phytotelm breeding and from microphagy to macrophagy as well as the significance of the revealed adaptations to different habitats and larval life modes.

The range and habitat suitability of François' langur (Trachypithecus francoisi) in Mayanghe Nature Reserve, China.

The François' langur (Trachypithecus francoisi) is an endangered primate living in limestone forests in Vietnam and China. From October 2017 to August 2018, the habitat preferences and the range of the Francois' langur were surveyed in the Mayanghe Nature Reserve, Guizhou, People's Republic of China. To estimate the range and predict suitable habitat of François' langur, a Gaussian normal kernel density estimation and species distribution models (BIOMOD2) were used along with data on environmental variables and records of the langur's occurrence. The total range of François' langur in the reserve is 68.76 km2, accounting for 22.1% of the total area of the reserve. The elevation of the main utilisation area is 500-800m, accounting for 48.53% of the total area of the reserve. The maximum slope utilised is 20°-30°, 30.19 km2 and accounting for 30.56% of the total area. The habitat used is largely distributed along valleys, preferred broad leaf forest, lower elevation, and close to rivers. Broad leaf forest is the main habitat type utilised, totalling 25.57 km2 and accounting for 37.19% of the total area. Our models predicted that the suitable habitat in the reserve is 62.46 km2, accounting for 20.08% of the total reserve area, with 32.93-km2 suitable habitat occurring in the core zone, 22.44 km2 in the buffer zone, and 7.02 km2 in the experimental zone. Our results indicate that only limited suitable habitat (51%) adverse reserve zoning exists in the Mayanghe Nature Reserve of François' langur.

Allometric relationships among tree-size variables under tropical forest stages in Gia Lai, Vietnam

Allometric models play an undeniable role for estimating hard-to-measure quantities such as volume, biomass and carbon stock in forests. However, so far there has been limited model development for native forests in Vietnam. Therefore, this study was conducted to build and analyze the effectiveness of nonlinear and mixed models for secondary and old-growth forests in Gia Lai, Vietnam. The study measured diameter at breast height, total height, commercial height and crown width of forest trees in 20 plots (10 plots for each forest stage). The results showed that diameter had the strongest relationship with height. In the secondary forest, the Power, Korf and Ratskowky models were the best for pairs of variables, while Prodan, Weibull and Power models were the best fit in the old-growth forest. The nonlinear mixed-effect models were better than classic nonlinear models in both forest stages. Fixed and mixed models developed in this study are very valuable for estimating difficult-to-measure quantities and contribute to effective forest management in the study region.

Coarse Woody Debris in Monsoon Tropical Forests of Vietnam

Coarse Woody Debris in Monsoon Tropical Forests of Vietnam

Implications of tropical cyclones on damage and potential recovery and restoration of logged forests in Vietnam.

Many natural forests in Southeast Asia are degraded following decades of logging. Restoration of these forests is delayed by ongoing logging and tropical cyclones, but the implications for recovery are largely uncertain. We analysed meteorological, satellite and forest inventory plot data to assess the effect of Typhoon Doksuri, a major tropical cyclone, on the forest landscapes of central Vietnam consisting of natural forests and plantations. We estimated the return period for a cyclone of this intensity to be 40 years. Plantations were almost twice as likely to suffer cyclone damage compared to natural forests. Logged natural forests (9-12 years after cessation of government-licensed logging) were surveyed before and after the storm with 2 years between measurements and remained a small biomass carbon sink (0.1 ± 0.3 Mg C ha-1 yr-1) over this period. The cyclone reduced the carbon sink of recovering natural forests by an average of 0.85 Mg C ha-1 yr-1, less than the carbon loss due to ongoing unlicensed logging. Restoration of forest landscapes in Southeast Asia requires a reduction in unlicensed logging and prevention of further conversion of degraded natural forests to plantations, particularly in landscapes prone to tropical cyclones where natural forests provide a resilient carbon sink. This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

A Comparative Study on the Anatomical Characteristics of Acacia mangium and Acacia hybrid Grown in Vietnam

This study aimed to investigate and compare the qualitative and quantitative anatomical characteristics of Acacia mangium and Acacia hybrid in plantation forests in Vietnam. The qualitative and quantitative anatomical characteristics were evaluated according to the International Association of Wood Anatomists list of microscopic features for hardwood identification. In terms of qualitative features, A. mangium had a rough, hard, and fissured bark surface with a golden brown to dark brown color, whereas A. hybrid had a smooth and slightly scaly bark surface with greenish brown to greyish brown color, and yellowish white to pale white spots. Moreover, the heartwood–sapwood color and microscopic features of both species were identical. In terms of quantitative features, A. mangium had higher values in the tangential diameter of vessel lumina, vessel per square millimeter, ray number per millimeter, fiber length, and fiber wall thickness than A. hybrid, whereas A. hybrid had a higher ray height and lumen diameter than A. mangium. Thus, it is suggested that bark morphology and some quantitative anatomical characteristics can be used for identification and evaluation of wood quality between A. mangium and A. hybrid growing in Vietnam.

Plant species diversity and composition in limestone forests of the Vietnamese Cat Ba National Park

Plant species diversity and composition play crucial roles in many ecosystem services and are largely influenced by environmental conditions, as well as natural and/or anthropogenic disturbances. However, our knowledge of the drivers of plant species diversity and composition in the limestone forests of Vietnam, a hotspot of biodiversity, is limited. To fill this knowledge gap, we surveyed plant species in the Cat Ba National Park (CBNP), located on a limestone archipelago. We hypothesised that: (1) topography, accessibility and spatial isolation drive the diversity and composition of plant communities in the CBNP and that (2) isolated areas contribute to high floristic regional diversity by supporting unique species assemblages. We expected high tree species diversity within the tropical limestone forests of the CBNP, but also that: (3) the abundance of non-tree species negatively affects tree regeneration diversity and abundance. Data were obtained from 90 random sample plots (500 m2) and 450 sub-sample plots (25 m2) in three areas of the CBNP. We differentiated four different plant species communities and found a total of 302 species belonging to 112 families. Tree species contributed 50% to total species richness. The distribution of different plant communities in the CBNP was driven mainly by topography; that is, the percentage of rock surface and slope and concomitant differences in soil depth. Contrary to our expectations, isolated areas did not contribute greatly to the CBNP’s plant species diversity. It seems that isolated areas and, as in our case, rough topography, may act as natural barriers to seed dispersal, creating an environmental filter for tree species. Across the CBNP, there was no effect of non-tree species on tree species regeneration, but regeneration patterns differed between communities. In species-rich communities growing under favourable site conditions (e.g. low rock surface and slope), greater coverage by non-tree species had an increasingly negative effect on tree species richness and abundance in the regeneration layer. The opposite was observed in communities growing under harsh site conditions. We conclude that plant species diversity in the CBNP is high, particularly in easily accessible lowland areas where tree species contribute greatly to biodiversity. However, here, non-tree species can even restrict tree regeneration.

Effects of tree diversity and stand structure on above-ground carbon storage in evergreen broad-leaved and deciduous forests in Southeast Vietnam

Understanding the relationship between tree species diversity and above-ground carbon (AGC) storage in tropical forests is essential for a sustainable flow of ecosystem goods and services. Although tropical forests of Vietnam are of particular interest due to their high biodiversity and carbon density, few studies have evaluated the relative importance of species composition, tree species diversity and forest structure on AGC storage by forest vegetation type. In this study, we tested for the influence of taxonomic diversity, forest structure and species composition on AGC storage in evergreen broad-leaved and deciduous forests of Southeast Vietnam. Data was collected within 137 rectangular plots (25 m × 20 m), randomly selected across a deciduous forest (DF) and four evergreen broad-leaved forest (EB) categories, with different stand­ing volumes levels: very poor (EBG), poor (EBP), medium (EBM) and rich (EBR). In total, we identified 3687 individuals from 110 tree species belonging to 46 families in 6.85 hectares of sampled area. AGC stor­age significantly differed among forest categories, ranging from 14.81 Mg ha−1 in EBG to 146.74 Mg ha−1 in EBR. There was higher AGC in the medium diameter class (20-40 cm), except for EBR where there was higher AGC within individuals of 40-60 cm in diameter. Taxonomic diversity was weakly correlated with AGC while stand structure (stem density and maximum diameter) were strongly correlated. Our results suggest that maintaining the abundance distributions of remnant tree species, particularly that of large trees, is one important method to enhance AGC storage in the tropical ecosytems of southern Vietnam.

De Novo Metagenomic Analysis of Microbial Community Contributing in Lignocellulose Degradation in Humus Samples Harvested from Cuc Phuong Tropical Forest in Vietnam

We aimed to investigate the microbial diversity, mine lignocellulose-degrading enzymes/proteins, and analyze the domain structures of the mined enzymes/proteins in humus samples collected from the Cuc Phuong National Park, Vietnam. Using a high-throughput Illumina sequencer, 52 Gbs of microbial DNA were assembled in 2,611,883 contigs, from which 4,104,872 open reading frames (ORFs) were identified. Among the total microbiome analyzed, bacteria occupied 99.69%; the five ubiquitous bacterial phyla included Proteobacteria, Bacteroidetes, Actinobacteria, Firmicutes, and Acidobacteria, which accounted for 92.59%. Proteobacteria (75.68%), the most dominant, was 5.77 folds higher than the second abundant phylum Bacteroidetes (13.11%). Considering the enzymes/proteins involved in lignocellulose degradation, 22,226 ORFs were obtained from the annotation analysis using a KEGG database. The estimated ratio of Proteobacteria/Bacteroidetes was approximately 1:1 for pretreatment and hemicellulases groups and 2.4:1 for cellulases. Furthermore, analysis of domain structures revealed their diversity in lignocellulose-degrading enzymes. CE and PL were two main families in pretreatment; GH1 and GH3-FN3 were the highest domains in the cellulase group, whereas GH2 and GH43 represented the hemicellulase group. These results validate that natural tropical forest soil could be considered as an important source to explore bacteria and novel enzymes/proteins for the degradation of lignocellulose.