Journal of Tropical Science and Engineering

SPATIAL PATTERNS OF WOODY PLANT SPECIES: A CASE STUDY IN MIXED BROADLEAF - CONIFEROUS FORESTS FROM KON CHU RANG NATURE RESERVE, VIETNAM

Hung Cuong Dang

This study examined the structure and spatial organization of the mixed broadleaf-conifer forest community in the Kon Chu Rang Nature Reserve, a protected area within Vietnam’s Central Highlands known for its ecological diversity and role as a watershed for surrounding regions. Using detailed field inventories, we characterized both floristic composition and stand structure, assessing importance value indices (IVI) to gauge species dominance and combining these metrics with quantitative analyses of canopy stratification and tree-size distributions. Results indicate a diverse stand in an intermediate successional stage, with no single taxon attaining absolute dominance; several species exhibited IVI values above 5 %, suggesting the community is functionally balanced with multiple key contributors. Vertical structure analysis revealed the canopy is stratified into three layers, with the majority of individuals occupying the mid‑canopy between approximately 15.5 m and 21.5 m. Tree height distribution approximated a normal curve and diameter distribution followed an inverted J‑shape, patterns typically associated with natural stands that maintain both structural stability and strong regenerative capacity. Spatial point‑pattern analysis using Ripley’s K‑function identified roughly 12m as a critical spatial threshold for aggregation, capturing interactions among seedlings, saplings, and adult trees and corresponding to the biological neighbourhood of competitive influence in this ecosystem. This multi‑scale perspective underscores the importance of selecting appropriate spatial scales when interpreting ecological processes and highlights the value of maintaining a mosaic of size classes across the landscape. Together, these findings suggest that mixed broadleaf - conifer stands in Kon Chu Rang are resilient under current conditions. Sustainable management should therefore prioritize maintaining natural conditions, limiting large‑scale disturbance, and supporting regeneration processes, particularly within a 10 - 12 m radius around mature trees, to ensure long‑term ecosystem sustainability, biodiversity conservation, and continued provision of ecosystem services.

CLIMATOLOGY, VARIABILITY, AND LARGE-SCALES INFLUENCE ON RAINY SEASON ONSET AND CESSATION OVER CENTRAL HIGHLANDS AND SOUTHERN VIETNAM DURING 1981–2019

Duy Dinh

This study investigates the climatology, variability, and large-scale influences on the onset (RSOD) and cessation (RSCD) of the rainy season across the Central Highlands and Southern Vietnam during 1981–2019, based on daily rainfall data from 19 meteorological stations. A rainfall-based criterion was applied to determine RSOD and RSCD. The results indicate that the RSOD typically occurs earlier in the Central Highlands, around April 26, compared to the Southern region, where it occurs around May 8. This difference is largely attributed to orographic influences and the timing of southwest monsoon onset. Similarly, RSCD tends to occur earlier in the Central Highlands, approximately October 30, compared to around November 15 in the Southern region, likely due to the seasonal retreat of the Intertropical Convergence Zone (ITCZ). Interannual variability in both RSOD and RSCD ranges from 20 to 35 days, with higher variability observed in western and southwestern stations of Southern Vietnam, possibly influenced by fluctuations in summer monsoon intensity. Trend analysis indicates a shift toward earlier RSOD and RSCD at rates of approximately 5–7 days and 2–3 days per decade, respectively. Principal Component Analysis (PCA) reveals that the EOF1 explains 30% of the total variance in RSOD and 40% in RSCD. ENSO-related indices exhibit strong and statistically significant correlations with EOF1s, particularly for RSOD. El Niño events are generally associated with delayed onset and earlier cessation of the rainy season, resulting in a shorter duration, while La Niña tends to promote earlier onset and later cessation, thereby extending the season. These findings suggest that ENSO is a key large-scale climate driver and a potential predictor for seasonal forecasting frameworks of RSOD and RSCD in Vietnam.

BIODIVERSITY OF CELLULOLYTIC BACTERIA IN SOIL COLLECTED FROM SOME WOOD PROCESSING AREAS IN VIETNAM

Duc Tan Phung

Cellulose-degrading microorganisms play an important role in the decomposition of organic matter and have potential applications in biotechnology and environmental remediation. In this study, nine soil samples were collected from wood-processing areas in three different regions of Vietnam (three samples per region): the North (Lao Cai province), the Central region (Thanh Hoa province), and the South (Dong Nai province). A total of 28 bacterial strains with CMC-degrading activity were successfully isolated from these soil samples, with the northern region yielding the highest number of isolates (12 strains). All 28 isolates were then evaluated for their morphological, which allowed classification into seven distinct morphological groups. Based on the CMC degradation ability, five strains (D183.1.B1, D111.1.B1, D183.2.B3, D751.1.B2 and D111.3.B2) exhibiting the highest cellulolytic activity (respectively: 24.33 ± 0.33; 23.0 ± 0.58; 21.33 ± 0.33; 21.33 ± 0.67; 18.33 ± 0.33) were selected for further characterization. 16S rRNA gene sequencing results identified these five strains as: Bacillus velezensis D183.1.B1, Bacilus amyloliquefaciens D183.2.B3, Bacillus cellulosilyticus D111.1.B1, Pseudomonas aeruginosa D111.3. B2, Pseudomonas fluorescens D751.1.B2. The effects of pH, temperature, and incubation time on cellulase enzyme production were also investigated. The results indicated that pH 6–8, temperature around 35 °C, and culture time of 48–72 hours yielded the highest cellulase activities, ranging from 1.7 to 7.8 U/mL. These findings enhance the understanding of the diversity and enzymatic potential of cellulose-degrading bacteria inhabiting wood-processing environments in Vietnam and provide a scientific basis for their application in biomass decomposition and sustainable wastewater management.

EVALUATION OF HEART RATE VARIABILITY, SOME CARDIOVASCULAR INDEXES AND NEUROTROPHIC FACTORS IN MILITARY PERSONNELS UNDER PROFESSIONAL DEPRESSIA

Thi Bich Pham

Objective: To evaluate selected cardiovascular physiological parameters and serum concentrations of mature brain-derived neurotrophic factor (mBDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) in 40 military personnel with depression treated at Military Hospitals 175 and 103, and in 80 controls. Methods: Heart rates and blood pressures were measured using standard clinical procedures. Heart rate variability (HRV) was analyzed from 128 consecutive beats using photoplethysmographic measurement. Serum mBDNF, NT-3, and NT-4 concentrations were quantified by enzyme-linked immunosorbent assay (ELISA). Results: In the depression group, heart rate (89.0 ± 16.6 bpm), mean arterial pressure (86.4 ± 8.4 mmHg), pulse pressure (36.8 ± 8.9 mmHg), cardiac index (2.33 ± 0.19 L·min⁻¹·m²), and total peripheral resistance (0.874 ± 0.107) differed significantly from the control group (p < 0.05). The cardiovascular adaptive potential index was 2.51 ± 0.34 units, indicating an adaptation level under stress. HRV metrics - MeanNN (0.698 ± 0.130 s), SDNN (0.026 ± 0.013 s), and CV (3.70 ± 1.58%) - were below normal reference values and lower than in controls, indicating sympathetic predominance in heart-rate regulation. Serum mBDNF (13.9 ± 7.9 ng/mL), NT-3 (59.5 ± 16.0 pg/mL), and NT-4 (59.7 ± 13.3 pg/mL) were significantly reduced compared with controls (p < 0.05). No statistically significant associations were observed between HRV indices or mBDNF, NT-3, NT-4 concentrations, and age or depression severity; pulse pressure showed a moderate inverse correlation with depression severity (r = -0.338). Conclusion: Reduced heart rate variability and decreased serum mBDNF, NT-3, and NT-4 may serve as potential biomarkers to support the diagnosis of depression.

DEVELOPMENT OF MOLECULARLY IMPRINTED POLYMERS FOR THE SELECTIVE ADSORPTION AND PRECONCENTRATION OF AURAMINE O DYE

Anh Nguyen Thi Phuong

For the selective adsorption and enrichment of Auramine O, this study effectively synthesized and characterized molecularly imprinted polymers (MIPs) via precipitation polymerization of ethylene glycol dimethacrylate (EGDMA) as a cross-linker and methacrylic acid (MAA) as a functional monomer. SEM, EDS and FT-IR characterization verified the formation of imprinted cavities designed for Auramine O recognition. A mesoporous structure with an average pore diameter of 7.334 nm, a large pore volume (0.6166 cm³ g⁻¹), and a high specific surface area (336.31 m² g⁻¹) were determined by nitrogen adsorption–desorption analysis, enabling improved adsorption performance. Adsorption studies demonstrated a maximum capacity (qmax) of 125.521 mg g⁻¹, with high selectivity toward Auramine O relative to structurally similar dyes and minimal suppression from electrolytes. Additionally, by optimizing the extraction process, an enrichment factor of 50 was achieved. The MIPs demonstrated remarkable reusability by retaining the high adsorption and desorption efficiencies over up to five cycles. Applying the proposed method on bamboo shoot samples, the recoveries ranged from 78.45% to 96.87%, with relative standard deviations below 7%. These results exhibit the method's suitability and robustness for the sensitive, selective detection of prohibited dyes in complex food matrices, highlighting its potential for routine food safety monitoring and regulatory compliance.