Mixed-species plantations involving Eucalyptus and Acacia trees are an effective alternative for managing sustainable plantations. In this study, we evaluated the growth, productivity, nutrient return, and soil properties of a mixed Eucalyptus hybrid (Eucalyptus camaldulensis Dehnh. × E. urophylla S.T. Blake; E) and Acacia auriculiformis A. Cunn. ex Benth. plantation (A) and Eucalyptus hybrid and A. auriculiformis plantations. The mixed Eucalyptus hybrid and A. auriculiformis plantation included three ratios at E33:A67, E50:A50, and E67:A33, while the Eucalyptus (E100) and A. auriculiformis (A100) plantations were established on degraded lands in the Had Wanakorn Forestry Research and Student Training Station, Prachuap Khiri Khan province, Thailand. Three replications within a plot size of 20 × 20 m² were designed to plant Eucalyptus hybrid and A. auriculiformis seedlings at a spacing of 2 × 3 m². The diameters at breast height (DBH) and height (H) of the Eucalyptus hybrid and A. auriculiformis were measured and monitored after planting for five years. The aboveground biomass of the five-year-old mixed and monoculture plantations was then estimated. Litterfall production and nutrient return from the mixed and monoculture plantations were measured for three years. In addition, soil samples at depths of 0–5, 5–10, and 10–20 cm were collected to analyze the soil’s chemical properties. Differences in growth, aboveground biomass, litterfall production, nutrient return, and soil properties were analyzed and tested using Tukey’s HSD. The results indicated that both the DBH and H of the Eucalyptus hybrid in the mixed and monoculture plantations were not significantly different (p > 0.05). Similarly, the DBH and H of A. auriculiformis in each treatment were also not significantly different (p > 0.05). However, the DBH and H of the Eucalyptus hybrid were higher than those of A. auriculiformis. The aboveground biomass for the mixed plantation ratios E50:A50, E100, E67:A33, and E33:A67 was not significantly different, while the stem biomass was the highest in E100. Litterfall production was influenced by the proportion of the Eucalyptus hybrid relative to A. auriculiformis, but the monoculture A100 plantation had the highest litter production. The nitrogen return estimated for the mixed plantation was between A100 and E100. Similarly, the total nitrogen in the topsoil (0–5 cm) of the mixed plantation was higher than that in the monoculture E100 plantation. These results indicate that mixing A. auriculiformis with Eucalyptus can improve soil nutrients and nutrient cycling and increase nutrient returns, suggesting that mixed plantations are an effective option for sustainable plantation management and can mitigate the negative environmental impacts of Eucalyptus monocultures.

Thinning is an important practice for promoting growth and maintaining forest plantation for wood production from the remaining trees. In this study, thinning was carried out in a naturally regenerated 8-year-old Acacia mangium plot in the Phangnga Forestry Research Station. Three thinning schemes, with 175 (T1), 300 (T2) and 600 (T3) remaining trees/ha, were compared with the control (no thinning) of 831 trees/ha. The diameter at breast height (DBH) and height (H) of the trees were measured. The differences in growth, current annual increment (CAI), aboveground biomass, and stem volume (V) were analyzed. We observed that the thinning of A. mangium increased the growth rate, with the DBH being clearly affected by thinning. CAIDBH increased significantly, with the DBH class of thinned A. mangium plots also improving after thinning. The stem volume and aboveground biomass of T3 plot was similar to the control plot after thinning. In addition, the number of large saw logs was the highest in T3 plot. The large saw logs can be used for multi-utilization and have a high value. These results suggest that thinning can promote stem growth, and increase the proportion of large saw logs in naturally regenerated A. mangium stands.

Microplastic contamination is a growing environmental concern in coastal ecosystems, particularly on recreational beaches where human activities may influence plastic inputs. This study investigated microplastic abundance and particle characteristics across five recreational zones along Hatwanakorn Beach in the Gulf of Thailand, focusing on fine-scale variability within a spatially continuous beach system and across management regimes. Supratidal sediments were collected using a quadrat-based approach, and polymer types were identified using Fourier Transform Infrared spectroscopy (FTIR). Fibers were the predominant particle type, followed by fragments, and most particles were classified as large microplastics (1–5 mm). Significant spatial differences in abundance were observed among recreational zones (Kruskal–Wallis test, χ² = 13.37, p = 0.0096). At the management regime scale, a negative binomial generalized linear model also indicated significant differences (χ² = 30.58, p < 0.001), with higher abundance in the Hatwanakorn Forestry Research and Student Training Station (HWK Station) and Community regimes than in the National Park regime. These results indicate that microplastic distribution can be spatially heterogeneous even within a continuous recreational beach system, underscoring the importance of accounting for fine-scale spatial variability when assessing microplastic contamination in coastal environments.