The impacts of climate change, in particular via elevated temperature and atmospheric CO₂ concentrations, cause differential photosynthetic responses between native and invasive alien plants, often resulting in varying magnitudes of plant growth and productivity. This study investigated variations in photosynthetic responses of an invasive alien Acacia species and two successional groups of tropical heath forest species: early secondary (Buchanania arborescens and Dillenia suffruticosa) and secondary (Calophyllum inophyllum and Ploiarium alternifolium) groups at elevated temperature (25 to 30°C) and CO₂ levels (400 to 700 ppm). Invasive A. mangium appears better adapted to higher temperature and CO₂. High temperature improved CO₂ assimilation of A. mangium compared to heath species, which was attributed to increased transpiration rate and stomatal conductance but decreased water-use efficiency. Photosynthetic responses showed no differences in early secondary species at elevated temperature and CO₂ but invasive A. mangium and P. alternifolium were stimulated by elevated CO₂. The greater maximum net photosynthesis of A. mangium coincided with lower light compensation point and electron transport rate for RuBP regeneration, to a certain extent. Findings provide insights into possible underlying ecophysiological mechanisms contributing to the invasion success of Acacias in degraded tropical heath forests in response to future climate change.

Greenhouse gases can cause acid rain, which in turn degrades soil chemical properties. This research was conducted to determine the effects of simulated acid rain (SAR) on the chemical properties of Nyalau series (Typic paleudults). A 45-day laboratory leaching and incubation study (control conditions) was conducted following standard procedures include preparing simulated acid rain with specific pH levels, followed by experimental design/plan and systematically analyzing both soil and leachate for chemical changes over the 45-day period. Six treatments five of which were SAR (pH 3.5, 4.0, 4.5, 5.0, and 5.5) and one control referred to as natural rainwater (pH 6.0) were evaluated. From the study, the SAR had significant effects on the chemical properties of the soil and its leachate. The pH of 3.5 of SAR treatments decreased soil pH, K⁺, and fertility index. In contrast, the contents of Mg²⁺, Na⁺, SO₄²⁻, NO₃⁻, and acidity were higher at the lower SAR pH. Furthermore, K⁺ and Mg²⁺ in the leachate significantly increased with increasing acidity of the SAR. The changes in Ca²⁺ and NH₄⁺ between the soil and its leachate were positively correlated (r = 0.84 and 0.86), whereas the changes in NO₃⁻ negatively correlated (r = − 0.82). The novelty of these results lies in the discovery of significant alterations in soil chemistry due to simulated acid rain (SAR), particularly impacting soil fertility and nutrient availability, with notable positive and negative correlations among specific ions where prolonged exposure to acid rain could negatively affect the moderately tolerant to acidic and nutrient-poor soils. Acid rain can negatively affect soil fertility and the general soils ecosystem functions. Long-term field studies are required to consolidate the findings of this present study in order to reveal the sustained impact of SAR on tropical forest ecosystems, particularly concerning soil health, plant tolerance, and potential shifts in biodiversity and ecological balance.

The uncontrolled invasive spread of exotic Acacias is a growing concern for many tropical ecosystems, particularly due to their negative impact upon nutrient cycling. Studies investigating the effects of Acacia invasion on nutrient cycling have focused on litterfall and litter decomposition, although its impact on ion deposition in tropical ecosystems is less understood. We quantified and compared the rates of ion deposition (Ca²⁺, Mg²⁺, NH₄⁺, NO₃⁻) between Acacia-invaded and non-invaded tropical heath (Kerangas) forest sites in Brunei Darussalam, Southeast Asia. Ion exchange resin (IER) sampler, IER ring and IER bags were used to determine ion depositions via throughfall, in soils and in stream water respectively. Throughfall in Acacia-invaded heath forest sites recorded significantly higher NH₄⁺ and Ca²⁺ depositions but lower Mg²⁺ than non-invaded, intact sites. For ion deposition in soil, all depths recorded significantly higher Ca²⁺ (except for 0 cm depth), Mg²⁺ and NH₄⁺ depositions, but significantly lower NO₃⁻ depositions, in Acacia-invaded sites. Ion deposition in stream water showed significant monthly variations, with Acacia-invaded sites recording significantly higher Mg²⁺ depositions in June, August and September 2015 but lower NH₄⁺ depositions in June, July and September, lower NO₃⁻ and Ca²⁺ depositions in June and September than non-invaded heath forest sites. Overall, these findings demonstrate that ion deposition via throughfall, in soil and in stream water were all affected by Acacia invasion, thus confirming the influence of alien invasive Acacias on nutrient cycling of tropical heath forests.

Agriculture is essential for human survival, but unsustainable practices threaten its long-term viability. Intensive agricultural activities such as tillage, residue burning, and agrochemical use can lead to soil erosion and degradation. Sustainable practices such as intercropping, agroforestry, and home gardening are known to improve soil health and reduce environmental impact. This study investigates the effects of these practices on selected soil properties in Siburan, Sarawak. Soil samples were collected from three sites representing intercropping, agrisilviculture, and home gardening at depths of 0–20 cm, 20–40 cm, and 40–60 cm. The samples were analysed for moisture content, bulk density, pH, organic matter, organic carbon, total acidity, and exchangeable aluminium and hydrogen ions according to the standard procedure. Results show that soil moisture content in home gardening (57.89%) is significantly higher (p < 0.05) than in agrisilviculture (47.84%) and intercropping (25.60%). Organic matter content was also highest in-home gardening at 8.38%, while soil acidity and exchangeable aluminium were significantly elevated in home gardening soils compared to other practices. In contrast, the cations exchangeable capacity under home gardening is the lowest compared to agrisilviculture and intercropping. These findings emphasize the need to understand how different agricultural practices influence soil properties, providing practical insights for improving soil management strategies in Siburan, Sarawak.