This study evaluated the stabilization of dam sediment using a blended binder of eucalyptus wood ash (EWA) and cement for cost-effective and environmentally safe pavement material development. The sediment is classified as a sandy lean clay. EWA, a pozzolanic byproduct, was used as a partial cement replacement to enhance the material's geotechnical properties and reduce environmental impact. The optimized mixture showed a 12-fold increase in unconfined compressive strength (1.4 MPa) and a California bearing ratio of 70%, meeting Thailand Department of Highways' specifications for subbase and base layers. The microstructural analysis confirmed the formation of calcium silicate hydrates, improving durability and reducing weight loss by 30% under wetting-drying cycles. Leachate tests showed that heavy metal concentrations remained within regulatory limits. EWA also reduced costs by 2.6 times compared to conventional stabilization methods, highlighting its potential for pavement applications.

Context. The incorporation of trees into integrated crop-livestock systems (ICLS) has been encouraged because of their role in climate change mitigation through plant and soil carbon sequestration. One challenge is to minimize competition (especially for light) and the damage caused by cattle to trees. Aim. This study sought to evaluate the performance of beef heifers grazing on cool-season grasses in two ICLS, crop-livestock (CL) and crop-livestock with immature Eucalyptus grandis trees (CLT), at two nitrogen (N) rates (50 and 150 kg/ha) on pasture. Because these were the first stocking seasons after tree planting, the physical impact of animals (e.g. debarking) on the trees was also evaluated. Methods. The experimental design was randomized blocks with treatments arranged in a 2 x 2 factorial scheme (2 systems x 2 N fertilization rates), with three replicates. Forage production (as dry matter, DM) and animal performance were evaluated for 2 years. Key results. Total forage production and liveweight (LW) gain per area over 117 days of grazing were on average higher for CL (6736 +/- 565 kg DM/ha and 505 +/- 58.6 kg LW/ha respectively) than for CLT (5455 +/- 372 kg DM/ha and 364 +/- 42.3 kg LW/ha), regardless of N rate, and even at similar sward heights (similar to 24 cm). The damage caused by heifers to the bark of the trees was classified as high intensity in 91.1% of the trees, even after the trees had reached a diameter at breast height of 9.9 cm. Conclusions. The interaction between livestock and trees was detrimental to the system's productivity, affecting pasture growth, animal performance and the quality of trees as sawn wood. This finding underscores the importance of selecting appropriate tree species, plant density and species arrangement in ICLS. Implications. Lower tree densities (<237 trees/ha) and preventive measures regarding the use of E. grandis in CLT systems with cool-season grasses are necessary in subtropical regions.

Salinity is an abiotic factor limiting plant fitness and therefore forest crop productivity, and salt-affected areas have been expanding throughout the world. Ectomycorrhizal (ECM) fungi can improve the salt tolerance of woody plants, including Eucalyptus species To screen for salt-resistant Pisolithus albus (PA) isolates, 16 PA isolates were cultivated on modified Melin-Norkrans agar containing NaCl at concentrations of 0, 10, 20, and 30 dS m(-1). The P. albus isolate PA33 had the greatest salt resistance under 10 and 20 dS m(-1) NaCl, which are soil salinity levels in salt-affected areas of Thailand. We studied the effect of PA33 on Eucalyptus camaldulensis x E. pellita cuttings under salt stress (0 and 16 dS m(-1)) for 1 month. PA enhanced the growth of the Eucalyptus seedlings, as indicated by higher relative growth rates in height and root collar diameter of inoculated seedlings compared with non-inoculated seedlings. Moreover, the inoculated seedlings had less cell damage from NaCl, as indicated by significantly lesser leaf thickness and electrolyte leakage than the controls. These findings could lead to practices conferring socioeconomic and environmental benefits, as abandoned salt-affected areas could be reclaimed using such Eucalyptus seedlings inoculated with salt-tolerant ECM fungi.

Allelopathy is an underlying and controversial mechanism for detrimental environmental effects in the management of Eucalyptus plantations. However, little attention has been paid to the dynamics of allelochemicals and phytotoxicity in soil fauna during litter decomposition. To explore the relationship between the dynamics of phytotoxicity and allelochemicals, a decomposition experiment was conducted using 4-year-old and 8-year-old Eucalyptus grandis litter (0, 10, 20, 30, and 45 days). The acute toxicity of Eisenia fetida was assessed, and a chemical analysis of the eucalyptus leaves was performed. Biochemical markers, including total protein, acetylcholinesterase (AChE) activity, and oxidative stress levels (SOD and MDA) were measured. A comet assay was used to determine DNA damage in E. fetida cells. The results showed that after 20-30 days of decomposition, E. grandis litter exhibited stronger phytotoxic effects on E. fetida in terms of growth and biochemical levels. After 20 days of decomposition, the weight and total protein content of E. fetida first decreased and then increased over time. SOD activity increased after 20 days but decreased after 30 days of decomposition before increasing again. MDA content increased after 20 days, then decreased or was stable. AChE activity was inhibited after 30 days of decomposition and then increased or stabilized with further decomposition. Soluble allelochemicals, such as betaine, chlorogenic acid, and isoquercitrin, significantly decreased or disappeared during the initial decomposition stage, but pipecolic acid significantly increased, along with newly emerging phenolic fractions that were present. More allelochemicals were released from 8-year-old litter than from 4-year-old E. grandis litter, resulting in consistently more severe phytotoxic responses and DNA damage in E. fetida. Scientific management measures, such as the appropriate removal of leaf litter in the early stages of decomposition, might help support greater biodiversity in E. grandis plantations.

Penetrometers and penetrographers are widely used to measure soil resistance to penetration, but the results are associated with other soil properties (such as bulk density, water content, and particle size distribution). Thus, for an adequate interpretation of results, site-specific studies are necessary to identify which properties are more related to soil resistance. We aimed to measure the resistance to penetration of a Typic Paleudalf under distinct soil uses and to identify soil properties that influence soil resistance. The soil uses in this study included anthropized forest (composed of tree and shrub species), pasture (5-year-old pasture), Eucalyptus 20 (a 20-year-old Eucalyptus saligna stand), and Eucalyptus 4.5 (a 4.5-year-old Eucalyptus saligna under the second rotation). Soil resistance to penetration was measured with an impact penetrometer, and the data were correlated with other physical and mechanical properties of soil, such as the particle size, soil moisture, air permeability, saturated hydraulic conductivity, porosity, bulk density, precompression stress, and compressibility index. We observed that a resistance of 1.3 MPa matches with other soil property values corresponding to soil compaction, and values greater than 1.3 MPa were verified at depths of 0-8 cm for pasture and 8-30 cm for Eucalyptus 4.5. Analyzing all soil uses together, the correlation was significant (p < 0.05) with gravel (r = 0.34), silt (r = -0.32), clay (r = 0.26), gravimetric moisture (r = -0.27), macroporosity (r = 0.24), and soil bulk density at the end of the compressibility test (r = 0.27). The penetrometer is useful for evaluating the physical conditions of soil, but we highlight that soil resistance is influenced by factors such as particle size and soil moisture, as examples. We recommend using a set of soil properties for a better interpretation of penetration resistance data and to support decision-making regarding soil management.

AimIncreased tree mortality linked to droughts and fires is occurring across temperate regions globally. Vegetation recovery has been widely reported; however, less is known about how disturbance may alter forests structurally and functionally across environmental gradients. We examined whether dry forests growing on low-fertility soils were more resilient to coupled extreme drought and severe fire owing to lower tree mortality rates, higher resprouting success and persistence of juveniles relative to wetter forests on more fertile soils.LocationFire-tolerant eucalypt forests of temperate southeastern Australia.Time period2020-2023.Major taxa studiedEucalyptus, Corymbia, Angophora.MethodsDemographic surveys of tree mortality and regeneration in all combinations of dry/wet forest, fertile/less fertile substrates exposed to extreme drought and fire were conducted. We used Bayesian regression modelling to compare tree mortality, diameter, response traits, population structure and occurrence of fire scars between substrates/forest types.ResultsOverall mortality (20%-33%) and topkill (34%-41%) were within historically reported ranges for various forests and soil types. However, we observed an atypical trend of increased mortality and topkill in the largest trees, particularly when they had structural damage from past fires. Trees in wet forests on more fertile soils had the highest levels of mortality. Numbers of persistent resprouting juveniles were highest in dry forests on low-fertility soils. Dry forests growing on low-fertility soils appear more resilient to compound disturbances due to lower rates of mortality and higher rates of juvenile persistence. Wet forests on more fertile soils may experience greater demographic change due to higher mortality of small and large trees.Main conclusionsMesic forests on relatively fertile soils were found to be at relatively high risk of demographic change from compound disturbances. Combined, fire and drought are likely to reduce the number of large trees in affected areas, with consequences for forest carbon cycling and storage.

Climate change has accelerated the frequency of catastrophic wildfires; however, the drivers that control the time-to-recover of forests are poorly understood. We integrated remotely sensed data, climate records, and landscape features to identify the causes of variability in the time-to-recover of canopy leaf area in southeast Australian eucalypt forests. Approximately 97% of all observed burns between 2001 and 2014 recovered to a pre-fire leaf area index (+/- 0.25 sd) within six years. Time-to-recover was highly variable within individual wildfires (ranging between = 5 years), across burn seasons (90% longer January to September), and year of fire (median time-to-recover varying four-fold across fire years). We used the logistic growth function to estimate the leaf area recovery rate, burn severity, and the long-term carrying capacity of leaf area. Time-to-recover was most correlated with the leaf area recovery rate. The leaf area recovery rate was largest in areas that experienced high burn severity, and smallest in areas of intermediate to low burn severity. The leaf area recovery rate was also strongly accelerated by anomalously high post-fire precipitation, and delayed by post-fire drought. Finally we developed a predictive machine-learning model of time-to-recover (R2: 0.68). Despite the exceptionally high burn severity of the 2019-2020 Australian megafires, we forecast the time-to-recover to be only 15% longer than the average of previous fire years. Australian eucalypt forests have evolved different strategies to recover from fire. While the meteorological drivers of bushfire are reasonably well understood, the various processes explaining how long a forest takes to recover from fire are not. We investigated a range of static (landscape) and dynamic (vegetation condition or meteorological) factors that could influence how long a forest's canopy leaf area would take to recover from fire. Time-to-recover after fire is highly variable, ranging from less than 1 year to more than 5 years even within an individual burn location. More intense fires cause greater forest canopy damage and generally (but not always) lead to longer recovery times, whereas wetter conditions after the fire can accelerate recovery. Using these factors and others, we developed a model capable of predicting the time-to-recover and applied it to the 2019-2020 Australian megafires. Our analysis suggests the canopy damage caused by these fires was far more severe than fires in years prior. This would normally lead to a prolonged time-to-recover, however we predict that anomalously high rainfall in the year following the fires will shorten recovery time, compensating for the high burn severity. Ultimately we predict the time-to-recover will be only slightly longer than average. Pre-fire leaf area, burn severity, and post-fire meteorological conditions combine to determine time-to-recover after fire Large geographic variation in time-to-recover can be explained by mean climate and landscape differences Time-to-recover can be predicted with high accuracy using information limited to the first year following fire

While soil salinization is a major concern for agriculture worldwide, the application of sodium (Na) can stimulate growth in many plant species, due to its ability to replace potassium (K) in some physiological functions. We present an overview of the potential and risks associated with replacing KCl fertilizer with a mixture of KCl and NaCl in tropical plantations, with a focus on Eucalyptus. A wide range of responses of Eucalyptus species to the salinization of the soil is well documented and the planting of Eucalyptus rows in salinity-damaged landscapes has been used in Australia to lower the water table and reduce soil salinization. A positive effect of NaCl application on Eucalyptus growth in K-deficient environments has been demonstrated in hydroponics, which is consistent with comprehensive studies conducted on entire rotations in Brazil. The addition of NaCl to K-deficient soils increased above-ground biomass at harvest in E. grandis plantations by a factor of 1.4, whereas the addition of the same amount of KCl increased biomass by a factor of 2. A comparison between KCl and K2SO4 applications suggested a positive response of E. grandis to Cl, in addition to the response to Na. The effects of Na application on the physiology of E. grandis support the hypothesis of a functional role for Na in K-deficient soils. Consistent results have been reported on the physiology of olive tree, coconut palm and cocoa tree. Atmospheric inputs of Na depend on the distance from the ocean, ranging from approximately 30 to 5 kg ha1 yr-1 in coastal and inland forests, respectively. Na is an essential nutrient for animals, maintaining homeostasis and playing a crucial role in neural networks. Substantial quantities of Na are routinely fed to animals in extensive livestock farming. A growing body of evidence suggests that a shortage of Na can limit the activity of insects, particularly plant decomposers. The application of Na in tropical plantations could therefore accelerate the release of nutrients during litter decomposition, thereby promoting tree growth. However, Na application could also stimulate herbivory and lead to leaf area losses. We recommend setting up multi-location experiments covering a wide range of soils and climates in tropical regions, for perennial species of commercial interest. In-depth studies should be carried out on certain sites to understand how tree physiology, soil functioning and herbivory are influenced by the addition of NaCl.

The pulp and paper industry in Sumatra, Indonesia, completely changed its key plantation forest species during 2012-2017 from their previous mainstay, Acacia mangium (which had become severely damaged by diseases) to Eucalyptus pellita and related hybrids. This rapid wholesale change posed major challenges to management and ongoing wood production. We present here long-term experimental results and operational pre-harvest inventory of the two species covering five successive rotations, spanning three decades. This is the first such report of longterm, multi-rotation productivity trends for plantations from a tropical equatorial environment. Highlights include: (i) the trends in productivity in the experiments and inventory are parallel and were characterised by an initial increase, followed by a decrease and then recovery of productivity in response to ecosystem stress, species change and management interventions, (ii) the growth rates of E. pellita are significantly lower than those of A. mangium across soils and sites (iii) the conservation of site organic matter during the inter-rotation phase is as critical for eucalypt as it was for acacia, (iv) the response to applied P is more widespread and stronger in E. pellita than in A. mangium, and (v) significant production losses are occurring due to high tree mortality. We also highlight some of the emerging issues warranting attention. Productivity varies widely across sites, so does the relative responses to management inputs in this environment. The reasons for this need to be better understood so that site-specific management practices can be applied. For example, the depth at which an impeding horizon occurs in some soil profiles is a strong factor influencing growth, regardless of species. The legacy effects of A. mangium, especially of fixed N and nutrient cycling are benefitting eucalypts. The adoption of research outcomes by managers have enabled gains of 8-19% in the productivity of eucalypts planted in recent years compared to that obtained in the first eucalypt rotation. Further improvements are possible through adaptive management, guided by both experimental results and inventory, aimed at gains in operationally realisable productivity. The companies are committed to using only plantation grown wood for processing and are not expanding their own land base allocated for production. The imperative, therefore, is to focus on sustainably increasing the productivity per unit area on their existing land management units that are now under the fifth or sixth rotation.