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Eucalyptus pellita and Acacia mangium are widely planted in the tropics and managed over five-to-fifteen-year rotations for wood and wood products. This study compares the growth of routine plantings of A. mangium with trial plantings of E. pellita and nearby native forests across six broadly distributed locations on Melville Island, northern Australia. In addition to tree growth measurements, litter mass and chemical properties, and topsoil (0–10 cm) physical and chemical parameters were assessed. Melville Island has a pronounced seasonal rainfall and soils that range from loamy sand to sandy loam textures; across the sites sampled soils comprised 65–85% sand and 8–16% clay. Across our sites, the maximum mean annual increment of E. pellita was 31.12 m3/ha/year compared to 14.64 m3/ha/year for A. mangium , with stand volume strongly positively correlated with clay content. On a site basis tree volume growth correlated strongly with soil clay content, with lower survival on sites with less clay in the predominantly sandy soils. The higher E. pellita growth compared with A. mangium reduced available phosphorous and calcium in topsoil, indicating that addition of P and Ca in subsequent rotations will be important to maintain and increase E. pellita productivity. The N 2 -fixing species, A. mangium , significantly increased nitrogen in litter (1.88 ± 0.04%) and in top soil (0.15 ± 0.01%) compared to E. pellita (litter 0.93 ± 0.05%; topsoil 0.11 ± 0.01%) so that carbon to nitrogen (C/N) ratios in Acacia litter (23.90 ± 0.81) and soil (23.06 ± 0.91) were significantly lower than in Eucalyptus (litter 46.30 ± 2.66; top soil 27.66 ± 1.65). Topsoil C/N also decreased with increasing soil clay content in all land uses (A. mangium, E. pellita, native forests) indicating better conditions for decomposer activity and turnover in sites with higher clay content soils. The Eucalyptus plantation drawdown of N and PO 4 3- in topsoil suggests that future plantings of E. pellita may benefit from additional N fixed into biomass and soil organic matter by the preceding A. mangium plantations. Tree growth correlations with rainfall and soil characteristics showed growth is best explained by annual rainfall, soil texture (as a percentage of clay or of sand), soil electrical conductivity, and soil bulk density. Overall, in tropical long dry season regions, for plantation development on sandy soils, E. pellita is a better choice than A. mangium. • Eucalyptus pellita had higher productivity than Acacia mangium. • While A. mangium increased soil N, E. pellita tended to decline soil N status. • E. pellita was more efficient at taking up soil available P and Ca. • E. pellita growth is influenced by rainfall, bulk density, and sand content. • Stocking rate should be higher in clayey sites with higher water availability. [ABSTRACT FROM AUTHOR]

Achieving a precise assessment of the aboveground biomass (AGB) in mangroves is a critical foundation for sustainable management and carbon sequestration assessment within climate change mitigation strategies. Conserving existing mangrove forests can maintain and enhance AGB over time. This study used a support vector regression (SVR) model, and vegetation indices derived from Sentinel-2 data for a comparative analysis of mangrove AGB within conservation and restoration projects in Madagascar and Abu Dhabi Emirate. The results confirmed that the SVR model based on vegetation indices, once calibrated against the field inventory data, was effective for estimating mangrove AGB at project scale. For the Madagascar project, the model achieved an R2 of 0.81 and RMSE of 27.99 Mg ha−1 for the 2015 timepoint, and an R2 of 0.79 and RMSE of 32.82 Mg ha−1 for 2019. In Abu Dhabi, an R2 of 0.76 and RMSE of 20.51 Mg ha−1 in 2015 and R2 of 0.75 and RMSE of 22.29 Mg ha−1 in 2020 were obtained. The SVR model estimated a decline in AGB from 116.78 Mg ha−1 to 109.63 Mg ha−1 during 2015–2019 in Madagascar, representing a decrease of 7.15 Mg ha−1 (6.13%). While in Abu Dhabi, the average AGB was estimated at 37.51 Mg ha−1 in 2015 and 42.69 Mg ha−1 in 2020, indicating an increase of 5.18 Mg ha−1 (13.76%) which can be attributed to conservation efforts in this region. This study suggested that Sentinel-2 can facilitate the comparison of AGB changes before and after conservation efforts, enabling the quantification of long-term shifts in mangrove AGB. • The SVR model and vegetation indices obtained from Sentinel-2 was used for monitoring mangrove AGB changes. • Red, NIR, red-edge bands and SWIR2 demonstrated higher correlation with AGB. • The deforestation is major driver of the decrease in AGB in Madagascar Bay of Assassins. • Monitoring AGB is crucial for mangrove sustainable management and conservation. [ABSTRACT FROM AUTHOR]

Fire is an important component of many forest ecosystems, yet climate change is now modifying fire regimes all over the world, driving a need to understand the impact of fires on the physical and biological processes. In 2022, Elsevier launched a Special Collection that spanned across several journals, inviting papers under the theme of fires. Here we summarize the articles published in this collection, considering them to be broadly grouped into following themes: impact of fires on flora and fauna, fire modelling, and reshaping forest landscapes. [ABSTRACT FROM AUTHOR]

Highlights • Refinement of the IPCC equation for estimating greenhouse gas emission from forest fires using country specific information. • Provides key recommendations for improving forest fire emissions estimations. • Highlights the complexity of using data from multiple sources and provides possible solutions. Abstract Forest fires are a significant contributor to global greenhouse gas (GHG) emissions. Accurate reporting of GHG emissions from forest fires requires development of detailed methodologies and country specific data for estimating emissions. In recent years, Australia has updated its national methodology for reporting GHG emissions from fires on temperate forested lands, using a Tier 2 approach of the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories. This involved refinement of the equation for estimating GHG emissions from fires provided in the Guidance, and the revision of country specific data which was derived from a comprehensive literature review. The refinements were key to transparent reporting and evaluation of the climatic impacts of mitigation actions such as forest fire management. In this paper we describe the steps required to develop a Tier 2 method in reporting fire emissions using this Australian example, the lessons learnt, and the steps required to reduce uncertainties in estimates. This paper may assist other countries seeking to estimate and report GHG emissions from forest fires by moving from the default Tier 1 method to Tier 2 using country-specific information. [ABSTRACT FROM AUTHOR]

Forest mega-fires have become a global phenomenon in recent decades including in south-eastern Australia where large areas of forest have been fire-killed with loss of human lives and property and impacting carbon sequestration and greenhouse gas emissions. The vast extent and impact of mega-fires has induced a re-evaluation of fuel reduction methods as a key management strategy in wildfire risk mitigation in many countries. This study investigated the impact of a commercial thinning in Eucalyptus delegatensis forest on fuel hazard, fuel loads and wildfire behaviour, eight years after completion of a bay and outrow thinning operation. At the stand level, thinning reduced overstorey tree stocking by more than 50%, increased canopy openness and stimulated the growth of retained trees. Thinning also encouraged the profuse regeneration of over 1000 saplings ha −1 of E. delegatensis, mostly in the outrows, compared with no sapling regeneration in unthinned forest. A system of additive biomass equations was developed to estimate total biomass and component biomass (stem wood, bark, branches and foliage) of individual trees. The aboveground tree carbon was 433 ± 49 Mg C ha −1 in unthinned forest and 322 ± 47 Mg C ha −1 in thinned forest. Thinning decreased surface fuel hazard ratings and fuel loads but had no significant effect on the mass of coarse woody fuels. Fire simulation under severe to extreme weather conditions, as occurred in the 2006/7 Great Divide Fires, indicated an almost 30% reduction in fireline intensity and about 20% reduction in the rate of spread and spotting distance in thinned forest compared with unthinned forest. This study indicates the potential of thinning to reduce wildfire severity and to increase the fire-survival of E. delegatensis . [ABSTRACT FROM AUTHOR]

• E. pellita is a promising species for plantation development. • Water requirements of E. pellita plantation are unstudied. • Benefits of intercropping E. pellita with N-fixing species remain unclear. • Knowledge to support E. pellita plantations in tropics is not well-developed. • Benefits of E. pellita harvest residues on soil and tree growth remain unclear. This paper reviews current knowledge of Eucalyptus pellita plantations to identify management practices for optimizing productivity and maintaining sustainability in the equatorial and tropical environments where it is grown. A combination of genetic improvement and silvicultural practices have markedly improved E. pellita productivity in recent decades. The productivity of E. pellita plantations around the world ranges from 9.4 to 34.9 m3/ha/year, with a tendency to be more productive in regions that receive higher annual rainfall. Because responses vary on water-limited sites, site-specific management practices such as the planting of superior hybrids and clones, and stocking management, are important for optimizing E. pellita growth. We identified several research gaps in understanding the impact of E. pellita harvest residue management on tree growth, benefits of intercropping E. pellita with N-fixing species, the capability and required management of E. pellita coppices to develop new rotation, and E. pellita water use and water requirements. The uncertain taxonomic status of E. pellita is also noted – with the possibility that E. biterranea is a separate species in the more continuously warm and wet equatorial far northern Queensland and Papua/Papua New Guinea geographic range of E. pellita. This may have implications for the continuous development of genetic material for the range of environments currently planted with E. pellita – and for understanding the potential impacts of climate change on productivity, and pest and disease resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Peat fires reduce tree species diversity. • Tree species richness and diversity recovers 30 yr after fires at site level. • At landscape scale species richness and diversity continues to increase at fire frequency > 80 yr. • Revegetation strategies recommended with 'the increaser group' trees. Tropical peat swamp forests contain diverse plant communities that support many endangered flora and fauna species. These forests are increasingly threatened by disturbances such as drainage, logging, and subsequent fire, yet little is known about tree species recovery from these threats. Tree species richness and diversity were measured in peat swamp forests of Central Borneo regenerating naturally after fires from 139 chronosequence plots. Our findings indicated that two to three decades after fire, similar levels of richness and diversity to relatively undisturbed reference forest are reached within sites. However, when averaged across landscapes our modelling shows that fires of average frequency of 50 years, or even 100 years, can substantially suppress tree species richness and diversity. Thus, even rare fires can reduce the species richness and diversity of tropical peat swamp forests. Two groups of tree species drove the difference in richness and diversity between disturbed and reference forests: 'decreasers', occupying recently burnt forest and declining with fire exclusion, and 'increasers', that were only present in less disturbed forests and absent or rare in recently burnt forests. The decreasers were more common than the increasers. We conclude that peat swamp forests can recover adequately from fires through natural regeneration, and it is possible that artificial planting may speed up this process. Where possible, excluding fire from tropical peat forests will help to maintain the diversity of these threatened ecosystems and promote their recovery. [ABSTRACT FROM AUTHOR]

The aboveground biomass and carbon stock of less commercialized Eucalyptus open forests of south-eastern Australia are not well-known due to a lack of accurate biomass equations for even the prevalent species in these forests. To improve biomass and carbon estimates of these forests, a total of 245 trees of 11 eucalypt species with DBH (diameter overbark at the breast height of 1.3 m above ground level) up to 139 cm and height up to 39 m were destructively sampled across three broad study sites in north-central Victoria. Trees were sampled as the four aboveground components of lower stem, upper stem, crown, and dead attached stem and branch materials. All four components were weighed completely in the field. To determine the dry to fresh weight ratio for each of the four components, 90 of these trees were further subsampled for moisture content. General linear models were used to relate dry to fresh weight ratio to site, species and tree size and the parameters of the models were estimated through generalized estimating equations. The model-estimated dry to fresh weight ratios were used to convert fresh weight to dry weight for all biomass components of fresh weight sample trees. Using the derived dry weight data, two systems of nonlinear additive biomass equations for stem, crown and total tree biomass were developed for each of the 11 species, with DBH as the independent variable in one system and the combined variable of DBH and tree height in another. Residual error variances and approximate confidence bands containing about 90% of the observed data about the mean curve of predicted biomass were estimated and derived for all biomass components of each species. In addition to the species-specific equations, two sets of site-specific biomass equations were developed using pooled biomass data from each site regardless of species. These systems of additive biomass equations will improve the accuracy of biomass and carbon estimation of open eucalypt forests in south-eastern Australia. [ABSTRACT FROM AUTHOR]

• The radiant energy required to raise the cambium to 60 °C was directly proportional to the moisture content and the specific heat capacity of the bark. • Moisture content is a major factor in regulating heat transfer and retention in bark and the cambium cell viability following heat exposure. • A critical specific heat capacity was defined and measured as a loss of > 63 % of cambial cell viability and the critical specific heat capacity of bark varied from 3444 to 4657 J kg−1 °C−1 depending on the bark characteristics. • Energy required for the cambium-phloem cells to achieve critical temperature is 3.5–13.6 MJ m−2. • Twenty to 40 min exposure to a low heat flux of 10 kW m−2 can cause significant cambium damage. Tree bark reduces energy transfer from the bark surface towards the cambium during fires. To date, the heat reflection, absorption, and transmission properties of bark has been interpreted mainly in terms of elapsed time to increase temperature in the region of the cambium in response to external heating. To better understand bark protective properties, this study combines a known energy input and a cambium cell viability measure of heat impact, to develop an understanding in terms of characteristics that alter the heat capacity of bark. In this way three Eucalyptus species with different bark types are compared in terms of their heat absorption and transmission responses to heating. Stem sections from freshly felled trees of the three Eucalyptus species with contrasting bark types were exposed to a heat source that produced a constant 10 kWm−2 at the bark surface, that was applied until the cambium reached 60 °C. After stems cooled the viability of cambial cells from both the heated and non-heated sides of the stem were tested to determine the extent of heat impairment of cell function. Radiant heat between 3.5 and 13.6 MJ m−2 was required for the cambium to reach 60 °C, with more heat required for thicker and wetter bark, among the stem sections tested. The capacity of bark to protect the viability of cambium cells was strongly associated with bark moisture content, as well as with bark thickness. Bark with higher moisture content required more energy to heat the cambium to 60 °C, but once heated the moist bark retained the heat for longer than drier bark, resulting in a higher degree of cambial cell impairment. The critical specific heat capacity of bark varied between 3444 and 4657 J kg−1 °C−1 depending on the bark type. When exposed to a constant 10 kWm−2 heat source the critical exposure time for loss of cambium cell viability was between 20 and 40 min depending on bark type. This study provides a strong scientific basis to predict the tree impacts of heat released from fuels during planned fire and during wildfire over a range of fireground conditions – with applications to limit tree damage and increase survival. [ABSTRACT FROM AUTHOR]

Highlights: [•] C emission from forest fires is poorly described for Australian forests. [•] Loss of forest C to the atmosphere is low in planned fire. [•] Low intensity planned fire emitted C is similar to redistributed C. [ABSTRACT FROM AUTHOR]

• Forest experimentally treated with thinning and recent burning did not ignite in wildfire. • Fuel hazard reduction benefits extend for at least three years after fuel treatments. • Active management of fuels reduces wildfire risk and wildfire severity. • In-field measures of fuel hazard strongly correlate with wildfire severity. • Field assessed fire severity strongly correlates with remote sensed fire severity. Climate change is increasing the area of seasonally dry forests burnt by wildfire in many parts of the world, compelling a revision of management strategies to reduce risk and improve the resilience of forest ecosystems. While prescribed burning is a common strategy used to reduce bushfire risk, mechanical thinning has not been as widely applied in Australia's temperate forests in comparison with the USA and Europe. In this study we report results from a prescribed burning and mechanical thinning experiment in a 37-year-old naturally regenerated Eucalyptus open forest that was burnt through by wildfire in January 2020, providing an opportunity to determine how pre-wildfire fuel status and burning and thinning treatments influenced wildfire severity. Fuel hazard assessments in the experimental forest, made prior to the wildfire, indicated that untreated forest, and thinned forest, had very high to extreme fuel hazard scores, while forests treated with prescribed burning, or with thinning plus burning, had low fuel hazard scores. These fuel hazard scores explained more than 70% of the variation in wildfire severity, indicating that the fire was largely fuel driven and responsive to fuel reduction measures. Forest areas treated with thinning only recorded extreme fuel hazard, largely due to the increase in forest floor residues, which were ignited by the wildfire resulting in a high fire severity ranking. Forest areas treated with thinning and prescribed burning, or with high intensity prescribed burning, did not ignite from the advancing front of the wildfire, clearly demonstrating the effectiveness of fuel reduction management under low to moderate forest fire danger weather. Fuel hazard reduction benefits extend for at least three years after the application of fuel modification treatments in Eucalyptus sieberi forests. The results from this forest experiment demonstrate that the active management of fuels, including thinning with prescribed burning, can reduce wildfire risk and fire severity. [ABSTRACT FROM AUTHOR]