Eucalypt Forest Research Articles

Developing a New Method to Rapidly Map Eucalyptus Distribution in Subtropical Regions Using Sentinel-2 Imagery

Eucalyptus plantations with fast growth and short rotation play an important role in improving economic conditions for local farmers and governments. It is necessary to map and update eucalyptus distribution in a timely manner, but to date, there is a lack of suitable approaches for quickly mapping its spatial distribution in a large area. This research aims to develop a uniform procedure to map eucalyptus distribution at a regional scale using the Sentinel-2 imagery on the Google Earth Engine (GEE) platform. Different seasonal Senstinel-2 images were first examined, and key vegetation indices from the selected seasonal images were identified using random forest and Pearson correlation analysis. The selected key vegetation indices were then normalized and summed to produce new indices for mapping eucalyptus distribution based on the calculated best cutoff values using the ROC (Receiver Operating Characteristic) curve. The uniform procedure was tested in both experimental and test sites and then applied to the entire Fujian Province. The results indicated that the best season to distinguish eucalyptus forests from other forest types was winter. The composite indices for eucalyptus–coniferous forest separation (CIEC) and for eucalyptus–broadleaf forest separation (CIEB), which were synthesized from the enhanced vegetation index (EVI), plant senescing reflectance index (PSRI), shortwave infrared water stress index (SIWSI), and MERIS terrestrial chlorophyll index (MTCI), can effectively differentiate eucalyptus from other forest types. The proposed procedure with the best cutoff values (0.58 for CIEC and 1.29 for CIEB) achieved accuracies of above 90% in all study sites. The eucalyptus classification accuracies in Fujian Province, with a producer’s accuracy of 91%, user’s accuracy of 97%, and overall accuracy of 94%, demonstrate the strong robustness and transferability of this proposed procedure. This research provided a new insight into quickly mapping eucalyptus distribution in subtropical regions. However, more research is still needed to explore the robustness and transferability of this proposed method in tropical regions or in other subtropical regions with different environmental conditions.

Reconciling Top‐Down and Bottom‐Up Estimates of Ecosystem Respiration in a Mature Eucalypt Forest

AbstractEcosystem respiration (Reco) arises from interacting autotrophic and heterotrophic processes constrained by distinct drivers. Here, we evaluated up‐scaling of observed components of Reco in a mature eucalypt forest in southeast Australia and assessed whether a land surface model adequately represented all the fluxes and their seasonal temperature responses. We measured respiration from soil (Rsoil), heterotrophic soil microbes (Rh), roots (Rroot), and stems (Rstem) in 2018–2019. Reco and its components were simulated using the CABLE–POP (Community Atmosphere‐Biosphere Land Exchange–Population Orders Physiology) land surface model, constrained by eddy covariance and chamber measurements and enabled with a newly implemented Dual Arrhenius and Michaelis‐Menten (DAMM) module for soil organic matter decomposition. Eddy‐covariance based Reco (Reco.eddy, 1,439 g C m−2 y−1) was slightly higher than the sum of the respiration components (Reco.sum, 1,295 g C m−2 y−1) and simulated Reco (1,297 g C m−2 y−1). The largest mean contribution to Reco was from Rsoil (64%) across seasons. The measured contributions of Rh (49%), Rroot (15%), and Rstem (22%) to Reco.sum were very close to model outputs of 46%, 11%, and 22%, respectively. The modeled Rh was highly correlated with measured Rh (R2 = 0.66, RMSE = 0.61), empirically validating the DAMM module. The apparent temperature sensitivities (Q10) of Reco were 2.22 for Reco.sum, 2.15 for Reco.eddy, and 1.57 for CABLE‐POP. This research demonstrated that bottom‐up respiration component measurements can be successfully scaled to eddy covariance‐based Reco and help to better constrain the magnitude of individual respiration components as well as their temperature sensitivities in land surface models.

On Canopy Rainfall Interception Modeling in a Eucalyptus Plantation

The interaction between the forest canopy and precipitation is a fundamental process for understanding the hydrological cycle in forests. Physical models have been applied to estimate canopy water interception, and their efficiency has been tested based on metrics used to assess hydrological models. For eucalyptus plantations in Brazil, more studies are needed on the canopy rainfall interception model. Thus, we calibrated the Gash model using two complete hydrological years of observation in a eucalyptus plantation in southeastern Brazil. The model’s parametrization was conducted using 17 trees individually in different planting spacings (3 m × 2 m, 3 m × 3 m, and 3 m × 5 m). The average values of the model’s parameters were taken to represent the forest, and the average parameters for each planting spacing were used to assess the model’s performance according to the planting spacings. We used NSE, KGE, and Pbias statistical metrics to assess the model’s performance. For individual trees and rainfall events, the model showed an average NSE and Pbias of 0.59 and 18.2%, respectively, meaning a “satisfactory” performance for eight trees and “poor” performance for nine trees. When the model was averaged for the entire forest and individual rainfall events were considered, the metrics were improved, being 0.643 for NSE and 8.2% for Pbias, indicating a “good” model performance, which was strengthened by an average KGE of 0.746. Regarding the model for the planting spacings, the best results were found for the 3.0 m × 2.0 m spacing (“a good performance”). For the other spacings, Pbias was higher than 15%, leading to inferior performance, but with the NSE and KGE compatible with “good” performance. The practical implications of our findings are significant, as they can be used to enhance the accuracy of models for a better understanding of the hydrological cycle in eucalyptus forests in Brazil, thereby contributing to more effective forest management and conservation.

Downscaling Vapor Pressure Deficit across Complex Forested Terrain

Abstract The forest microclimate shapes many aspects of forest functioning, including plant regeneration and wildfire occurrence. In complex landscapes with varying terrain, the forest microclimate varies at fine spatial scales (10–100 m2). However, accurately mapping this variation remains challenging. Vapor pressure deficit (VPD) is an important microclimatic variable for plant growth and fire activity, yet few studies have specifically focused on downscaling VPD. The aim of this study was to examine the drivers of in-forest VPD in temperate eucalypt forests and develop a model to predict in-forest VPD. We use microclimate data from 37 in-forest weather stations, installed across an aridity gradient in southeastern Australia. We used linear mixed models within an information theoretic approach to develop a predictive model for daily maximum in-forest VPD using open VPD and topographic variables. The highest-ranked model included fundamental topographic drivers of vegetation structure and microclimate in forested landscapes: aspect, elevation, and slope, in addition to open VPD. The model had high accuracy when tested against independent data. We used this model to map fine-scale (30 m2, daily) maximum in-forest VPD across a topographically complex case study landscape. Predicted in-forest VPD showed considerable spatial and temporal variations not captured by coarse-scale open VPD. This represents a significant advancement in our ability to model microclimatic conditions in temperate eucalypt forests and has the potential to advance our understanding of how ecosystem processes vary at fine spatial scales.

Technical and economic performance of a feller buncher in eucalyptus forests with different yields in Southern Bahia, Brazil

Technical and economic performance of a feller buncher in eucalyptus forests with different yields in Southern Bahia, Brazil

Multi‐year responses of reptiles to prescribed burning in a eucalypt forest ecosystem

AbstractPrescribed burning is the primary method used to reduce wildfire risk in a range of ecosystems globally. Knowledge of how animal populations respond to prescribed burns is essential for designing fuel management plans that are sensitive to ecological values. We conducted a before–after, control‐impact experiment in the temperate jarrah forest ecosystem of south‐western Australia to examine how reptiles respond to season of burning (spring or autumn) and time since burning (0–5 years). Through pitfall trapping at 10 survey grids over 7 years, we captured 1808 reptiles from 22 species. Bayesian mixed effects models revealed that six of the eight species analysed showed either a decrease or increase in capture rate at burnt compared to unburnt sites, and most of these effects only occurred within the first 2 years post fire. Species richness showed a weak negative response to one autumn burn and no relationship with time since fire. Fire effects were more common in autumn compared to spring burns, which is likely a reflection of differing fire severities. These results suggest that prescribed burning can temporarily reduce habitat suitability and abundance for some species, particularly those that rely on leaf litter for shelter and foraging. Our findings emphasise the dynamic nature of reptile responses to prescribed burns and underscore the importance of considering both fire seasonality and recency of burning in wildlife management plans.

Niche separation of three species of tree-rat (black-footed tree-rat, M. gouldii, golden-backed tree-rat, Mesembriomys macrurus, and brush-tailed rabbit-rat, Conilurus penicillatus) on the Mitchell Plateau, Western Australia

Context Distribution and abundance of the three northern Australian tree-rat species, Conilurus penicillatus, Mesembriomys macrurus and M. gouldii, have contracted significantly since European settlement. All three species were recorded from the Mitchell Plateau, Western Australia, in the 1980s, enabling their niche separation to be assessed. Despite this study being conducted in 1987, the results remain relevant for conservation strategies for these species. Aims To determine the ecological separation among three tropical tree-rat species by documenting habitat preferences, habitat use and diet. Methods Live-trapping, radiotracking and spotlighting were used to assess relative abundance, habitat preference and movements of each species at nine sites on the Mitchell Plateau. Diet was determined using scat analysis; vegetation communities were described and characterised by pattern analysis. Key results C. penicillatus (number of individuals trapped (n) = 24) was most abundant, followed by M. macrurus (n = 8) and M. gouldii (n = 2). Mature open forest with a well-developed understorey was preferred by the predominantly arboreal M. gouldii (1 site), M. macrurus occupied more varied habitats (four sites), especially ecotones between vine thicket and open eucalypt forest and the boulder edges of the plateau, and C. penicillatus occupied the greatest variety of habitats (four sites) in open eucalypt woodland with a diverse shrub layer and ground cover almost absent to very dense, tall grass. Diet analysis identified M. gouldii as a frugivore (fruits, some flowers), M. macrurus as an omnivore (seeds, fruits, flowers, termites, other invertebrates), and C. penicillatus as a generalist (monocot and dicot leaves, seeds, flowers, fruits, some arthropods). Conclusions The largest of the species, M. gouldii, appeared to have the narrowest ecological niche, preferring more stable, structurally diverse, mature open forest that is infrequently burnt. The mid-sized M. macrurus occupies a broader range of habitats, particularly ecotones between vine thickets and eucalypt forest/woodland and woodland. C. penicillatus preferred open eucalypt woodland with a variable understorey. Implications With a changing climate, increased fire frequency, habitat degradation by introduced herbivores and predation by cats across the tropical savanna distribution of these threatened tree-rats, this study provides data to underpin actions that may ensure their survival.

Carbon-phosphorus cycle models overestimate CO2 enrichment response in a mature Eucalyptus forest.

The importance of phosphorus (P) in regulating ecosystem responses to climate change has fostered P-cycle implementation in land surface models, but their CO2 effects predictions have not been evaluated against measurements. Here, we perform a data-driven model evaluation where simulations of eight widely used P-enabled models were confronted with observations from a long-term free-air CO2 enrichment experiment in a mature, P-limited Eucalyptus forest. We show that most models predicted the correct sign and magnitude of the CO2 effect on ecosystem carbon (C) sequestration, but they generally overestimated the effects on plant C uptake and growth. We identify leaf-to-canopy scaling of photosynthesis, plant tissue stoichiometry, plant belowground C allocation, and the subsequent consequences for plant-microbial interaction as key areas in which models of ecosystem C-P interaction can be improved. Together, this data-model intercomparison reveals data-driven insights into the performance and functionality of P-enabled models and adds to the existing evidence that the global CO2-driven carbon sink is overestimated by models.

Long-term assessment of historical disturbances in the dry land ecosystems of Mutis Timau Nature Reserve, East Nusa Tenggara, Indonesia

Long-term assessment using historical satellite imagery is critical for gaining meta-information and identifying trends in land cover change. Informed policymaking about this assessment ensures forest sustainability and mitigates climate change to consider the identified trends in land cover changes and historical disturbances. Therefore, this study aimed to describe the trend of land cover change and historical disturbances in Mutis Timau Nature Reserve (CA Mutis Timau), Indonesia using the LandTrendr platform. The land cover classification is based on SNI 7645-1:2014, with a 1:50,000 scale. The data was processed using Google Earth Engine’s LandTrendr platform, which covered the vegetation index, specifically the normalized burn ratio (NBR). The results showed that the trend of land cover change in CA Mutis Timau remained stable from 1986 to 2023. These disturbance locations have low slopes and are located near neighborhoods. In specifics, the Eucalyptus forest land cover experienced the largest land cover change between 1986 and 2023, losing 945.68 ha of vegetation, or 8% of the total area of CA Mutis Timau. Over a duration of 38 years, from 1986 to 2023, the Eucalyptus forest had a cover change that turned into marble stone, barren land, grassland, and shrubs. Forest management policies, such as establishing a nature reserve area on Mount Mutis areas, had an impact on the long-term sustainability of vegetation land cover.

Do Tasmanian devil declines impact ecosystem function?

Tasmanian eucalypt forests are among the most carbon-dense in the world, but projected climate change could destabilize this critical carbon sink. While the impact of abiotic factors on forest ecosystem carbon dynamics have received considerable attention, biotic factors such as the input of animal scat are less understood. Tasmanian devils (Sarcophilus harrisii)-an osteophageous scavenger that can ingest and solubilize nutrients locked in bone material-may subsidize plant and microbial productivity by concentrating bioavailable nutrients (e.g., nitrogen and phosphorus) in scat latrines. However, dramatic declines in devil population densities, driven by the spread of a transmissible cancer, may have underappreciated consequences for soil organic carbon (SOC) storage and forest productivity by altering nutrient cycling. Here, we fuse experimental data and modeling to quantify and predict future changes to forest productivity and SOC under various climate and scat-quality futures. We find that devil scat significantly increases concentrations of nitrogen, ammonium, phosphorus, and phosphate in the soil and shifts soil microbial communities toward those dominated by r-selected (e.g., fast-growing) phyla. Further, under expected increases in temperature and changes in precipitation, devil scat inputs are projected to increase above- and below-ground net primary productivity and microbial biomass carbon through 2100. In contrast, when devil scat is replaced by lower-quality scat (e.g., from non-osteophageous scavengers and herbivores), forest carbon pools are likely to increase more slowly, or in some cases, decline. Together, our results suggest often overlooked biotic factors will interact with climate change to drive current and future carbon pool dynamics in Tasmanian forests.

Plant Multi-element Coupling as an Indicator of Nutritional Mismatches Under Global Change

Global biogeochemical cycles have been widely altered due to human activities, potentially compromising the ability of plants to regulate their metabolism. We grew experimental herbaceous communities simulating the understory of eucalypt forests from southeastern Australia to evaluate the effects of elevated CO2 (400 vs. 650 ppm) and changes in soil resource availability (high-low water and high-low P) on the concentration of fourteen essential plant macro- and micronutrients, and their degree of coupling. Coupling was based on correlations among all elements in absolute value and a null modeling approach. According to the ancient nature of Australian soils, P addition was the main driver of changes in plant tissue chemistry, increasing the concentrations of P, Mg, Ca, and Mn and reducing the concentrations of C, N, S, Na, and Cu. Most treatment combinations showed coupled patterns of plant elements, particularly under ambient CO2. However, under elevated CO2, elements in plant tissues became more decoupled, which was interpreted as the result of a lack of enough supply of a range of elements to satisfy greater demands. Across treatments, P, Mn, and N were the least coupled elements, while K, Ca, and Fe were the most coupled ones. We provide evidence that plant element coupling was positively related to the concentration and coupling of elements measured in soils worldwide, suggesting that plant element coupling is conserved. Our results provide compelling evidence that evaluating the coupling of a representative range of chemical elements in plant tissues may represent a highly novel and powerful indicator of nutritional mismatches between demand and supply under specific environmental circumstances, including in a resource-altered global change context.

Koala density, habitat, conservation, and response to logging in eucalyptus forest; a review and critical evaluation of call monitoring

ABSTRACT This study is the second in a series that examines the habitat requirements and response to logging of koalas (Phascolarctos cinereus) inhabiting tall eucalypt forests of north-east NSW. It presents the findings of koala population and habitat monitoring surveys in Pine Creek State Forest and Bongil Bongil National Park using a combination of call-counting and direct observation (spotlighting). The 6400 ha study area was mapped into 6 zones of increasing koala habitat quality by ground survey of forest structure and floristics on a 200 m grid. The accuracy of habitat definition and mapping was tested by stratified transect counts of koala calls and sightings over two consecutive years (1997–98). Average koala density increased steeply and significantly, from 0.02 – 0.20 koalas/hectare, with increasing mapped habitat quality based on increasing forest age, structural complexity, local food tree species diversity, history of prior koala occurrence and decreased past logging intensity. This relationship was driven primarily by breeding females, with the number of male koala calls weakly or uncorrelated with koala sightings and mapped habitat quality. Male koalas were more widely and uniformly distributed than females, including areas of low quality, plantation, and intensively logged forest. This finding explains the discrepancy between our results and those of other recent studies which concluded that koalas are tolerant of intensive logging based on modelling of calling male koalas and reliance on an untested assumption that male calling is indicative of female breeding success. Koala density in a subset of the highest quality habitat was relatively stable at 0.28 koalas/ha (3 hectares/koala) over the long term (1997–98 and 2012–2023). Key characteristics of the forest koala population, including low stable density, large home ranges, preference for high food tree diversity and locally unique food trees (including Allocasuarina torulosa and Syncarpia glomulifera), are not adequately explained by existing koala habitat models. We present a new paradigm to explain regional variation in koala distribution, habitat and foraging preferences based on variations in foliage chemistry (toxicity and nutritional value) determined by the duration and stability of local plant-koala interactions in response to past fire, hunting, predation and logging disturbance history. We hypothesize that koala density in stable forest populations is regulated at low levels by a combination of selected and induced increases in leaf toxicity and decreases in leaf nutrition that limit koala browsing to benign levels of about 1-2% of annual leaf production. Large home ranges, complex mature forest structure, high food tree diversity and a specialized or diverse gut microbiome may be essential to allow females to rotate and change food trees frequently to minimize induced toxicity and select individual leaves with sufficient nutrients to support breeding and lactation with minimal risk of predation. High density koala populations (> 0.6/ha) occur primarily in areas where koalas have been introduced or re-introduced to planted habitats and natural areas where aboriginal hunters and dingoes were historically present but are now absent, and where food trees have not been selected for resistance to koala browsing pressure.

How an unprecedented wildfire shaped tree hollow occurrence and abundance—implications for arboreal fauna

BackgroundTree hollows are an important habitat resource used by arboreal fauna for nesting and denning. Hollows form when trees mature and are exposed to decay and physical damage. In the absence of excavating fauna, hollow formation can take up to 200 years in Australian temperate Eucalyptus forests, making tree hollows a critical but slow forming habitat feature. The increasing frequency and severity of wildfires due to climate change has led to increased concern about the landscape-scale loss of nesting space for arboreal fauna, including endangered species such as the folivorous southern greater glider (Petauroides volans). To understand patterns of nesting resource availability, we assessed drivers of hollow occurrence in southeastern Australian mixed-species Eucalyptus forests and quantified the effects of an unprecedented large-scale wildfire, the 2019/2020 Black Summer bushfires, on hollow occurrence and abundance.ResultsTree size and shape, as well as site productivity and topography, were important predictors for hollow occurrence both before and after the fires. The occurrence of the southern greater glider was strongly dependent on high proportions of hollow-bearing trees. While high fire severities had a negative impact on southern greater glider occurrence, the number of hollow-dependent arboreal species was not affected. While the wildfires significantly reduced hollow abundance, we did not find significant effects on hollow occurrence. Fires altered the relationship between tree size and hollow occurrence expressed as a change in the probability of hollow occurrence, with a higher likelihood at smaller tree sizes after the fires.ConclusionsOur findings suggest that post-fire nesting space may be reduced at the tree-scale, while at the stand-scale, hollow-bearing trees persist as biological legacies. These persisting trees can support the recovery of hollow-dependent arboreal fauna, such as the endangered southern greater glider by providing denning and nesting space. Hollow-bearing trees that survived the fires have the potential to form new hollows faster compared to undisturbed mature trees.

Temporal Dynamics of Canopy Properties and Carbon and Water Fluxes in a Temperate Evergreen Angiosperm Forest

The forest–atmosphere exchange of carbon and water is regulated by meteorological conditions as well as canopy properties such as leaf area index (LAI, m2 m−2), photosynthetic capacity (PC μmol m−2 s−1), or surface conductance in optimal conditions (Gs,opt, mmol m−2 s−1), which can vary seasonally and inter-annually. This variability is well understood for deciduous species but is poorly characterized in evergreen forests. Here, we quantify the seasonal dynamics of a temperate evergreen eucalypt forest with estimates of LAI, litterfall, carbon and water fluxes, and meteorological conditions from measurements and model simulations. We merged MODIS Enhanced Vegetation Index (EVI) values with site-based LAI measurements to establish a 17-year sequence of monthly LAI. We ran the Community Atmosphere Biosphere Land Exchange model (CABLE-POP (version r5046)) with constant and varying LAI for our site to quantify the influence of seasonal canopy dynamics on carbon and water fluxes. We observed that the peak of LAI occurred in late summer–early autumn, with a higher and earlier peak occurring in years when summer rainfall was greater. Seasonality in litterfall and allocation of net primary productivity (FNPP) to leaf growth (af, 0–1) drove this pattern, suggesting a complete renewal of the canopy before the timing of peak LAI. Litterfall peaked in spring, followed by a high af in summer, at the end of which LAI peaked, and PC and Gs,opt reached their maximum values in autumn, resulting from a combination of high LAI and efficient mature leaves. These canopy dynamics helped explain observations of maximum gross ecosystem production (FGEP) in spring and autumn and net ecosystem carbon loss in summer at our site. Inter-annual variability in LAI was positively correlated with Net Ecosystem Production (FNEP). It would be valuable to apply a similar approach to other temperate evergreen forests to identify broad patterns of seasonality in leaf growth and turnover. Because incorporating dynamic LAI was insufficient to fully capture the dynamics of FGEP, observations of seasonal variation in photosynthetic capacity, such as from solar-induced fluorescence, should be incorporated in land surface models to improve ecosystem flux estimates in evergreen forests.

Foraging ecology of eucalypt forest and woodland birds in the Great Western Woodland I: Small insectivores

ABSTRACT Australian warblers (Acanthizidae) and pardalotes (Pardalotidae) are abundant keystone species in Australia. Collectively they help regulate arthropod populations and dampen outbreaks of phytophagous insects. Their conservation in the face of habitat degradation and climate change is essential for the retention of healthy forest ecosystems and biodiversity. Information at the level of detail required for effective conservation management is missing for most Australian birds, including warblers and pardalotes. It is unlikely the data needed for the conservation of these species will be obtained in time to prevent further losses of avian biodiversity. However, it is important to try. This paper describes the foraging behaviour during spring of seven species of Australian warblers and pardalotes (small insectivores) in the Great Western Woodland, Western Australia and expands our knowledge of the ecology of these birds. As reported for small insectivores elsewhere in the world, species differed in prey-attack behaviours, foraging substrates, plant species used for foraging, foraging heights, and habitats. These data are used to explain why, without changes in how Australia approaches the preservation of biodiversity, abundant birds, such as Australian warblers and pardalotes will decline towards extinction.

Short-Interval, High-Severity Wildfire Depletes Diversity of Both Extant Vegetation and Soil Seed Banks in Fire-Tolerant Eucalypt Forests

Many plant species are well-adapted to historical fire regimes. An increase in the severity, frequency, and extent of wildfires could compromise the regenerative capacity of species, resulting in permanent shifts in plant diversity. We surveyed extant vegetation and soil seed banks across two forest types with contrasting historical fire regimes—Shrubby Dry Forest (fire return interval: 10–20 years) and Sub-Alpine Woodland (50–100 years). Over the past 20 years, both forests have been subject to repeated, high-severity wildfires at intervals significantly shorter than their historical return intervals. We examined the soil seed bank response to fire-cued germination, and whether the plant diversity in soil seed banks and extant vegetation demonstrated similar responses to short-interval, high-severity wildfires. The soil seed bank demonstrated a positive response to heat in combination with smoke, and for the Sub-Alpine Woodland, this was limited to sites more frequently burnt by fire. With an increase in fire frequency, there was a decline in species richness and Shannon’s Diversity and a shift in species composition in both extant vegetation and the soil seed bank. The fire frequency effects on the relative richness of trait associations were restricted to the Shrubby Dry Forest, and included an increase in short-lived obligate seeders, wind-dispersed species, and ant-dispersed shrubs in burnt relative to long unburnt sites in both extant vegetation and the soil seed bank. Graminoids were the most abundant component of the soil seed banks of Sub-Alpine Woodlands, and this increased with more frequent fire, with a similar trend (p = 0.06) in extant vegetation. Clear shifts in plant diversity in both soil seed banks and extant vegetation in forest types with contrasting historical fire regimes suggest that emerging fire regimes are pushing ecosystems beyond their historical range of variability, including potentially more flammable states and a decline in the buffering capacity of soil seed banks.

Emissions of N2O AND CH4 gases and soil bacterial community under integrated systems in the tropical region

The use of integrated production systems is widespread, mainly in tropical areas. This practice could contribute to soil conservation, increasing biodiversity and environmental services while reducing greenhouse gases emissions. The present work assessed bacterial biodiversity and correlations with nitrous oxide (N2O) and methane (CH4) emissions in soils under integrated production systems. Analyses of bacterial diversity and community structure were carried out using DGGE (denaturing gradient gel electrophoresis). Samples for the evaluation of greenhouse gases were collected in the field and measured using a gas chromatograph. The assessed treatments in a rainy and dry season were: crop (L), pasture (P), planted eucalypt forests (F), pasture followed by crop (IPL), crop followed by pasture (ILP), crop with forest (ILF); pasture with forests (IPF); crop with forest followed by pasture with forests, pasture with forests followed by crop with forest and crop, grassland and forest. In the rainy season, most N2O emissions occurred in the ILP with an average flow of 42.33 µg N m−2 h−1, and the lowest flow was observed in the ILF, with an average flow of 5.53 µg N m−2 h−1. In the dry season, higher emission occurred in the IPL, with an average flow of 4.17 ug N m−2 h−1. In this period, we observed gas consumption in F, the highest N2O consumer with a flow of −4.14 µg N m−2 h−1. In both seasons, CH4 was consumed, with IPF as the most significant consumer with an average flow of −14.19 µg C m−2 h 1(dry); F was the most significant consumer with an average flow −12.32 µg of C m−2 h−1. Bacterial community structure was affected by the agricultural production system and the seasons. Methane emissions and pH showed a correlation with bacterial diversity in different treatments. In contrast, nitrous oxide was negatively correlated with bacterial diversity. Based on our results, we suggest that integrated production systems and plant coverage modulate soil bacterial community structure and biodiversity which, in turn, affect soil processes related to higher or lower methane and nitrous oxide emissions.

Demographic change and loss of big trees in resprouting eucalypt forests exposed to megadisturbance

AbstractAimIncreased 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.

Estimating fine fuel loads in Eucalypt forests using forest inventory data and a modelling approach

Eucalypt forests are vital for biodiversity and fire dynamics, with fine fuels serving as the primary ignition source and critical factors in determining fire intensity. Accurate measurement of fine fuel via destructive field methods is location and time-restricted, hindering the tracking of their dynamic variations across diverse landscapes. In response, this study utilised forest inventory data collected by the Victorian Forest Monitoring Program (VFMP) in Victoria, southeastern Australia, along with allometric models, to estimate fine fuel loads across four vertical layers (surface, near-surface, elevated, and canopy). The average total fine fuel load in Victorian Eucalypt forests was estimated at 18.45 t ha−1 (ranging from 2.23 to 39.54 t ha−1), with surface litter contributing 58.2% of this total, followed by canopy (22.1%), near-surface (13.4%), and elevated (6.6%) fine fuels. We also conducted a comprehensive investigation and found distinct variations in fine fuel loads across different bioregions, forest covers, and vegetation types. Furthermore, stepwise multiple regression was employed to develop predictive models for estimating fine fuel loads from forest structural and environmental variables. Results show that total and canopy fine fuels can be reasonably explained by forest height, density, and climate-related variables (with R2 = 0.38 and 0.51, respectively). However, the explanatory power of these models diminished when applied to elevated, near-surface, and surface fine fuels. This study underscores the intricacies of fine fuel distribution in Eucalypt forests, emphasising the necessity for comprehensive factors in fire management planning. Further research is needed to better comprehend the relationship between forest characteristics and fine fuel dynamics to enhance wildfire risk assessment and mitigation strategies.

Atmospheric dryness removes barriers to the development of large forest fires

Large forest fires have far-reaching impacts on the environment, human health, infrastructure and the economy. Forest fires become large when all forest types across a landscape are dry enough to burn. Mesic forests are the slowest to dry and can act as a barrier to fire growth when they are too wet to burn. Therefore, identifying the factors influencing fire occurrence in mesic forests is important for gauging fire risk across large landscapes. We quantified the key factors influencing the likelihood that an active wildfire would propagate through mesic forest. We analysed 35 large forest fires (> 2500 ha) that occurred in Victoria, Australia where mesic and drier eucalypt forests are interspersed across mountainous terrain. We used a random forest model to evaluate 15 meteorological, topographic and disturbance variables as potential predictors of fire occurrence. These variables were extracted for points within burnt and unburnt patches of mesic forest. The likelihood of an active wildfire spreading through mesic forest increased by 65 % as vapour pressure deficit (VPD, i.e., atmospheric dryness) rose from 2.5 to 7 kPa. Other variables had substantially less influence (< 20 % change in fire occurrence) and their effects were further reduced when VPD was very high (> 6.5 kPa). Mesic forests were less likely to burn in areas with lower aridity, shallower slopes, and more sheltered topographic positions. Mesic forests 13–15 years following stand-replacing disturbance had 6 % higher chance of burning than long undisturbed forests (50 years post-disturbance). Overall, we show that topography and disturbance history cannot substantially counter the effects of high VPD. Therefore, the effectiveness of mesic forest as a barrier to the development of large forest fires is weakening as the climate warms. Our analysis also identifies areas less likely to burn, even under high VPD conditions. These areas could be prioritised as wildfire refugia.