Wet Eucalypt Forest Research Articles

The Grove of Giants: Tasmania's most carbon‐dense forest

AbstractThe Grove of Giants in the Huon Valley of Tasmania, Australia is renowned for its large trees. A team of tree climbers and citizen scientists undertook a carbon assessment of a 2 hectare plot within the Grove of Giants. The largest 16 trees in the plot (>2.5 m DBH) were measured by tree climbers allowing for accurate estimation of tree volume. Understory trees, coarse woody debris, root biomass and soil carbon were also estimated, making this study the most comprehensive assessment of forest carbon in Tasmania. Total forest carbon was estimated to be 1312 tonnes per hectare. Large trees had the highest carbon stocks, accounting for 44% of the total store. Coarse woody debris represented 19% of the forest's carbon, root biomass was 14%, while the understory trees accounted for 12% and soil carbon for 11%. This is the highest carbon stock recorded in Tasmania and is above the average estimates for temperate forest ecosystems in other parts of the world. Protecting Tasmania's forests, especially mature wet Eucalypt forests, is important to avoid potential greenhouse gas emissions and ensure safe storage of the carbon in the land sector.

Browsing by non-native invasive sambar deer dramatically impacts forest structure

Large herbivores introduced to novel habitats can cause major ecosystem impacts. While impacts of overabundant deer have been documented around the world, there are few examples from Australia, where deer are non-native and natural predators are absent.Here, we outline the impacts of sambar deer in wet eucalypt forest understoreys of the Yarra Ranges National Park, south-eastern Australia. Using data obtained from a full and partial (permitting native herbivores) exclusion experiment over four years, we (i) demonstrate differences between native herbivore and introduced deer browsing, (ii) identify plant species commonly browsed by deer, and (iii) provide evidence that vegetation condition can recover in the absence of deer.While species richness and composition were unaffected, the exclusion of deer led to substantial recovery of several attributes of forest understorey vegetation. Treatments excluding deer (partial and full exclosures) saw increases in the cover of understorey trees, shrubs, ferns and climbers. Within the 1–2 m height class (the primary deer browse zone), vegetation cover-abundance increased 3–4 fold over time in full and partial exclusion plots compared to non-exclusion controls.Tree ferns (Dicksonia antarctica and Cyathea australis) were particularly impacted by deer, and browsing impacts to tree ferns were dramatically reduced from ∼50% of fronds browsed to negligible levels with deer exclusion. Deer exclusion also saw substantial reductions in browsing to individual trees, shrubs and ground ferns. The growth of commonly browsed trees, e.g. Pomaderris aspera, were demonstrably higher in partial and full exclosures than unfenced control plots. The low levels of browsing on trees and shrubs that persisted in partial exclosures probably indicates the background levels of browsing pressure attributable to native herbivores in these forests.In the absence of effective deer control, commonly browsed understorey trees, shrubs and tree ferns are likely to decrease substantially in cover over coming decades, potentially leading to increased light availability, drying of the understorey, and increased susceptibility to wildfire. The potential cascading ecological effects of unabated and increasing deer impacts may be substantial and pose major challenges to forest management.Despite management culls and recreational hunting in recent years, deer populations are increasing across Australia. As sambar populations increase, ecological impacts are likely to exacerbate. It is therefore critically important to reduce sambar numbers, before negative and potentially irreversible changes occur to forest structure, composition and function.

Do Fire Cues Enhance Germination of Soil Seed Stores across an Ecotone of Wet Eucalypt Forest to Cool Temperate Rainforest in the Central Highlands of South-Eastern Australia?

Soil seed banks play an important role in plant species persistence in fire-prone systems. Response to fire related germination cues often reflect historical fire regimes and can be important in maintaining ecotones between different forest types. We assessed the effects of heat and/or smoke on the soil stored seed banks across an ecotone of eucalypt to rainforest overstorey comprising wet forest, cool temperate mixed forest, and cool temperate rainforest in south-eastern Australia. Soils from five replicates of each forest type were subjected to very low (45 °C), low (65 °C) and high (90 °C) heat with or without two different smoke treatments: –smoke-infused vermiculite, and karrikinolide—a phytoreactive compound derived from smoke. Soils were placed in a glasshouse and germinants were identified and counted at weekly intervals. Response to fire cues was consistent among forest types despite underlying differences in the diversity of soil seed banks. There was no overall response of species richness, abundance, or composition to fire cues. Phanerophytes and ant-dispersed species with hard seed coats demonstrated positive response, and endozoochores negative response, to high heat independent of smoke. Endozoochores were concentrated (albeit at low densities) in cool temperate rainforest with no overall effect of seral affiliation on response to fire cues. Given the lack of response to karrikinolide, response to soil disturbance would most likely be associated with mechanical seed abrasion and/or exposure to increased light availability than to non-fire related production of smoke products. Forest type was a stronger determinant of floristics in the germinated soil seed bank than simulated fire related germination cues. Both smoke treatments had little influence on floristics in the germinated seed bank suggesting other, non-fire disturbances such as treefalls and soil turnover by fauna may be more important for germination for many of the species in these forest types.

Forest restoration in a time of fire: perspectives from tall, wet eucalypt forests subject to stand-replacing wildfires.

Wildfires have the potential to add considerably to the already significant challenge of achieving effective forest restoration in the UN Decade on Ecosystem Restoration. While fire can sometimes promote forest restoration (e.g. by creating otherwise rare, early successional habitats), it can thwart it in others (e.g. by depleting key patch types and stand structures). Here we outline key considerations in facilitating restoration of some tall wet temperate forest ecosystems and some boreal forest ecosystems where the typical fire regime is rare high-severity stand-replacing fire. Some of these ecosystems are experiencing altered fire regimes such as increased fire extent, severity and/or frequency. Achieving good restoration outcomes in such ecosystems demands understanding fire regimes and their impacts on vegetation and other elements of biodiversity and then selecting ecosystem-appropriate management interventions. Potential actions range from doing nothing (as the ecosystem already maintains full post-fire regenerative capacity) to interventions prior to a conflagration like prescribed burning to limit the risks of high-severity fire, excluding activities that impair post-fire recovery (e.g. post-fire logging), and artificial seeding where natural regeneration fails. The most ecologically effective actions will be ecosystem-specific and context-specific and informed by knowledge of the ecosystem in question (such as plant life-history attributes) and inter-relationships with attributes like vegetation condition at the time it is burnt (e.g. young versus old forest). This article is part of the theme issue 'Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration'.

Predicting ignitability from firebrands in mature wet eucalypt forests

Forest ignitability varies spatially and temporally across landscapes as a function of fuel moisture. Wetter forests are often more difficult to ignite and therefore act as a barrier to the spread of wildfire. However, when these forests dry out and transition to an ignitable-state, the landscape is primed for large wildfires. Fire managers require information about forest ignitability to predict the timing of this switch. Yet, an understanding of the drivers and thresholds for ignitability in wetter forests remains incomplete. Our study sought to address this knowledge gap by evaluating a range of in-forest and landscape variables as predictors of ignitability in wet eucalypt forests. We conducted ignition experiments over two fire seasons at six sites in mature wet and damp eucalypt forest in south-eastern Australia. Each experiment involved 30 ignition attempts within each site on a single day using two types of flaming firebrands with different heats of combustion. The success and sustainability of each ignition attempt was recorded and this process repeated 8–9 times per site culminating in 1590 ignition attempts across a range of fuel moisture conditions. Ignition results were evaluated against 21 different in-forest and landscape variables. In-forest variables were generally stronger predictors of ignition and sustained ignition than landscape variables. The more energetic firebrand yielded more successful ignitions and sustained ignitions, but rankings for the predictor variables were similar for both types of firebrand. The strongest predictor of ignition and sustained ignition was in-forest vapour pressure deficit (VPD) (R2 = 0.65 for ignition and R2 = 0.55 sustained ignition), which is a measure of atmospheric dryness that is strongly associated with dead fuel moisture content. Past studies have identified strong links between VPD, burned area and fire severity at broader spatial and temporal scales. Our results show that VPD is also important at the time of ignition and could be used to predict wildfire risk in wet eucalypt forests.

Differential effects of ecosystem engineering by the superb lyrebird Menura novaehollandiae and herbivory by large mammals on floristic regeneration and structure in wet eucalypt forests.

Ecosystem engineers that modify the soil and ground‐layer properties exert a strong influence on vegetation communities in ecosystems worldwide. Understanding the interactions between animal engineers and vegetation is challenging when in the presence of large herbivores, as many vegetation communities are simultaneously affected by both engineering and herbivory. The superb lyrebird Menura novaehollandiae, an ecosystem engineer in wet forests of south‐eastern Australia, extensively modifies litter and soil on the forest floor. The aim of this study was to disentangle the impacts of engineering by lyrebirds and herbivory by large mammals on the composition and structure of ground‐layer vegetation. We carried out a 2‐year, manipulative exclusion experiment in the Central Highlands of Victoria, Australia. We compared three treatments: fenced plots with simulated lyrebird foraging; fenced plots excluding herbivores and lyrebirds; and open controls. This design allowed assessment of the relative impacts of engineering and herbivory on germination rates, seedling density, vegetation cover and structure, and community composition. Engineering by lyrebirds enhanced the germination of seeds in the litter layer. After 2 years, more than double the number of germinants were present in “engineered” than “non‐engineered” plots. Engineering did not affect the density of seedlings, but herbivory had strong detrimental effects. Herbivory also reduced the floristic richness and structural complexity (<0.5 m) of forest vegetation, including the cover of herbs. Neither process altered the floristic composition of the vegetation within the 2‐year study period. Ecosystem engineering by lyrebirds and herbivory by large mammals both influence the structure of forest‐floor vegetation. The twofold increase in seeds stimulated to germinate by engineering may contribute to the evolutionary adaptation of plants by allowing greater phenotypic expression and selection than would otherwise occur. Over long timescales, engineering and herbivory likely combine to maintain a more‐open forest floor conducive to ongoing ecosystem engineering by lyrebirds.

Contrasting successional responses of soil bacteria and fungi to post-logging burn severity

Globally, forest ecosystems are increasingly impacted by natural and anthropogenic disturbances including fire, timber harvesting and land clearance. Understanding how soil bacteria and fungi are impacted by logging and burning is important for resource management, as these microbiota underpin many essential ecosystem processes such as nutrient cycling and soil formation. Using amplicon sequencing and qPCR of the bacterial 16S rRNA gene and fungal ITS1 region, we quantified the abundance, diversity, and composition of soil bacterial and fungal communities in undisturbed forest and adjacent logged and burnt sites, which included a mosaic of burning severities (unburnt, low severity and high severity burns). Our study was conducted over a 12-month time series post-burn, in the temperate wet eucalypt forests of Tasmania, Australia. We found that over this 12-month period i) after high severity burns, total abundance and diversity returned to pre-disturbance levels in bacterial communities but not in fungal communities and ii) for each disturbance severity, the composition of bacterial communities became more similar to the undisturbed reference communities over time, while fungal communities did not. We also characterised the succession of disturbance responsive taxa in logged and burnt communities, with the relative dominance of copiotrophic bacteria and fire-associated Ascomycota fungi shifting towards oligotrophic bacteria and fire-associated Basidiomycota fungi by 12-months. Further, we highlight specific taxa that respond positively or negatively to the impacts of fire disturbance and discuss the ecological implications of our findings for forest management.

Using topographic attributes to predict the density of vegetation layers in a wet eucalypt forest

ABSTRACT Mapping the structure of forest vegetation with field surveys or high-resolution light detection and ranging (LiDAR) data is costly. We tested whether landscape topography and underlying geology could predict the vegetation density of a 19 km2 area of wet eucalypt forest at the Warra Long-Term Ecological Research Supersite, Tasmania, Australia. Using spatial layers for 12 topographic attributes derived from digital terrain models (DTMs) and a geology layer, we predicted the vegetation density of three strata with a high degree of accuracy (validation root mean square error ranged from 9.0% to 13.7%). The DTMs with 30 m resolution provided greater predictive accuracy than DTMs with higher resolution. The importance of different variables depended on spatial resolution and strata. Among the predictor variables, geology generally had the highest predictive importance, followed by solar radiation. Topographic Position Index, aspect, and System for Automated Geoscientific Analyses (SAGA) Wetness Index had moderate importance. This study demonstrates that geological and topographic attributes can provide useful predictions for the density of vegetation layers in a tall wet sclerophyll primary forest. Given the good performance of the model based on 30 m DTM resolution, the predictive power of the models could be tested on a larger geographical area using lower-density LiDAR point clouds combined with medium-resolution satellite data.

Using permanent forest plots to evaluate the resilience to fire of Tasmania’s tall wet eucalypt forests

The vulnerability to repeated high severity fires of tall wet eucalypt forests (TWEF) dominated by obligate seeder species is widely understood. However, 80% of Tasmania’s TWEF are dominated by resprouter species, and while these forests are more resilient to wildfire than those dominated by obligate seeders, the degree of their resilience is not well documented. Recently, two wildfires affected five 1-ha forest plots that had been previously measured, providing the opportunity to assess fire effects on these forest stands. We characterised these wildfires using remote sensing and field measurements of char height (a proxy for fire intensity) and canopy scorch (fire severity). We assessed the influence of tree diameter, fire intensity and seedling densities on the survival and resprouting responses of eucalypt overstorey trees and mixed species understorey trees. Our results showed that these fires were predominantly of low to moderate intensity and severity. Our results showed that mature TWEF were resilient to these wildfires, with overall eucalypt survival of 75%. The major eucalypt species were either mostly not defoliated (E. regnans), or could recover rapidly by epicormic resprouting (E. delegatensis and E. obliqua). Results from this and other studies show recovery from topkill caused by high severity fires occurs but is slower, by basal resprouting (E. obliqua) or from seed (all species). By contrast, understorey species suffered high mortality (85% overall), with few species showing substantial resprouting. Fire resistance in both groups increased markedly with tree diameter.Our results have implications for forest management. The high survival of overstorey eucalypts leads to a multi-aged stand structure in most unlogged old growth TWEF in Tasmania. On the other hand, clearfell logging, originally designed to mimic stand replacing wildfire in obligate seeder systems, creates a vulnerable, even aged stand of young regrowth, and at a landscape scale, it also reduces average tree size, reducing overall resistance to fire. Adopting alternatives to clearfelling, such as partial logging systems, will increase landscape resilience to fire, as well as providing other previously shown benefits.

Tree crown segmentation and species classification in a wet eucalypt forest from airborne hyperspectral and LiDAR data

ABSTRACT To sustainably manage forest biodiversity and monitor changes in species patterning, mapping the spatial distribution of tree species is indispensable. Remote sensing can provide powerful tools for mapping species, but this task is complex in areas with high plant diversity and multi-layered canopies. This paper addresses the issue of classifying wet eucalypt forest plants by examining tree crown segmentation and species classification using different combinations of remote sensing datasets against mapped tree locations. This study explores optimal segmentation parameters for tree crown delineation compared to manually digitized tree crowns. The best segmentation accuracy of 88.71%, resulted from segmenting a combined Minimum Noise Fraction (MNF) dataset derived from hyperspectral imagery (HSI) and a LiDAR-derived Canopy Height Model (CHM). Object-based classification of tree species was performed using a random forest classifier. The fused dataset of MNF and CHM produced the highest overall accuracy of 78.26% for four vegetation classes, while the fused HSI, indices, and CHM performed best (66.67%) with five vegetation classes. However, both approaches had a high overall performance. The CHM contributed to tree crown segmentation and species classification accuracy, and fused datasets were more robust to spatially discriminate wet eucalypt forest species compared to a single dataset. Eucalyptus obliqua was classified with the highest accuracy of 90.86% for four classes using the fused MNF and CHM dataset, and 86.11% for five classes using the fused HSI, indices, and CHM dataset. An important understorey species – the tree fern (Dicksonia antarctica) – was classified with the highest accuracy of 83.54% for four classes using HSI. Therefore, fusing hyperspectral and LiDAR data could classify both the overstorey and dominant understorey species, and thus play a crucial role in identifying forest biological diversity. This approach will be useful for forest managers and ecologists to plan sustainable management of eucalypt forest biodiversity and produce maps for monitoring species of interest.

Diversity and abundance of soil microbial communities decline, and community compositions change with severity of post-logging fire.

Understanding the effects of logging and fire on forest soil communities is integral to our knowledge of forest ecology and effective resource management. The resulting changes in soil biota have substantial impacts on forest succession and associated ecosystem processes. We quantified bacterial and fungal abundance, diversity and community composition across a logging and burn severity gradient, approximately one month after fire, in temperate wet eucalypt forests in Tasmania, Australia. Using amplicon sequencing and real-time quantitative PCR of the bacterial 16S rRNA gene and fungal ITS1 region, we demonstrate that (i) burn severity is a strong driver of soil microbial community composition, (ii) logging and high severity burning substantially reduce the biomass and diversity of soil bacteria and fungi, and (iii) the impacts of logging and burning on soil microbial communities are largely restricted to the top 10cm of soil, with weak impacts on the subsoil. The impacts of disturbance on microbial community composition are greater than the effects of site-to-site edaphic differences. Fire also drives more divergence in community composition than logging alone. Key microbial taxa driving differences in severely burnt soils include bacterial genera implicated in plant-growth promotion and producing antifungal compounds as well as saprotrophic fungi that are also capable of forming ectomycorrhizal associations. Our research suggests that low-moderate severity burns are important for maintaining diversity and biomass in soil microbial communities but having a range of burn severities across a site contributes to the overall diversity of habitat conditions providing for both microbial and plant diversity.

Darker, cooler, wetter: forest understories influence surface fuel moisture

The moisture content of dead leaves, twigs and bark on the forest floor is a key determinant of fire behaviour. The microclimate inside forests, which drive the moisture content of these dead fuel components, is typically measured at screen height (150 cm). However, in some forest types, the surface fuel at ground level may be subject to additional sheltering from low shrubs, ferns and grasses, which could alter the microclimate near the surface (hereafter near-surface). In such cases, screen height measurements may not adequately represent the near-surface conditions that determine dead fuel moisture contents.We sought to quantify the effect of understorey vegetation on near-surface microclimate. We measured in-forest temperature, relative humidity and solar radiation in eucalypt forests over two fire seasons at both screen height and the near-surface using weather stations at 25 sites. The sites encompassed wet eucalypt forest (n=18) with a dense, mesic understorey and dry eucalypt forest (n=7) with a sparser, scleromorphic understorey.Wet forests with dense understorey vegetation had near-surface air temperatures that averaged 1.3°C lower, relative humidities that averaged 13.1% higher and total solar radiation that was 0.84 MJ less per day compared with those measured at screen height. These microclimate differences led to predicted fuel moistures which averaged 4.7% higher at the near-surface compared with screen height – this was statistically significant. In contrast, dry forests with less understorey vegetation, had near-surface air temperatures that averaged 4.2°C higher, and relative humidities that averaged 3.1% lower compared to screen height. These differences were not large enough to translate into statistically significant differences in predicted fine fuel moisture between heights.Overall, these findings show that understorey vegetation plays an important role in moderating near-surface microclimate in some forest types and this needs to be taken into consideration when predicting fuel moisture.

Modelling the factors influencing Sambar Deer (Rusa unicolor) occurrence in the wet eucalypt forests of south-eastern Australia

ABSTRACT Many invasive species have had negative effects on the Australian environment, including the introduced Sambar Deer (Rusa unicolor). However, there is a paucity of information on the factors influencing the fine scale distribution and abundance patterns of Sambar Deer in south-eastern Australia. We present the results of a field survey of Sambar Deer in the Critically Endangered Mountain Ash (Eucalyptus regnans) forests of the Central Highlands, Victoria. Our key question was: What factors influence detections of Sambar deer (based on scat counts) within the Mountain Ash forests of the Victorian Central Highlands? We surveyed 86 long-term field sites and detected a total of 245 groups of Sambar Deer pellets on 42% of these sites. Negative binomial regression modelling identified three factors associated with the occurrence of deer pellets. We recorded more pellets: (1) in 30 and 80 year old forest that remained unburned in fires that occurred in 2009, (2) on sites within closed National Parks relative to sites in State Forest, and (3) close to streams.

DNA metabarcoding captures subtle differences in forest beetle communities following disturbance

DNA metabarcoding is an emerging approach for monitoring biodiversity, but uncertainties remain about its capacity to detect subtle differences in invertebrate community composition comparable to those achievable based on conventional morphological identification. In this study, DNA metabarcoding and morphology‐based approaches were compared as tools for investigating whether logging history impacted beetle communities in Tasmanian wet eucalypt forests. We compared 12 unlogged mature forest sites with 12 neighboring regeneration sites that had been logged approximately 55 years previously. The number of species identified based on morphology (173) was close to the number of zero‐radius operational taxonomic units (ZOTUs) identified by DNA metabarcoding of cytochrome c oxidase subunit I (COI, 176) and 16S ribosomal RNA (16S, 156) markers. Subtle but significant differences in beetle species composition between regeneration and unlogged mature forests were captured by both morphology‐based and COI DNA metabarcoding approaches, but not by 16S DNA metabarcoding. Our results support the suitability of mitochondrial COI for studying invertebrate biodiversity. A slight loss of signal compared to the morphology‐based approach may be resolved by developing more comprehensive DNA reference databases. While confirming forest recovery of 48–58 years did not fully restore mature forest beetle communities, we suggest that DNA metabarcoding can be used for monitoring biodiversity and probing subtle differences in community composition.

The response of arboreal marsupials to long‐term changes in forest disturbance

AbstractQuantifying the long‐term population trajectory of species and the factors affecting these trends is a fundamental part of animal conservation. We describe the results of a long‐term investigation of temporal changes in the occurrence of arboreal marsupials in the wet eucalypt forests of south‐eastern Australia. The assemblage includes habitat specialists such as the vulnerable greater glider Petauroides volans and the critically endangered Leadbeater’s possum Gymnobelideus leadbeateri, as well as common and widespread taxa. Using data gathered between 1997 and 2018, we quantified relationships between site occupancy of four marsupial species and spatio‐temporal site and landscape‐level variables, including the number of hollow‐bearing trees at a site, and the extent of fire and logging in the surrounding landscape. We found evidence that: (1) The number of hollow‐bearing trees (which are critical den sites for arboreal marsupials) has declined substantially in the past two decades. (2) There was a decline in all species of arboreal marsupials. (3) The presence of all species of arboreal marsupials was positively linked to the number of large old hollow‐bearing trees at a site. (4) The extent of logging disturbance in the landscape surrounding a site had a positive impact on the sugar glider Petaurus breviceps but a negative effect on Leadbeater’s possum. This suggests that ongoing logging will have further negative impacts on Leadbeater’s possum. (5) The presence of the greater glider and sugar glider declined with increasing amounts of fire in the landscape. Negative fire effects are a concern as montane ash forests are increasingly susceptible to high‐severity wildfires. Stronger efforts are needed to reduce the extent and frequency of logging and fire disturbance in mountain ash forests to protect arboreal marsupial populations.

RETRACTED: Winoto-Lewin et al. Propensities of Old Growth, Mature and Regrowth Wet Eucalypt Forest, and Eucalyptus Nitens Plantation, to Burn during Wildfire and Suffer Fire-Induced Crown Death. Fire 2020, 3, 13

The authors were informed of some errors in the categorization of forest types by a colleague [...]

Can Carbon Sequestration in Tasmanian “Wet” Eucalypt Forests Be Used to Mitigate Climate Change? Forest Succession, the Buffering Effects of Soils, and Landscape Processes Must Be Taken into Account

Small areas of the wetter parts of southeast Australia including Tasmania support high-biomass “wet” eucalypt forests, including “mixed” forests consisting of mature eucalypts up to 100 m high with a rainforest understorey. In Tasmania, mixed forests transition to lower biomass rainforests over time. In the scientific and public debate on ways to mitigate climate change, these forests have received attention for their ability to store large amounts of carbon (C), but the contribution of soil C stocks to the total C in these two ecosystems has not been systematically researched, and consequently, the potential of wet eucalypt forests to serve as long-term C sinks is uncertain. This study compared soil C stocks to 1 m depth at paired sites under rainforest and mixed forests and found that there was no detectable difference of mean total soil C between the two forest types, and on average, both contained about 200 Mg·ha−1of C. Some C in subsoil under rainforests is 3000 years old and retains a chemical signature of pyrogenic C, detectable in NMR spectra, indicating that soil C stocks are buffered against the effects of forest succession. The mean loss of C in biomass as mixed forests transition to rainforests is estimated to be about 260 Mg·ha−1over a c. 400-year period, so the mature mixed forest ecosystem emits about 0.65 Mg·ha−1·yr−1of C during its transition to rainforest. For this reason and because of the risk of forest fires, setting aside large areas of wet eucalypt forests as reserves in order to increase landscape C storage is not a sound strategy for long-term climate change mitigation. Maintaining a mosaic of managed native forests, including regenerating eucalypts, mixed forests, rainforests, and reserves, is likely to be the best strategy for maintaining landscape C stocks.

Exploring the key drivers of forest flammability in wet eucalypt forests using expert-derived conceptual models

Fire behaviour research has largely focused on dry ecosystems that burn frequently, with far less attention on wetter forests. Yet, the impacts of fire in wet forests can be high and therefore understanding the drivers of fire in these systems is vital. We sought to identify and rank by importance the factors plausibly driving flammability in wet eucalypt forests, and describe relationships between them. In doing so, we formulated a set of research priorities. Conceptual models of forest flammability in wet eucalypt forests were elicited from 21 fire experts using a combination of elicitation techniques. Forest flammability was defined using fire occurrence and fireline intensity as measures of ignitability and heat release rate, respectively. There were shared and divergent opinions about the drivers of flammability in wet eucalypt forests. Widely agreed factors were drought, dead fine fuel moisture content, weather and topography. These factors all influence the availability of biomass to burn, albeit their effects and interactions on various dimensions of flammability are poorly understood. Differences between the models related to lesser understood factors (e.g. live and coarse fuel moisture, plant traits, heatwaves) and the links between factors. By documenting alternative conceptual models, we made shared and divergent opinions explicit about flammability in wet forests. We identified four priority research areas: (1) quantifying drought and fuel moisture thresholds for fire occurrence and intensity, (2) modelling microclimate in dense vegetation and rugged terrain, (3) determining the attributes of live vegetation that influence forest flammability, (4) evaluating fire management strategies.

Propensities of Old Growth, Mature and Regrowth Wet Eucalypt Forest, and Eucalyptus nitens Plantation, to Burn During Wildfire and Suffer Fire-Induced Crown Death

There are conflicting conclusions on how the flammability of wet eucalypt forests changes in the time after disturbances such as logging or wildfire. Some conclude that forests are most flammable in the decades following disturbance, while others conclude that disturbance has no effect on flammability. The comparative flammability of Eucalyptus nitens plantations in the same environment as wet eucalypt forest is not known. We determined fire incidence and fire severity in regrowth, mature and old growth wet eucalypt forest, and E. nitens plantation, in the Huon Valley, Tasmania after the January–February 2019 wildfire. To control for topographic variation and fire weather, we randomly selected sites within the fire footprint, then randomly located a paired site for each in different forest types in the same topographic environment within 3 km. Each pair of sites was burned on the same day. Old growth forest and plantations were the least likely to burn. Old growth and mature forest exhibited scorched eucalypt crowns to a much lesser degree than regrowth forests. In a comparison of paired sites, plantation forest was less likely to burn than combined mature and old growth forests, but in all cases of detected ignition the canopy of plantation was scorched. The lower flammability of older forests, and their importance as an increasing store of carbon, suggests that a cessation of logging outside plantations might have considerable benefits.

The multi-element stoichiometry of wet eucalypt forest is transformed by recent, frequent fire

Fires can alter the elemental stoichiometry of ecosystems, reflecting altered patterns of biogeochemical cycling in the post-fire environment. However, elements other than carbon (C), nitrogen (N), and phosphorus (P) have rarely been studied in this context. Thus, we aimed to expand the understanding of fire’s stoichiometric and biogeochemical effects to encompass a broader suite of biogenic elements. We compared the stoichiometric ratios of C, N, P, potassium (K), sodium (Na), magnesium (Mg), and sulfur (S) in soil, plant litter, and beetles (Thalycrodes pulchrum) between forest plots that have been burned biennially at low intensity since 1972 and plots that have remained unburned. Multi-element stoichiometry differed strongly between the fire regimes. Low intensity biennial burning was associated with depletion of C, N, and S relative to P, K, and to a small extent Mg and Na, in soil and litter. The stoichiometry of T. pulchrum biomass was not significantly affected by fire regime, but fire regime-associated variation in the stoichiometry of T. pulchrum biomass was positively correlated with the fire-induced stoichiometric shifts in soil. The effects of low intensity prescribed fire on ecological stoichiometry extend to Na, K, Mg, and S in ways consistent with the respective potentials of these elements to volatilize during fire or accumulate in the absence of fire. These effects vary among ecosystem components in a manner that reveals the importance of biological processes and constraints as factors that determine the nature, magnitude, and potential consequences of the stoichiometric signatures of fire regimes. We conclude that long-term changes in fire regime can disrupt or even decouple the biogeochemical cycles of numerous biogenic elements in the soil–plant system.