Old-growth forests provide many ecosystem services and benefits. However, they are becoming increasingly rare and thus are an urgent priority for conservation. Accurately mapping old-growth forests ...is a critical step in this process. Here, we used LiDAR, an improved individual tree crown delineation algorithm for broadleaved forests, Gaussian mixture modelling, and a rule-based classification key to map the extent and location of old-growth forests across a topographically and ecologically complex landscape of 337,548 ha in southeastern Australia. We found that variation in old growth extent was largely driven by the old growth definition, which is a human construct, rather than by uncertainty in the technical aspect of the work. Current regulations define a stand as old growth if it was recruited prior to 1900 (i.e., >120 years old) and is undisturbed (i.e., <10% regrowth canopy cover and no visible disturbance traces). Only 2.7% (95% confidence intervals ranging from 1.4 to 4.9%) of the forests in the study landscape met these criteria. However, this definition is overly restrictive as it leaves many multi-aged stands with ecologically mature elements (e.g., one or more legacy trees amid regrowth) unprotected. Removing the regrowth filter, an indicator of past disturbances, increased the proportion of old-growth forests from 2.7% to 15% of the landscape. Our analyses also revealed that 60% of giant trees (>250 cm in diameter at breast height) were located within 50 m of cool temperate rainforests and cool temperate mixed forests (i.e., streamlines). We discuss the implication of our findings for the conservation and management of high-conservation-value forests in the region.
Understanding how past disturbances have influenced the development of forests is critical for deciphering their current structure and composition and forecasting future changes. In this study, ...dendrochronological methods were applied to uncover the disturbance history of old-growth hemlock-dominated forests in central Bhutan. Analysis of tree-ring samples from two old-growth hemlock stands, located in two different topographic settings, identified the importance of gap-phase dynamics in facilitating recruitment and growth releases and producing complex, multi-aged structures over time. One site showed evidence of a near stand-replacing disturbance in the late 1700s, while the other showed no evidence of high-severity disturbance at any time over the last 400 years. At both sites low-to medium-severity disturbances, some of which appear to be associated with cyclones originating in the Bay of Bengal, dominated the disturbance regime. The hemlock stands exhibited a significant positive association between cyclone occurrence and growth release events and between recruitment pulses and growth release events. From 1800 to 1970 there was an increase in recruitment of angiosperm tree species at most sites and a corresponding decline in conifer recruitment. Over the past 50 years there has been little new recruitment; this may be due to light limitation in the understory from shade-tolerant angiosperms and bamboo in the lower strata of these stands. Significant variations in disturbance dynamics and recruitment were observed across the study sites, suggesting that other factors, such as topography and climate, may be influencing long-term stand development patterns. This study highlights the complex interplay between historical disturbance regimes and tree recruitment in shaping the age and size structures of old-growth hemlock forests in central Bhutan. It also provides new insights into the dynamics of these forests that can be used to support effective forest conservation and management in the future.
A fundamental requirement of sustainable forest management is that stands are adequately regenerated after harvesting. To date, most research has focused on the regeneration of the dominant timber ...species and to a lesser degree on plant communities. Few studies have explored the impact of the regeneration success of dominant tree species on plant community composition and diversity. In this study, we quantified the influence of variability in tree density and climatic and edaphic factors on plant species diversity in montane regrowth forests dominated by Eucalyptus regnans in the Central Highlands of Victoria in southeastern Australia. We found that Acacia density shaped plant biodiversity more than Eucalyptus density. Edaphic factors, particularly soil nutrition and moisture availability, played a significant role in shaping species turnover and occurrence. Our findings suggest that the density of Acacia is a key biotic filter that influences the occurrence of many understorey plant species and shapes plant community turnover. This should be considered when assessing the impacts of both natural and anthropogenic disturbances on plant biodiversity in the montane forests of southeastern Australia.
In the forested landscapes of southeastern Australia, bushfires and timber harvesting are the primary catalysts for regeneration in Eucalyptus regnans, E. delegatensis, and high elevation mixed ...species (HEMS) forests. Quantifying the role of climate, topography and edaphic conditions on plant regeneration is important for understanding current and future risks of climate change. In this study, we investigated the post-disturbance regeneration dynamics in these forests. We sought to determine the direct impact of climate variability on regeneration and the interactive effects of climate, topography, and edaphic factors on the regeneration success of Eucalyptus. Data was collated from regeneration surveys conducted in 881 coupes, totaling ~55,000 ha of forest harvested and regenerated between 2004 and 2012. The time-period analyzed included the Millennium Drought, an intense and prolonged drought that lasted from 1996 to 2010. To test the influence of climatic, topographic, and edaphic variables on the occurrence and abundance of Eucalyptus regeneration, we used machine learning models. We found that regeneration success was closely tied to the timing of the Millennium Drought. Between 2004 and 2005 Eucalyptus seedlings occurred in less than 50% of survey plots across all three forest types. Declines in regeneration during the period of drought were greater in E. regnans and E. delegatensis than HEMS forests, suggesting that regeneration in the HEMS forests is more resistant to drought. We found that seasonal precipitation and temperature had the greatest influence on regeneration success of Eucalyptus. Responses varied by species, however autumn precipitation had the strongest influence on abundance of regeneration of E. regnans and E. delegatensis, while summer temperature was more important for HEMS species. Our findings highlight the importance of seasonal and annual climate variability on Eucalyptus regeneration and portend potential declines in regeneration success in a warmer and drier future for E. regnans and E. delegatensis.
Les effets de la densité du peuplement, du statut social et des conditions locales de bilan hydrique estival ont été analysés sur la résistance (Rt), la récupération (Rc) et la résilience (Rs) à la ...sécheresse de 2003. La croissance radiale a été étudiée sur 269 jeunes chênes sessiles échantillonnés dans le réseau d’expérimentations sylvicoles du GIS Coop. Il apparaît une interaction forte entre les conditions locales de bilan hydrique et la densité : diminuer la densité augmente la résistance, la récupération et la résilience des arbres particulièrement sur les sites secs. Cet effet est indépendant du statut social.
Messages clés :• Les peuplements en situation hydrique favorable ont été les plus exposés à la sécheresse de 2003.• Diminuer la densité a augmenté la résistance, la récupération et la résilience des chênes sessiles.• L’effet a été particulièrement fort dans les conditions stationnelles les plus sèches.
Context
Effective conservation planning for species depends on vegetation models that can capture the dynamics of habitat elements across both spatial and temporal domains. Incorporating these ...dynamics at landscape scales is essential for understanding the impact of natural disturbance, management, and climate change on habitat availability and stability on fauna.
Objectives
To explore the impact of resource availability, wildfire, forest management (timber harvesting and planned burning), and climate change on the habitat of the critically endangered Leadbeater’s possum (LBP;
Gymnobelideus leadbeateri
McCoy) with the goal of understanding the importance of these factors on future habitat availability.
Methods
We used a spatially explicit landscape-simulation model, LANDIS-II, linked to habitat suitability and patch modelling, to identify quantity, configuration, and temporal stability of habitat for LBP. We used boosted regression trees and general additive modelling to explore the importance of management and disturbance factors on future LBP habitat availability.
Results
Wildfire was the main factor determining all habitat components for LBP, both alone and in interaction with climate change and forest management. We identified stable habitat patches that will likely persist under future conditions, and that might be prioritised for conservation in a dynamic landscape.
Conclusions
We highlight how the current reserve network could be augmented to improve the future conservation status of LBP. Our approach provides conservation planners with a spatially and temporally explicit framework for incorporating the key dynamic processes that are typically omitted in conservation planning.
Predictive vegetation mapping is an essential tool for managing and conserving high conservation-value forests. Cool temperate rainforests (Rainforest) and cool temperate mixed forests (Mixed Forest, ...i.e., rainforest spp. overtopped by large remnant Eucalyptus trees) are threatened forest types in the Central Highlands of Victoria. Logging of these forest types is prohibited; however, the surrounding native Eucalyptus forests can be logged in some areas of the landscape. This requires accurate mapping and delineation of these vegetation types. In this study, we combine niche modelling, multispectral imagery, and LiDAR data to improve predictive vegetation mapping of these two threatened ecosystems in southeast Australia. We used a dataset of 1586 plots partitioned into four distinct forest types that occur in close proximity in the Central Highlands: Eucalyptus, Tree fern, Mixed Forest, and Rainforest. We calibrated our model on a training dataset and validated it on a spatially distinct testing dataset. To avoid overfitting, we used Bayesian regularized multinomial regression to relate predictors to our four forest types. We found that multispectral predictors were able to distinguish Rainforest from Eucalyptus forests due to differences in their spectral signatures. LiDAR-derived predictors were effective at discriminating Mixed Forest from Rainforest based on forest structure, particularly LiDAR predictors based on existing domain knowledge of the system. For example, the best predictor of Mixed Forest was the presence of Rainforest-type understorey overtopped by large Eucalyptus crowns, which is effectively aligned with the regulatory definition of Mixed Forest. Environmental predictors improved model performance marginally, but helped discriminate riparian forests from Rainforest. However, the best model for classifying forest types was the model that included all three classes of predictors (i.e., spectral, structural, and environmental). Using multiple data sources with differing strengths improved classification accuracy and successfully predicted the identity of 88% of the plots. Our study demonstrated that multi-source methods are important for capturing different properties of the data that discriminate ecosystems. In addition, the multi-source approach facilitated adding custom metrics based on domain knowledge which in turn improved the mapping of high conservation-value forest.
The effects of population density and summer drought were analysed by means of diameter and height growth in sessile oaks (Quercus petraea) on the stand and individual tree scales. Dendrometric ...inventory data collected from two networks of silvicultural experimentation were used (LERFOB and GIS Coop networks, 9 sites, 31 plots, 99 inventories, ages from 10 to 120 years). These networks study the effects of a broad range of densities, from freely growing trees (relative density index, or RDI, close to 0) to maximum density situations where self-thinning occurs (RDI equal to or in excess of 1). Climate conditions vary from 660 to 850 mm per year with a heat gradient of 9.5 to 11.5 °C (average 1990-2010). Generally speaking, density very strongly affects tree and stand growth, with drought playing a secondary role that is nonetheless significant. Overtopped trees contribute very little to the growth of the stand, particularly when the stand is dense. Drought reduces growth, particularly that of non-dominant trees. Density and drought therefore have the same effect: they accentuate growth differences between trees when stresses are greater. By allocating more resources to diameter growth as compared to height growth, trees in open stands are more “stocky”. In contrast, in densely populated stands, there is “a race for light” making for greater height growth, especially that of overtopped trees. In all cases, drought has a greater effect in reducing height growth than in reducing diameter growth. Finally, following a particularly severe drought (1976), trees recovered most quickly at the drier sites (recovery in 2 years) while the overtopped trees in the higher density stands recovered very little (still no recovery 7 years later). These results suggest that sessile oak adapts better in drier conditions.
Les effets de la densité du peuplement et de la sécheresse estivale ont été analysés sur la croissance en diamètre et en hauteur du Chêne sessile (Quercus petraea) à l’échelle du peuplement et de l’arbre. Les données des inventaires dendrométriques issues de deux réseaux d’expérimentations sylvicoles ont été utilisées (réseaux LERFOB et GIS Coop, 9 sites, 31 placettes, 99 inventaires, âges de 10 à 120 ans). Ces réseaux étudient les effets de larges gradients de densité, depuis des arbres en croissance libre (relative density index, ou RDI, proche de 0) jusqu’à des situations de densité maximale avec des phénomènes d’autoéclaircie (RDI supérieur ou égal à 1). Les conditions climatiques varient de 660 à 850 mm par an pour un gradient thermique de 9,5 à 11,5 °C (moyenne 1990-2010). D’une façon générale, la densité module très fortement la croissance des arbres et du peuplement, la sécheresse jouant un rôle secondaire mais néanmoins significatif. Les arbres dominés participent peu à la croissance du peuplement et ceci est d’autant plus vrai que le peuplement est dense. La sécheresse réduit la croissance et ceci particulièrement pour les arbres non dominants. Ainsi densité et sécheresse ont le même effet, c’est-à-dire qu’elles accentuent les différences de croissance entre arbres quand les contraintes augmentent. En allouant davantage de ressources à leur croissance en diamètre par rapport à leur croissance en hauteur, les arbres dans les peuplements ouverts sont « trapus ». Au contraire, dans les peuplements denses, c’est la « course à la lumière » avec une croissance en hauteur accrue et ceci d’autant plus que l’arbre est dominé. Dans tous les cas, la sécheresse réduit davantage la croissance en hauteur que la croissance en diamètre. Enfin, après une sécheresse exceptionnelle (1976), la récupération des arbres a été la plus rapide sur les sites les plus secs (récupération après 2 ans) et elle fut très faible pour les arbres dominés dans les peuplements les plus denses (toujours pas de récupération après 7 ans). Ces résultats suggèrent une meilleure adaptation des chênes sessiles dans les conditions plus sèches.
Biological invasions are a growing threat to biodiversity, food security, and economies. Rising pressure from increased global trade requires improving border inspection efficiency. Here, we depart ...from the conventional consignment-by-consignment approach advocated in current inspection standards. Instead, we suggest a broader perspective: evaluating border inspection regimes based on their ability to reduce propagule pressure across entire pathways. Additionally, we demonstrate that most biosecurity pathways exhibit superspreading behavior, that is, consignments from the same pathway have varying infestation rates and contain rare right-tail events (also called overdispersion). We show that greater overdispersion leads to more pronounced diminishing returns, with consequences on the optimal allocation of sampling effort. We leverage these two insights to develop a simple and efficient border inspection regime that can significantly reduce propagule pressure compared to current standards. Our analysis revealed that consignment size is a key driver of biosecurity risk and that sampling proportional to the square root of consignment size is near optimal. In testing, our framework reduced propagule pressure by 31 to 38% compared to current standards. We also identified opportunities to further improve inspection efficiency by considering additional pathway characteristics (i.e., overdispersion parameters, zero inflation, relative risk, sampling cost, detectability) and developed solutions for these more complex scenarios. We anticipate our result will mitigate biological invasion risk with significant implications for biodiversity conservation, food security, and economies worldwide.
Infrequent, high-intensity disturbances can have profound impacts on forested landscapes, changing forest structure and altering relative species abundance. However, due to their rarity and the ...logistical challenges of directly observing such extreme events, both the spatial variability of disturbance intensity and the species-specific responses to this variability are poorly understood. We used observed patterns of mortality across a fire severity gradient following the 2009 Black Saturday fires in southeastern Australia to simultaneously estimate (1) species- and size-specific susceptibility to fire-induced mortality and (2) fire intensity. We found broad variation in patterns of fire susceptibility among the 10 tree species (five eucalypts and five non-eucalypts) sufficiently abundant for analysis. Among the eucalypts, Eucalyptus obliqua was the most resistant to fire-induced mortality, with trees of ~25 cm DBH having a 50% probability of surviving even the most intense fires. In contrast, E. regnans had 100% mortality across all size classes when subjected to high-intensity fire. Basal resprouting occurred in six of the study species and, when accounted for, fundamentally changed the mortality profile of these species, highlighting the importance of resprouting as an adaptation to fire in these landscapes. In particular, the two iconic cool temperate rainforest species (Nothofagus cunninghami and Atherosperma moschatum) were strong resprouters (~45% of individuals were able to resprout after being top-killed by fire). We also found evidence for compositional shifts in regeneration above threshold values of fire intensity in cool temperate rainforest and mixed forest sites, both of which have important conservation values within these landscapes. The observed patterns of species- and size-specific susceptibility to fire-induced mortality may be used to anticipate changes in forest structure and composition in the future. In addition, they may also help guide forest management strategies that reduce the length of time individual trees are exposed to potentially lethal fires, thereby increasing the resilience of these forests to future fires.
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