Density Of Hollow-bearing Trees Research Articles

Long-term monitoring of an endangered population of Yellow-bellied Glider Petaurus australis on the Bago Plateau, New South Wales, and its response to wildfires and timber harvesting in a changing climate

ABSTRACT A population of Yellow-bellied Glider Petaurus australis on the Bago Plateau, on the NSW south-western slopes, was first surveyed across 126 sites in 1995 and this subsequently became the baseline for further population monitoring. A subset of 48 sites was resurveyed in 2010, and about one third of the sites (~40) were surveyed annually on a rotating panel between 2013–2019. Wildfire significantly impacted the Bago Plateau during 2020 and 51 sites were resurveyed post-fire in 2020/21. An occupancy modelling approach was used to estimate trends in occupancy between 1995 and 2020/21, including the influence of various covariates. Initial occupancy was positively associated with the extent of Montane Gums and mixed Wet Peppermint/Montane Gum forest types within a 450 m radius of the survey site. Supported models revealed that colonisation over time was positively associated with the density of hollow-bearing trees at a site, while extinction was positively associated with the extent of high severity wildfire at a site. Despite wide confidence intervals, the long-term occupancy trend showed a stable to slight increase between 1995 and 2019, but a ~26% reduction following wildfire. The increasing trend occurred despite a long-term rainfall deficit that was punctuated by occasional above average years during the survey period. There was no evidence that timber harvesting influenced occupancy by the gliders, although harvesting is predominantly focused within stands containing Alpine Ash Eucalyptus delegatensis, with monospecific stands generally avoided by the glider.

Habitat requirements of an arboreal Australian snake (Hoplocephalus bitorquatus) are influenced by hollow abundance in living trees

The value of tree hollows (cavities) to wildlife is well documented among birds and mammals, however few studies focus on their importance for snakes. Given increasing concern about the global net loss of hollow-bearing trees, it is imperative that studies extend to other vertebrate classes that may be dependent on this structural habitat component. We tested the hypothesis that habitat selection of an arboreal elapid, the pale-headed snake (Hoplocephalus bitorquatus), is primarily influenced by shelter requirements at multiple spatial scales. Consistent with our hypothesis, snake detection was biased towards a riparian ecosystem where hollow-bearing tree density was on average nine times greater than adjoining vegetation communities. In contrast, we found that the relative abundance of potential prey was equivalent among vegetation communities (frogs: P = 0.882; geckos: P = 0.306). At the microhabitat scale, snakes selected live hollow-bearing trees that were significantly larger (mean diameter: 74.5 cm ± 3.4, s.e.) than those otherwise available (42.4 ± 1.2 cm, s.e.) and estimated to be on average 111 years old. We recorded temperatures inside tree cavities to investigate whether the preference for live trees might be influenced by temperature buffering. Temperatures inside live trees were up to 16.4 °C below ambient in summer and 13.0 °C above ambient in winter. Temperature buffering was more pronounced in living trees (regression of cavity temperature against ambient, winter: r = −0.621; summer: r = −0.630) compared to dead trees (winter: r = −0.219; summer: r = −0.328), suggesting microhabitat selection may be driven by thermal requirements. Our study demonstrates the important role that mature, live hollow-bearing trees play in habitat selection by the pale-headed snake. It also suggests that the conservation of this species will be difficult in environments where such trees have been depleted due to land management practices. Managing forests for the persistence and recruitment of live hollow-bearing trees must be the primary conservation objective for threatened hollow-dependent fauna globally.

Experimental evaluation of the initial effects of large-scale thinning on structure and biodiversity of river red gum (Eucalyptus camaldulensis) forests

Context Multi-use management of global forests has seen even-aged, high-stem density regrowth represent >50% of the world’s forest cover. Large areas of river red gum (Eucalyptus camaldulensis) forests have declined in ecological condition. Thinning has been promoted as a tool to reduce competition in dense, young stands of E. camaldulensis regrowth, yet responses of forest structure and fauna to large-scale thinning are largely unclear. Aims To establish a before-after-control-impact experiment to assess responses of forest structure and fauna to large-scale (compartment-level; ~440 ha) silvicultural thinning. Methods We measured immediate (<2 yrs) responses of forest structural components (living, dead and hollow-bearing stem densities, coarse woody debris (CWD) density and volumes and ground cover) and components of biodiversity (bats, birds, volant insects and non-volant mammals) before and after thinning within five control and three impact compartments. Key results Thinning reduced stem density by approximately two-thirds and was associated with a substantial increase in activity and richness of bats and a change in bat species composition. There was no change in richness for birds and non-volant mammals, nor insect biomass in relation to thinning. However, thinning affected composition of non-volant mammals, with the common brushtail possum (Trichosurus vulpecula) and red fox (Vulpes vulpes) less active post-thinning at impact plots relative to control plots. Thinning reduced the density of dead stems, though these were predominantly small (~13 cm diameter at breast height over bark, or dbhob) and mostly lacked hollows. Hollow-bearing tree density was not affected by thinning. Although thinning increased CWD densities, volume of CWD did not change, indicating that thinning contributed small-sized CWD. Thinning did not affect densities of hollow- and fissure-bearing CWD or ground cover, which was low (<7%) in control and impact plots. There were no other negative effects on biodiversity detected. Conclusions Short-term fauna responses to thinning were generally neutral or positive. Implications Ongoing monitoring is required to detect long-term changes that may result from colonisation or altered breeding success after thinning. We recommend that some unthinned stands should be retained throughout the landscape to provide a mosaic forest structure suitable for a diverse fauna.

The effect of thinning on structural attributes of a low rainfall forest in eastern Australia

Abstract Forest thinning is a widely used silvicultural practice that has potential to provide benefits for biodiversity, but there is little direct evidence for this, particularly for regrowth in low rainfall forests and woodlands. This study examined the long-term effects of thinning on structural attributes of white cypress pine (Callitris glaucophylla) in the Pilliga forests of eastern Australia. A chronosequence approach was used which included six replicates of five forest management treatments; Unthinned (>80 years) with high density regrowth; Recent thinning ( 80 years) with large Callitris and Eucalyptus trees present. Thinning reduced the dominance of species that form dense single-aged stands (Allocasuarina luehmannii and Callitris spp.). Following thinning there was a ∼4-fold reduction in small stems ( 90 trees ha−1) where thinning had occurred (recent, intermediate and old thinning treatments) or where stem density of Allocasuarina and Callitris regrowth was low (long undisturbed), suggesting both these species competitively exclude recruitment of Eucalyptus spp.. The post-thinning reduction in woody vegetation was accompanied by an initial increase in the volume of downed coarse woody debris (DCWD), which was long lasting (21–40 years) and four to eight times greater than in long undisturbed sites, with greatest mean hollow diameter occurring in the old thinning treatment. Commercial thinning, in which some residue is removed from sites, still supported up to four times the DCWD volume as the long undisturbed treatment. There was a trend for a negative effect of thinning on the density of dead trees, but no effect on density of hollow-bearing trees and large trees (>50 cm DBH). Overall, our results indicate thinning had a mixed effect on key structural attributes that contribute to habitat structural complexity, indicating a need to record the direct responses of biodiversity.

Determinants of microbat communities in urban forest remnants: a rapid landscape scale assessment

Urbanisation affects fauna in many ways; with some species persisting and going on to dominate urban habitats, while other species decline over time due to habitat disturbance and modification. Microbats comprise a major component of remnant mammalian fauna in urban areas but we have a comparatively poor understanding of how they respond to urbanisation compared to other taxonomic groups. We investigated the impacts of an urban gradient on microbat communities of habitat remnants on the Gold Coast, south-east Queensland, Australia. We conducted acoustic surveys of 34 sites categorised as urban, peri-urban or rural, with an additional five reference sites. A combination of landscape and habitat elements were quantified for each site and their influence on the richness and calling activity of microbats determined. Overall, more microbat species were detected in reference sites followed by peri-urban sites. Rural and urban sites had similar richness, but only 50 % overlap in species recorded. After accounting for sampling effort peri-urban sites were found to have the greatest species richness and calling activity. Three species accounted for 45.4 % of the variation in microbat species detected. Using generalised linear mixed models we found that site area and the extent of urban development in the landscape (i.e. urbanisation index) had the greatest impact on microbat richness and calling activity. Models including logging (clearfelling) and hollow-bearing tree measures were also important. Our results support the use of the urbanisation gradient as a key measure to quantify the impacts of urbanisation on biodiversity. Logging history plays an important role across the landscape as it is a potential driver of other landscape variables such as tree species diversity, stand density and hollow-bearing tree density.

The impacts of historical land-use and landscape variables on hollow-bearing trees along an urbanisation gradient

Hollow-bearing trees provide habitat for diverse taxonomic groups and as such they are recognised for their importance globally. There is, however scant reference to this resource relative within urban forest patches. The functional ecology of habitat remnants along an urbanisation gradient plays an important ecological, social and economic role within urban landscapes. Here we quantify the impacts of urbanisation, landscape, environmental, disturbance (past and present) and stand variables on hollow-bearing tree density within urban forest patches. This was undertaken by surveying 45 forest patches on the Gold Coast, south-east Queensland, Australia. Sites were categorised as; urban, peri-urban or rural along an urbanisation gradient, with an additional five control sites. Historical logging practices were found to be the driving factor influencing hollow-bearing tree density along the urbanisation gradient; while the impacts of urbanisation itself are not as yet discernible. These findings highlight the significance of incorporating historical land use practise into current and future urban planning, as these will have continuing impacts on remaining urban biodiversity values. These findings, will benefit natural resource managers and urban planners when making decisions about where and how best to manage for hollow-bearing trees along urbanisation gradients.

The influence of urban encroachment on squirrel gliders (Petaurus norfolcensis): effects of road density, light and noise pollution

Context Loss and degradation of habitat from urban development is a key threat to the squirrel glider (Petaurus norfolcensis), because its distribution coincides where most people live in Australia. Squirrel gliders are known to occur in or around urban fringes where native vegetation is retained; however, little is known about specific anthropogenic factors that may affect their persistence. Aims We investigated the relative influence of biophysical and urban factors on the use of large hollow-bearing Eucalyptus trees, which are a key resource for squirrel gliders. The study was located in a typical urban growth area located in southern New South Wales. Methods A stratified random sampling approach was used to survey squirrel gliders in urban and rural areas. Infrared, motion-sensor cameras were placed in 34 selected trees for 17 nights to record squirrel glider occupancy and activity. Data on urban (e.g. light and noise pollution levels, road and housing density) and biophysical (e.g. tree height, hollow-bearing tree density, vegetation cover) variables were recorded at each survey tree. Data were statistically analysed using general linear modelling approaches. Key results Squirrel gliders were detected more frequently in the rural matrix (23.4% of camera trap-nights) than in urban areas (9.5%). Model results showed that tree height, and the distance to neighbouring trees, had a significant influence on the occurrence and activity of squirrel gliders. Road density and light pollution were included in ‘best’ models to explain glider activity (a negative influence), and noise pollution negatively influenced glider occurrence. Although gliders used large trees in both urban and rural areas, activity generally decreased as levels of urbanisation increased. Conclusions and implications Access to and availability of key resources such as tall, hollow-bearing trees is critical for gliders to persist in urban environments. Squirrel gliders will tolerate human stressors such as roads, noise and light pollution to a certain extent, but impacts on population viability remain largely unknown. Novel solutions need to be developed to lessen the effects of anthropogenic factors (such as light and noise) on patches of native vegetation retained in urban areas for conservation purposes.

Distribution and abundance of hollow-bearing trees in urban forest fragments

Habitat structures, such as hollow-bearing (i.e. cavity-bearing) trees, are globally recognised as important forest features for wildlife conservation and for providing important structural heterogeneity in natural and modified landscapes. The depletion of structural resources, such as hollow-bearing trees, within a landscape, may therefore be limiting to biota where no other functional substitutes exist. We surveyed 45 natural forest remnants across the rapidly urbanising City of Gold Coast, south-east Queensland, Australia to quantify the distribution and abundance of hollow-bearing trees. Tree and tree-hollow variables were quantified within the selected 91 plots. In total 6048 trees from 34 eucalypt species were sampled and 916 hollow-bearing trees containing 2159 hollows were recorded. The average hollow-bearing tree density (37.5±3.13/ha) was much higher than those found in other studies within Australia. Hollows were more prevalent in large trees and the majority (50.4%) of hollows were bayonets (10cm). Dead and decaying trees also had a greater likelihood of having a hollow than healthy trees. Our results highlight the value of urban forest remnants in maintaining the functional capacity of urban landscapes for biodiversity by protecting hollow-bearing trees as habitat resources. This information will assist conservation managers and planners to establish sound adaptive management plans to conserve biodiversity and ecosystem function in natural and modified landscapes.

Forest structure, habitat and carbon benefits from thinning floodplain forests: Managing early stand density makes a difference

Forest ecosystems are increasingly expected to produce multiple goods and services, such as timber, biodiversity, water flows, and sequestered carbon. While many of these are not mutually exclusive, they cannot all be simultaneously maximised so that management compromise is inevitable. We used a 42-year dataset from a naturally regenerating floodplain forest of the river red gum (Eucalyptus camaldulensis) to investigate the effects of pre-commercial thinning on long-term patterns in habitat quality, forest structure and rates of carbon storage (i.e. standing aboveground carbon). Estimates of habitat quality were based on the density of hollow-bearing trees because hollows are ecologically important to many species of vertebrates and invertebrates in these forests. Thinning improved habitat value by producing 20 (±8) hollow-bearing trees per ha after 42 years, while the unthinned treatment produced none. Unthinned (highest density) stands were dominated by many slender trees, mostly <25cm in diameter, whereas thinned stands produced negatively skewed size distributions with higher median and maximum stem diameters. Moderately thinned stands (560treesha−1) had the highest aboveground carbon storage rate (4.1tCyear−1) and the highest aboveground carbon stocks (200.2±9.6tCha−1) after 42 years, while the unthinned treatment had the lowest carbon storage rate (1.6tCyear−1) and an intermediate level of aboveground standing carbon (165.1±31.1tCha−1). Our results highlight the importance of early stand density as a determinant of long-term forest structure, habitat quality and carbon storage rates. We recommend that thinning be considered as one component of a broader strategy for enhancing the structure, habitat value and aboveground carbon storage of developing floodplain forests.

Nest-box use by arboreal mammals in a peri-urban landscape

Context. Nest boxes provide important nesting, denning and shelter sites for many fauna species worldwide, but we know little about the factors that influence the suitability of nest boxes for particular species. Such information is crucial in urban landscapes where natural hollows are scarce. Aims. The aim of this study was to record the use of nest boxes by sugar gliders (Petaurus breviceps), squirrel gliders (P. norfolcensis) and other fauna in a peri-urban landscape in northern Victoria and examine factors at multiple spatial scales that may influence nest-box use. Methods. We monitored the use of 102 nest boxes over three seasons in 2006. Attributes that may influence nest-box occupancy were measured at five different spatial scales: (i) landscape; (ii) the habitat beyond 20 m of the nest box; (iii) the habitat within 20 m of the nest box; (iv) the tree that the nest box was located in; and (v) the nest box. Key results. At the landscape scale, topography influenced nest-box occupancy with squirrel gliders using boxes in flat or gully areas, and sugar gliders using boxes in gully, mid-slope or ridge areas. For habitat beyond 20 m of the nest box, sugar gliders were more likely to occupy boxes with a higher density of surrounding nest boxes and a higher density of residential dwellings. Within 20 m of the nest box, boxes occupied by sugar gliders were more likely to occur in areas with a higher density of acacia shrubs and lower density of hollow-bearing trees, whereas the presence of acacia did not influence nest-box use by squirrel gliders. At the scale of the nest-box tree, boxes occupied by sugar gliders were more likely to be on smaller trees (based on height and diameter) and on box (e.g. red box Eucalyptus polyanthemos) species. The only nest-box characteristic to have a strong relationship with occupancy was date of establishment, with longer established boxes more likely to be occupied. Conclusions. Our study demonstrates that various factors influence nest-box use at different scales and nest boxes remain an important conservation and management tool in heavily modified landscapes. Implications. Land managers and groups should be aware that nest boxes may help to alleviate some of the negative impacts of the loss of hollow-bearing trees in low density urban areas, but nest-box use will vary depending on landscape context, habitat factors, box design, and the ecological traits of the target species. Each of these factors must be considered to maximise the conservation benefits of nest-box programs.

Tree hollow incidence in Victorian state forests

Summary The availability of tree hollows in timber production forests is a contentious issue facing forest and wildlife managers in Australia. To integrate conservation priorities for hollow-dependent fauna in forest stewardship, public land managers need information on the quantity and spatial distribution of hollow-bearing trees. This information has previously been lacking, but an extensive hollows database exists in the Victorian Statewide Forest Resource Inventory (SFRI). We use the SFRI to estimate simple stand-level models for the density of hollow-bearing trees, and the density of hollow size classes. Models were of borderline predictive ability but were statistically significant. This is consistent with previous models of hollow incidence that have found hollow formation to be intrinsically stochastic. We then applied these models in a geographic information system (GIS) to generate spatial predictions of hollow availability in Victorian state forests. The resulting GIS layers are available from the Department of Sustainability and Environment (DSE) and are a valuable resource for forest and wildlife managers, researchers and the interested public. We also created tables describing hollow abundance for different forest types, and important stand-level trends in hollow availability emerged. We found that hollow density in ash forests (Eucalyptus regnans, Eucalyptus delegatensis) was consistently low and strongly influenced by the presence of non-ash species that are more susceptible to hollow formation. Hollows occurred in E. regnans forest at particularly low density, with less than 37% of trees having hollows until diameter exceeded 125 cm. The density of hollows in non-ash forests was comparatively greater, with more than 49% of trees containing hollows when their diameter exceeded 75 cm.

Habitat requirements of the yellow-footed antechinus (Antechinus flavipes) in box - ironbark forest, Victoria, Australia

Understanding the habitat requirements of a species is critical for effective conservation-based management. In this study, we investigated the influence of forest structure on the distribution of the yellow-footed antechinus (Antechinus flavipes), a small dasyurid marsupial characteristic of dry forests on the inland side of the Great Dividing Range, Australia. Hair-sampling tubes were used to determine the occurrence of A. flavipes at 60 sites stratified across one of the largest remaining tracts of dry box–ironbark forest in south-eastern Australia. We considered the role of six potential explanatory variables: large trees, hollow-bearing trees, coppice hollows, logs, rock cover and litter. Logistic regression models were examined using an information-theoretic approach to determine the variables that best explained the presence or absence of the species. Hierarchical partitioning was employed to further explore relationships between occurrence of A. flavipes and explanatory variables. Forest structure accounted for a substantial proportion of the variation in occurrence of A. flavipes between sites. The strongest influence on the presence of A. flavipes was the cover of litter at survey sites. The density of hollow-bearing trees and rock cover were also positive influences. The conservation of A. flavipes will be enhanced by retention of habitat components that ensure a structurally complex environment in box–ironbark forests. This will also benefit the conservation of several threatened species in this dry forest ecosystem.

The status of hollow-bearing trees required for the conservation of arboreal marsupials in the dry sderophyll forests of south-east Queensland, Australia

At 38 sites in the dry sclerophylJ forests of south-east Queensland, Australia, hollow-bearing trees were studied to determine the effects of past forestry practices on their density, size and spatial distribution. The density of hollow-bearing trees was reduced at sites that had been altered by poisoning and ringbarking of unmerchantable trees. This was especially the case for living hollow-bearing trees that were now at densities too low to support the full range of arboreal marsupials. Although there are presently enough hollow-bearing stags (i.e., dead hollow-bearing trees) to provide additional denning and nesting opportunities, the standing life of these hollow-bearing stags is lower than the living counterparts which means denning and nesting sites may be limited in the near future. The mean diameter at breast height (DBH) of hollow-bearing stags was significantly less than that of living hollow-bearing trees. This indicated that many large hollow-bearing stags may have a shorter standing life than smaller hollow-bearing stags. Hollow-bearing trees appear to be randomly distributed throughout the forest in both silviculturally treated and untreated areas. This finding is at odds with the suggestion by some forest managers that hollow-bearing trees should have a clumped distribution in dry sclerophyll forests of south-east Queensland.

Habitat Requirements for the Conservation of Arboreal Marsupials in Dry Sclerophyll Forests of Southeast Queensland, Australia

Abstract The habitat requirements of arboreal marsupials were investigated in the dry sclerophyll forests of southeast Queensland, Australia. Species richness and abundance of arboreal marsupials was correlated to the proportion of total stand basal area occupied by lemon-scented gum (Corymbia citriodora), the height of the tallest trees, and density of hollow-bearing trees. The first two factors suggested that the most productive forests were also the most suitable habitats for arboreal marsupials. Importantly, the number of hollow-bearing trees was a significant factor in determining species richness and abundance of arboreal marsupials in this study, with the maximum number of species reached at sites containing≥4 hollow-bearing trees/ha, and maximum abundance occurring at sites with≥6 hollow-bearing trees/ha. The proportion of C. citriodora was significant for the presence of the common brushtail possum (Trichosurus vulpecula), greater glider (Petauroides volans), and the yellow-bellied glider (Petaurus australis), while understory Acacia sp. density was important for the presence of the sugar glider (Petaurus breviceps). The yellow-bellied glider was also affected by two other variables: the density of hollow-bearing trees &amp;gt;50 cm diameter at breast height (dbh), and the time since the last logging. Current “Codes of Practice” regulating the density of hollow-bearing trees and silvicultural practices in state-owned timber production forests appear to provide adequate protection for arboreal marsupials, but the recently introduced increase in timber extraction rates within state forests may be detrimental to the animals. Also, protective prescriptions do not apply to the privately owned and leasehold estates, which contain the majority of the dry sclerophyll forests in southeast Queensland. FOR. SCI. 48(2):217–227.

Nocturnal forest birds and arboreal marsupials of the southwestern slopes, New South Wales

A regional survey of 253 forest sites on the southwestern slopes and adjacent highlands of New South Wales recorded a total of 530 animals from five species of nocturnal forest birds and nine species of arboreal marsupials. One additional species, the Squirrel Glider Petaurus norfoicensis, was tapped during supplementary searches. Elevation (climate) and best type were the major factors accounting for the distribution of this fauna. Minor environmental gradients included geology, the density of hollow-bearing trees, topography, logging intensity and fire. The patterns of landuse in the region contributed to interactions between elevation, forest type and management history (logging, fire and grazing) which restricted inferences about the habitat requirements of animals.Forest types occurring at either end of the elevational (wet-dry) gradient (Alpine Ash and Box-Stringybark) were poorer in species than forests occurring at intermediate elevations (Alpine Gums, Wet Peppermint and Dry Peppermint). The Wet P...