Obliqua Forest Research Articles

Ecophysiological responses of Nothofagus obliqua forests to recent climate drying across the Mediterranean-Temperate biome transition in south-central Chile.

The forests of south-central Chile are facing a drying climate and a megadrought that started in 2010. This study addressed the physiological responses of five Nothofagus obliqua stands across the Mediterranean-Temperate gradient (35.9 ° -40.3° S) using carbon isotope discrimination (Δ13 C) and intrinsic water use efficiency (iWUE) in tree rings during 1967-2017. Moreover, δ18O was evaluated in the northernmost site to better understand the effects of the megadrought in this drier location. These forests have become more efficient in their use of water. However, trees from the densest stand are discriminating more against 13C, probably due to reduced photosynthetic rates associated with increasing competition. The strongest associations between climate and Δ13C were found in the northernmost stand, suggesting that warmer and drier conditions could have reduced 13C discrimination. Tree growth in this site has not decreased, and δ18O was negatively related to annual rainfall. However, a shift in this relationship was found since 2007, when both precipitation and δ18O decreased, while correlations between δ18O and growth increased. This implies that tree growth and δ18O are coupled in recent years, but precipitation is not the cause, suggesting that trees probably changed their water source to deeper and more depleted pools. Our research demonstrates that forests are not reducing their growth in central Chile, mainly due to a shift towards the use of deeper water sources. Despite a common climate trend across the gradient, there is a non-uniform response of N. obliqua forests to climate drying, being their response site specific. Keywords: Tree rings, stable isotopes, tree physiology, climate gradient, megadrought, climate change.

Tree Cover Species Modify the Diversity of Rhizosphere-Associated Microorganisms in Nothofagus obliqua (Mirb.) Oerst Temperate Forests in South-Central Chile

Chilean native forests have been subjected to several types of disturbances, with one of them being the replacement by exotic species. Pinus radiata D. Don is a widespread exotic tree that forms extensive plantations in southern Chile. It covers extended areas, affecting the landscape, biodiversity, and ecosystem services associated with native forest ecosystems. Although advances in assessing the impact of exotic plant species have been conducted, few studies have focused on the alteration of soil microorganisms. This study aimed to characterize the rhizosphere bacterial and fungal communities associated with the tree species Nothofagus obliqua inside a native forest stand and within a P. radiata plantation growing nearby. We used a 16S rRNA gene and ITS region metabarcoding approach. Using bioinformatics, diversity indices, relative abundance, preferential taxa, and predicted functions and guilds were estimated. The β-diversity analysis showed that both factors, the type of soil (rhizosphere or bulk soil) and the type of site (native forest or P. radiata plantation), were significant, with the site explaining most of the variation among bacterial and fungal communities. Proteobacteria and Basidiomycota were the most abundant bacterial and fungal phyla in both types of soil and sites. Similarly, bacteria showed similar abundant taxa at the family level, independent of the soil type or the site. The main fungal taxa associated with native forests were Tricholomataceae and Cantharellales, whereas in P. radiata plantations, Russulaceae and Hyaloscyphaceae were the most abundant families. The main bacteria functional groups were chemoheterotrophy and aerobic chemoheterotrophy, without significant differences between the type of soil or sites. Overall, these results demonstrate that the composition and diversity of bacterial and fungal communities associated with native N. obliqua forest are influenced by the surrounding forest, and mainly depend on the site’s characteristics, such as the lignin-rich wood source. These results improve our understanding of the impact of native forest replacement on soil microbial communities, which can alter microbial-related soil ecosystem services.

Climate response and drought resilience of Nothofagus obliqua secondary forests across a latitudinal gradient in south-central Chile

The climate response and resilience of tree growth to drought events have been widely reported for forests from the Northern Hemisphere. However, studies are much scarcer in the extra-tropical forests of southern South America. Mediterranean and Temperate forests of Chile are suffering from a moderate warming and a sustained precipitation decrease, occurring on top of an unprecedented megadrought since 2010. This study evaluated tree-growth patterns, the climate response and drought resilience of nine secondary Nothofagus obliqua forests across a latitudinal gradient from Mediterranean to Temperate climate in the Andes of Chile (35.7° to 40.3° S). Moreover, to improve the understanding of the spatial variation in productivity patterns, this research assessed trends in the maximum Normalized Difference Vegetation Index (peak in the NDVI) across the gradient for 2001–2018. Tree-growth patterns were highly influenced by stand dynamics, with steep decreasing trends in most of the stands related to a gradual canopy closure. Productivity trends had a flat pattern north of 38oS, but positive trends south of this latitude, which were mostly attributed to stand development. Tree growth was positively related to precipitation in all the sites, with annual and summer rainfall being more important in the north (Mediterranean climate) and south (Temperate climate), respectively. Conversely, maximum temperature had a negative effect on growth in most of the studied forests. This implies that projected warmer and drier conditions may have a detrimental effect on N. obliqua growth during coming decades. The two northern stands, located at the species dry range edge, were among the most resilient to drought and have not been strongly affected by the current megadrought in the area. Overall climate conditions, however, do not define the tolerance of stands to droughts, likely because local environmental and forests conditions play a key role. Although droughts have not strongly impacted the growth of N. obliqua across its distribution so far, future studies should assess the effects of the current long-term megadrought on growth resilience, and physiological studies should address the impacts of droughts and heat waves on forest function beyond what growth can unveil.

Strengthening mycorrhizal research in South America.

Strengthening mycorrhizal research in South America.

Geographical patterns of variation in susceptibility of Eucalyptus globulus and Eucalyptus obliqua to myrtle rust

Myrtle rust, caused by the pathogen Austropuccinia psidii, is a disease affecting numerous species of Myrtaceae around the globe. Many Australian ecosystems are dominated by Myrtaceae, making them, along with the industries that rely on them, particularly vulnerable to this disease. With over 800 endemic species, Eucalyptus is a major genus within the Myrtaceae in Australia. Wide variation in response to A. psidii infection, from extreme susceptibility to resistance, has been reported among Eucalyptus species in which any pre-formed resistance to this invasive pathogen is unexpected. This study aims to define and contrast geographical patterns of variation in rust susceptibility within the overlapping, natural ranges of Eucalyptus globulus and Eucalyptus obliqua, two commercially and ecologically important species from different Eucalyptus subgenera. Phenotypic disease screening of seedlings of E. globulus races and E. obliqua forest districts (defined geographically) showed E. obliqua to be more susceptible than E. globulus with significant differences in disease susceptibility and symptomatic trait expression. Eucalyptus globulus showed a trend for decreased susceptibility to A. psidii from south- to north-eastern Tasmania, eastwards along the Otway Ranges and southward from the Strzelecki Ranges to the Wilson Promontory Lighthouse in Victoria, but no such geographical patterns were observed within E. obliqua. No significant correlations were found between climatic conditions (i.e. rainfall, temperature and elevation) and rust susceptibility at provenance levels in either species. Taken together, these results support a hypothesis that population divergence in resistance to A. psidii has not been driven by climate.

DIAMETRIC SITE INDEX: AN ALTERNATIVE METHOD TO ESTIMATE SITE QUALITY IN Nothofagus obliqua AND N. alpina FORESTS

ABSTRAT The first step for constructing models of tree growth and yield is site quality assessment. To estimate this attribute, several methodologies are available in which site index (SI) is a standard one. However, this approach, that uses height at a reference age of trees, can be simplified if age is replaced by another reference variable easier to measure. In this case, the diametric site index (DSI) represents the mean height of dominant trees at a reference mean diameter at breast height. The aim of this work was to develop DSI in pure and mixed Nothofagus alpina and N. obliqua forests, and compare these models with the classical proposals based on height-age variables, within the temperate forest of northwestern Patagonia from Argentina, South America. Data originated from temporary plots and stem analyses were used. Tree age and diameter at breast height were obtained from each plot and used for establishing DSI family functions, following the guide-curve methodology. Site classes were proportionally represented among DSI curves of 17.0, 21.5, 26.0, 30.5 and 35.0 m of dominant tree height. Reference diameter instead of reference age can be cautiously used in order to fit site index models.

Prescribed fire increases pyrogenic carbon in litter and surface soil in lowland Eucalyptus forests of south-eastern Australia

Low intensity prescribed fire is widely practiced in seasonally dry forests in many countries to reduce fuel loads and the risk of uncontrollable wildfires. Associated with low intensity fire is the heating and alteration of organic matter of the litter and surface soil to create pyrogenic carbon (PyC). This study reports changes in total carbon (TC) and PyC in the litter (as char particles) and the top 2cm of soil (as oxidation resistant carbon, PyC) in Eucalyptus obliqua forests in south-eastern Australia. Litter and surface soil were sampled and carbon (C) measured before and immediately after low intensity prescribed fire on the same sites. Post-fire, lightly burnt (FIRE-300) and heavily burnt (FIRE-600) forest floor areas were sampled separately. On average, net loss of 1.55Mgha−1 C (10% of initial) from litter was largely offset by increase of 1.67Mgha−1 C in soil (which was restricted to the 0–2cm layer) with no net change in the initial litter+soil C stock of 21.9Mgha−1C. Concurrently, fire increased PyC by 0.3Mgha−1 in litter and 0.4Mgha−1 in surface soil, which together were equivalent to about 11% of the 6.1Mgha−1C emitted to the atmosphere as a result of the prescribed burn.

Comparing Generalized Linear Models and random forest to model vascular plant species richness using LiDAR data in a natural forest in central Chile

Abstract Biodiversity is considered to be an essential element of the Earth system, driving important ecosystem services. However, the conservation of biodiversity in a quickly changing world is a challenging task which requires cost-efficient and precise monitoring systems. In the present study, the suitability of airborne discrete-return LiDAR data for the mapping of vascular plant species richness within a Sub-Mediterranean second growth native forest ecosystem was examined. The vascular plant richness of four different layers (total, tree, shrub and herb richness) was modeled using twelve LiDAR-derived variables. As species richness values are typically count data, the corresponding asymmetry and heteroscedasticity in the error distribution has to be considered. In this context, we compared the suitability of random forest (RF) and a Generalized Linear Model (GLM) with a negative binomial error distribution. Both models were coupled with a feature selection approach to identify the most relevant LiDAR predictors and keep the models parsimonious. The results of RF and GLM agreed that the three most important predictors for all four layers were altitude above sea level, standard deviation of slope and mean canopy height. This was consistent with the preconception of LiDAR's suitability for estimating species richness, which is its capacity to capture three types of information: micro-topographical, macro-topographical and canopy structural. Generalized Linear Models showed higher performances (r2: 0.66, 0.50, 0.52, 0.50; nRMSE: 16.29%, 19.08%, 17.89%, 21.31% for total, tree, shrub and herb richness respectively) than RF (r2: 0.55, 0.33, 0.45, 0.46; nRMSE: 18.30%, 21.90%, 18.95%, 21.00% for total, tree, shrub and herb richness, respectively). Furthermore, the results of the best GLM were more parsimonious (three predictors) and less biased than the best RF models (twelve predictors). We think that this is due to the mentioned non-symmetric error distribution of the species richness values, which RF is unable to properly capture. From an ecological perspective, the predicted patterns agreed well with the known vegetation composition of the area. We found especially high species numbers at low elevations and along riversides. In these areas, overlapping distributions of thermopile sclerophyllos species, water demanding Valdivian evergreen species and species growing in Nothofagus obliqua forests occur. The three main conclusions of the study are: 1) appropriate model selection is crucial when working with biodiversity count data; 2) the application of RF for data with non-symmetric error distributions is questionable; and 3) structural and topographic information derived from LiDAR data is useful for predicting local plant species richness.

Redistribution and emission of forest carbon by planned burning in Eucalyptus obliqua (L. Hérit.) forest of south-eastern Australia

We applied standard forest inventory and soil sampling techniques to estimate carbon stocks in aboveground forest components and belowground in soil and fine roots to 30cm depth before, and immediately after, low intensity planned burning. Three areas within Eucalyptus obliqua forest that had not been burnt for more than 20years were sampled and, based on the calculated mass of components prior to and immediately following burning, the redistribution of carbon within the forest and carbon emission from the forest to the atmosphere were estimated. Of the 165Mg C ha−1 in aboveground components, about 7.8Mg C ha−1 was redistributed through accession of tree components to the forest floor and deposition of incompletely combusted plant structures and litter on the soil surface. A further 6.7Mg C ha−1 was emitted to the atmosphere, mostly from the on-ground and near surface components of litter, coarse woody debris and understorey. Overall, these E. obliqua forests sequester around 244Mg C ha−1 to 30cm soil depth (excluding woody roots) and planned burning transferred about 3% of this C to the atmosphere and a further 3% was transformed to charred and fragmented organic matter and deposited on the soil surface. Estimating long term C balance of burnt forests will require a much better understanding of the decay characteristics of these charred organic materials and good measures of post-fire aboveground carbon accumulation. The more intense a fire becomes the greater will be C emission from coarse woody debris and understorey, indicating the importance of quantifying these components in emission estimates for more intense planned burns and for wildfires.

A simplified inventory approach for estimating carbon in coarse woody debris in high-biomass forests

Forests carrying large quantities of live and dead wood are important carbon (C) stores. Here, we investigate how the inventory of coarse woody debris (CWD) and its embedded C (CWD-C) may be designed efficiently at the scale of logs, plots, and the landscape in Tasmanian tall Eucalyptus obliqua forests, which have very high levels of CWD (here 375–1085 m³ ha–1). From a set of 12 sites representing different times since disturbance, a thorough census of dead wood >10 cm in diameter was carried out at five sites using a fixed-plot (50 × 50 m) approach. This showed that 90% of the volume can be captured by recording only CWD logs >40 cm in diameter. Based on this approach and on the known density and C content of five different decay-classes, volume, mass, and CWD-C was determined for all 12 sites. To obtain an accurate estimate of CWD-C at the landscape scale, it was found to be sufficient to allocate entire individual logs to single decay-classes and to use one global value for C content instead of decay-class-specific values. The most decayed logs, which are difficult to measure, could be ignored. However, at the plot level, no relationships were found between CWD mass and either standing or downed CWD or standing-tree biomass, limiting the utility of these proxies for assessing CWD volume.

Diversity and ecology of epigeous ectomycorrhizal macrofungal assemblages in a native wet eucalypt forest in Tasmania, Australia

Abstract This paper investigates the diversity and ecology of the epigeous ectomycorrhizal (EcM) fungal assemblages of four plots in native Eucalyptus obliqua forest in Tasmania at different ages of regeneration since the natural disturbance of wildfire. From fortnightly visits to 1 ha of forest over a period of 14 months, 331 EcM species were documented. The family Cortinariaceae (particularly the genus Cortinarius ) dominated the EcM communities, with the youngest plot (72 yr since the last wildfire) having the greatest number of EcM species. Each plot was divided up into 25 10 × 10 m subplots, and both unconstrained and constrained ordination procedures showed a significant association between the woody perennial plant community of the subplots and their EcM assemblages, reflecting the co-variation of plant and fungal communities. The study provides benchmark knowledge of EcM communities in a specific forest type in Tasmania, serving as a good basis for further studies in those forests and in similar forest types elsewhere.

Wood-inhabiting macrofungal assemblages in 43-year-old regenerating wet Eucalyptus Obliqua L'Her.Forest

This study focuses on the diversity and ecology of wood-inhabiting macrofungal species assemblages in a regenerating tall, wet, native Eucalyptus obliqua forest in southeast Tasmania, 43 years after natural and anthropogenic disturbances. Two plots subjected to "clearfell, burn and sow" silviculture were compared with two other nearby plots that had experienced wildfire. A total of 90 species was identified from 619 macro fungal records during six fortnightly visits between May and July 2010. The plots with abundant live Pomaderris ape tala trees in the understorey (i.e., those at Edwards Rd) had markedly different macrofungal assemblages from those with no or with sparse Pomaderris apetala (i.e., at Hartz Rd). This study provided evidence that a 43-year-old regenerating forest maintains a core of common wood-inhabiting macrofungal species irrespective of type of disturbance. Furthermore, species most frequently observed in older forests in Tasmania can also occur in younger managed forests if biological legacies such as large diameter wood, well-decayed wood, large living trees and a diversity of tree species remain after silvicultural treatment.

The ecology and diversity of wood-inhabiting macrofungi in a native Eucalyptus obliqua forest of southern Tasmania, Australia

The ecology and diversity of the macrofungal species assemblages associated with woody material in four plots with differing wildfire histories in a Tasmanian tall, wet, native Eucalyptus obliqua forest were investigated. The four woody substrata (CWD, other dead wood ODW, stags and living trees) supported substantially different macrofungal assemblages, although there was some degree of overlap between CWD and ODW. The best separation between assemblages occurring on all kinds of wood, or on individual pieces of CWD, was obtained when the 100 10 × 10 m subplots of the study were grouped into classes based on the most frequently occurring higher vascular plant species within each subplot. Three polypore species were identified as being possible indicators of biodiverse old E. obliqua forests. The sustainable management of these forests will require retaining dead wood of all sizes, species and decay stages to maintain wood-inhabiting fungal diversity.

Diversity and phenology of the macrofungal assemblages supported by litter in a tall, wet Eucalyptus obliqua forest in southern Tasmania, Australia

Litter in the tall, wet Eucalyptus obliqua forests of southern Tasmania supports rich and diverse macrofungal assemblages, with a total of 146 macrofungal species found fruiting in or on litter in a 1 ha area of native forest encompassing a range of fire histories. Of these, less than half (65 species) can be considered as preferring litter as a substratum, the remainder being more commonly found on soil or wood. Although each plot of differing wildfire history had a characteristic litter mycota, this distinctiveness was not so pronounced as for the macrofungal assemblages associated with soil and wood. The time line for the fruiting of most litter-preferring macrofungal species was narrower than that for species on wood and soil, with peak fruiting occurring during April–July. Fruiting at other times correlated with rainfall events in warm dry weather. Species richness and diversity were correlated with the three main vegetation types which generated the litter.

Stand-replacing wildfires?: The incidence of multi-cohort and single-cohort Eucalyptus regnans and E. obliqua forests in southern Tasmania

The natural age structure of wet eucalypt forest has important implications for biodiversity conservation and the mode of wood production. Southern Tasmanian wet eucalypt forests were sampled to describe age class variation and to test the following hypotheses that relate to it: (1) Eucalyptus regnans stands are more likely to be single-cohort than Eucalyptus obliqua and mixed stands; (2) old-growth trees are associated with multi-cohort wet eucalypt forests; (3) the E. regnans stands are more multi-cohort than Victorian E. regnans stands. Data from 762 stands, all with either E. obliqua or E. regnans were analysed to determine how stand characteristics related to forest type and to the presence of old-growth trees. Over half the stands studied were multi-cohort. Stands with E. regnans had a lesser tendency towards multi-cohortness than stands lacking this species, although most old-growth stands, including those dominated by E. regnans, were multi-cohort. In contrast, most regrowth stands of all species combinations were single-cohort. The proportions of E. regnans stands that were multi-cohort were similar to some estimates from the same type of forest in Victoria. Modifications of forestry regimes in wet eucalypt forests could help to maintain the existence of these biodiverse multi-cohort forests in the landscape.

An examination of stocking and early growth in the Warra silvicultural systems trial confirms the importance of a burnt seedbed for vigorous regeneration in Eucalyptus obliqua forest

Clearfelling of wet eucalypt forest followed by high intensity burning and aerial sowing, a silvicultural system designed to mimic the natural dynamic of sporadic regeneration following cataclysmic disturbance, has attracted criticism for not maintaining the structural diversity that is associated with natural disturbance. A silvicultural systems trial was established at the Warra Long-Term Ecological Research site in southern Tasmania to explore alternatives to clearfelling in tall wet eucalypt forest. Stocking, density and growth of the seedling regeneration were monitored for up to 3 years after harvesting and regeneration treatments were applied from 1998 to 2007. The treatments were clearfell with understorey islands, a patchfell, stripfell, dispersed retention, aggregated retention, and single-tree/small-group selection. High intensity burning, low intensity burning and no burning were variously applied as part of these treatments. The nature of the seedbed in each coupe was related to the harvesting and regeneration treatment. Where high intensity burns were applied there was a higher proportion of burnt seedbed available than in coupes where low intensity burns were applied. The highest seedling densities and fastest early seedling growth rates occurred on the hottest burnt seedbeds. The lowest seedling densities occurred on unburnt and undisturbed seedbeds and the slowest early growth rates occurred on unburnt and compacted seedbeds. Treatments that created the most burnt seedbed had the highest seedling densities and the fastest seedling growth. Aggregated retention is considered the most promising alternative to clearfelling. Because high intensity burns as applied to clearfell burn and sow coupes cannot be conducted in aggregated retention coupes as they would probably burn the aggregates, the lower proportion of burnt seedbed will, on average, result in lower seedling density and growth, and may compromise longer term productivity compared to clearfelled and high intensity-burnt coupes. If aggregated retention is to be successfully applied, as measured by the density and height growth of the regeneration, finding ways of successfully and consistently burning such coupes post-harvesting will be essential.

Does hollow occurrence vary with forest type? A case study in wet and dry Eucalyptus obliqua forest

The distribution of hollow-using fauna is frequently related to forest type. If hollow occurrence varies with forest type, the use of generic prescriptions for managing the hollow resource may be inappropriate. This study examined the relationship between the occurrence and abundance of tree hollows and site and tree attributes in wet and dry Eucalyptus obliqua forest in Tasmania, Australia. A total of 388 trees at 39 sites were examined before and after being felled. Evidence of invertebrate damage contributing to hollow formation was more common in wet forest than either dry or damp forest. Evidence of hollow formation by fire and fungi was more prevalent in drier than wetter forest. There was no difference among forest types in the proportion of hollows showing evidence of limb breakage. Examination of the site and tree factors related to hollow presence and abundance was done using Classification Trees, Random Forests and generalised linear models. The variables found to be most practical for predicting hollow occurrence were the number of hollows observed before the tree was felled, tree diameter and the amount of dead wood in the canopy. Tree age, an important variable to consider when planning harvest rotations, was strongly associated with hollow presence but had less bearing on hollow abundance. The size of hollows that were found in a tree was related to greater senescence. Although significantly more hollows of all sizes were found in wet forest than either dry or damp forest, the age at which trees began to produce hollows was similar among the different forest types. The models predicted that trees needed to be at least 100 years old before they are likely to contain a hollow and that medium-sized hollows rarely occur in trees younger than 140 years old. Trees grow slightly more slowly in dry forest than wet which means that smaller diameter trees were found to contain hollows in dry forest than wet and that even the largest trees may not contain large hollows in wet forest. Despite this, no differentiation between the forest types was found in the predictive models. It is recommended that trees retained for faunal habitat be at least 100 cm in diameter.

The use of hollow-bearing trees by vertebrate fauna in wet and dry Eucalyptus obliqua forest, Tasmania

The loss of hollow-bearing trees in production forest areas can have large impacts on animal populations that rely on them for shelter. This study facilitates the selection of appropriate trees for retention by examining the proportion and type of trees that were used by vertebrate fauna in mature wet and dry Eucalyptus obliqua forest in Tasmania. Felled trees were searched for hollows and secondary evidence of use by fauna. Classification Trees and Bayesian logistic regression modelling were used to examine the site and tree attributes that best explained the use of a tree by fauna. We did two separate analyses: one using attributes expected to be causally related to hollow use, and a second using attributes that might be correlated with hollow use and could be easily assessed in standing trees. In all, 28% of hollow-bearing trees examined showed evidence of use, which is at the lower end of the scale found in other areas of Australia. The variables most strongly related to the use of a tree were hollow abundance, tree size and senescence. Random Forest modelling indicated that the likelihood of a hollow being used increased with hollow size, particularly hollow depth. Counting the number of hollows in standing trees was the best way to identify a tree that is likely to be used by fauna and this was particularly important for younger and healthier trees. It was recommended that trees to be retained should contain at least one large hollow. It was estimated that 8–15 trees per hectare were used by hollow-using fauna in mature wet and dry E. obliqua forest in Tasmania.

Estimating the accuracy of tree ageing methods in mature Eucalyptus obliqua forest, Tasmania

Summary Estimates of tree age are important for making management decisions on the tree hollow resource because hollows suitable for fauna occur with greater frequency in older trees. The methods used to age trees vary with the practicalities of obtaining wood samples and the quality of the wood samples available. Ring counting is commonly used on smaller sample sizes when complete wood samples are available. When wood samples are incomplete, a combination of ring counting and extrapolation is often used. When no wood samples are obtained, growth models are generally used to estimate tree age. This paper uses all three methods, including three different growth models, to examine the accuracy of ageing trees. Simple regressions between tree age and diameter at breast height (over bark, dbh) provided the most accurate growth models at a site. Age estimates obtained from such models, however, had unacceptably large errors when few trees were used or when variable growth rates occurred. Under these circumstances, smaller errors margins were obtained from using a model based on tree dbh and site attributes than when averaging growth rates across sites. The estimated error in tree age estimates when using ring counting and extrapolation was about 10% of the tree age. The error of extrapolation increased with the amount of wood sample that was missing. Error margins were large for the oldest trees (average ±42.4 y for trees >350 y old) but less than ± 15 y for most (73%) of the trees estimated to be 100–300 y of age. These middle-aged trees are often the most useful to study when examining the rate of hollow production in eucalypts. Therefore, age estimates acquired in this way are generally accurate enough to be useful for making management decisions regarding the tree-hollow resource in production forests.

Errors associated with two methods of assessing tree hollow occurrence and abundance in Eucalyptus obliqua forest, Tasmania

Tree hollows provide important habitat for fauna, but difficulties associated with detecting tree hollows can impede the formulation of appropriate management action. This paper examines the accuracy and errors associated with two methods commonly used to assess the presence/absence or abundance of tree hollows; ‘ground-based’ surveys and ‘tree-felling’ surveys. Three hundred and forty-six trees in Tasmania's State Forest were surveyed for hollows both before and after being felled. In order to assess the type and frequency of errors associated with each method, the fate of every potential hollow identified during the ground-based survey was determined after the tree had been felled. Three main types of error were identified: hollows misidentified during the ground-based survey; hollows not detected during ground-based surveys; and hollows not found during tree-felling surveys. Bayesian models were used to examine the association between site, tree and hollow variables and the occurrence of these errors. The likelihood that a tree would have a misidentified hollow increased with the number of potential hollows that were seen during the ground-based survey. Smaller hollows were more likely to be misidentified during ground-based surveys than larger hollows, particularly in trees that have little dead wood. For both of the survey methods the rate at which hollows were not detected was found to increase with tree size and hollow abundance. Hollows located in the branches were more likely to remain undetected during both survey methods, while small hollows, hollows high off the ground and those facing upwards were more likely to be missed during ground-based surveys. Although ground-based surveys provide inaccurate hollow counts, they are useful for assessing relative rather than true hollow abundance, which is valuable in the selection of habitat trees for retention in production forests. Tree-felling surveys provide a more accurate measure of actual hollow counts, particularly when a correction is made for the proportion of tree that cannot be surveyed. Tree-felling surveys are therefore useful for doing research such as developing models predicting hollow abundance.