Christine Stone - Academia.edu (original) (raw)

Papers by Christine Stone

Australian Forestry, Mar 1, 2013

ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first d... more ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first detected in Australia in 1998 and is now a major damaging agent in Pinus radiata plantations throughout south-eastern Australia. Tree-level crown damage was visually assessed over four years, from 2006 to 2009, in 120 plots located in Green Hills State Forest (Hume Region, Forests NSW). The plots represented 30 tree-age classes and a range of related stocking densities. We applied random forests and linear mixed modelling (ASReml) to examine the relationships between crown damage and a series of silvicultural and local climatic and terrain attributes. Consistent with previous observations, our results showed that crown damage due to E. californica is highly variable and is influenced by a suite of interacting and confounding factors. We identified prevailing climatic conditions, stand age and tree genotype as being the most influential, as well as threshold values associated with these relationships. These predictor variables can be used to stratify plantation planning units according to risk of defoliation by E. californica and for prioritising and targeting management activities such as aerial surveillance, release of the introduced biological control agent Diaeretus essigellae, possible late-age fertiliser application and in the future, the deployment of Essigella-resistant pine genotypes.

International Journal of Applied Earth Observation and Geoinformation, 2019

Fine-scale characterisation of forest stands using very high-density aerial lidar data holds cons... more Fine-scale characterisation of forest stands using very high-density aerial lidar data holds considerable potential for improving the accuracy of area-based forest inventories. To realise these gains, new methods of characterising dense aerial point clouds are required. This research presents one potential approach using voxel-based metrics often associated with the analysis of terrestrial lidar data. This was accomplished by comparing predictions of forest inventory attributes made using voxel-based metrics, more standard lidar metrics and a combination of both classes of metrics. A high-density lidar dataset was acquired using a helicopter-mounted RIEGL VUX-1UAV laser scanner to produce point clouds with a minimum density of 280 pulses m −2. Data were obtained from 73 plots presenting a wide range of stand conditions located within two adjacent plantations of Pinus radiata D.Don in southeastern New South Wales. Random forests regression models were developed to predict top height, basal area, stand density and total stem volume. To assess the interaction between metric type and pulse density, the point clouds were thinned to 18 pulse densities ranging from 1 to 280 pulses m −2 before fitting models using the metrics generated from data at each target density. Data thinning had little effect on the predictive accuracy of models for any of the four forest attributes predicted from either voxel-based, standard lidar metrics or their combination. Averaged across all pulse densities, models created for top height, basal area, stand density and total stem volume from standard lidar metrics had R 2 of 0.72, 0.44, 0.34 and 0.53 with normalised RMSE (RMSE expressed as a percentage of the mean for each dimension) of 6,6, 25.2, 60.1 and 25.5% respectively. Use of voxel-based metrics resulted in substantial gains in model precision for all dimensions, apart from top height, with R 2 increasing by 0.04, 0.23, 0.24, and 0.22 and nRMSE averaging 6.1, 19.6, 48.6, and 18.7%, respectively, for top height, basal area, stand density, and total stem volume. The precision of models that used both types of lidar metrics was very similar to the precision of models that used only voxelbased metrics. These results demonstrate the considerable potential of voxel-based metrics for improving the accuracy of forest measurement. The gains from voxelised-metrics were not dependent on very high pulse densities and could be achieved at densities typical of conventional lidar surveys undertaken using fixed-wing aircraft.

Tuart (Eucalyptus gomphocephala) is an iconic woodland tree, endemic to Western Australia, and is... more Tuart (Eucalyptus gomphocephala) is an iconic woodland tree, endemic to Western Australia, and is one of the few eucalypts able to dominate on calcareous soils. Unfortunately, less than one third of the original extent of the E. gomphocephala woodland ecosystem remains in existence today, largely as a result of clearing for urbanisation, agriculture and industry. Equally disturbing is the extensive decline of the E. gomphocephala ecosystem within the Yalgorup region, south of Mandurah, from unknown but probably complex abiotic andlor biotic causes. The recently described species Phytophthora multivora was isolated from the rhizosphere of declining tuart and may be contributing to this decline. A large collaborative, integrated research effort is focused on finding the cause(s) of this decline. Intensive ground-based studies are being used in conjunction with digital remotely sensed imagery and other spatially explicit datasets to aid establishment of research sites, map the spatial ...

Australian Forestry, 2018

Accurate mapping of timber resources in commercial forestry is essential to support planning and ... more Accurate mapping of timber resources in commercial forestry is essential to support planning and management operations of forest growers. Over the last two decades, Light Detection and Ranging (LiDAR) systems have been successfully deployed for the collection of point-cloud data for accurate modelling of forest attributes that are traditionally obtained from plot-based inventory. In recent years, studies conducted in North America and Scandinavia have shown that three-dimensional point clouds derived from digital aerial photogrammetric (AP) data can be used to model forest attributes with a level of accuracy similar to traditional LiDAR-based approaches. A comparative analysis of the performance of the two point-cloud technologies has never been attempted in Australian plantations. In this study, we compared the performance of LiDAR-based and AP-based point clouds for estimating total recoverable volume in a Pinus radiata plantation at Springfield in northeastern Tasmania, using volume data collected by harvesting machines as a reference. Our results showed that AP point clouds can be used for mapping total recoverable volume in P. radiata plantations with levels of accuracy that are comparable to LiDAR-based estimates. Plot-level relative root mean squared error (RMSE%) values were 23.85% for LiDAR and ranged from 22.07 to 27.10% for the three AP dense point-cloud settings evaluated. At the stand level, RMSE% decreased to 9.86 and 8.91% for LiDAR and AP, respectively. Both LiDAR-based and AP-based modelled volumes showed a close agreement with volumes measured using harvester head data, demonstrating the potential of AP technology for the management and planning of forestry operations in softwood plantations.

Australian Forestry, 2013

Summary Surveying the location and level of damage by insect pests and diseases, such as canopy d... more Summary Surveying the location and level of damage by insect pests and diseases, such as canopy damage by the Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), a common defoliating pest of Pinus radiata, is now formally embedded in the management practices of most Australian softwood-growing companies. Aerial surveys, also known as aerial sketch-mapping, are a cost-effective means of mapping broad-scale canopy damage, but their accuracy is dependent on a range of factors including the spatial and temporal expression of symptoms associated with different damaging agents. For E. californica, the most distinctive symptom is yellowing (needle chlorosis) of the crown followed by defoliation of affected needles. The aim of this study was to compare canopy damage categories obtained by aerial sketch-mapping with mean crown damage estimates derived from a systematic, plot-based sampling scheme of a Pinus radiata plantation in Green Hills State Forest in southern New South Wales with a known history of E. californica infestations. We identified significant challenges to rating accurately the level of canopy damage from E. californica by aerial sketch-mapping. While the location of chlorotic crowns may be mapped reliably, our results suggest that it is much more difficult to visually resolve different levels of canopy damage within affected stands. Using an ‘incidence × severity’ damage rating score, only two classes of canopy damage were confidently separated (i.e. Low (not detected or trace levels) and High (having a damage score of greater than 25%)). Accurate location of these classes of damage allows targeted, ground-based surveys for follow-up diagnostics and more detailed estimates of damage at the crown scale.

Determining the impacts of climate change on iconic West Australian trees, woodlands and forest e... more Determining the impacts of climate change on iconic West Australian trees, woodlands and forest ecosystems. Brouwers, N.C.

Journal of Agricultural, Biological, and Environmental Statistics, 2015

This paper explores and develops design-based and model-based methods which are suited to samplin... more This paper explores and develops design-based and model-based methods which are suited to sampling strategies developed for LiDAR-assisted plantation inventories. Much of the model-based theory is either recent or adapted from other areas of sampling. The design-based theory extends and adapts previous work to the present situation. The methodology is developed around the increasing utility and precision of LiDAR as a sampling tool for operational forest inventory. Flexible-radius plots, as a means of optimizing the sampling effort, are examined from a sampling perspective. Mixed models are also employed to model the residual variance using specified correlation structures and this includes predictors which utilize local trend such as those employed in kriging. In the design-based setting, model-assisted estimators are used, including regression and ratio estimators. A plot-based survey of a young, single-aged stand located within a Pinus radiata plantation in the northern tablelands of New South Wales is used to illustrate the theory. Model covariates are obtained from airborne laser scanning (LiDAR) data.

The increase in atmospheric concentration of greenhouse gases due to human activity, particularly... more The increase in atmospheric concentration of greenhouse gases due to human activity, particularly combustion of fossil fuels and land clearing, is increasing global temperatures and affecting global and regional climate systems. In NSW, temperature has increased by 0.9°C between 1910 and 2005, and the average rainfall since 2000 is 20% lower than the average rainfall received in the second half of last century. Irrespective of success in curbing future emissions, further warming is expected, due to the lagged effects of past greenhouse gas emissions. Climate change is predicted to increase average temperatures in NSW by 0.7° to 6.4°C by 2070, with the greatest increase in the west of the state. Rainfall is likely to be reduced across the state, apart from in the northeast. Projections suggest an increased incidence of bushfire and intense storms. Drought frequency may increase, especially in winter and spring. These predicted impacts of climate change are likely to have serious negative impacts on all NSW primary industries, including the forest industry. The potential impacts on forests from these changes are not clearly understood, especially for Australian tree species under typical Australian conditions. Besides the impacts of changes in the climatic variables, plants will be directly influenced by the increasing concentration of CO 2 in the atmosphere. Physiological impacts International research carried out over the past 20 years has generated general understanding of the direct effects of increasing CO 2 concentration on plant growth and function. Doubling of CO 2 concentration generally increases plant growth by 10%-25% (Nowak et al. 2004; Luo et al. 2005b; Norby et al. 2005), through the so-called "CO 2 fertilisation effect". Most of the research has been conducted on Northern Hemisphere species under environmental conditions different to those typical of Australia. Furthermore, most research does not consider the feedbacks at the ecosystem level that need to be factored in when predicting effects on whole forests from results measured on individual trees/saplings. Importantly, plant physiologists and modellers alike now recognise that the effects of elevated carbon dioxide measured in experimental settings and implemented in models may overestimate actual field responses, due to many limiting factors, such as pests, weeds, competition for resources, soil water and air quality, which are neither well understood on large scales, nor well implemented in leading models (

Australian Forestry, 2013

ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first d... more ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first detected in Australia in 1998 and is now a major damaging agent in Pinus radiata plantations throughout south-eastern Australia. Tree-level crown damage was visually assessed over four years, from 2006 to 2009, in 120 plots located in Green Hills State Forest (Hume Region, Forests NSW). The plots represented 30 tree-age classes and a range of related stocking densities. We applied random forests and linear mixed modelling (ASReml) to examine the relationships between crown damage and a series of silvicultural and local climatic and terrain attributes. Consistent with previous observations, our results showed that crown damage due to E. californica is highly variable and is influenced by a suite of interacting and confounding factors. We identified prevailing climatic conditions, stand age and tree genotype as being the most influential, as well as threshold values associated with these relationships. These predictor variables can be used to stratify plantation planning units according to risk of defoliation by E. californica and for prioritising and targeting management activities such as aerial surveillance, release of the introduced biological control agent Diaeretus essigellae, possible late-age fertiliser application and in the future, the deployment of Essigella-resistant pine genotypes.

Forest Ecology and Management, 2009

New Zealand Journal of Forestry Science, 2015

Current biosecurity arrangements for plantation forestry are poorly defined, at least relative to... more Current biosecurity arrangements for plantation forestry are poorly defined, at least relative to other plant-based industries. Serious pest and disease outbreaks in forestry are relatively rare events. Preparedness for rare events is difficult. Part of the difficulty stems from the competing views of managers and stakeholders. This project sought to directly capture alternative views concerning the key objectives of plantation forest biosecurity, alternative strategies for achieving those objectives, and ultimately recommend preferred actions that might be broadly supported by stakeholders. The outcomes from the workshop were used as a basis to draft a list of strategic actions required to improve forest biosecurity in Australia and to be implemented over the next 2-5 years. Research priorities were identified as research to support cost benefit analyses; investigating the effects of changed environmental conditions on forest biosecurity; pathway analysis for functional pest guilds...

Remote Sensing

Digital aerial photogrammetry (DAP) has emerged as a potentially cost-effective alternative to ai... more Digital aerial photogrammetry (DAP) has emerged as a potentially cost-effective alternative to airborne laser scanning (ALS) for forest inventory methods that employ point cloud data. Forest inventory derived from DAP using area-based methods has been shown to achieve accuracy similar to that of ALS data. At the tree level, individual tree detection (ITD) algorithms have been developed to detect and/or delineate individual trees either from ALS point cloud data or from ALS- or DAP-based canopy height models. An examination of the application of ITDs to DAP-based point clouds has not yet been reported. In this research, we evaluate the suitability of DAP-based point clouds for individual tree detection in the Pinus radiata plantation. Two ITD algorithms designed to work with point cloud data are applied to dense point clouds generated from small- and medium-format photography and to an ALS point cloud. Performance of the two ITD algorithms, the influence of stand structure on tree de...

Australian Forestry

Recent advances and commercialisation of unmanned aerial vehicle/red blue green (RGB) camera syst... more Recent advances and commercialisation of unmanned aerial vehicle/red blue green (RGB) camera systems and digital photogrammetric techniques now provide a cheap and flexible alternative to higher-cost airborne platforms for routine monitoring of canopy health in timber plantations. Structure-from-Motion photogrammetry produces very dense three-dimensional (3D) point clouds which can be used to derive metrics for inventory estimation. Unmanned aerial vehicle RGB photography also captures data that can relate to tree health. In contrast to the more common use of orthorectified RGB photography to extract this spectral information, we used the software package Agisoft Photoscan to assign a simple Vegetation Index value directly to each point in the 3D point cloud. Using data acquired by a DJI Phantom 4 Pro, we present a simple processing and photogrammetric workflow solution for detecting dead and dying trees in a young Eucalyptus pellita plantation located in the provenance of Riau, Sumatra. Trees affected by the bacterial wilt Ralstonia sp. present symptoms of necrotic foliage on individual branches or the whole crown. Assigning the Visible Atmospheric Resistant Index Vegetation Index colour-coded values to individual points in the 3D point cloud significantly enhanced visualisation of necrotic foliage on individual trees in both the point cloud and the associated orthophoto compared to the RGB equivalent images. This approach could easily be operationally deployed for the rapid detection and mapping of unhealthy trees with symptoms of necrotic foliage.

Remote Sensing

Surveying of woody debris left over from harvesting operations on managed forests is an important... more Surveying of woody debris left over from harvesting operations on managed forests is an important step in monitoring site quality, managing the extraction of residues and reconciling differences in pre-harvest inventories and actual timber yields. Traditional methods for post-harvest survey involving manual assessment of debris on the ground over small sample plots are labor-intensive, time-consuming, and do not scale well to heterogeneous landscapes. In this paper, we propose and evaluate new automated methods for the collection and interpretation of high-resolution, Unmanned Aerial Vehicle (UAV)-borne imagery over post-harvested forests for estimating quantities of fine and coarse woody debris. Using high-resolution, geo-registered color mosaics generated from UAV-borne images, we develop manual and automated processing methods for detecting, segmenting and counting both fine and coarse woody debris, including tree stumps, exploiting state-of-the-art machine learning and image pro...

International Journal of Applied Earth Observation and Geoinformation

Forest inventory operations have greatly benefitted from remotely sensed data particularly airbor... more Forest inventory operations have greatly benefitted from remotely sensed data particularly airborne laser scanning (ALS) which has become a popular technology choice for large-area forest inventories. For remote regions, for fragmented estates or for single stand-level inventories ALS may be unsuitable because of the high cost of data acquisition. Point cloud data generated from digital aerial photography (DAP) is emerging as a cost-effective alternative to ALS. In this study we compared area-based forest inventory attributes derived from point cloud datasets sourced from ALS, small-format and medium-format digital aerial photography (SFP and MFP). Non-parametric modelling approach, namely RandomForest, was employed to model forest structural attributes at both plot- and stand-levels. The results were evaluated using field data collected at 105 inventory plots. At plot-level, the maximum difference among relative RMSEs of basal area (BA), top height (Htop), stocking (N) and total stem volume (TSV) of the three datasets was 2.46%, 0.55%, 13.29% and 2.53%, respectively. At stand-level, the maximum difference among relative RMSEs of BA, Htop, N and TSV of the three datasets was 3.86%, 1.25%, 7.85% and 6.04%, respectively. This study demonstrates the robustness of DAP across different sensors, and thus informs forest managers planning data acquisition solutions to best suit their operational needs.

Southern Forests: a Journal of Forest Science

A new strategic inventory across all publicly managed forests has been installed in Victoria. For... more A new strategic inventory across all publicly managed forests has been installed in Victoria. For the preceding two decades, Victoria’s forest inventory has been compiled from various data sources from across the state, an approach that doesn’t allow information about the nature and rate of changes to the resource to be estimated, or for projections or forecasts to be made. To address these limitations, the Victorian Forest Monitoring Program (VFMP) was established, to monitor Victoria’s progress in meeting a commitment towards sustainable forest management, and to satisfy requirements for state and national reporting. The purpose of the new program is to ‘assess and monitor the extent, state and sustainable development of Victoria’s public forests in a timely and accurate manner.’ The VFMP consists of a plot-based system of permanent observational units located on a state-wide grid. A combination of ground-based and aerial photo plots and remotely sensed data are used to capture a set of basic attributes that are used to derive indicators of sustainability. To meet the monitoring needs a remeasurement framework has been developed to guide the change estimation procedures. The program was designed and implemented between 2009 and 2015 and used to generate data and information for the most recent Victoria’s State of the Forest Report. The first annual change estimate is due to be completed in 2017. A summary of implementation and proposed maintenance is presented and discussed in this paper.

Current Forestry Reports

Purpose of Review In this review, we highlight recent developments and applications in remote sen... more Purpose of Review In this review, we highlight recent developments and applications in remote sensing that can improve the accuracy and timeliness of health assessments in plantations managed for timber and pulp production. The detection and mapping of damage extent and severity caused by insect pests and fungal pathogens is a common requirement of foresters managing plantations. The objectives of these surveys can range from early detection for targeted intervention to more strategic aims of predicting stand susceptibility or evaluating the performance of management strategies. Recent Findings Recent developments in remote sensing technologies and big data modelling techniques can now provide spatially explicit, quantitative solutions for these management objectives that are more accurate than manual fieldbased assessments of tree damage or airborne visual mapping. Past studies have identified a large number of spectral, textural and structural metrics that have been used in models to classify specific tree crown damage symptoms. This process requires a detailed understanding of the chronology of crown symptoms for specific damaging agents and the spectral responses to these symptoms. Continuing increases in the spatial This article is part of the Topical Collection on Remote Sensing

Australian Forestry, Mar 1, 2013

ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first d... more ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first detected in Australia in 1998 and is now a major damaging agent in Pinus radiata plantations throughout south-eastern Australia. Tree-level crown damage was visually assessed over four years, from 2006 to 2009, in 120 plots located in Green Hills State Forest (Hume Region, Forests NSW). The plots represented 30 tree-age classes and a range of related stocking densities. We applied random forests and linear mixed modelling (ASReml) to examine the relationships between crown damage and a series of silvicultural and local climatic and terrain attributes. Consistent with previous observations, our results showed that crown damage due to E. californica is highly variable and is influenced by a suite of interacting and confounding factors. We identified prevailing climatic conditions, stand age and tree genotype as being the most influential, as well as threshold values associated with these relationships. These predictor variables can be used to stratify plantation planning units according to risk of defoliation by E. californica and for prioritising and targeting management activities such as aerial surveillance, release of the introduced biological control agent Diaeretus essigellae, possible late-age fertiliser application and in the future, the deployment of Essigella-resistant pine genotypes.

International Journal of Applied Earth Observation and Geoinformation, 2019

Fine-scale characterisation of forest stands using very high-density aerial lidar data holds cons... more Fine-scale characterisation of forest stands using very high-density aerial lidar data holds considerable potential for improving the accuracy of area-based forest inventories. To realise these gains, new methods of characterising dense aerial point clouds are required. This research presents one potential approach using voxel-based metrics often associated with the analysis of terrestrial lidar data. This was accomplished by comparing predictions of forest inventory attributes made using voxel-based metrics, more standard lidar metrics and a combination of both classes of metrics. A high-density lidar dataset was acquired using a helicopter-mounted RIEGL VUX-1UAV laser scanner to produce point clouds with a minimum density of 280 pulses m −2. Data were obtained from 73 plots presenting a wide range of stand conditions located within two adjacent plantations of Pinus radiata D.Don in southeastern New South Wales. Random forests regression models were developed to predict top height, basal area, stand density and total stem volume. To assess the interaction between metric type and pulse density, the point clouds were thinned to 18 pulse densities ranging from 1 to 280 pulses m −2 before fitting models using the metrics generated from data at each target density. Data thinning had little effect on the predictive accuracy of models for any of the four forest attributes predicted from either voxel-based, standard lidar metrics or their combination. Averaged across all pulse densities, models created for top height, basal area, stand density and total stem volume from standard lidar metrics had R 2 of 0.72, 0.44, 0.34 and 0.53 with normalised RMSE (RMSE expressed as a percentage of the mean for each dimension) of 6,6, 25.2, 60.1 and 25.5% respectively. Use of voxel-based metrics resulted in substantial gains in model precision for all dimensions, apart from top height, with R 2 increasing by 0.04, 0.23, 0.24, and 0.22 and nRMSE averaging 6.1, 19.6, 48.6, and 18.7%, respectively, for top height, basal area, stand density, and total stem volume. The precision of models that used both types of lidar metrics was very similar to the precision of models that used only voxelbased metrics. These results demonstrate the considerable potential of voxel-based metrics for improving the accuracy of forest measurement. The gains from voxelised-metrics were not dependent on very high pulse densities and could be achieved at densities typical of conventional lidar surveys undertaken using fixed-wing aircraft.

Tuart (Eucalyptus gomphocephala) is an iconic woodland tree, endemic to Western Australia, and is... more Tuart (Eucalyptus gomphocephala) is an iconic woodland tree, endemic to Western Australia, and is one of the few eucalypts able to dominate on calcareous soils. Unfortunately, less than one third of the original extent of the E. gomphocephala woodland ecosystem remains in existence today, largely as a result of clearing for urbanisation, agriculture and industry. Equally disturbing is the extensive decline of the E. gomphocephala ecosystem within the Yalgorup region, south of Mandurah, from unknown but probably complex abiotic andlor biotic causes. The recently described species Phytophthora multivora was isolated from the rhizosphere of declining tuart and may be contributing to this decline. A large collaborative, integrated research effort is focused on finding the cause(s) of this decline. Intensive ground-based studies are being used in conjunction with digital remotely sensed imagery and other spatially explicit datasets to aid establishment of research sites, map the spatial ...

Australian Forestry, 2018

Accurate mapping of timber resources in commercial forestry is essential to support planning and ... more Accurate mapping of timber resources in commercial forestry is essential to support planning and management operations of forest growers. Over the last two decades, Light Detection and Ranging (LiDAR) systems have been successfully deployed for the collection of point-cloud data for accurate modelling of forest attributes that are traditionally obtained from plot-based inventory. In recent years, studies conducted in North America and Scandinavia have shown that three-dimensional point clouds derived from digital aerial photogrammetric (AP) data can be used to model forest attributes with a level of accuracy similar to traditional LiDAR-based approaches. A comparative analysis of the performance of the two point-cloud technologies has never been attempted in Australian plantations. In this study, we compared the performance of LiDAR-based and AP-based point clouds for estimating total recoverable volume in a Pinus radiata plantation at Springfield in northeastern Tasmania, using volume data collected by harvesting machines as a reference. Our results showed that AP point clouds can be used for mapping total recoverable volume in P. radiata plantations with levels of accuracy that are comparable to LiDAR-based estimates. Plot-level relative root mean squared error (RMSE%) values were 23.85% for LiDAR and ranged from 22.07 to 27.10% for the three AP dense point-cloud settings evaluated. At the stand level, RMSE% decreased to 9.86 and 8.91% for LiDAR and AP, respectively. Both LiDAR-based and AP-based modelled volumes showed a close agreement with volumes measured using harvester head data, demonstrating the potential of AP technology for the management and planning of forestry operations in softwood plantations.

Australian Forestry, 2013

Summary Surveying the location and level of damage by insect pests and diseases, such as canopy d... more Summary Surveying the location and level of damage by insect pests and diseases, such as canopy damage by the Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), a common defoliating pest of Pinus radiata, is now formally embedded in the management practices of most Australian softwood-growing companies. Aerial surveys, also known as aerial sketch-mapping, are a cost-effective means of mapping broad-scale canopy damage, but their accuracy is dependent on a range of factors including the spatial and temporal expression of symptoms associated with different damaging agents. For E. californica, the most distinctive symptom is yellowing (needle chlorosis) of the crown followed by defoliation of affected needles. The aim of this study was to compare canopy damage categories obtained by aerial sketch-mapping with mean crown damage estimates derived from a systematic, plot-based sampling scheme of a Pinus radiata plantation in Green Hills State Forest in southern New South Wales with a known history of E. californica infestations. We identified significant challenges to rating accurately the level of canopy damage from E. californica by aerial sketch-mapping. While the location of chlorotic crowns may be mapped reliably, our results suggest that it is much more difficult to visually resolve different levels of canopy damage within affected stands. Using an ‘incidence × severity’ damage rating score, only two classes of canopy damage were confidently separated (i.e. Low (not detected or trace levels) and High (having a damage score of greater than 25%)). Accurate location of these classes of damage allows targeted, ground-based surveys for follow-up diagnostics and more detailed estimates of damage at the crown scale.

Determining the impacts of climate change on iconic West Australian trees, woodlands and forest e... more Determining the impacts of climate change on iconic West Australian trees, woodlands and forest ecosystems. Brouwers, N.C.

Journal of Agricultural, Biological, and Environmental Statistics, 2015

This paper explores and develops design-based and model-based methods which are suited to samplin... more This paper explores and develops design-based and model-based methods which are suited to sampling strategies developed for LiDAR-assisted plantation inventories. Much of the model-based theory is either recent or adapted from other areas of sampling. The design-based theory extends and adapts previous work to the present situation. The methodology is developed around the increasing utility and precision of LiDAR as a sampling tool for operational forest inventory. Flexible-radius plots, as a means of optimizing the sampling effort, are examined from a sampling perspective. Mixed models are also employed to model the residual variance using specified correlation structures and this includes predictors which utilize local trend such as those employed in kriging. In the design-based setting, model-assisted estimators are used, including regression and ratio estimators. A plot-based survey of a young, single-aged stand located within a Pinus radiata plantation in the northern tablelands of New South Wales is used to illustrate the theory. Model covariates are obtained from airborne laser scanning (LiDAR) data.

The increase in atmospheric concentration of greenhouse gases due to human activity, particularly... more The increase in atmospheric concentration of greenhouse gases due to human activity, particularly combustion of fossil fuels and land clearing, is increasing global temperatures and affecting global and regional climate systems. In NSW, temperature has increased by 0.9°C between 1910 and 2005, and the average rainfall since 2000 is 20% lower than the average rainfall received in the second half of last century. Irrespective of success in curbing future emissions, further warming is expected, due to the lagged effects of past greenhouse gas emissions. Climate change is predicted to increase average temperatures in NSW by 0.7° to 6.4°C by 2070, with the greatest increase in the west of the state. Rainfall is likely to be reduced across the state, apart from in the northeast. Projections suggest an increased incidence of bushfire and intense storms. Drought frequency may increase, especially in winter and spring. These predicted impacts of climate change are likely to have serious negative impacts on all NSW primary industries, including the forest industry. The potential impacts on forests from these changes are not clearly understood, especially for Australian tree species under typical Australian conditions. Besides the impacts of changes in the climatic variables, plants will be directly influenced by the increasing concentration of CO 2 in the atmosphere. Physiological impacts International research carried out over the past 20 years has generated general understanding of the direct effects of increasing CO 2 concentration on plant growth and function. Doubling of CO 2 concentration generally increases plant growth by 10%-25% (Nowak et al. 2004; Luo et al. 2005b; Norby et al. 2005), through the so-called "CO 2 fertilisation effect". Most of the research has been conducted on Northern Hemisphere species under environmental conditions different to those typical of Australia. Furthermore, most research does not consider the feedbacks at the ecosystem level that need to be factored in when predicting effects on whole forests from results measured on individual trees/saplings. Importantly, plant physiologists and modellers alike now recognise that the effects of elevated carbon dioxide measured in experimental settings and implemented in models may overestimate actual field responses, due to many limiting factors, such as pests, weeds, competition for resources, soil water and air quality, which are neither well understood on large scales, nor well implemented in leading models (

Australian Forestry, 2013

ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first d... more ABSTRACT The Monterey pine aphid, Essigella californica Essig (Hemiptera: Aphididae), was first detected in Australia in 1998 and is now a major damaging agent in Pinus radiata plantations throughout south-eastern Australia. Tree-level crown damage was visually assessed over four years, from 2006 to 2009, in 120 plots located in Green Hills State Forest (Hume Region, Forests NSW). The plots represented 30 tree-age classes and a range of related stocking densities. We applied random forests and linear mixed modelling (ASReml) to examine the relationships between crown damage and a series of silvicultural and local climatic and terrain attributes. Consistent with previous observations, our results showed that crown damage due to E. californica is highly variable and is influenced by a suite of interacting and confounding factors. We identified prevailing climatic conditions, stand age and tree genotype as being the most influential, as well as threshold values associated with these relationships. These predictor variables can be used to stratify plantation planning units according to risk of defoliation by E. californica and for prioritising and targeting management activities such as aerial surveillance, release of the introduced biological control agent Diaeretus essigellae, possible late-age fertiliser application and in the future, the deployment of Essigella-resistant pine genotypes.

Forest Ecology and Management, 2009

New Zealand Journal of Forestry Science, 2015

Current biosecurity arrangements for plantation forestry are poorly defined, at least relative to... more Current biosecurity arrangements for plantation forestry are poorly defined, at least relative to other plant-based industries. Serious pest and disease outbreaks in forestry are relatively rare events. Preparedness for rare events is difficult. Part of the difficulty stems from the competing views of managers and stakeholders. This project sought to directly capture alternative views concerning the key objectives of plantation forest biosecurity, alternative strategies for achieving those objectives, and ultimately recommend preferred actions that might be broadly supported by stakeholders. The outcomes from the workshop were used as a basis to draft a list of strategic actions required to improve forest biosecurity in Australia and to be implemented over the next 2-5 years. Research priorities were identified as research to support cost benefit analyses; investigating the effects of changed environmental conditions on forest biosecurity; pathway analysis for functional pest guilds...

Remote Sensing

Digital aerial photogrammetry (DAP) has emerged as a potentially cost-effective alternative to ai... more Digital aerial photogrammetry (DAP) has emerged as a potentially cost-effective alternative to airborne laser scanning (ALS) for forest inventory methods that employ point cloud data. Forest inventory derived from DAP using area-based methods has been shown to achieve accuracy similar to that of ALS data. At the tree level, individual tree detection (ITD) algorithms have been developed to detect and/or delineate individual trees either from ALS point cloud data or from ALS- or DAP-based canopy height models. An examination of the application of ITDs to DAP-based point clouds has not yet been reported. In this research, we evaluate the suitability of DAP-based point clouds for individual tree detection in the Pinus radiata plantation. Two ITD algorithms designed to work with point cloud data are applied to dense point clouds generated from small- and medium-format photography and to an ALS point cloud. Performance of the two ITD algorithms, the influence of stand structure on tree de...

Australian Forestry

Recent advances and commercialisation of unmanned aerial vehicle/red blue green (RGB) camera syst... more Recent advances and commercialisation of unmanned aerial vehicle/red blue green (RGB) camera systems and digital photogrammetric techniques now provide a cheap and flexible alternative to higher-cost airborne platforms for routine monitoring of canopy health in timber plantations. Structure-from-Motion photogrammetry produces very dense three-dimensional (3D) point clouds which can be used to derive metrics for inventory estimation. Unmanned aerial vehicle RGB photography also captures data that can relate to tree health. In contrast to the more common use of orthorectified RGB photography to extract this spectral information, we used the software package Agisoft Photoscan to assign a simple Vegetation Index value directly to each point in the 3D point cloud. Using data acquired by a DJI Phantom 4 Pro, we present a simple processing and photogrammetric workflow solution for detecting dead and dying trees in a young Eucalyptus pellita plantation located in the provenance of Riau, Sumatra. Trees affected by the bacterial wilt Ralstonia sp. present symptoms of necrotic foliage on individual branches or the whole crown. Assigning the Visible Atmospheric Resistant Index Vegetation Index colour-coded values to individual points in the 3D point cloud significantly enhanced visualisation of necrotic foliage on individual trees in both the point cloud and the associated orthophoto compared to the RGB equivalent images. This approach could easily be operationally deployed for the rapid detection and mapping of unhealthy trees with symptoms of necrotic foliage.

Remote Sensing

Surveying of woody debris left over from harvesting operations on managed forests is an important... more Surveying of woody debris left over from harvesting operations on managed forests is an important step in monitoring site quality, managing the extraction of residues and reconciling differences in pre-harvest inventories and actual timber yields. Traditional methods for post-harvest survey involving manual assessment of debris on the ground over small sample plots are labor-intensive, time-consuming, and do not scale well to heterogeneous landscapes. In this paper, we propose and evaluate new automated methods for the collection and interpretation of high-resolution, Unmanned Aerial Vehicle (UAV)-borne imagery over post-harvested forests for estimating quantities of fine and coarse woody debris. Using high-resolution, geo-registered color mosaics generated from UAV-borne images, we develop manual and automated processing methods for detecting, segmenting and counting both fine and coarse woody debris, including tree stumps, exploiting state-of-the-art machine learning and image pro...

International Journal of Applied Earth Observation and Geoinformation

Forest inventory operations have greatly benefitted from remotely sensed data particularly airbor... more Forest inventory operations have greatly benefitted from remotely sensed data particularly airborne laser scanning (ALS) which has become a popular technology choice for large-area forest inventories. For remote regions, for fragmented estates or for single stand-level inventories ALS may be unsuitable because of the high cost of data acquisition. Point cloud data generated from digital aerial photography (DAP) is emerging as a cost-effective alternative to ALS. In this study we compared area-based forest inventory attributes derived from point cloud datasets sourced from ALS, small-format and medium-format digital aerial photography (SFP and MFP). Non-parametric modelling approach, namely RandomForest, was employed to model forest structural attributes at both plot- and stand-levels. The results were evaluated using field data collected at 105 inventory plots. At plot-level, the maximum difference among relative RMSEs of basal area (BA), top height (Htop), stocking (N) and total stem volume (TSV) of the three datasets was 2.46%, 0.55%, 13.29% and 2.53%, respectively. At stand-level, the maximum difference among relative RMSEs of BA, Htop, N and TSV of the three datasets was 3.86%, 1.25%, 7.85% and 6.04%, respectively. This study demonstrates the robustness of DAP across different sensors, and thus informs forest managers planning data acquisition solutions to best suit their operational needs.

Southern Forests: a Journal of Forest Science

A new strategic inventory across all publicly managed forests has been installed in Victoria. For... more A new strategic inventory across all publicly managed forests has been installed in Victoria. For the preceding two decades, Victoria’s forest inventory has been compiled from various data sources from across the state, an approach that doesn’t allow information about the nature and rate of changes to the resource to be estimated, or for projections or forecasts to be made. To address these limitations, the Victorian Forest Monitoring Program (VFMP) was established, to monitor Victoria’s progress in meeting a commitment towards sustainable forest management, and to satisfy requirements for state and national reporting. The purpose of the new program is to ‘assess and monitor the extent, state and sustainable development of Victoria’s public forests in a timely and accurate manner.’ The VFMP consists of a plot-based system of permanent observational units located on a state-wide grid. A combination of ground-based and aerial photo plots and remotely sensed data are used to capture a set of basic attributes that are used to derive indicators of sustainability. To meet the monitoring needs a remeasurement framework has been developed to guide the change estimation procedures. The program was designed and implemented between 2009 and 2015 and used to generate data and information for the most recent Victoria’s State of the Forest Report. The first annual change estimate is due to be completed in 2017. A summary of implementation and proposed maintenance is presented and discussed in this paper.

Current Forestry Reports

Purpose of Review In this review, we highlight recent developments and applications in remote sen... more Purpose of Review In this review, we highlight recent developments and applications in remote sensing that can improve the accuracy and timeliness of health assessments in plantations managed for timber and pulp production. The detection and mapping of damage extent and severity caused by insect pests and fungal pathogens is a common requirement of foresters managing plantations. The objectives of these surveys can range from early detection for targeted intervention to more strategic aims of predicting stand susceptibility or evaluating the performance of management strategies. Recent Findings Recent developments in remote sensing technologies and big data modelling techniques can now provide spatially explicit, quantitative solutions for these management objectives that are more accurate than manual fieldbased assessments of tree damage or airborne visual mapping. Past studies have identified a large number of spectral, textural and structural metrics that have been used in models to classify specific tree crown damage symptoms. This process requires a detailed understanding of the chronology of crown symptoms for specific damaging agents and the spectral responses to these symptoms. Continuing increases in the spatial This article is part of the Topical Collection on Remote Sensing