Automated tree crown detection and size estimation using multi-scale analysis of high-resolution satellite imagery

We tested an automated multi-scale approach for detecting individual trees and estimating tree crown geometry using high spatial resolution satellite imagery. Individual tree crowns are identified as local extrema points in the Laplacian-of-Gaussian scale-space pyramid that is constructed based on linear scale-space theory. The approach simultaneously detects tree crown centres and estimates tree crown sizes (radiuses). We evaluated our method using two 0.6-m resolution QuickBird images of a forest site that underwent a large shift in tree density between image captures due to drought-associated mortality. The automated multi-scale approach produced tree count estimates with an accuracy of 54% and 73% corresponding to the dense and sparse forests, respectively. Estimated crown diameters were linearly correlated with field-measured crown diameters (r = 0.73–0.86). Tree count accuracies and size estimates were comparable with alternative methods. Future use of the presented approach is merited based on the results of our study, but requires further investigation in a broader range of forest types.     

Tree crown segmentation based on a tree crown density model derived from Airborne Laser Scanning

ABSTRACT

This letter describes a new algorithm for automatic tree crown delineation based on a model of tree crown density, and its validation. The tree crown density model was first used to create a correlation surface, which was then input to a standard watershed segmentation algorithm for delineation of tree crowns. The use of a model in an early step of the algorithm neatly solves the problem of scale selection. In earlier studies, correlation surfaces have been used for tree crown segmentation, involving modelling tree crowns as solid geometric shapes. The new algorithm applies a density model of tree crowns, which improves the model’s suitability for segmentation of Airborne Laser Scanning (ALS) data because laser returns are located inside tree crowns. The algorithm was validated using data acquired for 36 circular (40 m radius) field plots in southern Sweden. The algorithm detected high proportions of field-measured trees (40–97% of live trees in the 36 field plots: 85% on average). The average proportion of detected basal area (cross-sectional area of tree stems, 1.3 m above ground) was 93% (range: 84–99%). The algorithm was used with discrete return ALS point data, but the computation principle also allows delineation of tree crowns in ALS waveform data.     

Seed production in white box (Eucalyptus albens) in the South West Slopes region of New South Wales

Capsules were collected from 32 white box (Eucalyptus albens) trees growing in the vicinity of Wagga Wagga, N.S.W. and aspects of seed production were assessed on an individual tree basis. On average there were 2.0 seeds per capsule, which is low for eucalypts, and there were 1012 seeds per 10 g of capsule contents, which is only ca. 40% of the previously published figures for white box. There was a large tree to tree variation in both these measurements. The average number of seeds per capsule and the number of seeds per 10 g of capsule contents were significantly lower in isolated trees (1.1 and 422, respectively) than in trees in woodland environments (2.1 and 1122, respectively). Larger capsules were not correlated with greater numbers of seeds per capsule but were correlated with larger seeds.     

Evaluating wood volume estimates derived from Quickbird imagery with GEOBIA for Pinus nigra trees in the Pentalofo forest,northern Greece

The objective of this research was to evaluate wood volume estimates of Pinus nigra trees in forest stands, which were derived utilizing Geographic Object-Based Image Analysis. Information on forest parameters such as wood volume and number of trees is useful for forest management facilitating forest sustainability. Most of the existing approaches used to estimate wood volume of forest trees require field measurements, which are laboursome. In this study, the collected field data were utilized only in order to investigate the results. Wood volume was estimated based on an individual tree crown approach and using monoscopic satellite images in combination with allometric data. The study area is the Pentalofo forest, which is located in Kozani prefecture in western Macedonia, Northern Greece. About 1 plot surface of 0.1143 ha was utilized. During the preprocessing, a pansharpened image was produced from two Quickbird satellite images (one multispectral image of 2.4 m spatial resolution and one panchromatic image of 0.6 m spatial resolution). Bands of this image were utilized single or in combination in order to delineate the tree crowns individually. The allometric equation served in order to calculate the tree Diameter at Breast Height (DBH) utilizing the detected tree crowns. The evaluation was conducted on three levels: (i) number of trees, (ii) DBH class distribution and (iii) wood volume. On the third level, the evaluation procedure was conducted twice; once using field height and once without. The difference between the results and the field data for the wood volume reached a maximum of approximately 30%. The total number of trees was exactly the same as counted in the field and the DBH distribution showed a tendency for the trees to move to a higher DBH class, resulting in an overestimation of the wood volume.     

Biomass and nutrient distribution in relation Pine in relation to previous land use I. Biomass

Above-ground biomass data are compared for 21-year-old radiata pine stands on three sites which had different types of land use prior to plantation establishment. The three sites, previously under native forest, grazed pasture and a pasture site subsequently used for crop production (cultivated) formed a continuous section of plantation in the 1968 age class. Biomass equations were developed for each tree component in relation to stem diameter for each site. There were no significant differences between sites in the coefficients for stemwood and bark, but different coefficients were required to relate stem diameter to the biomass of branches in the dead crown and foliage in the lower live crown. Stands on previously cultivated pasture (pasture followed by crops) accumulated 362,745 kg ha^?1 in the above-ground biomass; 40% and 13% more than the ex-native forest (259,183 kg ha^?1) and ex-pasture (320,055 kg ha^?1) sites, respectively. Trees on the previously cultivated pasture allocated a larger proportion of the total biomass to branches (17.4%) compared with the ex-native forest and ex-pasture trees (11.1%). This is attributed to reduced stocking and enriched soil resulting from different previous land use practices. The high frequency of multi-leadered trees in the ex-cultivated pasture increased the non-merchantable components to 26.7% of the total biomass.     

JARRAH STEM DISTRIBUTIONS

Laboratory bioassays were conducted on the susceptibility of air-dried sapwood specimens, from trees of both regrowth and mature karri (Eucalyptus diversicolor) and jarrah (Eucalyptus marginata), to attack by the powder post borer (Lyctus brunneus). The susceptibility of regrowth karri was determined using material collected from 10 trees (five trees x two areas) each at three positions (the butt, midway along the bole and the crown). Material from the butts of 64 mature trees, representing three different areas in the south west of Western Australia, was similarly assessed. Both regrowth and mature karri specimens were collected from trees within the main karri estate. The susceptibility of both regrowth and mature jarrah was compared concurrently in a bioassay which evaluated butt specimens of approximately 20 trees from each of three different areas in the jarrah forest. Prior to the bioassays, all specimens were assessed for starch concentration in the sapwood.

Some sapwood specimens of both regrowth and mature karri were susceptible to attack by L. brunneus. Specimens cut from the butt position of regrowth karri trees contained the highest concentration of starch and were more heavily attacked by L. brunneus. Similarly, some regrowth and mature jarrah specimens from some areas were susceptible to attack.

Differences in starch concentration and susceptibility between areas from which each timber species was harvested were revealed. Positive correlations, between starch concentration and susceptibility of mature karri and regrowth and mature jarrah, were obtained. A revision of previously published ratings for both karri and jarrah is recommended. We further recommend that a re-assessment of the susceptibility to L. brunneus of all commercially available hardwood timber species be undertaken, particularly if a regrowth resource of those species is being utilised or likely to be utilised in the near future.     

Estimation of forest stand diameter class using airborne lidar and field data

In this study, a method for estimating the stand diameter at breast height (DBH) classes in a South Korea forest using airborne lidar and field data was proposed. First, a digital surface model (DSM) and digital terrain model (DTM) were generated from the lidar data that have a point density of 4.3 points/m², then a tree canopy model (TCM) was created by subtracting the DTM from the DSM. The tree height and crown diameter were estimated from the rasterized TCM using local maximum points, minimum points and a circle fitting algorithm. Individual tree heights and crown diameters were converted into DBH using the allometric equations obtained from the field survey data. We calculated the proportion of the total number of individual trees belonging to each DBH class in each stand to determine the stand DBH class according to the standard guidelines. More than 60% of the stand DBH classes were correctly estimated by the proposed method, and their area occupied over 80% of the total forest area. The proposed method generated more accurate results compared to the digital forest type map provided by the government.     

Factors influencing the performance of jarrah leafminer (Lepidoptera) within stands of jarrah forest of Western Australia

The survival rate among larvae of jarrah leafminer Perthida glyphopa in crowns of pole-sized jarrah Eucalyptus marginata at 14 m above ground level significantly exceeds that on leaves in foliage of ground coppice (< 2 m above ground), although the oviposition rate is similar in both cases. This is associated with greater concentrations of leaf N and P, lower concentrations of Ca, Mg and leaf phenols, and lower temperatures within pole crowns. Rate of parasitization of larvae in mines in leaves of pole-sized trees is similar to that in leaves of ground coppice. Poles with foliage inherently resistant to feeding by jarrah leafminer larvae have similar numbers of mines per leaf to susceptible poles, but the larvae in mines of resistant jarrah experience higher mortality than those on susceptible jarrah, and die sooner so that mean area of mines is only about one-third of that on susceptible jarrah. The area of mines is also directly dependent on the mean maximum temperature but not on the mean minimimum temperature. Resistance is associated with lower concentrations of leaf N in young leaves but not with higher concentrations of leaf phenols or lower concentrations of other major nutrients. Explicit criteria for discriminating resistant jarrah are provided; as a result, resistant jarrah can be retained, and susceptible jarrah selectively removed, during timber harvesting operations.     

Effects of wind sway on stem form and crown development of Scots pine (Pinus sylvestris L.)

The distribution of growth was examined in 45-year-old Scots pine (Pinus sylvestris L.) trees stayed with wires attached at 30% and at 30% and 60% of the tree height, and in trees with a metal sail attached in the top of the crown. The treatments commenced in 1983 and 16 trees per treatment, including the control, were sampled in 1988. Increments of stem diameter, height, and volume in treated and control trees were estimated from stem and branch mensuration. Staying the trees promoted radial growth by about 10% above the point of attachment. Increasing the wind sway with sails promoted radial growth below the crown. Changes in the distribution of growth within the crown were not as obvious as the changes along the stem below the crown.     

The effect of tree spacing on the production of flowers in Eucalyptus nitens

The effect of spacing on the production of flowers and capsules in Eucalyptus nitens was studied in two spacing trials located in northern Tasmania. Tree density in these trials ranged from 468 to 4216 stems ha^?1. Reproductive structures were collected in litter traps and these data were used to calculate reproductive output on a per tree and per hectare basis. Between 8735 (5-y-old site, 1333 stems ha”¹) to 234098 (13-y-old site, 1082 stems ha”¹) flowers were produced per hectare over a single flowering season at these two study sites at the planting densities expected of a pulpwood plantation. This represented 8 and 211 flowers per tree respectively. As tree density decreased, the production of flowers and capsules increased on both a per-tree and per-hectare basis. It is estimated that the number of flowers per hectare is likely to be anywhere between between 1.4 and 10-fold greater under the spacing expected in sawlog regimes (250 trees ha^?1). This difference in reproductive output between plantations of E. nitens that use different spacing regimes is one of the many factors that need to be considered in assessing the risk of wilding establishment or hybridisation with adjacent native eucalypts.     

Mortality of Eucalyptus marginata (jarrah) and E. calophylla (marri) trees following stem injection: effects of herbicide,dose, season,and spacing of injections

Mortalities of Eucalyptus marginata Donn ex Smith (jarrah) and E. calophylla R.Br, (marri) trees injected with Roundup^TM (360 g glyphosate l^?1 ) or Tordon Timber Control^TM (50 g picloram l^?1 and 100 g triclopyr l^?1 ) (P+T) were determined at doses of 5 to 80 grams of active ingredient (g.a.i.) m^?2 of stem basal area for glyphosate, and 2 to 40 g.a.i. m^?2 for P+T. The effect of spacing of injections around the tree bole was examined. Seasonal variation in mortality was examined in relation to atmospheric vapour pressure deficit (v.p.d.) and soil water deficits.

Glyphosate was more effective in killing E. marginata trees, whereas P+T tended to be more effective in killing E. calophylla trees. The optimum doses of glyphosate and P+T for E. marginata trees were 20 g.a.i. m^?2 and 15 g.a.i. m^?2 respectively, and for E. calophylla 80 g.a.i. m^?2 and 15 g.a.i. m^?2 respectively. Spacing of injections around the circumference of the tree did not have a significant effect on the mortality of E. marginata trees injected with glyphosate. However, mortality of E. calophylla trees injected with P+T declined from 89% at 10–15 cm spacing to 70% at 25–50 cm spacing.

There were strong seasonal effects with both herbicides and in both species, with mortality higher (70 - 90 % mortality) in seasons other than summer (30 - 50 % mortality). For E. marginata trees injected with glyphosate, mortality declined linearly with increasing v.p.d., from 95% at a v.p.d. of 0.5 kPa, to 25% at 4.5 kPa. For E. calophylla trees injected with P+T, mortality declined linearly with increasing v.p.d., from 85% mortality at a v.p.d. of 0.5 kPa, to 50% at 3.0 kPa. Stem injection of both species should only be carried out when the vapour pressure deficit on the day prior to stem injection is less than 1.5 kPa.     

Ecology of the pest insect jarrah leaf miner (Lepidoptera) in relation to fire and timber harvesting in jarrah forest in Western Australia

During a period of 7 years we undertook 25 investigations of the ecology of jarrah leafminer Perthida glyphopa Common in relation to fire and logging of jarrah Eucalyptus marginata Donn ex Sm. forest. Prescribed low intensity fires in spring or timber harvesting did not consistently favour jarrah leafminer or disfavour parasitization of its mines. Moderate intensity fire in autumn reduced the density of jarrah leafminer for 18 months.

We integrate these findings with other relevant ecological and historical knowledge and theorize that scarcity of extensive scorching of codominant crowns in jarrah forest from the mid 1950s may have facilitated the spread of the outbreak. We recommend that more extensive autumn burning should be operationally introduced to both test the theory and subdue outbreaks of jarrah leafminer.     

Canopy surface reconstruction from a LiDAR point cloud using Hough transform

Tree height and canopy volume are critical forestry parameters that are used to derive estimates of growth, carbon sequestration, standing timber volume, and biomass. Through the use of light detection and ranging, these attributes can be estimated rapidly over large areas. At the stand level, estimates of these attributes have been derived successfully from canopy height models. However, a number of challenges identified in using canopy height models remain, such as correcting for height underestimation and canopy surface irregularities, such as data pits and holes that may result from acquisition and/or post-processing, and consistent delineation of tree crowns – all of which can limit the accurate retrieval of individual tree and crown attributes. In this letter, a novel canopy model is proposed in which individual tree crowns are represented as objects for which delineations can be derived through geometric operations. The technique is based on fitting simple geometric shapes to the raw light detection and ranging point cloud and thereby compensates for this underestimation, reduces data size, and allows effective and efficient modelling at the individual tree level.     

Development of an automated individual tree detection model using point cloud LiDAR data for accurate tree counts in a Pinus radiata plantation

We develop and evaluate a new individual tree detection (ITD) algorithm to automatically locate and estimate the number of individual trees within a Pinus radiata plantation from relatively sparse airborne LiDAR point cloud data. The area of interest comprised stands covering a range of age classes and stocking levels. Our approach is based on local maxima (LM) filtering that tackles the issue of selecting the optimal search radius from the LiDAR point cloud for every potential LM using metrics derived from local neighbourhood data points; thus, it adapts to the local conditions, irrespective of canopy variability. This was achieved through two steps: (i) logistic regression model development using simulated stands composed of individual trees derived from real LiDAR point cloud data and (ii) application testing of the model using real plantation LiDAR point cloud data and geolocated, tree-level reference crowns that were manually identified in the LiDAR imagery. Our ITD algorithm performed well compared with previous studies, producing RMSE of 5.7% and a bias of only ?2.4%. Finally, we suggest that the ITD algorithm can be used for accurately estimating stocking and tree mapping, which in turn could be used to derive the plot-level metrics for an area-based approach for enhancing estimates of stand-level inventory attributes based on plot imputation.     

EFFECTS OF FIRE ON SEEDSHED FROM EUCALYPTUS REGNANS

Patterns of seedshed were studied in several burnt and unburnt stands of Eucalyptus regnans F. Muell. in central Tasmania by catching the seed in traps and examining the capsules on the trees. Timing of the seedshed is important because the bulk of the natural regeneration must normally come from the seed which is shed within one year after burning.

In unburnt stands seed was shed throughout the year. During some years the pattern of seedshed was irregular, but after hot, dry summers one-half to three-quarters of the year's seedshed occurred in February-March-April. The capsules themselves were cast off in a less regular pattern; the fallen capsules still contained 16 per cent of the full seed loading.

Fire may accelerate seedshed. If the leaves and twigs are scorched, the capsules also are killed and their seed is shed as soon as they dry out; this may take hours or weeks. If the tree is girdled the crown will wilt within days or months, depending on the depth of girdling and the subsequent weather. Seedshed occurs when the crown is wilting. Even if the crown remains green and apparently healthy seedshed may be affected. Sometimes all or nearly all the capsules of a heavy crop are abscissed in less than one month after the fire. More often only a proportion of the capsules is affected by the fire. It is considered that the pattern of seedshed after fire is generally such that the available seed is reasonably effective in producing regeneration.     

Effect of Prescribed Burning in a Forest on Wood Characteristics of Jarrah

Wood specimens have been examined which were collected from three positions along the merchantable bole of jarrah (Eucalyptus marginata Sm.) trees growing in Western Australia. These trees had been subjected to a series of two experimental fires at either of two intensities in either spring or autumn. The more intense fire caused crown and trunk damage and resulted in kino vein formation. If such burning took place in autumn, loss of radial growth resulted. The less intense fire treatment did not result in external damage. Minor disturbances to the density profiles in the first year after the fire were the only observed effects on characteristics of the wood.     

Polynomial taper model for Queensland plantation hoop pine

A stem taper model, involving a high order polynomial developed using plantation hoop pine (Araucaria cunninghamii Ait. ex D. Don) trees grown in Queensland, is presented. The stem profile for each tree was initially modelled using functions of diameter under bark and height, as the dependent and independent variables respectively. Parameter estimates from these individual tree regressions were subsequently modelled, using total height and diameter at breast height under bark (DBHub) as the independent variables. Finally, total height and DBHub were modelled in terms of predominant height' and diameter at breast height over bark (DBHob).

The largest mean error in the estimates of stem diameter predicted using the final model, with predominant height and DBHob as the independent variables, was 0.12 cm. The overall mean relative error in the estimate of volume, based on coefficients modelled using predominant height and DBHob, was 0.20 per cent. Apart from its accuracy, the main advantages of the model include its simplicity and its ability to model the whole tree using a single function.     

MINUTES OF THE BIENNIAL GENERAl MEETING

Dimethoate injected into the tree trunk as a 30 per cent emulsifiable concentrate (Rogor 40) successfully controlled the jarrah leaf miner in Eucalyptus marginata Sm. and in E. rudis Endl. Good control of psyllids on E. rudis was also achieved.

The dosage required for trees of 8 in. dbh was 8 g active ingredient. For smaller and larger trees, dosages should be calculated on the assumption that they will be proportional to the breast-high cross-sectional areas, that is. 2 g for a tree of 4 in. dbh. and 32 g for a tree of 16 in. dbh.

Technical crystalline dimethoate placed in holes drilled into the tree trunk achieved satisfactory control of both pests, but the results were not as consistent as with the emulsifiable concentrate.     

Sensitivity of LiDAR-derived three-dimensional shape signatures for individual tree crowns: a simulation study

Following previous research that demonstrates the effectiveness of three-dimensional (3D) shape signatures for characterizing individual tree crowns derived from Light Detection and Ranging (LiDAR) data, this letter presents a simulation study on the sensitivity of 3D shape signatures. Based on the observation of LiDAR point clouds for tree crowns, a mathematical model is designed to generate simulation data. Factors affecting LiDAR-derived 3D shape signatures of individual tree crowns are then tested, including the number of points, the size and location of sampling circles and the influence of neighbouring crowns. The results suggest that it is possible to obtain 3D shape signatures of individual crowns based on automated treetop detection, and that a combination of multiple sample circles may provide more reliable results than single sample circles in characterizing 3D crown shapes.     

Crown Recovery of Eucalyptus dives Following Wildfire

The restoration of crowns of 5–7 m tall trees of E. dives of coppice origin was studied after a wildfire on October 1, 1971, near Captains Flat, N.S.W. Unburned plants were compared with those which had their crowns completely scorched but not burned and those which had their leaves completely burned off by crown fire. All trees survived. Approximately 50 per cent of the height of crown-burned trees was killed and 30 per cent in the case of crown-scorched trees. While these results were significantly different most measurements of crown recovery were similar for these two classes of fire-affected plants. Leaf weight was restored within 8 months of the fire. The clumped pattern of epicormic shoots emergent along surviving trunks soon after the fire was replaced by that of the normal branching pattern less than three years later.