Detection of dead standing Eucalyptus camaldulensis without tree delineation for managing biodiversity in native Australian forest

In Australia, many birds and arboreal animals use hollows for shelters, but studies predict shortage of hollows in near future. Aged dead trees are more likely to contain hollows and therefore automated detection of them plays a substantial role in preserving biodiversity and consequently maintaining a resilient ecosystem. For this purpose full-waveform LiDAR data were acquired from a native Eucalypt forest in Southern Australia. The structure of the forest significantly varies in terms of tree density, age and height. Additionally, Eucalyptus camaldulensis have multiple trunk splits making tree delineation very challenging. For that reason, this paper investigates automated detection of dead standing Eucalyptus camaldulensis without tree delineation. It also presents the new feature of the open source software DASOS, which extracts features for 3D object detection in voxelised FW LiDAR. A random forest classifier, a weighted-distance KNN algorithm and a seed growth algorithm are used to create a 2D probabilistic field and to then predict potential positions of dead trees. It is shown that tree health assessment is possible without tree delineation but since it is a new research directions there are many improvements to be made

Health Assessment of Eucalyptus Trees Using Siamese Network from Google Street and Ground Truth Images

Urban greenery is an essential characteristic of the urban ecosystem, which offers various advantages, such as improved air quality, human health facilities, storm-water run-off control, carbon reduction, and an increase in property values. Therefore, identification and continuous monitoring of the vegetation (trees) is of vital importance for our urban lifestyle. This paper proposes a deep learning-based network, Siamese convolutional neural network (SCNN), combined with a modified brute-force-based line-of-bearing (LOB) algorithm that evaluates the health of Eucalyptus trees as healthy or unhealthy and identifies their geolocation in real time from Google Street View (GSV) and ground truth images. Our dataset represents Eucalyptus trees’ various details from multiple viewpoints, scales and different shapes to texture. The experiments were carried out in the Wyndham city council area in the state of Victoria, Australia. Our approach obtained an average accuracy of 93.2% in identifying healthy and unhealthy trees after training on around 4500 images and testing on 500 images. This study helps in identifying the Eucalyptus tree with health issues or dead trees in an automated way that can facilitate urban green management and assist the local council to make decisions about plantation and improvements in looking after trees. Overall, this study shows that even in a complex background, most healthy and unhealthy Eucalyptus trees can be detected by our deep learning algorithm in real time

Multiscale forest health mapping: the potential of air- and space-borne remote sensing sensors

Forest health decline triggered by extensive periods of drought and high temperatures is increasingly common across Australia. In this respect remote sensing technology may help with understanding and managing forest health decline by providing information on a scale that field-based studies cannot match. In this thesis I explore the potential of air- and space-borne remote sensing in characterizing and monitoring forest health expressed in terms of tree dieback at multiple scales. I conducted my experiments in the largest river red gum forest in the world, located in the south-east of Australia that has experienced episodes of severe dieback over the past six decades. First, I propose a new algorithm that utilizes high point density airborne laser scans (ALS) for delineating individual trees with complex shapes, such as eucalypts, in Chapter 2. My algorithm was able to accurately delineate up to 68% of trees depending on forest and ALS point density. Second, I investigate the utility of ALS and imaging spectroscopy in classifying forest health at the individual tree level and diagnosing potential causes of forest health decline, in Chapter 3. According to my results the health of individual trees can be classified with an overall accuracy of 81% and a kappa score of 0.66, while infrequently flooded areas were most susceptible to tree health decline. Finally, I assess how low point density ALS, Synthetic Aperture Radar and multispectral satellite imagery can estimate forest health at the plot level, in Chapter 4. My findings demonstrate that individual tree health could be scaled up to the plot level with substantial level of accuracy (R2 of up to 0.64). Overall, my results provide a robust and peer-reviewed methodology that utilizes air- and space-borne remote sensing to accurately classify forest health at multiple scales. Moreover, the forest health map produced as a result of my research will potentially enable forest managers to perform demographic reporting on forest dynamics, diagnose ecological processes linked to forest health, and prioritize areas for forest health promotion and conservation of biodiversity

Forest diversity in fragmented landscapes of northern Ethiopia and implications for conservation

Deforestation and habitat fragmentation that arise largely due to the conversion of forests to other agricultural land-use types and over-utilization of forest resources to satisfy the food and energy requirements of the increasing population are major environmental concerns in northern Ethiopia. Understanding plant species diversity and spatial distribution along environmental gradients is crucial in the management of the remnant forest ecosystems. However, the ecology of the forest remnants in northern Ethiopia is poorly studied. The purpose of this study is therefore to (i) investigate plant species diversity and natural regeneration in relation to selected environmental factors, (ii) quantify the elevation patterns of species diversity and community composition, (iii) examine the extent and spatial distribution pattern of standing dead stems and the effect of mass tree dieback on forest structure and diversity, and (iv) compare the regeneration response of Juniperus procera and Olea europaea subsp. cuspidata in an openaccess forest area to a closed forest management system. The study was conducted in the Desa’a and Hugumburda Afromontane forest remnants, which are the largest forest fragments in northern Ethiopia and are national forest priority areas. A total of 153 species belonging to 63 families was found in the study area; shrub and herb species dominate (ca. 70 %). The vegetation is mainly a dry Afromontane forest type with Juniperus and Olea as the dominant species; a riverine plant community in Hugumburda forest represents a moist forest type. Elevation, slope, soil depth, distance to the nearest stream, soil moisture, and forest disturbance are the main environmental factors influencing species distribution and partitioned plant communities. The diversity of species and the composition of plant communities in Desa’a forest significantly respond to elevation. Species richness and diversity show a unimodal, humpshaped relationship with elevation that peaked at mid elevation (1900 – 2200 m). The beta diversity values indicate medium species turnover along an elevational gradient. The percentages of dead standing trees (snags) due to natural disturbance at Desa’a forest are high for both J. procera (57 ± 7 %) and O. europaea subsp. cuspidata (60 ± 5 %), but show a decreasing trend with increasing elevation suggesting that restoration is more urgent at the lower elevations. Higher tree dieback at the lower elevation has pushed the tree species to the higher elevation by about 500 m, and this can lead to a shift in the forest-shrubland ecotone to higher elevations. Total stand density and basal area are reduced by 30 and 44 % when excluding snags of the two species, respectively. Thus, mass tree dieback of the two key species strongly influences the forest structure. High amounts of dead standing biomass are a particular risk in a fire-prone semi-arid forest environment, and controlling snag densities is of critical concern in the management of the remaining dry Afromontane forests in northern Ethiopia. The natural regeneration of native tree species in both forest remnants is low. Exclosure was found to be an effective management option to improve the regeneration of O. europaea, but it does not improve the regeneration of J. procera. Thus, a closed management system in the open-access and degraded forests may not guarantee a successful regeneration of native woody species. It rather favors grass and herbaceous species and can lead to a gradual conversion of the forest land to wooded grassland. Most of the seedlings in forest remnants are shrubs, while tree species are less diverse and abundant. The standing vegetation is only partly represented in the seedling bank and many of the rare tree species, e.g. Afrocarpus falcatus, show poor or no regeneration. A smaller number of saplings than mature individuals suggest that locally some forest species are experiencing extinction. Thus, it is important to give conservation priority to the last Afromontane forest remnants in northern Ethiopia to achieve local, national and international biodiversity conservation goals.Biodiversität in den Wäldern der fragmentierten Landchaften von Nordäthiopien und die Folgerungen für ihren Schutz Abholzung und die Fragmentierung der Lebensräume, hauptsächlich als Folge der Umwandlung der Wälder in andere landwirtschaftliche Nutzungen sowie die Ausbeutung der Waldressourcen, um den Nahrungsmittel- und Energiebedarf der wachsenden Bevölkerung zu befriedigen, verursachen erhebliche Umweltprobleme in Nordäthiopien. Kenntnisse der Pflanzenvielfalt und räumlichen Verteilung entlang Umweltgradienten ist entscheidend bei der Bewirtschaftung der verbleibenden Waldökosysteme. Jedoch ist die Ökologie der noch vorhandenen Waldfragmente in Nordäthiopien nur wenig untersucht. Das Ziel dieser Studie ist daher (i) die Vielfalt der Pflanzenarten und ihre natürliche Regeneration im Zusammenhang mit ausgewählten Umweltfaktoren zu untersuchen, (ii) die höhenabhängige Verteilung der Artenvielfalt und die Zusammensetzung der Pflanzengemeinschaften zu quantifizieren, (iii) das Ausmaß und die räumliche Verteilung stehender toter Baumstämme sowie die Auswirkungen eines Baumsterbens auf die Waldstruktur und -vielfalt zu untersuchen, und (iv) den Einfluss eines geschlossenen Waldbewirtschaftungssystems mit dem eines zugänglichen Waldes auf die Regeneration von Juniperus procera und Olea europaea subsp. cuspidata zu vergleichen. Die Studie wurde in den afromontanen Wäldern Desa’a und Hugumburda, die größten Waldfragmente in Nordäthiopien und mit nationaler Schutzpriorität, durchgeführt. Insgesamt 153 Arten aus 63 Familien kommen im Untersuchungsgebiet vor; Strauch- und Kräuterarten dominieren (ca. 70 %). Die Vegetation ist hauptsächlich vom trockenen afromontanen Waldtyp mit den dominierenden Arten Juniperus und Olea; eine gewässernahe Pflanzengesellschaft im Hugumburda Wald ist vom Typ Feuchtwald. Höhenlage, Hangneigung, Bodentiefe, Nähe zum nächsten Kleingewässer, Bodenfeuchte und anthropogene Störungen sind die wichtigsten Umweltfaktoren, die die Artenverteilung und die Zusammensetzung der Pflanzengesellschaften beeinflussen. Die Artenvielfalt und die Zusammensetzung der Pflanzengesellschaften in Desa’a Wald sind signifikant abhängig von der Höhenlage. Artenreichtum und Diversität bilden eine unimodale Beziehung mit der Höhenlage; der höchste Wert ist bei einer mittleren Höhenlage (1900 - 2200 m). Die Betadiversitätswerte deuten auf einen mittleren Artenwechsel entlang eines Höhengradienten hin. Die Anteile stehender toter Baumstämme als Folge natürlicher Störungen im Desa’a Wald sind hoch, sowohl für J. procera (57 ± 7 %) als auch für O. europaea subsp. cuspidata (60 ± 5 %), zeigen jedoch einen abnehmenden Trend mit zunehmender Höhenlage, was darauf hindeutet, dass Rekultivierungsmaßnahmen in den unteren Höhenlagen dringender sind als in höheren. Das stärkere Baumsterben in den unteren Höhenlagen hat dazu geführt, dass das Vorkommen der betroffenen Baumarten sich um ca. 500 m nach oben verschoben hat. Dies kann auch zu einer Verschiebung der Wald-Buschland-Vegetation in höhere Lagen führen. Bestandsdichte bzw. Basalfläche sind um 30 bzw. 44 % reduziert wenn die stehenden toten Individuen der beiden Arten nicht berücksichtigt werden; das Absterben der beiden Hauptbaumarten beeinflusst also stark die Waldstruktur. Große Mengen toter Baumbiomasse sind ein besonderes Waldbrandrisiko in einem semiariden Wald und die Kontrolle der Dichte des Totholzes ist von entscheidender Bedeutung bei der Bewirtschaftung der noch verbleibenden trockenen afromontanen Wälder in Nordäthiopien. Die natürliche Regeneration der einheimischen Baumarten in den beiden untersuchten Waldfragmenten ist niedrig. Es zeigt sich, dass eingezäunte Flächen eine wirksame Bewirtschaftungsoption sind, um die Regeneration von O. europaea zu begünstigen. Diese Maßnahme bleibt jedoch ohne Wirkung auf J. procera. Daher würde ein Bewirtschaftungssystem mit Zugangsbeschränkungen in den offenen, degradierten Wäldern eine erfolgreiche Regeneration der einheimischen Holzgewächse nicht garantieren. Es werden eher Gras- und Kräuterarten begünstigt, was zu einer langsamen Umwandlung des Waldes in Grasland mit Gehölzen führen kann. Die meisten Keimlinge in den Waldfragmenten sind von Straucharten, während Baumarten weniger vielfältig bzw. zahlreich sind. Die bestandsbildenden Arten sind nur zum Teil in der Samenbank vertreten, und viele der seltenen Arten, z. B. Afrocarpus falcatus, zeigen wenig bzw. gar keine Regeneration. Die geringe Bedeutung von Jungwuchs im Vergleich zu den voll ausgewachsenen Baumindividuen deutet daraufhin, dass lokal einige bestandsbildenden Baumarten aussterben könnten. Daher muss den letzten afromontanen Waldfragmenten in Nordäthiopien eine hohe Schutzpriorität eingeräumt werden, auch um die lokalen, nationalen und internationalen Ziele zum Schutze der Artenvielfalt zu erreichen