Tree Expansion Research Articles

Large changes in vegetation composition seen over the last 50 years in British limestone pavements

Abstract Limestone pavements contain a unique flora, dominated by ferns with a mix of herbaceous species more often found in woodlands, heathlands and grasslands. The crevices between the rocks are known as grikes, they provide a shaded habitat which, depending on pavement structure, can protect plants from grazing. Despite being of conservation importance and supporting a number of rare and scarce plant species there has been very little research into vegetation change in limestone pavements. This study repeated a survey originally conducted between 1972 and 1975. The Ward and Evans survey visited 535 limestone pavement units spread across England, Scotland and Wales and recorded grike vegetation. This study was able to resurvey 516 of those pavements and repeat the survey using the original methods. Expansion of tree and shrub cover has been observed in some pavements but not previously quantified so tree cover was assessed using historic aerial photographs and satellite imagery. On average species richness per pavement increased but there was a very wide range of change in species richness across individual pavement units ranging from a loss of 56 species to an increase of 38. Dissimilarity averaged 0.41. The area of pavement covered by trees or large shrubs increased by 62% between the two surveys but the number of pavements with zero tree cover also increased. Breaking down pavement units into those with low (<5%), medium (5%–30%) and high (>30%) current tree cover shows that species richness increased in open pavements but was reduced in pavements with high tree cover. Pavement units with high tree cover also showed higher dissimilarity and lower levels of indicators of disturbance. In pavements with high tree cover Ellenberg light (L) values were significantly lower than in open pavements. Open pavements showed higher levels of competitive species (based on Grime CSR values) but no change difference in Ellenberg nutrient (N) values. Vegetation in limestone pavements has changed considerably in the period between the two surveys with negative effects of high tree and shrub cover particularly problematic. There is an urgent need for investigation to support management decisions in this habitat. Read the free Plain Language Summary for this article on the Journal blog.

Radiocarbon dating and isotopic paleoecology of Notiomastodon platensis (Mammalia: Proboscidea) from the late Pleistocene of Minas Gerais, Brazil

Proboscidea is a group of large mammals abundant in the fossil record and in Brazil it is represented by Notiomastodon platensis (Ameghino, 1888). To improve the understanding on its taxonomy, chronology, annual diet, and habitats paleoenvironmental aspects, we conducted a morphological description, absolute dating, and analysis of stable isotopes of carbon and oxygen (δ13C and δ18O) in Notiomastodon' remains from the northern (Norte de Minas) and western (Triângulo Mineiro) mesoregions of Minas Gerais State, Brazil. The material includes isolated teeth, mandibular portions, and postcranial bones at different levels of fragmentation, associated with at least eight adults and one juvenile. The only individual from Triângulo, found in Campina Verde municipality, was dated at 27,715–27,903 Cal yr BP. It presented a mixed diet based on C4 plants (piC4 = 90 %; δ13C = 0.5 ‰), which implies the occupation of an open environment, mostly pasture. The region was relatively humid (δ18O = 24.7 ‰), which is supported by the existence of humidity corridors in the Amazon region. A similar phytophysiognomy was inferred for the Norte de Minas region between at least 21,966–22,279 Cal yr BP and 18,944–19,157 Cal yr BP. However, one specimen showed a different δ13C value (piC3 = 0.87 %; δ13C = −10.2 ‰). This indicates it lived in a transitional environment between low-density forest and arboreal savannah. This likely occurred during a period that favored the expansion of trees and shrubs. The region underwent climate change, from relatively humid conditions (δ18O = 25.6 ± 0.2 ‰) to expressively dry (δ18O = 34.6 ‰) between the dated periods, a change corroborated by some palynological data. The multiannual paleoecological analysis, based on sequential sampling of three dentin layers of an incisor, indicated the relative stability of vegetation and climate despite fluctuations in hydrology. The perceived disassociation between vegetation dynamics and local hydrology corroborates the idea that factors other than precipitation may play a significant role in the environmental dynamics of the Cerrado biome.

The Impact of Juniper Removal on Shrubs and Understory Vegetation and its Implications for Sagebrush Dependent Vertebrate Herbivores

The expansion of trees into previously grass- and shrub- dominated ecosystems is a global phenomenon threatening ecosystem integrity and function in encroached systems, including the North American sagebrush biome. This ecosystem is currently in peril, threatened in part by juniper (Juniperus sp.) encroachment. Sagebrush (Artemisia sp.) ecosystems contain a diversity of forage, including grasses, forbs, and shrubs, that serve as a key food source for vertebrate herbivores. Removal of encroached juniper has been used by land managers as a widespread restoration technique in sagebrush ecosystems, however, the long-term impact of this restoration action on shrubs and understory vegetation has not been thoroughly examined in the context of sagebrush dependent vertebrate herbivores. In 2020 and 2021, we studied shrub and understory vegetation response to juniper treatment in the sagebrush of northern Nevada and northeastern California. Juniper treatments completed between 2008 and 2020 were surveyed and sampled to assess the impact of this restoration action on grasses, forbs, and shrubs over time. Forage biomass was higher in old treatments than untreated reference sites, which was a trend that persisted across all vegetation functional groups. Differences in plant cover were slight or had inconsistent nonlinear trends between reference sites and treatments. Forage from treated sites had higher crude protein levels than forage from untreated sites, although the nutritional difference was slight. Our results suggest that juniper treatments that increase forage quantity and improve forage quality may benefit sagebrush dependent wildlife or domestic livestock in conifer-encroached ecosystems.

Tree expansions of some Lie idempotents

Tree expansions of some Lie idempotents

Path Planning for Mobile Robots Based on the Improved DAPF-QRRT* Strategy

The rapidly exploring random tree star (RRT*) algorithm is widely used to solve path planning problems. However, the RRT* algorithm and its variants fall short of achieving a balanced consideration of path quality and safety. To address this issue, an improved discretized artificial potential field-QRRT* (IDAPF-QRRT*) path planning strategy is introduced. Initially, the APF method is integrated into the Quick-RRT* (Q-RRT*) algorithm, utilizing the attraction of goal points and the repulsion of obstacles to optimize the tree expansion process, swiftly achieving superior initial solutions. Subsequently, a triangle inequality-based path reconnection mechanism is introduced to create and reconnect path points, optimize the path length, and accelerate the generation of sub-optimal paths. Finally, by refining the traditional APF method, a repulsive orthogonal vector field is obtained, achieving the orthogonalization between repulsive and attractive vector fields. This places key path points within the optimized vector field and adjusts their positions, thereby enhancing path safety. Compared to the Q-RRT* algorithm, the DPF-QRRT* algorithm achieves a 37.66% reduction in the time taken to achieve 1.05 times the optimal solution, and the IDAPF-QRRT* strategy nearly doubles generated path safety.

A study on path-planning algorithm for a multi-section continuum robot in confined multi-obstacle environments

Abstract In confined multi-obstacle environments, generating feasible paths for continuum robots is challenging due to the need to avoid obstacles while considering the kinematic limitations of the robot. This paper deals with the path-planning algorithm for continuum robots in confined multi-obstacle environments to prevent their over-deformation. By modifying the tree expansion process of the Rapidly-exploring Random Tree Star (RRT*) algorithm, a path-planning algorithm called the continuum-RRT* algorithm herein is proposed to achieve fewer iterations and faster convergence as well as generating desired paths that adhere to the kinematic limitations of the continuum robots. Then path planning and path tracking are implemented on a tendon-driven four-section continuum robot to validate the effectiveness of the path-planning algorithm. The path-planning results show that the path generated by the algorithm indeed has fewer transitions, and the path generated by the algorithm is closer to the optimal path that satisfies the kinematic limitations of the continuum robot. Furthermore, path-tracking experiments validate the successful navigation of the continuum robot along the algorithm-generated path, exhibiting an error range of 2.51%–3.91%. This attests to the effectiveness of the proposed algorithm in meeting the navigation requirements of continuum robots.

Microsite preferences of three conifers in calcareous and siliceous treeline ecotones in the French alps

AbstractSeedling establishment is crucial for elevational advance of tree species above the treeline ecotone, but the characteristics and availability of safe sites for tree regeneration in alpine ecosystems are not well understood. To better understand the potential of treeline ecotones to show infilling or upward shifts, we assessed microsite preferences of the conifers Larix decidua, Pinus uncinata, and Pinus cembra in upper treeline ecotones with different bedrock chemistry in the French Alps. At each of two sites on calcareous and two on siliceous bedrock, we compared microsites of 50 tree individuals to 50 randomly-selected reference microsites, considering substrate, ground cover, topography, and shelter proximity. In addition, we related these characteristics with the health of the individuals. We found that the three species were established in similar microsites, usually with some shelter. The occupied microsites reflected the available microsites in the area, but certain extreme microsite types remained unoccupied. Most individuals had a krummholz form or were bent, while only a small proportion presented signs of recent mechanical damage, desiccation, snow mold or herbivory, independent of microsite characteristics. Our study shows that the availability of safe sites unlikely limits the establishment of these conifers in the studied sites, suggesting that, instead, seed availability may be a major limitation for tree establishment in these alpine-treeline ecotones. Even in safe sites, the harsh alpine conditions limit the development of tree-species individuals into tree stature, but the strong recent length growth observed suggests favorable conditions for eventual tree expansion in and above current treeline ecotones.

The impacts of modelling prescribed vs. dynamic land cover in a high-CO2 future scenario – greening of the Arctic and Amazonian dieback

Abstract. Terrestrial biosphere models are a key tool in investigating the role played by land surface in the global climate system. However, few models simulate the geographic distribution of biomes dynamically, opting instead to prescribe them using remote sensing products. While prescribing land cover still allows for the simulation of the impacts of climate change on vegetation growth and the impacts of land use change, it prevents the simulation of climate-change-driven biome shifts, with implications for the projection of future terrestrial carbon sink. Here, we isolate the impacts of prescribed vs. dynamic land cover implementations in a terrestrial biosphere model. We first introduce a new framework for evaluating dynamic land cover (i.e., the spatial distribution of plant functional types across the land surface), which can be applied across terrestrial biosphere models alongside standard benchmarking of energy, water, and carbon cycle variables in model intercomparison projects. After validating simulated land cover, we then show that the simulated terrestrial carbon sink differs significantly between simulations with dynamic vs. prescribed land cover for a high-CO2 future scenario. This is because of important range shifts that are only simulated when dynamic land cover is implemented: tree expansion into the Arctic and Amazonian transition from forest to grassland. In particular, the projected change in net land–atmosphere CO2 flux at the end of the 21st century is twice as large in simulations with dynamic land cover than in simulations with prescribed land cover. Our results illustrate the importance of climate-change-driven biome shifts for projecting future terrestrial carbon sink.

Participatory Assessment of Agriculture Land and Vegetation Associated Issues and Possible Interventions in Gurage Zone, Ethiopia

Land degradation and depletion of natural forests made agriculture unsustainable and threaten communities and ecosystems as a whole. The objective of this participatory assessment was to identify researchable issues related to agricultural land and vegetation cover in Gurage zone. Accordingly, seven representative districts were selected and from each district two representative kebeles were purposively selected. Focus Group Discussion with farmers, development agents and subject matter specialists and direct observation were important primary sources of information. The survey result depicts in the Gurage zone land degradation, undulating steep slope topography, small and overwhelmed land tenure, inappropriate land use system, cultural landscape mismanagement, deforestation of indigenous trees and expansion of eucalyptus tree, and decreasing enset production are the major identified problems associated with land use and vegetation cover of the study area. In the mixed farming system, enset is produced as a homestead farm and its coverage is decreasing due to disease, lack of processing machines, and shortage of organic matter. Due to the expansion of eucalyptus and land use change, the majority of native trees are disappearing or decreasing in area coverage. Therefore, enset and eucalyptus require suitable policy attention. In the mountainous areas of Gurage; limited land availability, soil degradation, shortage of appropriate farm technologies, water scarcity, lack of knowledge for alpine agriculture and inconvenient topography for mechanized farming machines issues threaten agriculture of area. Despite the fact that there are few attempts to control land degradation; the issue still needs much attention. Appropriate agricultural technologies and knowledge suited for mountain agriculture, dense populations, enset-based farming systems, and small land tenure are important priority research focus areas for future research.

Changes in plant diversity of European lowland forests: Increased homogenization and expansion of shade-tolerant trees

European lowland forests have undergone significant transformations over the past century due to increased canopy closure, eutrophication and plant invasions. The new millennium has brought plant invasions, alien fungal pathogens, and extreme weather conditions, all contributing to forest diebacks. However, the response of plant diversity remains poorly understood. We examined changes in understorey vegetation following a decade (2012–2021) of severe drought in four temperate lowland forest types (dominated by oaks, hornbeams, ashes, and willows) to understand how water availability, canopy openness, and alien fungal pathogens altered diversity in interaction with climate change. Following an exceptionally warm decade, the vegetation exhibited increased homogeneity, with denser shrub and herb layers, likely resulting from diminished tree canopy, particularly in hornbeam and ash forests. Homogenization was manifested by the colonization of plants with conservative life-history strategies (higher leaf dry matter content) to cope with increased drought. Consequently, communities with fewer species increased their species richness, while species-rich communities experienced impoverishment. Conversely, herbaceous species with higher specific leaf area were declining. Compositional changes were particularly prominent in hornbeam and oakwoods at the drier end of moisture gradient where the understorey became dominated by woody plants. Ashwoods were opening up due to ash dieback by fungal pathogens, causing replacement of wetland forbs by nitrophilous forbs and woody saplings. The overall number of species decreased in oakwoods but increased in hornbeam and ashwoods due to increased cover of grasses and shade-tolerant woody species, mostly Acer campestre. Conversely, willow understorey vegetation at the wetter end of the moisture gradient remained relatively stable. Our findings suggest shifts towards more homogeneous vegetation. Conservation plans for managing the remnants of species-rich lowland forests should consider the accelerated environmental changes linked to canopy alterations, biological invasions, and extreme climate events.

Bio-inspired mobile robot design and autonomous exploration strategy for underground special space

PurposeTo make the robot that have real autonomous ability is always the goal of mobile robot research. For mobile robots, simultaneous localization and mapping (SLAM) research is no longer satisfied with enabling robots to build maps by remote control, more needs will focus on the autonomous exploration of unknown areas, which refer to the low light, complex spatial features and a series of unstructured environment, lick underground special space (dark and multiintersection). This study aims to propose a novel robot structure with mapping and autonomous exploration algorithms. The experiment proves the detection ability of the robot.Design/methodology/approachA small bio-inspired mobile robot suitable for underground special space (dark and multiintersection) is designed, and the control system is set up based on STM32 and Jetson Nano. The robot is equipped with double laser sensor and Ackerman chassis structure, which can adapt to the practical requirements of exploration in underground special space. Based on the graph optimization SLAM method, an optimization method for map construction is proposed. The Iterative Closest Point (ICP) algorithm is used to match two frames of laser to recalculate the relative pose of the robot, which improves the sensor utilization rate of the robot in underground space and also increase the synchronous positioning accuracy. Moreover, based on boundary cells and rapidly-exploring random tree (RRT) algorithm, a new Bio-RRT method for robot autonomous exploration is proposed in addition.FindingsAccording to the experimental results, it can be seen that the upgraded SLAM method proposed in this paper achieves better results in map construction. At the same time, the algorithm presents good real-time performance as well as high accuracy and strong maintainability, particularly it can update the map continuously with the passing of time and ensure the positioning accuracy in the process of map updating. The Bio-RRT method fused with the firing excitation mechanism of boundary cells has a more purposeful random tree growth. The number of random tree expansion nodes is less, and the amount of information to be processed is reduced, which leads to the path planning time shorter and the efficiency higher. In addition, the target bias makes the random tree grow directly toward the target point with a certain probability, and the obtained path nodes are basically distributed on or on both sides of the line between the initial point and the target point, which makes the path length shorter and reduces the moving cost of the mobile robot. The final experimental results demonstrate that the proposed upgraded SLAM and Bio-RRT methods can better complete the underground special space exploration task.Originality/valueBased on the background of robot autonomous exploration in underground special space, a new bio-inspired mobile robot structure with mapping and autonomous exploration algorithm is proposed in this paper. The robot structure is constructed, and the perceptual unit, control unit, driving unit and communication unit are described in detail. The robot can satisfy the practical requirements of exploring the underground dark and multiintersection space. Then, the upgraded graph optimization laser SLAM algorithm and interframe matching optimization method are proposed in this paper. The Bio-RRT independent exploration method is finally proposed, which takes shorter time in equally open space and the search strategy for multiintersection space is more efficient. The experimental results demonstrate that the proposed upgrade SLAM and Bio-RRT methods can better complete the underground space exploration task.

Vegetation and glacier dynamics are sensitive to summer (not winter) warming and the evidence for larch refugia in the ‘Northern Pole of Cold’ inferred from sedimentary ancient DNA and geochemistry

Climate seasonality critically influences the functioning and dynamics of ecosystems in continental areas. The ecological importance of winter temperatures on high-latitude vegetation changes has recently been argued to be largely overlooked in comparison to summer temperatures. The Oymyakon region from eastern Siberia, with its strong continentality of extremely cold winters and moderately warm summers, is ideally suited to study the response of past vegetation to seasonal temperature changes based on long ecological time-series. However, few paleorecords are available from this area. The history of regional glacial activity and potential plant refugia since Marine Isotope Stage (MIS) 3 is not well understood. Here, we present geochemical and plant DNA metabarcoding records retrieved from a sediment core from Lake Ulu in the Oymyakon region, which provides detailed information on glacier and vegetation dynamics over the last 43 cal. ka BP. Our results suggest that glacial fluctuations were primarily driven by summer insolation, and Lake Ulu was likely initiated by glacial retreat during MIS 3. The catchment experienced multiple glacial advance/retreat cycles until the Last Glacial Maximum, and the glaciers fully retreated by 20 cal. ka BP. In addition, a tundra-steppe landscape dominated by Dryas, Papaver, Saliceae, and Anthemideae occupied the catchment for most of the time and began to collapse around 19 cal. ka BP following the expansion of trees and shrubs such as Larix, Betula, Alnus, and Vaccinium. Postglacial plant assemblages in the Oymyakon region exhibit a high sensitivity to summer temperature variations, with minimal impact from winter temperatures. This can be explained by the dominance of summer insolation amplitude, extreme continentality, extended plant growing season, and plant genetic adaptation to cold. Notably, our ancient DNA record show the earliest postglacial expansion of larch in eastern Siberia (around 18.6 cal. ka BP), which is likely related to the presence of local refugia. This implies that the Oymyakon region may be one of the earliest sources for larch recolonization and that more research should be implemented to provide insights into larch expansion and migration, and to better predict the future scenarios for Siberian larch forests.

Eucalyptus tree expansion and land use and land cover dynamics in Ethiopia- empirical evidence from Gurage Zone, Ethiopia

Gurage Zone is one of the areas of Ethiopia experiencing rapid land use and land cover (LULC) changes over the past few decades. This study assessed the contribution of eucalyptus expansion to LULC changes based on a detailed household level survey, key informant interviews, focus group discussions and a set of Landsat imageries. Both descriptive statistics and econometric model were employed for the analysis of drivers of eucalyptus plantation. LULC change detection technique was used to examine the changes in LULC over time. This study achieved a mean classification accuracy of 89.17% and 0.83 overall Kappa statistics for the tree LULC maps. The result of descriptive analysis revealed that more than 42% of the sampled households have planted eucalyptus trees on crop land. The study indicated that eucalyptus plantation which was fourth in LULC ranking in 2000 has increased by 68.3% in 2021 to become the second largest land cover next to crop land. On the other hand, from 2010 to 2021, the area covered by crops showed a decline. This indicates eucalyptus tree to be the major cause of LULC change in the study area. The econometric estimation identified the micro-level drivers such as land size and access to market to be important factors influencing eucalyptus plantation. This study suggests that the rapid expansion of eucalyptus plantation on fertile soil requires an immediate policy response in order to balance food crop production and eucalyptus plantation in Gurage Zone.

OLEAtool: An open-source software for morphopalynological research in Olea europaea L. pollen

In this paper we present OLEAtool, a new software tool for palynological research to facilitate morphological analysis and measurements of Olea pollen. OLEAtool is a macro extension for use with ImageJ, an open-access and freely available image analysis software, and was developed as a component of the OLEA-project. This larger project examines olive tree expansion and mosaic landscape formation on the Balearic Islands. Pollen analysis of both fossil and modern grains has been proven useful for characterizing cultivars and therefore an important method for studying olive tree cultivation in the Mediterranean. However, these methods still struggle with distinguishing between wild and cultivated varieties. Traditional morphological analysis of pollen grains can be a difficult and time-consuming task. However, OLEAtool dramatically increases the speed of collecting data on pollen grains, expands the number of variables an analyst can measure, and greatly enhances the replicability of morphological analysis.

Discrete Event Systems Theory for Fast Stochastic Simulation via Tree Expansion

Discrete Event Systems Theory for Fast Stochastic Simulation via Tree Expansion

Urban Ecohydrology: Accounting for Sub‐Grid Lateral Water and Energy Transfers in a Land Surface Model

AbstractAlthough urbanization fundamentally alters water and energy cycles, contemporary land surface models (LSMs) often do not include key urban vegetation processes that serve to transfer water and energy laterally across heterogeneous urban land types. Urban water/energy transfers occur when rainfall landing on rooftops, sidewalks, and driveways is redirected to lawns or pervious pavement and when transpiration occurs from branches overhanging impervious surfaces with the corresponding root water uptake takes place in nearby portions of yards. We introduce Noah‐MP for Heterogenous Urban Environments (Noah‐MP HUE), which adds sub‐grid water transfers to the widely used Noah‐MP LSM. We examine how sub‐grid water transfers change surface water and energy balances by systematically increasing the amount of simulated water transfer for four scenarios: tree canopy expanding over pavement (Urban Tree Expansion), tree canopy shifting over pavement (Urban Tree Shift), and directing impermeable runoff onto surrounding vegetation (Downspout Disconnection) or into an engineered pavement (Permeable Pavement). Even small percentages of sub‐grid water transfer can reduce runoff and enhance evapotranspiration and deep drainage. Event‐scale runoff reduction depends on storm depth, rainfall intensity, and antecedent soil moisture. Sub‐grid water transfers also tend to enhance (reduce) latent (sensible) heat. Results highlight the importance not only of fine‐scale heterogeneity on larger scale surface processes, but also the importance of urban management practices that enhance lateral water transfers and water storage–so‐called green infrastructure–as they change land surface fluxes and, potentially, atmospheric processes. This work opens a pathway to directly integrate those practices in regional climate simulations.

Expanding and invading plant species in sagebrush steppe affect multiple aspects of small‐mammal ecology

AbstractInvasion and expansion of non‐native and native plants have altered vegetation structure in many terrestrial ecosystems. Small mammals influence multiple ecosystem processes through their roles as ecosystem engineers, predators, and prey, and changes to vegetation structure can affect habitat use, community composition, and predator‐prey interactions for this assemblage of wildlife. In the sagebrush (Artemisia spp.) shrublands of the western United States, invasion by non‐native grasses and expansion of native conifer trees beyond their historical range has altered vegetation structure. These changes may potentially affect distributions and interactions of deer mice (Peromyscus maniculatus), which are generalist omnivores, and Columbia Plateau pocket mice (Perognathus parvus), more specialized granivores. To assess the extent to which altered habitat affects small‐mammal density, survival, and home‐range size, we examined these aspects of small‐mammal ecology along a gradient of cheatgrass (Bromus tectorum) invasion and western juniper (Juniperus occidentalis) establishment in sagebrush shrublands in southwestern Idaho, USA. From 2017–2019, we used a spatially explicit mark‐recapture design to examine attributes of small‐mammal ecology along an invasion gradient. We did not find support for an effect of cheatgrass cover on density or survival of either species. Home‐range size of deer mice was 2.3 times smaller in heavier cheatgrass cover (60%) compared to areas with little or no cheatgrass cover. Density of deer mice was highest (5 individuals/ha) in areas with 10% juniper cover and decreased with increasing juniper cover, whereas density of pocket mice was positively influenced by shrub cover. Survival of deer mice declined as juniper stem density increased. Conversely, survival of pocket mice increased with increasing juniper stem density. We found evidence for interspecific interactions between these 2 species, in the form of a density‐dependent effect of deer mice on pocket mouse home‐range size. Home‐range size for pocket mice was 2 times smaller in areas with the highest estimated density of deer mice compared to areas with low densities of deer mice. Our data provides unique information about how small mammals in the sagebrush steppe are affected by expanding and invasive plant species and potential ways that habitat restoration efforts, in the form of conifer removal, may influence small mammals. Understanding the response of small mammals to conifer expansion or removal may shed light on the demographic and numerical responses of other wildlife associated with the sagebrush biome, including predators.

Quad-Rotor Unmanned Aerial Vehicle Path Planning Based on the Target Bias Extension and Dynamic Step Size RRT* Algorithm

For the path planning of quad-rotor UAVs, the traditional RRT* algorithm has weak exploration ability, low planning efficiency, and a poor planning effect. A TD-RRT* algorithm based on target bias expansion and dynamic step size is proposed herein. First, random-tree expansion is combined with the target bias strategy to remove the blindness of the random tree, and we assign different weights to the sampling point and the target point so that the target point can be quickly approached and the search speed can be improved. Then, the dynamic step size is introduced to speed up the search speed, effectively solving the problem of invalid expansion in the process of trajectory generation. We then adjust the step length required for the expansion tree and obstacles in real time, solve the opposition between smoothness and real time in path planning, and improve the algorithm’s search efficiency. Finally, the cubic B-spline interpolation method is used to modify the local inflection point of the path of the improved RRT* algorithm to smooth the path. The simulation results show that compared with the traditional RRT* algorithm, the number of iterations of path planning of the TD-RRT* algorithm is reduced, the travel distance from the starting position to the end position is shortened, the time consumption is reduced, the path route is smoother, and the path optimization effect is better. The TD-RRT* algorithm based on target bias expansion and dynamic step size significantly improves the planning efficiency and planning effect of quad-rotor UAVs in a three-dimensional-space environment.

Coagulation, non-associative algebras and binary trees

We consider the classical Smoluchowski coagulation equation with a general frequency kernel. We show that there exists a natural deterministic solution expansion in the non-associative algebra generated by the convolution product of the coalescence term. The non-associative solution expansion is equivalently represented by binary trees. We demonstrate that the existence of such solutions corresponds to establishing the compatibility of two binary-tree generating procedures, by: (i) grafting together the roots of all pairs of order-compatible trees at preceding orders, or (ii) attaching binary branches to all free branches of trees at the previous order. We then show that the solution represents a linearised flow, and also establish a new numerical simulation method based on truncation of the solution tree expansion and approximating the integral terms at each order by fast Fourier transform. In particular, for general separable frequency kernels, the complexity of the method is linear-loglinear in the number of spatial modes/nodes.

Ambiguity and forest-based bioeconomy: The case of forest fires in the Southern Highlands of Tanzania

The forest-based bioeconomy plays an important role in the transition towards a bio-based economy, also offering solutions for mitigating global climate change. Tanzania has seen a swift expansion of commercial tree growing, especially in the Southern Highlands, since the early 2000s. The increasing demand for timber has attracted both resident inhabitants and small and medium-scale investors from elsewhere to exploit this new investment opportunity. The spread of highly fire-sensitive eucalyptus and pine plantations has radically altered the fire regime in the landscape. The underlying driving forces of forest fires are related to ambiguous and conflicting social processes in land management. We conducted field data collection in the Iringa and Njombe regions to study these uncertainties, mapping a wide array of interpretations related to small and medium-scale plantation forestry in general and to forest fires specifically. Our research methods incorporated individual interviews, focus group discussions (FGDs) and direct observations. The smallholder farmers, urban-based investors, large forest companies and other actors share a common interest in mitigating the impacts of destructive forest fires, yet ambiguity exists in how to manage these fires. This results in a scenario in which both interest in and resources for firefighting are limited. We encourage the co-creation of well-defined, transparent village fire management committees and village fire funds to ensure localised and efficient fire management.