Chengrui Liao

Bio: Chengrui Liao is an academic researcher from Nanjing Forestry University. The author has contributed to research in topics: Plateau & Restoration ecology. The author has an hindex of 4, co-authored 8 publications receiving 53 citations.

A Novel Tree Height Extraction Approach for Individual Trees by Combining TLS and UAV Image-Based Point Cloud Integration

Abstract: Research Highlights: This study carried out a feasibility analysis on the tree height extraction of a planted coniferous forest with high canopy density by combining terrestrial laser scanner (TLS) and unmanned aerial vehicle (UAV) image–based point cloud data at small and midsize tree farms. Background and Objectives: Tree height is an important factor for forest resource surveys. This information plays an important role in forest structure evaluation and forest stock estimation. The objectives of this study were to solve the problem of underestimating tree height and to guarantee the precision of tree height extraction in medium and high-density planted coniferous forests. Materials and Methods: This study developed a novel individual tree localization (ITL)-based tree height extraction method to obtain preliminary results in a planted coniferous forest plots with 107 trees (Metasequoia). Then, the final accurate results were achieved based on the canopy height model (CHM) and CHM seed points (CSP). Results: The registration accuracy of the TLS and UAV image-based point cloud data reached 6 cm. The authors optimized the precision of tree height extraction using the ITL-based method by improving CHM resolution from 0.2 m to 0.1 m. Due to the overlapping of forest canopies, the CSP method failed to delineate all individual tree crowns in medium to high-density forest stands with the matching rates of about 75%. However, the accuracy of CSP-based tree height extraction showed obvious advantages compared with the ITL-based method. Conclusion: The proposed method provided a solid foundation for dynamically monitoring forest resources in a high-accuracy and low-cost way, especially in planted tree farms.

Effect of topography and protecting barriers on revegetation of sandy land, Southern Tibetan Plateau.

Abstract: Revegetation on sandy land has attracted worldwide attention, especially on the extremely fragile alpine eco-region of the Tibetan Plateau. However, the effectiveness of revegetation and its controlling factors have rarely been reported. We collected plant growths and species composition from seven field sites in 2011 and conducted a follow-up random investigation in 2016. The indicators, including richness and diversity, were used to compare the differences among these sites based on redundancy and cluster analyses. The results indicated that plant growth has different characteristics in different land types. The distribution and growth of Artemisia sphaerocephala, Artemisia younghusbandii and Heteropappus gouldii varied with topography, and the crown widths of A. sphaerocephala were 100.6 cm × 87.2 cm on barchan dune and 26.0 cm × 25.4 cm on moving sandy land at valley slopes. These species are likely the pioneer plants for revegetation on sandy land. It seems that sand-protecting barriers play an important role in revegetation. The stone and plastic checkerboard barriers increase plant diversity, while straw barrier promotes the plant growth. These findings provide useful guidance to the ongoing vegetation recovery on sandy land, an important component of the Project on Construction and Protection of Ecological Security Barriers on the Tibetan Plateau.

Can ecological restoration improve soil properties and plant growth in valley-slope sand dunes on southern Tibetan Plateau?

Abstract: Global warming poses a serious threat to the alpine grassland on the Tibetan Plateau. Ecological restoration is an effective measure for adapting to climate change and controlling desertification. ...

Recent Advances in Unmanned Aerial Vehicles Forest Remote Sensing—A Systematic Review. Part II: Research Applications

Abstract: Forest sustainable management aims to maintain the income of woody goods for companies, together with preserving non-productive functions as a benefit for the community. Due to the progress in platforms and sensors and the opening of the dedicated market, unmanned aerial vehicle–remote sensing (UAV–RS) is improving its key role in the forestry sector as a tool for sustainable management. The use of UAV (Unmanned Aerial Vehicle) in precision forestry has exponentially increased in recent years, as demonstrated by more than 600 references published from 2018 until mid-2020 that were found in the Web of Science database by searching for “UAV” + “forest”. This result is even more surprising when compared with similar research for “UAV” + “agriculture”, from which emerge about 470 references. This shows how UAV–RS research forestry is gaining increasing popularity. In Part II of this review, analyzing the main findings of the reviewed papers (227), numerous strengths emerge concerning research technical issues. UAV–RS is fully applicated for obtaining accurate information from practical parameters (height, diameter at breast height (DBH), and biomass). Research effectiveness and soundness demonstrate that UAV–RS is now ready to be applied in a real management context. Some critical issues and barriers in transferring research products are also evident, namely, (1) hyperspectral sensors are poorly used, and their novel applications should be based on the capability of acquiring tree spectral signature especially for pest and diseases detection, (2) automatic processes for image analysis are poorly flexible or based on proprietary software at the expense of flexible and open-source tools that can foster researcher activities and support technology transfer among all forestry stakeholders, and (3) a clear lack exist in sensors and platforms interoperability for large-scale applications and for enabling data interoperability.

Recent Advances in Unmanned Aerial Vehicle Forest Remote Sensing—A Systematic Review. Part I: A General Framework

Abstract: Natural, semi-natural, and planted forests are a key asset worldwide, providing a broad range of positive externalities. For sustainable forest planning and management, remote sensing (RS) platforms are rapidly going mainstream. In a framework where scientific production is growing exponentially, a systematic analysis of unmanned aerial vehicle (UAV)-based forestry research papers is of paramount importance to understand trends, overlaps and gaps. The present review is organized into two parts (Part I and Part II). Part II inspects specific technical issues regarding the application of UAV-RS in forestry, together with the pros and cons of different UAV solutions and activities where additional effort is needed, such as the technology transfer. Part I systematically analyzes and discusses general aspects of applying UAV in natural, semi-natural and artificial forestry ecosystems in the recent peer-reviewed literature (2018–mid-2020). The specific goals are threefold: (i) create a carefully selected bibliographic dataset that other researchers can draw on for their scientific works; (ii) analyze general and recent trends in RS forest monitoring (iii) reveal gaps in the general research framework where an additional activity is needed. Through double-step filtering of research items found in the Web of Science search engine, the study gathers and analyzes a comprehensive dataset (226 articles). Papers have been categorized into six main topics, and the relevant information has been subsequently extracted. The strong points emerging from this study concern the wide range of topics in the forestry sector and in particular the retrieval of tree inventory parameters often through Digital Aerial Photogrammetry (DAP), RGB sensors, and machine learning techniques. Nevertheless, challenges still exist regarding the promotion of UAV-RS in specific parts of the world, mostly in the tropical and equatorial forests. Much additional research is required for the full exploitation of hyperspectral sensors and for planning long-term monitoring.

Research on Landscape Pattern Construction and Ecological Restoration of Jiuquan City Based on Ecological Security Evaluation

Abstract: Jiuquan City is a typical ecologically fragile area in the arid areas of Northwest China, and unreasonable human activities directly affect the regional ecological security. Scientifically, it is necessary to construct an ecological landscape pattern on the basis of ecological security evaluation. This paper selected evaluation factors based on the perspective of “environmental base and human interference”, used spatial principal component analysis (SPCA) to comprehensively evaluate the regional landscape ecological security, and used the minimum cumulative resistance (MCR) model to construct the regional ecological security pattern. The results show that the overall ecological security level of the study area is low, and the area with a moderate safety level and below is 122,100 km2, accounting for 72.57% of the total area of the study area. The total area of the identified ecological source area is 6683 km2, the spatial distribution is extremely uneven, and it is extremely concentrated in the southern region; 32 ecological corridors with a total length of 3817.8 km are identified, of which corridor NO. 1–4 run through the Qilian Mountains, 11 oasis areas, and 14 nature reserves. The length of ecological corridors is 1376.1 km, accounting for 36.04% of the total. Forty-two ecological nodes are identified, and the central corridor area is more distributed; four ecological restoration zones are divided, including an ecological conservation zone, ecological improvement zone, ecological control zone, and ecological restoration zone, with areas of 34,380.3 km2, 61,884.4 km2, 21,134.4 km2, and 50,648.3 km2, respectively. Through the delineation of the urban ecological network pattern composed of source areas, corridors, and nodes, as well as the delineation of ecological restoration zones, the ecological security level of the study area will be effectively improved. Furthermore, a new method of ecological restoration zoning will be used, hoping to provide a useful reference for improving the quality of the ecological environment in arid areas and optimizing the spatial pattern of the land.