Digital Terrestrial Photogrammetry to Enhance Field-Based Forest Inventory across Stand Conditions

This paper explores the application of forest inventory to design silvicultural operations and its implementation to community forests. Four-time series forest inventory data (2005, 2010, 2013 and 2016) of Terai community forests were analysed, focusing on the type and size of tree removals from the forests. In addition, content analysis of the management plans of the forests was carried out and consultations were held with key informants. Though the forest inventory was prepared during the preparation of management plans, the results did not provide proper guidance on the selection of silvicultural operations, which were decided without a clear definition of the management objectives. They were very generic and largely ignored site-specific forest stand conditions. Most commonly practised silvicultural operations were cleaning and selective harvesting, which were similar for all forest blocks, though they varied in respect of forest stand conditions. The time series analysis of the inventory data showed that pole-sized trees were consistently removed in all four periods and emphasis was on extracting good quality trees without considering its effects on the stand. The study concludes that the current forest inventory is not very relevant in making a choice about silvicultural operations and the current practices might cause economic and ecological losses. Hence, we argued for identifying minimum forest management requirement necessary for the sustainable forest management that the silvicultural operations should be decided based on the management objectives and conditions of the forest, considering the ecological and economic value of the forest. Banko JanakariA Journal of Forestry Information for Nepal Special Issue No. 4, 2018, Page : 65-75

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Extraction of Sample Plot Parameters from 3D Point Cloud Reconstruction Based on Combined RTK and CCD Continuous Photography

Remote Sensing ◽

10.3390/rs10081299 ◽

2018 ◽

Vol 10 (8) ◽

pp. 1299 ◽

Cited By ~ 12

Author(s):

Jincheng Liu ◽

Zhongke Feng ◽

Liyan Yang ◽

Abdul Mannan ◽

Tauheed Khan ◽

...

Keyword(s):

Forest Inventory ◽

Point Cloud ◽

Forest Canopy ◽

Measurement Data ◽

Sample Plot ◽

3D Point Cloud ◽

Automatic Data ◽

3D Point Clouds ◽

Measurement Efficiency ◽

Terrestrial Photogrammetry

Enriching forest resource inventory is important to ensure the sustainable management of forest ecosystems. Obtaining forest inventory data from the field has always been difficult, laborious, time consuming, and expensive. Advances in integrating photogrammetry and computer vision have helped researchers develop some numeric algorithms and methods that can turn 2D (images) into 3D (point clouds) and are highly applicable to forestry. This paper aimed to develop a new, highly accurate methodology that extracts sample plot parameters based on continuous terrestrial photogrammetry. For this purpose, we designed and implemented a terrestrial observation instrument combining real-time kinematic (RTK) and charge-coupled device (CCD) continuous photography. Then, according to the set observation plan, three independent experimental plots were continuously photographed and the 3D point cloud of the plot was generated. From this 3D point cloud, the tree position coordinates, tree DBHs, tree heights, and other plot characteristics of the forest were extracted. The plot characteristics obtained from the 3D point cloud were compared with the measurement data obtained from the field to check the accuracy of our methodology. We obtained the position coordinates of the trees with the positioning accuracy (RMSE) of 0.162 m to 0.201 m. The relative root mean square error (rRMSE) of the trunk diameter measurements was 3.07% to 4.51%, which met the accuracy requirements of traditional forestry surveys. The hypsometrical measurements were due to the occlusion of the forest canopy and the estimated rRMSE was 11.26% to 11.91%, which is still good reference data. Furthermore, these image-based point cloud data also have portable observation instruments, low data collection costs, high field measurement efficiency, automatic data processing, and they can directly extract tree geographic location information, which may be interesting and important for certain applications such as the protection of registered famous trees. For forest inventory, continuous terrestrial photogrammetry with its unique advantages is a solution that deserves future attention in the field of tree detection and ecological construction.

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