Browsing by Subject "Biomass"
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- ItemOpen AccessEvaluating the performance of multi-rotor UAV-Sfm imagery in assessing simple and complex forest structures: comparison to advanced remote sensing sensors(2021) Onwudinjo, Kenechukwu Chukwudubem; Smit, JulianThe implementation of Unmanned Aerial Vehicles (UAVs) and Structure‐from‐Motion (SfM) photogrammetry in assessing forest structures for forest inventory and biomass estimations has shown great promise in reducing costs and labour intensity while providing relative accuracy. Tree Height (TH) and Diameter at Breast Height (DBH) are two major variables in biomass assessment. UAV-based TH estimations depend on reliable Digital Terrain Models (DTMs), while UAV-based DBH estimations depend on reliable dense photogrammetric point cloud. The main aim of this study was to evaluate the performance of multirotor UAV photogrammetric point cloud in estimating homogeneous and heterogeneous forest structures, and their comparison to more accurate LiDAR data obtained from Aerial Laser Scanners (ALS), Terrestrial Laser Scanners (TLS), and more conventional means like manual field measurements. TH was assessed using UAVSfM and LiDAR point cloud derived DTMs, while DBH was assessed by comparing UAVSfM photogrammetric point cloud to LiDAR point cloud, as well as to manual measurements. The results obtained in the study indicated that there was a high correlation between UAVSfM TH and ALSLiDAR TH (R2 = 0.9258) for homogeneous forest structures, while a lower correlation between UAVSfM TH and TLSLiDAR TH (R2 = 0.8614) and UAVSfM TH and ALSLiDAR TH (R2 = 0.8850) was achieved for heterogeneous forest structures. A moderate correlation was obtained between UAVSfM DBH and field measurements (R2 = 0.5955) for homogenous forest structures, as well as between UAVSfM DBH and TLSLiDAR DBH (R2 = 0.5237), but a low correlation between UAVSfM DBH and UAVLiDAR DBH (R2 = 0.1114). This research has demonstrated that UAVSfM can be adequately used as a cheaper alternative in forestry management compared to more highcost and accurate LiDAR, as well as traditional technologies, depending on accuracy requirements.
- ItemOpen AccessNo adverse signs of the effect of environmental change on tree biomass in the Knysna forest during the 1990s(2006) Midgley, J J; Seydack, AWe analysed the growth of all trees greater than 10 cm diameter at breast height in 108 plots of 0.04 ha each in an unharvested nature reserve in the Knysna forest for the period 1991-2001. Gross growth rates (in-growth plus growth of survivors) of trees were extremely slow (<1%) and thus the forest is extremely sensitive to changes in mortality of large trees. Over the 10-year study period, total basal area and biomass increased by 2%, in part because overall stem density increased by 1.2%. Rainfall in the 1990s was slightly below the longterm mean for the study area. At this stage, therefore, the Knysna forest biomass is not showing a negative response to environmental change.