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ABSTRACT Resource development in the form of cyclical commercial logging activities results in a short period of often severe land disturbance followed by a prolonged phase of recovery. The monitoring of catchment sediment yield gives some indication of the gross erosion processes within the catchment as a result of the disturbance and may also effectively measure any ameliorative processes. Studies in Ulu Segama, Sabah, East Malaysia, recorded significant increases in stream suspended sediment loads as a result of logging. Stream loads were derived from a combination of daily sample measurements and storm event sampling using automated liquid samplers. Measured loads were then compared to computed loads from sediment discharge rating sets derived from the actual samples. Application of these ratings in the disturbed catchment initially underestimated sediment loads; however, a progressive overestimation of loads occurred as the catchment vegetation recovered. When using sediment rating curves as a tool to measure catchment erosion rates in disturbed environments, considerable caution has to be used. Vegetation recovery is reflected in the rapid recovery of stream water quality, making it necessary to continually review the rating. [ABSTRACT FROM AUTHOR]

The procedure describes a simple and functional method of using a commercial spreadsheet (Lotus 1-2-3) to calculate water and sediment yields from measured or given data sets. Suspended sediment concentrations are located on a storm hydrograph and concentrations for unsampled points on the hydrograph are estimated using the principle that thechange in concentration between two sampled points will be proportional to the change in discharge between the same two points. The relationships are then solved by a cross-correlation equation using simpleformulae in the form of triangle-square equations to calculate waterand sediment yields between each sample time. The technique is applied to a 51 month data set from a long-term monitoring programme assessing the impacts of commercial logging operations in Sabah, East Malaysia. Yields for the monitoring period derived by the spreadsheet technique are compared with results from the application of more traditional discharge-sediment rating techniques. In the undisturbed catchment, yields derived from some rating equations compare favourably withthe spreadsheet technique. However, in the disturbed catchment, rating techniques proved less applicable because of the continuously changing nature of the catchment in relation to vegetation recovery, exacerbating variation and scatter in the data set. The application of the spreadsheet technique provides detailed information at an individual storm level; however, working with the method on long-term discharge records requires a significant commitment of time as compared to the straightforward application of rating equations. [ABSTRACT FROM AUTHOR]

Unprecedented deforestation and forest degradation in recent decades have severely depleted the carbon storage in Borneo. Estimating aboveground biomass (AGB) with high accuracy is crucial to quantifying carbon stocks for Reducing Emissions from Deforestation and Forest Degradation-plus implementation (REDD+). Airborne Light Detection and Ranging (LiDAR) is a promising remote sensing technology that provides fine-scale forest structure variability data. This paper highlights the use of airborne LiDAR data for estimating the AGB of a logged-over tropical forest in Sabah, Malaysia. The LiDAR data was acquired using an Optech Orion C200 sensor onboard a fixed wing aircraft. The canopy height of each LiDAR point was calculated from the height difference between the first returns and the Digital Terrain Model (DTM) constructed from the ground points. Among the obtained LiDAR height metrics, the mean canopy height produced the strongest relationship with the observed AGB. This single-variable model had a root mean squared error (RMSE) of 80.02 t ha-1 or 22.31% of the mean AGB, which performed exceptionally when compared with recent tropical rainforest studies. Overall, airborne LiDAR did provide fine-scale canopy height measurements for accurately and reliably estimating the AGB in a logged-over forest in Sabah, thus supporting the state's effort in realizing the REDD+ mechanism. [ABSTRACT FROM AUTHOR]