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RapidEye multispectral imagery is effective in vegetation assessment. This research intends to investigate the utility of using 5-m-resolution RapidEye-5 imagery combined with a machine learning algorithm to detect and map important forage fibre biochemicals such as neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin in an African tropical grassland. These fibre biochemicals are significant indicators of the palatability of forage digested by grazing ungulates. Analysis was conducted on 140 grass samples collected at plot level and then correlated and mapped using two competent tree ensemble modelling techniques. Results showed that the random forest (RF) method successfully mapped NDF, ADF and lignin with R2 values ranging between .67 and .74. In comparison, stochastic gradient boosting (SGB) was implemented as an alternative method, which produced very similar R2 values ranging between .65 and 0.72. Overall, the results showed that multispectral remote sensing can detect and map key forage fibre biochemicals in a grassland environment. [ABSTRACT FROM AUTHOR]

Coryphodema tristis is a wood-boring insect, indigenous to South Africa, that has recently been identified as an emerging pest feeding on Eucalyptus nitens, resulting in extensive damage and economic loss. Eucalyptus plantations contributes over 9% to the total exported manufactured goods of South Africa which contributes significantly to the gross domestic product. Currently, the distribution extent of the Coryphodema tristis is unknown and estimated to infest Eucalyptus nitens compartments from less than 1% to nearly 80%, which is certainly a concern for the forestry sector related to the quantity and quality of yield produced. Therefore, the study sought to model the probability of occurrence of Coryphodema tristis on Eucalyptus nitens plantations in Mpumalanga, South Africa, using data from the Sentinel-2 multispectral instrument (MSI). Traditional field surveys were carried out through mass trapping in all compartments (n = 878) of Eucalyptus nitens plantations. Only 371 Eucalyptus nitens compartments were positively identified as infested and were used to generate the Coryphodema tristis presence data. Presence data and spectral features from the area were analysed using the Maxent algorithm. Model performance was evaluated using the receiver operating characteristics (ROC) curve showing the area under the curve (AUC) and True Skill Statistic (TSS) while the performance of predictors was analysed with the jack-knife. Validation of results were conducted using the test data. Using only the occurrence data and Sentinel-2 bands and derived vegetation indices, the Maxent model provided successful results, exhibiting an area under the curve (AUC) of 0.890. The Photosynthetic vigour ratio, Band 5 (Red edge 1), Band 4 (Red), Green NDVI hyper, Band 3 (Green) and Band 12 (SWIR 2) were identified as the most influential predictor variables. Results of this study suggest that remotely sensed derived vegetation indices from cost-effective platforms could play a crucial role in supporting forest pest management strategies and infestation control. [ABSTRACT FROM AUTHOR]