Finding a method for simplified biomass measurements on Sahelian grasslands

Sammanfattning: Traditional measurements for determination of aboveground biomass (AGB) are widely used in ecological studies. However, they are labor demanding and time consuming, why this study performed on a grassland in Senegal has focused on finding a simplified AGB estimation method that could be applied on larger areas in the Sahel. The brightness values in the visible spectral range of digital camera images (DCIs) have been tested for correlation with traditional AGB using three already established indices leading to r2 values of 0.57, 0.56 and 0.43 (all attained p=<0.0001) when including all four measurement occasions, and r2 values of 0.63, 0.61 and 0.51 (p=<0.0001) when excluding the last occasion, which had a high amount of yellowing grasses. Some of the DCIs were also visually interpreted after performing an unsupervised image classification in two groups. This did not seem to reveal any new insights in the usage of DCIs as estimation of AGB. Grass height, on the other hand, showed a higher correspondence with AGB (r2=0.79 and p<=0.0001 for all occasions and r2=0.70 and p<=0.0001 when excluding the last occasion). In addition to the higher correlation, measuring grass height is also the least expensive and the quickest of the methods investigated in this study and can hopefully be applied on larger areas by local farmers.