Here we describe the standardized protocol used by the Canadian Airborne Biodiversity Observatory (CABO) to measure carbon fractions in leaf samples, using the ANKOM2000 Fiber Analyzer. Prior to the analysis, leaf samples are oven-dried, and then ground with a cyclone mill (2-mm screen). Then, carbon fractions are measured using a sequential digestion procedure to measure neutral detergent fiber (NDF, acid detergent fiber (ADF), acid detergent lignin (ADL). Finally, the residues are ashed in a muffle furnace to determine inorganic recalcitrant materials. This protocol is based on the manufacturer's protocols.