Measuring plant biomass remotely using drones in arid landscapes

Measurement of variation in plant biomass is essential for answering many
ecological and evolutionary questions. Quantitative estimates require
plant destruction for laboratory analyses, while field studies use
allometric approaches based on simple measurement of plant
dimensions. We estimated the biomass of individual shrub-sized
plants, using a low cost Unmanned Aerial System (drone), enabling rapid
data collection and non-destructive sampling. We compared volume
measurement (a surrogate for biomass) and sampling time, from the simple
dimension measurements and drone, to accurate laboratory-derived biomass
weights. We focused on three Australian plant species which are
ecologically important to their floodplain and terrestrial ecosystems:
porcupine grass Triodia scariosa, Queensland
bluebush Chenopodium auricomum and lignum Duma
florulenta. Estimated volume from the drone was more accurate than simple
dimension measurements for porcupine grass and Queensland bluebush,
compared to estimates from laboratory analyses but, not for lignum. The
latter had a sparse canopy, with thin branches, few vestigial leaves and a
similar colour to the ground. Data collection and analysis consistently
required more time for the drone method than the simple dimension
measurements, but this would improve with automation.