New opportunities for an old method: using fluorescent colours to measure seed dispersal.
Seed dispersal is of high applied relevance as it governs colonization processes in rare species and during plant invasions. Seed tracking is a powerful approach to analysing dispersal processes and usually requires seed tagging. Marking diaspores with fluorescent colours is a promising tagging method, but comes with several technical limitations. We analysed the durability of different colours, associated changes in weight gain and lift-off velocity, visibility under ultraviolet (UV) light and recapture rates for different diaspore types (samaras, plumed diaspores and small, round diaspores). Weight gain ranged from 20% to 61% and loss of colour after 1 month of outdoor exposure ranged from 1% to 31%, with airbrush technique offering the best retention of colour, followed by pigment colour application and common aerosol spray treatment. Seed tagging with aerosol spray paint or by airbrush technique increased the lift-off velocity of samaras by 6-7%. Good results for recapture experiments with fluorescently marked diaspores can be achieved using UV torches: large diaspores are visible at distances of up to 8 m in open habitats, and small diaspores up to 3.5 m. Recapture rates on asphalt and grass lawn were close to 100% for large diaspores, and ranged from 85% to 90% for other diaspores. An area of c. 0.1 ha could by thoroughly searched within 1 h. Pigment colour application is suitable for large diaspores (>3 cm in length). Aerosol spray application is easy but induces a high weight gain and is practicable only for use over short sampling periods. Airbrush application requires special equipment but combines the advantages of low weight gain and high durability and is even appropriate for plumed diaspores. Synthesis and applications. Our study revealed strengths and weaknesses of different methods of tagging diaspores with fluorescent colours. Quantifying the changes that colouring has on seed traits helps to reduce data bias, especially in modelling. The choice of the appropriate tagging method combined with the use of modern UV torches provides considerable methodological advance in studying seed dispersal over long distances and could improve studies on colonization processes of endangered species and on plant invasions.