The use of phenology models in plant conservation programmes: the establishment of the earliest cutting date for the wild daffodil Narcissus radiiflorus Original Research Article

A phenology model was developed for the wild daffodil Narcissus radiiflorus growing in alpine meadows. The model is based on temperature-dependent growth rates and on the rate summation method, and represents the development from 1 January to full bloom, i.e. phase I, and from full bloom to 50% fruit maturity, i.e. phase II. Published data obtained in the laboratory and observations made at different altitudes near the villages of Seewis i. P. and Fanas in the canton of the Grisons, Switzerland, were used for estimating model parameters. To conserve N. radiiflorus the first cut should be delayed until completion of phase II. The time in days between full bloom and 50% fruit maturity at different altitudes was simulated by using 16 years of temperature data. These data were recorded at a nearby weather station and adapted to different altitudes by assuming a 0.5°C decrease in temperature for a 100 m increase in altitude. Significant differences between the length of phase II at different altitudes were found. However, in the main areas where Narcissus occurs, a subset of equal mean duration of phase II could be identified. This is explained by the compensation of the altitude-dependent temperature decrease caused by the general increase in temperature during phase II, i.e. in June and July. For this subset the logistic function was fitted to the frequency distribution of the number of days required to complete phase II. When accepting a 10% risk of mowing too early, the first cut should be delayed by 34 days after full bloom. The 34-day rule is considered a more adequate and efficient method to plan meadow management than the method actually used based on predefined calendar days.