How well do first flowering dates measure plant responses to climate change? The effects of population size and sampling frequency
Article first published online: 24 SEP 2008
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
Journal of Ecology
Volume 96, Issue 6, pages 1289–1296, November 2008
How to Cite
Miller-Rushing, A. J., Inouye, D. W. and Primack, R. B. (2008), How well do first flowering dates measure plant responses to climate change? The effects of population size and sampling frequency. Journal of Ecology, 96: 1289–1296. doi: 10.1111/j.1365-2745.2008.01436.x
- Issue published online: 15 OCT 2008
- Article first published online: 24 SEP 2008
- Received 15 March 2008; accepted 23 July 2008; Handling Editor: Richard Bradshaw
- climate change;
- date of first flowering;
- global warming;
- Rocky Mountain Biological Laboratory;
- sampling frequency
- 1First flowering dates are occurring earlier than they did in the past in many locations around the world. It is sometimes assumed, implicitly or explicitly, that the changes in first flowering dates describe the phenological behaviour of entire populations. However, first flowering dates represent one extreme of the flowering distribution and may be susceptible to undesirable confounding effects.
- 2We used observations of flowering in Colorado and Massachusetts to test whether changes in population size and sampling frequency affect observations of first flowering dates.
- 3We found that the effect of population size on first flowering dates depended on location. Changes in population size were strongly related to the dates on which first flowering was observed in Massachusetts but not in Colorado. The lack of a significant effect in Colorado may reflect the rapid onset of spring after snowmelt and fixed developmental schedules of the plants at this sub-alpine site, or the scale of the plots sampled during the study.
- 4We also found that changes in sampling frequency can influence observed changes in first flowering dates and other aspects of the flowering distribution. Similar to the effect of declines in population size, lower sampling frequency caused later observations of first flowering. However, lower sampling frequency, if maintained consistently throughout a study, did not significantly affect estimates of changes in flowering dates over time or in response to climate.
- 5Synthesis. Researchers should consider the effects of changes in population size and sampling frequency when interpreting changes in first flowering dates. In some cases, past results may need to be reinterpreted. When possible, researchers should observe the entire flowering distribution or consider tracking peak or mean flowering dates to avoid the confounding effects of population size and sampling frequency.