ORIGINAL PAPER One man, 73 years, and 25 species. Evaluating phenological responses using a lifelong study of first flowering dates K. Bolmgren & D. Vanhoenacker & A. J. Miller-Rushing Received: 21 December 2011 / Revised: 26 May 2012 / Accepted: 27 May 2012 / Published online: 30 June 2012 # ISB 2012 Abstract Phenological shifts linked to global warming reflect the ability of organisms to track changing climatic conditions. However, different organisms track global warming differently and there is an increasing interest in the link between phenological traits and plant abundance and distribution. Long-term data sets are often used to estimate phenological traits to climate change, but so far little has been done to evaluate the quality of these esti- mates. Here, we use a 73-year long data series of first flowering dates for 25 species from north-temperate Sweden to evaluate (i) correlations between first flowering dates and year for different time periods and (ii) linear regression models between first flowering date and mean monthly temperatures in preceding months. Furthermore, we eval- uate the potential of this kind of data to estimate the phenological temperature sensitivities (i.e. number of days phenological change per degree temperature change, β 60 ) in such models. The sign of the correlations between first flowering dates and year were highly incon- sistent among different time periods, highlighting that estimates of phenological change are sensitive to the specific time period used. The first flowering dates of all species were correlated with temperature, but with large dif- ferences in both the strength of the response and the period(s) of the year that were most strongly associated with phenolog- ical variation. Finally, our analyses indicated that legacy data sets need to be relatively long-term to be useful for estimating phenological temperature sensitivities (β 60 ) for inter-specific comparisons. In 10-year long observation series only one out of 24 species reached ≥80 % probability of estimating temper- ature sensitivity (β 60 ) within a ±1 range, and 17 out of 24 species reached ≥80 % probability when observation series were 20 years or shorter. The standard error for β 60 ranged from 0.6 to 2.0 for 10-year long observation series, and 19 out of 24 species reached SE < 1 after 15 years. In general, late flowering species will require longer time series than early flowering species. Keywords Accuracy . Climate change . Flowering time . Monitoring . Phenology . Temperature sensitivity Introduction Considering the vast variation in life histories represented in most ecological communities, we expect directional change in an environmental parameter to affect coexisting species in Electronic supplementary material The online version of this article (doi:10.1007/s00484-012-0560-8) contains supplementary material, which is available to authorized users. K. Bolmgren (*) Department of Biology, Theoretical Population Ecology and Evolution Group, Lund University, SE-22362 Lund, Sweden e-mail: kjell.bolmgren@slu.se K. Bolmgren Swedish National Phenology Network, Swedish University of Agricultural Sciences, Asa, Sweden D. Vanhoenacker Department of Botany, Stockholm University, 106 91 Stockholm, Sweden D. Vanhoenacker Swedish Natural History Museum, Box 50007, 104 05 Stockholm, Sweden A. J. Miller-Rushing National Park Service, Schoodic Education and Research Center and Acadia National Park, PO Box 177, Bar Harbor, ME 04609, USA Int J Biometeorol (2013) 57:367–375 DOI 10.1007/s00484-012-0560-8