Phenology is one of the best indicators to observe plant responses to climate change and predict future changes in plant communities. Choosing indicator species to monitor biological responses to climate change may be improved if herbarium specimens are combined with ongoing monitoring efforts to understand phenological responses over longer periods. We analyzed herbarium specimen data from Colorado’s alpine region, as alpine areas are predicted to be especially sensitive to climate change. We assessed phenological patterns in relation to temperature and precipitation for 287 species and Growing Degree Days (GDD) for 235 species.
Results/Conclusions
Average low temperature, maximum GDD, and average precipitation increased over the study period. As temperature and GDD increased, phenology advanced, but as precipitation increased, phenology was delayed. Even with this variability of environmental responses, a significant trend of earlier flowering appeared when all species were analyzed together. Of the species that showed significantly earlier flowering dates, they advanced on average more than 39 days over the 61 years of the study. When assessing only specimens of species monitored in a national program (USA National Phenology Network), we found that these species showed similar trends to the entire dataset. When selecting species for ongoing monitoring efforts, herbarium specimens are an important resource to incorporate historical patterns into assessments of climate change and phenological drivers.