Comparing fruiting phenology across two historical datasets: Thoreau’s observations and herbarium specimens

Abstract

Background and Aims Fruiting remains under-represented in long-term phenology records, relative to leaf and flower phenology. Herbarium specimens and historical field notes can fill this gap, but selecting and synthesizing these records for modern-day comparison requires an understanding of whether different historical data sources contain similar information, and whether similar, but not equivalent, fruiting metrics are comparable with one another. Methods For 67 fleshy-fruited plant species, we compared observations of fruiting phenology made by Henry David Thoreau in Concord, Massachusetts (1850s), with phenology data gathered from herbarium specimens collected across New England (mid-1800s to 2000s). To identify whether fruiting times and the order of fruiting among species are similar between datasets, we compared dates of first, peak and last observed fruiting (recorded by Thoreau), and earliest, mean and latest specimen (collected from herbarium records), as well as fruiting durations. Key Results On average, earliest herbarium specimen dates were earlier than first fruiting dates observed by Thoreau; mean specimen dates were similar to Thoreau’s peak fruiting dates; latest specimen dates were later than Thoreau’s last fruiting dates; and durations of fruiting captured by herbarium specimens were longer than durations of fruiting observed by Thoreau. All metrics of fruiting phenology except duration were significantly, positively correlated within (r: 0.69–0.88) and between (r: 0.59–0.85) datasets. Conclusions Strong correlations in fruiting phenology between Thoreau’s observations and data from herbaria suggest that field and herbarium methods capture similar broad-scale phenological information, including relative fruiting times among plant species in New England. Differences in the timing of first, last and duration of fruiting suggest that historical datasets collected with different methods, scales and metrics may not be comparable when exact timing is important. Researchers should strongly consider matching methodology when selecting historical records of fruiting phenology for present-day comparisons.

Wildflower phenological escape differs by continent and spring temperature

“…Previously reported sensitivities were determined in separate studies using either observational data 7 , 8 or long-term observation-based weather station data 27 . The general consistency between our findings suggests that phenology data from herbarium collections are good indicators of patterns in natural systems 29 – 31 , a point supported by a recent study of phenological sensitivity derived from herbaria and from observed citizen science data 32 . These herbarium-based results provide evidence that phenological sensitivity differs across the temperate forest biome (but see ref.…”

Wildflower phenological escape differs by continent and spring temperature

“…Previously reported sensitivities were determined in separate studies using either observational data 10,24 or long-term observation-based weather station data 37 . The general consistency between our findings suggests that phenology data from herbarium collections are good indicators of patterns in natural systems 39–41 , a point supported by a recent study of phenological sensitivity derived from herbaria and from observed citizen science data 42 . These herbarium-based results provide some of the first evidence that phenological sensitivity differs across the temperate forest biome (but see ref 43 for evidence of differences in response to warming and chilling accumulation).…”

A comparison of herbarium and citizen science phenology datasets for detecting response of flowering time to climate change in Denmark

“…Our inability to detect a relationship between the first flowering day of year and temperature could be due to an inability to account for these factors, along with a lower range of temperatures and another environmental variability in comparison with the other two datasets. Statistical methods have been proposed for combining the first observation of the season with peak observations in phenology studies, however, the practical value of such approaches has not been settled (Pearse et al 2017;Miller et al 2021).…”