Lesser Celandine (Ranunculus ficaria) is an invasive early spring ephemeral, which has been steadily expanding its range since initial introductions around 1877. Lesser Celandine (LC) has perennial tubers and some subspecies produce vegetative bulbils which can float in water allowing it to easily disperse downstream of source populations. Increases in temperature due to climate change may cause shifts in the peak flowering time and life cycle length of LC causing a disruption of efforts to manage the species on sensitive sites. The objective was to examine herbarium records to compare flowering dates over time and determine if increases in temperature are causing earlier peaks in LC flowering due to climate change indicating the potential for life cycle shifts seen in other perennial forbs.
To examine shifts in peak flowering time, 77 herbarium records from two localities were included, 52 from Southeast PA representing the time period from 1892-1998 and 25 from Central MD representing 1948-1993. All specimens were positively identified as LC and were in full flower. Julian date of collection for each specimen was collected and subject to regression for a line of best fit to assess change in peak flowering over time.
Results/Conclusions
LC populations in Southeast Pennsylvania flowered an average of one day earlier for every 17 years since the first record, equating to an average of 7 days earlier in 2012 than in 1892. In the shorter time period from 1948-1993, Central Maryland LC populations flowered an average of one day earlier for every 4.4 years since the first record. This indicates a more recent warming trend in the last half of the 20th century which is supported by previous studies.
The average annual temperature increased ~0.5C between 1895 and 1997 and it appears LC is responding to increasing temperature by flowering earlier. According to the Hadley Centre Model this region could experience another 1.4C increase by 2030. If LC flowering continues to respond to temperature increases with earlier and earlier flowering, it is possible that life cycle shifts may occur as seen in other perennial forbs. Typically an early spring ephemeral, the LC life cycle may shorten, having implications for management of invasive populations. There is already a brief window for management and a requirement for multi-year applications for control due to perennial root structures. Any changes in life cycle length or peak flowering times will likely affect management decisions.