Springtime Blooms Seen Earlier Now Than In The Past, Say Boston University Biologists

What has influenced this rush to flower? Primarily temperature, says Richard Primack, a BU biology professor and head of the research team. Since 1885, Boston's mean annual temperature has increased 1.5 degrees Celsius or nearly 3 degrees Fahrenheit. According to Primack's team, this increase in mean temperature, especially in the months February through May, has influenced the shift in flowering times.

In addition to its scientific insights, the study may provide a model for public participation in climate change research. The relatively low-tech, data-from-the-community protocol used by the team might open such studies to participation by botanical gardens, zoos, museums, or even individuals who, over the years, have carefully collected and tended records on how biological organisms respond to their environment.

"It's an untapped resource that could have widespread applications," says Abraham Miller-Rushing, a graduate student on the BU research team. "There's always a pressure to find out what's happened in the past so as to better understand what's happening today. This is a new and different way to find out what's happened."

Assisted by BU undergraduates Carolyn Imbres and Daniel Primack and by Peter Del Tredici, a senior research scientist at the Arboretum, the researchers combed herbarium records dating back to 1885 to determine when plants had flowered in the past. They focused on records for 229 plants, all of which are still alive and blooming in the Arboretum.

By comparing current flowering dates of the woody plants selected with their past flowering dates recorded in the Arboretum's herbarium, the researchers found a significant trend toward earlier flowering. On average, they found the plants flowered eight days earlier during the period 1980 to 2002 than they did 100 years ago.

The data also showed the plants' flowering times were quite sensitive to relatively small shifts in temperature, advancing 3.9 days per 1 C of temperature change. The team's analyses showed the plants were most responsive to temperature changes in the months before and during flowering -- February through May. In general, throughout the past century, the warming temperatures were found to have caused the Arboretum's plants to flower about five days earlier.

Changes to Boston's temperature, however, did not explain completely the trend toward earlier flowering over time. According to the team, the results suggest that more localized effects, such as the size and age of the plants and conditions in and around the Arboretum, including warming caused by roads and buildings, probably contributed another three days to the observed earlier flowering times over the years.

The researchers conclude that it is viable to use existing collections from herbaria, museums, or other such institutions around the world to measure regional effects of climate change on phenological events. Analyses of such data could allow scientists to clarify the extent and character of the variation in natural responses local species have to climate change. Such analyses also could help improve predictions of the effects that future climate change might have on biological communities.

The full paper describing these findings will appear in an upcoming issue of the American Journal of Botany.

The Arnold Arboretum is managed by Harvard University. Located in Jamaica Plain, Mass., it is the oldest arboretum in the U.S. It has a collection of 15,000 living woody plants and an herbarium of 80,000 specimens, many of which were gathered from plants still growing on the grounds.

Faculty in the Biology Department at Boston University conduct research on issues related to ecology, behavior, and evolution; physiology, endocrinology, and reproduction; neurobiology; marine biology; and cell and molecular biology. The department is part of the College of Arts and Sciences, one of 17 schools and colleges that make up Boston University, the nation's fourth-largest independent university.