Document: JOH-3-35-2

Woody species phenology, 1990-1999, at Harvard Forest, Petersham, MA.

O'KEEFE, J.F.* and S.A.JOHNSON

Harvard Forest, Harvard University, Petersahm, MA, U.S.A. ¹

Abstract:
Each spring since 1990 bud break, leaf development, flowering and fruit development have been observed on two to five individuals of 33 native woody species, at 3 to 7 day intervals from April through June. Weekly observations of leaf color and drop have been made from early September through leaf fall since 1993. All individuals are located along a transect near the Harvard Forest headquarters in Petersham, MA, at about 350 meters elevation. Individuals within a species span a variety of size classes and habitats (forest, swamp margin, field edge). There is a continuous sampling record of gas exchange and comprehensive climate data at an eddy-flux correlation tower located approximately 1 km from the transect. Depending on species, we have observed a range of 14 to 20 days in the timing of bud break and 17 to 29 days in the timing of 75% leaf development between the earliest (1991, 1993, 1998) and latest (1992, 1997) years. Leaf fall has been much less variable (5 to 11 days). Leafout timing explains much of the interannual variation in carbon uptake measured at the tower. In some springs plants have developed consistently early or late throughout the season, in other years plant development has varied in response to changing climatic conditions. Combining phenology and gas exchange measures may improve our ability to model carbon budgets in a changing climate.

Keywords: phenology, bud break, leaf development, leaf fall, carbon budget, climate change

This abstract is being presented at: 10:30 AM in session:
GAS EXCHANGE