The Boston Area Climate Experiment (BACE) in Waltham, Massachusetts, exposes an old-field community to a factorial combination of warming and precipitation treatments. The BACE is set up as a complete randomized block design with four temperature treatments (from ambient to +4^oC) and three precipitation treatments (ambient, -50%, and +50%). We planted four seedlings of each of four dominant New England tree species (Acer rubrum, Betula lenta, Quercus rubra, and Pinus strobus) into subplots in April/May 2008. We measured the growth, survival, and fall phenological changes of all tree seedlings. We also measured the species richness, species evenness, and aboveground biomass production of the old-field herbaceous community by harvesting plant biomass in July and October 2008. All warming and watering treatments were operational by July 2008, in time for the second half of the growing season. We analyzed responses of plant growth and phenology to continuous gradients of temperature and soil moisture at the end of the season.

Results/Conclusions

Late season herbaceous biomass was highest in plots with high early season biomass, high average soil moisture, and high soil temperatures. Herbaceous species richness decreased slightly with warming. Warming extended the time between first signs of fall coloration and full leaf drop for all deciduous tree seedlings. Among these deciduous species, the period of leaf drop was shortest for Q. rubra, slightly longer in A. rubrum, and longest in B. lenta, and increased significantly with warming for B. lenta. Tree mortality was highest among P. strobus and Q. rubra seedlings, in dry treatments, and higher in warmed than in ambient temperature plots. Preliminary results from the BACE suggest that interactive climate effects will play an important role in structuring future ecosystems.