Scientists agree that Earths climate is changing. However, there remains uncertainty about the rate at which temperatures will rise, how precipitation will change, and for how long the warming will continue. To date, several experiments have advanced our understanding of how ecosystems will respond to changes in temperature or precipitation, but few have studied both factors simultaneously. In addition, almost all experiments that have warmed ecosystems have examined the effect of one sudden and sustained temperature increase. In reality, climate will change gradually, and the endpoint of this change is unknown. Will the processes and properties of communities and ecosystems respond linearly to changes in temperature, or are there important threshold temperatures that could be reached? To what extent does an ecosystems response to warming depend on precipitation patterns? The Boston-Area Climate Experiment is designed to answer these questions. The experiment will warm plots of an old-field ecosystem by five different amounts, while subjecting the plots to three different precipitation regimes (wet, ambient, and dry). Researchers will measure responses of several variables, including growth of herbs, grasses, and tree seedlings.
This experiment will improve our understanding of how ecosystems and the services they provide will respond to climate change. Some of these ecosystem responses will determine how the planets biota will affect the rate of climate change. The experiment will also have a broad community impact, both directly, as a public education installation, and by involving K-12 students and teachers, student educators, and university students.
Researchers used this grant to construct the Boston-Area Climate Experiment (BACE) in Waltham, Massachusetts. Using overhead heaters and sprinklers, the experiment simulates twelve possible future climates; it warms plots of an old-field ecosystem by four different amounts (up to about 7 degrees Fahrenheit), while subjecting groups of plots to three different precipitation regimes (by either allowing all rain and snow to fall on the plots, removing half of incoming precipitation, or supplementing incoming precipitation during the growing season). With funding from this and other grants, researchers measured responses of several variables, including growth of herbs, grasses, and tree seedlings, and the processing of dead organic matter by microorganisms.? On their own, warming and changes in precipitation led to changes in the composition of the herbaceous plant community, but had relatively little effect on the overall growth of herbaceous plants. However, in the driest treatment, warming suppressed plant growth and reduced the number of plant species present. This result suggests that, in a warmer world, plant production will become more sensitive to interannual changes in precipitation. In general, our results indicate that old-field ecosystems in this region are unlikely to produce more forage in response to climate change, and are also unlikely to slow climate change by storing additional carbon. Warming is known to accelerate decomposition of organic matter under most conditions. However, in some cases, susceptibility of organic matter to decomposition can be affected by the conditions in which it is grown. Research at the BACE showed that growth conditions (particularly drought and warming combined) dramatically affect the chemical composition of red maple leaves. Leaves grown under warm, water-stressed conditions produced much greater amounts of condensed tannins; chemicals that would likely slow decomposition and release of nutrients in the soil. Research at the BACE has also shown that warming affects the microbial decomposition of organic material in soils differently depending on the season. In some seasons, particularly when the soils are quite dry, warming has little effect on decomposition rates. In other seasons, warming can have a much larger effect. To accurately represent the release of carbon from soils under future conditions, models of the Earth system must be able to replicate this pattern. Another pattern that models should replicate (although most do not) is the attenuation of the temperature response of plants over time. Currently, the Earth system models used for climate change projections accurately represent short-term responses of photosynthesis and respiration to temperature, but most do not have the capability to simulate commonly observed longer-term adjustments. Work at the BACE on this topic led to recommendations for how to implement longer-term plant responses to temperature and CO2 increases into these models. As part of the grant, the lead investigator taught a course in which students developed a public display about climate change, which was later installed next to the BACE. This display has been viewed by thousands of individuals (~10-15k) and won an award from the Massachusetts Horticultural Society. The experiment has been featured on local television news stations and in the Boston Globe and other local papers. Hundreds of visitors have toured the site, including annual groups of middle- and high-school science teachers (~150 teachers total, including a field trip of teachers attending the National Science Teachers Association annual meeting) and classes and groups of faculty from Lasell University, Babson College, and Bradley University. Researchers from ten institutions now collaborate at the site, including three smaller, local, non-research-intensive institutions. In the lead investigator’s lab, ten undergraduates have conducted research experiences at the site and have participated (officially and unofficially) in an NSF-funded UMass Boston summer program providing research experiences for undergraduates. Ten additional undergraduates have worked at the site, and undergraduates and high school students from six additional institutions have volunteered and/or worked at the site. The BACE has hosted research comprising all or part of seven Ph.D. theses. Data from the project have contributed to an international database on precipitation experiments and a large international analysis of soil moisture effects being conducted in Europe. The initial funding from this grant primarily supported construction and maintenance of the Boston-Area Climate Experiment. Supplemental awards to this project supported undergraduate research, and research by investigators from small, non-research-intensive institutions. Additional funding to the lead investigator and researchers at other institutions supported many of the research activities accomplished at this experiment. At the time of this writing, the BACE continues to run, and many additional research projects are being conducted and/or completed.
