Researchers at the Ecosystems Center have engaged in long-term research on ecosystems ranging from the coast of Massachusetts to the Alaskan tundra. Over the past few decades, ecologists have found that long-term ecological studies are valuable to understanding and predicting ecosystem behavior. Because some ecological changes occur slowly and at non-linear rates, long-term observations and long-term experiments are valuable methods to study how systems change over time and respond to internal and external changes. The Ecosystems Center has been affiliated with three Long Term Ecological Research (LTER) projects from their start: the Arctic LTER (established in 1987), the Harvard Forest LTER (established in 1989), and the Plum Island Ecosystem LTER (established in 1998).
Before the Ecosystems Center was founded in 1975, some ecologists who would later become researchers at the Ecosystems Center participated in two experiments that attracted special attention in long-term ecological research: the International Biological Program (IBP) and the Hubbard Brook ecosystem study. The IBP was an international consortium of scientists who aimed to bring biology and ecology to a global scale. From 1970 to 1975, researchers made observations and conducted experiments in different biomes, or ecological zones, around the world. These studies focused especially on carbon, nitrogen, and phosphorus cycling in ecosystems. Scholars have noted that the IBP funding and programs trained a generation of ecosystem ecologists. Ecosystems Center researchers John Hobbie and Gus Shaver both participated in the IBP’s Tundra Biome research program in Alaska.
The Hubbard Brook ecosystem study, on the other hand, was a much smaller site than the IBP. The ecologists Gene E. Likens and F. Herbert Bormann at Dartmouth College started this experiment in 1963. Likens and Bormann attracted a set of researchers to study differences between and changes in the seven watersheds contained at the Hubbard Brook. This study was seen as an ideal example of ecosystems ecology in the 1970s. Ecosystems Center researchers Jerry Melillo and Bruce Peterson were both involved in the Hubbard Brook study area for a period of time.
In 1980, the US National Science Foundation (NSF) created the Long Term Ecological Research program to specifically support long-term ecological studies. The NSF holds sporadic proposal competitions for new LTERs. Every six years, researchers leading already-funded LTERs must reapply for funding. The NSF LTER program aimed to support the study of biological growth and processes at multiple scales and locations, as well as the movements of nutrients through ecosystems. Although there is a high degree of variation in the locations, methods, and overall research programs of each LTER research site, together they constitute a research network that has provided incredible insights into our understanding of how ecosystems change.
A consistent finding of the three Ecosystems Center-affiliated LTER programs was that short-term study results were often not useful for making long-term predictions of the future behavior of ecosystems. Feedback between different ecological processes, climate variability, and organismal adaptation all contributed to the difficulty in making long-term predictions based on short-term studies. Researchers learned that instead of extrapolating short-term results, better predictions could be made using process-based mathematical models. Process-based models incorporate ecological principles, such as the flow of energy in a system, to predict behavior of a system over time. Researchers have used data from the LTER sites to develop, calibrate, and validate mathematical models of ecosystem processes. These models can then help make longer-term predictions, or to test experiments that would be difficult to conduct in the field.