The Big Picture
The National Science Foundation began to make a serious investment in ecological research in the 1960s and in 1980 launched its pioneering Long-Term Ecological Research (LTER) program. Currently more than 1,000 researchers are working at twenty-four ecologically distinct LTER sites, where studies often last for decades.
A temperate coniferous forest teeming with hemlocks, red cedar, and firs. An Arctic tundra animated by icy lakes and headwater streams. An East Coast city interlaced with deciduous trees, houses, and parks. A tallgrass prairie. A tropical rainforest. A coastal estuary. A fiery desert.
For every ecological domain on Earth, there seems to be an LTER site devoted to unmasking its secrets. Each location hosts an average of eighteen different principal investigatorsoften affiliated with nearby universitieswho head up various studies that last anywhere from the few years it may take a graduate student to complete her thesis to the decades needed to understand the ongoing effects of, say, fire on the prairie. The sites themselves are much larger than the average experimental plot, ranging in size from the 3,000 acres under continuous study at the Harvard Forest LTER to the 5 million acres that make up the Central Arizona/Phoenix site.
The rationale behind the LTER program is based on several conclusions that environmental scientists reached by the end of the 1970s. One conclusion is that changes in many of the most important ecological processes, such as nutrient levels in the soil, occur slowly. Relatively rare events such as flash floods have a major impact on an ecosystem, but they can only be properly studied if researchers have, in effect, anticipated the occurrences with ongoing studies. Another conclusion is that many ecological processes vary greatly from year to year; only a long-term view can discern inherent patterns. Finally, the kind of long-term, multidisciplinary databases established by LTER researchers are critical for providing a context in which shorter-term studies can be understood.
Although each site boasts its own array of studies designed for that particular ecological system, all studies undertaken at an LTER site must address one or more of what ecologist Steward Pickett, project director for the Baltimore LTER, calls "the holy commandments of LTER." These commandments come in the form of five questions that are fundamental to how any ecosystem functions: What controls the growth of plants? What controls the populations of plants and animals? What happens to the organic matter that plants produce? What controls the flow of nutrients and water in the system? How do disturbances affect the system?
While these five themes provide focus to individual LTER studies, they also allow researchers from very different locales to do an "apples-to-apples" comparison of their data so that even larger lessons can be learned. Clues to how an ecosystem functions are more readily apparent when scientists can compare how the same process works across ecologically diverse sites. For example, the LTER program allows researchers to observe how nutrients travel through two different types of grasslands and how grasslands differ from forests in terms of nutrient flow. To help make these kinds of comparisons, representatives from each LTER site meet formally twice a year and also communicate regularly via email and the LTER program's Web site.
Key to the success of the LTER approach, of course, are long-term funding and large-scale areas. With the proper time and space, "you can do riskier experiments," says NSF's LTER program director Scott Collins, "or you can do experiments that take a long time to have an effect, or big experiments that require a lot of space, or ones that need a certain kind of team."
Long-term studies also provide an increasingly important baseline of how the environment worksa baseline against which crucial management decisions can be measured. "As the sites are studied longer," Collins says, "their value increases [because] the findings can be applied to policy and conservation issues."