Human hands leave prominent ecological footprints

Early human activity has left a greater footprint on today's ecosystem than previously thought, says a CHANS-Net scientist working with colleagues at the University of Pittsburgh and in the multidisciplinary Long Term Ecological Research (LTER) Network, created by the National Science Foundation to investigate ecological processes over long temporal and broad spatial scales. Highlighted in the June issue of BioScience, the study shows how historic human actions caused changes in nature that continue to reverberate throughout present-day ecosystems.

In the article, researchers take a retrospective look at the impact of human activity on LTER Network sites spanning states from Georgia to New Hampshire and propose methods for measuring the effects of such activity. The study of legacy effects is important because it provides insights into how today's actions can affect tomorrow's ecological systems, said CHANS-Net member Daniel Bain, coprincipal investigator at the Baltimore Ecosystem Study LTER Network site and assistant professor of geology and planetary science at the University of Pittsburgh. Bain noted that decision makers at all levels, including those creating policy, need historical information about ecosystems to make more effective environmental policies.

In a democracy, said Bain, a diverse group of stakeholders -- such as outdoor enthusiasts like Trout Unlimited, fiscal watchdog groups such as Common Cause, and individual landowners -- needs this kind of data to effectively engage in the management of common resources.

"Increasingly, we propose to manage our ecosystems with sophisticated and complicated strategies," Bain said. "For example, we are attempting to manage agricultural runoff by changing how streams and floodplains are arranged. However, while designing these strategies, we tend to address the most recent impacts rather than the entire history of impacts. This can lead to wasted effort and misuse of relatively limited resources."

Legacy effects from human activities are all around us, said Bain, but few people ever give them a thought. For example, urban systems accumulate a lot of human-made materials, some of which have large ecological footprints and will ultimately leave a legacy. Bain cited the example of lead, which has been banned from gasoline and paint in the United States for several decades but can remain in soils for much longer periods of time.

"We should be careful about growing food close to roads or near old houses," he cautioned.

In agriculture, areas that were plowed hundreds of years ago react differently to contemporary acid deposition from air pollutants when compared with adjacent unplowed areas. Similarly, extensive use of cement may add substantial amounts of calcium to urban soils, although the ecological impact of this practice is not yet fully understood, Bain added.

Indeed, many landscapes that provide baseline ecological data for evaluating environmental change were structured in part by previous human interactions, such as settlements and agricultural practices. To make sense of the observed ecological patterns on such landscapes, Bain said, it's important to know something of the history of the processes acting to shape those patterns. A recent example of the need for historical data associated with the impact of humans is the debate over global warming and its associated climate change -- the legacy of increased emissions of carbon dioxide and other greenhouse gases over millennia, but hugely accelerated since the industrial revolution and, especially, over the past several decades.

Bain pointed out that without a systematic collection of data recorded by the LTER Network, the broader geographical patterns of legacy effects would be much more difficult to detect. For example, scientists have discovered that recently glaciated areas have much less dirt accumulation than unglaciated areas. When Europeans first arrived in the eastern United States and dramatically changed local agricultural practices, eroded soil ultimately found its way into waterways. However, the glaciated areas produced less dirt, leaving less of an erosional signal in contrast to unglaciated areas, which lost more dirt and left such erosional legacies as buried valley bottoms and filled harbors.

"In terms of policy, the management of glaciated and unglaciated areas requires different approaches," Bain said.

"Although LTER sites have decades of data to draw from, we do not necessarily capture these changes, even with our best multidecade studies," Bain continued. "It's hard to know what we might have been able to understand now had the LTER Network been established six or nine decades ago instead of three."