《Research Shows How Prehistoric Humans Impacted the Everglades》
Excavations show the role early humans played in forming the tree islands that dot the river of grass.
Dotting the landscape of Everglades National Park are teardrop-shaped elevations of hardwood trees (or hammocks) named, “tree islands.” The significance of tree islands as the only dry ground has long been acknowledged, but their significance also lies beneath the earth, as archeological findings from a dig in 2010 present data that prehistoric humans played a significant role in the formation of tree islands, and in turn, the archeological discoveries should be considered in current Everglades restoration models.
“Tree islands are the nucleus of the Everglades,” said Traci Ardren, chair and professor of anthropology at the University of Miami’s College of Arts and Sciences. “They are rich habitats for plants, birds, and other animals and provide higher ground and stability for the Everglades drainage system.”
Ardren says Everglades restoration models used by scientists and government entities do not take human factors into account, specifically prehistoric human occupation.
“This research provides an example of how humans were involved in the way tree islands were formed, so if we want to have the best models we can for Everglades restoration, we need first to understand the original formation of tree islands,” she said.
Ardren’s research, entitled “Prehistoric human impact on tree island lifecycles in the Florida Everglades,” was published in the journal The Holocene and illustrates the archeological discoveries from a tree island known as the Booth site. There are currently hundreds of archeological sites in the Everglades, and almost every tree island has evidence of prehistoric human occupation; unfortunately, most tree islands have not been archeologically investigated.
In 1998, a team visited the Booth site and uncovered archeological artifacts of pre-Columbian human occupation, but according to Ardren, the research was minimal. When she and her team visited the site in 2010, there was extensive digging and richer analysis of the findings. “The activities on the site were not that different from the 1998 visit, but it was more about the conclusions we drew from the data collected,” she added.
Overall, archeological research in the Everglades is very minimal due to the belief that the terrain is very challenging; these perceptions may contribute to the lack of archeological research and excavation.
“We do not think of the Everglades as a place where there were people living for thousands of years,” Ardren explains.
“Tree islands in the Everglades certainly present a nutrient anomaly in the otherwise oligotrophic wetland. Currently, there are three major hypotheses explaining this nutrient enrichment: nutrient enrichment via plant transpiration; bird guano as birds nest in the islands; and pre-Columbian human occupation,” said Cooper Fellow and Professor of Biology Leonel Sternberg. “Indeed, there is evidence for all three factors and Dr. Ardren’s research points out that these hypotheses are not mutually exclusive, and they all could be part of the explanation why tree islands are nutrient sinks.”
Ardren says the main point of her research is to contribute quantifiable data on the human influence in tree island formation, which is a major factor ignored in most Everglades restoration research and models. She hopes her research will generate discussion among scientists today who are working on Everglades restoration in many disciplines with the outcome to collaborate and take into account the human impact on the landscape, not just in the 21st century but thousands of years into the past.
Over the last two decades, the Earth has seen an increase in foliage around the planet, measured in average leaf area per year on plants and trees. Data from NASA satellites shows that China and India are leading the increase in greening on land. The effect stems mainly from ambitious tree planting programs in China and intensive agriculture in both countries.
Credits: NASA Earth Observatory
The world is literally a greener place than it was 20 years ago, and data from NASA satellites has revealed a counterintuitive source for much of this new foliage: China and India. A new study shows that the two emerging countries with the world’s biggest populations are leading the increase in greening on land. The effect stems mainly from ambitious tree planting programs in China and intensive agriculture in both countries.
The greening phenomenon was first detected using satellite data in the mid-1990s by Ranga Myneni of Boston University and colleagues, but they did not know whether human activity was one of its chief, direct causes. This new insight was made possible by a nearly 20-year-long data record from a NASA instrument orbiting the Earth on two satellites. It’s called the Moderate Resolution Imaging Spectroradiometer, or MODIS, and its high-resolution data provides very accurate information, helping researchers work out details of what’s happening with Earth’s vegetation, down to the level of 500 meters, or about 1,600 feet, on the ground.
Taken all together, the greening of the planet over the last two decades represents an increase in leaf area on plants and trees equivalent to the area covered by all the Amazon rainforests. There are now more than two million square miles of extra green leaf area per year, compared to the early 2000s – a 5% increase.
“China and India account for one-third of the greening, but contain only 9% of the planet’s land area covered in vegetation – a surprising finding, considering the general notion of land degradation in populous countries from overexploitation,” said Chi Chen of the Department of Earth and Environment at Boston University, in Massachusetts, and lead author of the study.
An advantage of the MODIS satellite sensor is the intensive coverage it provides, both in space and time: MODIS has captured as many as four shots of every place on Earth, every day for the last 20 years.
“This long-term data lets us dig deeper,” said Rama Nemani, a research scientist at NASA’s Ames Research Center, in California’s Silicon Valley, and a co-author of the new work. “When the greening of the Earth was first observed, we thought it was due to a warmer, wetter climate and fertilization from the added carbon dioxide in the atmosphere, leading to more leaf growth in northern forests, for instance. Now, with the MODIS data that lets us understand the phenomenon at really small scales, we see that humans are also contributing.”
China’s outsized contribution to the global greening trend comes in large part (42%) from programs to conserve and expand forests. These were developed in an effort to reduce the effects of soil erosion, air pollution and climate change. Another 32% there – and 82% of the greening seen in India – comes from intensive cultivation of food crops.
Land area used to grow crops is comparable in China and India – more than 770,000 square miles – and has not changed much since the early 2000s. Yet these regions have greatly increased both their annual total green leaf area and their food production. This was achieved through multiple cropping practices, where a field is replanted to produce another harvest several times a year. Production of grains, vegetables, fruits and more have increased by about 35-40% since 2000 to feed their large populations.
How the greening trend may change in the future depends on numerous factors, both on a global scale and the local human level. For example, increased food production in India is facilitated by groundwater irrigation. If the groundwater is depleted, this trend may change.
“But, now that we know direct human influence is a key driver of the greening Earth, we need to factor this into our climate models,” Nemani said. “This will help scientists make better predictions about the behavior of different Earth systems, which will help countries make better decisions about how and when to take action.”
The researchers point out that the gain in greenness seen around the world and dominated by India and China does not offset the damage from loss of natural vegetation in tropical regions, such as Brazil and Indonesia. The consequences for sustainability and biodiversity in those ecosystems remain.
Overall, Nemani sees a positive message in the new findings. “Once people realize there’s a problem, they tend to fix it,” he said. “In the 70s and 80s in India and China, the situation around vegetation loss wasn’t good; in the 90s, people realized it; and today things have improved. Humans are incredibly resilient. That’s what we see in the satellite data.”
This research was published online, Feb. 11, 2019, in the journal Nature Sustainability.
For news media:
Members of the news media interested in covering this topic should get in touch with the science representative on the NASA Ames media contacts page.
Author: Abby Tabor, NASA's Ames Research Center, Silicon Valley
Last Updated: Feb. 12, 2019
Editor: Abigail Tabor
ESHA Research makes The Food Processor and Genesis R&D - the most widely-used nutrition software programs in the world - in addition to providing the nutrition industry with web-based applications and the most comprehensive food/nutrient databases available. Our customers rely on ESHA for accuracy, timeliness and unparalleled service.