Raised-Fields Back from the Dead?

With Shrinking Forests and Expanding Savannas, Amazonia’s Future May Benefit from Past Lessons

Prehistoric Amazonian farmers suppressed rather than encouraged grassland fires, according to a report in Monday’s PNAS (Proceedings of the National Academy of Sciences). Researchers claim that applying the indigenous farming techniques offers a route to sustainably develop the region while simultaneously reducing carbon emissions.

From 800 to 500 years ago, farmers on the French Guiana coast of South America 

Map from Iriarte et al. 2012

mounded muck from the seasonally flooded savannas to form raised-fields. This farming strategy “could have supported large and concentrated populations,” according to the study. Suppressing fires from breaking out prevented wasting valuable soil chemicals. While the fields are still visible today, they were abandoned roughly at 1500 AD with the arrival of Europeans.

Europeans’ arrival in 1500 meant big changes for lowland South America, which includes both expansive rainforests and grasslands. The “Columbian Exchange” of crops, animals, and people between New World and Old also included infectious diseases which tragically lowered indigenous populations by as much as 95%. When the farmers died, the raised-fields they tended – which require enormous maintenance and care – fell out of use with the new, European-style farmers.

The scientists, from institutions like the University of Exeter and the Natural History Museum of Utah, used a core drilled from a coastal swamp next raised-fields and archaeological sites to reconstruct the environment from the last 2,150 years. By analyzing pollen, charcoal, and phytoliths (silica from plant structures that can identify specific plants) in the core, they noticed three distinct periods in land use.

The first phase, from approximately 2,150 years ago to 1200 AD, features pollen and phytoliths from a classic savanna environment. There is little charcoal from burning. In the next phase, from ~1200 AD to 1500 AD, new savanna plants arrive along with evidence of maize cultivation. This is when raised-field building was occurring, as also observed in the archaeological record. At 1500 AD, however, raised-field construction stops and the swamp core shows steadily increasing amounts of charcoal.

This research is particularly relevant to debates about deforestation, which, as it progresses, leaves behind new (but steadily degraded) savanna environments in its path. The charcoal produced from slash and burn agriculture – the cause of much of Amazonian deforestation because it is practiced on a massive scale – and the charcoal from burning savannas leads to increased carbon emissions. Couple this feedback loop of more carbon emitted (by burning) and less taken in (by trees) with grassland being used for methane-producing cattle, and you have a pretty short shrift for future inhabitants of the planet and lowland South America.

Adapted from Iriarte et al. (2012), the top half of the image shows the study area after it was burned. Below, different grass species occupy the original raised-fields (in light green).


That serves to explain why media coverage of the article and its authors themselves emphasize the potential these farming techniques offer to the savannas’ sustainable development. The University of Exeter’s press release quotes lead author Dr. José Iriarte (a respectable Amazonian archaeologist, by the way) on the possibilities:

             “This ancient, time-tested, fire-free land use could pave the way for the modern     implementation of raised-field agriculture in rural areas of Amazonia. Intensive raised-field agriculture can become an alternative to burning down tropical forests for slash and burn agriculture by reclaiming otherwise abandoned and new savannah ecosystems created by deforestation. It has the capability of helping curb carbon emissions and at the same time provide food security for the more vulnerable and poorest rural populations.”

As Dr. Iriarte explains, there’s a lot to conditionally hope for from this research. However, the economic and political realities of deforestation and land-use in Brazil and Amazonia should temper that optimism.

Bolivians have tried raised-field before. Clark Erickson (another respectable South American archaeologist) and numerous NGOs encouraged indigenous farming communities to reconstruct the fields in the late 1980s, but despite initial success, most of those farmers went back to the plow by the mid-90s. Why? Raised-fields, as the article and news release frequently mention, are honestly and truly labor-intensive. What’s more, raised-fields are not productive enough to justify that intensity. The article cites experiments that claim raised-fields can yield between 2 and 5.8 tons/hectare of maize (that’s corn, folks, and the data was collected archaeologically). Compare that with the average US yield of 8.93 tons/hectare and Brazil’s of 3.38, according to 2004/5 estimates from the USDA. From an economic perspective, subsistence farmers will find the initial construction and continuous maintenance of their raised-fields an unwieldy substitute for the slash and burn they practice right now.

Most agriculture in Brazilian savannas (natural or recently deforested) is practice by large agribusinesses that produce soybeans or farm cattle. Fortunately for sustainable development, these companies have the necessary equipment to efficiently create raised-fields on a large scale. But, their ease of harvest (imagine a combine harvesting crops in a field of speed bumps) and usefulness in cattle ranching (in a semi-submerged field) make them a prospect that Brazilian businesses will likely pass by.

Still, for all the hype, the prospect of a productive, sustainable, and low-carbon producing Amazon is a worthy goal worth pursuing for any sustainability entrepreneurs in Brazil and researchers there and elsewhere. In addition, it’s a great example of how archaeology can be made relevant in issues of great relevance to people other than archaeologists – and 800 year old farmers.

Burmese Python: Another invasive species threatens conservation efforts in the Everglades

Throughout the 1980s raccoons in the Everglades National Park were such a nuisance, a special program had to be initiated to keep them under control. Yet today the number of raccoons has decreased by over 90 percent. What is causing the raccoon and other mammals in the park to decline? An invasive python imported by the pet trade.

The Burmese Python (Python molurus bivittatus), a large constrictor from South East Asia, can grow up to 19 feet in length making them one of the largest snakes in the world. Pythons are a popular pet but since they are so large they can be difficult to take care of or simply grow too big to be kept as pets by inexperienced owners. Such people often will release their snake into the wild instead of putting in the effort to find it a new home.  In most areas in the US, these released snakes or escapees would simply die. However, the Florida everglades are a perfect home for them. The pythons released in Florida mingled with some that escaped during the destruction of Hurricane Andrew have thrived and formed their own population. The snakes are now breeding in the wild and have established a range spanning thousands of kilometers including the Everglades National Park (1.5 million acres).

Baby burmese python (above) are small at first but grow quickly. Inexperienced owners that purchase them when small often find they can't care for the adults.

Severe mammal decline coincides with proliferation of invasive Burmese pythons in Everglades National Park, a recent study lead by Michael Dorcas, is the first study to show these snakes are having an ecological effect on their new home. To try to determine the impact the pythons are having on native species, researchers compared road survey data from before and after the introduction of the python. Road surveys are a simple procedure where researchers drive down certain roads and record the number of observed live and road kill species. The surveys in this study were conducted at night on Main Park Road and Research Road in the Everglades National Park.

Their data showed that prior to the introduction of the pythons, native mammals like raccoons, opossums, and rabbits were the most common animals found in Everglades National Park. Data from 2003-2011, after the introduction of the python, showed a 99.3% decrease in raccoons, 98.9% decrease in in opossums, 94.1% decrease in white tailed deer, and 87.5% decrease in bobcats. Additionally, no rabbits or foxes could be found in the pythons’ range.

Adult pythons can weigh up to 200 pounds and eat prey as large as alligator and deer.

Scientists believe that the pythons are responsible for the reduced mammal populations for several reasons. The timing of the pythons’ introduction to the area coincides with the beginning of the mammal disappearances.  Data also showed that in areas where the pythons were only introduced recently, the populations of native vertebrates had not declined as much as in areas where they have been long established. Most of the species that have been declining are known to be prey of the pythons. Since the number of snakes has been increasing, it makes sense that the missing mammals are feeding the growing population. Some people have suggested that the decline in these species could be attributed to a disease. However experts disagree, arguing that the likelihood of a disease affecting such a broad range of mammals in separate families is extremely low. Scientists have also ruled out human interference as the cause since the Everglades National Park is protected from hunting and trapping.

Because of the effects of this and other studies, the Burmese Python has been labeled as an invasive species in the United States. The term invasive species refers to a non-native group of animals that adversely affects the habitat they invade. Other invasive snakes have been implicated in native vertebrate decline in the past. In the case of the Brown Tree Snake, it took more than 30 years for their impact in Guam to be recognized. Cases like these need to be learned from so that similar mistakes are not made. Large scale efforts need to be made to remove the python now before irrevocable damage occurs.

Since so many common species are declining, researchers are concerned that rare species may be on the menu as well. In addition to eating medium sized mammals, the pythons are consuming endangered species like the Wood Stork and the Key Largo Woodrat along with (can you believe it?) American Alligators and White tailed deer. Conservationists fear that since the pythons are already consuming such large prey, they may expand their diet to include the highly endangered Florida panther. This species is already so threatened that adding a powerful predator like the python may wipe it out completely. Since the pythons have been known to consume leopards in Asia, steps need to be taken to ensure the panthers’ safety.

In Asia, the python feed on wild leopard. This poses concern for the endangered Florida panther (above).

However, some ecologists remain skeptical about the threat. Whit Gibbons, head of outreach for the Savannah River Ecology Lab at the University of Georgia, believes the native species that have been declining will adapt the longer the python remains in Florida and their numbers will again increase. Regardless, scientists agree that although it is unlikely that common species will become extinct in Florida, conservation efforts need to be made to remain proactive in this fight. They can’t wait until the python wipes out an endangered species to their threat seriously. Action needs to be taken now.

Luckily, some conservation efforts are already underway. Workers in the Everglades National Park have been removing snakes as quickly as they can find them but the numbers have grown so large that it’s difficult to keep up. In 2010 over 300 snakes were caught and removed from the park. This number has been drastically increasing from 2000 when the snakes were first established there. To attempt to prevent more snakes from being introduced to the area, on January 17th the US Department of the Interior banned importation of a number of snakes including the Burmese python. The Nature Conservancy’s “Python Patrol” is also hard at work taking steps to ensure that the pythons don’t spread to the Florida Keys.

The invasion of the Burmese python is just one more example of the ecological implications of importing foreign species. The potential effects of such invasive like the Burmese python, Gypsy moth, Kudzu, Zebra muscle, and Multiflora rose were not considered before their introduction to the United States. Now they are producing devastating ecological effects. To prevent future invasives, stricter regulation of importation of non-native species needs to be implemented. In addition, people who choose to own exotic pets like the Burmese need to be educated about their pets beforehand and tighter restriction should be placed on owners of such pets to ensure that they understand the responsibilities involved. I believe that if proper education of such people had occurred when they were first considering owning such a large snake, many would have chosen to purchase a better “starter” snake that they could have provided appropriate care for. In addition, even experienced owners should make sure that their snakes are in good quality cages to prevent escapees from adding to the problem. I just hope that the python can be stopped before it is responsible for the extinction of one of Florida’s endangered species.

Disclaimer: Photos do not belong to me. They link to their source.