- As we seek to reverse global trends of deforestation and forest degradation, researchers are peering into the past to help chart a course forward for imperiled tropical forests.
- A study published in Nature Ecology & Evolution earlier this month found that, prior to the arrival of European colonists, indigenous peoples in the cloud forests of Ecuador cleared even more of the forests than we have cleared today.
- By studying this history, researchers hope to aid in the restoration of the forests that have once again been degraded for human purposes.
At 1,200 to 3,200 meters above sea level, the montane cloud forests on the eastern Andean flank in Ecuador lie between the Andes’ high-elevation grasslands (known as páramo) and the tropical rainforests of the Amazon Basin. They are incredibly biodiverse and densely populated with moisture-loving trees and plants that cling to the steep Andean slopes, but the more accessible areas have been cleared for agriculture and cattle ranching, while ongoing deforestation is making landslides and fires worse.
Of course, Ecuador’s cloud forests are hardly unique in this respect: forests the world over are being destroyed to make way for agriculture and ranching operations. As we seek to reverse global trends of deforestation and forest degradation, researchers are peering into the past to help chart a course forward for imperiled tropical forests.
A study published in Nature Ecology & Evolution earlier this month shows that tropical forests may be more resilient in the face of human pressures than previously thought. The study, led by Nicholas Loughlin of the UK’s Open University (OU), determined that indigenous peoples farmed the land intensively before European colonists arrived. In fact, “prior to European arrival, indigenous peoples in the cloud forests of Ecuador modified landscapes to a greater degree than modern human populations,” including clearing even more of the cloud forests than we have cleared today, Loughlin told Mongabay.
These intensive cultivation practices came to an abrupt end in the late 1500s as a result of the violence perpetrated against the indigenous peoples inhabiting the cloud forests by Spanish colonists. But by studying that history, Loughlin hopes to aid in the restoration of the forests that have once again been degraded for human purposes.
Loughlin led a team that studied the Quijos Valley, an area in the eastern Andes of northern Ecuador that was a key trade route between the Incan Empire and native Amazonian peoples. From atop a floating platform, the researchers cored a small lake called Lake Huila in order to extract sediment and examine the charcoal, pollen, pottery, and spores trapped that had accumulated in the lakebed. Through radiocarbon dating the sediment layers, the researchers were able to put together a narrative of human influence in the region covering the past 1,000 years.
They found that the cloud forests returned to a “structural form equivalent to ‘pre-human’ forests” just 130 years after the land was abandoned, Loughlin said. That means that “the 19th century explorers who described a ‘pristine’ wilderness were observing a ‘shifted’ ecological baseline that was, in fact, influenced by hundreds of years of previously unseen human activity.”
Loughlin added that it’s likely that all areas of tropical forest have at some point been directly altered by people in some way, but that “this is along a gradient of human impact from almost unidentifiable (slight increase in species useful to indigenous peoples) to obvious (intensive maize agriculture) — which we see at our site.”
A growing body of research aims to determine just how much of a hand humans have had in shaping what we today consider to be untouched forest. For instance, another recent study, published in Nature Plants, found that ancient farmers had a much more profound impact on the Amazon rainforest than was previously thought, introducing new crops to some areas, planting more of their preferred edible tree species, and using fire to improve the nutrient content of soil.
Dr. Yoshi Maezumi of the University of Exeter led the Nature Plants study, which also used lake sediments, as well as charcoal, pollen, and plant remains in soil at archaeological sites, to examine the history of human influence in eastern Brazil. Maezumi suggests that we might have a lot to learn from these pre-Columbian farming practices.
“People thousands of years ago developed a nutrient rich soil called Amazonian Dark Earths,” Maezumi said in a statement. “They farmed in a way which involved continuous enrichment and reusing of the soil, rather than expanding the amount of land they clear cut for farming. This was a much more sustainable way of farming.”
While these ancient communities likely cleared some trees and weeds from the forest’s understory to accommodate their crops, they maintained a closed canopy forest, Maezumi added. “This is a very different use of the land to that of today, where large areas of land in the Amazon is cleared and planted for industrial scale grain, soya bean farming and cattle grazing. We hope modern conservationists can learn lessons from indigenous land use in the Amazon to inform management decisions about how to safeguard modern forests.”
Such historical studies can also play an important role in efforts to restore forests that have already been cut down or degraded, Loughlin said: “Palaeoecology allows us to observe vegetation composition and structure over periods beyond that of observational studies and has the potential to offer restoration ecologists and land managers a range of options in regards to the ecosystem services that can be restored to human impact environments.”
Loughlin is now preparing a paper that connects his findings summarized in Nature Ecology & Evolution to specific restoration practices.
“Next we are looking to link the past to the future of the cloud forest,” Loughlin wrote in a blog post. “Can the re-establishment of the forest observed by 19th Century explorers be used as a restoration target despite its history of human influence? Can palaeoecology itself help inform restoration and conservation efforts in the biodiverse forests of Ecuador and in the future how will a forest inherently linked to cloud cover and rainfall respond to predictions of human driven climate change?”
• Loughlin, N. J., Gosling, W. D., Mothes, P., & Montoya, E. (2018). Ecological consequences of post-Columbian indigenous depopulation in the Andean–Amazonian corridor. Nature ecology & evolution, 1. doi:10.1038/s41559-018-0602-7
• Maezumi, S. Y., Alves, D., Robinson, M., de Souza, J. G., Levis, C., Barnett, R. L., … & Iriarte, J. (2018). The legacy of 4,500 years of polyculture agroforestry in the eastern Amazon. Nature Plants, 1. doi:10.1038/s41477-018-0205-y
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