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Neotropical Paleoecology Research Group

(NPRG)

Andean prehistory and manufactured landscapes

Our work in the Andes began as a quest to look at the impacts of the last ice age, but increasingly we are drawn to looking at the deglacial period and the current interglacial. In other words, the portion of time that humans arrived in and occupied the Andes. Ecologists studying modern systems are realizing that you cannnot separate human from 'natural' influences. We change fire regimes, we load the atmosphere with CO2 and nitrates,such that every ecosystem is modified by human activity. Should we draw a bright line and say that this was only true of an industrialized world or should we establish a longer timeframe to evaluate how humans have changed landscapes?

Our research interest converged on this investigation somewhat organically. We were already documenting the first fire histories in the Andes, we were investigating the timing of population declines of megafauna, the interaction betwen crop cultivation and climate change, and the extent of pre-Columbian lowland Amazonian forest modification. As our research matured a clear linkage emerged - that humans were resourceful, adaptive, but above all influential in shaping landscapes wherever they went. The key questions became where did they go? When did they get there? and What were their behavioral adaptations to changing conditions through time?

We have three geographic centers that we are investigating that offer a precipitational gradient across the Andes. In the direst region around Cusco, Peru, where precipitation is ~700 mm per yr, we have a series of lake records, some of which are about 100,000 years in age that allow us to establish natural variance long before human entry. Other records are shorter and provide detailed reconstructions spanning the period of human occupations - which we believe to be older than any Andean archaeological setting found so far. Our second research area is the Chachapoyas region in northern Peru, where rainfall is 1500-3000 mm. Here a transect of lakes from the Amazonian lowlands to the highlands provides a history that led to the development of the distinctive Chachapoyan occupation. This pre-Inkan civilization is known for highly decorated buildings and the interment of mummies, some of which we have found at our field sites. The third setting is the wet mountain systems of southern Ecuador that receive > 3000 mm of rain. This design will help us to answer our research questions of when? where and what? as they relate to human modification of the Andes and the creation of modern landscapes.

 

What happened to the megafauna?

At the end of the last ice age >80% of mammals weighing >50 kg went extinct in South America. Although the North American extinction is better known, the number of species lost and the proportion lost was highest in South America. Three prevailing hypotheses are that the extinction was caused by a human-induced overkill as people entered the landscape, a climatically induced die-off as the ice age ended, or an ecological cascade of effects as keystone species were lost.

Through paleoecological analyses we are investigating the timing of this extinction event relative to human presence, climate change, and fire frequency. We use lake sediments as a source of our microfossil material and use the pollen to tell us about vegetation changes, diatoms to tell us about water quality, charcoal to quantify fire frequency, and a spore from a fungus that only grows on herbivore dung to tell us about herbivore biomass around the lake. The spore belongs to a genus called Sporormiella, and after doing some studies in modern lakes with and without large herbivores (horses, llamas, and cows) we can show that Sporormiella provides an accurate measure of their presence and does not record the presence of small mammals.

We are analyzing cores from Ecuador, Peru, Brazil, and Panama, for changes in the past abundance of Sporormiella and finding that there is a large decline in its abundance at the end of the last ice age. Many lakes show an extinction between 12,800 and 12,500 years ago, and this appears to be strongly related to human activity. But intriguingly, in some lakes there appears to be an earlier decline. Does this indicate a very early human presence in the Andes or that the megafaunal populations initially collapsed due to climate change? Work goes on.

Projects

Pre-Columbian human occupation in the Amazon Basin

Amazonia was believed to be a pristine ecosystem with little to no human influences when Europeans arrived in 1492. However, recent evidence suggests that pre-Columbian human settlements were present throughout the basin and that people caused widespread landscape modifications, resulting in a “manufactured ecosystem”. This belief is deemed the 1491 hypothesis and data supporting it originate from some archaeological sites in Amazonia. However, the inference of widespread landscape modification is an extension of localized patterns onto the entire basin. With this idea also comes an implied resiliency of the rainforest to landscape modifications. Assuming this to be truth without basin wide testing may lead to unsound conservation and management policies in Amazonia. To test the 1491 hypothesis, we are trying to determine the spatial and temporal extent of pre-Columbian human impacts in Amazonia by recreating the fire history of the basin (as fire is the most widespread landscape modification by humans). We are using soil charcoal analysis to determine local fire histories and lake sediment charcoal analysis to determine regional fire histories. We are also using phytolith analysis (from soils) and pollen analysis (from lake cores) to reconstruct vegetation shifts associated with fire. We want to combine these data to produce spatial and temporal models of human occupation in Amazonia. These models will be tested with a basin wide road transect survey of the Brazilian Amazon scheduled for Summer 2009/2010.

Andean treeline histories and fire regimes

Our research in the Andes looks at the long-term dynamics of the vegetation and climate in that region. Framed within the Andes Biodiversity and Ecosystems Research Group (ABERG, http://darwin.winston.wfu.edu/andes/index.php), the goal of this project is to reconstruct tree line changes during the past in the Peruvian Andes and to understand how these changes relate to fire regimes and human occupation. Sediment cores have been raised above and below modern treeline, Peru. The lakes are located just upslope from an altitudinal transect that forms the backbone of the ABERG project, where productivity and forest dynamics measurements have been underway since 2003.

Extensive soil charcoal and pollen analyses are also underway in an area of 50,000 ha near the Kosñipata Valley, in 15 transects crossing the treeline and 100 random points both within the Puna and the forest cover. Sample points are stratified to be representative of elevation, slope and aspect. The goal is to identify in situ fires and changes in vegetation cover during the recent past (c. 2000 years). Additionally, total soil carbon and aboveground biomass are being determined for all sample points with the aim to characterize carbon stocks in the region.

Shifted Baselines: Quantifying Past Human Influences on Andean Landscape

Knowing what is natural in terms of an ecosystem, rather than simply accepting what appears to be natural, is important for all investigation of natural processes. In marine biology this concept has been summarized as ‘shifting baselines’ in which each generation accepts a degradation of the environment and perceives it to be ‘natural’. Carbon storage, rates of growth, vegetation succession, and potential biodiversity are all important components of ecosystem services modified by human actions. Sometimes societal changes enhance one process at the cost of another. Historically, water retention may have been paramount in a dry setting such as the high Andes, whereas faced with global climate change it may be that carbon storage becomes more pressing. As policy makers grapple with climate change and loss of biodiversity there is a clear need to understand the trajectory of landscape change and define what is natural. This research project will investigate an area of very high biodiversity in the Peruvian Andes, where efforts to conserve Andean habitats to promote both biodiversity and carbon sequestration are being undertaken in a landscape that has been manipulated for millennia by humans. Present plans for high elevation carbon sequestration center around Polylepis, a tree that can grow at higher altitudes than any other. Woodlands of this tree are important habitat for endemic species. While afforestation efforts are fueled by the belief that Polylepis were once much more abundant than present, this hypothesis has not been tested. Borrowing from marine science we will define ‘natural baselines’ for ecosystems across a range of elevations, determine the natural height of tree line (important for above ground carbon storage), and the trajectory of landscape change relative to climate change for the last 11,000 years. Paleoecology can, through analysis of fossil pollen and charcoal recovered from soils and lake sediments, provide detailed information about how systems have changed. The climate of the early Holocene, c. 11,000 – 9000 years ago was quite similar to that of today, and yet human populations in the Andes were very low. Consequently, this period offers insights into the Andean ecosystem without human activity. In the study area, ten lakes and 200 soil cores will be analyzed to provide the historical data for those natural baselines. We will investigate how climate change interacted with human activity to produce altered fire regimes, crop use and forest cover.

Forming regional conservation policy with regard to local landuse or even global carbon budgets requires an understanding of the trajectory of human influence on ecosystems. The project will provide new data on the timing, extent and nature of human-induced change in Andean landscapes and provide baseline data relevant to ongoing efforts to constrain the effects of climate change through carbon sequestration while conserving biodiversity. Carbon sequestration is on the brink of becoming a transforming influence in tropical conservation. Collaborations with scientists in complimentary disciplines (soil science, plant physiology, ecology and remote sensing) will allow our results to be integrated into a larger prediction of appropriate policy for Andean conservation and for attempts to mitigate carbon release within Andean ecosystems.

Vegetation and climate history of the Galápagos Islands

Research in the Galapagos Islands is focused on mid to late Holocene climate in the tropical Pacific, with particular emphasis on the frequency and intensity of El Niño and the Southern Oscillation, as well as the Little Ice Age and Mediaeval Warm Period. Human impact on the islands is also being assessed from recent paleorecords from high resolution lake records. During field seasons between 2004 and 2007, sediment cores have been retrieved from crater lakes such as from Lago Guerrero (Genovesa), Lago Bainbridge (Rochas Bainbridge), El Junco (San Cristobal), and Paul’s Bog (Santa Cruz). A pollen trapping study involving c. 140 traps and ten Hobo temperature and humidity data loggers was conducted on each of these islands between December 2004 and December 2005. These modern pollen records will provide baseline data to assist in the interpretation of the fossil pollen records.

Paleoenvironmental history of Central America

One of the principal obstacles to understand the linkages between the climate of low and high latitudes during the Quaternary has been the scarcity of long-term well-dated high-resolution records from the tropical lowlands. In this respect, Lake Petén Itzá (Yucatán Peninsula) provides an exceptional opportunity to explore the climate of the past, its relationships with global climatic features over time (e.g. D-O and Heinrich events, ITCZ displacements, etc.), and the processes of human occupation and disruption of the natural landscape. Petén Itzá is the deepest lake in the Central American lowlands, and its basin remained submerged even during the most critical dry episodes of the late Quaternary, providing a continuous archive of lacustrine sediments. In spring of 2006 Petén Itzá Scientific Drilling Project recovered several cores which together comprise a composite record for the last 85,000 years. As part of the scientific team that is currently working on the sediments, we intend to use pollen and charcoal analysis to reconstruct the paleoecology and biogeography of the area. Additionally, we want to use modern sediments from the Yucatán Peninsula and the mountains of Mexico and Guatemala to build transfer functions and spatial models that allow us to estimate changes in temperature, precipitation and vegetation cover in the past. The final results will provide us with a dataset suitable to test hypotheses about the climatic and ecological history of the area, and will offer information relevant to the global scale processes taking place during the Late Quaternary.