Historical ecology is a research program that focuses on the intermingling of people and the environments in which they live. Rather than just looking at a quick snapshot, historical ecology involves studying and understanding this relationship in both time and space in order to gain a full picture of all of its accumulated effects. Through this interaction humans manipulate the environment and further the transformation of landscapes.
William Balée, Professor of Anthropology at Tulane University has proposed four hard-core postulates which are interdependent and set historical ecology apart from other more traditional research programs, as evident in its intellectual background. Basically summarized, these are:
1. Humans have had an effect on nearly all environments of Earth
2. Humans are seen as morally neutral: they are not inherently bad and programmed to destroy the land and biodiversity in their environments nor are they inherently good
3. Different types of societies influence their landscapes in different ways
4. The relationship between people and the landscape can be comprehended holistically
An important aspect of historical ecology is that human culture and the environment are in a dialogue. They influence and respond to one another in continuous cycles. This is different from saying that throughout time, as the environment has changed, the human species has adapted to these changes. Instead, humans have brought their cultures to new lands, impacted these landscapes, and then made the necessary changes to adjust their culture or lifestyle to the now altered landscape. In fact, as the first postulate holds, it is very difficult to find a landscape anywhere on the planet that has not somehow been changed as a result of humans. These alterations can be referred to as human-mediated disturbance.
As the second and third postulates imply, it is important that we do not overgeneralize humans and society. Humans impact nearly every environment but this can create an increase in biodiversity of certain landscapes at certain times. When indigenous people use broadcast fires they often consequently create more niches for new species. However, the changes some humans make to the landscape are not always beneficial to all humans and all biota. Just as human cultures and languages vary, different societies and political systems have distinct impacts on the landscape.
Finally, people and the landscape can be studied as a connected trend because when one looks at the landscape, people and the environment coexist. They each are so dependent on one another that it is more efficient and accurate to study them together as a single entity. The landscape is visual evidence of the totality, or interaction, of culture and the environment.
(R) William Balée, Anthropology professor at Tulane University, with (L) indigenous consultant on landscape transformation in Brazil
While historical ecology is an interdisciplinary research program, it borrows heavily from the rich intellectual history of environmental anthropology. Western scholars have known since the time of Plato that the history of environmental changes, induced by natural catastrophes and human activities, is an integral part of human history. Greek and Roman philosophers developed several ideas to describe human-environmental interactions, many of which have been retained or reflected in contemporary environmental theories. The first of these ideas is the concept of the Great Chain of Being, or inherent design in nature. In this, all species on earth are arranged in an ascending hierarchical scale, with humanity topping the scale. Humanity, as the highest being, has the knowledge and ability to modify nature. These two ideas lend to a third, the concept of "another," or manmade nature. The first nature is the design inherent in nature, and second nature has been modified by humanity.
Interest in environmental transformation increased in the 18th, 19th, and 20th centuries, and a series of new intellectual approaches emerged. One of these approaches was environmental determinism, developed by human geographer Friedrich Ratzel. This view held that it was environmental conditions, not social conditions, which determined the culture of a population. Proponents of environmental determinism held that humans are restricted by nature, in a teleological sense, to certain levels in the great chain of being. A later approach was the historical viewpoint of Franz Boas. Boas refuted environmental determinism by saying that culture, not nature, is the primary molder of human cultures. While the environment produces limitations on societies, the form and meaning of the modification the environment can provide depends on the culture itself. The cultural ecology of Julian Steward is thought to be a fusion of environmental determinism and the historical approach of Franz Boas. Steward felt it was neither nature nor culture that had the most impact on a population, but it was the mode of subsistence used by the people.
Anthropologist Roy Rappaport introduced the field of ecological anthropology. Rappaport coined the new term in a deliberate attempt to move away from cultural ecology. He was explicitly interested in the role of religion in society, and felt that in order to fully understand religion and ritual, the researcher has to look beyond humans. Studies in ecological anthropology borrow heavily from the natural sciences, in particular the concept of the ecosystem. Under this approach, which is also called systems theory, human populations are seen as one of many aspects in a self-regulating ecosystem. Systems theorists gave increased attention to time and change in populations and the individual actors in them. Systems theory treated communities as static populations in harmonious equilibrium with the local environment.
All these intellectual approaches are important because they provide the framework for historical ecology. These viewpoints have been critiqued, expanded, and improved to create the current approaches in environmental anthropology; one approach is historical ecology. Eric Wolf, a student of Julian Steward, was prominent in the critique of late twentieth century anthropology. The revisions of Wolf and others are especially pertinent to the development of historical ecology. Most of these theories do not take a long view of history. In other words, they view a population as static, as a slice in time. This, according to historical ecology, does not provide a deep enough understanding of a culture or landscape because it ignores the events that helped create it. Other problems arose when many of these theories were applied to complex societies. Cultural ecology can be useful in understanding classless or simple societies, where factors such as indigenous technology, low population size, and less political organization directly correlate to the modes of subsistence. However, it is more difficult to explain the complex factors in peasantries and urban societies only in terms of their modes of production. wiki wiki pedia Some of the main tenets of historical ecology have specific influences as well. One of them, the cultural landscape, is directly attributed to American geographer Carl Sauer. Sauer’s theories developed as a critique of environmental determinism, which was a popular theory in the early twentieth century. Sauer’s pioneering 1925 paper “The Morphology of Landscape” is now fundamental to many disciplines and defines the domain. In this, the term landscape is used in a geographical sense to mean an arbitrarily selected section of reality; morphology means the conceptual and methodological processes for altering it. Hence to Sauer wherever humans lived and impacted the environment, landscapes with determinate histories resulted.
Landscapes in historical ecology
In historical ecology, the landscape is defined as an area of interaction. The landscape provides the story of the place, it is a realistic place that changes throughout time. Historical ecology dispenses the notion of an ecosystem and replaces this notion with the concept of a landscape. While the ecosystem is perpetual and cyclic, a landscape is historical, cultural, and evolutionary.
Historical ecologists have received influence on their idea of landscapes from various time periods and individuals. The idea that humans are long-term agents of change to the land goes back to the classical, distant past. A recent influence is from cultural and historical geographers. These geographers believe that humans and the environment are inseparable. They received this idea from nineteenth-century German architects, gardeners, and landscape painters in Europe, Australia, and North America.
The perception of the landscape in historical ecology differs from other disciplines, such as landscape ecology. Landscape ecologists often criticize wildlife preserves for the depletion of biodiversity. Historical ecologists recognize that this is not always true. These changes are due to multiple factors that contribute to the ever-changing landscape. Landscape ecology still focuses on areas defined as ecosystems. In this, the ecosystem perpetually returns to an equilibrium state. Also, landscape ecologists view noncyclical human events and natural disasters as disturbances, while historical ecologists view this as part of the landscape’s history. Historical ecologists recognize that landscapes undergo continuous alteration over time and these modifications are part of that landscape’s history.
Historical ecology recognizes that there is a primary and a secondary succession that occurs in the landscape. These successions should be understood without discrimination towards human nature. Primary succession occurs when an area that once had no life on it is colonized. An example of this is colonization on newly formed volcanic atolls. Over a long timescale of millions of years, primary succession is the replacement of one phyla with a totally new phyla. Secondary succession is the replacement of organisms with completely new organisms. This occurs when the area has been disturbed by things such as hurricanes and extensive agriculture. Landscapes can undergo mulitple stages of transformation. These stages demonstrate the history of the landscape. Also, these stages can be brought on by humans or natural causes.
Historical ecology challenges the implication of a pristine landscape, such as virgin rainforests. The belief of historical ecology is that most landscapes are untouched and unaltered. This notion was configured from several precursors in the fields of history, ecology, and anthropology. Combining concepts from these fields provided for an interdisciplinary view of the changes of landscapes prior to western civilizations. Historical ecologists have recognized that all landscapes have been altered by various organisms and mechanisms. These organisms altered the land prior to human existence on Earth. The alteration of these landscapes provides evidence as to the cultural history of the land. The history of the landscape can be seen through traces of the various mechanisms that have altered it, such as epidemic disease and anthropogenic fire.
The landscape is a concrete replacement to the idea of an ecosystem. Historical proceedings unfurl in tangible places which leads to changes in the landscapes. These changes have been studied through the archeological record of modern humans and their history. The evidence that classless societies, like foragers and trekkers, were able to change a landscape was a breakthrough in historical ecology. Understanding the concept of the individuality of every landscape, in addition to relations among landscapes and the forms which comprise the landscape, is key to understanding historical ecology.
Throughout their history Homo sapiens have interacted with their environments, and in most cases their interactions have had lasting effects. Humans have, at times, taken active conscious roles in changing their landscapes, while at other times changes have come about as secondary effects of human action. These changes in landscapes are called human-mediated disturbances of landscapes, and act through various mechanisms. Mechanisms of human-mediated disturbances vary in the effect they have on the landscape in that they may be detrimental in some cases, and advantageous in others. Some of the main mechanisms of human-mediated disturbances include anthropogenic fire, biological invasion, spread of disease, and soil and water management.
Of all the mechanisms of human-mediated disturbances, anthropogenic fire is the one that is most immediately visible, both destructive and at times constructive, and its absence may prove to be catastrophic. Humans have practiced controlled burns of forests on all continents for thousands of years, shaping landscapes in order to better suit their needs. They burned off fuel creating space for their crops, and in many cases allowed for greater biodiversity. Controlled burns also aided in prevention of natural wildfires which spread uncontrollably and cause severe damage, and in the absence of indigenous populations (most notably in North America and Australia) who once practiced controlled burns we have seen an increase in the frequency of naturally ignited wildfires. Along with an increase of natural wild fires there has been destabilization of "ecosystem after ecosystem, and there is good documentation to suggest fire exclusion by Europeans has led to floral and faunal extinctions."
Biological invasions and the spread of pathogens and disease are two mechanisms that spread both inadvertently and purposefully, although they often have different effects. They can be spread by castaways on ships in the form of rodents, with the intention of adding a useful new species to a landscape, or even as weapons in warfare. Biological invasions are introductions of foreign species or biota into an already existing environment. The effects of such an introduction can be positive or negative; in some cases a new species may wreak havoc on a landscape, causing the loss of native species and destruction of the landscape. In other cases, the new species may fill a previously empty niche, and play a positive role. Conversely, the spread of new pathogens, viruses, and diseases may happen in the same way as biological invasions, but rarely if ever have any positive effects. New pathogens and viruses often cause the destruction of populations of native species or populations lacking immunities to those diseases. Some pathogens have the ability to transfer between species, and may be spread as a secondary effect of a biological invasion. This also acts as an example of a secondary effect of a mechanism of human-mediated disturbance in that one mechanism serves as a catalyst for another to work.
Other mechanisms of human-mediated disturbances include water management and soil management. These have been recognized as ways of landscape alteration since the time of the Roman Empire. Cicero noted that through fertilization, irrigation, and other activities humans had essentially created a second world. While Cicero may have been able to witness the effects of ancient fertilization and irrigation techniques, he had no way of knowing how destructive they would become. At present, fertilization serves as a means of creating larger more productive crop yields, but has had adverse effects on the landscapes. Fertilizers also decrease biodiversity of plant species and add harmful pollutants to the soil that often seep down to the water table and contaminate rivers, streams, and lakes.
The mechanisms of human-mediated disturbances are numerous and have various effects. They may be beneficial to landscapes in that they allow for an increase in biodiversity or protect them from catastrophic fires. In other cases, like those of certain biological invasions or the spread of pathogens and disease, they can prove to be extremely detrimental to landscapes and the biodiversity within them. Mechanisms of human-mediated disturbances may also have unforeseen secondary effects that can lead to further damage of landscapes.
Anthropogenic fire is a mechanism of human-mediated disturbance, defined within historical ecology as a means of altering the landscape in a way that better suits human needs. Humans have met their needs by employing anthropogenic fire in its most common forms of controlled burns, or broadcast burning. Though the words burn, fire, and forests usually have negative connotations when they are paired together, the controlled burns humans have used for thousands if not hundreds of thousands of years have proven to have more favorable than adverse effects on landscape biodiversity, formation, and even protection.
When looking at the effects of broadcast burning upon the biota of a landscape we can see a gradual change from detriment to prosperity. The immediate effect of a forest fire is a decrease in biodiversity. However, after a few cycles of burning depending on the intensity, frequency, timing, and size of the fires there is an increase in biodiversity and adaptation to fire regimes. It is the adaptation to fire that has shaped most of the Earth's landscapes.
A swidden fire, an example of a controlled burn
In addition to creating biodiversity controlled burns have helped shape and change landscapes. These changes can range from grass to woods, from prairies or forest-steppes, to scrub to forest. Whichever may be the case the transformations increase biodiversity and create landscapes more suitable to human needs creating patches rich in utilitarian and natural resources.
While broadcast burning has led to increases in biodiversity and landscapes better suited to human needs they have also become a source of protection. Humans had essentially fireproofed landscapes by burning off undergrowth and using up potential fuel, leaving little or no chance for a wild fire to be sparked by lightning. In a stark contrast to its benefits, the absence of controlled burns can have immensely destructive effects because there are no checks being placed on undergrowth and fuel allowing for wildfires to start with greater ease.
Of all of the mechanisms of human-mediated disturbances, anthropogenic fire has become one of great interest to ecologists and anthropologists alike. For anthropologists studying the effects of anthropogenic fire has been a way to measure cultural identities and landscape needs of past cultures. In the wake of the industrial revolution and the migration of populations from rural areas to urban areas there has been an increase in the frequency and strength of wildfires because there have been no means to curb or prevent them. For this reason the study of anthropogenic fires has become of great interest as ecologists look to the methods used in past anthropogenic fires in order to revive and put them into use again. The interest of historical ecology is essentially a fusing of the interests of ecologists and anthropologists with an added interest in the effects on the landscapes.
Biological invasions are exotic biota, including invasive species and diseases, that enter a landscape and replace species that resemble the same structure. Much like weeds, they multiply and grow quickly, causing the destruction of existing flora and fauna by different mechanisms such as direct competitive exclusion. Invasive species typically spread at a faster rate when they have no natural enemies or when they fill an empty niche. Often these invasions occur in a context of human history and are known as a type of human-mediated disturbance called human-mediated invasions.
Invasive species can be transported intentionally or accidentally. Often invasive species are located near shipping areas where they are unintentionally transported to their new location. This method allowed red tides to become invasive after 1500. Sometimes populations intentionally introduce species into new landscapes for various purposes that range from being ornamentals to aiding in erosion control. These species can later become invasive and totally modify the landscape, like the Kentucky Coffee Tree, chestnut blight and Butternut in North America and the Walnut and Sweet Chestnut in the British Isles. It is important to note that not all exotic species are invasive; in fact, the majority of newly introduced species never become invasive.
In the Mississippi River Delta, the introduction of the nutria has caused a change in the ecology of the wetlands. They outcompeted and perhaps aided in the rapid decline of the indigenous muskrat population. They also exceeded the carrying capacity and destroyed large portions of the marsh by eating nearly all of the vegetation, especially roots. The destruction is long-term and leads to erosion and habitat loss. This invasion is an example of a human-mediated disturbance as people introduced the nutria to its new environment and also caused a number of factors that have allowed for the explosion of nutria. During a hurricane in 1941 the nutria escaped from their pens off the coast at Avery Island, where they had been imported to help control the spread of water hyacinth. Overhunting of the American Alligator and preference for muskrat fur rather than nutria fur in the market were major reasons for the huge growth of the nutria population.
Regardless of the way they were introduced, biological invasions have an effect on the landscape. The goal of eliminating invasive species is not new; Plato wrote about the benefits of biodiversity centuries ago. However, eliminating invasive species is a difficult notion because there is no set rule on how long a species must be in a specific environment until it is no longer classified as invasive. European forestry defines plants as being archaeotypes if they existed in Europe before 1500 and neophytes if they arrived after 1500. This classification is still arbitrary and some species have unknown origins while others have become such a key component of their landscape that they are a keystone species. As a result, their removal would have an enormous impact on the landscape, but not necessarily cause a return to the state that existed before the invasion.
A clear relationship between nature and people is expressed through human disease. Human diseases emerge from interactions among parasites, hosts, and their environment. All three of these factors are intertwined; if there were no humans, there would be fewer hosts, and a different amount of infectious disease. In this way, infectious disease is another method of human-mediated disturbance. The study of infectious disease requires a holistic approach, using knowledge from the fields of history, biology, geography, population dynamics and anthropology.
Studies of human disease have shown the reciprocal relationship between humans and parasites. The variety of parasites found within the human body, especially the small intestine, often reflects the diverse environment where that person lives. For example, Bushmen and Australian Aborigines have half as many intestinal parasites as African and Malaysian hunter-gatherers living in a species-rich tropic rainforest. Human activity can either increase or decrease species diversity in a landscape, causing a corresponding decrease in pathogenic diversity.
Infectious diseases are categorized as either chronic or acute, and can be either epidemic or endemic. Chronic diseases occur over long periods of time, change very little, and confer no immunity to the host. Chronic diseases include herpes simplex and tuberculosis. In contrast, acute diseases like measles, rubella, and smallpox have short periods of infection with high mortality rates. Acute infection survivors usually acquire immunity. Chronic infections often turn endemic, taking a regular toll on a population. Acute infections often become epidemic, and the effects are especially important to historical ecologists. Invasive species are often the ones that turn epidemic. Bacterial, protozoan, viral, and prion infections can take on epidemic characteristics when interacting with previously unexposed native flora and fauna, including human. Historically, evidence of epidemic diseases is associated with the beginnings of agriculture and sedentary communities. Prior to that, human populations were too small and mobile for most infections to become established chronic human diseases. Diseases often faded out if they could not be transferred from one community to another. The permanent settlements with more inter-community interaction as a result of agriculture allowed infections to develop as specifically human pathogens.
Transformation of waterways
Historical ecologists postulate that landscape transformations have occurred throughout history, even before the dawn of western civilization. Human-mediated disturbances are predated by soil erosion and animals damming waterways which contributed to waterway transformations. Landscapes, in turn, were altered by waterway transformation. Historical ecology, views the effects of human-mediated disturbances on waterway transformation as both subtle and drastic occurrences. Waterways have been modified by humans through the building of irrigation canals, expanding or narrowing waterways, and multiple other adjustments done for agricultural or transportation usage.
The evidence for past and present agricultural use of wetlands in Mesoamerica suggests an evolutionary sequence of landscape and waterway alteration. Pre-Columbian, indigenous agriculturalists developed capabilities with which to raise crops under a wide range of ecological conditions, giving rise to a multiplicity of altered, cultivated landscapes. The effects of waterway transformation were particularly evident in Mesoamerica, where agricultural practices ranged from swiddening to multicropped hydraulically transformed wetlands.
Historical ecologists view the Amazonian landscape as cultural and embodying social labor. The Amazon River has been altered by the local population for crop growth and water transportation. Previous research failed to account for human interaction with the Amazonian landscape. Recent research, however, has demonstrated that the landscape has been manipulated by its indigenous population over time. The continual, natural shifting of rivers, however, often masked the human disturbances in the course of rivers. As a result, the indigenous populations in the Amazon are often overlooked for their ability to alter the land and the river.
However, waterway transformation has been successfully identified in the Amazonian landscape. Clark Erickson observes that prehispanic savanna peoples of the Bolivian Amazon built an anthropogenic landscape through the construction of raised fields, large settlement mounds, and earthen causeways. Erickson, on the basis of location, form, patterning, associations and ethnographic analogy, identified a particular form of earthwork, the zigzag structure, as fish weirs in the savanna of Baures, Bolivia. The artificial zigzag structures were raised from the adjacent savanna and served as a means to harvest the fish who used them to migrate and spawn.
Further evidence of waterway transformation is found in Igarapé Guariba in Brazil. It is an area in Amazonia where people have intervened in nature to change rivers and streams with dramatic results. Researcher Hugh Raffles notes that British naturalists Henry Walter Bates and Alfred Russel Wallace noted waterway transformation as they sailed through a canal close to the town of Igarapé-Miri in 1848. Archival materials identifies that it had been dug out by slaves. In his studies he notes an abundance of documentary and anecdotal evidence which supports landscape transformation by the manipulation of waterways. Transformation continues in more recent times as noted when in 1961, a group of villagers from Igarapé Guariba cut a canal about two miles (3 km) long across fields thick with tall papyrus grass and into dense tropical rain forest. The narrow canal and the stream that flowed into it have since formed a full-fledged river more than six hundred yards wide at its mouth, and the landscape in this part of the northern Brazilian state of Amapá was dramatically transformed..
In general, with an increase in global population growth, comes an increase in the anthropogenic transformation of waterways. The Sumerians had created extensive irrigations by 4000 BC. As the population increased in the 3,000 years of agriculture, the ditches and canals increased in number. By the early 1900s, ditching, dredging, and diking had become common practice. This led to an increase in erosion which impacted the landscapes. Human activities have affected the natural role of rivers and its communal value. These changes in waterways have impacted the floodplains, natural tidal patterns, and the surrounding land.
The importance of understanding such transformation is it provides a more accurate understanding to long-standing popular and academic insights of Amazonia, as well as other ecological settings, as places where indigenous populations have dealt with the forces of nature. Ecological landscapes have been portrayed as an environment, not a society. Recent studies supported by historical ecologists, however, understand that ecological landscape like the Amazon are biocultural, rather than simply natural and provide for a greater understanding of anthropogenic transformation of both waterways and landscapes.
Soil management, or direct human interaction with the soil, is another mechanism of anthropogenic change studied by historical ecologists. Soil management can take place through rearranging soils, altering drainage patterns, and building large earthen formations. Consistent with the basic premises of historical ecology, it is recognized that anthropogenic soil management practices can have both positive and negative effects on local biodiversity. Some agricultural practices have led to organically and chemically impoverished soils. In the North American Midwest, industrial agriculture has led to a loss in topsoil. Salinization of the Euphrates River has occurred due to ancient Mesopotamian irrigation, and detrimental amounts of zinc have been deposited in the New Caliber River of Nigeria. Elsewhere, soil management practices may not have any effect on soil fertility. The iconic mounds of the Hopewell Indians built in the Ohio River valley likely served a religious or ceremonial purpose, and show little evidence of changing soil fertility in the landscape.
The case of soil management in the Neotropics (including Amazonia) is a classic example of beneficial results of human-mediated disturbance. In this area, prehistoric peoples altered the texture and chemical composition of natural soils. The altered black and brown earths, known as Amazon Dark Earths, or Terra preta, are actually much more fertile than unaltered surrounding soils.. Furthermore, the increased soil fertility improves the results of agriculture. Terra preta is characterized by the presence of charcoal in high concentrations, along with pottery shards and organic residues from plants, animal bones, and feces. It is also shows increased levels of nutrients such as nitrogen, phosphorus, calcium, zinc, and manganese; along with high levels of microorganic activity. It is now accepted that these soils are a product of a labor intensive technique termed slash-and-char. In contrast to the commonly known slash-and-burn technique, this uses a lower temperature burn that produces more charcoal than ashes. Research shows these soils were created by human activity between 9000 and 2500 years ago. Contemporary local farmers actively seek out and sell this dark earth, which covers around 10% of Amazonia. Harvesting Terra preta does not deplete it however, for it has the ability to regenerate at the rate of one centimeter per year by sequestering more carbon.
Scorched land resulting from slash-and-burn agriculture
Interest in and the study of Amazon dark earths was advanced with the work of Wim Sombroek. Sombroek's interest in soil fertility came from his childhood. He was born in the Netherlands and lived through the Dutch famine of 1944. His family subsided on a small plot of land that had been maintained and improved for generations. Sombroek's father, in turn, improved the land by sowing it with the ash and cinders from their home. Sombroek came across Terra preta in the 1950s and it reminded him of the soil from his childhood, inspiring him to study it further. Soil biologist from the University of Kansas William W. Woods is also a major figure in Terra preta research. Woods has made several key discoveries and his comprehensive bibliography on the subject doubles in size every decade.
Globally, forests are well-known for having greater biodiversity than nearby savannas or grasslands. Thus, the creation of ‘forest islands’ in multiple locations can be considered a positive result of human activity. This is evident in the otherwise uniform savannas of Guinea and central Brazil that are punctured by scattered clumps of trees. These clumps are the result of generations of intense resource management. Earth works and mounds formed by humans, such as the Ibibate mound complex in the Llanos de Mojos in Bolivia, are examples of built environments that have undergone landscape transformation and provide habitats for a greater number of species than the surrounding wetland areas. The forest islands in the Bolivian Amazon not only increase the local plant species diversity, but also enhance subsistence possibilities for the local people.