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Towards a Historical Ecology

"Global" and "local" perspectives

At present, whenever the conservation of tropical rainforests around the world is raised as an issue, emphasis is placed on the fact that is a "global issue." The destruction of tropical rainforests leads to loss of biodiversity, including rare species and genetic resources, and contributes to global warming by increasing atmospheric carbon dioxide levels. These constitute challenges to humanity as a whole and require responses at the global-scale. Based on this recognition, substantial sums of money and personnel have been expended on research and conservation efforts in tropical rainforest around the world. Today, activities related to tropical rainforests cover a broad spectrum of areas including politics and economy, research, education, and public relations, along with actual implementation of conservation plans, all based on a global network.

Amidst these various activities related to tropical rainforests, however, there was a problem that had largely been overlooked. That is the relation between local residents and forests. To those wishing to protect tropical rainforests from a global perspective, local residents were often seen as agents who, due to their poverty, ended up contributing to the destruction of forests. At best, they were considered groups that needed to be compensated when their access to forest resources was taken away as a result of conservation efforts and as groups that required "environmental education" to understand the importance of forest conservation. The question of how these groups had recognized, utilized, and maintained forest had rarely been asked, and the cultural and historical relation of these groups to forests was the concern of a handful of anthropologists and other scholars.


Hunter-Gatherer Societies of Central Africa and Research at Kyoto University

Since the 1970s, we have continued to conduct research on hunter-gatherer and swidden farming societies in Africa’s tropical rainforests. The primary goal has been to clarify how peoples whose livelihoods rely heavily on forests recognize and utilize nature. Although attention has recently started to be paid to this issue, when we began our research, there was little interest in the topic, even among anthropologists. However, it was a great joy for us to be able to make inroads, with the help of locals into this deep and rich world of knowledge regarding the relation between forests and people.


Even a short walk through the forest with the locals was enough to reveal their abundant knowledge of plants and animals of the forest. They spoke unbelievable volumes about trees large and small, tracks left by animals, the various sounds echoing throughout the forest. Just looking at their camps, one could tell how much these people relied on the forest. Their small huts, their baskets and ropes for transporting goods, all were made from materials collected in the forest. Scattered everywhere around the camps were fruits and roots harvested in the forest. Many of the children’s toys were also crafted from fruits and leaves from the forest. After sunset, they would sing and dance with the "spirits" that seemed to respond as a polyphonic chorus out of the night forest. The intimate relation these people have with the forest, not only in terms of diet, residence, tools, and other material goods, but in all aspects of life including play and ceremony/rituals was clear to see, and it was evident that their culture was based on making full use of the various potentials provided by the forest.

While we are continuing our research with the goal of understanding the "forest culture" of such peoples, within this overall objective, one area in which are expending particular effort is the collection and organization of knowledge related to plants. In the project known as AFlora, we are attempting to record the material, spiritual, direct and indirect utilization and recognition of forest plants―in other words, to generate a comprehensive description of knowledge regarding forest plants. It can be said to be an attempt to create an "encyclopedia of plant culture," an attempt to preserve the intellectual legacy of these societies that has been accumulated over countless centuries.


Tropical Rainforests as Human Habitat

While it is evident that these people rely on a diverse set of forest resources, the question of whether they can survive by relying solely on materials collected by hunting and gathering is currently under debate. Although tropical rainforests tend to evoke images of abundance itself in terms of comprising vast quantities of biomass, the evaluation differs when thinking about tropical rainforests as human habitat. It was long believed that the hunter-gatherers of Central Africa represented the region’s indigenous population, inhabiting the region before farming peoples, who constitute a majority of this region, migrated from the savannas of western Africa to the forests. However, starting in the latter part of the 1980s, this equation of hunter-gatherers with the indigenous population has been called into question. Reasons for this skepticism include three points, (1) the fact that a large share of the diet of present day hunter-gatherers in tropical rainforests includes foodstuffs obtained through exchange with nearby farming groups or through the hunter-gatherers’ own farming activities, (2) the fact that no archaeological evidence that exclusive hunter-gatherers inhabited rainforest in the past has been found, and (3) the fact that rainforests do not, in the first place, provide enough of a food base to support human life and are especially deficient in energy resources in the dry season when fruits are not available. In particular, the last question of adequacy as a food base has been discussed with the wild yam serving as the key (focal) plant. This so-called "wild yam question" has been the topic of discussion based on a number of studies. The majority of such research, however, has focused on types of wild yam and distributions thereof, and none constituted an empirical examination of the issue based on actual observation of hunter-gatherers’ lives.


Hirokazu Yasuoka, a graduate student in ASAFAS, accompanied a group of hunter-gatherer Baka in Cameroon for the duration of their long-term foraging expedition during the dry season known as molongo. Based on quantitative data on livelihood activities and diet collected during this period, he was able to demonstrate, for the first time ever, that it was possible to survive while relying exclusively on hunting and gathering, even during the dry season when food resources are generally scarce. The Baka’s diet during the molongo consisted of 20 or so types of mammalian and reptilian meat, 10 or so types of plants, along with river fish, honey, and edible insects. Most important among these were wild yams, which accounted for nearly 70% of total energy intake. In a subsequent study, Yasuoka thoroughly examined the distribution of wild yams and, based thereupon, arrived at an extremely interesting hypothesis regarding forest history. That is, the habitation and livelihood activities of peoples in the past have affirmatively influenced the formation of areas in which wild yams, on which the hunter-gatherers rely heavily, grow in high concentrations.

The route of the molongo in which Yasuoka participated.

The Impact of Human Activity on the Vegetative Environment

The idea that the habitation and livelihood activities of people in the past may have had a non-negligible impact on the natural vegetation had crossed our minds even before then. For example, in the 1980s, when we were investigating plants used as food by the hunter-gatherer Mbuti people who lived in the Ituri forest in northeastern Congo, we realized that many of these plants were so-called shade-intolerant species that only germinated and grew in locations receiving a lot of sunlight. The only places in tropical rainforests that receive a lot of sunlight are locations where there are "gaps" in the canopy due to fallen trees that are downed by wind, rain, or lightning. However, besides such areas, in the forest, there are many other gaps created through human activity. For example, such a gap is created when a tree is felled to harvest honey, or when large and small trees are cleared to create a space for a campsite that is more open than would occur naturally, allowing shade-intolerant plants to grow and thrive. In addition, in areas used as campsites, roots left uneaten and seeds from fruits germinate and develop into new plants. In fact, walking around a campsite, one can see the sprouts of many useful plants growing here and there. Among the sweet-fleshed forest fruit, there are some fruit whose flesh is difficult to separate from the seeds. In such cases, the seeds are eaten along with the flesh. There are plants whose seeds are, in this manner, disseminated (or the germination thereof promoted) after passing through the digestive tracts of humans and animals.


There is another effect that arises from life in camps. With several dozens of people living in the same place for many days, ash and waste resulting from kindling and foodstuffs collected from a wide area of the surrounding forest accumulates and fertilizes the soil in the area. Making a rough calculation, a group of fifty people staying in a camp for one month would result in accumulation in the areas surrounding the camp of 200 to 250 kg of ammonium sulfate and a similar amount of nitrogen from the foodstuff alone. The soil of tropical rainforests is said to be nutrient-poor. However, camps represent areas in forests where soil nutrients that are distributed thinly throughout the forest are accumulated through human activity. In this manner, while it may well be that, over the short term, resources around camps are consumed and reduced, the seeds of future regeneration are, literally, sown through this consumption. In other words, these people have been contributing to the cycling of materials, including forest resources, within the ecosystem (although, in recent years, this cycle has been increasingly disrupted by the removal of large quantities of material from the forest as a result of the commercialization of forest products and deforestation).


Because farming activities require the clearing of arable land―i.e. the removal of vegetative cover from the soil, they have an even greater impact on the forest environment. However, the impacts are not all negative. It goes without saying that field sites help the growth of plants that prefer lots of light. In addition, many edible plants continue to exist in recently-abandoned swidden plots, attracting numerous wild animals. Furthermore, it is reported that, several years after a plot is abandoned, secondary forests on average comprise more than twice as many wild edible plants as old-growth forests. Moreover, it is known that, prior to migrating to villages alongside major roadways as a result of colonial government policy, both farming and hunting and gathering peoples lived scattered throughout the forest and maintained a highly nomadic lifestyle. In fact, in satellite photos, it is possible to see old secondary thickets dispersed throughout the forest marking the remains of old villages.

The village and fields belong to a group of swidden farmers. In the past such villages and fields were scattered throughout the forest.

At present, research regarding the impact of human activity on the forest environment is being conducted, led primarily by young researchers who graduated from the ASAFAS and current graduate students of the same program. They are engaged in detailed investigation of various topics including native forest vegetation, vegetation associated with camps, villages, fields and remains thereof, the optimal growing environment for useful plant species, and artifacts of human activity and their impact, etc. Particular attention is being paid to the above-described distribution of wild yams and other useful plant species as well as the impact of past human activity related to these plant species. Also being investigated is the history of migration by swidden farmers, who were once active in a wide area of the forest region, and the change in vegetation after abandonment of villages. Based on this research, it has been shown that the area currently slated to become a national park also contains old secondary coppices that mark the remains of historical human residences. There may, perhaps, be an ecological relationship between the areas abundant wildlife and past human activity. In any case, if it can be shown, through this series of research, that human activity has had a positive impact on the natural environment, the argument can be made that these forest residents have not simply depended on the forest and forest products but, rather, that they have contributed to organizing conditions for its regeneration.


Reinterpreting the Forest Landscape of the Congo Basin

Signs of human activity in the Congo Basin had already been discovered many years ago. While studying the forest soil next to the Motoba River in the north region of the Republic of the Congo in 1992, our colleagues (Rosei Hanawa and Hiroyoshi Chujo) discovered a buried carbide layer consisting of several layers. Carbon dating of these layers revealed that charcoal excavated from the deepest of these layers was 2,600 years old. As it is rare in the tropical rainforests for natural fires to develop into wild fires covering large areas, it is believed that these layers are human artifacts, i.e. remnants of field burning associated with swidden farming. We were deeply impressed by the discovery of evidence of such ancient practice of swidden farming in forests of the Congo Basin.

Buried carbide layer found in soil in the western region of the Congo Basin (photo by Rosei Hanawa).

As far as human artifacts are concerned, there is something else that also comes to mind. There are seemingly random areas covered with red soil scattered throughout the forests. This intrigued me, as I had heard that these areas are formed when the ground surface is directly exposed to rain and sunlight. It is possible that these areas represent fairly large previously-exposed spaces such as farm fields or villages. Even leaving that aside, it is suspected that humans contributed to the very formation of forests in this region. Rainfall in the western part of the Congo Basin varies by season, and, unlike typical tropical rainforests, semi-deciduous trees are distributed widely throughout the region. Among these, the most common trees are the large Triplochiton in the Sterculiaceae family and Terminalia in the Combretaceae family, which sometimes reach 1 to 2 meters in diameter. These, however, are so-called shade-intolerant species requiring fairly sizable open spaces for germination and growth. Furthermore, upon exploring forest areas in which these species dominate, one rarely finds saplings of these trees to succeed the current generation, and the only examples of the species are large, mature trees. Based on these observations, Kagari Shikata (currently a special research fellow at ASFAS) argues that the environment in which these trees developed may have differed from the closed-canopy environment of today and comprised fairly large open spaces. If human activity such as forest clearing for swidden farming did indeed contribute to the formation of such spaces, our understanding of the forests in this region would change dramatically.

The central region of the Ituri forest. The yellow area in the satellite image (right) represents a secondary forest and appears to mark the remains of one of the many villages that, in the past, were scattered next to roads and throughout the forest.

Seeing the Congo Basin from above, the primeval forest seems to continue on as far as the eye can see. However, even if it appears that the current forest landscape of the Congo Basin remains in a primeval state, in many cases, it has, in fact, been impacted by human activity for several centuries. More than a thousand years ago, Bantu swidden farmers who migrated from the savannas of West Africa to the forests of the Congo Basin nearly 3,000 years ago had spread throughout the entire forest region, with the exception of some wetlands. Their population density, of course, was most likely very low. However, three thousand years is more than enough time for these groups, who frequently and repeatedly moved around, to have left their footprint in every part of the forest. Even the plant ecologist P. W. Richards, who wrote The Tropical Rain Forest: An Ecological Study, noted that although the forests of Africa appear at first glance to be magnificent primeval forests, they are, in fact, old secondary forests. There is a need to re-examine the region’s forest landscape from the standpoint of historical ecology. Would the "value" of the forest decline if it was demonstrated that the footprint of human activity exists in the vast forest of the Congo Basin? Quite to the contrary, I would hope that such a demonstration would lead to the development of a new approach to forest conservation that takes into consideration the culture and history of the forest’s residents.


An aerial photo of the western region of the Congo Basin. Although it appears that the forest goes on forever, actually stepping foot in the forest, one sees signs of presence left by humans everywhere.