Environment, Society and the Black Death

by Desconhecido

  125 Persson 2001, 355–357

  126 See discussion in Chap. 4

  PART III

  CONCLUSIONS IN A WIDER PERSPECTIVE

  7.

  Environment–society interactions

  Per Lagerås

  The dominating trend in the relationship between human society and the natural environment in a long-term perspective is one of increased human impact through time. This impact has affected plants and animals as well as soil, bedrock, water and the atmosphere and it has increased tremendously during the last one or two centuries. It has now become such a major factor in altering the conditions and processes on Earth, that it has been suggested that the latest part of the Holocene, from the late eighteenth century onwards, should be distinguished as a new geological epoch – the Anthropocene.1 The technological development, including the introduction of fossil fuels, has enabled fast population growth and (for parts of the population) increased consumption per capita, but it has also put enormous pressure on ecosystems, resources and the natural environment. Today, much environmental concern is about anthropogenic global warming, which may be seen as the ultimate and most spectacular effect of human impact on the environment witnessed so far.2

  However, these accelerating effects during the last few centuries should not blind us to the fact that human influence on the environment has a much longer history. Already early hunter-gatherers had great influence on ecosystems, whereas a systematic manipulation of the environment started with the first agriculture about 12,000 years ago.3 Since then, woodland clearing, cultivation, herding and fodder collection have gradually transferred natural environments to cultural landscapes as agriculture has spread around the globe. Tightly linked to agricultural expansion is deforestation. Even though half of the world’s deforestation has happened in the last 50 years (due to strong deforestation in the tropics), there has been a long-term process of deforestation from the introduction of agriculture to the present day.4

  On the very broad temporal scale, the historical development of global population numbers and human pressure on the environment shows an exponential increase, with slow and steady expansion during prehistory and most of history, followed by a very sharp increase during the last century. However, this is a matter of scale. The incredibly strong population growth during the last century – the number of people in the world first reached 1 billion in 1825 whereas the latest 1-billion-increase (from 6 to 7 billions) took only 12 years – tends to diminish any previous variations in population numbers and to make past developments look linear, smooth and steady. By large this is a false impression. A zooming in on almost any period or specific region would reveal a much more complex development, characterised not only by gradual population growth and agricultural expansion, but also by periods of stagnation and decline.

  The late-medieval crisis of Europe, which has been the topic of this book, is one such period of decline and it is far from the only one. There have been several other major social crises during the course of history. Some of them have gained much attention, like the collapses of the Western Roman Empire, the Classic Lowland Maya and the Rapa Nui on Easter Island,5 but these are only a few grand and well-studied examples of a common phenomenon. Even though the long-term trend on a global scale is characterised by expansion and population growth, stagnation periods and crises of different magnitude and duration are part of human history. In many regions, due to recurring and alternating periods of expansion and decline, population numbers tend to show a cyclic or wavelike development superimposed on a long-term increase, rather than just exponential growth.6 This cyclic appearance of population growth has been much discussed. In particular Thomas Malthus’ view that population growth would eventually outstrip food production, leading to population check by famine, disease or warfare, has been criticised for being too deterministic.7 However, regardless if periods of crisis and decline are direct consequences of previous expansion and population growth in a Malthusian sense, or if they are caused by other independent factors, it is an important observation that there have been recurrent periods of decline throughout history. These periods were also periods of decreased human impact on the environment.

  Fig. 56. A recently abandoned farm in the uplands of southern Sweden. Farm abandonment and reforestation was not restricted to the late-medieval crisis, but have happened several times during history (photo: Per Lagerås)

  In Sweden, as in much of Europe, particularly two such periods of decline during the last two millennia have gained attention. One is, of course, the Black Death and the late-medieval crisis of the fourteenth and fifteenth centuries. The other is a societal crisis during the sixth century. The causes and processes behind the sixth-century crisis are unclear and several different contributing factors have been suggested. Like for the late-medieval crisis plague may have been involved also in this crisis. The so-called Justinian Plague ravished the Mediterranean and much of Europe in 541–43,8 but it is still unclear if it reached Sweden. Also climatic deterioration has been suggested, in particular a series of unusually cold summers that started in 536, caused by volcanic dust in the atmosphere.9 A third explanation may be political and social unrest, possibly as an indirect effect of the fall of the Western Roman Empire.10 Probably several different factors worked in combination. When it comes to agricultural change and environmental responses, the sixth-century crisis shows great similarities with the late-medieval crisis, with settlement abandonment and woodland regrowth, in particular in marginal areas. The latter is reflected in several pollen records from northern Europe, including Sweden.11

  Hence, the long-term history of environment-society interactions cannot be characterised simply as a one-way development of agricultural expansion and deforestation and an ever-increasing human impact on the environment – there have also been periods when the pressure from agriculture eased. Depending on the natural and climatic conditions as well as the duration of a crisis, abandonment would in most environments eventually lead to reforestation. In Europe during the last two millennia we have seen two major periods of reforestation – the sixth century and the fourteenth–fifteenth centuries – both periods connected to population decline. In many regions there has also been a third one, which started in the nineteenth century and continues today. Unlike the two earlier ones, the latest one is not a reflection of a societal crisis or a general population drop, but rather the transformation of non-profitable agricultural land to forest plantations, particularly in poor uplands (Fig. 56).12 Parallel to this reforestation of marginal land there has been an intensification of agriculture on the most productive land.

  In addition to these three major periods of farmland abandonment and reforestation, there have been several short-lasting interruptions and more local crises that affected smaller areas or regions. Some were caused by outbreaks of plague and other epidemic diseases, either among people or their livestock.13 Others were caused by war and plundering. In Sweden, for instance the late sixteenth century was a period of warfare, which left parts of the countryside devastated.14 In areas with poor conditions for agriculture there may also have been abandonment due to soil depletion and climate deterioration. Occasionally, also harvest failures due to poor weather may have resulted in famine and depopulation. Very little is known about these short-term and local crises and their possible environmental consequences.

  Studies of the relationship between societal crisis and environmental change have focused primarily on those cases where overexploitation and mismanagement appear to have been the origin of the crisis, or where cultural maladaptation or societal rigidity prevented necessary actions and decisions to be made.15 Less attention has been paid to environmental changes that followed upon other types of crises, like disease and warfare.16 Such crises were not caused by environmental mismanagement, but may still have had important environmental and ecological consequences.

  Urban Emanuelsson suggests that recurrent periods of decreased human impact in the history of the European c
ultural landscape have been beneficial for the overall biodiversity.17 Several species of plants and animals are favoured by secondary succession and reforestation and would probably have gone extinct if there had not been interruptions in the agricultural land use. Many species are favoured by agriculture – in particular the many herbaceous plants that thrive in open grasslands – but few species would tolerate a continuous pressure from agriculture in the long run. The key to high biodiversity is the dynamic, both temporal and spatial, between well-managed agricultural land, abandoned land in different stages of secondary succession and grown-up forest. This dynamic has provided a rich variety of ecological habitats, species richness and genetic variety within species.

  This is a hypothesis, and still little is known about the ecological consequences of societal crises in Europe’s history. However, in the study presented here a couple of vegetation changes in Sweden in the wake of the Black Death have been identified, which may be a starting point for a discussion on the ecological consequences of this particular crisis. First of all, pollen and dendrochronological data show that some abandoned land was overgrown by woodland. These data thus confirm the generally held belief that forest cover increased during the crisis, at least in marginal uplands. The abandonment of fields in combination with decreased grazing pressure enabled the sprouting of shrubs and trees and started a process of natural woodland succession. In particular birch woodland expanded but there was also regeneration of oak and pine and to some degree spruce. Several forest plants and animals must have been favoured by this change, particularly those associated with light, early-successional woodland.

  But not all abandoned farms were overgrown by forest. Even though settlements and arable fields were abandoned, many of them were used for grazing and occasionally for hay mowing, which kept the landscape open by holding back the forest. Hence, another vegetation change was associated with the turning of arable fields into pastures and meadows. When cultivation ceased, the immediate effect would have been enhanced flowering of annual weeds, but soon a grass sward would develop and a rich flora of perennial herbs typical of grazed and mowed environments would take over.

  The most apparent vegetation changes after the Black Death, such as the expansion of birch woodlands, lasted for about 200 years until the sixteenth century. By the late sixteenth century, the re-establishment of arable fields, meadows and pastures had again replaced much of the secondary woodland. There may, however, also have been more long-lasting ecological effects. Dendrochronological data show that some trees, particularly of pine, that germinated in connection to abandonment in the mid-fourteenth century lasted for several hundred years. They consisted the oldest tree generation of the forest for a long time to come. Still in the early eighteenth century there were living trees that had germinated around the time of the Black Death. By that time they were about 350 years old. Such old trees are usually the home for a large number of plants and animals, like fungi, lichens and insects, and contribute significantly to the species richness of forests.18 We may therefore conclude that the Black Death of the mid-fourteenth century still affected biodiversity more than 300 years later.

  There have been no studies on changes in the fauna in Sweden in the wake of the Black Death, but such changes certainly occurred. Insects and other invertebrates, birds and also mammals were affected by the expansion of woodland and other changes in the vegetation. Herbivores like deer and elk could browse the new shrub vegetation on abandoned land and benefit from decreased competition by domestic animals.19 Mammals, and particularly carnivores, may also have been more directly affected by the decrease in human population numbers, due to reduced hunting pressure. A royal letter from 1376 indicates that this was actually the case. According to the king, people complained that wolves and bears everywhere made much damage to humans and their livestock. He therefore proclaimed increased hunting and demanded one wolf skin to be delivered to the bailiffs each year by six farmers together. Janken Myrdal interpreted this as a direct effect of the population drop.20 With a much smaller population in the wake of the plague, particularly in marginal woodlands, it was impossible to maintain hunting pressure on carnivores at the same level as before (Fig. 57). Another immediate effect of the plague may have been that there were unguarded cattle and sheep roaming the woods. Accessible prey and decreased hunting pressure gave the populations of wolves and bears, and possibly also of lynx and foxes, the opportunity to grow stronger during the crisis.

  Fig. 57. Wood carving from Olaus Magnus’ History of the Nordic People, published in 1555, showing wolves attacking a sledge. A letter from 1376 indicates that wolves may have increased in numbers in the wake of the Black Death

  In addition to changes in vegetation and fauna, the population drop may have had wider environmental consequences. According to a hypothesis by William Ruddiman, reforestation in Europe in the wake of the Black Death, together with reforestation in the Americas in connection to the population drop of the sixteenth and seventeenth centuries, affected global climate.21 Expanding woodlands resulted in lower levels of carbon dioxide in the atmosphere, a reduced greenhouse effect and a colder climate. Hence, the Little Ice Age may have been a consequence of the Black Death, at least to some degree. The hypothesis has been debated and climate modelling indicates that the observed changes in carbon dioxide concentrations may also be explained by natural factors.22 According to Ruddiman the observed increase in carbon dioxide concentrations during the Late Middle Ages amounts to an average reforestation in Europe at a level of 25–45%.23 The study presented in this book confirms that there was reforestation due to farm abandonment, at least in marginal uplands of southern Sweden, but to a lesser degree. According to the pollen-based landscape reconstruction, woodland expanded by approximately 20% in the higher parts of the uplands, whereas reforestation at lower elevations was less or insignificant. However, studies from several parts of Europe are needed to fully test the hypothesis.

  The Black Death and the late-medieval crisis may also have affected marine environments. Today, nutrient leaching from modern agriculture leads to eutrophication and the spread of hypoxia (low oxygen conditions) in the bottom waters of the Baltic Sea. However, sedimentological studies show that hypoxia occurred in the Baltic Sea also during specific periods of the past. Warm climate seems to have been a driving force during most of the Holocene, but for later periods also human impact may have contributed. One such period of hypoxia corresponds to the Medieval Warm Period of AD 800–1300, which was also a period of agricultural expansion. It was followed by a period of oxic condition, 1300–1850, which roughly corresponds to the Little Ice Age, and then again hypoxia from 1850 to present. Lovisa Zillén and Daniel Conley suggest that the period of hypoxia, 800–1300 may have been caused by a combination of warm climate and increased agricultural land use in the Baltic catchment, and that the turn to more oxic conditions that followed was the combined effect of colder climate and a sudden decline in agriculture due to population drop.24 Similar to the Ruddiman hypothesis it is difficult to separate natural factors from human impact, but taken together the two examples suggest that the environmental consequences of the late-medieval crisis may have been more far-reaching than what has been hitherto believed.

  Leaving the still hypothetical impact on climate and sea aside, we can conclude that there were changes in the vegetation and fauna as direct consequences of the crisis. The next question is whether these changes had any influence back on society. Some of the changes may have had a positive effect by creating good preconditions for agricultural re-expansion. Others may have had a negative effect by making re-expansion difficult, troublesome and laborious.

  Starting with the positive effects, the period of agricultural abandonment was a period of soil recovery and may be compared with long-term fallow. Before the introduction of chemical fertilisers, recurrent fallow periods were an integrated an important part of most agricultural systems. The aim of fallow was to restore some of the nutrients extracted from t
he soils by the crops during cultivation. However, fallow periods were usually not long enough to restore all the lost nutrients, leading to long-term declining fertility and gradually smaller yields.25 When fields were abandoned in the wake of the plague, they were turned to grassland used for pasture or mowing, or they were overgrown with shrubs and trees and eventually turned into woodland. In either case, this unintended fallow transformed depleted arable fields to rich and fertile brown-earth soils. After the crisis, when abandoned farms were re-established and fields were put under the plough again, the new settlers could enjoy fully restored soils and high yields.

  Also some other agricultural changes that were originally caused by necessity may have been beneficial for agricultural expansion after the crisis. Due to shortage of labour and excess of land, animal husbandry had gained in relative importance in comparison to crop growing during the crisis. Surviving farms had expanded their pastures and livestock by incorporating the land of abandoned farms. When population numbers started to recover and fields were put under the plough again, larger livestock provided rich access to manure to enrich the soils. In some regions, the incorporation of abandoned land may also have facilitated the introduction of crop-rotating systems that were based on systematic fallow in the infields.26 In comparison to the older one-field system, they provided a better basis for a productive and sustainable agriculture.

  It can be concluded that environmental and agricultural changes in the wake of the plague in some ways created good conditions for agricultural expansion and thereby may have facilitated societal recovery. But they had negative consequences as well. One example is the increased number of big carnivores. If reduced hunting pressure during the crisis led to expanding populations of wolf and bear, it certainly made the forests more insecure. New settlers who tried to reclaim abandoned land in forested areas had to accept a higher than normal predator pressure on their livestock. Furthermore, the responsibility to watch over the animals and to protect them from wolves and other threats was now on the shoulders of women and children. They had taken over the herding task from adult men during the crisis, probably as a consequence of labour shortage.27