Historical Records and Collections

This chapter introduces the use of historical documents and other forms of information that depend on written explanation, such as natural history collections and historical photographs. After a general explanation of the unique values of these data for establishing historical baselines and trajectories, it gives a brief introduction to the methods used to assess the validity of the sources, including consideration of various biases that are integral to written documents. These include a consideration of scale. The chapter then describes a variety of sources, including historical data, maps, photographs, government documents, and plant and animal collections, with examples of how each has been used to establish some condition or process in the past.

Conclusion

This extensive revision of the first edition of People and the Land Through Time incorporates research over the last two decades to bring the field of historical ecology from an ecological perspective up to date. It emphasizes the use of new sources of data and interdisciplinary data analysis to interpret ecological processes in the past and their impacts on the present. It describes a diversity of past ecosystems and processes, with an emphasis on their effects on affect current ecosystem structure and function. This historical perspective highlights the varied and complex roles of indigenous people in historic ecosystems as well as the importance of past and present climatic fluctuations. The book begins with an introduction to the importance of history for ecological studies. The next three chapters explain methods and approaches to reconstructing the past, using both traditional and novel sources of data and analysis. The following five chapters discuss ways people have influenced natural systems, starting with the most primitive, manipulating fire, and proceeding through altering species ranges, hunting and gathering, agriculture and finally structuring landscapes through land surveys, trade and urbanization. Two chapters then deal with diversity, extinction and sustainability in a changing world. The final chapter specifically focuses on the importance of history in basic ecological studies, in conservation and in understanding the consequences of global change, using a variety of examples. Throughout, the emphasis is on the potential for evidence-based research in historical ecology, and the new frontiers in this exciting field.

Agriculture and Its Residual Effects

This chapter shows how detailed historical ecological research indicates that the impacts of historical agriculture are more widespread than previously thought, and often more subtle. Even apparently obvious connections, such as that between nomadic grazing and erosion, are now being questioned by historical analyses. Agriculture has not resulted universally in decreased biodiversity; in fact, grazing over millennia has in places increased biodiversity. Historical agriculture is also being implicated in millennial scale increases in CO2 and CH4 in the atmosphere, the former from deforestation and fires and the latter from paddy rice agriculture starting five thousand years ago. The discovery of hidden field systems under mature temperate and tropical forests and grasslands in Europe and the Americas are allowing reassessment of the impact of prehistoric agricultural systems on soils, species diversity, landscape patterns, and climate. The concept of "landnam" episodes proposed by Iversen for northern Europe may be applicable much more broadly. This has major consequences for considering human impact on global environments.

Extending Species’ Ranges

This chapter considers movement of species over time. Many land managers and ecologists consider invasive species to be the most important factor in disrupting "natural" ecosystems today, at least in North America. This chapter takes a historical approach to the process of species range extensions beginning with changes in the absence of human vectors, then considering the specifically human role in disseminating species world-wide. Human-mediated species' range extensions are ancient in many parts of the world so that what we might think of as "natural" may also have a human aspect. Using examples of range extensions of plants, animals, and disease-causing organisms, the discussion offers cautionary tales of species that have been introduced on purpose or inadvertently and have later caused severe disruptions to native ecosystems, as well as more positive examples of cultural landscapes in which non-native species are fully integrated into diverse and functional ecosystems. Comparing change over time in species diversity and importance may show unexpected patterns, such as the increase in both native and non-native plant species at the same sites in England. Historical studies also indicate that removal of the exotics may not lead to reestablishment of the native flora. Integration of some non-native species into a new ecosystem may eventually be more or less complete.

The Sedimentary Record

This chapter introduces the use of materials found in sediments for reconstructing the past. After summarizing methods for collecting, processing and dating sediment, it presents a variety of organisms, minerals and other chemicals useful for interpreting the history of both the surroundings of a sedimentary basin and of the basin itself. A critical part of this analysis is understanding the processes by which materials get to the basin and the sediment and are changed after sedimentation. The relationship between the evidence, for example, pollen, and the organisms or landscapes that produce the evidence is illustrated by examples taken from different types of landscapes. The chapter discusses multidisciplinary studies and models that integrate independent indicators of climate and vegetation to arrive at a composite picture of landscape change and allows interpretation of causes of changes seen in the sediment.

Field Studies: Bringing Historical Records Down to Earth

There are many field techniques that take research beyond what can be found in written documents. Clues to the past are hidden in such subtle (and not so subtle) features as topographic modifications, soils, and tree trunks. Field studies search for evidence of conditions and for their resultant effects through a variety of techniques. Features may be evident from a ground survey, located precisely through GPS. Remote imaging, using a variety of techniques from simple aerial photography to lidar, reveal hidden patterns, that may then be studied on the ground. Archeological study relates the patterns found on the ground to human activities, as they have changed over time. Dendroecology interprets records left in tree rings. Some studies look at stands of different ages to study change over time, and long-term studies trace change in individual stands. In these field studies that look at the past, soil characteristics and materials hidden in the soil, such as DNA, stable isotopes and charcoal, can reveal details of past processes and species. These methods are illustrated with examples from a wide range of biomes.