Reconstructing Egetation Di Ersit in Coastal Landscapes
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This thesis will be published as a volume in the series Advances in Archaeobotany. English text editing SuzanneNeeds-Howarth,Toronto AnnetteHansen,GIA,Groningen Book and cover design ChristineKlein,Bremen www.christineklein.nl Photos MansSchepers,RenéCappersandIngerWoltinge Production RoelfBarkhuis www.barkhuis.nl StichtingNederlandsMuseumvoor Financial support AnthropologieenPraehistorie S•N•M•A•POL.indd 1 3/28/12 4:04:30 PM © 2014 Mans Schepers Allrightsreserved.Nopartofthispublicationmaybereproducedortransmittedinanyform orbyanymeans,electronicormechanical,includingphotocopying,recording,orbyany informationstorageorretrievalsystem,withoutpermissioninwrittenformfromtheauthor. ISBN (dissertation edition) 978-90-367-6975-4 ISBN (digital edition) 978-90-367-6974-7 Aan Nicolien Bottema Mac-Gillavry en Henk Woldring Voor het wijzen van planten en het planten van wijsheid Opdat die ooit bloeien moge… Contents Chapter1 General introduction 009 Chapter2 An objective method based on assemblages of subfossil plant 029 macro-remains to reconstruct past natural vegetation: a case study at Swifterbant, The Netherlands Box1 A pure sample 061 Chapter3 Wet, wealthy worlds: The environment of the Swifterbant river 073 system during the Neolithic occupation (4300–4000 cal BC) Box2 Why sample ditches? 109 Chapter4 Dung Matters: An experimental study into the effectiveness 123 of using dung from hay fed livestock to reconstruct local veg- etation Chapter5 A review of prehistoric and early historic mainland salt marsh 159 vegetation in the northern-Netherlands based on the analysis of plant macrofossils Chapter6 General discussion 195 References 219 Samenvatting 243 Dankwoord 253 List of publications 259 Affiliation of co-authors 261 Chapter 1 009 General introduction People AND VEGETATION Reconstructing vegetation is far from a walk in the park ‒ yet it is a prerequisite for a fuller understand- ing of past human behaviour in all its aspects. The exploitation of the landscape is not restricted to the direct use of plants. It is the grass we will not let grow under our feet, the forest we can- not see for the trees, and the nettle we are willing to grasp. To reduce vegetation to the berries we chew, the meadows we graze our livestock on, and the oaks we fell to support our roofs is an anthropocentric simplification of the complicated interaction between humans and their environment. This relationship is relevant to, and has been studied from, a variety of perspectives, both historical and contemporary (Sukopp 1969). Traditionally, archaeological studies (and archaeolo- gists) have split into two camps. On the one hand, there are the so-called ‘specialist studies’, such as ceramic analysis, lithic analysis, and zooarchaeological analysis. On the other hand, 0010 there are the more general studies, in which various aspects of one period are brought together. In this tradition, the study of past vegetation would be regarded as a specialist palaeobo- tanical (also known as archaeobotanical) study. However, the relevance of the natural environment for understanding hu- man behaviour has long been acknowledged by more generalist archaeologists, in some cases as a result of the archaeologist’s background in biology or physical geography (two Dutch exam- ples are Louwe Kooijmans [1974, 1985] and Waterbolk [1954]). Two main research questions underlie this study, of which the first governs the second: Is it possible to improve upon the reconstruction of past vegetation at the most detailed level? To answer this first research question, several approaches are adopted. First, the potential of applying both recent and long-established methodology and data from present-day vege- tation ecology to archaeobotanical data is explored. Modern ecological field studies are an essential element for the inter- pretation of the archaeobotanical record (Butzer 1982, 171–172). Second, the relationship between some frequently studied types of archaeological contexts and their botanical composi- tion (as opposed to standing vegetation) is studied in detail. It is alleged that it is possible to successfully address past vegeta- tion composition by seeking novelty in the analysis, rather than by seeking new proxies (stage 5 rather than 4 in Fig. 1.5). In this study, the emphasis lies on the reconstruction of vegetation in wetland environments where an open coast profoundly influ- enced landscape dynamics. The second research question follows directly from the first: Does a more detailed reconstruction of vegetation enable us to expand our understanding of past human interaction with the landscape? To explore this, new approaches are applied to two coastal wetland areas in the northern Netherlands, where several botanical and geological studies dealing with land- scape and vegetation have been carried out previously by oth- er researchers. These areas, the Swifterbant river system and the terp region, are the subjects of major lines of research by the Groningen Institute of Archaeology. Having already been studied intensively, these two regions combine the challenge of Chapter1 011 being able to add original results and ideas with the benefit of a substantial corpus of available data. Both new primary data and previously published data are used, thus making internal reports and reports resulting from Dutch commercial archaeol- ogy accessible to the international community. T HEORy OF VEGETATION RECONSTRuCTION In order to be able to ad- dress the difficulties we encounter when dealing with the recon- struction of past vegetation, it is essential that we define what vegetation actually is and how it differs from a list of (quantified) taxa, as typically results from archaeobotanical analysis. The difference between raw archaeobotanical data and past vegeta- tion is analogous to the difference between the terms ‘flora’ and ‘vegetation’. The primary difference lies in the spatial compo- nent. The flora of a certain area is a list of taxa encountered in a certain area. While walking through this area, one would notice that these plants are not randomly distributed; they are, in stead, grouped in a systematic way (Meltzer and Westhoff 1942, 17). Vegetation is the spatial distribution and coverage ratio among the taxa of a flora. Whereas flora is thus a rather abstract concept, vegetation is the factual spatial manifestation of plants, high or low, open or dense, that one can actually walk through (Cappers and Neef 2012, 93; Westhoff et al. 1995, 15). Archaeobotanical data, which are basically a list of identified (quantified) plant taxa, can be considered an incomplete past flora. The complex relationship between archaeobotanical sam- ples and vegetation is visualized in Figure 1.1. A number of major differences exist between taxon lists (at whatever taxonomic level) and reconstructed vegetation. First, the axes of the matrix summarizing the results differ, and so do the units of measurements in which these are expressed. Whereas vegetation is mostly expressed in ‘coverage’ per de- fined surface area (‘relevé’), archaeobotanical data are ex- pressed in ‘number of remains’ per sample. Number of remains is the most common form, but alternatives do exist (e.g. categories of number of remains, presence/absence). In addition, synoptic tables of vegetation descriptions can be designed in various ways (Schaminée et al. 1995b). 012 Figure 1.1 Diagramshowingthethreestepsthatmaybeusedtotransformthecompositionof archaeobotanicalsamplesintovegetation Taxon lists already differ from past flora at the qualitative level. This difference primarily concerns taxa that are present in the past vegetation but are lacking in the archaeobotanical archive. The cause may be differences in seed production, seed dispersal, and preservation conditions, or the fact that some taxa are hard to distinguish at a lower taxonomic level. Moreover, the palaeo- botanical archive may also include taxa that were not part of the vegetation during the period under study ‒ for example, when erosion of peat layers results in the inclusion of Sphagnum leaves in samples from a salt marsh environment (see Chapter 5). Additional complications are that most archaeobotani- cal samples represent a mixture of vegetation types and that many factors, known as formation processes, influence the chances of remains ending up in an archaeological sample (Mik- sicek 1987; Willerding 1991). All of these formation processes combined are sometimes referred to as taphonomy, but this is strictly spoken not exactly the same thing (Gifford 1981). In this study, site formation and taphonomy are used interchangeably. The model presented by Cappers (1995a) discusses the formation Chapter1 013 of seeds in the soil. Other contexts, such as drift lines, dung lay- ers, hearths, or post holes, may be subject to profoundly differ- ent processes that determine sample composition (e.g. Charles 1998; Out 2012; Van Vilsteren 1984; Wolters and Bakker 2002). Furthermore, because many vegetation types gradually merge into others, the translation of numbers of remains in a sample into relative coverage is invalid for reasons that go beyond differ- ences in taphonomy among species. For example, the remains may represent a sequence of vegetation types from a limes diver- gens (Westhoff and Van der Maarel 1978, 303–305), in which the same taxa occur, but in different