Biological Indicators of Past Environments

As noted above, plant and animal remains are key indicators of past environments, and may range in size from whole trees to microscopic organisms such as diatoms. Tree remains can be particularly useful where they are of species suitable for tree-ring dating or dendrochronology (e. g., oak or pine). Tree rings can also yield information on past climate change, which may result in variations in ring width and changes in stable isotope ratios of the wood. Periods of very narrow tree rings have also been linked to the short-term effects of major volcanic eruptions on climate, potentially involving a drop in temperature of a few tenths of a degree for up to a decade.

The most useful and widely employed biological remains for palaeoenvironmental reconstruction are those groups which occur abundantly in a range of contexts, can be identified to species level, and have a narrow ecological range. Assemblages of the remains of such organisms can be used to reconstruct past environments on the basis of knowledge of their ecological requirements, applying the principle of unifor-mitarianism (‘the present is the key to the past’). Thus, if a species requiring a particular set of conditions today is found in a Neolithic context, we might assume that similar conditions existed in the Neolithic period in that area. In practice such an approach is best applied where many different species are present, as a single species today may not occupy all possible niches in which it might be able to survive.

The type of context is key in determining which plant and animal remains are available for palaeoenviron-mental reconstruction. The most widely used biological method is analysis of pollen grains and spores (‘paly-nology’), which are commonly preserved in huge numbers in waterlogged environments, allowing changes in vegetation to be traced over thousands of years. Not all species of flowering plant produce distinctive pollen, but there are several key indicators of human activity that allow the effects of people on the environment to be reconstructed. In naturally wooded landscapes human activity involving woodland clearance may be detected by a decline in tree pollen and increase in that of sun-loving herbs, while agriculture may be evident from remains of crop plants or plants that benefit from grazing, for example, ribwort plantain (Plantago lanceolata) in northwest Europe (see Pollen Analysis).

Pollen analysis is often accompanied by analysis of other biological remains to assist in interpretation, including larger (macroscopic) plant remains such as seeds. These have the advantage that they are usually more closely identifiable than pollen grains, but they are rarely as abundant. Microscopic charcoal particles are also commonly used to complement the pollen record. Such particles may originate from fires of natural or human origin, but in parts of the world where natural fires are rare they may help in identification of the role of human activity in environmental change.

An example of an area where several types of biological remains have been used to reconstruct past environments is the Vale of Pickering in northeast England. The well-known early Mesolithic site of Star Carr lay on the edge of a large lake that gradually filled with sediment during the Late Upper Palaeolithic and Mesolithic periods. Analysis of plant and animal remains from the archaeological site showed the range of animal species hunted by the occupants, the nature of the local environment over the several decades of its occupation, and the use of fire for burning local reedswamp. This was complemented by the longer-term and more regional picture of environmental change provided by analysis of the deep sediments from the center of the lake. Here analysis of sediment composition, pollen, charcoal particles, macroscopic plant remains, mollusks, and ostracods, combined with radiocarbon dating, showed how the environment was affected by climate change and use of fire by human groups both at the Star Carr site, and elsewhere in the landscape, throughout the period from c. 13 000 to 6500BP.

See also: Human-Landscape Interactions; Insect Analysis; Invertebrate Analysis; Macroremains Analysis; Paleoenvironmental Reconstruction in the Lowland Neotropics; Phytolith Analysis; Pollen Analysis; Soils and Archaeology; Vertebrate Analysis.