Reconstructing Environmental Impacts of Fire from the Holocene Sedimentary Record

Summary

Assuming that the charcoal record preserved in lake sediments is a record, albeit an incomplete and biased record, of past fire occurrence and extent, I outline quantitative approaches to the reconstruction of the impacts that fires may have had on environmental variables during the Holocene. An important distinction in considering the environmental impacts of fires is between natural fires and fires initiated by humans for forest destruction and land- use management. The palaeoecological record of fire-related environmental impacts is strongest when considering fire as a management tool. Such fires can be shown from palaeolimnological studies to raise the nutrient level and pH of lakes and to increase soil erosion and inwashing of minerogenic matter. The environmental impact of natural fires is more difficult to demonstrate unambiguously. Such demonstrations require extremely fine-resolution stratigraphical data and quantitative palaeoenvironmental reconstructions with a high precision. As is so often the case in palaeoecology, alternative hypotheses may be possible to explain observed stratigraphical patterns. Statistical techniques such as constrained ordinations, variance partitioning, and Monte Carlo permutation tests to derive empirical probability values provide useful means of testing and falsifying alternative hypotheses involving complex stratigraphical data. Recent developments in quantitative environmental reconstructions and in the statistical analysis of stratigraphical data that are relevant to the assessment of the environmental impacts of fire during the Holocene are briefly outlined and illustrated with three recently published examples. Current research techniques are briefly discussed and some difficulties and limitations are outlined.