Methodological falsification and the interpretation of palaeoecological records: the cause of the early Holocene birch decline in western Canada

Abstract

The use of palynological data to test hypotheses concerning biological interactions, pedological development, or climatic change is often based upon speculative assumption about the causes of past vegetation change. In this study the approach of methodological falsification is used to investigate the causes of the decline of Betula in the western interior of Canada between 9000 and 7000 yr. BP. The approach consists of the following steps: (1) determining the timing and geographic extent of the Betula decline; (2) reviewing information on the modern ecology of Betula papyrifera and the modern environment and late Quaternary palaeoenvironments of western Canada to develop a series of parsimonious and testable hypotheses regarding causes for the birch decline; and (3) testing the hypotheses using internal evidence from the pollen record and independent palaeoenvironmental data. This approach leads to the conclusion that hypotheses linking the birch decline to a pathogen, interspecific competition or progressive soil development should be rejected. The surviving hypothesis is that the birch decline represents an individualistic response to climate change. However, the process of erecting and testing these hypotheses demonstrates that great uncertainty exists in extracting the causes of vegetation change from palaeoecological records.