From Scandinavian evidence, a cooler, drier, more continental climate phase that followed the Atlantic climatic optimum (though with summers still warmer than those at present). In Britain, clear evidence for climatic change (e.g. differing peat deposits) is lacking, and the Atlantic/Sub-Boreal boundary is usually taken as the point of marked decline in elm pollen in the pollen stratigraphy (see pollen analysis). The reason for the elm decline (which, irrespective of elm species, is characteristic of pollen chronologies throughout Europe) has been the subject of much research. Hypotheses range from colder climate to epidemic disease to anthropogenic causes. The latter is linked to the selective use of elm as fodder for stalled livestock, now thought to have been a characteristic practice of Neolithic, forest-dwelling peoples. In many pollen chronologies this initial elm decline is followed quickly by a general decline in tree pollen caused by temporary forest clearance (‘landnam’) to provide land for slash-and-burn agriculture. The Sub-Boreal forms Pollen Zone VIIb, and lasted from about 5000 to 2800 BP.