The case study in Part III summarized five different explanations for the mid-Holocene European elm decline and found all either inadequate or inconclusive. Climatic deterioration, soils depletion, human exploitation of the species, human competition for the tree's habitat, and disease were all shown to be inadequate to comprehend the evidence. The hypothesis invoking climatic deterioration to explain the widespread loss of elms from the temperate forests was poorly supported on several counts, as was the hypothesis of soils depletion. The diversity of habitats, elm species, soils, and topography across the prehistoric elm range in central and western Europe undermines the appropriateness of both these hypotheses as explanations. Looking for single causal explanations for the behavior of complex systems is fruitless (Chapter 2).

Decline in elm pollen began in southeastern Europe early in the sixth millennium b.p., even as the Holocene spread of elms reached its maximum distribution (Huntley and Birks 1983: 412). The decline was time-transgressive westward until around 5000 b.p., when it spread rapidly to its northern limits (Fig. a). The near-coincidence with evidence for the initiation of farming in northern Europe long supported speculation that the elms were killed by pastoralists and farmers establishing agricultural landscapes.