Quantifying the last 7500 years of land-use changes on the island of Karmøy, southwestern Norway, with focus on three periods with monumental burial mounds

• Landscape changes investigated during three phases with monumental burial mounds. • Agriculture began c. 500–700 years before the first burial mounds were constructed. • Agriculture was introduced c. 2000 BC and expanded in the Roman Iron Age (1–550 CE). • The strategic location near the Karmsund Strait became increasingly important over time. The northern part of the island Karmøy in southwestern Norway contain one of Scandinavia’s largest assemblages of monumental burial mounds. The size and rich grave goods of the mounds demonstrate three separate periods of elite societies from the Bronze Age Period II/III (1300 BCE) until the final ship graves were constructed in the Merovingian Period (550–800 CE). In this study, the vegetation history and land-use practices are reconstructed from 5500 BCE to 2000 CE, with a focus on the three phases with burial mounds. We examine whether the elite societies formed due to a surplus in the agro-pastoral economy or due to the islands strategic position near the Karmsund Strait. The regional scale vegetation is reconstructed using REVEALS and the local scale vegetation is based on a pollen record from Lake Bøvatn and the LOVE model. The results show that the breakthrough of agriculture with cereal production started in the region c. 2000 BCE with a reduction in forest cover 500–700 years before the first monumental burial mounds were constructed. This agricultural practice probably created the surplus needed for the development of the first elite society. Woodland cover was reduced to c. 50 % on a regional scale between c. 1 and 500 CE (representing the second phase of burial mounds), while on a local scale around Lake Bøvatn the woodland cover was absent. A simultaneous increase in animal husbandry and cereal cultivation, suggests population expansion. During the third phase, between c. 650 and 820 CE, the subsistence strategy appears to be more focused on animal husbandry, which is less labour intensive. The pollen composition from one of the ship graves, Storhaug, indicates that the surrounding landscape was dominated by heather and grassland. The strategic location near the Karmsund Strait became increasingly important over time, especially in the period corresponding to the third phase of burial mounds. This study shows the complex relationship between physical landscape properties and the development of elite societies as well as the benefit of combining archaeological and palaeoecologial data to study past societal change.