Stratigraphic sequences on Tikopia reveal extensive burning (marked by charcoal in sediments), erosion of the volcanic slopes, and deposition of terrigenous sediments on the coastal plain as the island’s forest was cleared for gardening during the Kiki Phase (950–100 B.C.). During the island’s Sinapupu Phase (∼100 B.C. to A.D. 1200) the use of fire in agriculture gradually declined as the population developed the sophisticated system of arboriculture RO4929097 purchase or “orchard gardening” for which Tikopia is known ethnographically. This arboricultural system mimics the multi-story layering of the tropical rainforest, allowing for extremely high population
densities (∼250 persons/km2). Virtually every hectare of the Tikopia land surface consists of intensively managed orchard gardens, a classic case of the total transformation of an island landscape into an anthropogenic ecosystem.
Mangaia, like other islands within central Eastern Polynesia, was not colonized by Polynesians until ca. A.D. 900–1000. With a land area of 52 km2, the island consists of a 20-million year old central volcanic core surrounded by a ring of upraised coral limestone or makatea. The old, laterized volcanic terrain is nutrient depleted and was highly vulnerable to intensive human land use activities. Archeological investigation of several stratified rockshelters (especially the large MAN-44 site) and sediment coring and palynological analysis of valley-bottom Selleck BMS-754807 swamps and lakes revealed a detailed history of land cAMP use and human impacts on Mangaia ( Steadman and Kirch, 1990, Ellison, 1994, Kirch et al., 1995 and Kirch, 1996). The sediment cores and pollen records reveal rapid deforestation following Polynesian colonization, with an initial spike in microscopic charcoal particles indicative of anthropogenic burning, probably in an effort to cultivate the volcanic slopes
using shifting cultivation. Once the thin organic A horizon had been stripped off of hillslopes through erosion, the lateritic soils were incapable of supporting forest regrowth; the island’s interior became a pyrophytic fernland dominated by Dicranopteris linearis fern and scrub Pandanus tectorius. Agricultural efforts were then directed at the narrow valley bottoms, which were developed into intensive pondfield irrigation systems for taro (Colocasia esculenta) cultivation. The faunal record from the Mangaia rockshelters, especially site MAN-44, exhibits an especially well-documented sequence of significant impacts on the native biota, as well as the introduction of invasive and domestic species (Steadman and Kirch, 1990 and Steadman, 2006). Of 17 species of native land birds present in the early phases of the sequence, 13 became extinct or extirpated.