Persistency of native species through the period of early human habitation on Kohala Peninsula, Hawai‘i Island

An extensive dryland agricultural system was developed on Kohala Peninsula, on the northwestern tip of Hawai‘i Island, beginning about 700 years ago. It was cultivated almost continuously over the following six centuries. Archeobotanical studies from this field system and adjacent residential sites revealed considerable information about native vegetation that was growing in the vicinity and was gradually accompanied and/or replaced by Polynesian and exotic species. Analyses of wood charcoal, found below agricultural walls and within cultivated fields, suggest that the most common trees and shrubs during the early phases of agriculture were Chenopodium oahuense, Myoporum sandwicense, Chamaesyce spp., Sida cf. fallax and Sophora chrysophylla. Radiocarbon dates indicate that at least some of them persisted through the period of early habitation. Land snails from various contexts provide additional evidence of native environment during the same period. They present a mixed assemblage of native species e.g. from the families Amastridae, Gastrocopta and Endodontidae, some of which are extinct today. Charcoal further records early cultivation of Ipomoea batatas and Cordyline fruticosa, which were Polynesian introductions. Charred seeds from agricultural and residential sites mostly belong to the endemic Chenopodium oahuense. However, the presence and early appearance of exotic species such as Chenopodium murale and Portulaca pilosa indicate human disturbance. Intensive agricultural activity is also reflected by pollen of grasses and agricultural colonizers such as Chenopodiaceae. The simultaneous occurrence of endemic, indigenous, Polynesian and exotic taxa suggests substantial human impact on natural vegetation and the persistence of some native shrubs and trees through time.