Late Holocene human-environment interactions in New Zealand: a biomarker approach

The recent colonization history of New Zealand makes it an excellent test site for investigating the early impact of human activities on natural ecosystems. The arrival of humans around 700-800 yr BP is marked by a neat increase in fire activity and land clearance, as documented by charcoal and pollen records [1]. Here, the validity of biomarkers was tested in a multi-proxy study including three different categories of organic molecular markers. Results were compared with existing paleoecological data. Samples from a small alpine lake in the South Island of New Zealand (Lake Kirkpatrick, Otago), covering a time span of about 800 years (~AD 1153-1961), were analyzed for polycyclic aromatic hydrocarbons (PAHs) as combustion tracers, monosaccharide anhydrides (levoglucosan and its isomers, MAs) as specific markers of biomass burning and fecal sterols (FeSt) for the reconstruction of human/animal presence, organic matter input and chemical conditions of the basin. All tracers peak sharply and abruptly in a brief period centered at about AD 1350, which corresponds to the first increase in fire activity and decline in arboreal species in the South Island. Values decrease to background after ~AD 1400, until the beginning of the 19th century, when a huge increase is registered in FeSt after the European arrival. Results are confirmed also by the FeSt record from Lake Diamond, not far from Lake Kirkpatrick, that is coherent with significant human presence and increased erosion and sedimentation during the 14th century. Such changes are consistent with the so-called “AD 1300 event”, a short period of increased precipitation and erosion observed in many records from Pacific Islands [2]. Whether natural changes affected human settlement and land use or vice-versa is matter of debate [3], and multi-proxy studies look promising in the reconstruction of such complex interactions and feedbacks.