Pollen evidence for Holocene climate change in the Eglinton Valley, western Southland

Numerous palaeoclimatic investigations have been undertaken throughout New Zealand in an attempt to reconstruct the vegetation and climatic history of the Holocene (10,000 yr B.P. to present). It is surprising therefore, that to date no detailed investigations have been undertaken in western Southland; one of New Zealand’s most climatically sensitive areas. Pollen analysis was undertaken on a 450 cm (5,030 ± 20 year old) peat core extracted from Eglinton Bog, western Southland, to reconstruct the mid to late Holocene vegetation and climatic history of this area. By 2,300 yr B.P. Nothofagus Fuscospora had expanded throughout the Eglinton area and by ~ 1,000 yr B.P. a species poor N. fusca/ Nothofagus solandri var. cliffortioides forest had largely replaced the pre-existing N. menziesii forest. The transition is believed to be associated with the further deterioration of the mid to late Holocene climate to the cooler, wetter, frostier and cloudier climatic conditions that dominate the area today. Using evidence from Eglinton Bog as a starting point a detailed integrated regional comparison of southern New Zealand’s Holocene vegetation and climatic history was established by comparing individual site elevation, mean annual temperature and precipitation, and pollen records. A regional expansion of N. menziesii and N. Fuscospora was recorded throughout southern New Zealand between approximately 5,000 – 1,500 yr B.P. However, the timing, rate of change and extent that species became dominant varied between locations. It is suggested that while climate change was the main forcing factor behind the transition from tall Podocarp forest to N. menziesii forest, and eventually N. Fuscospora; for the vast majority of southern New Zealand, the variation in the rate, timing and magnitude of the species expansion between different locations within southern New Zealand appears to have also been influenced by a combination of site specific variables including local climatic conditions, altitude, the absence of refugia, fire frequency and the symbiotic relationship between Nothofagus roots and fungi.