A multi-millennial palaeoclimatic resource from Lagarostrobos colensoi tree-rings at Oroko Swamp, New Zealand

We describe the first results of a new dendroclimatic study in New Zealand using Lagarostrobos colensoi (silver pine) growing at Oroko Swamp in the West Coast of the South Island. This research has produced the first millennium-length tree-ring chronology from New Zealand, covering the period AD 816–1998. Statistical analysis of the climate signal in the chronology indicates that it reflects Austral summer temperatures with a high degree of fidelity, except for the post-1957 period when a stand-wide disturbance apparently impacted the trees. Locally abundant sub-fossil wood on the swamp surface has been used to extend the present chronology back beyond the ages of the living trees. However, a large amount of material is still available, so the prospect of extending this chronology further back in time is good. A comparison of the pre-20th Century temperatures estimated using the chronology with instrumental data over the 1900–1999 period indicates a change in variability from that of the 20th century. In addition, it appears that summer temperatures estimated over the period of most reliable tree-ring data prior to the instrumental record (AD 1200–1865) were considerably more variable and persistent than those found in the “modern” record. This result has implications in detection and attribution studies of greenhouse gas forcing because it suggests that Austral summer temperatures in this sector of New Zealand have been anomalous during the 20th Century relative to earlier times.