Drought uncovers kauri climate clues

Northland's long drought has uncovered dozens of ancient kauri logs that could help scientists discover what caused dramatic climate changes thousands of years ago.

Scientists are in a race to recover the semi-fossilised kauri from farms before the wood is turned into tables and bowls for people's living rooms.

Logs buried in Northland farmland contain a record of ancient climate that scientists say is unique because of the age of the trees and the way they have been preserved in former swamps.

But the wood is also worth a lot of money when turned into furnishings.

The director of Waikato University's radiocarbon dating laboratory, Dr Alan Hogg said the dry summer revealed 50 or 60 buried kauri when the grass above them died, leaving lines of dead brown grass marking their locations.

Scientists were able to fly over farms and spot the logs from the air, in some cases reaching agreements with millers that allowed them to test samples before the wood was turned into furniture.

The logs are a boon for efforts to understand past climate.

An effort is being made to to reconstruct temperatures from 200BC to 1950 using kauri rings.

Trees are valuable for reconstructing climate because they store records of rainfall and temperature in their rings. The width of the rings depends on the growing conditions the year they were formed.

Scientists hope the newly found logs will help them understand what caused a sudden period of rapid cooling in the middle of a time of global warming 12,000 to 13,000 years ago. The mini-ice age lasted about 1000 years.

But Dr Hogg said the logs were disappearing from farmland at an alarming rate. They were usually difficult to find, but this summer "the soil was so dry and powdery you could just stick a rod through and hit one every time".

Dr Hogg said the most sought-after logs were those that grew 10,000 to 20,000 years ago, a period for which tree records are scarce.