Carbon dating of the trees carried out at a laboratory in Miami, Florida, showed the oldest of them first set root about 8,000 years ago, making it the world's oldest known living tree, Umea University Professor Leif Kullman said.

California's "Methuselah" tree, a Great Basin bristlecone pine, is often cited as the world's oldest living tree with a recorded age of between 4,500 and 5,000 years.

Two other spruces, also found in the course of climate change studies in the Swedish county of Dalarna, were shown to be 4,800 and 5,500 years old.

"These were the first woods that grew after the Ice Age," said Lars Hedlund, responsible for environmental surveys in the county of Dalarna and collaborator in climate studies there.

"That means that when you speak of climate change today, you can in these (trees) see pretty much every single climate change that has occurred."

Although a single tree trunk can become at most about 600 years old, the spruces had survived by pushing out another trunk as soon as the old one died, Professor Kullman said.

Rising temperatures in the area in recent years had allowed the spruces to grow rapidly, making them easier to find in the rugged terrain, he added.

"For quite some time they have endured as bushes maybe 1/2 metre tall," he said.

"But over the past few decades we have seen a much warmer climate, which has meant that they have popped up like mushrooms in the soil."