Old postcards show North American redwoods large enough for cars to drive through , thousand-year-old kauri trees in New Zealand with trunks the size of tanks , and European oaks older than the Roman empire with branches covering half a football field .

Some of these monumental trees are still alive, but scientists say that the worlds oldest and largest trees are dying out fast as climate change attracts new pests and diseases to forests, and settlements and new roads fragment ecosystems.

The latest of the botanical giants to succumb are some of the worlds oldest baobab trees that dominate the southern African savannah and can live to well over 2,500 years.

New research published in Nature Plants records that nine of the worlds oldest 13 baobabs and five of the six biggest ones, have partially or completely died in the last 12 years. The Romanian and South African researchers involved in the study speculate that repeated droughts, linked to climate change, may be responsible, but they want more research.