Among the nine were four of the largest African baobabs.
"Something obviously is going on in nearly selectively affecting the largest and oldest", Thomas Lovejoy, an environmental scientist and Amazon rain forest expert at George Mason University, wrote in an email comment on the study. But his finding about the deaths came as no surprise: Anecdotal evidence of a die-off was already spreading in the baobab research community. But during their study period, the researchers discovered that the oldest and largest had died.
Until late a year ago, the Platland tree in South Africa, also known as Sunland, was their queen. They were surprised that most of the oldest and biggest died within those 12 years.
It is also said that the intertwined baobab trees in Madagascar symbolise a couple from different villages who fell in love against the wishes of their elders. It is found naturally in Africa's savannah region, and outside the continent in tropical areas to which it was introduced. The authors believe that climate change is the culprit.
Some of these trees are more than 2000 years old, the team reports today in Nature Plants. Another famous baobab, the Chapman tree in Botswana, collapsed in 2016.
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"We report that nine of the 13 oldest and five of the six largest individuals have died, or at least their oldest parts/stems have collapsed and died over the past 12 years", wrote the worldwide team of researchers. It's a unusual feeling, because these are trees which may live for 2,000 years or more, and we see that they're dying one after another during our lifetime.
"It is definitely shocking and dramatic to experience during our lifetime the demise of so many trees with millennial ages", said the study's co-author Adrian Patrut of the Babes-Bolyai University in Romania.
They suspect climate change-and underground water that's harder for the roots to reach-may have something to do with the trees' demise, but also point out that over each one's life span, it has undergone wetter, drier, colder, and warmer conditions that stress the tree and sometimes kill other plants. That includes Panke, a sacred baobab in Zimbabwe that was estimated to be about 2,450 years old, with an 82-foot-wide trunk and a height of 51 feet. The increased temperature and drought are the major threats, says Patrut.
"We felt as if we were the ones outliving the baobabs, instead of them outliving many generations of humans". The common theory, Baum said, is that as the tree slowly grows around these scars, they can become large hollows.
"It is very surprising to visit monumental baobabs, with ages greater than 1,000 to 2,000 years, which seem to be in a good state of health, and to find them after several years fallen to the ground and dead", Patrut told National Geographic.