According to a recent study looking into the tree health of the South American/African/Southeast Asia tropical zone, in some areas, the mortality rates for trees has almost doubled over the past 35 years. And unfortunately, it looks like that trend is set to continue.





“No matter how you look at it, trees in the moist tropics will likely die at elevated rates through the end of this century relative to their mortality rates in the past,” said the lead author of the study, Nate McDowell. “There is a host of factors that appear to be driving mortality, and the likelihood of those factors occurring is increasing.”

As part of their research, McDowell and colleagues took a look at several different factors that appeared to be affecting the trees in those moist tropic areas. This included the rising carbon dioxide levels and temperatures, fires, drought, extreme storms, and insect infestation.

Results from the study confirmed that nearly all of these drivers are rising along with the tree mortality rate in the area. A lot of the time tree mortality in the tropics is caused by either carbon starvation brought on by a lack of food, or hydraulic failure caused by a lack of water.





You would think that the increase in carbon dioxide would be good for the trees as it’s a source of food for them, but it’s not. Instead, the higher temperatures that come with the increase in carbon dioxide hinders the trees in such a way that they’re unable to absorb it. “It’s like going to an all-you-can-eat buffet with duct tape over your mouth,” said McDowell. “There may be plenty of food, but it doesn’t matter how much food is on the table if you can’t eat.”

Trees need water to survive but when it’s hot they lose a lot of this water. The increased temperatures cause higher evaporation rates meaning more moisture is pulled out of the tees. Fires also add to this. As well as burning the tree altogether, they too can be responsible for sucking the moisture out.

Those trees that are able to withstand these rising temperatures are at higher risk of death in other ways. Bigger trees are more prone to being hit by lightning and being damaged by strong winds. They also need more water to survive than smaller trees.

While trees have grown to become quite resilient in a number of ways, they’re not invincible. “Trees have a great ability to survive, but there is only so much they can withstand – the question we now face is identifying those thresholds so we can predict risk to tropical forests,” said McDowell.





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