ARIZONA, USA — A new study finds Ponderosa pines are becoming stressed after dealing with 23 years of megadrought in the Southwest.
Brandon Strange, a Research Scientist at the University of Arizona and the study's lead author, is looking at how the Ponderosa pines handle the megadrought in forests in the Four Corners region.
“So if some pest or pathogen comes in, that could be enough to push them over. If we get a really insane heatwave one year or the monsoon does not show up, that is kind of going to compound with their already high drought stress and really be bad for the forest,” Strange said.
The study found that forests reacted in two different ways to the 23 years of drought.
Ponderosa pine forests that do not get as much rain from the North American monsoon are faring worse than those that do get more rain from the monsoon.
“They have a lot of drought stress, and they’re starting to dry up,” Strange said.
One of the ways Ponderosa pine needles cope with drought is to close off their pine needles to hold in water for when it’s hot and dry, but the megadrought has stressed them further.
“It’s so hot and so dry that despite their kind of best efforts, they’re still losing a ton of water to the atmosphere,” Strange said.
That kind of stress makes them not function as well, Strange said and can make them more prone to die.
But the Ponderosa pines in Arizona are getting some relief from the monsoon and have become reliant on the megadrought on the monsoon rains.
“They’re still doing quite poorly on a similar trajectory as those other forests but just a little bit behind because they do have that kind of built-in buffer with the North American Monsoon.
Strange said he’s not expecting the megadrought alone to kill off all the trees, but the future of the forests is dependent on two unpredictable things: the ongoing drought and the monsoon.
"The future of these forests and for their drought stress is really uncertain right now,” Strange said.
What’s also uncertain are the potential further impacts.
“If these trees are constantly stressed out, they’re not going to be as productive or remove as much carbon dioxide from the atmosphere,” Strange said.
Which is what makes the monsoon and other precipitation all that more important.
“One of the things that we can do is go appreciate these forests, try and empathize with the natural world, and then folks may start to understand the really important role and just intrinsic value of these forests,” Strange said.
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