Is this the end of forests as we’ve known them?

 

“…The possibility of worldwide mass forest mortality linked to climate change was flagged in the first Intergovernmental Panel on Climate Change assessments in 1990. But today, many researchers are expressing particular concern about the tree mortality crisis building in California and other parts of the west.
 
“Since 2010, 129m trees are estimated to have died in California’s national forests, as a result of a hotter climate, insects and other factors. Astonishingly, 48.9% of all trees in a comprehensive study of the southern Sierra Nevada mountain range were killed. The effects of a warming planet on trees were already obvious in summer 2016, as California was emerging from its driest four-year period since scientific record-keeping began…
 
“Researchers acknowledge that there is considerable ambiguity in their predictions about tree mortality. For one thing, it is unclear how many of the trees now dying essentially weren’t meant to be there in the first place. Western forests are denser than they were historically because of human influence: the practice of tamping out wildfires, beginning in the early 20th century, has interfered with a natural process in which blazes weed out younger trees and undergrowth…
 
“Around the globe, research has suggested that the tree mortality rate in some temperate and tropical forests has doubled or more in recent decades. While in some places there will be wholesale tree die-offs as a result of climate change, in other places it will alter the very composition and feel of forests. They will not be what they were.
 
“In the Amazon, climate change has lengthened the dry season and caused the rainfall to decline in parts. These shifts are reorganizing the forest: trees that prefer drier conditions are thriving, while those that prefer wetter conditions, and which make up the majority of tree species in Amazonia, are dying off in greater numbers, a study has found.
 
“These changes demonstrate just how far-flung the impacts of climate change can be. The Amazon ‘is one of the most remote places on Earth.’ said lead author Adriane Esquivel Muelbert, a lecturer at the University of Birmingham and researcher at the Birmingham Institute of Forest Research. ‘Humans are managing to change the environment even very far away from where they are living, or most of them are living.’

“With the combined impacts of global heating and rampant logging, some researchers warn that large parts of the rainforest ecosystem could collapse and convert to savanna. ‘Today, we stand exactly in a moment of destiny,’ two leading academics declared in a 2019 editorial. ‘The tipping point is here, it is now.’

“…A great irony of this shift is that trees are dying just as we understand them better than ever. It has become clear that far from being inert and silent, and little more than a backdrop for wildlife, trees are able to communicate with one another and even share resources.

“Forests also absorb around one-quarter of all human carbon emissions annually, and increasingly there are worries that if forests die back they will switch from storing carbon to emitting it, because dead trees will release all the carbon they have accumulated. This helps explain why much-touted proposals to plant millions of trees to suck up carbon and ameliorate the climate crisis are encountering skepticism; they won’t work if conditions on Earth don’t allow for forests to reproduce and thrive.

“It is true that forests could find new footholds in places that were formerly too cold or otherwise unsuited to them. But trees can take centuries to reach maturity, and in terms of global heating, older, large trees store much more carbon than younger, smaller ones. Instead of focusing on new trees, researchers say, the best answer to the mortality crisis is to preserve the forests we already have – by cutting carbon emissions.

“For Camille Stevens-Rumann, the fire ecologist studying tree mortality in the Rockies, watching these changes in places she has known for years – and where she has backpacked and rafted – has required an adjustment. ‘As a person who loves trees and has spent my career so far looking predominantly at trees, it is a bit of a stark difference and a shift of mindset to think about these landscapes as not ‘treed’ for a longer period of time – or indefinitely,’ she said.

“Even so, she is able to find beauty in them, and in what humbler plants are able to make a comeback even if the pine and fir trees cannot. She is a realist. Life marches on. ‘This is the beginning of a new ecological state’” (Alastair Gee, The Guardian).