#zombie forests

[pcttrailsidereader]

'Zombie' Forests

Over the past several years we have written a great deal about the impact of climate change on the PCT experience. The changing health of forests is among those impacts. Although this is not just occurring in the California mountains, the level of urgency seems to be most pronounced in California. I have definitely seen firsthand the phenomenon Avery Hill describes in his research.

The story below is an excerpt from an article written by Elena Shao in the March 6, 2023 NY Times.

A warming climate has left a fifth of the conifer forests that blanket California's Sierra Nevada stranded in habitats that no longer suit them, according to a study published last week by researchers at Stanford University.

In these “zombie forests,” older, well-established trees — including ponderosa pines, Douglas firs and sugar pines — still tower overhead, but few young trees have been able to take root because the climate has become too warm and dry for them to thrive.

Mature trees are able to survive even after their local climate has shifted, but the species is not likely to grow back in these areas after a major disturbance, like a catastrophic wildfire, logging event or period of extreme drought. Instead, the study found, the forest is more likely to be replaced by smaller, shrublike vegetation that is adapted to warmer, drier conditions.

For their analysis, Dr. Hill and colleagues examined historical data going back more than eight decades, comparing detailed survey data plotted by the U.S. Forest Service in the 1930s with more recent vegetation maps. They found that during that time period, the Sierra Nevada’s conifer forests had, on average, shifted about 112 feet higher in elevation. The most suitable temperature range for the conifers had shifted even faster, climbing upslope by about 600 feet.

That has left an estimated 11 percent of today’s conifer forest in the Sierra Nevada mismatched to its current climate conditions, with another 8 percent considered “severely” mismatched, according to the study.

Global climate change has put pressure on many species of plants and animals to move to higher elevations or toward polar latitudes in order to stay in climate zones they have historically adapted to. Longer-lived species, like conifer trees, which can live for centuries, often find it harder to keep up with the velocity of climate change, said Chris Field, the director of the Stanford Woods Institute for the Environment and senior author on the study. They can only move as fast as their seeds get dispersed.

[rjzimmerman]

A fifth of the Sierra Nevada’s conifer forests are out of sync with the warming climate around them, which makes them less likely to grow back after a major wildfire.

Source: The Global Ecology and Climate Solutions Lab at the Stanford Woods Institute for the Environment, using data from the U.S. Forest Service’s Wieslander Survey and Existing Vegetation maps. Note: The data looks at changes in conifer forests across the Sierra Nevada between the 1930s and the 2010s.

Excerpt from this story from the New York Times:

A warming climate has left a fifth of the conifer forests that blanket California's Sierra Nevada stranded in habitats that no longer suit them, according to a study published last week by researchers at Stanford University.

In these “zombie forests,” older, well-established trees — including ponderosa pines, Douglas firs and sugar pines — still tower overhead, but few young trees have been able to take root because the climate has become too warm and dry for them to thrive.

Zombie forests are “cheating death, in a way,” said Avery Hill, an ecologist and the study’s lead author.

Mature trees are able to survive even after their local climate has shifted, but the species is not likely to grow back in these areas after a major disturbance, like a catastrophic wildfire, logging event or period of extreme drought. Instead, the study found, the forest is more likely to be replaced by smaller, shrublike vegetation that is adapted to warmer, drier conditions.

For their analysis, Dr. Hill and colleagues examined historical data going back more than eight decades, comparing detailed survey data plotted by the U.S. Forest Service in the 1930s with more recent vegetation maps. They found that during that time period, the Sierra Nevada’s conifer forests had, on average, shifted about 112 feet higher in elevation. The most suitable temperature range for the conifers had shifted even faster, climbing upslope by about 600 feet.