Climate change explainer
How climate change will impact your region
01:57 - Source: CNN
CNN  — 

If you like to take a walk in the woods in the United States or you prefer to decorate a Douglas fir at Christmas, you should know that climate change is making both of those activities a lot harder.

Looking at two ecologically and economically important species – the Douglas fir and the Ponderosa pine – scientists found that fires and drought exacerbated by climate change make new growth difficult, especially in low-elevation forests, according to a study published Monday in the Proceedings of the National Academy of Sciences.

The 2000 Canyon Ferry Complex Fire site in the Helena National Forest, Montana, 17 years later.

Some forests in four regions in California, Colorado, the Northern Rockies and the southwestern part of the United States have crossed “a critical climate threshold for postfire tree generation,” the study says.

Climate conditions over the past 20 years have accelerated changes that would have otherwise taken decades or even centuries to play out across broad regions of the country. This is leading to the abrupt decline of trees and making these lands increasingly unsuitable for tree regeneration.

Climate change is endangering our forests now, not just in some distant future.

“Maybe in areas where there are really abundant seed sources, there could be some trees, but it is becoming really hard to get these trees back due to climate change,” said study co-author Kim Davis, a postdoctoral research associate in the W.A. Franke College of Forestry & Conservation at the University of Montana.

The scientists figured this out by examining tree rings to determine when nearly 3,000 trees were established in these regions, which saw 33 wildfires between 1988 and 2015.

Seedlings and juvenile trees are vulnerable to climate change. “Seedlings are really sensitive,” Davis said.

Adult trees have better survival mechanisms to deal with poor climate conditions, but intense wildfires are wiping out these Ponderosa pines and Douglas firs. The trees have thick bark that make them typically good at surviving surface level fires, but they can’t survive the more intense fires that move through the canopy, like this region has seen. Had there not been such intense fires, these trees may have lived for centuries.

The problem probably won’t get any better, as climate change is making intense wildfires much more common, studies show. Western foresters say there used to be a fire season, but devastating and costly fires have become a reality all year long. In 2018, fires cost California more than $9.05 billion, according to the state insurance commissioner, the deadliest and most destructive wildfire season in state history.

Twelve years after the 2004 Peppin Fire in the Lincoln National Forest, New Mexico, an area previously dominated by conifer forest is now predominantly resprouting shrubs, grasses and exotic plants.

A higher number of fires and low seed availability means a high probability that these trees in these regions won’t come back, Davis said. This study concentrated on the driest and hottest areas of the Western forests, but researchers will next try to determine how much will be impacted.

The loss of forests is doubly bad for the planet, studies have found. Forests act as great carbon dioxide absorbers. Additional carbon dioxide, created by power plants and generated when we travel, is what’s fueling climate change.

Trees are also great for erosion control. They protect area watersheds and are home to a wide variety of plants and animals.

The US timber industry heavily relies on the Ponderosa pine and Douglas fir because they have been so plentiful, Davis said. They are also the trees that are closest to towns and are where people like to hike, camp, hunt and fish.

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There are some things people can do to mitigate some of this problem, Davis said. Forest management plans that reduce high-severity burns can help. Increasingly, forest managers are considering allowing some fires to burn under more moderate conditions, Davis said. Forest managers can also replant trees after fire, at least in the areas where climate conditions will allow.

“The people we work with who manage forests are planning for climate change,” Davis said. “They have to, because this isn’t something we are predicting for the future. Climate change is already here.”