Climate Change and Fire

The Berry Fire, in 2016, burned across the Grassy Lake Road, shown here.

NPS Photo / CJ Adams

Climate change is expected to affect fire in Grand Teton in several ways, mainly driven by warmer temperatures and longer, drier summers. Under these conditions, we will have more frequent fires, larger fires, and a longer fire season. However, it’s important to remember that each year will be different, and some summers will be cool and wet even as average temperatures rise, as has been observed over the last decade. Imagine floating on a lake where the level is slowly rising—with each wave you may move up or down, but over time, the water level is going up.

Warmer temperatures and lower levels of precipitation both contribute to drying out vegetation (which fire managers call fuels). The drier the fuels, the more readily a fire will burn and spread. Fires spread most rapidly on days with warm temperatures, strong winds, and very low humidity levels—often called red flag days. With overall warmer temperatures and drier fuels, we will see more cases of extreme fire behavior.

Climate change will also affect how forests regenerate after they burn. For example, some trees, like aspen, can quickly re-sprout from their roots after the rest of the plant burns in a fire. Ceanothus seeds actually wait in the soil for up to 150 years for a fire to “scarify”, or open, their seeds. Both of these plants have a strong advantage in regeneration after a fire. However, it may be more difficult for plants and trees that must germinate from seed after a fire, such as lodgepole pines. Many of these species are adapted to a relatively cool and wet climate, which this region has had for the past several thousand years. But as temperatures warm, some areas, like hot, south-facing slopes, may just be too hot for these conifer seedlings. Instead, those places would see more shrubby plants and wildflowers.

 

An opened serotinous cone sits on the burned ground, near a tiny, just-sprouted lodgepole pine seedling.

NPS Photo

More frequent fires on the landscape may change forest structure as well. Historically, forests in this area have burned in large, infrequent (every 100-300 years), stand-replacing fires that kill most of the mature trees. Lodgepole pines in particular are well-adapted to this, since their serotinous cones open during a fire to release their seeds, which take root on the freshly-cleared ground, where they don't need to compete with other vegetation. However, most young trees do not develop cones until they are ten to fifteen years old, or later—and even then, the cones are fewer in number and develop slowly. So if a young stand of trees burns again within the first thirty years, it may not be able to re-seed sufficiently.

Learn more about how scientists are expecting climate change to affect fires and forests in Grand Teton in the Fire History Audio Tour.

 

Lodgepole pines and serotinous cones

In any given stand of lodgepoles, some of the trees will have serotinous cones and some won't. The proportion is heavily influenced by the age of the stand, since the percentage of trees with serotinous cones increases with age. Very young trees (under ten years old) may not even have cones at all, and stands of trees under 50 years old generally have less than 10% serotiny. Moderately aged trees (50-100 years old) have slightly more serotinous cones, on 10-30% of trees, and mature stands over 100 years old have the highest percentage of serotiny (about 40-60% of trees). Essentially, older, mature trees expect fire, so they hedge their bets with more serotinous cones. But younger lodgepoles have not evolved to expect it so soon, based on the past climate of this region. These young trees don't have as many serotinous cones, and therefore don't reseed as well in the event of a fire.