Fire is a natural, inevitable phenomenon, and one to which western North American ecologies are well-adapted, and even require to sustain themselves. The new fires, though, fueled by drought, a warming climate and forest mismanagement — in particular the buildup of small trees and shrubs caused by decades of fire suppression — may reach sizes and intensities too severe for existing ecosystems to withstand.

The Rim Fire may offer some of both patterns. At high elevations, vegetatively dominated by shrubs and short-needled conifers that produce a dense, slow-to-burn mat of ground cover, fires historically occurred every few hundred years, and they were often intense, reaching the crowns of trees. In such areas, the current fire will fit the usual cycle, said Thode.

Decades- and centuries-old seeds, which have remained dormant in the ground awaiting a suitable moment, will be cracked open by the heat, explained Thode. Exposed to moisture, they’ll begin to germinate and start a process of vegetative succession that results again in forests.

At middle elevations, where most of the Rim Fire is currently concentrated, a different fire dynamic prevails. Those forests are dominated by long-needled conifers that produce a fluffy, fast-burning ground cover. Left undisturbed, fires occur regularly.

“Up until the middle of the 20th century, the forests of that area would burn very frequently. Fires would go through them every five to 12 years,” said Carl Skinner, a U.S. Forest Service ecologist who specializes in relationships between fire and vegetation in northern California. “Because the fires burned as frequently as they did, it kept fuels from accumulating.”

A desire to protect houses, commercial timber and conservation lands by extinguishing these small, frequent fires changed the dynamic. Without fire, dead wood accumulated and small trees grew, creating a forest that’s both exceptionally flammable and structurally suited for transferring flames from ground to tree-crown level, at which point small burns can become infernos.

Though since the 1970s some fires have been allowed to burn naturally in the western parts of Yosemite, that’s not the case where the Rim Fire now burns, said Skinner. An open question, then, is just how big and hot it will burn.

Where the fire is extremely intense, incinerating soil seed banks and root structures from which new trees would quickly sprout, the forest won’t come back, said Skinner.

Those areas will become dominated by dense, fast-growing shrubs that burn naturally every few years, killing young trees and creating a sort of ecological lock-in.

Aerial diagram (above) and three-dimensional recreation (below) of 10-acre plot prior to logging in 1929 (left) and in 2008, after 79 years of fire suppression (right). (USDA/USFS/Pacific Southwest Research Station)

If the fire burns at lower intensities, though, it could result in a sort of ecological recalibration, said Skinner. In his work with fellow U.S. Forest Service ecologist Eric Knapp at theStanislaus-Tuolumne Experimental Forest, Skinner has found that Yosemite’s contemporary, fire-suppressed forests are actually far more homogeneous and less diverse than a century ago.