The fire is always there Shaped the California landscape. But today, it's burning hotter, more frequently, and more widely than ever before—a shift driven by human development, climate change, and the prevalence of invasive species, non-invasive species that negatively impact local ecosystems. Native plants. Grasses and trees brought to California for agriculture, landscaping or incidental changes in the state's fire dynamics.

“Many non-native species can spread fires faster than native plants,” said David Acuña, battalion chief for Cal Fire, the California Department of Forestry and Fire Protection. This shift is an overlooked driver of increasingly destructive wildfires in California and around the world.

Southern California is dominated by scrubland known as "jungle." Historically, this landscape was characterized by short, shrubby plants, and any native grasses were perennials that could retain moisture and stay green most of the year. Fires are rare because lightning strikes are rare. When fires do occur, they burn hot but don't spread too far because the gaps between plants act as natural firebreaks.

The introduction of exotic grasses in the 1700s fundamentally changed this balance. These grasses were brought by European settlers and evolved with heavy livestock grazing and daily burning, making them highly resistant to disturbance. They outcompete native species and fill gaps in the undergrowth, creating a continuous carpet of flammable material, especially in changing areas such as roads, which are common starting points for fires.

Unlike perennial native grasses, these non-native grasses are annual grasses, meaning they die and regrow from seed each year. Their short life cycle leaves behind a dense layer of dry, dead vegetation in late spring. "They have a very high surface area to volume ratio and they're very flat and thin, so they can hold a lot of stationary material almost year-round," said Carla D'Antonio, a plant community researcher and professor at the University of California. , Santa Barbara. By May, dead grass covered the ground. "It's so flammable that it could be ignited by anything — a cigarette, a spark trailing a chain on the highway or lightning," said Hugh Safford, a researcher in vegetation and fire ecology at the University of California, Davis.

Grass fills all available space—a phenomenon called fuel continuity. When a fire breaks out, the unbroken line of dry vegetation acts like a wick, carrying flames into the brush. "People underestimate how damaging grasses are because you can cut them down very quickly with a hoe, whereas shrubs are harder to cut down," D'Antonio said. "But if sparks and embers fly in the middle of an introduced pile of grass, then - boom - everything around you rises like gasoline. It spreads so quickly and so consistently. It's like throwing tissue paper Like on fire.”

Eucalyptus trees were introduced to California from Australia in the mid-19th century, adding another layer of fire risk. Known for their aromatic scent, these trees have extremely flammable, oily leaves. Their papery bark peels off and blows in the wind, carrying embers half a mile away. Acuña said the problem comes when people plant them next to their homes. "You put a very hot, very violent burning plant next to a house, like eucalyptus, which is mostly composed of petroleum material. It's a very violent fire," he explained.