How Invasive Plants Are Fueling California’s Wildfire Crisis

Fire is always there Shaped the landscape of California. But today it’s hotter, more frequent, and more widespread than ever before—a change driven by human development. climate changeand the prevalence of invasive species, which are native plants that negatively impact local ecosystems. Bring grass and trees California for agricultureLandscaping, or by accident, has changed the state’s fire dynamics.

“Many non-native species can propagate fire faster than native plants,” said David Acuna, battalion chief for Cal Fire, the state’s Division of Forestry and Fire Protection. This transition is an overlooked driver for increasingly destructive Fires in California and around the world.

Southern California is dominated by a shrubland known as chaparral. This landscape was historically characterized by short, bushy vegetation and any native grasses that are perennial, retain moisture, and remain green most of the year. Fires, when they occurred, were rare because lightning was rare. When fires start, they get hot but don’t spread much because the open gaps between the plants act as natural fire pits.

The introduction of non-native grasses in the 1700s fundamentally changed this balance. Brought by European settlers, these grasses evolved alongside heavy cattle grazing and regular burning, making them highly resilient to disturbance. They compete with native species and fill gaps in shrubs, creating a continuous carpet of combustible material, especially along modified areas such as roads – frequent starting points for fires.

Unlike perennial native grasses, these non-native grasses are annuals, meaning they die each year and regrow from seed. Their short life cycle leaves behind a thick layer of dry, dead vegetation in late spring. “They have such a high surface area in terms of volume and are very flat and thin, so they maintain a lot of dead standing material almost year-round,” says Carla D’Antonio, plant community researcher and professor at the University of California, Santa Barbara. By May, the ground blankets dead grass. “It’s so flammable that it takes any ignition — a cigarette, a spark from someone dragging a chain on the highway or lightning,” said Hugh Safford, a plant and fire ecology researcher at the University of California, Davis.

Grass fills every available space—a phenomenon called fuel continuity. When a fire sparks, the uninterrupted line of dry vegetation acts as a beacon, guiding the flames into the undergrowth. “People underestimate the destructiveness of grasses because you can cut them down quickly with a hoe, whereas cutting a bush is very difficult,” says D’Antonio. “But if sparks and embers fly into the middle of a clump of introduced grass, then — boom — everything around you goes up like gasoline. It spreads so fast and it’s continuous. It’s like throwing tissue paper on a fire.”

Eucalyptus trees, introduced to California in the mid-19th century from Australia, add another layer of fire risk. Known for their aromatic scent, these plants have incredibly fiery, oily leaves. Their papery bark fell off and stuck in the air, transporting the embers half a mile away. The problem comes when people plant next to their homes, Acuna says. “You put a very hot, very strong burning plant like a eucalyptus tree next to a house, which is primarily composed of petroleum material. It is a very strong fire,” he explained.