How invasive plants are fueling California’s wildfire crisis

Always fire It shaped the landscape of California. But today they burn hotter, more frequently, and more widely than ever before — a shift driven by human development, Climate changeThe spread of invasive species, which are non-native plants that have negative impacts on local ecosystems. Weeds and trees brought to ca to agricultureOr landscape or chance may have changed fire dynamics in the state.

“Many non-native species can spread fires faster than native plants,” says David Acuña, a battalion chief with Cal Fire, the state Department of Forestry and Fire Protection. This shift is an overlooked driver of what is increasingly destructive Wildfires in California And all over the world.

Southern California is dominated by shrubs known as chaparral. This landscape was historically characterized by short shrub vegetation, and all native grasses were perennial, conserving moisture and remaining green for most of the year. Fires, when they did occur, were rare, because lightning strikes were rare. When it caught fire, it burned intensely but did not spread far because the open gaps between plants served as natural firebreaks.

The introduction of non-native grasses in the 18th century fundamentally changed this balance. Brought by European settlers, these grasses evolved alongside heavy livestock grazing and routine burning, making them highly resilient to disturbances. They have outcompeted native species and filled gaps in shrublands, creating a continuous carpet of flammable material, especially along shifting areas such as roads – frequent starting points for fires.

Unlike perennial native grasses, these non-native grasses are annuals, meaning they die every year and regrow from seed. Its short life cycle leaves behind a dense layer of dry, dead plants by late spring. “They have a large surface area relative to their volume, and they’re very flat and thin, so they hold a lot of dead material almost year-round,” says Carla D’Antonio, a plant society researcher and professor at the University of California, California. Santa Barbara. By May, dead grass covers the ground. “It’s so flammable that it requires any ignition — a cigarette, a spark from someone pulling a chain on the highway, or lightning,” says Hugh Safford, a plant and fire ecology researcher at the University of California, Davis.

Weeds fill every available space, a phenomenon called fuel continuity. When fires break out, the continuous line of dry vegetation acts like a wick, carrying the flames into the undergrowth. “People underestimate the destructiveness of weeds, because you can cut them down quickly with a hoe, whereas it’s very difficult to cut down a shrub,” D’Antonio says. “But if sparks and embers fly into the middle of a clump of introduced weeds, everything around you goes up like gasoline. It spreads very quickly and it’s very persistent. It’s like throwing tissue paper on a fire.”

Eucalyptus trees, which were brought to California in the mid-1800s from Australia, add another layer of fire risk. These trees are known for their aromatic scent, and have incredibly flammable oily leaves. Its papery bark peels off and the wind picks it up, carrying the embers up to half a mile away. The problem comes when people plant them right next to their homes, Acuña says. “You put a very hot, very combustible plant like eucalyptus next to the house, which is basically petroleum. “This is a very powerful fire,” he explains.