My 15th page... Eucalyptus: Fire Hazard and Invasive Species

 

Eucalyptus: Fire Hazard and Invasive Species

Specialized reproductive structures called "epicormic shoots" sprout from buds on the bushfire damaged trunk of a Eucalyptus tree, about two years after the 2003 Eastern Victorian alpine bushfires. Near Anglers Rest, Victoria, Australia. (Photo: jjron)

 

Biologists now count invasive species as a major threat to biological diversity second only to direct habitat loss and fragmentation. Why do they worry when new species enter an ecosystem? More than 90 percent of introduced plants in California have overcome barriers to survival and reproduction in their new home without harming native species. But a fraction display invasive traits, displacing native species and reshaping the ecological landscape.

 

Tasmanian blue gum eucalyptus (Eucalyptus globulus), a symbol of California for some, never knew California soil until the 1850s, when seeds from Australia were planted, first as ornamentals, then mostly for timber and fuel. The California Invasive Plant Council (CAL-IPC) classifies blue gum eucalyptus as a “moderate” invasive because the trees need certain conditions to thrive. For the most part, they’re not a problem in the drier regions of Southern California or the Central Valley. But along the coast, where summer fog brings buckets of moisture, it’s a different story.

 

Blue gum invades neighbouring plant communities if adequate moisture is available for propagation, state resource ecologist David Boyd noted in a report for CAL-IPC. Once established, the trees can alter local soil moisture, light availability, fire patterns, nitrogen mineralization rates and soil chemistry.

 

Introduced species can disrupt ecological relationships among species that co-evolved over millennia, which is why many groups work to remove eucalyptus and restore coast live oaks. California’s native oak woodlands still sustain more biodiversity than any other terrestrial landscape even though more than a century of intensive agricultural, rangeland and urban development has claimed some 5 million acres of woodlands. (While settlers cleared the land of oaks, entrepreneurs planted eucalyptus trees by the millions.)

 

Historic fire risk

That’s why many ecologists welcome a plan to remove tens of thousands of eucalyptus and other non-native trees from the East Bay Hills to reduce fire risk. UC Berkeley, together with the City of Oakland and the East Bay Regional Park District, applied for up to $5.6 million in grants to remove the non-natives—primarily eucalyptus, Monterey pine and acacia—under the Federal Emergency Management Agency’s Pre-Disaster Mitigation and Hazard Mitigation Grant programs. The total project would cover just under 1,000 acres and includes plans to encourage regrowth of native oak and bay trees.

 

“Blue gum eucalyptus is one of the most fire-intensive plants,” says Klatt. Trees not only put a lot of fuel on the ground as they shed bark, leaves and twigs, but in intense fires, volatile compounds in foliage cause explosive burning. “Once bark catches fire, it gets blown ahead of the flame front and drops burning embers by the tens of thousands per acre in the urban community.”

 

Selected for flammability?

At very high temperatures, eucalypt species release a flammable gas that mixes with air to send fireballs exploding out in front of the fire. With eucalyptus, you see these ember attacks, with huge bursts of sparks shooting out of the forests, Bowman says. “It’s just an extraordinary idea for a plant.”

If you aren’t familiar with the idea of a plant designed to burn in its life cycle, you can get fooled by its beauty and nice smell, Bowman says. “But on a really hot day, those things are going to burn like torches and shower our suburbs with sparks. And on an extremely hot day, they’re going to shoot out gas balls.”

 

The evolutionary dimensions of fire ecology are controversial, Bowman allows. “But if eucalyptus are these evolutionary freak plants that massively increase fire risk,” he says, it raises a troubling question: Are these intense fires a consequence of climate change or the interaction of climate and biology? “If it’s the latter, then what the hell have humans done? We’ve spread a dangerous plant all over the world.”

 

Link (full article):

https://www.kqed.org/science/4209/eucalyptus-california-icon-fire-hazard-and-invasive-species

 

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