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Fast-Growing And Fire-Resistant Grasses Are Flourishing In Hawaii

It only took a few days before new grass was growing in the scorched earth left by the fires that raged across Maui and the Big Island starting on Aug. 8.

That’s perhaps not surprising considering that for 200 years Hawaii has been importing and encouraging numerous species of grass aimed at growing quickly to help optimize agricultural output and enhance ranching operations.

Now, invasive grasses cover an estimated 25% of Hawaii’s landscape.

Wildfire only fuels their spread. Many of them are adapted to fire, carrying traits that help them regrow faster and wider than native species.

But when that grass grows unchecked and is ignited — 99% of Hawaii’s fires are started by humans — it becomes a high-octane fuel.

Meanwhile, fire’s footprint has increased fourfold in recent decades, according to an examination by the University of Hawaii.

Less than two weeks after the Aug. 8 fires scorched land on the Big Island and Maui, one farmer had already seen regrowth with just a little watering. (Thomas Heaton/Civil Beat/2023)

The Grass Roots

At the turn of the 20th century, ranchers started to introduce grasses to replace Hawaii’s native but nutritionally lacking species, all to optimize cattle growth. 

“I would say just about every grass in the world has been introduced into Hawaii,” said UH Range and Livestock Specialist Mark Thorne.

The 1939 UH bulletin “Grasses of the Hawaiian Ranges” laid out a list of 239 grasses introduced across the state, from the Polynesian settlement-era arrival of sugarcane, to wheat and corn in 1772.

But it wasn’t until the early- to mid-1900s that grasses meant to maximize cattle growth started coming in.

“Grasses from the Eurasian steppe, all the way to Africa, have been introduced into the state because they were trying to find grasses that could support the cattle grazing,” Thorne said. 

Grasses represent a portion of the 10,000 foreign species of flora and fauna scientists estimate have been introduced to Hawaii – often dubbed the invasive capital of the world

Over the course of the past 100 years, ranchers found a mix of grasses best suited to raising cattle, including Guinea and kikuyu grasses from Africa. 

Both grow fast, ensuring a steady supply for cattle. Hawaii’s ranchers rotate cattle between paddocks to maintain grass growth. 

Kikuyu grasses are typically found on inland pastures, while Guinea grass is a hardy species found closer to the coast, alongside other grasses imported for their nutritional value.

Guinea grass is a major fuel of wildfires in Hawaii. (Nathan Eagle/Civil Beat/2023)

All grasses burn, but many of the imported pasture grasses are fire-adapted species, like buffelgrass — another grass used by ranchers.

They ignite quickly, which can lead to more frequent fires, then they regenerate faster than other species, crowding them out and fueling what researchers call the grass-fire cycle.

The grasses all have different chemical and physical traits that help them survive or thrive in fire. For instance, Guinea grass grows in dense bunches, dead foliage accumulating as it grows up to 10 feet tall at a rate of up to six inches a day.

Thorne does not call them invasive, because they have a use.

Grass was already growing back Aug. 13 south of the intersection of Lahainaluna Road and Ho’okahua Street. (Jack Truesdale/Civil Beat/2023)

“Ninety percent of those grasses are extremely valuable to our livestock industry,” Thorne said.

Not all grasses were introduced for livestock.

The most problematic grass species – fountain grass – was introduced as an ornamental around 1914.

Fountain grass is found on every one of Hawaii’s main islands. Its wispy leaves ignite easily and spread fire quickly. 

Fountain grass rates at 0.99 on a scale from 0 to 1 for fire susceptibility, according to the Hawaii Invasive Species Council’s Weed Risk Assessment database. Created last year by UH biology professor Curtis Daehler and graduate student Kevin Faccenda, the database includes more than 360 weed species. 

It draws on previous research into grasses’ growth patterns and biological make-up.

Buffelgrass, Guinea and molasses grasses also ranked high on the fire-risk scale, but still below fountain grass. 

“That’s pretty much as high as you go,” Daehler said. 

Breeding An Invasive

When grass is left to grow without grazing or mowing, wildfire becomes a greater risk in a landscape that includes at least 1,400 introduced plant species.

Some of these have negative effects, like the invasive grasses, while others may be useful, which is why the Hawaii Invasive Species Council does not target many of them.

“We don’t know if some of them … will become invasive species. New ones will be appearing,” Daehler said.

Many scientists agree that getting rid of the grasses entirely is impossible. That’s why fire officials and researchers take a holistic approach.

“There’s no one silver bullet,” said Chelsea Arnott, program supervisor for the invasive species council. “It’s about having integrated pest management.”

Among the measures are mowing or grazing in fallowed agricultural land, building more firebreaks and fuelbreaks and bolstering community defenses against wildfire.

One tool that has not been used by the state for at least 30 years is the state Department of Agriculture’s Noxious Weed Rules and list, created to help control of harmful flora statewide.

Those rules made it possible for agriculture department staff to manage and eradicate the species on the list, even on private property.

Fountain grass is on that list. Guinea grass, buffelgrass and molasses grass are not.

The list has not been updated since 1992.

Source : CivilBeat