Fire-prone invasive grasslands need intense work to restore native species

 Invasive grasslands, like those linked to the destruction of Lahaina, are remarkably stable systems, and will be difficult to change.

That’s a conclusion of a new report by federal foresters.

They determined that active and intensive wildland management will be required to restore native-dominated landscapes. The alternative is a continued dominance of fire-prone grasslands.

The study, in the journal Ecology and Evolution, is entitled “Invasive-dominated grasslands in Hawaiʻi are resilient to disturbance.” The authors are Stephanie Yelenik and Eli Rose of the U.S. Geological Survey’s Pacific Island Ecosystem Research Station and  Susan Cordell of the U.S. Forest Service’s Institute of Pacific Islands Forestry.

The conclude that once a native Hawaiian ecosystem is converted to an alien grassland, it becomes difficult to change to another system, such as one dominated by native species that might be less fire-prone.

They did the research by disturbing six 100-square-meter plots with different vegetation mixes.

“We implemented a disturbance experiment to assess how plant communities would reassemble,” they wrote. They included in each plot plantings of two native species, ‘a’ali’i (Dodonea viscosa) and a native bunchgrass known as Hawaiian lovegrass (Eragrostis atropioides.)

The plantings were done on Hawai'i Island, in the Keʻāmuku Maneuver Area of the Army’s Pōhakuloa Training Area.

They found that competitive invasive grasses tended to become dominant after disturbance. They generally do better than native species in disturbed habitats. And once they have taken over, they tend to stay in charge.

“Our results highlight that the altered post-agricultural, invaded grassland landscapes in Hawaiʻi are stable states,” they wrote.

Some of those invasive non-native species they found include buffel grass (Cenchrus ciliaris,) Kikuyu grass (Cenchrus clandestinus,) fountain grass (Cenchrus setaceus,) Natal red top (Melinis repens,) and a toxic daisy called fireweed or Madagascar ragwort (Senecio madagascariensis.)

This study involved bulldozing the land, but the reaction to this disturbance seems similar to that found after fires, they said.

“While the disturbances that we imposed differ significantly from fire, wildfire resulting from invasive grasses are increasing in Hawaiʻi,” they wrote. “Past research in Hawaiʻi shows that fire in invaded grasslands generally results in the return of the same grass species across various ecosystems including those dominated by invasive grasses…”

They conclude that active management is needed if the goal is to return alien-dominated grasslands to native-dominated ecosystems.

“If the desired management goal is native-dominated ecosystems, such stable states will likely take large inputs of time and resources to alter,” they wrote.

© Jan TenBruggencate 2024