PSW Research Spotlight from January 2024 - March 2024

California

Forest thinning and prescribed burning treatments reduce wildfire severity and buffer the impacts of severe fire weather

Photo Credit

USDA Forest Service photo by Eric Knapp

The road divides an untreated area on the left, and one that received prescribed burning and mechanical thinning on the right at Goosenest Adaptive Management Area.

Forest thinning and prescribed burning treatments reduce wildfire severity and buffer the impacts of severe fire weather

Brodie, Emily G.; Knapp, Eric E.; Brooks, Wesley R.; Drury, Stacy A.; Ritchie, Martin W. 2024. Forest thinning and prescribed burning treatments reduce wildfire severity and buffer the impacts of severe fire weather. Fire Ecology. 20(1): 11770.

Hawaiʻi & U.S. Affiliated Pacific Islands

Non-native Grasslands in Hawai'i are Resilient to Disturbance

Humans have facilitated the establishment of non-native grasslands in Hawaiʻi through the intentional introduction of ornamental plants and forage grasses for livestock, as well as through accidental species introductions. Today, non-native grasslands cover about 25% of the state, and many former pasture areas are no longer being actively grazed which can lead to high fuel loads. Disturbances in these systems vary in scale and intensity and include livestock and feral ungulate grazing, military training operations, housing and road development, and wildland fire. Understanding post-disturbance vegetation dynamics can help land managers prioritize resources and activities when considering how to promote desired vegetation compositions across varied landscapes.

To see what happens after grassland disturbance on Hawaiʻi Island, researchers used large equipment to move vegetation and a thin layer of topsoil in six types of grasslands dominated by different non-native and native grass and native shrub species. They then measured the vegetation composition every 3-4 months over the course of 21 months. They found that some species displayed colonizer patterns, in which a species dominated soon after disturbance (attributable to traits like fast seed germination and growth) then faded out over time as competitor species established a firm, longer-term presence. Some species were characterized as colonizer + strong competitor that dominated throughout the study. Overall, the species compositions of sites returned to the same plant assemblages as pre-disturbance (i.e., stable states), though the rates of return to pre-disturbance conditions varied. The results suggest that past research on post-fire vegetation dynamics in Hawaiʻi may extend to the different grass species included in this study, and that if the desired management goal is native-dominated ecosystems, it will likely take large inputs of time and resources to alter the grasslands' stable states.

Invasive-dominated grasslands in Hawaiʻi are resilient to disturbance

Yelenik, Stephanie; Rose, Eli; Cordell, Susan. 2024. Invasive-dominated grasslands in Hawaiʻi are resilient to disturbance. Ecology and Evolution. 14: e10948.