Experimental Restoration of an Indigenous Hawaiian Grassland after Invasion by Buffel Grass (Cenchrus ciliaris)

Abstract

Introduced grasses have displaced Hawaiian Pili grass (Heteropogon contortus) in most dry, leeward habitats of the Hawaiian Islands. The purpose of this study was to assess the feasibility of restoring an indigenous Heteropogon grassland at the Puukohola Heiau National Historic Site, where introduced Buffel grass (Cenchrus ciliaris) is now dominant. Heteropogon seeds (50 seedlings/m 2 ) were added to replicate plots within a Cenchrus grassland. Some plots were subjected to one-time herbicide or hand-pulling treatments to remove established Cenchrus. Because Hawaiians historically used fire to promote Heteropogon grasslands, the plots were burned biennially. Plots were also subjected to two levels of water supplementation. Heteropogon establishment was monitored over 2 and 4 years in the higher-and lower-water plots, respectively. In treatments containing established Cenchrus, Heteropogon establishment was consistently poor (<10% cover). But in the burned plots where established Cenchrus had been removed, as many as 31 Heteropogon seedlings per square meter were recorded, and Heteropogon became the dominant cover, averaging 34% absolute cover (81% relative cover) after 4 years in the lower-water plot and 34% absolute cover (60% relative cover) after 2 years in the higherwater plot. Few Cenchrus grass seedlings survived, possibly due to insufficient water. Water supplementation promoted growth of other alien grasses from the seed bank (Digitaria insularis and Eragrostis spp.); however, these grasses quickly declined after supplemental watering was terminated. Although initial suppression of Cenchrus was required, Heteropogon expanded quickly when seeds and fire were reintroduced, demonstrating that a Heteropogondominated grassland can be reestablished in 2-4 years.

Buffel grass (Cenchrus ciliaris) as an invader and threat to biodiversity in arid environments: A review

“…Data shows that adult populations persist but cannot replace and will face local extinction (Morales-Romero and Molina-Freaner, 2008) animal grazing. Chemical controls can be effective, but application must be strategically timed to coincide with the species' period of peak growth (Arizona-Sonora Desert Museum Staff and Volunteers, 2008;Daehler and Goergen, 2005;Dixon et al, 2002;Johnson and Kendall, 2008). Manual methods of control are costly, time consuming and therefore restricted to local removal efforts.…”

“…The grass was also introduced into the US state of Hawaii, where 33% of native grasslands were displaced by Cenchrus dominated grasslands within 30 years of its introduction to the island (Warren and Aschmann, 1993). Restoration of Hawaiian native grasslands has begun, and success has been demonstrated over a 4 year period (Daehler and Goergen, 2005).…”

Fire behavior characteristics of buffelgrass-fueled fires and native plant community composition in invaded patches

“…This study suggests buffelgrass does not preferentially invade species-poor communities, but rather invades favorable microsites and then decreases native plant cover and richness in and around those microsites. This pattern of invasive species being the cause of decreased richness is documented across many sites (Myers et al, 2000), with other non-native plants in the Sonoran Desert (Búrquez-Montijo et al, 2002;Mau-Crimmins, 2005) and has been documented in buffelgrass populations locally and around the world (Burgess et al, 1991;Daehler and Goergen, 2005;De la Barrera, 2008;Franks, 2002;Jackson, 2005;West and Nabhan, 2002).…”

Unassisted invasions: understanding and responding to Australia’s high-impact environmental grass weeds

“…Management options include the related objectives of counteracting the ecological novelties that confer advantage on alien species (for example, through increasing forest cover levels), reducing propagule pressure (for example, through timing of fire management activities) and creating disturbance regimes that favour the native community or disadvantage alien grasses. To date most attention has been on restoration (Daehler and Goergen 2005;Tjelmeland et al 2008;Brooks et al 2010); however, beyond localised asset protection, it remains unrealistic for extensive and remote conservation lands, and may also not in itself lead to the stable recovery of ecosystems (Reid et al 2009). In these cases, disturbance management, biocontrol and possibly the application of new genetic approaches such as CRISPR-based gene drive technology (Webber et al 2015) offer the greatest hope.…”

“…and Schult.) were successfully returned to pili grass dominance after invasion by buffel grass in an experiment that combined removal of buffel grass with seeding of H. contortus, watering and fire (Daehler and Goergen 2005). In Australia perennial veldtgrass abundance decreased following fire exclusion (Baird 1977).…”