Recovery of herbaceous species richness following herbicide treatment of Cenchrus Ciliaris (Buffel grass)- A pilot study in Onychogalea Fraenata (bridled nailtail wallaby) habitat restoration

Abstract

Cenchrus ciliaris (buffel grass) is a serious environmental weed driving native ecosystem collapse through altered fire regimes and competitive exclusion of native plant species (e.g. Tix 2000, Butler & Fairfax 2003, Marshall et al. 2012, Olsen et al. 2012). In Australia buffel grass invasion threatens fire sensitive rainforest and Acacia ecosystems while dense swards of buffel grass out-compete native ground storey species. This may impact on food availability to some species including the endangered marsupial-Onychogalea fraenata (bridled nailtail wallaby) (Green 2010). Literature suggested that reducing buffel grass cover triggers increased understorey richness. In degraded bridled nailtail wallaby habitat we applied herbicide, removing the buffel grass “canopy” and explored ground storey species richness recovery and persistence of any treatment effect. We measured species richness, and cover in treated and untreated plots. We also examined the influence of soil disturbance through shallow soil ripping. In the short term (12 months) species richness increased in response to reduced buffel grass cover (p < 0.05, r2=0.71). Mean richness ranged from 3 (s.d. 1.2) in control plots to 12 (s.d. 3.5) in plots that were sprayed and ripped while mean buffel grass cover ranged from 88% (s.d. 12.8) in control treatments to 51.4% (s.d. 11.3) in sprayed and ripped plots. Soil ripping may have increased richness over spraying alone, presumably by exposing more soil-banked seed to light. Treatment effect persisted up to 39 months although the relationship was with increasing bare ground area (p<0.05, r2=0.71) rather than reducing buffel grass cover. Here mean richness ranged from 4.6 (s.d. 1.2) in control plots to 16.6 (s.d. 3.5) in plots that were sprayed while mean bare ground ranged from 0.6% (s.d. 0.5) in control treatments to 4.9% (s.d. 1.3) in sprayed plots. Following treatment there were more herbaceous species and more bridled nailtail food species in herbicide treated plots than in untreated plots (p<0.05). These results suggest that herbicide treatment of buffel grass swards can release latent richness in herbaceous communities; the effect duration and increased bridled nailtail wallaby food species suggest the method has practical application in ecosystem restoration and in management of endangered species habitat.