Cenchrus ciliaris

The invasive exotic species has the ability to set up a negative relationship with the native species, creating dense populations that move away or exclude local species, compromising the herbaceous stratum that represents a significant portion of the biodiversity of Caatinga. In Hawaii, replacement of native vegetation to buffel grass has been demonstrated (Daehler & Carino, 1998. In Australia, several studies in eucalypt woodlands in Queensland have found a reduction of native vegetation cover or species richness caused by buffel grass (Franks, 2002; Fairfax & Fensham, 2002; Jackson, 2005). In central Australia, Clarke et al., (2005) found the presence of buffel grass caused the decline in abundance and diversity of all native herbaceous plant species over a twenty seven year period. Smyth et al., (2009), found a similar response of ground vegetation when comparing habitats with varying buffel grass cover. Buffel‐eradicated sites supported richer and more diverse vegetation and seed banks across all functional groups except perennial grasses. The effect was strongest for perennial forbs, annual/short‐lived forbs, and annual/short‐lived grasses. Buffel grass removal at localised scales provides islands of habitat with improved opportunities for native plant re‐establishment and abundant foraging resources for granivores. Buffel grass invasion can have major impacts on ecological processes and population dynamics of organisms that occupy invaded systems. Typically, invasion leads to the capture of large proportions of light, water and nutrient resources by buffel grass plants. This results in competitive displacement of native vegetation and a general reduction in plant diversity (Saucedo‐monarque et al., 1997; Jackson, 2004, 2005; Stevens and Fehmi, 2011; Castellanos et al., 2016; Farrell and Gornish, 2019). Cenchrus ciliaris-dominated sites had fewer herbaceous species than non-C. ciliaris sites at all scales investigated and this pattern was found for the major plant groups (perennial grasses, legumes and other forbs) present. Species richness was negatively associated with increasing C. ciliaris biomass at some scales and it appeared that C. ciliaris had a greater effect on richness than B. ewartiana. The negative association between C. ciliaris and species richness is consistent with the view that invasion by C. ciliaris poses a threat to biodiversity. Various herbaceous species; Australia: Buffel grass leachates shown to reduce seed germination of various Australian herbaceous species under laboratory conditions. (Eyre et al., 2009). Forbs (Cyperus gracilis, and Radscondons), Australia are 10% less abundant in Buffel grass pasture. Pili grass (Heteropogon contortus); Hawaii, USA: One of several non-indigenous grasses displacing Pili grass in most dry, leeward habitats of the Hawaiian Islands. (Daehler and Goergen, 2005)

Invasion can also lead to negative impacts on wildlife, causing reductions in dietary variety, altering wildlife foraging behaviour, and changing the structure of habitats (Franks, 2002; Smyth et al., 2009; Young and Schlesinger, 2014; Bonney et al., 2017; Dittmer and Bidwell, 2018).

Even when cover is low, buffel grass can have a detectable influence on some aspects of community dynamics. A study by Ludwig et al. (2000) of clearing and grazing impacts in eucalypt woodlands of Queensland provides data for six birds and two reptiles. They found that buffel grass cover together with two other variables (tree grove height and the cover of perennial grass clumps) negatively influenced the occurrence of grey butcherbirds (Cracticus torquatus) and Carnaby’s skink (Cryptoblepharus carnabyi). Both Ludwig et al., (2000) and Eyre et al., (2009) found negative responses of reptiles in the presence of buffel grass compared to non buffel areas. Bests (1998) study in central Australia showed invertebrate abundance and diversity decreased in areas of dense buffel grass. Smyth et al., (2009) found a change in composition of birds and the Hot-climate specialist functional groups of ants even at a low level of buffel grass.

Desert tortoise (Gopherus agassizii) and Mule deer (Odocoileus hemionus); Sonoran Desert Ecoregion. Habitat is threatened by Buffel grass fuelled fires. (Arizona-Sonora Desert Museum Staff and Volunteers, 2008). Woody layer: Negatively affected by Buffel grass fuelled fires. (Clarke et al., 2005) Invasion can also lead to negative impacts on wildlife, causing reductions in dietary variety, altering wildlife foraging behaviour, and changing the structure of habitats (Franks, 2002; Smyth et al., 2009; Young and Schlesinger, 2014; Bonney et al., 2017; Dittmer and Bidwell, 2018). Fire regimes can also be altered by buffel grass invasion, as the biomass and continuity of fuels generally increases after invasion (Albrecht and Pitts, 2004; Clarke et al., 2005; McDonald and McPherson, 2011). Consequently, buffel‐invaded systems often burn hotter and more regularly than native vegetation, and this can have detrimental effects on biodiversity in systems not adapted to high intensities or frequencies of pyric perturbation (Miller et al., 2010; McDonald and McPherson, 2011). Invasion of buffel grass has had a major impact on ant communities. While the increase in bare ground is the most likely mechanism, it is not a simple function of proportional increase in bare ground, but rather a broader effect of changed habitat structure. Substantial field evidence was found to support the existence of a buffel grass-initiated fire-invasion feedback. Buffel grass invasion was significantly correlated with increased fuel loads. Increased fuel loads were significantly correlated with increased burn severity (...) Burn severity was significantly correlated with the mortality of woodland overstorey species, and with the proportion of fire survivors that were reduced to basal resprouts. Field evidence largely supported the hypothesis that buffel grass has initiated a positive fire-invasion feedback in the Alice Springs region.

Shortlived forbes, suffruticose shrubs: More abundant when Buffel grass is present (Clarke et al., 2005) Trees, Peachwood shrub, False Sandlewood (Eremophila mitchellii); Australia: Following exposure to Buffel grass fuelled fire Tree canopy shows recovery in the form of epocormic shoots, Peachwood resprouts but does not fare so well as neighbouring trees, False Sandlewood did not re sprout (Butler and Fairfax, 2003) Many-headed Wiregrass (Aristida caput-medusae), Slender Chloris (Chloris divaricata), Fairy grass (Sporobulus caroli): Increaser response to Buffel grass infestation Cryptoblephaus pannous: Decreaser response to Buffel grass infestation

Giant Saguaro Cactus (Carnegiea gigantea); Arizona and Texas, USA and Mexico. Species devastated by Buffel grass fuelled fires, and competition for water. (Schiermeier, 2005, Arizona-Sonora Desert Museum Staff and Volunteers, 2008).

Cactus ferruginous pygmy owl (Glaucidium brasilianum cactorum); Arizona, USA, Threatened as a result of Buffel grass fuelled fires devastating cacti in which the pygmy owl lives. (Defenders of Wildlife, 2010). Giant Saguaro Cactus (Carnegiea gigantea); Arizona and Texas, USA and Mexico. Species devastated by Buffel grass fuelled fires, and competition for water. (Schiermeier, 2005, Arizona-Sonora Desert Museum Staff and Volunteers, 2008).

Growth examined in thorn scrub and in Buffel grass pastures – no significant effect on plant abundance but a major difference on size distribution. All seedlings that emerged on pasture died within one year. Data shows that adult populations persist but cannot replace and will face local extinction (Morales-Romero and Molina-Freaner, 2008).