General Impact
C. selloana can form dense stands that exclude other plants. Its sharp leaves cut skin and can limit recreational use of areas, and it can form dense colonies that can become or increase fire hazards (May et al., UNDATED). Once seedlings become established, it is a substantial threat to the ecological quality of preserves, particularly in coastal and grassland sites due to competition with native plants. Its rapid growth and accumulation of above ground and below ground biomass allow it to acquire light, moisture, and nutrients that would be used by other plants. It can be damaging even at low densities because of the amount of cover it can occupy (Starr et al. 2003). Studies comparing C. selloana with Cortaderia jubata a similar species found that C. selloana is genetically more diverse and could be one of the reasons of its success (Lambrinos, 2001).These results are consistent with the hypothesis that genetic variability enables better utilisation of heterogeneous habitats as well as promoting greater competitive abilities. In California, C. selloana inhabits a greater range of environmental conditions expanding into continental climatic zones. The rapid spread of pampas into exotic forests in New Zealand is a particular problem due to it's competition with pine, fire hazard, reduced accessibility and cost of control (Gadgil et al., 1984). Also the great quantity of fluffy seed has caused problems for kiwifruit growers since it clings to the fruit and causes it to be rejected for exprot (Knowles and Tombleson, 1987).
Location Specific Impacts:Rarotonga Is. (Cook Islands) 
Modification of fire regime: It produces large amounts of flammable material, increasing fire risk (PIER, 2002) New Zealand
Economic/Livelihoods: On plantation lands it can compete with planted seedlings, hinder access and provide a fire risk. This can have an implication on silvicultural costs. Seed clinging to kiwifruit rejected for export (Knowles and Tombleson, 1987)
Ecosystem change: Pampas has been listed as a wetland weed and a threat to the forest mire and forest-ecotone associations. It is reported to have the potential to invade scrub and forest margins and saline wetland habitats. C. selloana is known to affect the structure, species composition or regeneration of several sites with high conservation value. It has the potential to dominate sites and limit natural regeneration. This is especially so on islands and dunelands. It can disrupt vulnerable ecosystems and replace native vegetation especially on islands, island sea cliffs and dunelands.
Habitat alteration: On dunelands it can impact shorebird nesting sites and threaten plant habitat. Pampas is found on the fringes of geothermal areas. Fragile ecosystems can be damaged by invasion of pampas due to change of habitat. (McGlone MSc thesis, 2003)
Human nuisance: Encroachment onto walking and mountain biking tracks (McGlone Msc thesis, 2003).
Physical disturbance: It can hinder access especially on stream margins and invade surrounding vegetation. United States (USA)
Human nuisance: Cortaderia selloana's sharp leaves cut skin and can limit recreational use of areas.
Modification of fire regime: Cortaderia selloana can form dense colonies that can become, or increase, fire hazards.
Modification of successional patterns: Cortaderia selloana can form dense stands that exclude other plants. Hawaii (United States (USA))
Habitat alteration: In Hawaii Cortaderia selloana can invade a variety of environments from wet to dry climates and from disturbed to native environments.
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