For a detailed account of the environmental impacts of Imperata cylindrica please read: Imperata cylindrica (cogon grass) Impacts Information. The information in this document is summarised below.
Increases in I. cylindrica concern ecologists because this species displaces native plant and animal species and alters fire regimes (Lippincott 1997 2000, in Brewer & Cralle 2003). Dense swards of I. cylindrica create an intense competitive environment for commercially important species (Bryson and Carter 1993, Kuusipalo et al. 1995, Premalal et al. 1995, Dozier et al. 1998).
Displacement: Invasion of longleaf pine communities by I. cylindrica will likely cause significant losses of short habitat-specialists and reduce the distinctiveness of the native flora of these threatened ecosystems (Brewer 2008).
Agricultural: The interference of I. cylindrica with the growth of tropical crop species, both herbaceous and woody, is well documented (Brook 1989, in King & Grace 2000b).
Habitat alteration: I. cylindrica invasion of an emerging pine forest may be an example of a grass converting a woodland with high understory diversity into a grassland with low diversity. I. cylindrica presents a case where its ability to deprive competitors of N may lead to the conversion of the ecosystem (Daneshgar & Shibu 2009).
Modification of nutrient regime: The changes in nutrient cycling caused by exotic grasses can endanger young tree seedlings in a regenerating forest (Daneshgar & Shibu 2009). Because I. cylindrica allocates significant carbon below-ground, it is able to recover quickly after fire, which is why Lippincott (2000, in Daneshgar & Shibu 2009) suggested that frequent intense fires could convert a pine savanna into an I. cylindrica-dominated grassland.
Ecosystem change: A study by Holly and colleagues (2008) supports the growing consensus that invasive plant species alter normal ecological processes and highlights a possible mechanism (alteration of microbial assemblages) by which I. cylindrica may alter an ecosystem process (decomposition).
Competition: The results of a study by Brewer and Cralle (2003) suggest that I. cylindrica is a better competitor for phosphorus than are native pine-savanna plants, especially legumes. The competitive effects of this species on plant diversity may be of more immediate conservation concern relative to the effects of this species on fire regimes in longleaf pine ecosystems (Brewer 2008).
Threat to endangered species: Longleaf pine savannas of the southeastern USA contain extraordinarily species-rich plant communities and are home to numerous threatened endemic plant and animal species (Walker & Peet 1983, Bridges & Orzell 1989, Brockway & Lewis 1997, in Brewer & Cralle 2003).
Inhibits other species: The extensive rhizome network of I. cylindrica not only allows rapid regeneration of foliage, but also produces allelopathic root exudates that can inhibit germination and growth of other plants, including some pines (Hussain et al., 1994, in Ramsey et al. 2003).
Modification to fire regime: Lippincott (2000) found that sandhill invaded by I. cylindrica had significantly greater fine-fuel loads that resulted in fires that had higher maximum temperatures at greater heights. Fire-induced mortality of juvenile longleaf pine was higher for pines growing in invaded sandhill.
Other: The density of the below-ground rhizome network makes I. cylindrica a mechanical hindrance to root growth of native species. The rhizome tips are sharp: they may even penetrate the roots of native species, leading to damage or mortality by infection (Eussen & Soerjani 1975, in Daneshgar et al. 2008).