Glyceria maxima (aquatic plant, grass)

Ecology Distribution Management Info Impact Info References and Links Contacts

General Impact Glyceria maxima can be a troublesome drainage weed and although palatable it has been implicated in the cyanide poisoning of livestock (NIWA, 2005). G. maxima has been intentionally introduced as livestock forage in seasonally inundated pastures, to temperate North America, New Zealand and Australia. In its native distribution in Europe, G. maxima forms monocultures in wetlands that reduce plant species diversity. In areas of introduction, including North America and Australia, it also forms monocultures and is now of conservation concern. The large, dense monospecific stands are capable of crowding out native wetland vegetation (Clarke et al. 2004). Because it is both a poor food source and a poor nesting substrate for wetland wildlife, it has a significant potential to negatively affect wetland habitat dynamics (NIWA, 2005). G. maxima spreads aggressively in waterways and impedes water flow (Sainty and Jacobs 1994 in Clarke et al. 2004). It assimilates large amounts of nutrients and thrives in nutrient-enriched ecosystems (Sunblad and Robertson 1988 in Clarke et al. 2004). Clarke et al. (2004) undertook a study of three upland streams in Gippsland, Victoria, Australia to infer the impacts of G. maxima on macroinvertebrate abundance, morphospecies density, and morphospecies and functional feeding group (FFG) composition. The results of their study concluded that invasion by G. maxima appears to drive changes in macroinvertebrate morphospecies composition and FFG composition, reducing a diverse array of macroinvertebrates to a more uniform fauna. The authors describe G. maxima as an autogenic ecosystem engineer, with the ability to convert sections of fast-flowing aerobic streams into partially anaerobic swamps. They further observe that by generating a root-mat swamp with a high capacity to process nutrients, G. maxima may facilitate its own growth and spread, as well as that of secondary invaders.          Location Specific Impacts: New Zealand   Reduction in native biodiversity: Inanga are the adult lifestage of the whitebait species, Galaxias maculatus. Inanga spawn during spring-tide events during late summer and autumn, spawning takes place amongst tidally-inundated riparian vegetation. Eggs develop within the moist litter-layer for 2-4 weeks, and hatch when the eggs are flooded by a later spring tide. The larvae are washed out to sea on the ebbing tide, where they feed and grow over the winter months. In the following spring, the whitebait enter river mouths from the sea, and mature in fresh water over the summer. Inanga eggs, are susceptible to desiccation and ultimately death when exposed to air as they have no waterproof layer and thus rely on thick vegetation to provide a humid layer of air around the eggs. Suitable spawning vegetation in New Zealand comprise of pasture grasses like tall fescue, Yorkshire fog, and creeping bent in pasture areas. The roots of these grasses form thick mats on the ground surface providing moisture retention. They spawn at the base of flax bushes and raupo and also amonst thick stands of native reeds. An inanga spawning habit survey was conducted by NIWA in 2001 of streams and rivers in the western part of the Wellington Region, the authors observe that G. maxima which was recorded in a number of areas does not provide the right kind of micro-habitat required for inanga spawning. The weed clogs waterways. It has been recorded in the South Island where it has displaced tall fescue grass from riparian zones which would have been suitable for inanga spawing. The authors state that G. maxima is proving to be a national threat to inanga spawning grounds as it best suited to wet riparian habitats which are the ideal spawning habitat (Taylor and Kelly, 2001).