Grassroots Dec 2006

Grassroots: Newsletter of the Grassland Society of Southern Africa ▪ December 2006 ▪ Vol 6 ▪ No. 4 The highly invasive Glyceria maxima is threatening the Maloti- Drakensberg wetlands Donovan Kotze E-mail: [email protected] lyceria maxima (also known G as great mann grass and Poa aquatica ), occurs in several Maloti-Drakensberg wetlands. Al- though this species has high erosion control and forage production values, it is extremely invasive. Unless measures are taken soon to curb this species, it is likely to considerably increase in extent and abundance, which will be devastating for biodiversity. This species should not be in- tentionally spread or promoted Description Synonyms Glyceria maxima is a perennial rhizo- matous grass with unbranched erect Glyceria aquatica (L.) Wahlb, Glyc- stems up to 1.0-2.5 m. Leaf sheaths eria spectabilis Mert. & Koch, Molinia have prominent midribs and visible maxima Hartman, Panicularia transverse veins and leaf blades are aquatica (L.) Kuntze, Poa aquatica L. shallowly grooved with prominent (see). midribs. Leaf margins have short, stiff hairs which are rough to the Common names touch. Leaves are bright green but Glycérie aquatique (French), great sometimes tinged with red. mann grass, reed mannagrass, reed Spikelets are 6-12 mm long and the meadow grass, reed sweet grass inflorescence is a panicle which can (English), Wasser schwaden be opened or contracted and the (German). inflorescence branches have short, stiff hairs similar to those of the leaf margins. 22 Grassroots: Newsletter of the Grassland Society of Southern Africa ▪ December 2006 ▪ Vol 6 ▪ No. 4 Invasive potential of the plant. Based on the sites ex- amined in the Maloti-Drakensberg, Glyceria maxima is known to be one impediments to flow appear to be the of the most invasive grasses world- most important contributing factor. wide. It is a native of Eurasia, and has become a threat to wetland bio- Invasion pathways diversity where introduced, including North America, New Zealand and The seeds appear to be distributed Australia. Its dense monospecific primarily by water, less so by wind, stands are capable of rapidly out- and may also be distributed on the competing native wetland vegetation. feet of birds, on livestock as well as In addition, through its expanding in mud on machinery. Locally the root mat, Glyceria maxima is particu- plant spreads through vegetative larly well adapted to growing out into expansion, and it is also conceivable areas of open water, whether in that pieces of floating mat broken off dams, lakes or in flowing streams by high flows in a river could be and rivers. Small streams and those transported great distances down- that are not very fast flowing can be- stream and then become estab- come completely overgrown. In this lished. manner, the plant works as an eco- system engineer, with the ability to Potential impacts convert sections of fast-flowing aero- Not only are the direct impacts on bic streams into partially anaerobic biodiversity considerable, but the swamps. It is of particular threat to grass also has the potential to result native vegetation in permanently in impacts to the agriculture and saturated areas as well as invading sport fishing industries. Although it aquatic environments, which is to the provides forage, mortality of valuable detriment of aquatic macro- dairy cattle in the Underberg area invertebrates and other fauna. have been directly linked to prussic Glyceria maxima is strongly fa- acid poisoning from G. maxima . voured by human impacts on wet- Fish would be negatively impacted land and aquatic systems. Newly upon by G. maxima through its im- created shallow standing water re- pact on the habitat and food supply sulting from impediments to flow, of the fish. e.g. from road crossings, weirs and dams, provides ideal habitat. Physi- Reasons for its introduction cal disturbance of wetland vegetation also creates “space” into which the The plant is introduced both as a grass can more easily invade. In- forage for livestock and as an orna- creased nutrients (e.g. through mental plant. In South Africa it leaching from fertilized fields) further would appear to have been intro- favours the rapid vegetative spread duced as a forage species, as will be explained in the following section. 23 Grassroots: Newsletter of the Grassland Society of Southern Africa ▪ December 2006 ▪ Vol 6 ▪ No. 4 However, in contrast to the situation ago. Some farmers have had it on in New Zealand, the planting of this their farm for over 60 years. It was species was confined to a relatively not found in any of the wetlands re- localized area, and no record could cently surveyed in the western por- be found of it having been introduced tions of the Mzimvubu, namely the through government channels, i.e. Mooi River and Wildebeest sub- through Department of Agriculture. catchments nor has it been located in any catchments north of the Mko- Extent in the Maloti-Drakensberg mazi. While it is likely to be present planning area in more sites than During the course of the eight already a Maloti-Drakensberg identified, its distri- Project survey of 104 Not only are the di- bution appears to be wetlands in the rect impacts on restricted to a radius of approximately 150 Maloti-Drakensberg biodiversity consid- planning area, Glyc- km. eria maxima was dis- erable, but the Presently it appears to be confined covered in one of the grass also has the wetlands in the Mko- mainly to the general mazi catchment near potential to result area extending from where it was intro- Mpendle, and was in impacts to the particularly abundant duced over 60 years around the margin of agriculture and ago as a wetland pasture for livestock. a dam in the wetland. sport fishing indus- Based on further in- If it had been more vestigation in the field tries. widespread than this and contacting farm- then it was bound to ers telephonically, it have been discov- was located at sev- ered sooner or later. eral other sites, one site also in the It is a conspicuous Mkomazi catchment on the Luhane plant in several respects that is not River, three in the Underberg/ easily confused with any existing Himeville/Pevensey area in the Mko- species present in the Maloti- mazi and Mzimkulu catchments and Drakensberg planning area. three sites in the Kokstad/Franklin It flowers widely and is morpho- area in the eastern portion of the logically quite distinct from any other Mzimvubu catchment. Although grass species. Vegetatively it some- further investigation is required, it what resembles Echinochloa spp. appears that it was introduced as a but its inflorescence is distinctly dif- planted pasture grass by a farmer in ferent from species in this genus. the Underberg area over 70 years It is tall-growing and forms large, dense stands. 24 Grassroots: Newsletter of the Grassland Society of Southern Africa ▪ December 2006 ▪ Vol 6 ▪ No. 4 A floating mat that has ex- tended several metres into the permanent wa- ters of the river Invasion of seasonally wet banks of the river Invasion of a river situation Its commonly occurs as a float- cently. Furthermore, Milton (2004) ing mat growing out into open water does not list it as one of the invasive areas, with this unusual ability being grasses present in South Africa. It is unmatched by any other grass in the argued that had this species been Maloti-Drakensberg area. present more widely, it would have Furthermore, the KwaZulu-Natal been recognized as something differ- portion of the Maloti-Drakensberg, ent from known hydric grass species, where all the known sites are lo- and it would eventually have been cated, has been botanically relatively collected and identified. But no such intensively sampled. Yet despite this records existed until its recent dis- and the conspicuous nature of the covery. species, no records of its occurrence in South Africa existed until very re- 25 Grassroots: Newsletter of the Grassland Society of Southern Africa ▪ December 2006 ▪ Vol 6 ▪ No. 4 Its potential to invade in the future that a well planned and swiftly imple- mented strategy be developed to It would appear that much of the dis- eradicate this species. A major tribution of G. maxima can be ex- awareness campaign targeted par- plained through the passing on of ticularly at farmers is also required. vegetative material amongst farmers, but evidence suggests strongly that Control methods dispersal has also taken place natu- rally from some of the sites of intro- Roundup Biactive or Weedmaster duction. Based on what is reported 360 are listed as the permitted herbi- in the literature, further natural dis- cide to use against G. maxima in persal would appear likely. Given New Zealand, and the recommended that G. maxima is already present in technique is Foliar spray without sur- three major catchments, its potential factants. Dense revegetation with to expand is considerable. local native species is also sug- Based on the evidence at the gested to limit re-invasion. invaded sites as well as that reported in the literature, it is not being melo- dramatic to say that across a large part of the low to mid altitudes of the M a l o t i - Drakensberg, Glyc- eria maxima has the potential to radically change the habitat of both palustrine (marsh) wetlands as well as stream/river systems, particularly mid to low order streams that are slow flowing. Thus, it is considered a very high priority Invasion of a palustrine (marsh) situation 26 .

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