Spartina townsendii: A Valuable Grass On Tidal Mud Flats

New Zealand Journal of Agriculture, Volume 78, Issue 5, 16 May 1949, Page 507

Spartina townsendii: A Valuable Grass On Tidal Mud Flats

By ’

W. L. HARBORD,

Fields Instructor, Department of Agriculture,

Invercargill. FOR thousands of years tidal salt mud flats the world over have made entrances to harbours unsightly and treacherous and have remained as vast areas of waste flats along the coasts of islands and continents. They consist of soft, sticky, saline mud which in many cases appears almost bottomless, and because such areas are often completely devoid of vegetation in the past they have provided an j . cr c 11 a. a i-Ci r m -, nn almost unconquerable challenge to man. A little more than 100 years ago about the coasts of England there were large areas of this unsightly, useless, and dangerous mud. Now such mud can be conquered, and by the use of a comparatively-new plant it can be reclaimed, to form useful and stable farmlands. This plant which has , . . . . . . .. „ r ... such an important role is known botamcally as Spartina townsendii and is sometimes called rice grass or cord grass.

■pIRST recorded in England on the Southampton salt marsh areas near Hythe in 1870, by 1880 Spartina townsendii was recognised as a new and distinct species of the genus Spartina and given the name it now bears. There are a number of species of this genus, but it is thought that Spartina townsendii is a hybrid. plant whose parents were X. stricta, a native plant of the south and east coasts of England, and X. alterniflora, a North American species. X. altemiflora established in English waters about 1829, having crossed the Atlantic, it is thought, attached to a ship. By 1880 the native species X. stricta was quite common and, while the North American species was not very noticeable, the new species X. townsendii was recognised, though there was very little of it. By 1920 this new grass had increased and spread to such an extent that many thousands of acres of what had previously been waste mud was gradually reclaimed and converted to areas of flats which at least could be

improved until they were fit for a useful purpose. Now S'. townsendii covers thousands of square miles 1 of salt mud flats on the English coast alone. It has also spread to and is serving a valuable purpose on the coasts of France, Holland, Denmark, and other countries. Description of Plant 1 Spartina townsendii is a tall-grow-ing, robust, stiff-stemmed plant growing in some places up to 40in. above the mud. It has a system of aerating cells which allows it to thrive on deep, sticky, salt mud which is low in oxygen. The root system of the plant has two distinct sets of rootsanchoring roots which penetrate quickly and deeply into the mud, and feeding roots which, being comparatively short, grow more or less horizontally beneath the surface of the mud. With such a system the plant is able to establish itself despite being covered by tidal waters. In the Northern Hemisphere X. townsendii spreads both by means of seed, much of which does not germinate, and by means of underground stems or rhizomes. These rhizomes grow beneath the surface of the mud and spread out from the parent plant. Their shoots are able to produce roots, and in this way new plants are established, spreading until an area is covered completely. . , When Spartina grows on a mud flatthe level of the mud is raised by the silt carried in on the incoming tide being dropped among the plants when the speed of the current of the water is reduced. When the tide begins >to recede much of this silt is left among the stems of the plants, as the water current over the Spartina bed is not sufficiently strong to lift it again

Introduction to New Zealand In 1913 Mr. K. Dalrymple, of Bulls, procured some plants of Spartina townsendii from Southampton Water, England, and ultimately was successful' in establishing them near Foxton, in the estuary of the Manawatu River, The details of this establishment were described by H. W. Allan on page 189 of the “Journal” for March, 1930. From this area many plants have been distributed to various parts of New Zealand. Some have established well, others have been fairly successful, and one,, at Invercargill, has been outstandingly successful. In an endeavour to protect the exposed estuary banks from wave wash the Invercargill City Engineer, Mr. F. M. Corkhill, set out 6 plants of Spartina in the estuary of the Waihopai River during 1932. Within a few months only 1 plant remained, the others having failed to establish. In November, 1932, a further 1000 plants were obtained from Mr. Dalrymple and planted in several beds about the estuary, and on . this occasion establishment proved satisfactory in some of the beds. More plants were set out during September, 1936, and in November, 1938, the planting of an area

of .about 34 acres was begun. The planting of this area was completed in 1939, and an excellent stand of Spartina is now. growing there just north and east of the Stead Street Bridge. Since 1939 annual plantings have been undertaken and at present a total of about 70 acres of the mud flats of the estuary is being reclaimed by this grass. g o far no Spartina plants are known to have been established from seed in New Zealand. Though the plants flower prolifically each year, there is no evidence that viable seed has ever been set . This is not so in other countries such as England and France, . i r u j r ; j Level ot Mud Kaised Between June, 1941, and May, 1946, measurements of the mud level on one of the Spartina beds in the Waihopai estuary were taken by means of sticks embedded in the mud, and an over-all rise in the level of the mud was evident. On 11 out of 12 pegged places the level had been raised up to 9in. with an average of slightly more than 7Jin. On the remaining place the level had been lowered by -Jin. because of a runnel or stream carrying a fast flow of

water having washed the silt away. Observations by eye indicate that on some of the areas where measurements have not been taken the increase in the deposition of mud has been much greater. The rise and fall of the tide at Invercargill varies between 9ft. and 6ft. for spring and neap tides respectively. This grass is unique in that, while it will grow on a mud on which very little else will survive, it is very selective in the type of ground on which it will establish. It will not establish on sand and does not thrive unless the mud is covered periodically with salt water. It will grow well on. sticky mud containing some sand and over which flows a mixture of river discharge and sea water. Water which flows swiftly appears to retard the plant’s growth even if it establishes, and it grows best on an area near a stream, channel and over which the flow is comparatively slow. To establish the plants on the Waihopai estuary they were set into mud by cutting it open with a spade and tramping it about the plants. The plants were set 9ft. apart in rows 9ft. apart. The beds were well covered in from 5 to 6 years. On the coasts of European continental countries Spartina townsendii is used for agricultural purposes. A bed which has been built up sufficiently to keep tidal water out is grazed by such stock as horses to effect" initial consolidation. Then the area may be used for hay or silage crops, the Spartina supplying the crop material. This stage has not yet been reached in New Zealand. To what extent Spartina townsendii can be used in New Zealand is difficult to estimate because of the varying results secured. At Thames it has been established successfully and is spreading through the mangroves which are growing plentifully in the mud. It was also established at the mouth of the Hutt River a number of years ago, but the plantings were destroyed when.. the flats were reclaimed for building . sites. However, there may still be areas where it would prove valuable in inlets such as are present near Waitati and Paremata, as well as in the North Auckland and Bay of Plenty areas.