The Restiad Peat Bogs at Motumaoho and Moanatuatua

Transactions of the Royal Society of New Zealand : Botany, Volume 2, Issue 16, 14 February 1964, Page 219

The Restiad Peat Bogs at Motumaoho and Moanatuatua

Ella O. Campbell

By

[Received by the Editor, May 28, 1963.]

Summary

The Lower Waikato peat bogs are raised bogs of a type peculiar to northern New Zealand. The dominant plants are two members of the Restionaceae, one providing shelter and the other possessing water-retentive roots which substitute for the Sphagnum of the standard type of raised bog in the Northern Hemisphere.

Introduction

Extensive peat bogs some 40 m above sea level, set amongst low hills rising to a height of up to 100 m above sea level, were once a feature of the Lower Waikato landscape. Today as one travels speedily by car along the main roads one sees only flourishing dairy farms flanking the highway, but back from the roads the former pattern is still in existence.

The presence of the peat bogs is in large measure a consequence of the geological history of the region. As far back as the Pliocene the area was a river basin. Deposits of rhyolite, gravel, sand and silt, which had been laid down by ancestral rivers in Pliocene times, were first uplifted, then eroded into hills and valleys and finally covered with volcanic ash which weathered to a clayey soil (Taylor and Grange, 1939). At a still later period the Waikato River, spreading over the flats as it emerged from the gorges in its upper reaches, deposited its load of gravel, sand and silt in the form of a large fan. Terraces and disused stream beds indicate that the course of the river, along with that of its tributaries, was continually altering over a wide extent of country, as it deposited its load of alluvium, first in one place, then in another, until eventually it entrenched itself. Due to the instability of the drainage pattern some low-lying areas between the hills were left as poorly-draining flats and others as shallow lakes or swamps dammed off from the main stream by a deposit of alluvium. From these areas the free drainage of ground water was further impeded by clay-type deposits derived by weathering of the volcanic ash. On some of the flats peat bogs became established, the largest ones, some 3,000-23,000 hectares in extent and with peat 3-12 m deep, developing as at Rukuhia, Moanatuatua and Motumaoho. Data derived from peat borings support the origin of the large bogs on flats and not in lakes (Cranwell, 1939, 1953), and indicate an extension of the peat outwards over a former swamp forest which developed at the periphery.

The native vegetation throughout the Lower Waikato shows a complex pattern, due partly to recurrent changes of the habitat consequent on alteration of the water courses, and partly to the processes of drainage, burning and cultivation which began in pre-European times and are still continuing at an accelerated rate. Only a small portion of the area is considered here, but it is hoped that this will provide a basis for further investigations.

Two peat bogs were studied. The first, which was examined in April, 1963, was at Motumaoho, north-east of Hamilton; the second which was examined in November, 1962 and in April, 1963 was at Moanatuatua, south-east of Hamilton.

The part of the Motumaoho bog described in the present paper is that located at grid reference 943636 on sheet N 56 of the 1 inch to 1 mile New Zealand Topographical Map, 1944. This part constitutes portion of the dome of what was once a large bog some 23,000 hectares in extent, now drained and converted to farming at the periphery. The dome itself has not been drained and, although it has been burnt over in the past, a complete plant cover has regenerated. The vegetation would appear to be the natural type for the dome region of such bogs, although suitable areas for investigation at the present time are difficult to find owing to the conversion of so much Lower Waikato land to farming. Supporting evidence for the natural condition of the vegetation is provided by the information given by Gheeseman when recording the finding of Sporctdanthus in New Zealand, for he mentions its immense abundance towards the centre of the bogs to the exclusion of almost all other vegetation (Gheeseman, 1879).

The vegetation of the smaller bog at Moanatuatua, some 7,000 hectares in extent, was described some 25 years ago (Cranwell, 1939). The portion examined during the present study is situated half-way between the highest point and the periphery at grid reference 878304 on sheet N 65 of the 1 inch to 1 mile New Zealand Topographical Map, 1959. There is evidence that the area has been partially burnt over recently and is still at the recovery stage, with the result that the vegetation is in a rather unstable condition.

Environmental Factors

Only a few points are mentioned here as detailed records for adjacent areas are available (Kidson, 1939). The climate in the region of both bogs is mild to warm humid with a mean annual temperature of approximately 56° F. (Kidson, 1932). The rainfall is about 50 inches well distributed throughout the year (Seelye, 1945). Winds are frequent and often strong, the flat nature of the terrain offering no shelter. Recordings taken at Rukuhia Soil Research Station show only 6% of calm days during the years 1946-1954, and an average wind run over the years 1949—1958 of 4,500-6,200 miles per month.

The water table when the bogs were visited in the autumn was level with, or slightly below, the surface and without free water above the surface.

The Vegetation at Motumaoho

The vegetation of the dome region at Motumaoho is a closed community comprising three distinct tiers.

The distinctive feature of the uppermost tier is given by isolated clumps of terete, reed-like stems of the restiad, Sporadanthus traversii F. Muell., reaching to a height of 1.2-1.8 m, branching fastigiately above and bearing drooping, brown, terminal panicles. The individual clumps are 60-90 cm apart and range in size from seedling ones comprising 4 erect shoots to large ones up to 1 m in diameter. Individual stems are up to 7 mm in diameter, widening towards the base and bearing tightly fitting, leaf sheaths. Belonging also to this tier and

reaching to a height of 1.2 m is the southern heath, Epacris pauciflora A. Rich., the individual plants 40-50 cm apart and of fastigiate habit. The large Sporadanthus clumps break the force of the wind and Epacris plants adjacent to them are taller than elsewhere.

The middle tier consists almost wholly of a flourishing, rampant growth of the restiad, Hypolaena lateriflora Benth., its much-branched, slender, straggling, wiry stems of diameter 0.5 mm reaching to a height of 0.6 m in the open and rising to 1.2 m where the stout, erect stems of Sporadanthus provide support and also some protection from the wind. The flexuous, green branches of the Hypolaena arch outwards over the bog surface and interlace with those of adjacent individuals to form a more or less complete canopy, varying in thickness but at times so compact that no light penetrates beneath. The leaves of Hypolaena are represented by closely convolute sheaths, 6-8 mm long, terminating in a green or brown, subulate tip of length 2-6 mm. The sheath which tightly enwraps the stem is at first green in colour with a hyaline margin and later turns brown. Lying over the lateral bud and within the sheath is a membranous greenish scale, 1 mm long, margined along part of its length with crowded, filamentous, septate hairs, which by their construction hold air between them and later lengthen to project as a white or tawny tuft from the top of the sheath. Projecting to the top of the middle tier of the vegetation are stiff, erect stems of the sedge, Schoenus brevifolius R. Br. and the rather similar leaves of another sedge, Cladium teretifolium R. Br. but always these appear in groups of 2 to 5, never in vigorous clumps such as occur in drained, bumt-over areas.

A ground-cover tier is present in all except the most deeply-shaded portions of the bog surface. It is composed of a variety of species, one or other being dominant locally, sometimes to the exclusion of others. The tallest plant of this tier is Lycopodium later ale R. Br., its erect stems growing to a height of 6-12 cm above the surface and bearing green, lanceolate-subulate leaves of length 5-7 mm and lateral stroboli 11-15 mm long. Lycopodium serpentinum Kunze occurs less frequently, its prostrate, creeping stems lying close to the surface and only rarely producing erect shoots bearing terminal strobili. In contrast to the former species it is barely holding its position. Isolated plants of the orchid, Thelymitra venosa R. Br. occur, represented at this time of year by a single, grass-like leaf 6-8 cm high arising from an underground root tuber. A small, brownish-green moss, Campylopus kirkii Mitt., apud Beckett, carpets considerable areas, as do also the liverworts, Goebelobryum unguiculatum (Hi. & T.) Grolle and a small species of Riccardia. The sundew, Drosera spathulata Labill., appears as flat rosettes of insect-entrapping leaves, often reddish, on the bog surface. Less frequently Drosera binata Labill. with erect, bifid leaves occurs, but in this case always as dwarfed plants. Erect or arching, narrow, green leaves of length 4-10 mm indicate the presence of a small bladderwort, Utricularia delicatula Cheesem., which is widespread in the area. Its tiny bladders, 0.5-0.6 mm long, attached to slender, white stems, lie beneath the surface of the bog where they entrap and digest protozoa, rotifers, small Crustacea and desmids. The bog moss, Sphagnum cristatum Hpe., can be found as occasional small clumps but does not play a conspicuous role nor does it ever form large cushions. A lichen, Cladonia crispata (Ach.) Flot. forma infundibulifera (Schaer.) Vain., of a pale sea-green colour, grows in places, either on fallen Sporadanthus stems or on the bog surface. After careful searching two plants of the fern, Schizaea fistulosa Labill., growing to a height of 10 cm were located.

The Vegetation at Moanatuatua

The area studied at Moanatuatua consists of a large, well-established and relatively old area of Sporadanthus bounded by a regenerating area which has been burnt more recently and in which young plants of Sporadanthus are gradually and steadily overtopping Hypolaena and Schoenus. The vegetation is constructed along similar lines to that at Motumaoho. In the older established area the large Sporadanthus clumps have a diameter up to 1.4 m. A clump of average size comprises 220 branched, fruiting shoots reaching to a height of 2.2 m and 58 unbranched, unflowered shoots. The clumps not only are taller and larger than those at Motumaoho but also are closer together, thus increasing the density of the upper tier. The other species are there as previously and play a similar role. Sphagnum occurs as small, scattered patches but makes a negligible contribution to the formation of the peat. Noteworthy by their presence are the species exclusive to the Sporadanthus-Hypolaena community—namely, Utricularia delicatula and, as far as New Zealand is concerned, Lycopodium serpentinum. An additional exclusive species found at Moanatuatua but not seen at Motumaoho is the orchid Coryhas carsei (Gheesm.) Hatch with a solitary, cordate leaf lying on the bog surface. The fact that it occurs only after a burn (Garse, 1926) would account for its presence at Moanatuatua.

The Root and Rhizome Systems of the Plants

The root and rhizome systems were excavated in order to determine the contribution each species was making to the formation and accumulation of the peat. Sporadanthus has a fibrous, cylindrical rhizome of diameter 10 mm covered with overlapping chestnut-brown scales and growing horizontally at a depth of 5-8 cm below the bog surface (Fig. 1). Some of the lateral buds grow out horizontally at a wide angle and by their extension form an interweaving rhizome system which troubled the workmen who constructed the railway line in the Waikato (Gheeseman, 1879), while other buds grow into tall, erect stems. Closely crowded roots 4—5 mm in diameter, at first white and slimy to the touch and later of a chestnut-brown colour, grow vertically downwards from the under side of the rhizome to a depth of 60 cm or more. They bear a few short, fine, lateral roots but function largely in anchorage. Amongst the long, anchoring roots there are occasional shorter, very slender, absorbing roots. Epacris pauciflora has a tap-root system penetrating to a depth of some 8 cm, with a scanty development of fine, brown lateral roots terminating in extremely slender white rootlets of diameter 50-100/*.

Schoenus brevifolius has a tough, cylindrical rhizome 5 mm in diameter lying horizontally at a depth of 3-4 cm below the surface. The rhizome is covered with shiny brown scales and bears slender roots 0.5 mm in diameter, some of which grow out horizontally and others obliquely downward. Branching is sympodial, the growing tip giving rise to a sharp-pointed erect stem enveloped at the base by reddish-brown sheaths, and a lateral bud growing forward for a distance of 1.5-2 cm before it in turn grows erect.

Cladium teretifolium has a different habit of growth. From the base of each tuft of leaves at a depth of 2-5 cm below the bog surface there grow out several rhizomes of diameter 2.5 mm clothed with long, chaffy scales. After growing horizontally for a distance of 20-30 cm the tip produces a tuft of leaves which break the surface, possibly flowering stems, and also several slender, brown roots of diameter 0.5-1 mm. Other regions of the rhizome are free of roots. Hypolaena lateriflora has below the bog surface an erect rhizome, some 10 cm long and smm wide (Fig. 2). The upper portion is covered with chaffy, over-

lapping leaf-sheaths between which lies a copious, brown tomentum. Along the length of the rhizome there arise, on one side slender green stems which grow upwards, and on all sides tough roots 1-1.5 mm in diameter which grow more or less horizontally for a distance of 60-90 cm or more just beneath the surface of the bog and give rise to numerous fine roots, the finest of which are only 0.05 mm in diameter. Even in seedlings the second root to be formed is a long, horizontal one.

The roots of Hypolaena are the most curious feature of the plant. All the roots are covered throughout their length with closely crowded, persistent roothairs which in the fine roots are most conspicuous, projecting outwards on all sides to a distance of 0.5 or even 1.0 mm from the surface. The fine roots are produced in great abundance. Many of them grow erect, often vertically erect, above the surface of the bog and intertwine into a felted mat which in deep shade is white in colour but when exposed to light is pinkish. In deeply shaded areas they may form the sole cover to the bog surface. They build upwards in conical masses around the bases of the Sporadanthus stems. They grow up over the mosses and liverworts engulfing them into the peat and over old Hypolaena stems or any fallen leaves and bind them into the peat also. The white mass of roots resembles Sphagnum moss in superficial appearance and in behaviour; it holds water like a sponge to 15 times its dry weight, and this water derived from dew and rain is clear, unlike the brown, peaty water of deeper levels. Like Sphagnum the roots create acid conditions with a companion micro-population in which ciliates and desmids predominate. Amongst the roots grow fungal hyphae.

Lycopodium laterale is the only plant of the floor tier with a well-developed, underground system. Its whitish, branching rhizomes, 2 mm in width, spread more or less horizontally at a variable depth and bear whitish scale leaves and downwardly directed, whitish roots 1 mm in width. The tips of some of the rhizomes turn upwards into erect stems. The roots when sectioned show the presence of aerenchyma in the cortex, a feature lacking in the roots of Lycopodium serpentinum.

The other plants of the floor tier have only scanty, shallow roots or rhizoid systems, and apart from the orchids are growing perched on the masses of fine Hypolaena roots. Where the Hypolaena roots mound up around the Sporadanthus stems, Drosera, Utricularia and Goebelobryum perch on them at some height above the bog surface.

The Root Anatomy of the Restiads

When the roots of the restiads, which form the essential components of the bog vegetation, are examined by sectioning, they show the presence of aerating tissue which is lacking in the roots of the sedges.

A transverse section of a thick root of Sporadanthus shows the structure to be as follows, proceeding from the outside inwards. Externally there is an epidermal layer with root hairs which later wither off. The outer cortex consists of 5-7 layers of small, compact cells with brownish, suberized and slightly lignified walls. The rest of the cortex is an extensive aerating tissue some 40 cells in width with large, intercellular air spaces between the spherical, thin-walled cells, which for the most part are uniform in size but become smaller and more compact at the inner margin. A well-marked endodermis, composed of cells which have a radial diameter twice the tangential one, at first shows a wide casparian strip on the radial walls and later a suberin lamella on all the walls together with a heavy deposit of yellow-brown, lignified thickening on the radial and inner tangential walls. The centrally placed stele consists of two layers of

pericycle, a restricted amount of conducting tissue and a central core of lignified sclerenchyma.

The larger roots of Hypolaena have on the outside a piliferous layer bearing closely crowded, persistent root hairs with walls formed of cellulose (Figs. 4 and 5). A subepidermal layer consists of thin-walled cells some of which may contain a magenta pigment giving the roots a pinkish tinge. The next 4-6 layers are of compact cells with slightly thickened, suberized walls of a yellowish-brown colour, and are followed by a zone of aerenchyma, up to 17 cells deep, consisting of more or less spherical, thin-walled cells interspersed with air spaces. The endodermis takes the form of sclereids with extremely thick, lamellated walls of an orange-brown colour. The central stele has a limited amount of conducting tissue, and a ground tissue in the form of lignified, sclerotic cells. Fine roots of Hypolaena (Fig. 3) differ in that the brown-walled zone of the cortex is I—3 layers deep and is not suberized, the aerating tissue is only I—2 cells in width, and the stele is progressively reduced in size until in the finest roots specialised conducting tissue is at a minimum and such ground tissue as is present is parenchymatous.

Discussion

The bogs described in this paper have been called restiad peat bogs since the two dominant species, Sporadanthus traversii and Hypolaena lateriflora, belong to the Restionaceae, a family with its centre of diversity on the dry plains of South Africa and Australia and with very limited extensions into South-east Tropical Africa, Chile, Malaya, Thailand, Vietnam and New Zealand (Hutchinson, 1959). Sporadanthus traversii is known from North Auckland, the Hauraki Plains, the Waikato and the Chatham Islands; Hypolaena lateriflora occurs throughout New Zealand and also in Australia. In the Waikato the two species are uniquely associated in the formation of peat. A community formerly in existence in North Auckland has been destroyed, the community on the Hauraki Plains is complex and the Chatham Island bogs contain an admixture of species.

The stout, branching, horizontal rhizomes of Sporadanthus form a scaffolding platform upheld, or perhaps buoyed up from below, by the vertical, stilt-like roots and supporting the weight of all the remaining bog vegetation. Aerating tissue in the roots and rhizomes and in the bases of the erect stems allows survival under the water-logged conditions. That such aerating tissue is significant for the growth of roots in soils saturated with water has been determined experimentally in the case of Cladium mariscus (L.) Pohl (Conway, 1940). The tall, stout stems of Sporadanthus break the force of the wind and provide shade, so reducing the rate of evaporation from the surface of the bog.

The underground systems of Cladium, Schoenus, Epacris, Hypolaena and Lycopodium laterale by interweaving contribute to the unstable decking across the base network of Sporadanthus rhizomes, but neither Schoenus nor Cladium shows vigorous growth in the water-logged conditions while Epacris and Lycopodium laterale play only a minor role.

On the other hand with shelter from the Sporadanthus and a high water table Hypolaena flourishes, providing additional shade and building up mats of fine surface roots which are retentive of rain-water, a habit which it does not develop under other conditions. The surface roots provide a substratum on which other species may establish themselves and as well they overgrow small plants or fallen leaves and stems on the bog surface and incorporate them into the peat. The roots themselves are resistant to decay and form the major structural component of a fibrous peat; the liverworts become gelatinous, so binding the fibrous material

together and contributing to the lack of aeration below the surface. The central region of the bog builds up to a level higher than that at the periphery and appears as a cushion-shaped dome when viewed from a distance, but remains saturated with water. Measurements are not available for Motumaoho but at Moanatuatua the highest point of the dome is 15 m above that at the periphery (Taylor and Grange, 1939). The vegetation of the dome differs from that on its sloping sides and also from that of the swampy, moat-like perimeter drained by a sluggish stream, but these latter regions now present a complex pattern due to drainage and burning.

The Sporadanthus-Hypolaena bog, although falling within the category of a high-moor or raised bog, is a type peculiar to the northern region of New Zealand. It originates on a poorly draining river flat and develops under mild to warm, humid, climatic conditions, in contrast to the standard type of raised Sphagnum bog of the central Irish plain and some other parts of Europe, which originates in a small lake lying in a glaciated valley and develops at its best in a relatively cool, moist climate. The raised Sphagnum bogs of North America, also developing under uniformly cool, moist, climatic conditions, are more varied in nature, originating in depressions on valley floors or on undulating surfaces where there is a high water table and building up from either Sphagnum or sedges (Rigg, 1940 a, b).

The essential conditions necessary for the formation of a raised bog would appear to be a consistently high water table of telluric origin, the presence of some plant retentive of rain water which builds the dome, and suitable conditions of macroclimate or microclimate to enable this particular plant to flourish. Under uniformly cool, moist climates in northern Europe and some parts of North America Sphagnum constructs the dome; in a warmer, less uniform climate in northern New Zealand Hypolaena substitutes for Sphagnum provided its roots have the shade, shelter and support given by Sporadanthus.

Acknowledgments

The writer is indebted to Mr W. Martin for identification of the species of Cladonia, to Mr E. W. E. Butcher, who for many years has made a study of the Moanatuatua Bog, for helpful discussion and information about that area, and to the staff of Rukuhia Soil Research Station, who as a team have made such an outstanding contribution to the development of agriculture on the peat soils, for co-operation and provision of facilities.

References

Carse, H., 1926. Three Interesting Plants. N.Z. Journ. Sci. Tech. 8; 168-169. Gheeseman, T. F., 1879. On the Occurrence of the Genus Sporadanthus in New Zealand. Trans. N.Z. Inst. 7: 324^325. Conway, V. M., 1940. Aeration and Plant Growth in Wet Soils. Bot. Rev. 6; 149-163. Cranwell, L. M., 1939. Soils and Agriculture of Part of Waipa County, Section 2G. Native Vegetation. D.S.I.R. Bulletin 76; 23-30. Government Printer, Wellington. ■— 1953. An Outline of N.Z. Peat Deposits. Proc. 7th Pac. Sci. Cong. 5; 186-298. Hutchinson, J., 1959. The Families of Flowering Plants. 2nd Edition. Vol. II; 700-704. Clarendon Press.

Kidson, E., 1932. Mean Temperatures in New Zealand. N.Z. Journ. Sci. Tech. 13; 143. D.S.I.R. Bulletin 76; 9-12. Government Printer, Wellington. Rigg, G. 8., 1940 a. The Development of Sphagnum Bogs in North America. Bot. Rev. 6; 666-693. Coast, the Interior and the Pacific Coast. Amer. Journ. Bot. 27; 1-14. Seelye, C. J., 1945. Maps of Average Rainfall in New Zealand. N.Z. Meteorological Service, Wellington. Taylor, N. H. and Grange, L. 1., 1939. Soils and Agriculture of Part of Waipa County. Section 28. Topography and Geology. D.S.I.R. Bulletin 76; 12-23.

Ella O. Campbell, Massey University College of Manawatu, Palmerston North.