New Zealand Journal of Botany ISSN: 0028-825X (Print) 1175-8643 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzb20 Botany of northern Horowhenua lowlands, North Island, New Zealand Prances C. Duguid To cite this article: Prances C. Duguid (1990) Botany of northern Horowhenua lowlands, North Island, New Zealand, New Zealand Journal of Botany, 28:4, 381-437, DOI: 10.1080/0028825X.1990.10412326 To link to this article: http://dx.doi.org/10.1080/0028825X.1990.10412326 Published online: 05 Dec 2011. Submit your article to this journal Article views: 346 View related articles Citing articles: 4 View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tnzb20 Download by: [121.75.88.191] Date: 28 March 2017, At: 19:51 New Zealand Journal ofBotany. 1990. Vol. 28: 381-437 381 0028-825X/90/2804-D381$2.50/0 © Crown copyright 1990 Botany of northern Horowhenua lowlands, North Island, New Zealand PRANCES C. DUGUID My study began in earnest in 1941 after the 12 Tawa Street formation of the Levin Native Flora Club, a group of Levin people anxious to extend their knowledge of native New Zealand plants. Botany Section, later Botany Division, DSIR, under Dr H. H. Allan, had recently been established in Wellington, and Wellington Botanical Society Abstract The studyregion covers afarmingdistrict had just been formed. Members of these groups with coastal dunes, alluvium and peat, terraces of shared activities, and Botany Division members and older sediments and low hills at the foot of the others provided instructive programmes and Tararua Range. Small communities of native plant accompanied the clubs in the field. By 1950 it was speciesremain in adiversityof habitats.Four hundred apparent thatsome plants seen earlier were becoming and seventy-eight native and 503 alien taxa are lost. My early recollections and notes on the native recorded with information on their abundance, plants from 1929, and records of the naturalised distribution and habitat, together with historical plants from the 1950s, provide the basis for this notes on the vegetation. It is considered that about account of the wild plants of the Horowhenua 418 of the aliens are fully naturalised. lowlands. Keywords forest; wetland; dunes; native flora; naturalised flora; abundance; habitat; history THE ENVIRONMENT Horowhenuais a region on the western margin of the Wellington Province (Fig. 1). The northern INTRODUCTION Horowhenua lowlands covered in this study are There are few botanical records of the Horowhenua centred on the town of Levin (Fig. 2). They extend lowlands. The account of the vegetation of the south from Tokomaru and the lower reaches of the Tararua Range (Zotov et al. 1939) included the Manawatu River to include the banks of the Otaki foothills but made no specific mention of the River as far upstream as the Otaki Forks and a little Horowhenua foothills. The most comprehensive beyond in the Waiotauru valley. The eastern margin early botanical description of the lowlands was by runs along the lower slopes of the Tararua Range Cockayne (1909) and included an account of dune mostly below 350 m. From the eastern margin the plant associations of western Wellington. Aston land slopes down the lower flanks of the Tararua (1910), in an account of native plants of the Range and marine terraces to the alluvial plain and Wellington Province, made reference to plants in the belt of coastal sand which created Lakes Otaki. Some early settlers and visitors described Horowhenua and Papaitonga. salient features of the local vegetation, but in little On the moderately steep slopes of the Tararua detail. Later botanists collected specimens and Range the soils are thin, friable or granular silt recorded plant localities in the region. loams. Pockets of rolling land have a heavy coating of volcanic ash. Much of the native forest has been cleared from the hills and replaced with low quality pasture and radiata pine plantations. The terraces sloping gently from the greywacke uplands are formed of marine deposits of silt, sand B90015 and gravel, and are capped with loess. In parts, Received 30 March 1990; accepted 19 July 1990 particularly near Tokomaru and Shannon, they are 382 New Zealand Joumal of Botany, 1990, Vol. 28 'PARAPARAUMU «:-,:>'1- MASTER~ON ,\'1-«-'1' (J WELUN~}ON LOCATION MAP ROADS 1 Poplar 2 Okuku 3 Makarua-Rangitane 4 Heights 5 Arapaepae 6 Tararua 7 Kimberley 8 Gladstone 9 Muhunoa E. BUSH REMNANTS 10 Florida 11 Kuku E W Whirokino 12 Rahui P Poroutuwhao o Ohau 13 Otaki Gorge 14 Waikawa Beach 15 Kuku Beach Boundary of study area 16 Muhunoa W. 17 Buller Margin of dune belt 18 C,D,Farm 19 Arawhata • Greywacke foothills 20 Hokrc Beach 21 Moutere The area referred to as plains 22 Koputaroa lies between the dune bell 23 Paiaka and the greywacke hills, 24 Oturoa Study area includes river margins to road end Fig.l Map of the northern Horowhenua lowlands. The eastern boundary is mostly under 350 m above sealevel. The plain (terraces, alluvium, and peatland) is bordered by the dune belt on the west and the greywacke hills to the east. Duguid-Botany of northern Horowhenua 383 deeply dissected by flat-bottomed steep-sided because of the complex interfingering of their valleys. Gravel is carrieddown those streams which boundaries. have headwaters in the greywacke mountain range. Horowhenua has a moist, windy climate with Sandstone outcropping on the western margin from warm summers and mild winters. Figures quoted Koputaroa to Otaki is formed from windblown sand below are fromNew ZealandMeteorological Service deposited much earlier than the coastal sands. Soils (1983). The mean annual rainfall is 899 mm on the of the terraces are silt loams requiring topdressing coast at Hokio and 1120 mm at Levin. At Levin, and drainage for satisfactory sheep and cattle farming, February is the driest month with 70 mm of rain, and dairying, and cropping. July the wettestwith 116 mm. Mean temperatures in The Ohau and Otaki Rivers, and the large streams these months are 17.4°C and 9.1°C. Air frosts occur between them, deposit large quantities of gravel on 10.7 days per year between April and October from the Tararua Range on their immediate flood (28.4 at Waitarere and 22.0 at Hokio). Sunshine plains. Further from the streams on lower land, finer hours are 2054 per year. Wind run is less than in sediments form sandy loams and silt loams requiring districts to the north and south of the study region. drainage to realise their full potential for intensive West to north-west directions prevail. Dry spells are farming and horticulture aroundLevin, Ohau, Kuku, not a regular feature but the 1969-70 drought had Manakau,and Otaki. The extensiveMakeruaswamp effects on native forest similar to those near near Opiki created peaty soils which are now mostly Palmerston North reported by Atkinson & drained for cropping and pastoral farming. Greenwood (1972). In this and other droughts, gaps Sand from the prograding shore hasblowninland caused by the death of trees exposed the forest to form a belt about 6 km wide but reaching 11 km interior to further drying winds and windborne salt. wide at one point. The character of the sand deposits A series of long, hot summers in the 1980s have depends partlyon time since stabilisation, the oldest caused the ageing forests of the plain to deteriorate generally being further inland. The dune sands near considerably. The water table on parts of the dune the beach are thinly vegetatedwith spinifex (Spinifex belt and plain buffers the effects of drought to some sericeus) and marram grass (Ammophila arenaria). extent. On the coast some communities of plants are Old sand has adequate topsoil to supportpoorpasture, obliterated by moving sand in dry periods. The tree lupin (Lupin us arboreus), and bracken fern climate of the region is reviewed by Coulter (1966). (Pteridium esculentum). Further inland on more Zotov et al. (1939) mention the devastating 1936 rolling topography the black topsoil is up to 30 cm gale. deep, less erodable, and carries drought-pronepasture of better quality with fewer shrubby weeds. THE NATIVE VEGETATION Transientsand plains near the shore with a partial cover of small rhizomatous herbs become invaded Horowhenua lowlands, like many other parts of byLeptocarpus similisandScirpusnodosus, and later New Zealand, received little early attention from by toetoe(Cortaderia toetoe)and tall fescue (Festuca botanists and there were only brief accounts of the arundinacea) which more effectively annihilate the vegetation by other visitors. Sawmilling from the small herbs. Damp parts sheltered by toetoe are 1840s, and drainage from the 1890s, changed the invaded by Eleocharis acuta and Potentilla face of the land. Sand country vegetation remained anserinoides. Olderplains carry pasture thatrequires intact a little longer because it was less exploitable drainage where the water table is high. On the low­ and contained habitats not so readily colonised by lyingplains extensive peat swamps of flax(Phormium alien plants. An attempt is made here to construct an tenax), and patches of semi-swamp have been more image of the early plantcover, to recordthe changes, difficult to drain for farming and retain some native and to describe the scant relics of vegetation of the vegetation. sand country, the wetlands, and the forests. In this In this paper the three major geological zones are paper, forest is mostly referred to as bush, the referred to as the foothills (of which the Arapaepae vernacular for native vegetation over 4 m tall hills are a major part), the plain (which includes containing little or no Kunzea or Leptospermum. terraces, alluvium, and peatland), and the dune belt. Where the canopy is fairly open the term light bush These are shown in Fig.