It is tempting to attribute to climatic causes the pattern of pre-European vegetation, but this is surely superficial, for no allowance is made for the effect of Maori occupance upon vegetation, or for the complexities involved in demonstrating the relationship of climatic change and vegetation. The southern Wairarapa is, however, unquestionably drier than the northern part. This is due in a considerable part to the rain-shadow effect produced by the Tararua Range, which attains its greatest altitude to the east (Hector, 5,016 ft) and north-west (Mitre, 5,154 ft) of Masterton, but which in the northern Wairarapa descends to a low saddle so that the effect is less pronounced. The range forms the western limit of the whole region and is paralleled by a broad “vale” extending from Palliser Bay in the south to the Manawatu River in the North. The vale is claimed by two river systems, that of the southward-flowing Ruamahanga and its tributaries and that of the north-flowing Mangatainoka and Mangaone. The watershed between the two systems is never very high (c. 1,300 ft), but it separates two distinct morphological districts, thus once more emphasising the contrasts between the northern and southern parts of the Wairarapa.
In its western part the southern Wairarapa is morphologically a faulted depression which has been filled in by the alluvial fans and deposits of the Ruamahanga, Waingawa, Waiohine, and Tauherenikau, to form a plain. The fans often appear as flat, even stretches of country with hardly discernible changes in level, but when viewed, for instance, from Bidwills Ridge, the gradual rise of the fans towards the western foothills is quite clear. The western and wetter parts of the plain where, in addition, the holdings are smaller in size, contain most of the dairying units. At Greytown the presence of extremely favourable river silts has aided the establishment of small-fruit growing, but over most of the area fat-lamb farming predominates. In the east a wide belt of hill country is taken up with store sheep and cattle, though the upper slopes of the Aorangi Mountains (3,226 ft) remain in bush. Some parts have experienced marked soil erosion with a consequent aggrading of the rivers. The hill country as a whole is isolated, unfrequented, and lightly populated. The difficulties presented to the farmers by isolation, steep terrain, erosion, and reversion of pasture are reflected in the relatively small increase in the number of sheep shorn between 1951–52 and 1959–60 in Featherston County, 7·78 per cent, compared with Masterton and Wairarapa South Counties, 42·44 per cent and 1717 per cent respectively.
In the northern part of the Wairarapa the “vale” does not present the aspect of a level even plain. It consists of a series of flat-bottomed river valleys separated by broad interfluves, a pattern which is striking to anyone who travels eastwards from Pahiatua. Dairying is the predominant activity, with factories located at such places as Nireaha, Ballance, and Mangatainoka. Immediately east of Pahiatua or Eketahuna one again enters the hill country which attains its maximum elevation in the Puketoi Range (2,000 ft), whose summit remains partly covered in bush. It is impossible in a few words to present intelligibly the topography of the hill country. While the terrain is never so broken as to be a real hindrance to movement, it was sufficiently steep when covered with bush and so distant from the major traffic lines as to render settlement difficult, even in the latter part of the last century. Consequently, small settlements like Pongaroa and Makuri were not founded until the late 1890s. Store-sheep farming now prevails. Over much of the area there is a need for closer fencing, more discing, and greater control of second growth. Relatively poor roads, though admittedly undergoing some improvement during the last decade, raise the cost of fertilisers and materials considerably. Isolation is a feature of the district, and its consequences are difficult to ignore and costly to overcome. The population of Akitio County, which is probably the one most representative of this eastern hill country, totalled 1,421 in 1911, and 1,189 in 1961. In the period 1951–52 to 1959–60 the number of sheep shorn increased by 12·24 per cent, compared to the 13·20 per cent more for the whole region, and the percentage increase of lambs shorn was only 12·17, compared with the regional average of 54·53 per cent.