From comparative meteorological observations, it would appear that four times more rain falls on the west than on the east coast; and this, as may be expected, produces a marked difference in the character of the flora. Moreover, owing to the influence of the mountains which thus intercept the moist winds, a comparatively arid district occurs in the interior of the province, which approaches to within a variable distance of the east coast, according to the form of the surface and the prevalence of dry, shingly soils.
Whatever may have been the original botanical features of this district, it is now, at least, characterized by an almost total absence of forest. That heavy timber at one time grew upon the ranges is indicated by the occurrence of large half-consumed logs; but it is very improbable, from the nature of the soil on the flat basin-like plains, that they ever supported any other kind of vegetation than grasses and low scrub.
In addition, therefore, to the division of the flora into zones according to altitude, it is intended, in the diagram, to represent the three parallel districts of the west, central, and eastern parts of the province.
Zone A—consists of mixed bush. A1 is the forest of the West Coast, that clothes steep slopes and confined valleys which open directly on the sea without the intervention of open or alluvial land. It presents no essential difference of character between the sea level and an altitude of 4,200 feet, (which is the highest limit ever reached by the sylvan zone in any part of Otago), while in many instances it ceases, without obvious reason, at a much lower elevation.
As indicated by the prevalence of certain trees, the western forest may be subdivided as follows:—
(a.) Along the shore there is a profusion of shrub Veronicas and Olearias, and large Ironwood trees with gnarled branches.
(b.) The flat land and low spurs are covered with the common species of Pines and Birch, such as Rimu, Totara, Weinmannia (Karmahi), and Fagus (Tawai), with a dense undergrowth, and many tree ferns, among which the most remarkable is the Mamaku (Cyathea medullaris), a Tree-fern only found in Otago, on the West Coast, though common in the northern provinces.
(c.) From 1,000 feet upwards the Pines diminish in number but are still well grown; and in addition to the common kinds, the Toatoa, or Celery Pine (Phyllocladus alpinus), becomes abundant. The Rata (called Ironwood in the south) acquires an immense size on the loftier ridges; but, on the whole, the trees which predominate are the Red and White Birches, which gradually become dwarfed, and form, along with the heath-like and composite shrubs, the belt of dense scrub which always marks the upper
