Silver Beech. The main feature is the relationship of silver beech to the other two species. 4,200ft is a critical altitude above which mountain beech is dominant; scattered large, heavily branched trees of silver beech occur at higher altitudes, but are confined almost entirely to sheltered locations where there is no younger growth. Mountain beech is here clearly supplanting silver beech. Between 4,200ft and 4,000ft, however, abundant silver-beech generation 4ft to 7ft high under a mountain beech canopy, is characteristic. This is of more than limited occurrence, as it has also been observed on the Kaimanawa side of the ecotone in the Waiotapuritia Valley, and further afield above Rangataua on the slopes of Ruapehu. Its vigour here in forest otherwise heavily browsed by deer, both red and Japanese, is unexpected and perplexing. Below 4,000ft the relationship between the two species is less clear. There is a complicated patchwork of pure stands of one or the other species and of areas where the two are apparently codominant, with large canopy trees. Here silver beech is approximately three times the age of mountain beech of comparable size, and pockets of pure silver beech tend to be overmature with a discontinuous canopy, while the mountain beech is younger and more vigorous. It appears possible that in this situation the two species may alternate, with shade-tolerant silver beech favoured under a mountain-beech canopy and eventually supplanting it; the longer-lived silver beech with its denser canopy then suppressing all regeneration until, with over-maturity, gaps in the silver-beech canopy favour light-demanding mountain beech. Not all stages of this sequence have been observed, as the browsing of a large deer population distorts the pattern of regeneration. Red Beech. What should be the red-beech zone (below 3,600ft), is occupied largely by Danthonia rigida tussock in the Ngaruroro Valley and by tongues of induced manuka scrub in the Mohaka Between the two, red beech with silver beech sub-dominant occupies the Oamaru Valley, which is a geographical, not an ecological boundary. Despite the manuka scrub, red beech is more or less continuous down the Mohaka Valley, but in the Ngaruroro the zone is pinched out. Mountain beech not only occurs above it, but also forms the forest margin with tussock grassland below it. The last continuous red beech forest forms a narrow tongue in the Purungetungetu Valley near the head of the Oamaru, and here it is all-aged and appears self-perpetuating. South of this red beech appears only sporadically, though there are several pockets down the Ngaruroro River. Bogs. A line of three small clearings is conspicuous on aerial photographs at the head of the Purungetungetu Stream, and a fourth at the head of the Ngaawa-purua. All are bogs on sloping surfaces, and appear to have been formed by a heavy wash of pumice from steep neighbouring slopes blocking pre-existing drainage systems. All have a well established bog vegetation on peat of varying depths underlain by a hard pan. Their altitude is about 3,300ft—i. e., in the red beech/silver beech zone, but each is surrounded by a belt of mountain beech, which forms a series of concentric rings. The inner ring, together with scattered trees on hummocks within the bog, is of stunted trees of considerable age with heavy growth of Usnea;, the second is of taller, largely moribund trees, the third of still taller, healthy mountain beech. Behind, there is an abrupt change to silver beech forest. Induced Forest Margins It is not safe to say that any outer forest margin of the Kaweka has not been affected by fire. At present there are three types of forest margin in Area 1: 1. Mountain beech—Danthonia rigida tussock in the upper Ngaruroro and Ngaawapurua; 2. Silver beech—Festuca novae-zealandiae at the head of the Mohaka; 3. Beech-manuka in the Mohaka Valley.