Fresh Water Swamp Forest
In the lowlands throughout New Zealand, swamp forest often occurs in localised areas depressed below the general level of the landscape. Such depressions can be found in the irregular terrain of volcanic and formerly glaciated areas; in areas where land blocks have sunk along faults; where meandering rivers have changed their courses; and between consolidated sand dunes.
If there is some depth of water initially, then water plants begin the succession. Some of these are completely submerged and grow on the bottom of the pond or lake; others are free floating at the surface. Where the latter grow near the shore they gradually reduce the water page 116
depth with the accumulation of their own remains and the streamborne silt they trap. In the shallower water which results, some aquatic plants with submerged roots but foliage raised well above the water enter the progression. Notable among these is the raupo (Typha orientalis).
The raupo in turn raises the ground level to coincide (more or less) with the water level and then gradually gives way to the so-called New Zealand flax (Phormium tenax
) intermixed with toetoe (Cortaderia toetoe
) and Carex secta.
This stage is an impressive sight when the Phormium
is bearing its spiky reddish flower heads and the toetoe its creamy yellow-
Figure 66 Swamp with cabbage trees (Cordyline australis) and New Zealand 'flax' (Phormium tenax). Near Kaeo, northern North Island.
Photo: J. W. Dawson.
plumes. In time shrubs tolerant of poorly drained soil become established — manuka (Leptospermum scoparium
), koromiko (Hebe stricta
), karamu (Coprosma robusta
) and a variety of divaricating shrubs including several coprosmas. The first trees to appear are often cabbage trees (Cordyline australis
) (Fig. 66
), so characteristic of many New Zealand landscapes. Finally come the trees of the closed forest, the most prominent of these being kahikatea (Dacrycarpus dacrydioides
). In kahikatea swamp forest (Fig. 67
), as it is often called, the trunks of the dominant trees may be close-set and exceedingly tall with relatively small grayish-
Figure 67 (opposite) Exterior view of kahikatea (Dacycarpus dacrydioides) swamp forest. Harihari, west coast, South Island. Photo: J. H. Johns.
crowns. In the North Island, and northern parts of the South Island, pukatea (Laurelia novaezelandiae
) is a common associate of kahikatea and in this type of forest often has well-developed plank buttresses which extend into roots raised above the forest floor with shield-like pneumatophores here and there. The swamp maire (Szygium maire
) has a similar distribution, but it is a smaller tree.
There is an often rather open undergrowth of small-leaved and largeleaved shrubs, many of which persist from earlier stages in the succession, and sedges are prominent among the forest floor plants. Herbaceous and woody epiphytes are often common and among the vines kiekie (Frejcinetia baueriana var. banksii) is particularly abundant, covering the forest floor in places and completely obscuring the trunks of trees up to a considerable height (Fig. 32).
Over time, when the soil has built up sufficiently above the water table, the swamp forest will give way to ordinary conifer broadleaf forest.