The different plant types found in freshwater wetlands mainly depend on the wetland’s water supply and nutrient levels.
In the Waikato region there are two main types of wetland; low nutrient wetlands (bogs) and highly fertile wetlands (swamps). Fens are intermediate in fertility and sometimes occur at the edges of bogs.
No two wetlands are exactly alike. The look of a wetland and its mix of plants and animals vary with local conditions (for example, climate, water flow, altitude and substrate). Several different types of plant and animal communities may be present in larger wetlands and all wetlands may change over time as environmental conditions change.
Bogs are areas of low nutrient peat (partly decayed and waterlogged plant material) that are fed by rainwater alone and have high and relatively stable water levels. In these conditions, things decay very slowly. The dead plant material does not readily break down and builds up as peat, forming low domes, like the Kopuatai Peat Dome in the Hauraki Plains.
The most common plants in Waikato bogs are jointed rushes, including the rare endemic giant cane rush (Sporadanthus) and the small wire rush (Empodisma).
Other peat bog plants include:
Fernbirds, rare black mudfish, insects and the large orb-weaving spider live among the rushes in peat bogs. Many other types of bird and fish live on the more fertile edges of the bog. The rare cane rust month (Houdinia flexilissima) is found only in Waikato bogs, living inside the stems of the giant cane rush.
Fertile wetlands are fed by nutrient-rich ground and surface water, as well as rainwater. Their water levels vary seasonally and they are often flooded by water loaded with silt and nutrients when river or lake levels are high.
Moderately fertile fens are found at the edges of low-nutrient peat bogs and peat lakes, and in depressions where there is some groundwater influence. Kahikatea, manuka and sedges may be found in these wetlands.
Highly fertile swamps are greatly influenced by groundwater and surface run-off and may be found on the edges of lakes, in poorly drained river deltas and in wet gullies. Common plants include raupo, harakeke (flax) and some sedges. Swamps are very productive and support a wide variety of plants and animals adapted to seasonally changing water levels. They are readily invaded by introduced plants such as grey and crack willow, which can dominate the vegetation and degrade the wetland.
Stands of kahikatea trees are a familiar sight around the Waikato lowlands. Native birds and other animals feed on kahikatea fruit and native bats may roost in them. Other trees that often grow alongside kahikatea include matai, kowhai, cabbage tree, and pukatea.
Large stands of kahikatea swamp forest occur alongside the Awaroa Stream, which enters Lake Whangape, near Huntly.
Find out more about kahikatea stands in the Waikato region.
This versatile tree grows in a wide range of habitats, not just swamps. Cabbage trees often dot the landscape in manuka wetlands. Large populations of fernbird can be found among the dense manuka.
Manuka wetlands are widely distributed across the region with major concentrations in the Waikato lowlands, including the Whangamarino wetland and the edge of the Kopouatai peat dome.
Sedgelands occur in areas with still water, and are dominated by a wide range of sedges and rushes such as Carex, Juncus, Eleocharis, and Machaerina. Sedgeland is excellent fernbird and crake habitat, particularly where it grows alongside areas of manuka scrub or raupo.
Sedgelands are widespread, but occur mainly in the large wetlands of the lower Waikato such as the Whangamarino wetland and the edges of Kopuatai peat dome.
Raupo (bullrush) is a distinctive plant found in still, shallow water around lake edges and even ditches. Spotless crake and the threatened Australasian bittern often make their home in raupo.
Large areas of raupo wetland are found in the Tongariro River delta at the southern side of Lake Taupo, and at the edge of the Lower Waikato lakes.
This hardy plant thrives in lowland swamps but can also cope in quite dry conditions. Cabbage trees are often scattered through harakeke wetlands and manuka may occur around the edges. Native fish, such as the giant kokopu, use flax and raupo at the edges of lakes and waterways.
Flax dominated wetlands are most common in the Taupo area, particularly at higher altitudes (above 300 m). A large flax wetland occurs at Lake Rotoaira, with another at Waitahauni, adjacent to Lake Taupo.
Updated August 2017