Dept. of Conservation Report
The Moumahaki Lakes are a chain of lakes running north to south along the Moumahaki Stream and an unnamed tributary. They include Lake Moumahaki itself, (approximately 30ha), seven smaller unnamed lakes (each between three and ten hectares) and a number of smaller ponds. The lakes are in adjoining valleys which have been formed by the streams cutting down through marine terraces. A series of slips has dammed these valleys, forming the lakes.
For the most part, particularly in the north and east and to a lesser extent in the south, the sides of the valleys containing the lakes rise steeply (around 30 degrees) to ridges 100 m or more above the lake edges. These valley sides are in a series of gentle spurs. The western and central parts of the valley system are characterized by slump topography which is generally of a gentler slope but very uneven. Between the lakes there are some eutrophied, flatter areas but these only occupy a few hectares at most.
Most of the beds of the smaller lakes and a small part of the main lake are already administered by the Department of Conservation as lake Beds Conservation Area. Two parts of the Moumahaki Lakes catchment have been recommended for protection in this report. These are both in the valley of the tributary stream, and include the entire catchment north of the northern lake (" Lake 1 " in Ogle and Baxter; 1990), and most of the land bounding the east and west of that lake (and extending south, to the west of a smaller, western lake), as well as the bulk of the catchment of the lake three lakes further south (" Lake 4" in Ogle and Baxter, 1990 see the adjoining maps for a more exact location of the RAP). These include mostly slope landforms, with less of the slump landforms.
An interesting feature of the RAP is a flat area which protrudes into the west of the northern lake. This appears to have arisen from a slump which has come down in one more or less intact piece (C.Ogle, pers comm.). The rim of this flat area is not solid, but appears to float on the water and is held together by the vegetation.
To the north of the RAP is indigenous, tall forest. Otherwise, the vegetation outside the RAP is principally pasture, particularly on the gentler slump topography. On the steeper slopes, there is also a range of seral communities dominated by either ponga, manuka or both. Lake Moumahaki is bounded mostly by pasture with little scrub, while the lakes further north have considerably more scrub around them. To the south and east of the southern part of the RAP, there are two stands of exotic pine trees.
The most common vegetation type around the lake margins is an association dominated by giant umbrella sedge, toetoe and manuka. Generally manuka is the least common of these and giant umbrella sedge the most common but the relative proportions of these species varies considerably. At the time of survey this vegetation was all emergent; that is, there was water round the base of the plants. Other common species in these areas are Carex secta,especially in wetter areas, and Juncus gregiflorus, especially where the wetland vegetation merges to pasture.This vegetation type occupies a thin band along the edges of most of the lakes and to a certain extent along the stream which connects the north eastern lakes. On the west side of the northern lake, similar vegetation surrounds the flat area referred to in the "landform" section (above), and is the "floating" vegetation referred to there. Here, manuka becomes dominant.
In the northern arm of the northern lake the vegetation changes sharply to an association of wheki growing over Carex secta. Because of access difficulties, this part of the RAP was not surveyed closely. Consequently it was not possible to determine what other plants occur in this wetland. There is a gradual change away from the main lake with more Carex secta nearer the lake being overtopped by more and more wheki. Wheki in turn merges to either ponga or tall forest. Adjoining this area is a small patch heavily dominated by Carex lessoniana. There is another similar area in the southwest of the southern part of the RAP.
Most of the RAP is forested. There are basically two types of forest, which tend to alternate following landform patterns. The most common, on the slopes above the lakes, is tawa dominated. The other forest type is dominated by black beech, which mostly occurs higher up on drier ridges and gentle spurs but also down the slopes to the lake edges in a few places.
North of the northern lake the two forest types alternate evenly, following the contours of the land. This pattern is less well defined elsewhere. Beech forest also covers the flat area on the west of the northern lake, where it is fringed by wetland vegetation. This is unusual because elsewhere in the district where there are similar landforms the forest is either a tawa dominated type or a swamp forest type.
The tawa dominated forest which covers much of the RAP is typical of that which covers so much of the ecological district. Several rimu emerge above the canopy. Other podocarp species are also present, including totara, miro and matai, though none of these are very common. While the canopy is dominated by tawa, hinau is also plentiful and rewarewa and pukatea are locally common, Puka is well established as an epiphyte in the canopy but rare as a free standing tree. The forest differs from otherwise similar forests nearby in Manawatu Plains Ecological District in that there is not the same well defined sub canopy. There are, however, several smaller trees scattered under the main canopy, including mahoe, pigeonwood, ramarama, mapou and small leaved milk tree, with marbleleaf nearer the lake edges. The understorey is relatively dense and contains many small tree and shrub species, particularly near the edges of the forest or where it merges with black beech forest. Amongst those species noted are kanono, shining karamu and other species of Coprosma, kawakawa, hangehange, rangiora, pate and the shrub daisy, Olearia townsonii.
Prominent amongst the climbers is red rata vine, which appears to be particularly common, though two other species of climbing rata (Metrosideros diffusa and M. perforata) were also recorded. There is also some supplejack, New Zealand jasmine and Clematis paniculata. Nearer the lakes, kiekie, native passionfruit, and two species of bush lawyer (Rubus cissoides and R. schmidelioides) were also recorded. The ground cover where surveyed is diverse but sparse away from the edges, with several ferns, herbs and grasses present. Parataniwha is locally common as is bush rice grass. Where tracks have been cut through this forest, species such as snowberry and several willowherbs appear.
The black beech forest is more open than the tawa forest. Black beech dominates strongly, though a very few hinau and Hall's totara also reach the canopy. There is no subcanopy as such and the understorey differs greatly in composition from that under the tawa forest. Common plants here are heketara, mingimingi, Coprosma rhamnoides and Helichrysum aggregatum. There is little ground cover, except where the beech merges into tawa forest.
Little representative indigenous vegetation remains on the slump landforms, though there are a few pukatea and mahoe trees on the base of a slump at the edge of the southern part of the RAP. However, most of this slump area has been cleaned for pasture as it is of generally gentler contour and more easily managed and, consequently, very little is included in the RAP.
There is some gorse in the vicinity of the RAP which has potential to invade wetland areas. However it is not well established within the RAP itself and, could be readily controlled. It is unlikely to be a problem in the forested area. Ogle and Baxter (1990) recorded water lilies on the fringes of the northern lake. No other weeds were recorded which are likely to cause problems. Goats are present and have the potential to cause serious long term damage to the vegetation. However, they are not as numerous here as they are further inland and control is a realistic proposition. The natural areas are only partly fenced and domestic stock, including cattle and sheep, browse the edges of both forest and wetland vegetation.
Dracophyllum strictum and Gaultheria oppositifolia have been recorded from within a few hundred metres of the RAP (C. Ogle, pers. comm.) and are likely to be present within the RAP. These two species, as well as Olearia townsonii, are at or near their southern distribution limits here.
The black beech forest on a slump terrace landform is almost certainly unique within the ecological district and needs further investigation.The RAP contains some of the best open water to dry ridge vegetation sequences within the ecological district.
There are populations of fernbirds and spotless crakes around the lakes. The forest provides habitat for a number of bird species,including North Island robin, New Zealand falcon and brown kiwi.
The lakes and associated forest have high scenic value and are more accessible to the public than most other lakes in the ecological district.
The northeastern series of the Moumahaki Lakes (including those adjoining the RAP) are surrounded by legal road. This land needs to be reclassified, ideally as scenic reserve. A more intensive vegetation survey should be undertaken in appropriate habitats to determine whether Dracophyllum strictum and Gaultheria oppositifolia grow within the RAP. If not, it would be desirable to also seek protection for another area of scrub/forest 500 m south-west of the RAP where these plants have been recorded.
Part of the northern fringe of Lake Moumahaki itself (which is administered by the Department of Conservation) is only periodically submerged and supports several small indigenous herbs characteristic of shallow lake edges, including Limosella lineata and Glossostigma elatinoides. The sedge Carex dipsacea grows on the lake edge. These three plant species have not been recorded elsewhere in the ecological district.
The RAP, along with nearby conservation land and legal road contain an excellent range of representative plant communities, much in an uninterrupted sequence from wetland to dry ridge forest. The area has a number of special features and, with some fencing wild animal control is viable in the long term.
Parts of the Moumahaki Lakes catchment have been recommended for protection on the basis of the vegetation of the lake catchments. This is because the bulk of the lakes themselves and most of the fringe vegetation are conservation land or unformed legal road. The RAP adds to these the best areas of surrounding forest and, in combination with crown land, includes the whole range of plant communities in the catchments, from submerged vegetation to dry ridge forest.
Matemateonga Ecological District PNA Report June 1996 Pages 29-33