Appendix 1 - Explanation of Nicholls Forest Types
The descriptions given below are a summarised version of the Nicholls classification. For a more detailed description, the reader is referred to Nicholls (1977) as listed in the references.
The broad classification followed by Nicholls is based around "the specific association of trees 30cm or more in dbh in high forest (15metres or more canopy height) and 10 to 30 cm dbh in low forest." For this study some classes have been further amalgamated due to the very small area of that class represented on Māori land.
The outline given here is adapted to meet the requirements of this study. Thus the focus is on current existing timber potential rather than regeneration capability or botanical complexity.
Beeches
This class is composed of all types of forest where one or more of the beeches (Nothofagus spp) clearly predominate. Softwoods are very rare and while hardwoods may be numerous in some areas, there are few species, always very shrubby and confined to the understorey.
In the North Island the beech species are restricted to mainly red, with some silver, some mountain beech and some hard beech. Many of the forests containing these species are at higher altitudes and as a result the trees are stunted and of generally poor form.
Much of this forest has limited potential for timber production, but some areas do offer that opportunity.
General Hardwoods
Most of this forest occurs below the altitudinal limits of rimu but all the types have in common an almost complete absence of softwoods as trees or poles and the normally common lowland hardwoods taraire and tawa are nearly as rare.
This class includes the remnant areas of coastal forest (usually containing pohutukawa), areas of regenerating rewarewa forest, areas of kanuka and areas of rata kamahi forest.
All of these forest classes have in common a complete absence of any current timber production potential, due to the species present. For large areas of this class previous timber extraction and farming have removed the timber that was originally present in these forests.
Highland Softwoods-Hardwoods-Beeches
This class occurs along the main ranges of the North Island and is generally above the altitudinal limit of rimu. The merchantable species of softwoods consist of various mixes of Hall's totara, silver pine, and the occasional miro.
These forests are high altitude forests resulting in trees that are often stunted and of poor form. The few areas of lower altitude forest of this class around Waimarino have generally been logged in the past.
Given the altitude, the history of harvesting, general location (upper mountain areas), the generally poor tree form, very low volumes per hectare and the very limited extent of this class on Māori land, this class has been assumed to have no current productive potential.
Lowland Steepland and Highland Softwoods-Hardwoods
This class contains many different mixtures of softwoods and hardwoods. Both the softwoods and hardwoods can range from occasional to locally abundant. The class occurs mainly where beech is absent on the high country and above the altitudinal limit of rimu. In this situation, it is usually low forest with stunted softwoods, malformed hardwoods and shrub hardwoods often prominent in the canopy.
Also included in this class is softwood-hardwood forest below the altitudinal limit of rimu on steep broken country or exposed ridges; that is to say, on sites where kauri or beeches are normally present.
Where rimu occurs it is usually small and outnumbered by miro, Hall's totara, or tanekaha. Tawa usually persists on these sites but several characteristic lowland hardwoods do not.
On Māori land there are significant areas in the Waikato, Bay of Plenty and Manawatu regions. These forests have often not been harvested previously due to the difficult terrain they occupy. With the advent of aerial extraction this constraint can be overcome without adverse environmental impact. As a result there exists some timber potential in this forest class.
Rimu-General Hardwoods-Beeches
This forest class is well represented in Hawkes Bay on Māori land, with smaller areas in the other central North Island regions.
As a rule beeches are abundant with occasional to frequent softwoods in the canopy, and small hardwoods form a large proportion of the understorey. Most of this class is confined to fairly narrow belts above the altitudinal limits for tawa.
Only limited areas of this class have been logged in earlier times.
Kauri -Softwoods-Hardwoods-Beeches
For the purposes of this study two classes have been combined into this one class. In Nicholls work he recognised three classes that contained kauri. These were a class of abundant kauri (of which none remains on Māori land), a class that included softwoods and hardwoods but excluded beech, and the third that included beech. The area of forest that includes beech on Māori land totals 14 hectares and as a result has been amalgamated with the class that did not include beech.
This group of classes can be described as containing occasional to frequent kauri among rimu, miro, Hall's totara plus a range of hardwoods. The hardwood component varies with location but often includes tawa and several other species that have some commercial value.
This class has potential to produce a timber volume consisting of several species and in many areas has the added advantage of containing a range of regeneration of the species which are likely to be removed during any timber harvest.
Rimu-Tawa
This class is one of the most well represented classes remaining on Māori land. The softwood component tends to be very occasional with rimu being the most common, and often as very large individuals. Rata is the only other large tree in this class and in most areas is dying out (commonly from the ravages of possum attack). Hardwoods are always abundant with tawa predominating almost throughout and a range of other commercial species also present.
The largest areas of this class occur between Mt. Pirongia and Wanganui, and in the Ureweras.
Rimu-Taraire-Tawa
This is a relatively small class in a national sense but is well represented on Māori land in Northland. It is a class that contains occasional softwoods with abundant hardwoods. The main softwoods are rimu and miro, while the hardwoods are taraire, tawa and kohekohe.
Taraire-Tawa
Formally rimu-taraire-tawa, this class consists of forest that has had the softwoods removed usually through logging, or occasionally fires. The hardwoods may have been damaged during logging but remain numerous. The commercial potential of this forest class on Māori land is considered limited due to the slow growth rates of the dominant species (tawa and taraire) and the reasonably small resource in existence.
Tawa
This class is composed of former softwood-hardwood forest containing tawa that has been reduced to a hardwood residue by the harvesting or other removal of the softwoods. As with other classes that have been modified by harvesting, the residual hardwoods have often been logged or damaged but remain plentiful and predominant.
Large areas of this class occur on Māori land in the Bay of Plenty and Waikato regions with lesser areas in the Gisborne and Manawatu regions.
Photo 1: Aerial view of tawa class in the Bay of Plenty foothills. As can be seen,
there is an almost complete canopy of hardwoods remaining after the removal of
the softwood component. The canopy is also showing signs of dieback, possibly as
a result of the earlier harvest and the subsequent exposure of the hardwoods to
frost and wind.
Rimu-General Hardwoods
This forest class occurs immediately above the altitudinal limits for tawa and taraire so these species are not present. Softwoods, most commonly rimu, but including miro and Halls totara, range from occasional to frequent, with abundant hardwoods.
The most common hardwood is kamahi (of no commercial value at present), much of which has died. The majority of other hardwoods present are of minor or no commercial value. Thus any short term potential for timber production is focused upon the softwoods.
This class is not widely represented on Māori land.
Rimu-Tawa-Beeches
This class is a rimu-tawa forest with irregular mixtures or frequent pockets of beech. The class occurs mainly in the eastern Bay of Plenty and between the Mokau River and Wanganui in Taranaki.
As a class it is very well represented on Māori land especially in the Bay of Plenty, Gisborne and Manawatu regions.
Several softwood species may be present especially rimu, Hall's totara, miro and sometimes tanekaha. Included in the hardwoods are many of the commercial species currently utilised in NZ.
All the beech species are present in different locations, with red and sliver offering the greatest commercial potential.
Photo 2: Aerial view of rimu-tawa-beech class in the East Cape area. Large emergent
rimu are seen in the centre of the photo with beech and hardwoods to the left
and right. This forest class has suffered significant damage from cyclones in
recent years, resulting in large areas of regenerating forest.
Tawa-Beeches
This class is largely forest that has been modified from the Rimu-tawa-beech class. The modification has been the removal of the rimu component usually by harvesting or occasionally by fire. In the case of forest that has been harvested there is likely to be some damage to the hardwood and beech component, but as a general rule these trees are still present.
The residual forest offers a diminished potential for timber production in the short term, but often supports good regeneration of timber species.
Softwoods
This class is restricted to high forest where softwoods dominate and to pole stands that are potential high forest. The species present include the major softwood timber species, often in quite high numbers. Thus on a per hectare basis, this forest class can support a significant timber volume.
Due to the limited original extent of this class, and its attractiveness for timber production in the past, the remaining extent of this forest is limited. On Māori land it is restricted to a few hundred hectares, some of which is in the form of regenerating poles rather than mature timber trees.
The relative scarcity of this class may also require some areas to be reserved under the terms of any approved Sustainable Forest Management Plan.
Rimu-Matai-Hardwoods
Similar to the softwood class, this class is dominated by rimu and matai, but also contains a hardwood component in the canopy.
Almost all the canopy species present have a commercial value, making this forest class an attractive management proposition. The class is well represented on Māori land and is an important class in the Bay of Plenty and Waikato regions.
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