Semi-quantitative Measurements of Canopy Composition as a Basis for Mapping Vegetation

This paper describes a ~emi-quantitative method of mapping vegetation at scales of the order of one mile to the inch using aerial photographs. It has been developed during a survey of Tongariro National Park in which more information than would normally be derived from a reconnaissance survey is required but where, due to the size of the area, time for sampling is limited. The aim has been to make all steps in the sampling and mapping procedure as repeatable as possible so that precise compm isons can be made between large areas of vegetation, and large-scale changes in the vegetation pattern can be followed over a long period of time. The composition of the canopy layers has been chosen as a basis for mapping. Reasons for this emphasis are: (i) It is not practical to show the distribution of all species present in the vegetation on a single map. Selecting the plants of the canopy layers recognises the fact that these plants to some extent control the light, moisture and plant nutrients available to all other plants besides contributing most to the structure of the vegetation. (ii) The composition of the canopy at a given time appears to be the most satisfactory starting point for following future largescale changes. This applies both to the quantitative description of a particular mapping unit and to changes in the positions of boundaries. It is not intended to imply by this emphasis on canopy layers that the lower layers arc not important; no description of a mapping unit would be complete without details of the lower layers. A single method of measuring canopy comnosition which can be used with equal facility in forest or tussockland is not at present available and for this reason two mc~surements have been used: