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Vegetation studies in the Taranaki land district, New Zealand

Sampling of the indigenous vegetation of the Taranaki Land District was carried out to describe and explain significant features of vegetational change along environmental gradients. Five major locations were sampled; the three volcanic mountains of Egmont National Park (Egmont, Pouakai and Kaitake), the associated volcanic ring plain and the Taranaki Upland. The sampling which was mainly along altitudinal and moisture gradients involved the collection of both quantitative and semi-quantitative plot data. Direct and indirect gradient analyses were then carried out on the data; the techniques employed included graphing, ordination and classification. Analysis enabled the definition of the main vegetation types at each of the sampling locations and of the important environmental factors associated with the vegetation pattern. Comparison of the results obtained at each of the sampling locations revealed differences in the structure and composition of the vegetation and in the pattern of vegetational change along the gradients. The three volcanic mountains within Egmont National Park show differences in the vegetation consistent with the sequence of volcanic activity (the Taranaki Volcanic Succession). Sectors of Mt Egmont exhibit differences which relate closely to the pattern of recent eruptions particularly the Burrell eruption of 1655 A.D. The vegetation at equivalent altitudes on Pouakai, an older more eroded volcanic remnant, is at a more advanced stage of development. A complex pattern of species (woody species and tree ferns) distribution on the three mountains (Egmont, Pouakai and Kaitake) is outlined and attributed in some instances to the changing availability of habitats on each mountain. This is associated with the sequence of mountain building, erosion and dissection. The vegetation pattern of the Taranaki Upland by contrast more closely reflects the pattern of topography and substrate and the forests are richer in vascular species. Analysis of the distribution of species (woody species and tree ferns) shows that inland Taranaki was the probable source for almost all of the species found in the forests of Egmont National Park. Comparisons of the pattern of vegetational change along altitudinal gradients of the mountains of Egmont National Park and some other southern hemisphere mountains reveal certain similarities. With respect to other North Island (New Zealand) volcanic mountains examined the similarities are marked. Like Mt Egmont, Pouakai and Kaitake these mountains all support podocarp-broadleaved forests from which the beech species (Nothofagus spp.) are absent. The forests of Egmont National Park are interpreted as illustrating stages of a landscape and vegetation succession apparent on volcanic mountains throughout the North Island. Features which characterise the present stage of development of the forests of Mt Egmont include the overwhelming dominance of kamahi (Weinmannia racemosa var. racemose), the absence of forest tree species such as quintinia (Quintinia serrata) and the relatively low altitude tree-line.
Type of thesis
The University of Waikato
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