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Growth and management of planted and naturally regenerating stands of Podocarpus totara D. Don

Podocarpus totara D. Don (totara), a highly valued, naturally durable coniferous tree species, is widely distributed in indigenous lowland forest throughout New Zealand. As harvesting from natural forests has declined there has been increasing interest in planting and managing totara for timber production. A ‘new’ indigenous forest resource not only gives landowners options for extraction of high value specialty timber in the long-term, but also fulfils a wide range of other non-timber objectives, such as increasing biodiversity and enhancing the cultural and heritage values of our flora. However, there is a lack of quantitative information on growth, productivity and wood characteristics of totara from planted stands. In addition, there is the potential to manage stands of totara that have regenerated naturally on farmland in many regions. Aspects influencing the growth of totara and relevant to management for timber production have been investigated, including genetic variation, age estimation techniques, growth and productivity of natural and planted stands, and tree form and wood quality. Thirty-six provenances of totara planted on a coastal site were assessed almost 11 years later. Some genetic differences between provenances were apparent. Totara from northern latitudes grew faster and with better stem form than provenances from more southern locations. There is also considerable variation within provenances, indicating that improvement of growth and stem form is possible within local populations. Breeding trials that capitalise on the fairly homogenous genetic variation in totara are likely to provide significant improvement in productivity and wood quality, as has been found in other conifer species. An assessment of increment cores from planted stands of totara of known age was undertaken to determine accuracy of this method for estimating age, and hence determining productivity of natural stands of unknown age. Using refinements of these techniques, increment cores were used to estimate age of a chronological sequence of naturally regenerating totara-dominant stands in three areas in Northland where they are a prominent feature on steep, hill country farmland. Evaluations of these stands support previous work that totara fits the catastrophic regeneration mode typical of shade-intolerant species. Clearance of original forest cover has provided conditions in which totara can successfully colonise open, grazed, steep slopes dominated by weedy pasture and bare ground, often in mixture with other unpalatable species such as manuka, kanuka and gorse. With natural thinning, most eventually develop into single-species, semi-mature stands that are relatively uniform in stem size and form; such stands have good potential for management as a future wood resource. An evaluation of the early performance of totara and other indigenous conifer tree species planted throughout the country indicates most stands have been established on sites unsuited to other land uses such as exotic forestry or farming. In addition, many stands received minimal after-planting care. A preliminary growth and yield model for totara based on a small number of established plantations indicates that while total stem volume growth is slow over the first 50 years, yield increases significantly over the following 50 years. A mean basal area of about 100 m²ha⁻¹ and mean volume of 800 m³ha⁻¹ are predicted at age 80 years. Growth of totara in natural stands that developed on steep hill slopes on Northland farms is considerably slower than in plantations mostly established on better sites. Plantations had a mean volume of 470 m³ha⁻¹ at 60 years but natural stands were estimated to take another 40 years to achieve a similar volume. Widely-spaced trees have a high proportion of multiple stems and coarse branching to low levels while trees in high density stands have better form. The few log sections sawn into boards indicate no major problems in timber quality although heartwood development is usually low. A descriptive model of totara following four pathways is presented showing growth and tree form development over time for natural and planted stands that have established under different conditions. A selected management regime and preliminary economic analysis for planting a stand of totara is also given. The timber and other benefits of planting and managing naturally regenerating totara stands are discussed along with constraints and suggestions for growing totara on new sites as a long-term specialty timber resource.
Type of thesis
Bergin, D. O. (2001). Growth and management of planted and naturally regenerating stands of Podocarpus totara D. Don (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14165
The University of Waikato
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