Water status and growth initiation in Populus : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University

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Massey University
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Within the last century, the vegetation of New Zealand has undergone a massive change. A high proportion of the steeplands, and virtually all of the flat and rolling country has been converted from temperate rain-forest to grassland which has resulted in considerably increased runoff. The inherently unstable nature of much of the sedimentary parent material has not resisted this change well, and erosion has become a significant problem in some areas. Techniques of soil conservation and runoff control have been based mainly on plantings of the genus Populus in the form of "poles" some 10 to 12 feet long which can be established in the presence of stock, under Farm Plans organised by local catchment authorities. The total number of poles planted in 1967 was 400,000 - double the number of 1962 - and this is expected to at least double again. However, in spite of advantages in propagation, adaptability, growth rate and root system characteristics, problems in the establishment of poplar and willow have arisen. The most obvious of these is animal damage, chiefly cattle (through rubbing and bark biting) and opossum (browsing of foliage). A survey commissioned by the Soil Conservation and Rivers Control Council in 1968 investigated the level of pole loss and found a mortality of 24.7% and 41.8% over the first and second years respectively (Edwards; 1968, 1969 a). Although the major factors could not be positively identified, it was apparent that site factors, and water stress in particular, were major causes of loss. This study investigated the importance of water relations in the vegetative propagation of Populus species. In particular, it was designed to establish the levels of water stress which would limit the initiation of growth in both root initials and buds.
Published in 1972.